Tehran, Iran

The Iran University of Science and Technology is a research institution and university of engineering and science in Iran, offering both undergraduate and postgraduate studies. Located on Hengam Street in the Narmak neighborhood in northeast Tehran, IUST and its surrounding communities provide a cultural and recreational environment suited to the work of a major research institution. The university consistently ranks among Iran's top three technical universities. Wikipedia.


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Ghoddousi P.,Iran University of Science and Technology | Shirzadi Javid A.A.,Iran University of Science and Technology
Construction and Building Materials | Year: 2014

This paper presents an experimental study on the influence of packing density of solid particles on the stability and rheology of self-consolidating concrete (SCC). Also it is tried to address a new method for determination the packing density of SCC mixtures. Seven powder-types of SCC mixtures with different packing density were made with inclusion of silica fume, metakaolin or low activity-granulated blast furnace slag as a substitution of Portland cement. Results demonstrated that there is an optimal packing density about 0.804 and a little lower than maximum packing density of 0.807 with minimum static segregation and final plastic settlement. Moreover in the optimum packing density of particles, the calculated velocity and rheological properties of SCC are improved. The results emphasized that the effects of mineral admixtures are completely different in the static and dynamic segregation. Mineral admixtures reduced static segregation (SCC at rest in vertical state) but increase dynamic segregation (SCC at flowing in horizontal state). This finding shows that the cementitious binder content must be sufficient in flowing state to restraint from dynamic segregation. © 2013 Elsevier Ltd. All rights reserved.


Ostadrahimi L.,University of California at Davis | Marino M.A.,University of California at Davis | Afshar A.,Iran University of Science and Technology
Water Resources Management | Year: 2012

Reservoir operation rules are intended to help an operator so that water releases and storage capacities are in the best interests of the system objectives. In multi-reservoir systems, a large number of feasible operation policies may exist. System engineering and optimization techniques can assist in identifying the most desirable of those feasible operation policies. This paper presents and tests a set of operation rules for a multi-reservoir system, employing a multi-swarm version of particle swarm optimization (MSPSO) in connection with the well-known HEC-ResPRM simulation model in a parameterization-simulation-optimization (parameterization SO) approach. To improve the performance of the standard particle swarm optimization algorithm, this paper incorporates a new strategic mechanism called multi-swarm into the algorithm. Parameters of the rule are estimated by employing a parameterization-simulation-optimization approach, in which a full-scale simulation model evaluates the objective function value for each trial set of parameter values proposed with an efficient version of the particle swarm optimization algorithm. The usefulness of the MSPSO in developing reservoir operation policies is examined by using the existing three-reservoir system of Mica, Libby, and Grand Coulee as part of the Columbia River Basin development. Results of the rule-based reservoir operation are compared with those of HEC-ResPRM. It is shown that the real-time operation of the three reservoir system with the proposed approach may significantly outperform the common implicit stochastic optimization approach. © 2011 Springer Science+Business Media B.V.


Younesian D.,Iran University of Science and Technology | Esmailzadeh E.,University of Ontario Institute of Technology
Journal of Sound and Vibration | Year: 2011

A new strategy for vibration suppression of a rotating beam using a time-increasing internal tensile force is proposed in this paper. Nonlinear coupled longitudinal and bending equations of motion are derived in non-dimensional form using the Hamilton principle. The first-order analytical solution of the equations of motion is obtained using the Galerkin technique combined with the multiple scales method (MSM). Numerical simulations are then performed for various increasing rates of the internal tensile force and performance of the vibration suppression strategy is studied. A very close agreement between the simulation results obtained by the numerical integration and the first-order analytical solution is achieved. Forced vibrations of the system for input excitations of either a sinusoidal or a random function with white noise time history are considered. The simulation results and dynamic performance of the suppressed system for an externally excited rotating beam show an interesting phenomenon of the form of remarkable effectiveness of the proposed vibration reduction strategy. © 2010 Elsevier Ltd. All rights reserved.


Younesian D.,Iran University of Science and Technology | Marjani S.R.,Iran University of Science and Technology | Esmailzadeh E.,University of Ontario Institute of Technology
Nonlinear Dynamics | Year: 2013

The frequency response of a cracked beam supported by a nonlinear viscoelastic foundation has been investigated in this study. The Galerkin method in conjunction with the multiple scales method (MSM) is employed to solve the nonlinear governing equations of motion. The steady-state solutions are derived for the two different resonant conditions. A parametric sensitivity analysis is carried out and the effects of different parameters, namely the geometry and location of crack, loading position and the linear and nonlinear foundation parameters, on the frequency-response solution are examined. © 2012 Springer Science+Business Media Dordrecht.


Mashadi B.,Iran University of Science and Technology | Emadi S.A.M.,Iran Khodro Company
IEEE Transactions on Vehicular Technology | Year: 2010

In this paper, an innovative power-split device (PSD) is introduced, and its application in a hybrid powertrain system is studied. The new PSD is a mechanism that allows operation in two different power-split modes through locking/unlocking of two clutches. In one mode, the PSD operates similar to a standard planetary gear unit, and in the other mode, it works the same as a compound planetary set. A well-known analogous system is the Toyota Hybrid System (THS) and is used for comparison purposes. It is demonstrated that by the new system, the transmission losses are reduced by a considerable extent, and thus, the efficiency is improved. A controller is designed based on fuzzy logic, which receives the battery state of charge (SOC), the vehicle speed, and the power that is requested at the wheels to coordinate each component in such a way as to optimize the entire system efficiency. A numerical optimization algorithm is applied to sustain the SOC in high regions and shift engine operating points to higher efficiency regions. Simulation results demonstrate notable improvements in fuel economy and performance characteristics. © 2006 IEEE.


Younesian D.,Iran University of Science and Technology | Esmailzadeh E.,University of Ontario Institute of Technology
Nonlinear Dynamics | Year: 2010

Non-linear vibration of a variable speed rotating beam is analyzed in this paper. The coupled longitudinal and bending vibration of a beam is studied and the governing equations of motion, using Hamilton's principle, are derived. The solutions of the non-linear partial differential equations of motion are discretized to the time and position functions using the Galerkin method. The multiple scales method is then utilized to obtain the first-order approximate solution. The exact first-order solution is determined for both the stationary and non-stationary rotating speeds. A very close agreement is achieved between the simulation results obtained by the numerical integration method and the first-order exact solution one. The parameter sensitivity study is carried out and the effect of different parameters including the hub radius, structural damping, acceleration, and the deceleration rates on the vibration amplitude is investigated. © Springer Science+Business Media B.V. 2009.


Sadjadi S.J.,Iran University of Science and Technology | Soltani R.,Iran University of Science and Technology
Computers and Industrial Engineering | Year: 2015

This paper deals with a redundancy allocation problem in series-parallel systems with the choice of redundancy strategy, including active and cold standby strategies in which component's time to failure follows an Erlang distribution. The scale parameter of Erlang distribution and consequently the reliability of each component are imprecise in terms of interval data, and only the lower and upper bounds are known. This problem, for the first time, is formulated through Min-Max regret criterion, which is commonly used to define robust solutions. The resulting problem formulation contains an unlimited number of constraints, and a Benders' decomposition method is implemented to deal with the given problem. This method is compared with an enumeration method to show its effectiveness. The performance of the proposed model using the Benders' decomposition method is examined over different problem sizes, and the associated results are analyzed. © 2014 Elsevier Ltd. All rights reserved.


Azami H.,Iran University of Science and Technology | Sanei S.,University of Surrey
2012 2nd International eConference on Computer and Knowledge Engineering, ICCKE 2012 | Year: 2012

Electroencephalogram (EEG) is generally known as a non-stationary signal. Dividing a signal into the epochs within which the signals can be considered stationary, segmentation, is very important in many signal processing applications. Noise often influences the performance of an automatic signal segmentation system. In this article, a new approach for segmentation of the EEG signals based on singular spectrum analysis (SSA) and imperialist competitive algorithm (ICA) is proposed. As the first step, SSA is employed to reduce the effect of various noise sources. Then, fractal dimension (FD) of the signal is estimated and used as a feature extraction for automatic segmentation of the EEG. In order to select two acceptable parameters related to the FD, ICA that is a more powerful evolutionary algorithm than traditional ones is applied. By using synthetic and real EEG signals, the proposed method is compared with original approach (i.e. without using SSA and ICA). The simulation results show that the speed of SSA is much better than that of the discrete wavelet transform (DWT) which has been one of the most popular preprocessing filters for signal segmentation. Also, the simulation results indicate the performance superiority of the proposed method. © 2012 IEEE.


Nasiri-Gheidari Z.,University of Tehran | Tootoonchian F.,Iran University of Science and Technology
Energy Conversion and Management | Year: 2010

In this paper a novel optimization algorithm based on imperialist competitive algorithm (ICA) is used for the design of a low speed single sided linear induction motor (LIM). This type of motors is used increasingly in industrial process specially in transportation systems. In these applications having high efficiency with high power factor is very important. So in this paper the objective function of design is presented considering both efficiency and power factor. Finally the results of ICA are compared with the ones of genetic algorithm and conventional design. Comparison shows the success of ICA for design of LIMs. © 2010 Elsevier Ltd.


Karimi A.,Iran National Institute of Genetic Engineering and Biotechnology | Karimi A.,Iran University of Science and Technology | Navidbakhsh M.,Iran University of Science and Technology | Faghihi S.,Iran National Institute of Genetic Engineering and Biotechnology
Materials Science and Engineering C | Year: 2013

Atherosclerosis is a common arterial disease which alters the stiffness of arterial wall. Arterial stiffness is related to many cardiovascular diseases. In this investigation, maximum stress and strain as well as physiological and maximum elastic modulus of 22 human coronary arteries are measured. In addition, the force-displacement diagram of human coronary artery is obtained to discern the alterations between the healthy and atherosclerotic arterial wall stiffness. The age of each specimen and its effect on the elastic modulus of human coronary arteries is also considered. Twenty-two human coronary arteries, including eight atherosclerotic and fourteen healthy arteries are excised within 5 hours post-mortem. Samples are mounted on a tensile-testing machine and force is applied until breakage occurs. Elastic modulus coefficient of each specimen is calculated to compare the stiffness of healthy and atherosclerotic coronary arteries. The results show that the atherosclerotic arteries bear 44.55% more stress and 34.61% less strain compared to the healthy ones. The physiological and maximum elastic moduli of healthy arteries are 2.53 and 2.91 times higher than that of atherosclerotic arteries, respectively. The age of specimens show no correlation with the arterial wall stiffness. A combination of biomechanics and mathematics is used to characterize the mechanical properties of human coronary arteries. These results could be utilized to understand the extension and rupture mechanism of coronary arteries and has implications for interventions and surgeries, including balloon-angioplasty, bypass, and stenting. © 2013 Elsevier B.V.


Abbasi-Moghadam D.,Shahid Bahonar University of Kerman | Tabataba Vakili V.,Iran University of Science and Technology
Wireless Personal Communications | Year: 2013

In this paper, effects of channel estimation error on time reversal (TR) UWB systems are investigated. In time reversal, a signal is prefiltered by using a time reversed complex conjugate of the channel impulse response as a transmitter prefilter. To investigate the effect of channel estimation error, an error function is added to TR-UWB prefilter. Analytical and simulation results show that channel estimation error degrade the performance. The signal-to-interference plus noise ratio decreases with increasing error variance. It is shown that the channel performance is degraded about 0.5 dB in CM1 and 1.3 dB in CM4 channel. © 2011 Springer Science+Business Media, LLC.


Vasquez J.C.,University of Aalborg | Guerrero J.M.,University of Aalborg | Savaghebi M.,Iran University of Science and Technology | Eloy-Garcia J.,Charles III University of Madrid | Teodorescu R.,University of Aalborg
IEEE Transactions on Industrial Electronics | Year: 2013

Power-electronics-based microgrids (MGs) consist of a number of voltage source inverters (VSIs) operating in parallel. In this paper, the modeling, control design, and stability analysis of parallel-connected three-phase VSIs are derived. The proposed voltage and current inner control loops and the mathematical models of the VSIs are based on the stationary reference frame. A hierarchical control scheme for the paralleled VSI system is developed comprising two levels. The primary control includes the droop method and the virtual impedance loops, in order to share active and reactive powers. The secondary control restores the frequency and amplitude deviations produced by the primary control. Also, a synchronization algorithm is presented in order to connect the MG to the grid. Experimental results are provided to validate the performance and robustness of the parallel VSI system control architecture. © 1982-2012 IEEE.


Savaghebi M.,Iran University of Science and Technology | Jalilian A.,Iran University of Science and Technology | Vasquez J.C.,University of Aalborg | Guerrero J.M.,University of Aalborg
IEEE Transactions on Industrial Electronics | Year: 2013

Recently, there has been an increasing interest in using distributed generators (DGs) not only to inject power into the grid but also to enhance the power quality. In this paper, a stationary-frame control method for voltage unbalance compensation in an islanded microgrid is proposed. This method is based on the proper control of DGs interface converters. The DGs are properly controlled to autonomously compensate for voltage unbalance while sharing the compensation effort and also active and reactive powers. The control system of the DGs mainly consists of active and reactive power droop controllers, a virtual impedance loop, voltage and current controllers, and an unbalance compensator. The design approach of the control system is discussed in detail, and simulation and experimental results are presented. The results demonstrate the effectiveness of the proposed method in the compensation of voltage unbalance. © 2012 IEEE.


Fadaee M.,University of Qom | Ilkhani M.R.,Iran University of Science and Technology
Acta Mechanica | Year: 2015

Because of the production process and constraint conditions, a circular graphene sheet may be opposed to structural defect and pin hole, respectively. Some of the defects and pin hole on a circular graphene sheet can be considered as an eccentric hole. So, analyzing the behavior of a circular graphene sheet with an eccentric hole is important. Free vibration of an eccentric annular graphene sheet, as the basis of any dynamical analysis, is analytically studied in this paper. Nonlocal thin plate theory is used to model the problem. The translational addition theorem for cylindrical vector wave functions is employed to solve the equation of motion for various boundary conditions. Results are compared with the literature, and their accuracy is approved. Effects of boundary conditions, geometrical properties and nonlocal parameter changes on symmetric and antisymmetric vibrational modes are investigated. It is approved that the eccentricity has a significant effect on the natural frequencies. Also, symmetric and antisymmetric modes of an annular graphene sheet have different behavior when geometrical and nonlocal parameters change. © 2014, Springer-Verlag Wien.


Eshaghi A.,Iran University of Science and Technology | Graeli A.,Iranian Academic Center for Education
Optik | Year: 2014

In this research, indium tin oxide (ITO) thin films of various thickness (200, 250, 300, 350, 400 nm) were deposited on polycarbonate polymer substrates using a magnetron sputtering technique. The structure, morphology, surface composition, optical and electrical properties of the thin films were investigated by X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FE-SEM), X-ray Photoelectron Spectroscopy (XPS), UV-VIS-NIR spectrophotometer and four point probe method, respectively. The results indicated that grain size increased as the thickness increased. The transmittance and sheet resistance of the ITO thin films showed that ITO thin films with 200 nm thickness had the highest transmission whereas ITO thin film with 400 nm had the best conductivity.


Savaghebi M.,Iran University of Science and Technology | Jalilian A.,Iran University of Science and Technology | Vasquez J.C.,University of Aalborg | Guerrero J.M.,University of Aalborg
IEEE Transactions on Smart Grid | Year: 2012

In this paper, a hierarchical control scheme is proposed for enhancement of sensitive load bus (SLB) voltage quality in microgrids. The control structure consists of primary and secondary levels. The primary control level comprises distributed generators (DGs) local controllers. Each of these controllers includes a selective virtual impedance loop which is considered to improve sharing of fundamental and harmonic components of load current among the DG units. The sharing improvement is provided at the expense of increasing voltage unbalance and harmonic distortion. Thus, the secondary control level is applied to manage the compensation of SLB voltage unbalance and harmonics by sending proper control signals to the primary level. DGs compensation efforts are controlled locally at the primary level. The system design procedure for selecting proper control parameters is discussed. Simulation results are provided in order to demonstrate the effectiveness of the proposed control scheme. © 2010-2012 IEEE.


Savaghebi M.,Iran University of Science and Technology | Jalilian A.,Iran University of Science and Technology | Vasquez J.C.,University of Aalborg | Guerrero J.M.,University of Aalborg
IEEE Transactions on Smart Grid | Year: 2012

The concept of microgrid hierarchical control is presented recently. In this paper, a hierarchical scheme is proposed which includes primary and secondary control levels. The primary level comprises distributed generators (DGs) local controllers. The local controllers mainly consist of power, voltage and current controllers, and virtual impedance control loop. The central secondary controller is designed to manage the compensation of voltage unbalance at the point of common coupling (PCC) in an islanded microgrid. Unbalance compensation is achieved by sending proper control signals to the DGs local controllers. The design procedure of the control system is discussed in detail and the simulation results are presented. The results show the effectiveness of the proposed control structure in compensating the voltage unbalance. © 2012 IEEE.


Hajabdollahi Z.,Shahid Bahonar University of Kerman | Hajabdollahi F.,Ferdowsi University of Mashhad | Tehrani M.,Iran University of Science and Technology | Hajabdollahi H.,Vali e Asr University of Rafsanjan
Energy | Year: 2013

An Organic Rankine Cycle for diesel engine waste heat recovery is modeled and optimized. The design parameters are nominal capacity of diesel engine, diesel operating partial load, evaporator pressure, condenser pressure and refrigerant mass flow rate. In addition four refrigerants including R123, R134a, R245fa and R22 are selected and studied as working fluids. Then, the fast and elitist NSGA-II (Non-dominated Sorting Genetic Algorithm) is applied to maximize the thermal efficiency and minimize the total annual cost (sum of investment cost, fuel cost and environmental cost) simultaneously. The results of the optimal design are a set of multiple optimum solutions, called Pareto optimal solutions. The optimization results show that the best working fluid is R123 in both of economical and thermo dynamical view point for a specified value of output power. R245fa, R134a and R22 are placed in the next ranking, respectively. The optimum result of R123 shows the 0.01%, 4.39%, and 4.49% improvement for the total annual cost in comparison with R245fa, R22, and R134a, respectively. The above values for efficiency are obtained 1.01%, 12.79% and 10.57%, respectively. Furthermore R123 needs the highest investment cost while the environmental and fuel costs are the lowest. © 2013 Elsevier Ltd.


Ahmadi P.,Sharif University of Technology | Hajabdollahi H.,Iran University of Science and Technology | Dincer I.,University of Ontario Institute of Technology
Journal of Heat Transfer | Year: 2011

In the present work, a thermal modeling is conducted for optimal design of compact heat exchangers in order to minimize cost and entropy generation. In this regard, an εNTU method is applied for estimation of the heat exchanger pressure drop, as well as effectiveness. Fin pitch, fin height, fin offset length, cold stream flow length, no-flow length, and hot stream flow length are considered as six decision variables. Fast and elitist nondominated sorting genetic algorithm (i.e., nondominated sorting genetic algorithm II) is applied to minimize the entropy generation units and the total annual cost (sum of initial investment and operating and maintenance costs) simultaneously. The results for Pareto-optimal front clearly reveal the conflict between two objective functions, the number of entropy generation units and the total annual cost. It reveals that any geometrical changes, which decrease the number of entropy generation units, lead to an increase in the total annual cost and vice versa. Moreover, for prediction of the optimal design of the plate fin heat exchanger, an equation for the number of entropy generation units versus the total annual cost is derived for the Pareto curve. In addition, optimization of heat exchangers based on considering exergy destruction revealed that irreversibilities, such as pressure drop and high temperature difference between cold and hot streams, play a key issue in exergy destruction. Thus, more efficient heat exchanger leads to have a heat exchanger with higher total cost rate. Finally, the sensitivity analysis of change in the optimum number of entropy generation units and the total annual cost with change in the decision variables of the plate fin heat exchanger is also performed, and the results are reported. © 2011 American Society of Mechanical Engineers.


Ahmadi P.,University of Ontario Institute of Technology | Almasi A.,Iran University of Science and Technology | Shahriyari M.,Iran University of Science and Technology | Dincer I.,University of Ontario Institute of Technology
International Journal of Energy Research | Year: 2012

The present study deals with a comprehensive thermodynamic modeling of a combined heat and power (CHP) system in a paper mill, which provides 50MW of electric power and 100tonh -1 saturated steam at 13bars. This CHP plant is composed of air compressor, combustion chamber (CC), Air Preheater, Gas Turbine (GT) and a Heat Recovery Heat Exchanger. The design parameters of this cycle are compressor pressure ratio (r AC), compressor isentropic efficiency (η AC), GT isentropic efficiency (η GT), CC inlet temperature (T 3), and turbine inlet temperature (T 4). In the multi-objective optimization three objective functions, including CHP exergy efficiency, total cost rate of the system products, and CO 2 emission of the whole plant, are considered. The exergoenvironmental objective function is minimized whereas power plant exergy efficiency is maximized using a Genetic algorithm. To have a good insight into this study, a sensitivity analysis of the results to the interest rate as well as fuel cost is performed. The results show that at the lower exergetic efficiency, in which the weight of exergoenvironmental objective is higher, the sensitivity of the optimal solutions to the fuel cost is much higher than the location of the Pareto Frontier with the lower weight of exergoenvironmental objective. In addition, with increasing exergy efficiency, the purchase cost of equipment in the plant is increased as the cost rate of the plant increases. © 2010 John Wiley & Sons, Ltd.


Naimi-Jamal M.R.,Iran University of Science and Technology | Mashkouri S.,Iran University of Science and Technology
Molecular Diversity | Year: 2010

Solvent-free one-pot synthesis of 2-amino-4H-chromene scaffold is described in a very simple, efficient, and environmentally benign method using sodium carbonate as a cheap and non-toxic catalyst with up to excellent yields. © 2010 Springer Science+Business Media B.V.


Daliri M.R.,Iran University of Science and Technology
Clinical EEG and Neuroscience | Year: 2013

Here, we propose a new kernel approach based on the earth mover's distance (EMD) for electroencephalography (EEG) signal classification. The EEG time series are first transformed into histograms in this approach. The distance between these histograms is then computed using the EMD in a pair-wise manner. We bring the distances into a kernel form called kernel EMD. The support vector classifier can then be used for the classification of EEG signals. The experimental results on the real EEG data show that the new kernel method is very effective, and can classify the data with higher accuracy than traditional methods. © EEG and Clinical Neuroscience Society (ECNS) 2013.


Sanaye S.,Iran University of Science and Technology | Dehghandokht M.,Islamic Azad University at Damavand | Fartaj A.,University of Windsor
Applied Energy | Year: 2012

This paper covers thermal modeling of a cabin in an automobile to find and control the air temperature by the means of fuzzy controller. Therefore, in first step, the thermal and ventilation loads were estimated then the equations of dry air mass and energy conservation as well as internal components of a cabin were derived and solved simultaneously. The performance of the proposed thermal modeling of a cabin was compared with the experimental hot room test. In the next step, to maintain the thermal comfort of a cabin and controlling the two effective parameters (blower outgoing air velocity and the circulated air percentage), a fuzzy controller was applied. Results showed that when using a fuzzy controller, the temperature control of a cabin took shorter time period and as a result, the time spent for ventilating and cooling the cabin as well as the fuel consumption are reduced. © 2012 Elsevier Ltd.


Davari S.A.,Iran University of Science and Technology | Khaburi D.A.,Iran University of Science and Technology | Kennel R.,TU Munich
IEEE Transactions on Power Electronics | Year: 2012

In this paper, an improved finite control set-model predictive control (FCS-MPC) with an optimized weighting factor is presented. The main goal of this paper is reducing the torque ripples when the FCS-MPC is implemented by means of the two-level inverter. For this purpose, the weighting factor is calculated via an optimization method. The optimization is based on dividing the control interval into two parts: active time for applying the active voltage vectors and zero time for applying the zero voltage. With this technique, the torque ripple is calculated as a function of weighting factor and it is optimized. The method is validated by simulations and experiments, using two-level inverter, at two speed regions (nominal speed and low speed). The results are compared with conventional FCS-MPC. © 2011 IEEE.


Bahiraei M.,Kermanshah University of Technology | Hosseinalipour S.M.,Iran University of Science and Technology
Journal of Dispersion Science and Technology | Year: 2013

Convective heat transfer characteristics of water/Al2O3 nanofluid flow inside a tube were evaluated in this study. A non-uniform concentration distribution was used in thermal dispersion model. Meanwhile, an experimental study was done to find the dispersion coefficient in addition to assess the accuracy of simulation results. The accuracy of the results of thermal dispersion model was compared with the numerical solution using discrete phase modeling and homogenous method, while the effective parameters on particle migration were considered to find the particle distribution for being used in the dispersion model. Non-uniformity of the particle distribution is increased by raising volume fraction and Reynolds number. Concentration distribution was obtained using discrete phase method and was compared with the distribution employed for the dispersion model. When a uniform concentration is used in the dispersion model, error of prediction is expected to be increased. The thermal dispersion model, in which the particles have followed a non-uniform distribution, provides acceptable results in spite of its lower calculational time as compared to the two-phase approach. © 2013 Copyright Taylor and Francis Group, LLC.


Fazlpour B.,Islamic Azad University at Babol | Banijamali A.,Iran University of Science and Technology
Advances in High Energy Physics | Year: 2015

We study dynamics of generalized tachyon scalar field in the framework of teleparallel gravity. This model is an extension of tachyonic teleparallel dark energy model which has been proposed by Banijamali and Fazlpour (2012). In contrast with tachyonic teleparallel dark energy model that has no scaling attractors, here we find some scaling attractors which means that the cosmological coincidence problem can be alleviated. Scaling attractors are presented for both interacting and noninteracting dark energy and dark matter cases. © 2015 Behnaz Fazlpour and Ali Banijamali.


Jafarian Y.,International Institute of Earthquake Engineering and Seismology | Vakili R.,Concordia University at Montréal | Sadeghi Abdollahi A.,Iran University of Science and Technology
Computers and Geotechnics | Year: 2013

Liquefaction resistance of granular soils is commonly characterized by the cyclic resistance ratio (CRR) in the simplified shear stress procedure of liquefaction potential assessment. This parameter is commonly estimated by cyclic tests on reconstituted samples or empirical correlations between liquefied/non-liquefied case histories. The current study employs results of cyclic triaxial tests on reconstituted soil specimens and presents a predictive equation for cyclic resistance ratio (CRR) of clean and silty sands. The CRR equation is a function of relative density, effective mean confining pressure, non-plastic fines content, number of harmonic cycles for liquefaction onset, and some other basic soil properties. It is demonstrated that the developed relationship obtains reasonable accuracy in the prediction of laboratory-based CRR. Based on the developed CRR model, new relationships are then presented for the coefficient of effective overburden pressure (Kσ) and magnitude scaling factor (MSF), two important modification factors in the simplified shear stress procedure. These new modification factors are then compared with those recommended by previous researchers. Finally, the possible application of the proposed CRR model in field condition is shown for a specific case. This study provides a preliminary insight into the liquefaction resistance of silty sands prior to the complementary laboratory studies. © 2013 Elsevier Ltd.


Akbari M.,Iran University of Science and Technology | Abdi Behnagh R.,Urmia University of Technology | Dadvand A.,Urmia University of Technology
Science and Technology of Welding and Joining | Year: 2012

Friction stir welding has been successfully used to weld the dissimilar metals. A few investigations have been carried out on the friction stir lap welding of Al to Cu, but the basic issue of how the position of the metals would affect the joint strength is still not resolved. In the present study, the 7070 Al and the commercially pure copper are lap joined using friction stir lap welding technology. Two test cases are considered. The distinction refers to the position of Al with respect to Cu. Microstructural analyses are carried out to gain intermetallic compounds and some microcracks. The effect of position of materials on the heat generation is investigated and justified through the temperature measurements. Mechanical properties of each sample are characterized using both shear and hardness tests. The results reveal that the maximum fracture load of the joint is obtained when Al is placed on the top of Cu. © 2012 Institute of MaterialsMaterials, Minerals and Mining.


Bahiraei M.,Kermanshah University of Technology | Hangi M.,Iran University of Science and Technology
Journal of Magnetism and Magnetic Materials | Year: 2015

Magnetic nanofluids (MNFs) are suspensions which are comprised of a non-magnetic base fluid and magnetic nanoparticles. In this modern set of suspensions which can be called smart or functional fluids, fluid flow, particles movement and heat transfer process can be controlled by applying magnetic fields. Regarding unique characteristics of MNFs, studies in this field have witnessed a phenomenal growth. This paper reviews and summarizes recent investigations implemented on MNFs including those conducted on thermophysical properties, natural convection, forced convection, boiling as well as their practical applications. Moreover, this review identifies the challenges and opportunities for future research. © 2014 Elsevier B.V.


Bahiraei M.,Kermanshah University of Technology | Hangi M.,Iran University of Science and Technology
Energy Conversion and Management | Year: 2013

The current study attempts to investigate the performance of water based Mn-Zn ferrite magnetic nanofluid in a counter-flow double-pipe heat exchanger under quadrupole magnetic field using the two-phase Euler-Lagrange method. The nanofluid flows in the tube side as coolant, while the hot water flows in the annulus side. The effects of different parameters including concentration, size of the particles, magnitude of the magnetic field and Reynolds number are examined. Distribution of the particles is non-uniform at the cross section of the tube such that the concentration is higher at central regions of the tube. Application of the magnetic field makes the distribution of particles more uniform and this uniformity increases by increasing the distance from the tube inlet. Increasing each of the parameters of concentration, particle size and magnitude of the magnetic field will lead to a greater pressure drop and also higher heat transfer improvement. At higher Reynolds numbers, the effect of magnetic force is diminished. Optimization was performed using genetic algorithm coupled with compromise programming technique in order to reach the maximum overall heat transfer coefficient along with the minimum pressure drop. For this purpose, the models of objective functions of overall heat transfer coefficient and pressure drop of the nanofluid were first extracted in terms of the effective parameters using neural network. The neural network model predicts the output variables with a very good accuracy. The optimal values were obtained considering different conditions for relative importance of the objective functions. © 2013 Elsevier Ltd. All rights reserved.


Fazlpour B.,Islamic Azad University at Babol | Banijamali A.,Iran University of Science and Technology
Advances in High Energy Physics | Year: 2013

Recently, nonminimal coupling between a noncanonical scalar field and gravity in the framework of teleparallelism has been proposed. Noncanonical scalar field is tachyon field, and the model is known as tachyonic teleparallel dark energy. Here, we perform a dynamical analysis of the model, find its critical points, and study their stability. We find that all the critical points are dark energy dominated solutions corresponding to an accelerating universe. It is also shown that there exist two critical lines which are stable attractors of the model. © 2013 Behnaz Fazlpour and Ali Banijamali.


Kargarnejad S.,Urmia University of Technology | Djavanroodi F.,Iran University of Science and Technology
Engineering Failure Analysis | Year: 2012

Nickel base superalloys are widely used in applications requiring strength at high temperature. During the operation of gas turbines, the blades and other elements of hot gas path suffer service induced degradation which may be natural or accelerated due to different causes. The failure analysis of the 3. MW gas turbine first stage blades made of nickel-base alloy Nimonic 80A is presented. The blade experienced base alloy degradation due to operation at high temperature. Initially the blade was sectioned for metallographic and microhardness test. The microstructure and microhardness was compared in four different blade zones i.e. root, 30%, 60%, and 90% of the total height of the hot region of the blade. On the basis of the observed microstructures and the phases present in the alloy, the main cause of failure was found to be creep damage. Finite element method (FEM) analysis is conducted considering peak loading of centrifugal force and surface (aerodynamic) loads. Based on FEM simulation results, the life of turbine blades is predicted using the Larson-Miller method. Finally to improve the blade life two heat treatment cycles were suggested and applied. The effect of heat treatments on grain size, volume friction of γ' primary phase, and micro hardness were investigated. A detailed analysis of the coating showed that, the loss of coatings resistant to high temperature is due to oxidation, corrosion, erosion and inters diffusion of coating-substrate, which results in diffusion of alloy elements into the coating. © 2012 Elsevier Ltd.


News Article | December 20, 2016
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SAE International announces that Katherine Avery, Research Scientist with Ford Motor Company’s Research and Innovation Center; and Mohammad J. Mahtabi, a third-year PhD student majoring in Mechanical Engineering at Mississippi State University, have been honored with the Henry O. Fuchs Student Award. Established in 1991, this award recognizes a graduate or recently graduated student (i.e. post doctorate or new professor) that is working in the field of fatigue research and applications. The purpose of this award is to promote the education of engineering students in the area of fatigue technology. This award honors the memory of Professor Henry O. Fuchs. Professor Fuchs participated in the SAE Fatigue Design & Evaluation Committee's research projects, was a member of the faculty who founded the SAE Fatigue Concepts in Design short course, published extensively in SAE and elsewhere in the technical community, and actively participated in the Surface Enhancement Division of the Committee which is responsible for many standards relating to surface treatments of metals for withstanding fatigue damage. As a graduate student, Avery was a visiting scholar at Ford, and had internships at Oak Ridge National Laboratory and Tenneco, Inc. She also served as a teaching assistant at the University of Michigan in 2011, and a guest lecturer at Kettering University in 2013. Avery has authored or co-authored several papers on durability and high temperature fatigue of metals through SAE International and ASME. Together with her research collaborators, Avery was a recipient of the 2012 SAE Arch T. Colwell Merit Award. At the University of Michigan, she and her faculty adviser, Dr. Jwo Pan, were honored with the 2015 Robert M. Caddell Award for Research for their joint contributions in the areas of materials and manufacturing. For her active role in student leadership, Avery was presented with the Distinguished Leadership Award and the MLK Spirit Award from the Deans of U of M’s College of Engineering in 2014. Avery serves on the Michigan Engineering Alumni Board and is a member of SAE International, ASME and SWE. She holds a bachelor’s degree in Mechanical Engineering from Kettering University, and a master’s degree and PhD in Mechanical Engineering from the University of Michigan. Mahtabi holds a bachelor’s degree from the University of Tehran and a master’s degree from Iran University of Science and Technology; he ranked as an honor student at both institutions. He is a third-year PhD student, majoring in Mechanical Engineering at Mississippi State University and is conducting his research at MSU’s Center for Advanced Vehicular Systems (CAVS) under supervision of Dr. Shamsaei. Mahtabi’s dissertation is on different aspects of fatigue behavior of NiTi, an equiatomic alloy of nickel and titanium. This material is categorized as a shape memory alloy (SMA), while also exhibiting superelastic behavior. NiTi has become a preferred choice for many applications in the automotive, aerospace and biomedical industries. In automotive industry, the material has been used in engine control systems, transmission control, and has the potential to be utilized in structural components, bumpers and crash structures. He is using several experimental, analytical, and computational techniques to model the fatigue behavior of SMAs and explain the relationship between various aspects of the material, such as microstructural features, phase transformation, and loading, including mean strain/stress and variable amplitude effects, on the fatigue resistance. His research involves many complex (and coupled) physical phenomena with the need to understand and model: cyclic deformation, phase transformation, superelasticity, and damage accumulation. Based on his dissertation research on experimental and computational fatigue and fracture analysis, he has published several journal articles, one book chapter, and presented in multiple conferences. SAE International is a global association committed to being the ultimate knowledge source for the engineering profession. By uniting more than 127,000 engineers and technical experts, we drive knowledge and expertise across a broad spectrum of industries. We act on two priorities: encouraging a lifetime of learning for mobility engineering professionals and setting the standards for industry engineering. We strive for a better world through the work of our philanthropic SAE Foundation, including programs like A World in Motion® and the Collegiate Design Series™.


Niknam T.,Shiraz University of Technology | Amiri B.,Iran University of Science and Technology
Applied Soft Computing Journal | Year: 2010

Clustering is a popular data analysis and data mining technique. A popular technique for clustering is based on k-means such that the data is partitioned into K clusters. However, the k-means algorithm highly depends on the initial state and converges to local optimum solution. This paper presents a new hybrid evolutionary algorithm to solve nonlinear partitional clustering problem. The proposed hybrid evolutionary algorithm is the combination of FAPSO (fuzzy adaptive particle swarm optimization), ACO (ant colony optimization) and k-means algorithms, called FAPSO-ACO-K, which can find better cluster partition. The performance of the proposed algorithm is evaluated through several benchmark data sets. The simulation results show that the performance of the proposed algorithm is better than other algorithms such as PSO, ACO, simulated annealing (SA), combination of PSO and SA (PSO-SA), combination of ACO and SA (ACO-SA), combination of PSO and ACO (PSO-ACO), genetic algorithm (GA), Tabu search (TS), honey bee mating optimization (HBMO) and k-means for partitional clustering problem. © 2009 Elsevier B.V. All rights reserved.


Hosseini S.H.,Islamic Azad University at Tehran | Mohseni S.H.,Iran University of Science and Technology | Asadnia A.,Imam Hossein University | Kerdari H.,Islamic Azad University at Sāveh
Journal of Alloys and Compounds | Year: 2011

Conductive polyaniline (PANi)-manganese ferrite (MnFe2O 4) nanocomposites with core-shell structure were synthesized by in situ polymerization in the presence of dodecyl benzene sulfonic acid (DBSA) as the surfactant and dopant and ammonium persulfate (APS) as the oxidant. The structure and magnetic properties of manganese ferrite nanoparticles were measured by using powder X-ray diffraction (XRD) and vibrating sample magnetometer (VSM), respectively. Its morphology, microstructure and DC conductivity of the nanocomposite were characterized by scanning electron microscopy (SEM), fourier transform infrared spectroscopy (FTIR) and four-wire-technique, respectively. The microwave absorbing properties of the nanocomposite powders dispersing in resin acrylic coating with the coating thickness of 1.4 mm were investigated by using vector network analyzers in the frequency range of 8-12 GHz. A minimum reflection loss of -15.3 dB was observed at 10.4 GHz. © 2010 Elsevier B.V. All rights reserved.


Karimi-Nasab M.,Islamic Azad University at Tehran | Sabri-Laghaie K.,Iran University of Science and Technology
International Journal of Production Research | Year: 2014

This paper formulates a new imperfect production problem that generates defectives randomly. The production manager conducts total inspections to screen defectives (including reworkable and non-reworkable items) from non-defectives. But, the inspection is error-prone due to different sources. The model determines rates of main and rework processes, batch size and backlog. As the model is a nonlinear programme and it is difficult to obtain an algebraic closed-form solution, three randomised approximation algorithms are developed. Under certain conditions, the algorithms can find the global optimum in polynomial time. Finally numerical analyses are reported. © 2013 Taylor & Francis.


Damghani K.K.,Islamic Azad University at Tehran | Sadi-Nezhad S.,Islamic Azad University at Tehran | Aryanezhad M.B.,Iran University of Science and Technology
Expert Systems with Applications | Year: 2011

In this paper, we have developed a modular Decision Support System (DSS) in order to select an optimum portfolio of several chances for investments in presence of uncertainty. The investments are considered as the projects so as their initial investment costs, profits, resource requirement, and total available budget are assumed to be uncertain. This uncertainty has been modeled using fuzzy concepts. The proposed DSS has two main modules. The first one is a fuzzy binary programming model which represents the mathematical model of the associated fuzzy capital-budgeting problem. It involves finding optimum combination of investment portfolio considering a multi-objective measurement function and subject to several set of constraints. The results of optimistic and pessimistic analysis of the aforementioned fuzzy binary programming model plus a managerial Confidence Level (CL) value are treated as input of a fuzzy rule based system which is the second module of the proposed DSS. Although some projects are simple to make a decision about at the final step of the first module but the unique output of the second module of the proposed DSS is Risk of Investment (ROI) for all remained project. The logic relations between precedence parts of the rules as well as CL value will work in favor of computational efforts in second module through diminishing some unessential rules. This will help to define a complete set of fuzzy IF-THEN rules more efficiently. The proposed DSS can help the decision makers to select an optimum investment portfolio with minimum risk in a complete ambiguous condition. © 2010 Elsevier Ltd. All rights reserved.


Hasheminejad S.M.,Iran University of Science and Technology | Gheshlaghi B.,Islamic Azad University at Tehran
Composite Structures | Year: 2012

A three-dimensional semi-analytic analysis based on the linear elasticity theory is offered to study the transient vibration characteristics of an arbitrarily thick, simply supported, functionally graded (FGM) rectangular plate, resting on a linear Winkler-Pasternak viscoelastic foundation, and subjected to general distributed driving forces of arbitrary temporal and spatial variations. The problem solution is obtained by adopting a laminate model in conjunction with the powerful state space solution technique involving a global transfer matrix and Durbin's numerical Laplace inversion algorithm. Numerical calculations are carried out for the transient displacement and stress responses of aluminum-zirconia FGM square plates of selected thickness parameters and compositional gradients, resting on " soft" or " stiff" elastic foundations, under the action of moving transverse forces as well as uniformly distributed blast loads. Also, the response curves for the FGM plates are compared with those of equivalent bilaminate plates containing comparable total volume fractions of constituent materials. It is observed that the material gradient variation is substantially more influential on the dynamic stress concentrations induced across the plate thickness than on the displacement response of the inhomogeneous plates. In particular, the displacement response of the equivalent bilaminate plates can provide an accurate estimate for prediction of the dynamic response of the corresponding FGM plates, especially for thick plates resting on a stiff foundation. Limiting cases are considered and good agreements with the data available in the literature as well as with the computations made by using a commercial finite element package are obtained. © 2012 Elsevier Ltd.


Zakariazadeh A.,Iran University of Science and Technology | Jadid S.,Iran University of Science and Technology | Siano P.,University of Salerno
Energy Conversion and Management | Year: 2014

Distribution system complexity is increasing mainly due to technological innovation, renewable Distributed Generation (DG) and responsive loads. This complexity makes difficult the monitoring, control and operation of distribution networks for Distribution System Operators (DSOs). In order to cope with this complexity, a novel method for the integrated operational planning of a distribution system is presented in this paper. The method introduces the figure of the aggregator, conceived as an intermediate agent between end-users and DSOs. In the proposed method, energy and reserve scheduling is carried out by both aggregators and DSO. Moreover, Electric Vehicles (EVs) are considered as responsive loads that can participate in ancillary service programs by providing reserve to the system. The efficiency of the proposed method is evaluated on an 84-bus distribution test system. Simulation results show that the integrated scheduling of EVs and renewable generators can mitigate the negative effects related to the uncertainty of renewable generation. © 2014 Elsevier Ltd.


Daeinabi K.,Islamic Azad University at Tehran | Korayem M.H.,Iran University of Science and Technology
Journal of Nanoparticle Research | Year: 2011

Atomic force microscopy is applied to measure intermolecular forces and mechanical properties of materials, nano-particle manipulation, surface scanning and imaging with atomic accuracy in the nano-world. During nano-manipulation process, contact forces cause indentation in contact area between nano-particle and tip/substrate which is considerable at nano-scale and affects the nano-manipulation process. Several nano-contact mechanics models such as Hertz, Derjaguin-Muller-Toporov (DMT), Johnson-Kendall-Roberts-Sperling (JKRS), Burnham-Colton-Pollock (BCP), Maugis-Dugdale (MD), Carpick-Ogletree-Salmeron (COS), Pietrement-Troyon (PT), and Sun et al. have been applied as the continuum mechanics approaches at nano-scale. In this article, indentation depth and contact radius between tip and substrate with nano-particle for both spherical and conical tip shape during nano-manipulation process are analyzed and compared by applying theoretical, semiempirical, and empirical nano-contact mechanics models. The effects of adhesion force, as the main contrast point in different nano-contact mechanics models, on nano-manipulation analysis is investigated for different contact radius, and the critical point is discussed for mentioned models. © 2010 Springer Science+Business Media B.V.


Moghimi Ghadikolaei H.,Iran University of Science and Technology | Ahmadi A.,Islamic Azad University | Aghaei J.,Shiraz University of Technology | Najafi M.,Iran University of Science and Technology
Renewable and Sustainable Energy Reviews | Year: 2012

In view of the intermittency and uncertainty associated with both the electricity production sector of restructured power system and their competitive markets, it is necessary to develop an appropriate risk managing scheme. So that it is desirable to trade-off between optimum utilization of intermittent generation resources (i.e. renewable energy resources), uncertain market prices and related risks in order to maximize participants benefits and minimize the corresponding risks in the multi-product market environment. The main goal of this paper is to investigate risk management by introducing a novel multi-risk index to quantify expected downside risk (EDR) which is caused by both the wind power and market price uncertainties. Value-at-Risk (VaR) method is used to assess the mentioned risk issue by the proposed weighted EDR, so that an optimal trade-off between the profit and risk is made for the system operations. Also, the roulette wheel mechanism is employed for random market price scenario generation wherein the stochastic procedure is converted into its respective deterministic equivalents. Moreover, the autoregressive integrated moving average (ARIMA) model is employed to characterize the stochastic wind farm (WF) generation by predetermined mean level and standard deviation of wind behavior as well as temporal correlation. The problem is formulated as a mixed-integer stochastic framework for a hydro-wind power system scheduling and tested on a generation company (GENCO). © 2012 Elsevier Ltd. All rights reserved.


Moghaddam A.A.,Shiraz University | Seifi A.,Shiraz University | Niknam T.,Shiraz University of Technology | Alizadeh Pahlavani M.R.,Iran University of Science and Technology
Energy | Year: 2011

As a result of today's rapid socioeconomic growth and environmental concerns, higher service reliability, better power quality, increased energy efficiency and energy independency, exploring alternative energy resources, especially the renewable ones, has become the fields of interest for many modern societies. In this regard, MG (Micro-Grid) which is comprised of various alternative energy sources can serve as a basic tool to reach the desired objectives while distributing electricity more effectively, economically and securely. In this paper an expert multi-objective AMPSO (Adaptive Modified Particle Swarm Optimization algorithm) is presented for optimal operation of a typical MG with RESs (renewable energy sources) accompanied by a back-up Micro-Turbine/Fuel Cell/Battery hybrid power source to level the power mismatch or to store the surplus of energy when it's needed. The problem is formulated as a nonlinear constraint multi-objective optimization problem to minimize the total operating cost and the net emission simultaneously. To improve the optimization process, a hybrid PSO algorithm based on a CLS (Chaotic Local Search) mechanism and a FSA (Fuzzy Self Adaptive) structure is utilized. The proposed algorithm is tested on a typical MG and its superior performance is compared to those from other evolutionary algorithms such as GA (Genetic Algorithm) and PSO (Particle Swarm Optimization). © 2011 Elsevier Ltd.


Gheshlaghi B.,Islamic Azad University at Tehran | Hasheminejad S.M.,Iran University of Science and Technology
Current Applied Physics | Year: 2012

An analytical model for predicting surface effects on the free transverse vibrations of piezoelectric nanowires (NWs) is developed based on the non-local Euler-Bernoulli beam theory. The governing equation of motion for the piezoelectric NW with consideration of both surface and non-local effects is initially obtained, and the exact expressions for the natural frequencies and the fundamental buckling voltage are derived for simple support conditions. In addition, an explicit relationship between the residual surface tension and the small scale parameter of the piezoelectric NW, in terms of the critical electric potential at which the axial buckling occurs, is offered. Accordingly, a design chart is presented which may assist in experimental characterization of the mechanical properties of piezoelectric NW-based devices. © 2011 Elsevier B.V. All rights reserved.


Moghimi H.,Iran University of Science and Technology | Ahmadi A.,Islamic Azad University | Aghaei J.,Shiraz University of Technology | Rabiee A.,Shahrekord University
International Journal of Electrical Power and Energy Systems | Year: 2013

The environmental advantage of distributed energy resources (DERs) application has attracted lots of research attention and encouraged to implement clean power producers. In spite of the environmental benefits of renewable energy sources application as distributed power generation, the variability of renewable energy, e.g. wind power uncertainty, can potentially endanger the operation of electric power system. This paper presents a new techno-economic factor (TEF) for DERs based on the effect of their generation on network losses and the relationship between active/reactive power loss and generated power from thermal power plants. In order to simultaneously investigate these new factors and wind power uncertainty on power network operation, a stochastic Security Constrained Unit Commitment (SCUC) for 24 h is defined consisting of generation and emission costs. The simulation results of IEEE57-bus case study show the effective role of RES application on operational cost minimization. © 2012 Elsevier Ltd. All rights reserved.


Ghadiri M.,Iran University of Science and Technology | Fakhri S.,RAMPCO Group | Shirazian S.,Iranian Research Organization for Science and Technology
Industrial and Engineering Chemistry Research | Year: 2013

A two-dimensional comprehensive model was developed to predict the transport of water in the nanoporous membrane contactors. The considered membrane distillation device was a counter-current flat-sheet membrane contactor for production of pure water from saline water. The developed model formulates the fundamental transport equations of heat, mass, and momentum in the membrane contactor. The computational fluid dynamics techniques were applied for numerical simulation of model equations. The simulation results were compared with experimental data obtained from literature and showed great agreement with the measured values. A combination of the Knudsen flow and Poiseuille flow was used in the model for estimation of diffusion inside the membrane pores and increased the accuracy of the model. Simulation results revealed that, in the regions adjacent to the membrane wall, the temperature difference is significant. This could be attributed to the fact that a temperature boundary layer is formed near the membrane wall and causes a high temperature decline in this region. © 2013 American Chemical Society.


Karami M.,Iran University of Science and Technology | Shayanfar H.A.,Iran University of Science and Technology | Aghaei J.,Shiraz University of Technology | Ahmadi A.,Islamic Azad University
Renewable and Sustainable Energy Reviews | Year: 2013

This paper presents the application of Mixed-Integer Programming (MIP) approach for solving the security-constrained daily hydrothermal generation Scheduling which takes into account the intermittency and volatility of wind power generation, which is called Security-Constrained Wind Hydrothermal Coordination (WHTC). In restructured power systems, Independent System Operators (ISOs) execute the Security-Constrained Unit Commitment (SCUC) program to plan a secure and economical hourly generation schedule for the daily/weekly-ahead market. The objective of security-constrained daily hydrothermal generation scheduling is to determine an optimum schedule of generating units for minimizing the cost of supplying energy and ancillary services with considering network security constraints. The problem formulation includes dynamic ramp-rate constraints for generation schedules and reserve activation, and minimum up-time and down-time of conventional units. Of particular interest in this study are considering more practical constraints and rigorous modeling of thermal and hydro units such as prohibited operating zones and valve loading effects. Furthermore, for the hydro plants, multi performance curve with spillage and time delay between reservoirs are considered. To assess the efficiency and powerful performance of mentioned method, a typical case study based on modified IEEE-118 bus system is investigated and the results are compared to each other in different test system. © 2013 Elsevier Ltd.


Esmaeilifar A.,Iran University of Science and Technology | Rowshanzamir S.,Iran University of Science and Technology | Eikani M.H.,Iranian Research Organization for Science and Technology | Ghazanfari E.,Iran University of Science and Technology
Energy | Year: 2010

While the use of a high level of platinum (Pt) loading in proton exchange membrane fuel cells (PEMFCs) can amplify the trade off towards higher performance and longer lifespan for these PEMFCs, the development of PEMFC electrocatalysts with low-Pt-loadings and high-Pt-utilization is critical and the limited supply and high cost of the Pt used in PEMFC electrocatalysts necessitate a reduction in the Pt level. In order to make such electrocatalysts commercially feasible, cost-effective and innovative, catalyst synthesis methods are needed for Pt loading reduction and performance optimization. Since a Pt-deposited carbon nanotube (CNT) shows higher performance than a commercial Pt-deposited carbon black (CB) with reducing 60% Pt load per electrode area in PEMFCs, use of CNTs in preparing electrocatalysts becomes considerable. This paper reviews the literature on the synthesis methods of carbon-supported Pt electrocatalysts for PEMFC catalyst loading reduction through the improvement of catalyst utilization and activity. The features of electroless deposition (ED) method, deposition on sonochemically treated CNTs, polyol process, electrodeposition method, sputter-deposition technique, γ-irradiation method, microemulsion method, aerosol assisted deposition (AAD) method, Pechini method, supercritical deposition technique, hydrothermal method and colloid method are discussed and characteristics of each one are considered. © 2010 Elsevier Ltd.


Pakzad M.A.,Islamic Azad University at Tehran | Moaveni B.,Iran University of Science and Technology
WSEAS Transactions on Systems and Control | Year: 2013

In this article, an observer with delay-dependent stability conditions has been presented for time delay systems with unknown inputs, where the time delay terms exist in the state and output of the system. The designing of this observer, whose performance index is the H2 norm, has been formulated as a nonlinear optimization problem. By using the finite characterization of a Lyapunov functional equation, sufficient conditions have been proposed to guarantee the existence of a desirable H2 filter. This finite characterization can be calculated by means of a matrix exponential function. Several numerical examples have also been simulated to show the effectiveness and simplicity of the proposed observer.


Ramezani K.,Iran University of Science and Technology | Rowshanzamir S.,Iran University of Science and Technology | Eikani M.H.,Iranian Research Organization for Science and Technology
Energy | Year: 2010

In this paper, parameters affecting castor oil transesterification reaction were investigated. Applying four basic catalysts including NaOCH3, NaOH, KOCH3 and KOH the best one with maximum biodiesel yield was identified. Using Taguchi method consisting four parameters and three levels, the best experimental conditions were determined. Reaction temperature (25, 65 and 80°C), mixing intensity (250, 400 and 600rpm), alcohol/oil ratio (4:1, 6:1 and 8:1) and catalyst concentration (0.25, 0.35 and 0.5%) were selected as experimental parameters. It was concluded that reaction temperature and mixing intensity can be optimized. Using the optimum results, we proposed a kinetic model which resulted in establishing an equation for the beginning rate of transesterification reaction. Furthermore, applying ASTM D 976 correlation, minimum cetane number of produced biodiesel was determined as 37.1. © 2010 Elsevier Ltd.


Fazlollahtabar H.,Iran University of Science and Technology | Mahdavi I.,Mazandaran University of Science and Technology | Mohajeri A.,Islamic Azad University at Tehran
Applied Soft Computing Journal | Year: 2013

Supply chain design problems have recently raised a lot of interest since the opportunity of an integrated management of the supply chain can reduce the propagation of undesirable events through the network and can affect decisively the profitability of the members. Often uncertainties may be associated with demand and relevant costs. In most of the existing models uncertainties are treated as randomness and are handled by appealing to probability theory. Here, we propose a fuzzy mathematical programming model for a supply chain which considers multiple depots, multiple vehicles, multiple products, multiple customers, and different time periods. In this work not only demand and cost but also decision variables are considered to be fuzzy. We apply two ranking functions for solving the model. The aim of the fuzzy mathematical program is to select the appropriate depots among candidate depots, the allocation of orders to depots and vehicles, also the allocation of the returning vehicles to depots, to minimize the total costs. To validate the model some numerical experiments are worked out and a comparative analysis is investigated. Also, a regression model is considered to analyze the applied fuzzy ranking methods. © 2012 Elsevier B.V.


Taghizadeh-Sarabi M.,Iran University of Science and Technology | Daliri M.R.,Iran University of Science and Technology | Daliri M.R.,Institute for Research in Fundamental Sciences | Niksirat K.S.,Islamic Azad University at Tehran
Brain Topography | Year: 2014

Decoding and classification of objects through task-oriented electroencephalographic (EEG) signals are the most crucial goals of recent researches conducted mainly for brain–computer interface applications. In this study we aimed to classify single-trial 12 categories of recorded EEG signals. Ten subjects participated in this study. The task was to select target images among 12 basic object categories including animals, flowers, fruits, transportation devices, body organs, clothing, food, stationery, buildings, electronic devices, dolls and jewelry. In order to decode object categories, we have considered several units namely artifact removing, feature extraction, feature selection, and classification. Data were divided into training, validation, and test sets following the artifact removal process. Features were extracted using three different wavelets namely Daubechies4, Haar, and Symlet2. Features were selected among training data and were reduced afterward via scalar feature selection using three criteria including T test, entropy, and Bhattacharyya distance. Selected features were classified by the one-against-one support vector machine (SVM) multi-class classifier. The parameters of SVM were optimized based on training and validation sets. The classification performance (measured by means of accuracy) was obtained approximately 80 % for animal and stationery categories. Moreover, Symlet2 and T test were selected as better wavelet and selection criteria, respectively. © 2014, Springer Science+Business Media New York.


Zakariazadeh A.,Iran University of Science and Technology | Homaee O.,Iran University of Science and Technology | Jadid S.,Iran University of Science and Technology | Siano P.,University of Salerno
Applied Energy | Year: 2014

The main goal of Distribution Automation (DA) is the real-time operation, usually without operator intervention, of distribution systems as a consequence of load demand or power generation variations and failure conditions in the distribution systems. As real time voltage control is known as a legacy system that can be fully activated by DA equipments, in this paper an analytical study is reported to demonstrate the effects of load curtailments on voltages profile in distribution network. A new method for real time voltage control, based on emergency demand response program, is also proposed. The proposed method uses the real-time measured data collected by RTUs and determines the tap changer condition and load curtailment required in order to maintain the distribution voltage profile. Emergency conditions include outages of generators and lines, and fluctuations due to unpredictable load demand and renewable generation. A novel voltage sensitivity matrix, based on performed voltage sensitivity analysis due to load participation in demand response program, is also proposed. In order to verify the effectiveness and robustness of the proposed control scheme, it is tested on a typical automated distribution network. Simulation results show that the proper selection of load curtailment can improve voltage profile and that, in emergency conditions, demand response is an effective way to keep the voltage in a permissible range. © 2013 Elsevier Ltd.


Zakariazadeh A.,Iran University of Science and Technology | Jadid S.,Iran University of Science and Technology | Siano P.,University of Salerno
Energy Conversion and Management | Year: 2014

When preparing for the widespread adoption of Electric Vehicles (EVs), an important issue is to use a proper EVs' charging/discharging scheduling model that is able to simultaneously consider economic and environmental goals as well as technical constraints of distribution networks. This paper proposes a multi-objective operational scheduling method for charging/discharging of EVs in a smart distribution system. The proposed multi-objective framework, based on augmented ε-constraint method, aims at minimizing the total operational costs and emissions. The Vehicle to Grid (V2G) capability as well as the actual patterns of drivers are considered in order to generate the Pareto-optimal solutions. The Benders decomposition technique is used in order to solve the proposed optimization model and to convert the large scale mixed integer nonlinear problem into mixed-integer linear programming and nonlinear programming problems. The effectiveness of the proposed resources scheduling approach is tested on a 33-bus distribution test system over a 24-h period. The results show that the proposed EVs' charging/discharging method can reduce both of operation cost and air pollutant emissions. © 2013 Elsevier Ltd. All rights reserved.


Mazidi M.,Iran University of Science and Technology | Zakariazadeh A.,Iran University of Science and Technology | Jadid S.,Iran University of Science and Technology | Siano P.,University of Salerno
Energy Conversion and Management | Year: 2014

Wind and solar energy introduced significant operational challenges in a Microgrid (MG), especially when renewable generations vary from forecasts. In this paper, forecast errors of wind speed and solar irradiance are modeled by related probability distribution functions and then, by using the Latin hypercube sampling (LHS), the plausible scenarios of renewable generation for day-head energy and reserve scheduling are generated. A two-stage stochastic objective function aiming at minimizing the expected operational cost is implemented. In the proposed method, the reserve requirement for compensating renewable forecast errors is provided by both responsive loads and distributed generation units. All types of customers such as residential, commercial and industrial ones can participate in demand response programs which are considered in either energy or reserve scheduling. In order to validate the proposed methodology, the proposed approach is finally applied to a typical MG and simulation results are carried out. © 2014 Elsevier Ltd. All rights reserved.


Ghadikolaei H.M.,Iran University of Science and Technology | Tajik E.,Iran University of Science and Technology | Aghaei J.,Shiraz University of Technology | Charwand M.,Tarbiat Modares University
Applied Energy | Year: 2012

This paper proposes a new framework for the operation of distribution companies (discos) in the liberalized electricity market environment considering distributed generation (DG) units and carbon dioxide (CO2) emission penalty cost. The proposed short-term framework is a two-stage model. The first stage, namely day-ahead stage, deals with the activities of discos. This stage includes a optimization problem to minimize the costs of distribution company (operational and CO2 emission costs). The first stage is formulated as a mixed integer nonlinear programming (MINLP) framework using the Benders decomposition to determine the decisions of discos to buy power from grid, schedule the DG units and contract with interruptible loads (ILs). The results of the first stage are imposed as the boundary constraints in the second stage which deals with the activities of discos in an hour-ahead period. In the hour-ahead stage, the retailers determine the amount of purchased active and reactive power from the grid and the production of each DG unit in the energy and reserve market keeping in mind its day-ahead decision to maximize the desired short-term profit. Finally, the efficiency of the proposed framework is studied on a case study. © 2012 Elsevier Ltd.


Janipour M.,Iran University of Science and Technology | Janipour M.,Sabanci University | Sendur K.,Sabanci University
Journal of Lightwave Technology | Year: 2016

In this study, we demonstrate enhanced transmission for out-of-plane stacked plasmonic apertures through the interaction of localized surface plasmons of apertures using both numerical and theoretical approaches. A dispersive finite-difference time-domain (D-FDTD) model is used to investigate the systems through the numerical simulations. To explain the results of the FDTD numerical simulations and to bring further insight to this interaction, we use a magnetic coupled dipole approximation as the theoretical basis. Our results demonstrate that near-field in-phase and out-of-phase interactions of the stacked nanoholes increase or decrease the optical transmission. Plasmon hybridization is discussed for stacked nanohole dimers on out-of-plane metallic films. © 2015 IEEE.


Zakariazadeh A.,Iran University of Science and Technology | Jadid S.,Iran University of Science and Technology | Siano P.,University of Salerno
Electric Power Systems Research | Year: 2014

The development of smart grids offers new opportunities to improve the efficiency of operation of Distributed Energy Resources (DERs) by implementing an intelligent Distribution Management System (DMS). The DMS consists of application systems that are used to support the DERs management undertaken by a Distribution System Operator (DSO). In this paper, a conceptual model for a Demand Response Management System (DRMS), conceived as an application system of a DMS, is presented. Moreover, an optimization tool, able to consider the available DERs (conventional or renewable Distributed Generations (DGs) and demand response) is proposed. The optimization tool uses a stochastic multi-objective method in order to schedule DERs and aims at minimizing the total operational costs and emissions while considering the intermittent nature of wind and solar power as well as demand forecast errors. In order to facilitate small and medium loads participation in demand response programs, a Demand Response Provider (DRP) aggregates offers for load reduction. The proposed scheduling approach for DERs is tested on a 69-bus distribution test system over a 24-h period. © 2014 Elsevier B.V.


Jamalpoor A.,Iran University of Science and Technology | Hosseini M.,Sirjan University of Technology
Composites Part B: Engineering | Year: 2015

Background/purpose This paper deals with analysis of biaxial buckling behavior of double-orthotropic microplate system including in-plane magnetic field, using strain gradient theory. Methods Two Kirchhoff microplates are coupled by an internal elastic medium and also are limited to the external Pasternak elastic foundation. Utilizing the principle of total potential energy, the equilibrium equations of motion for three cases (out-of-phase buckling, in-phase buckling and buckling with a plate) are acquired. In this study, we assumed boundary conditions of all the edges are simply supported. In order to get exact solution for buckling load of system, Navier approach which satisfies the simply supported boundary conditions is applied. Results Variations of the buckling load of double-microplate system subjected to biaxial compression corresponding to various values of the thickness, length scale parameter, magnetic field, stiffness of internal and external elastic medium, aspect ratio, shear stiffness of the Pasternak foundation and biaxial compression ratio are investigated. Furthermore, influence of higher modes on buckling load is shown. By comparing the numerical results, it is found that dimensionless buckling load ratio for in-phase mode is more than those of out of phase and one microplate fixed. Also it is shown that the value of buckling load ratio reduces, when non-dimensional length scale parameter increases. Conclusion However, we found when properties of plate are orthotropic the buckling load ratio is more than isotropic state. Also, by considering the effect of magnetic field, non-dimensional buckling load ratio reduces. © 2015 Elsevier Ltd All rights reserved.


Esmaili M.,Islamic Azad University at Tehran | Firozjaee E.C.,Iran University of Science and Technology | Shayanfar H.A.,Iran University of Science and Technology
Applied Energy | Year: 2014

Distributed Generations (DGs) can be an efficient solution to today's power system environmental and economical challenges. Installing DGs influences power system stability and losses. In this paper, a method is presented for locating and sizing of DGs to enhance voltage stability and to reduce network losses simultaneously. First, vulnerable buses from voltage stability point of view are determined using bifurcation analysis as the best locations to install DGs. Number of DGs is so chosen that system voltage profile is brought into the given permissible voltage security limits. Then, the global optimal size of DGs is determined employing the dynamic programming search method. It is shown that considering DG reactive limits makes different voltage stability bifurcations happen and it affects the optimal location, size, and number of DGs. Results of testing the proposed method and previous methods on a 34-bus distribution test system are discussed in detail and they show the efficiency of the proposed method. © 2013 Elsevier Ltd.


Zakariazadeh A.,Iran University of Science and Technology | Jadid S.,Iran University of Science and Technology | Siano P.,University of Salerno
Energy Conversion and Management | Year: 2014

In this paper a stochastic multi-objective economical/environmental operational scheduling method is proposed to schedule energy and reserve in a smart distribution system with high penetration of wind generation. The proposed multi-objective framework, based on augmented ε-constraint method, is used to minimize the total operational costs and emissions and to generate Pareto-optimal solutions for the energy and reserve scheduling problem. Moreover, fuzzy decision making process is employed to extract one of the Pareto-optimal solutions as the best compromise non-dominated solution. The wind power and demand forecast errors are considered in this approach and the reserve can be furnished by the main grid as well as distributed generators and responsive loads. The consumers participate in both energy and reserve markets using various demand response programs. In order to facilitate small and medium loads participation in demand response programs, a Demand Response Provider (DRP) aggregates offers for load reduction. In order to solve the proposed optimization model, the Benders decomposition technique is used to convert the large scale mixed integer non-linear problem into mixed-integer linear programming and non-linear programming problems. The effectiveness of the proposed scheduling approach is verified on a 41-bus distribution test system over a 24-h period. © 2013 Elsevier Ltd. All rights reserved.


Zakariazadeh A.,Iran University of Science and Technology | Jadid S.,Iran University of Science and Technology | Siano P.,University of Salerno
International Journal of Electrical Power and Energy Systems | Year: 2014

In this paper a stochastic operational scheduling method is proposed to schedule energy and reserve in a smart distribution system with high penetration of wind generation. The wind power and demand forecast errors are considered in this approach and the reserve is furnished by both main grid generators and responsive loads. The consumers participate in both energy and reserve scheduling. A Demand Response Provider (DRP) aggregates loads reduction offers in order to facilitate small and medium loads participation in demand response program. The scheduling approach is tested on an 83-bus distribution test system over a 24-h period. Simulation results show that the proposed stochastic energy and reserve scheduling with demand response exhibits a lower operation cost if compared to the deterministic scheduling. © 2014 Elsevier Ltd. All rights reserved.


Zakariazadeh A.,Iran University of Science and Technology | Jadid S.,Iran University of Science and Technology | Siano P.,University of Salerno
International Journal of Electrical Power and Energy Systems | Year: 2014

Demand side participation is one of the important resources that help the operator to schedule generation and consumption with lower cost and higher security. Customers can participate in both energy and reserve operational scheduling and earn benefit from reducing or shifting their consumption. In this paper, a novel stochastic energy and reserve scheduling method for a microgrid (MG) which considers various type of demand response (DR) programs is proposed. In the proposed approach, all types of customers such as residential, commercial and industrial ones can participate in demand response programs which will be considered in either energy or reserve scheduling. Also, the uncertainties related to renewable distributed generation are modeled by proper probability distribution functions and are managed by reserve provided by both DGs and loads. The proposed method was tested on a typical MG system comprising different type of loads and distributed generation units. The results demonstrate that the adoption of demand response programs can reduce total operation costs of a MG and determine a more efficient use of energy resources. © 2014 Elsevier Ltd. All rights reserved.


Razavi S.M.R.,Arak University | Razavi S.M.J.,Iran University of Science and Technology | Miri T.,Arak University | Shirazian S.,Iranian Research Organization for Science and Technology
International Journal of Greenhouse Gas Control | Year: 2013

A two-dimensional model for the mass transport of carbon dioxide from the gas mixture in nanoporous membrane contactors was developed in this work. A solution of 2-amino-2-methyl-1-propanol and piperazine (activator of absorption) is used as a chemical solvent for capture of CO2. The diffusion in the radial and axial direction of the fibers, through the membrane and the shell of membrane contactor was investigated. The convection inside the tube and shell was also investigated along with chemical analysis. Computational fluid dynamics technique was used to solve the model equations including continuity and momentum equations. The predictions of the model were compared with the experimental data and good agreements were observed which confirmed the validity of developed mass transfer model. According to the presented results, an increase in the gas and liquid flow rate results in an increase in the rate of CO2 absorption (at NRe<20). Also, an increase in the concentration of piperazine results in an increase in the CO2 absorption of the gas mixture. This study indicates that the proposed model is capable of predicting the rate of CO2 capture in membrane contactors with good precision. © 2013 Elsevier Ltd.


Nasiraghdam H.,Islamic Azad University at Tehran | Jadid S.,Iran University of Science and Technology
Solar Energy | Year: 2012

In this paper, a novel multi-objective artificial bee colony algorithm is presented to solve the distribution system reconfiguration and hybrid (photo voltaic/wind turbine/fuel cell) energy system sizing. The purposes of the multi-objective optimization problem include the total power loss, the total electrical energy cost, and the total emission produced by hybrid energy system and the grid minimization, and the voltage stability index (VSI) of distribution system maximization. In the proposed algorithm, an external archive of non-dominated solutions is kept which is updated in each iteration. In addition, for preserving the diversity in the archive of Pareto solutions, the crowding distance operator is used. This algorithm is tested on 33 bus distribution systems and obtained non-dominated solutions are compared with the well-known NSGA-II and MOPSO methods. The solutions obtained by the MOABC algorithm have a good quality and a better diversity of the Pareto front compared with those of NSGA-II and MOPSO methods. © 2012 Elsevier Ltd.


Esmaili M.,Islamic Azad University at Tehran | Gharani K.,Iran University of Science and Technology | Shayanfar H.A.,Iran University of Science and Technology
IEEE Transactions on Power Systems | Year: 2013

Phasor measurement units (PMUs) have made it possible to observe and control wide-area power systems. In this paper, a new redundant observability method as a mixed-integer linear programming (MILP) is presented for optimal PMU placement. Redundant observation of buses enhances measurement reliability. The proposed method improves observability redundancy by a new objective function while using the same number of PMUs as the existing methods. Because of using MILP, the global optimal integer solution is achieved with a zero optimality gap. In addition, a systematic novel approach is proposed to incorporate already installed branch flow measurements in the PMU placement problem leading to a reduced number of PMUs required for system observability. This approach is able to handle both single and multiple flow measurements incident to a bus. PMU placement in case of PMU failure or branch outage is also studied. The proposed method along with an existing method is tested on four IEEE and Polish 3375-bus test systems. Obtained results, discussed in detail, show the efficiency of the proposed method in both speed and accuracy. © 2013 IEEE.


Ahmadi A.,Iran University of Science and Technology | Charwand M.,Tarbiat Modares University | Aghaei J.,Shiraz University of Technology
International Journal of Electrical Power and Energy Systems | Year: 2013

In the medium term planning, the objective of an electricity retailer is to configure its forward contract portfolio and to determine the selling price offered to its clients. To procure the electricity energy to be sold to the clients, a retailer has to face by two major challenges. Firstly, at buying electricity energy, it must cope with uncertain pool prices and sign forward contracts at higher average prices. Secondly, at selling electricity, it should handle the demand uncertainty and consider this fact that customers might choose a different retailer if the selling price is not competitive enough. In this paper the financial risk associated with the market price uncertainty is modeled using expected downside risk, which is incorporated explicitly as a constraint in the mixed-integer stochastic optimization problem. Roulette wheel mechanism and Lattice Monte Carlo Simulation (LMCS) are employed for random scenario generation wherein the stochastic optimization problem is converted into its respective deterministic equivalents. The proposed optimization problem is solved by a decomposition technique using Benders decomposition algorithm. A realistic case study is implemented to demonstrate the capability of the proposed method. © 2013 Elsevier Ltd. All rights reserved.


Aghaei J.,Shiraz University of Technology | Amjady N.,Semnan University | Shayanfar H.A.,Iran University of Science and Technology
Applied Soft Computing Journal | Year: 2011

In this paper, a new multi-objective model for electricity market clearing, considering both voltage and dynamic security aspects of the power system, is proposed. The objective functions of the proposed model include offer cost, voltage stability margin (VSM) and corrected transient energy margin (CTEM). A new solution method incorporating the lexicographic optimization and augmented ε-constraint method is proposed to solve the multi-objective optimization problem. The New England test system is used to demonstrate the performance of the proposed method. The proposed strategy is also compared with the conventional ε-constraint technique. © 2011 Published by Elsevier B.V. All rights reserved.


Mokhtarian M.N.,Islamic Azad University at Tehran | Sadi-Nezhad S.,Islamic Azad University at Tehran | Makui A.,Iran University of Science and Technology
Computers and Industrial Engineering | Year: 2014

Facility location selection problem is one of the challenging and famous kinds of MCDM problems including both quantitative and qualitative criteria. For each Multiple Criteria Decision Making (MCDM) problem, when the ratings of alternatives with respect to the criteria and/or the values of criteria's weights are presented by Interval Valued Fuzzy Numbers (IVFNs), the conventional fuzzy MCDM methods (Type-1 fuzzy MCDM methods) tend to be less effective. Therefore, the IVF-MCDM (Interval Valued Fuzzy MCDM) methods should be applied for solving such fuzzy MCDM problems. In this paper, we propose an IVF-VIKOR (VlseKriterijumska Optimizacija I Kompromisno Resenje) method based on uncertainty risk reduction in decision making process. By using such method, the reliability of the captured decisions in an IVF decision making problem is significantly increased. The proposed method is applied for solving two numerical examples that the former of which is a real application problem related to selecting a suitable location for digging some pits for municipal wet waste landfill in one of the largest cities in Iran. The second numerical example is presented with an aim of comparing our method with the two other IVF-MCDM methods. As a result, we found out the proposed method is reliable and practical for the facility location selection problems and other MCDM problems. Moreover, the proposed method has a considerable accuracy and is flexible and easy to use. © 2014 Elsevier Ltd. All rights reserved.


Farajpour A.,Islamic Azad University at Tehran | Farajpour A.,Isfahan University of Technology | Dehghany M.,Iran University of Science and Technology | Shahidi A.R.,Isfahan University of Technology
Composites Part B: Engineering | Year: 2013

In this paper, the axisymmetric buckling analysis of circular single-layered graphene sheets is studied by decoupling the basic constitutive equations based on the nonlocal theory of Eringen. The influences of temperature change, surface parameters and nonlocality on the buckling response of single-layered graphene sheet are investigated considering size-dependent material properties. Numerical solutions for buckling loads are computed using differential quadrature method (DQM). For comparison purpose, Galerkin method is also used to solve the nonlocal governing differential equation. DQM results are successfully verified with those of Galerkin method. The comparison of present results with the available molecular dynamics simulation data from the literature shows that the present formulation with appropriate values of surface and nonlocal parameters provides more accurate results than those obtained by the classical plate model. The results of present work can be used as benchmarks to evaluate future analyses of the circular nanoplates. © 2013 Elsevier Ltd. All rights reserved.


Ghadiri M.,Iran University of Science and Technology | Shirazian S.,Iranian Research Organization for Science and Technology
Chemical Engineering and Processing: Process Intensification | Year: 2013

Theoretical study on extraction of alkali metals using a membrane contactor is carried out in this work. A novel model is built to simulate the flow and the concentration in a membrane extractor based on the finite element analysis. CFD model is applied by solving the 2D Navier-Stokes equations as well as mass conservation equations for steady state conditions in membrane extractors. The model predicts of the velocity field, the pressure and the concentration of alkali metal in the membrane module under laminar flow regime. The results of simulation were used for determination of concentration distribution and effect of extractant concentration on extraction efficiency and mass flux of cesium in the membrane extractor. Moreover, the simulation results for the extraction of cesium using the membrane extractor were compared with the experimental data in order to validate the proposed mass transfer model and showed great agreement. © 2013 Elsevier B.V.


Korayem M.H.,Iran University of Science and Technology | Esmaeilzadehha S.,Islamic Azad University at Tehran
International Journal of Advanced Manufacturing Technology | Year: 2012

Abstract Lacking real-time visual feedback is one of the main problems in working with AFM in a nanoenvironment. To overcome this problem, we begin to design a virtual reality environment. First, nano-image is enhanced by using image processing technique and genetic algorithms then the location and number of nano-particles and other properties are determined. A nano-manipulation environment is implemented and the forces between the tip of the probe and nano-particle are analyzed, so that we increase the ability of user in driving nano-particle in this environment. In the first step, nano-image quality will be improved by applying different filters that each one is appropriate to eliminate one type of noise. Genetic algorithms are applied to determine a suitable set of appropriate filters among filters bank, then the location and number of nano-particles will be extracted by using image processing technique. For nano-manipulation operation, the dimensions of the base plate and exact place of nano-particles on it should be defined, and the user can choose the primary and final location of the nano-particle. The second stage of simulation is driving the nano-particle in such a way that the tip of atomic force microscopy probe aims at nano-particle with constant velocity. At this moment, the movement of the tip of the probe begins, and the nano-particle moves to a chosen place, so that the user can see the manipulation process. ©Springer-Verlag London Limited 2012.


Behbahani M.,Islamic Azad University at Tehran | Saghaee A.,Islamic Azad University at Tehran | Noorossana R.,Iran University of Science and Technology
Computers and Industrial Engineering | Year: 2012

Statistical process control (SPC) is a sub-area of statistical quality control. Considering the successful results of the SPC applications in various manufacturing and service industries, this field has attracted a large number of experts. Despite the development of knowledge in this field, it is hard to find a comprehensive perspective or model covering such a broad area and most studies related to SPC have focused only on a limited part of this knowledge area. According to many implemented cases in statistical process control, case-based reasoning (CBR) systems have been used in this study for developing of a knowledge-based system (KBS) for SPC to organize this knowledge area. Case representation and retrieval play an important role to implement a CBR system. Thus, a format for representing cases of SPC and the similarity measures for case retrieval are proposed in this paper. © 2012 Elsevier Ltd. All rights reserved.


Fazilat H.,Islamic Azad University at Tehran | Akhlaghi S.,Islamic Azad University at Tehran | Shiri M.E.,Iran University of Science and Technology | Sharif A.,Tarbiat Modares University
Polymer | Year: 2012

A multi-structured architecture of artificial intelligence techniques including artificial neural network (ANN), adaptive-neuro-fuzzy-interference system (ANFIS) and radial basis function (RBF) were developed to predict thermal degradation kinetics (TDK) of nylon6 (NY6)/feather keratin (FK) blend films. By simultaneous implementation of back-propagation ANN and feed-forward ANFIS modeling on the experimental data obtained from thermogravimetric analysis (TGA) method, thermal degradation behavior of various compositions of NY6/FK blends was successfully predicted with minimum mean square errors (MSE). RBF networks were then trained on the TGA data at one heating rate for predicting analogs information at different heating rates, providing sufficient feed for TDK modeling. According to the comparison made between experimental and predicted kinetic parameters of thermal degradation process calculated from Friedman and Kissinger methods, the proposed prediction effort could effectively contribute to the estimation of precise activation energy (E a) and reaction order (n) values with least amount of experimental work and most accuracy. © 2012 Elsevier Ltd. All rights reserved.


Karimi A.,Iran University of Science and Technology | Karimi A.,Iran National Institute of Genetic Engineering and Biotechnology | Navidbakhsh M.,Iran University of Science and Technology | Faghihi S.,Iran National Institute of Genetic Engineering and Biotechnology
Journal of Biomaterials and Tissue Engineering | Year: 2014

The development of scaffolding materials for clinical applications depends on a thorough understanding of the mechanics of tissue-material interaction. Mechanical failure or failure strength of materials has a key role in their performance particularly in load bearing applications. An ideal scaffolding material should have the physical and mechanical properties as close as possible to those of the tissue being replaced as the same time as supporting cell adhesion and growth while maintaining its shape. Regarding the synthetic polymers used for scaffold preparation, polyvinyl alcohol (PVA) is one of the first synthetic macromolecules tested to produce spongy matrices for tissue regeneration. PVA has broad applications including tissue mimicking, vascular cell culture, vascular implanting, heart valves, cartilage substitute, contact lenses, and corneal implants. There is however, a lack of sufficient data on the mechanical failure of PVA-based materials and this brings about limited application of PVA in tissue engineering applications. In this study, a biomechanical method is used to characterize the mechanical failure of fabricated PVA sponge (P-sponge) and compared with two commercially available sponges (CENEFOM and EYETEC) using a biaxial puncture testing machine. It is revealed that the failure stress of P-sponge is 9.91% and 3.85% higher than that of the CENEFOM and EYETEC sponges. It is hoped that the mechanical information obtained here can provide insight into biomechanical approaches that elucidate the potential causes of early rupture, and suggest future treatments for prevention of mechanical failure of PVA sponges used as scaffolding materials. © 2014 American Scientific Publishers, All rights reserved.


Bisadi H.,Iran University of Science and Technology | Tavakoli A.,Islamic Azad University at Tehran | Tour Sangsaraki M.,Iran University of Science and Technology | Tour Sangsaraki K.,Islamic Azad University at Īlām
Materials and Design | Year: 2013

In last years, friction stir welding (FSW) method has represented better microstructure and mechanical properties than conventional methods in welding aluminum alloys. Many studies have been performed on joining aluminum alloys in cases of similar and dissimilar FSW lap joints. In this study FSW was used to join sheets of AA5083 aluminum alloy and commercially pure copper and the effects of process parameters including rotational and welding speeds on the microstructures and mechanical properties of the joints were investigated and different joint defects were analyzed. The experiments were performed with rotational speeds of 600, 825, 1115 and 1550. rpm each of them with welding speeds of 15 and 32. mm/min. It was observed that very low or high welding temperatures lead to many joint defects. Also intermetallic compounds and their effects on the mechanical properties of the joints were investigated. The best joint tensile shear properties were achieved at the rotational speed of 825. rpm and welding speed of 32. mm/min. © 2012 Elsevier Ltd.


Mosaddegh E.,Iran University of Science and Technology | Mosaddegh E.,Research Institute of Environmental science | Hassankhani A.,HIGH-TECH
Tetrahedron Letters | Year: 2011

A new, efficient, and environmentally benign protocol for the one-pot, four-component synthesis of 2,2-dimethyl-13-phenyl-2,3-dihydro-1H-indazolo[2,1- b]phthalazine-1,6,11(13H)-trione by condensation of phthalic anhydride, hydrazinium hydroxide, aromatic aldehydes, and dimedone catalyzed by Ce(SO 4)2·4H2O as an ecofriendly catalyst with high catalytic activity and reusability at 125 °C under solvent-free conditions is reported. The reaction proceeds to completion within 5-10 min in 71-95% yield. To the best of our knowledge, this new procedure provides the first example of an efficient synthetic method for 2H-indazolo[2,1-b] phthalazine-1,6,11(13H)-trione via a four-component reaction. © 2010 Elsevier Ltd. All rights reserved.


Ahmadi A.,Iran University of Science and Technology | Aghaei J.,Shiraz University of Technology | Shayanfar H.A.,Iran University of Science and Technology | Rabiee A.,Shahrekord University
Applied Soft Computing Journal | Year: 2012

This paper presents a method for hydro-thermal self scheduling (HTSS) problem in a day-ahead joint energy and reserve market. The HTSS is modeled in the form of multiobjective framework to simultaneously maximize GENCOs profit and minimize emissions of thermal units. In the proposed model the valve loading effects which is a nonlinear problem by itself is linearized. Also a dynamic ramp rate of thermal units is used instead of a fix rate leading to more realistic formulation of HTSS. Furthermore, the multi performance curves of hydro units is developed and prohibited operating zones (POZs) of thermal unit are considered in HTSS problem. Also, in the proposed framework, the mixed integer nonlinear programming (MINLP) of HTSS is converted to mixed integer programming (MIP) problem that can be effectively solved by optimization softwares even for real size power systems. The lexicographic optimization and hybrid augmented-weighted ε-constraint technique is implemented to generate Pareto optimal solutions. The best compromised solution is adopted either by using a fuzzy approach or by considering arbitrage opportunities to achieve more profit. Finally, the effectiveness of the proposed method is studied based on the IEEE 118-bus system. © 2012 Elsevier B.V.


Salari M.,University of Tehran | Tabar M.M.,Iran University of Science and Technology | Tabar A.M.,Islamic Azad University at Tehran | Danesh H.A.,Islamic Azad University at Tehran
Numerical Heat Transfer; Part A: Applications | Year: 2012

This article presents the results of a numerical study on mixed convection within a square lid-driven which was heated simultaneously by two finite heat sources on the bottom and side walls, and also filled with nanofluids. The results were presented for different nanofluids. The governing equations were solved using a finite volume approach by the SIMPLE algorithm. The effects of the Rayleigh number, Reynolds number, the solid volume fraction, the dimensions of heaters, and their locations on the streamlines and isotherms contours were investigated accurately. Also, the effects of the above parameters on the average Nusselt number along two heat sources were precisely presented. Moreover, variations of the average Nusselt number of two heaters were considered whenever one heater was fixed and the location of the other heater was varied along the wall. In addition, variations of the length of one heater on the average Nusselt number were also studied whenever the length of the other heater was fixed. © 2012 Copyright Taylor and Francis Group, LLC.


Sharifi Asl S.M.,Iran University of Science and Technology | Rowshanzamir S.,Iran University of Science and Technology | Eikani M.H.,Iranian Research Organization for Science and Technology
Energy | Year: 2010

The performance of a fuel cell can be expressed by the voltage-load current (V-I) characteristics. In this study, two mathematical modelling for computing the steady-state and dynamic voltage-current (V-I) characteristics of PEM fuel cell stacks have been developed. For determining the humidity of the membrane in steady-state conditions, mathematical and theoretical equations are considered. This value is not an adjustable parameter. The goal of dynamic modelling is to find the response of the system against the load variations. In this research, in addition to the charge double layer phenomenon, the effects of temperature and gas flows are taken into account, then the fuel cell system is divided into three control volumes and thus a lumped-parameter model for these sub-systems is established using the mass and heat transfer equations. The proposed models are implemented in Matlab/Simulink environment. Additionally, these models were tested for the SR-12Modular PEM Generator, the Ballard Mark V FC, the BCS 500-W stack and various experimental data in open literature. They exhibit excellent agreement with other simulation and experimental results. © 2009 Elsevier Ltd. All rights reserved.


Mokhtari A.,Iran University of Science and Technology | Moghadas Nejad F.,Amirkabir University of Technology
Construction and Building Materials | Year: 2012

In this study, different additives such as mineral fiber, cellulose fiber and styrene-butadiene-styrene (SBS) were used to modify stone matrix asphalt (SMA) mixtures, and performance tests were performed for modified and unmodified mixtures. A mechanistic-empirical design procedure was employed to assess the effect of different additives in improving the service life of the pavement or reduction in thickness of pavement layers. Based on the results, SBS was more effective in improving the performance of asphalt mixtures compared to the fibers. According to the results of mechanistic-empirical design, the service life of the pavement system modified with mineral, cellulose and SBS were 1.07, 1.081 and 1.243 times more than unmodified mix, respectively. © 2012 Elsevier Ltd. All rights reserved.


Hosseini-Toudeshky H.,Amirkabir University of Technology | Ghaffari M.A.,Amirkabir University of Technology | Mohammadi B.,Iran University of Science and Technology
Composite Structures | Year: 2012

Fatigue crack growth analyses of aluminum panels with stiffeners repaired by composite patches have been rarely investigated. Generally, cracks may occur around the rivets which are capable to propagate under cyclic loadings. A composite patch can be used to stop or retard the crack growth rate. In this investigation, finite element method is used for the crack propagation analyses of stiffened aluminum panels repaired with composite patches. In these analyses, the crack-front can propagate in 3-D general mixed-mode conditions. The incremental 3-D crack growth of the repaired panels is automatically handled by a developed ANSYS Parametric Design Language (APDL) code. Effects of rivets distances and their diameters on the crack growth life of repaired panels are investigated. Moreover, the obtained crack-front shapes at various crack growth steps, crack trajectories, and life of the unrepaired and repaired panels with various glass/epoxy patch lay-ups and various patch thicknesses are discussed. © 2012 Elsevier Ltd.


Farrokhabadi A.,Amirkabir University of Technology | Hosseini-Toudeshky H.,Amirkabir University of Technology | Mohammadi B.,Iran University of Science and Technology
Composite Structures | Year: 2011

The previously developed micromechanical approaches for the analysis of transverse cracking and induced delamination are limited for laminates with specific lay-ups such as cross-ply and specific loading conditions. In this paper a new micromechanical approach is developed to overcome such shortcomings. For this purpose, a unit cell in the ply level of composite laminate including transverse cracking and delamination is considered. Then, the governing equations for the stress and displacement fields of the unit cell are derived. The obtained approximate stress field is used to calculate the energy release rate for the propagation of transverse cracking and induced delamination. To show the capability of the new method, it is employed for the analyses of general laminates with [0/90]. s, [45/-45]. s, [30/-30]. s and [90/45/0/-45]. s lay-ups under combined loadings to calculate the energy release rate due to the transverse cracking and induced delamination. It is shown that the obtained energy release rates for transverse cracking and delamination initiation are in good agreement with the available results in the literature and finite element method. Furthermore, the occurrence priority of further transverse cracks and/or delamination at each damage state of the laminates will be discussed. © 2010 Elsevier Ltd.


Ramezanianpour A.A.,Amirkabir University of Technology | Ghahari S.A.,Amirkabir University of Technology | Esmaeili M.,Iran University of Science and Technology
Construction and Building Materials | Year: 2014

In this study microscopic and mechanical properties of ordinary concrete exposed to CO2 gas, saline water, and the combination of CO 2 gas and saline water were investigated by an accelerated test method. Specimens with different water to cement ratio of 0.35, 0.4, and 0.45 were retained in an apparatus which was developed to provide an environment to simulate tide cycles. The CO2 gas pressure, NaCl solution concentration, temperature, and relative humidity were kept constant and controlled, and tide cycles were executed automatically each 6 h. Specimens were retained in CO2 gas and in NaCl solution with environment characteristics tantamount to that of the apparatus. Microscopic structure and interfacial transition zones of the specimens maintained in all three conditions were studied by implementing scanning electron microscope (SEM). In order to identify crystalline phases and morphological and structural characteristics, nanographs were obtained by transmission electron microscopy (TEM), and phase change due to carbonation and chloride ion ingress were studied along with X-ray diffraction analysis (XRD). Moreover, in order to signify the mechanical properties of specimens, compressive strength, surface resistivity, and CO 2 consumption were measured. It was found that more C-S-H gel and CH crystals has been formed in the presence of sole CO2 gas, and higher compressive strength is achieved compared to the combined CO2 gas and chloride ion ingress, and separate saline water. Besides, due to the presence of moisture in the pore solution of specimens maintained in the combined condition, less CO2 gas and chloride ion ingresses were observed. © 2014 Elsevier Ltd. All rights reserved.


Mohammadi M.,Iran University of Science and Technology | Shahhosseini S.,Iran University of Science and Technology | Bayat M.,Research Institute of Petroleum Industry RIPI
International Journal of Heat and Fluid Flow | Year: 2012

Coalescence of two water droplets in the oil was simulated using Computational Fluid Dynamics (CFD) techniques. The finite volume numerical method was applied to solve the Navier-Stokes equations in conjunction with the Volume of Fluid (VOF) approach for interface tracking. The effects of some parameters consisting of the collision velocity, off-center collision parameter, oil viscosity and water-oil interfacial tension on the coalescence time were investigated. The simulation results were validated against the experimental data available in the literature. The results revealed that quicker coalescence could be achieved if the head-on collisions occur or the droplets approach each other with a high velocity. In addition, low oil viscosities or large water-oil interfacial tensions cause less coalescence time. Moreover, a correlation was developed to predict coalescence efficiency as a function of the mentioned parameters. © 2012 Elsevier Inc.


Faraji S.,Islamic Azad University at Varamin | Faraji A.H.,Islamic Azad University at Varamin | Noori S.R.,Iran University of Science and Technology
Materials and Design | Year: 2014

Cu-P/micro-SiC and Cu-P/nano-SiC composite coatings were deposited by electroless plating and their composition and microstructure were observed by EDX (energy-dispersive analysis), SEM (scanning electron microscope) and XRD (X-ray diffraction). The corrosion resistance, microhardness and the wear resistance of the Cu-P/nano-SiC composite coatings were measured and the comparison with those of Cu coatings and Cu-P/micro-SiC coatings were given. The anti-corrosion properties of Cu coatings were investigated in 3.5% NaCl solution by the potentiodynamic polarisation and electrochemical impedance spectroscopy (EIS) techniques. Among three kinds of Cu-P based coatings, the corrosion resistance, hardness and wear resistance of Cu-P/nano-SiC coatings were the largest. This indicates that the precipitation of nano-SiC particles would improve the corrosion resistance, hardness and wear resistance of the Cu-P coatings significantly. © 2013 Elsevier Ltd.


Ghoddousi P.,Iran University of Science and Technology | Eshtehardian E.,Tarbiat Modares University | Jooybanpour S.,Amirkabir University of Technology | Javanmardi A.,Iran University of Science and Technology
Automation in Construction | Year: 2013

Minimizing both project time and cost is an important matter in today's competitive environment. Therefore trade-off between project time and cost is necessary. In projects, each activity can be started at different time points, depending on its precedence relationship and resource availability. Also cost and duration of the activities could be changed depending on the allocated resources. In addition, another strategy that affects the project total time and cost is resource leveling, which is applied to reduce excessive fluctuations in the resource usage. In this paper multi-mode resource-constrained project scheduling problem (MRCPSP), discrete time-cost trade-off problem (DTCTP) and also resource allocation and resource leveling problem (RLP) are considered simultaneously. This paper presents the multi-mode resource-constrained discrete time-cost-resource optimization (MRC-DTCRO) model in order to select starting the time and the execution mode of each activity satisfying all the project constraints. To solve these problems, non-domination based genetic algorithm (NSGA-II) is employed to search for the non-dominated solutions considering total project time, cost, and resources moment deviation as three objectives. The results of MRC-DTCRO model presented in this paper show that adding the resource leveling capability to the previously developed multi-mode resource-constrained discrete time-cost trade-off problem (MRC-DTCTP) models provides more practical solutions in terms of resource allocation and leveling, which makes this research applicable to both construction industry and researchers. © 2012 Elsevier B.V. All rights reserved.


Rikhtegar F.,Iran University of Science and Technology | Ketabchi M.,Amirkabir University of Technology
Materials and Design | Year: 2010

The thixoextrusion process is a new method for manufacturing complicated and net shape components through which high strength materials can be formed more easily. In this study 7075 Al alloy which has low extrudability has been thixoformed by forward extrusion process. As it is known conventional extrusion of 7075 Al alloy has been very difficult due to high strength and multi-phase microstructural characterization. In this research, by applying the advantages of semisolid processing, the applied pressure for extrusion is decreased and desired mechanical properties were reached near the standard predictable properties for wrought 7075 Al alloy under T6 tempering conditions, for example tensile and yield strength and hardness of samples of thixoextrusion product sufficiently agree with same expected properties of wrought 7075 Al alloy and only elongation is decreased along this process. © 2010 Elsevier Ltd.


Kaveh A.,Iran University of Science and Technology | Shakouri Mahmud Abadi A.,Building Research Institute, Egypt
Journal of Constructional Steel Research | Year: 2010

In this study, cost optimization of a composite floor system is performed utilizing the harmony search algorithm and an improved harmony search algorithm. These algorithms imitate the musical performance process that takes place when a musician searches for a better state of harmony, similar to the optimum design process which looks for the optimum solution. A composite floor system is designed by the LRFD-AISC method, using a unit consisting of a reinforced concrete slab and steel beams. The objective function is considered as the cost of the structure, which is minimized subjected to serviceability and strength requirements. Examples of composite floor systems are presented to illustrate the performance of the presented algorithms. © 2010 Elsevier Ltd. All rights reserved.


Vahidi B.,Amirkabir University of Technology | Esmaeeli E.,Iran University of Science and Technology
Computer Applications in Engineering Education | Year: 2013

Differential protection was already applied toward the end of the 19th century and was one of the first protection systems ever used. Faults are detected by comparison of the currents flowing into and out of the protected plant item. As a result of the fast tripping with absolute selectivity, it is suited as main protection of all important items of plant. The article presents an approach to teaching relay laboratory using specially designed exercises that can be done using MATLAB-SIMULINK. This article presents a MATLAB-SIMULINK- based technology to simulate differential relay for determining behavior of it during transformer internal fault protection. The results show that this simulation method can work properly and this design can be used for power system simulation in MATLAB-SIMULINK. Evaluation of the simulation with more than 60 students is very positive in terms of their developing confidence in and understanding of this kind of relay operation. © 2010 Wiley Periodicals, Inc.


Khaledi A.G.,Iran University of Science and Technology | Afshar S.,Iran University of Science and Technology | Jahromi H.S.,Research Institute of Petroleum Industry RIPI
Materials Chemistry and Physics | Year: 2012

In this paper, ZnAl 2O 4 spinel powders were prepared by a sol-gel route using zinc nitrate and aluminium nitrate in polar solvent (e.g. water) as the starting materials from the viewpoint that they are low-cost. A study of the effect of chelating agents such as sucrose (S), citric acid (CA) and triethanolamine (TEA) with a different weight ratio on the structure of ZnAl 2O 4 is reported. The characterization of the synthesized ZnAl 2O 4 powder was performed by XRD, FT-IR, Diffuse reflectance spectroscopy (DRS) and scanning electron microscopy (SEM). The results show that the powders made by the weight ratio 1:4 (metal:chelating agent) had a better morphological structure than the other weight ratios (1:1 and 1:2). Crystallite sizes vary from 16 nm for ZAO(S) up to 26 nm for ZAO(TEA). It was found that crystallite size, specific surface area and morphology are strongly dependent on the chelating agent/metal ratio and kinds of chelating agents. © 2012 Elsevier B.V. All rights reserved.


Salamat-Talab M.,Iran University of Science and Technology | Nateghi A.,University of Tehran | Torabi J.,Amirkabir University of Technology
International Journal of Mechanical Sciences | Year: 2012

In this paper, Modified couple stress theory is developed for third-order shear deformation functionally graded (FG) micro beam. Classical Continuum theories are not able to capture size effects while higher order continuum theories consider material length scale parameters to improve the results in micro scales by interpreting size dependencies. By applying Hamilton's principle, governing equations, boundary and initial conditions are derived for a FG micro beam. It is assumed that properties of the FG micro beam follow a power law form through thickness. In addition, Poisson's ratio is assumed constant in the current model. Bending and free vibration of the simply supported FG micro beam is analyzed to illustrate size effects. It is observed that if the thickness of the beam is in the order of the material length scale parameter, size effects are more considerable. It is shown that size dependencies of FG micro beams are quite different from isotropic homogeneous beams as they have maximum and minimum size effects for certain values of power index of material distribution and Poisson's ratio. Moreover, it is shown that the results obtained by the present model deviates significantly from those in which Poissons effect is neglected. Also, the effect of Poisson's ratio on the deflection and natural frequency based on modified couple stress theory is proven to be different from Classical one. The numerical results for simply supported thin beams show that the first natural frequency estimated by the current model is higher than the classical one. In addition, it is observed that size effect is more significant for higher vibration modes. © 2012 Elsevier Ltd. All rights reserved.


Mokhtari A.,Iran University of Science and Technology | Nejad F.M.,Amirkabir University of Technology
Journal of Materials in Civil Engineering | Year: 2013

Stone-matrix asphalt (SMA) is a type of hot-mix asphalt that can reduce the cost of maintenance and rehabilitation of pavements through decreasing the amount of permanent deformation during its service life. In addition, warm-mix asphalt (WMA) has been recently used to reduce the mixing and compaction temperatures of asphalt concrete and potentiallydecrease the initial cost of asphalt mixtures, especially in countries for which energy costs are high. The primary purpose of this research is to combine these technologies to produce more efficient asphalt mixtures. To this end, two different additives [cellulose fiber and styrene-butadiene-styrene (SBS)] were used to construct typical SMA mixtures, and a type of WMA additive (wax) was used to prepare warm SMA specimens. Modified binders were subjected to binder properties tests. Mixture performance tests, including the Marshall, indirect tensile strength, moisture susceptibility, dynamic creep, and resilient modulus tests were also performed to evaluate the performance properties of different types of SMA mixtures. A mechanisticempirical design procedure was conducted to investigate the benefit of modification. The results indicate that Fischer-Tropsch (FT) wax is capable ofenhancing the base binder properties. Although different percents of wax could reduce theamount of binder drain down, this reduction was not adequate. Consequently, the use of anadditional additive may be necessary. The effect of wax on the performance properties of SMA mixtures was also insignificant, although there were some improvements. Moreover, by comparing the test results, good correlations were obtained between various performance properties of SMA mixtures, all of which were significant. The use of cellulose fiber, SBS, and FTwax would respectively increase the service life of the pavement 1.08, 1.243, and1.154 times more than the corresponding unmodified mixtures. © 2012 American Society of Civil Engineers.


Tehrani Dehkordi M.,Shahrekord University | Nosraty H.,Amirkabir University of Technology | Shokrieh M.M.,Iran University of Science and Technology | Minak G.,University of Bologna | Ghelli D.,University of Bologna
Materials and Design | Year: 2013

Low-velocity impact and compression after impact (CAI) tests were performed to investigate the impact behavior of hybrid composite laminates reinforced by basalt-nylon intraply fabrics. The purpose of using this hybrid composite is to combine the good mechanical property of basalt fiber as a brittle fiber with the excellent impact resistance of nylon fiber as a ductile fiber. Five different types of woven fabric with different contents of nylon (0%, 25%, 33.3%, 50% and 100%) were used as reinforcement. The effect of nylon/basalt fiber content on impact parameters, impact damage behavior and CAI strength was studied at different nominal impact energy levels (16, 30 and 40. J). The results indicate that at low impact energy, hybridization and variation in basalt/nylon fiber content cannot improve the impact performance of composite plates. With increasing impact energy, the impact performance becomes more and more dependent on the content of nylon and basalt. © 2012 Elsevier Ltd.


Jalalvand M.,Amirkabir University of Technology | Hosseini-Toudeshky H.,Amirkabir University of Technology | Mohammadi B.,Iran University of Science and Technology
Composite Structures | Year: 2013

Diffuse delamination induced by transverse cracking is usually the secondary damage mode when a composite laminate experiences tensile loading. The fist damage mechanism in such a laminate is transverse cracking which has been widely investigated with both analytical methods and " mechanism-based" constitutive laws. Delamination induced by matrix cracking is already studied extensively by analytical approaches, however, a proper homogenization way has not been proposed yet. In this paper, a modification to an available cohesive constitutive law is proposed which is capable of considering the effect of diffuse delamination without the necessity of consideration of an actual discontinuity between the layers. The proposed constitutive law is then compared against its equivalent models containing interlaminar discontinuity and it is shown that the obtained results from both models are in good. Then the proposed modification is used in Double Cantilever Beam (DCB) specimen and the obtained results are found coincident with the equivalent model with diffuse discontinuities at the interface. Finally, a damaged cross-ply laminate is modeled under the boundary conditions of tensile loading and also 3-point bending with and without the proposed cohesive modification. In tensile loading, the results of both cases are similar; however, it is shown that in bending, the unmodified cohesive law predicts the lateral stiffness larger than the proposed modification. The lateral stiffness of the equivalent model with discontinuities as crack indicates that the proposed modification is able to properly consider the lateral stiffness decrease. © 2013 Elsevier Ltd.


Talatahari S.,University of Tabriz | Kaveh A.,Iran University of Science and Technology | Sheikholeslami R.,Amirkabir University of Technology
Structural and Multidisciplinary Optimization | Year: 2012

The imperialist competitive algorithm is a new socio-politically motivated optimization algorithm which recently is applied for structural problems. This paper utilizes the idea of using chaotic systems instead of random processes in the imperialist competitive algorithm. The resulting method is called chaotic imperialist competitive algorithm (CICA) in which chaotic maps are utilized to improve the movement step of the algorithm. Some well-studied truss structures are chosen to evaluate the efficiency of the new algorithm. © 2012 Springer-Verlag.


Kaveh A.,Iran University of Science and Technology | Shakouri Mahmud Abadi A.,Building Research Institute, Egypt
International Journal of Civil Engineering | Year: 2011

Cost optimization of the reinforced concrete cantilever soil retaining wall of a given height satisfying some structural and geotechnical design constraints is performed utilizing harmony search and improved harmony search algorithms. The objective function considered is the cost of the structure, and design is based on ACI 318-05. This function is minimized subjected to design constraints. A numerical example of the cost optimization of a reinforced concrete cantilever retaining wall is presented to illustrate the performance of the presented algorithms and the necessary sensitivity analysis is performed.


Shahandeh H.,Iran University of Science and Technology | Ivakpour J.,Research Institute of Petroleum Industry RIPI | Kasiri N.,Iran University of Science and Technology
Energy | Year: 2014

HIDiC (Heat-Integrated Distillation Column) is an effective energy-saving configuration especially for the separation of close boiling point mixtures. In this work, the stochastic methodology has been applied for optimization of both internal and external HIDiCs. The use of GA (Genetic Algorithm) to find the optimal HIDiC configuration is presented while the fitness function is set to be the TAC (Total Annual Cost). HIDiC simulation has been performed based on the modified MESH equations using a rigorous thermodynamic model. Introducing a novel integer variable (the Layout number) leading to a more effective solution for the examined case study. This variable can generate systematically more energy efficient candidates for both internal and external HIDiCs. Benzene-toluene separation has been investigated by the proposed optimization procedure. The multivariable problem can be successfully optimized by GA while a good initial estimation is not essential. Based on the final results, up to 6.60% and 9.75% TAC reduction have been accomplished in external and internal HIDiCs optimization using the proposed method compared to the reported solutions in a previous work for the examined case study. However, VRC (Vapor Recompression Column) optimization at the end of presented work results 7.89% TAC reduction rather than optimal HIDiC. © 2013 Elsevier Ltd.


Hajmohammadi M.R.,Amirkabir University of Technology | Maleki H.,Iran University of Science and Technology | Lorenzini G.,University of Parma | Nourazar S.S.,Amirkabir University of Technology
Advanced Powder Technology | Year: 2015

Consideration is given to flow and heat transfer of nano-fluids over a permeable flat plate with convective boundary condition. The governing partial differential equations are transformed into ordinary differential equations using similarity solutions, before being solved numerically. Two types of nano-fluids, Cu-water and Ag-water are considered. The effects of nano-particles volume fraction, the type of nano-particles and permeability parameter on skin friction and convection heat transfer coefficient are studied and discussed. It is shown that the increment in skin friction is a considerable drawback imposed by Cu-water and Ag-water nano-fluids, especially in case of injection. In the cases of injection and impermeable surface, increasing the nano-particles volume fraction results in augmentation of convection heat transfer rate. However, in the case of suction, adding Cu and Ag particles reduces the convection heat transfer coefficient at the surface in spite of thermal conductivity enhancement imposed by the nano-particles. © 2014 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.


Ahmadizar F.,University of Kurdistan | Ghazanfari M.,Iran University of Science and Technology | Fatemi Ghomi S.M.T.,Amirkabir University of Technology
Computers and Operations Research | Year: 2010

This paper deals with a stochastic group shop scheduling problem. The group shop scheduling problem is a general formulation that includes the other shop scheduling problems such as the flow shop, the job shop and the open shop scheduling problems. Both the release date of each job and the processing time of each job on each machine are random variables with known distributions. The objective is to find a job schedule which minimizes the expected makespan. First, the problem is formulated in a form of stochastic programming and then a lower bound on the expected makespan is proposed which may be used as a measure for evaluating the performance of a solution without simulating. To solve the stochastic problem efficiently, a simulation optimization approach is developed that is a hybrid of an ant colony optimization algorithm and a heuristic algorithm to generate good solutions and a discrete event simulation model to evaluate the expected makespan. The proposed approach is tested on instances where the random variables are normally, exponentially or uniformly distributed and gives promising results. © 2009.


Karimi-Nasab M.,Iran University of Science and Technology | Ghomi S.M.T.F.,Amirkabir University of Technology
International Journal of Production Research | Year: 2012

The production scheduling problem is to find simultaneously the lot sizes and their sequence over a finite set of planning periods. This paper studies a single-stage production scheduling problem subject to controllable process times and sequence-dependent setups for deteriorating items. The paper formulates the problem by minimising two objectives of total costs and total variations in production volumes simultaneously. The problem is modelled and analysed as a mixed integer nonlinear program. Since it is proved that the problem is NP-hard, a problem-specific heuristic is proposed to generate a set of Pareto-optimal solutions. The heuristic is investigated analytically and experimentally. Computational experiences of running the heuristic and non-dominated sorting genetic algorithm-I over a set of randomly generated test problems are reported. The heuristic possesses at least 56.5% (in the worst case) and at most 94.7% (in the best case) of total global Pareto-optimal solutions in ordinary-size instances. © 2012 Copyright Taylor and Francis Group, LLC.


Moazami D.,University Putra Malaysia | Behbahani H.,Iran University of Science and Technology | Muniandy R.,University Putra Malaysia
Expert Systems with Applications | Year: 2011

With regard to limits in budget, inevitably, one must choose prioritized projects in pavements rehabilitation and maintenance process. This paper looks into prioritization based upon a model including all effects of important factors like pavement condition index, traffic volume, road width as well as rehabilitation and maintenance cost. Since defining a model that introduces all those factors was difficult, a more advanced modeling named fuzzy logic was referred for the problem of prioritization. Although analytical hierarchy process can be used for decision making process as well, fuzzy modeling lets one have more precise choices for the outcome. Finally with the help of MATLAB software and coded M-files, inference engines such as Product engine, Dienes-Rescher and Lukasiewicz were all tested and the logical favorite separation for this application was found in product inference engine. As a case study some streets located in district No. 6 of Tehran municipality were selected and the favorite mathematical model was executed on those streets. This model was used for prioritizing these 131 sections. © 2010 Elsevier Ltd. All rights reserved.


Kaveh A.,Iran University of Science and Technology | Talatahari S.,University of Tabriz
Engineering Computations (Swansea, Wales) | Year: 2011

Purpose: Meta-heuristic methods are powerful in obtaining the solution of optimization problems. Hybridizing of the meta-heuristic algorithms provides a scope to improve the searching abilities of the resulting method. The purpose of this paper is to provide a new hybrid algorithm by adding positive properties of the particle swarm optimization (PSO) algorithms to the charged system search (CSS) to solve constrained engineering optimization problems. Design/methodology/approach: The main advantages of the PSO consisting of directing the agents toward the global best (obtained by the swarm) and the local best (obtained by the agent itself) are added to the CSS algorithm to improve its performance. In the present approach, similar to the original CSS, each agent is affected by other agents considering the governing laws of electrical physics. However, the kind of the forces can be repulsive and attractive. In order to handle the constraints, the fly-to-boundary method is utilized as an improved feasible-based method. Findings: Four variants of hybrid methods are proposed. In these algorithms, the charged memory (CM) is changed to save the local best positions of agents. Utilizing this new CM to determine the direction and amount of movement of agents improve the power of the algorithms. When only this memory is utilized (method I), exploitation ability of the algorithm increases and when only two agents from CM in addition to other agents in the current iteration are used, then the exploration ability increases (method II). In order to have a good balance between exploration and exploitation of the algorithms, methods III and IV are proposed, where some agents of the memory and some other from the current agents are utilized. Method IV in which the numbers of used agents from the CM increase linearly, has a better search ability in addition to a powerful exploitation making this variant superior compared to the others. Originality/value: In this paper, four hybrid methods are presented and applied to some benchmark engineering optimization problems. The new algorithms are compared to those of the other advanced meta-heuristic methods to illustrate the effectiveness of the proposed methods. © Emerald Group Publishing Limited 0264-4401.


Kaveh A.,Iran University of Science and Technology | Talatahari S.,University of Tabriz
Structural and Multidisciplinary Optimization | Year: 2011

Dome structures provide cost-effective solutions for covering large areas without intermediate supports. In this article, simple procedures are developed to reach the configuration of the geodesic domes. A new definition of dome optimization problems is given which consists of finding optimal sections for elements (size optimization), optimal height for the crown (geometry optimization) and the optimum number of elements (topology optimization) under determined loading conditions. In order to find the optimum design, the recently developed meta-heuristic algorithm, known as the Charged System Search (CSS), is applied to the optimum design of geodesic domes. The CSS takes into account the nonlinear response of the domes. Using CSS, the optimum design of the geodesic domes is efficiently performed. © 2010 Springer-Verlag.


Bakhshandeh-Chamazkoti R.,Iran University of Science and Technology
International Journal of Geometric Methods in Modern Physics | Year: 2015

In the present paper, the equivalence problem for fourth-order differential operators with one variable under general fiber-preserving transformation using the Cartan method of equivalence is applied. Two versions of equivalence problems are considered. First, the direct equivalence problem and second equivalence problem is to determine the sufficient and necessary conditions on two fourth-order differential operators such that there exists a fiber-preserving transformation mapping one to the other according to gauge equivalence. © 2015 World Scientific Publishing Company.


Qodmanan H.R.,Iran University of Science and Technology | Nasiri M.,Iran University of Science and Technology | Minaei-Bidgoli B.,Iran University of Science and Technology
Expert Systems with Applications | Year: 2011

Multi objective processing can be leveraged for mining the association rules. This paper discusses the application of multi objective genetic algorithm to association rule mining. We focus our attention especially on association rule mining. This paper proposes a method based on genetic algorithm without taking the minimum support and confidence into account. In order to improve algorithm efficiency, we apply the FP-tree algorithm. Our method extracts the best rules that have best correlation between support and confidence. The operators of our method are flexible for changing the fitness. Unlike the Apriori-based algorithm, it does not depend on support. Experimental study shows that our technique outperforms the traditional methods. © 2010 Elsevier Ltd. All rights reserved.


Montazeri A.,Iran University of Science and Technology | Poshtan J.,Iran University of Science and Technology
Signal Processing | Year: 2010

Infinite impulse response filters have not been used extensively in active noise and vibration control applications. The problems are mainly due to the multimodal error surface and instability of adaptive IIR filters used in such applications. Considering these, in this paper a new adaptive recursive RLS-based fast-array IIR filter for active noise and vibration control applications is proposed. At first an RLS-based adaptive IIR filter with computational complexity of order O(n2) is derived, and a sufficient condition for its stability is proposed by applying passivity theorem on the equivalent feedback representation of this adaptive algorithm. In the second step, to reduce the computational complexity of the algorithm to the order of O(n) as well as to improve its numerical stability, a fast array implementation of this adaptive IIR filter is derived. This is accomplished by extending the existing results of fast-array implementation of adaptive FIR filters to adaptive IIR filters. Comparison of the performance of the fast-array algorithm with that of Erikson's FuLMS and SHARF algorithms confirms that the proposed algorithm has faster convergence rate and ability to reach a lower minimum mean square error which is of great importance in active noise and vibration control applications. © 2010 Elsevier B.V. All rights reserved.


Atashgar K.,Iran University of Science and Technology | Noorossana R.,Iran University of Science and Technology
International Journal of Advanced Manufacturing Technology | Year: 2011

Identifying the change point or the starting time of a disturbance in a process can play an essential role in root cause analysis. Although, in univariate environment, change point identification by itself could be a significant step in process improvement but in multivariate environment without conducting diagnostic analysis which leads to the identification of the variable(s) responsible for the change in the process, one cannot effectively perform root cause analysis. In this paper, a supervised learning approach based on artificial neural networks is proposed which helps to identify the change point in a bivariate environment when the process mean vector is allowed to shift linearly and simultaneously a diagnostic analysis is conducted to identify the variable(s) responsible for the change in the process mean vector. To the best of our knowledge, this is the first time that this problem is addressed in the literature of change point estimation. The performance of the proposed model is investigated through several numerical examples. Results indicate that the proposed model provides practitioners with a very accurate estimate of the change point in the process mean vector and simultaneously helps to identify the variable(s) responsible with the out-of-control condition. © 2010 Springer-Verlag London Limited.


Alavi A.H.,Iran University of Science and Technology | Gandomi A.H.,Tafresh University
Engineering Computations (Swansea, Wales) | Year: 2011

Purpose - The complexity of analysis of geotechnical behavior is due to multivariable dependencies of soil and rock responses. In order to cope with this complex behavior, traditional forms of engineering design solutions are reasonably simplified. Incorporating simplifying assumptions into the development of the traditional models may lead to very large errors. The purpose of this paper is to illustrate capabilities of promising variants of genetic programming (GP), namely linear genetic programming (LGP), gene expression programming (GEP), and multi-expression programming (MEP) by applying them to the formulation of several complex geotechnical engineering problems. Design/methodology/approach - LGP, GEP, and MEP are new variants of GP that make a clear distinction between the genotype and the phenotype of an individual. Compared with the traditionalGP, the LGP, GEP, and MEP techniques are more compatible with computer architectures. This results in a significant speedup in their execution.These methods have a great ability to directly capture the knowledge contained in the experimental data withoutmaking assumptions about the underlying rules governing the system. This is one of their major advantages over most of the traditional constitutive modeling methods. Findings - In order to demonstrate the simulation capabilities of LGP, GEP, and MEP, they were applied to the prediction of: relative crest settlement of concrete-faced rockfill dams; slope stability; settlement around tunnels; and soil liquefaction. The results are compared with those obtained by other models presented in the literature and found to be more accurate. LGP has the best overall behavior for the analysis of the considered problems in comparison with GEP and MEP. The simple and straightforward constitutive models developed using LGP, GEP and MEP provide valuable analysis tools accessible to practicing engineers. Originality/value - The LGP, GEP, and MEP approaches overcome the shortcomings of different methods previously presented in the literature for the analysis of geotechnical engineering systems. Contrary to artificial neural networks and many other soft computing tools, LGP, GEP, and MEP provide prediction equations that can readily be used for routine design practice. The constitutive models derived using these methods can efficiently be incorporated into the finite element or finite difference analyses as material models. They may also be used as a quick check on solutions developed by more time consuming and in-depth deterministic analyses. © Emerald Group Publishing Limited.


Abiri M.B.,Mazandaran University of Science and Technology | Yousefli A.,Iran University of Science and Technology
International Journal of Advanced Manufacturing Technology | Year: 2011

This paper considers location-allocation problem in the real uncertain world and develops a possibilistic non-linear programming model to deal with this problem. Fuzzy decision making in fuzzy environment concept is used to determine possibility distribution of location and allocation variables. To solve this model, a novel approach based on genetic algorithm structure is developed. As the proposed model includes both deterministic (location) and uncertain (allocation) parameters, the developed solution algorithm uses a hybrid chromosome structure. Also, to cover continuous nature of the problem and prevent GA from early convergence, a new crossover operator is introduced. Finally, performance of the developed algorithm is evaluated by an example. © 2010 Springer-Verlag London Limited.


Shojaei K.,Iran University of Science and Technology | Mohammad Shahri A.,Iran University of Science and Technology | Tarakameh A.,Iran University of Science and Technology
Robotics and Computer-Integrated Manufacturing | Year: 2011

In this paper, the integrated kinematic and dynamic trajectory tracking control problem of wheeled mobile robots (WMRs) is addressed. An adaptive robust tracking controller for WMRs is proposed to cope with both parametric and nonparametric uncertainties in the robot model. At first, an adaptive nonlinear control law is designed based on inputoutput feedback linearization technique to get asymptotically exact cancellation of the parametric uncertainty in the WMR parameters. The designed adaptive feedback linearizing controller is modified by two methods to increase the robustness of the controller: (1) a leakage modification is applied to modify the integral action of the adaptation law and (2) the second modification is an adaptive robust controller, which is included to the linear control law in the outer loop of the adaptive feedback linearizing controller. The adaptive robust controller is designed such that it estimates the unknown constants of an upper bounding function of the uncertainty due to friction, disturbances and unmodeled dynamics. Finally, the proposed controller is developed for a type (2, 0) WMR and simulations are carried out to illustrate the robustness and tracking performance of the controller. © 2010 Elsevier Ltd. All rights reserved.


Molladavoudi H.R.,Iran University of Science and Technology | Djavanroodi F.,Iran University of Science and Technology
International Journal of Advanced Manufacturing Technology | Year: 2011

Flow forming technology is widely used in the production of the axisymmetric industrial parts. The advantage of flow forming process over other manufacturing methods such as press forming is use of simple tooling, reduced forming loads due to localized deformation, and enhanced mechanical and surface quality of finished parts. In this study, the effects of thickness reduction on the mechanical properties and spinning accuracy are experimentally investigated on 7075-O aluminum tube. A prototype spinning machine has been designed and manufactured. The effects of spinning accuracy, surface roughness, percentage of elongation, yield strength, and the ultimate strength as a function of thickness reduction are experimentally examined. The experimental results show that with increment of thickness reduction, the yield strength, ultimate strength, surface hardness, and crystal refining increase, and on the other hand, it has adverse effect on diameter growth, geometrical accuracy, surface roughness, and percentage elongation of spun tube. © 2010 Springer-Verlag London Limited.


Jamili A.,Iran University of Science and Technology | Shafia M.A.,Iran University of Science and Technology | Tavakkoli-Moghaddam R.,University of Tehran
Expert Systems with Applications | Year: 2011

In this paper, we present on a periodic job shop scheduling problem (PJSSP) based on the periodic event scheduling problem (PESP), which is different from cyclic scheduling. The PESP schedules a number of recurring events, such that each pair of events fulfills certain constraints during a given time period. To solve such a hard PJSS problem, we propose a hybrid algorithm, namely EM-SA, which is based on electromagnetism-like mechanism (EM) and simulated annealing (SA). To evaluate this proposed EM-SA, some randomly constructed instances are solved, and the related results are compared with SA and optimum solutions obtained by the branch-and-bound (B&B) algorithm. The results demonstrate the efficiency and effectiveness of the proposed hybrid EM-SA algorithm to solve the PJSSP. © 2010 Elsevier Ltd. All rights reserved.


Jalali H.,Iran University of Science and Technology | Ahmadian H.,Iran University of Science and Technology | Pourahmadian F.,Iran University of Science and Technology
Mechanical Systems and Signal Processing | Year: 2011

Under high amplitude vibrations, contact interfaces experience micro-vibro-impacts and frictional slips. These nonlinear mechanisms can introduce response nonlinearity and energy dissipation into the structures containing them. Beams are widely used in engineering structures and almost in every application they are subjected to boundary conditions. Boundary conditions may contain nonlinear contact interfaces. Therefore, modeling accurately the micro-vibro-impacts and frictional slips developing at the boundary condition of a beam is important in structural dynamics. Ignoring this may result in major discrepancies between experimental observations and theoretical calculations. In this paper identification of micro-vibro-impacts and frictional slips at boundary condition of a nonlinear beam is considered. The structure, being modeled as an EulerBernoulli beam, is analyzed using nonlinear normal modes. A reduced-order model governing the dynamic response of the beam near its first resonant point is resulted from the analysis. Identification of the nonlinear boundary condition parameters can be performed by means of the reduced order model and using experimental results. © 2010 Elsevier Ltd.All rights reserved.


Javidrad F.,Iran University of Science and Technology | Pourmoayed A.R.,Iran University of Science and Technology
Robotics and Computer-Integrated Manufacturing | Year: 2011

In this study, a method for generation of sectional contour curves directly from cloud point data is given. This method computes contour curves for rapid prototyping model generation via adaptive slicing, data points reducing and B-spline curve fitting. In this approach, first a cloud point data set is segmented along the component building direction to a number of layers. The points are projected to the mid-plane of the layer to form a 2-dimensional (2D) band of scattered points. These points are then utilized to construct a boundary curve. A number of points are picked up along the band and a B-spline curve is fitted. Then points are selected on the B-spline curve based on its discrete curvature. These are the points used as centers for generation of circles with a user-define radius to capture a piece of the scattered band. The geometric center of the points lying within these circles is treated as a control point for a B-spline curve fitting that represents a boundary contour curve. The advantage of this method is simplicity and insensitivity to common small inaccuracies. Two experimental results are included to demonstrate the effectiveness and applicability of the proposed method. © 2010 Elsevier Ltd. All rights reserved.


Ashtiani B.,Iran University of Science and Technology | Leus R.,Catholic University of Leuven | Aryanezhad M.-B.,Iran University of Science and Technology
Journal of Scheduling | Year: 2011

We study the resource-constrained project scheduling problem with stochastic activity durations. We introduce a new class of scheduling policies for solving this problem, which make a number of a-priori sequencing decisions in a pre-processing phase while the remaining decisions are made dynamically during project execution. The pre-processing decisions entail the addition of extra precedence constraints to the scheduling instance, hereby resolving some potential resource conflicts. We obtain new competitive results for expected-makespan minimization on representative datasets, which are significantly better than those obtained by the existing algorithms when the variability in the activity durations is medium to high. © Springer Science+Business Media, LLC 2009.


Abbasi-Moghadam D.,Iran University of Science and Technology | Vakili V.T.,Iran University of Science and Technology
International Journal of Communication Systems | Year: 2011

In this paper, an indoor UWB communications system that applies time reversal (TR) for transmitting the desired signal is proposed. First we define equivalent channel model of TR-UWB, which is the convolution of channel impulse response and its complex conjugate time-reversed version. Then spatial, temporal and frequency characteristics of equivalent channel are analyzed and the analytical or semi-analytical results are validated by comparing measurements with simulation. (Semi) analytical expression of equivalent channel transfer function, TR UWB power delay profile (PDP), focusing gain, spatial correlation and power azimuth spectrum (PAS) is performed. Also probability density function (PDF) of TR-UWB amplitude and path-gain is derived. Analysis and simulation results of different distributions, such as uniform, Laplacian and Gaussian for PAS, are considered and presented. It is shown that uniform and truncated Laplacian distributions are appropriate fits to the measurement results for power azimuth spectrum of TR-UWB. It is seen that for distances greater than /2 from the authorized receiver, received signal decreases 10 dB, where is the wavelength of the central frequency. Finally, PDF of TR-UWB path-gain is described. Measurement results show that for small time windows, the densities of the path-gain are highly non-Gaussian. But for starting time of 10T w or more, and window size of 2T w or more the densities are nearly Gaussian, where T w is the transmitted pulse duration. © 2010 John Wiley & Sons, Ltd.


Kaveh A.,Iran University of Science and Technology | Fazli H.,Iran University of Science and Technology
Computers and Structures | Year: 2011

A structure is called regular if its model can be considered as a product graph. A great computational advantage of regular structures, especially in the context of free vibration analysis, is their capacity for decomposition. In the present paper, the idea of decomposition is extended to the analysis of practical structural systems emerging as slight perturbations of the regular ones. A free interface dynamic substructuring method is employed to reformulate the eigenproblem as an assemblage of a base model and the modification part. The proposed method is very efficient in estimating a few lower eigenpairs of large-scale modified regular structures. © 2010 Elsevier Ltd. All rights reserved.


Kaveh A.,Iran University of Science and Technology | Talatahari S.,University of Tabriz
Structural and Multidisciplinary Optimization | Year: 2011

The concept of the "fields of forces" is utilized as a general model of meta-heuristic algorithms from physics. This model is capable of representing the properties of different meta-heuristics and in this paper, it is used to enhance the recently developed meta-heuristic, the Charged System Search (CSS). The enhanced CSS is then applied to determine the configuration optimum design of structures. Comparison of the results for some examples, illustrates the efficiency of the enhanced CSS algorithm. © Springer-Verlag 2010.


Safari E.,Iran University of Science and Technology | Sadjadi S.J.,Iran University of Science and Technology
Expert Systems with Applications | Year: 2011

One of the most important assumptions in production scheduling is that the machines are permanently available without any breakdown. In the real world of scheduling, machines can be made unavailable due to various reasons such as preventive maintenance and unpredicted breakdown. In this paper, we explore flowshop configuration under the assumption of condition-based maintenance to minimize expected makespan. Furthermore, we consider a condition-based maintenance (CBM) strategy which could be used in most industrial settings. The proposed algorithm is designed for non-resumable flowshop state where the processing of jobs after preventive maintenance is restarted from the beginning. We propose a hybrid algorithm based on genetic algorithm and simulated annealing. Additionally, we conduct an extensive parameter calibration with the utilization of Taguchi method and select the optimal levels of the algorithm's performance influential factors. The preliminary results indicate that the proposed method provides significantly better results compared with other high performing algorithms in the literature. © 2010 Elsevier Ltd. All rights reserved.


Firoozjaee A.R.,Iran University of Science and Technology | Afshar M.H.,Iran University of Science and Technology
International Journal for Numerical Methods in Fluids | Year: 2011

A fractional step method for the solution of the steady state incompressible Navier-Stokes equations is proposed in this paper in conjunction with a meshless method, named discrete least-squares meshless (DLSM). The proposed fractional step method is a first-order accurate scheme, named semi-incremental fractional step method, which is a general form of the previous first-order fractional step methods, i.e. non-incremental and incremental schemes. One of the most important advantages of the proposed scheme is its capability to use large time step sizes for the solution of incompressible Navier-Stokes equations. DLSM method uses moving least-squares shape functions for function approximation and discrete least-squares technique for discretization of the governing differential equations and their boundary conditions. As there is no need for a background mesh, the DLSM method can be called a truly meshless method and enjoys symmetric and positive-definite properties. Several numerical examples are used to demonstrate the ability and the efficiency of the proposed scheme and the discrete least-squares meshless method. The results are shown to compare favorably with those of the previously published works. © 2010 John Wiley & Sons, Ltd.


Korayem M.H.,Iran University of Science and Technology | Sharahi H.J.,Iran University of Science and Technology
International Journal of Advanced Manufacturing Technology | Year: 2011

The dynamic behavior of atomic force microscopy (AFM) cantilevers in liquid is completely different from its behavior in air due to the applied hydrodynamic force. Exciting cantilever with frequencies close to resonance frequency and primary position alignment are two critical issues that should be considered in deriving frequency response function (FRF). In this paper, the hydrodynamic force has been modeled with string of spheres and the effect of the damping and the added mass on the model has been analyzed. Afterward, this force is applied to the dynamic equation so that the dynamic behavior of AFM cantilevers is studied in liquids by analyzing the effect of some important parameters such as added mass, internal, and fluid damping. By simulations of the dynamic equations for a silicon cantilever, FRF is determined in both air and liquid. In addition, the effects of two significant parameters of liquid mechanical properties (liquid viscosity and density) and geometrical parameters of cantilever on FRF are studied. The results for string of spheres model are compared with the other hydrodynamic model and the experimental data. When length/width ratio decreases, it is found that string of spheres model has a better agreement than the other hydrodynamic model with experimental data. © 2011 Springer-Verlag London Limited.


Mehrafrooz Z.,Iran University of Science and Technology | Noorossana R.,Iran University of Science and Technology
Computers and Industrial Engineering | Year: 2011

The close relationship between quality and maintenance of manufacturing systems has contributed to the development of integrated models, which use the concept of statistical process control (SPC) and maintenance. Such models not only help to improve quality of products but also lead to lower maintenance cost. In this paper, an integrated model is presented which considers complete failure and planned maintenance simultaneously. This model leads to six different scenarios. A new procedure for calculating average cost per time unit is also presented. Finally, a numerical example is used to evaluate sensitivity of the model parameters and compare performance of the developed model to a planned maintenance model. Results indicate satisfactory performance for the developed model. © 2011 Elsevier Ltd. All rights reserved.


Kaveh A.,Iran University of Science and Technology | Laknejadi K.,Iran University of Science and Technology
Expert Systems with Applications | Year: 2011

In this paper a new hybrid method is proposed for multi-objective optimization problem. In multi-objective particle swarm optimization methods, selecting the global best particle for each particle of the population from a set of Pareto-optimal solutions has a great impact on the convergence and diversity of solutions. Here, this problem is solved by incorporating charged system search method into the search process of the particle swarm optimization algorithm. In this approach, each particle is guided by its personal best and also resultant force which acted on this particle. This force is the consequence of the attraction field which is created around each archive member, where the magnitude of this force is related to the charge magnitude of the particles and also the distance between them. Each particle is guided by just archive members, which are located in the same region of the objective space as this particle. The proposed method is examined for different test functions and the results are compared to the results of three state-of-art multi-objective algorithms. © 2011 Elsevier Ltd. All rights reserved.


Kaupp G.,University of Oldenburg | Naimi-Jamal M.R.,Iran University of Science and Technology
Scanning | Year: 2010

The analysis of published loading curves reveals the exponent 3/2 to the depth for nanoindentations with sharp pyramidal or conical tips. This has geometric reasons, as it occurs independent on the bonding states and indentation mechanisms. Nevertheless, most mathematical deductions and finite element simulations of nanomechanical parameters in the literature continue using the experimentally not supported Hertzian exponent 2. Therefore, numerous published loading curves of various authors are plotted using the experimental exponent 3/2 to present unbiased proof for its generality with metals, oxides, semiconductors, biomaterials, polymers, and organics. Linearity is independent of equipment and valid for load controlled, or depth controlled, or continuous stiffness, or AFM force measurements. The linearity with exponent 3/2 often extends from the nano- into the microindentation ranges. The tip rounding and taper influence of the "geometrical similar" indenters are discussed. When kinks occur in such linear plots through the origin, these indicate change of the materials' mechanical properties under pressure by phase transition. These events are discussed for nanoindentations with respect to the known hydrostatic transformation pressures that are, of course, always higher than the necessary indentation mean pressure. Numerous Raman, as well as X-ray and electron diffraction results from the literature support the phase transitions that are now easily detected. Nanoporous materials first fill the pores upon indentation. Published loading curves exhibit more information than hitherto assumed. Copyright © 2010 Wiley Periodicals, Inc.


Gandomi A.H.,University of Akron | Yang X.-S.,University of Cambridge | Alavi A.H.,Iran University of Science and Technology
Computers and Structures | Year: 2011

In this study, a recently developed metaheuristic optimization algorithm, the Firefly Algorithm (FA), is used for solving mixed continuous/discrete structural optimization problems. FA mimics the social behavior of fireflies based on their flashing characteristics. The results of a trade study carried out on six classical structural optimization problems taken from literature confirm the validity of the proposed algorithm. The unique search features implemented in FA are analyzed, and their implications for future research work are discussed in detail in the paper. © 2011 Elsevier Ltd. All rights reserved.


Gandomi A.H.,Tafresh University | Alavi A.H.,Iran University of Science and Technology
Information Sciences | Year: 2011

This paper presents a new multi-stage genetic programming (MSGP) strategy for modeling nonlinear systems. The proposed strategy is based on incorporating the individual effect of predictor variables and the interactions among them to provide more accurate simulations. According to the MSGP strategy, an efficient formulation for a problem comprises different terms. In the first stage of the MSGP-based analysis, the output variable is formulated in terms of an influencing variable. Thereafter, the error between the actual and the predicted value is formulated in terms of a new variable. Finally, the interaction term is derived by formulating the difference between the actual values and the values predicted by the individually developed terms. The capabilities of MSGP are illustrated by applying it to the formulation of different complex engineering problems. The problems analyzed herein include the following: (i) simulation of pH neutralization process, (ii) prediction of surface roughness in end milling, and (iii) classification of soil liquefaction conditions. The validity of the proposed strategy is confirmed by applying the derived models to the parts of the experimental results that were not included in the analyses. Further, the external validation of the models is verified using several statistical criteria recommended by other researchers. The MSGP-based solutions are capable of effectively simulating the nonlinear behavior of the investigated systems. The results of MSGP are found to be more accurate than those of standard GP and artificial neural network-based models. © 2011 Elsevier Inc. All rights reserved.


Dekamin M.G.,Iran University of Science and Technology | Eslami M.,Iran University of Science and Technology
Green Chemistry | Year: 2014

An improved one-pot three-component and environmentally benign approach for the synthesis of a wide range of densely functionalized 2-amino-3-cyano-4H-pyran annulated derivatives has been described by the reaction of aryl aldehydes, malononitrile and diverse electron-rich phenolic or enolizable carbonyl compounds under mechanochemical ball milling conditions in the presence of potassium phthalimide (POPI), as a mild basic organocatalyst, at ambient temperature. In comparison to the conventional methods, the remarkable advantages of this green protocol are high to quantitative yields, avoiding the use of any hazardous transition metal-free catalyst or solvent, shorter reaction time at ambient temperature, low cost, and straightforward work-up procedure. © 2014 The Royal Society of Chemistry.


Korayem M.H.,Iran University of Science and Technology | Tourajizadeh H.,Iran University of Science and Technology
Journal of Intelligent and Robotic Systems: Theory and Applications | Year: 2011

One of the most important applications of cable robots is load carrying along a specific path. Control procedure of cable robots is more challenging compared to linkage robots since cables can't afford pressure. Meanwhile carrying the heaviest possible payload for this kind of robots is desired. In this paper a nonlinear optimal control is proposed in order to control the end-effector within a predefined trajectory while the highest Dynamic Load Carrying Capacity (DLCC) can be carried. This purpose is met by applying optimum torque distribution among the motors with acceptable tracking accuracy. Besides, other algorithms are applied to make sure that the allowable workspace constraint is also satisfied. Since the dynamics of the robot is nonlinear, feedback linearization approach is employed in order to control the end-effector on its desirable path in a closed loop way while Linear Quadratic Regulator (LOR) method is used in order to optimize its controlling gains since the state space is linearized by the feedback linearization. The proposed algorithm is supported by doing some simulation studies on a two Degrees of Freedom (DOF) constrained planar cable robot as well as a six DOFs under constrained cable suspended robot and their DLCCs are calculated by satisfying the motor torque, tracking error and allowable workspace constraints. The results including the angular velocity, motors' torque, actual tracking of the end-effector and the DLCC of the robot are calculated and verified using experimental tests done on the cable robot. Comparison of the results of open loop simulation results, closed loop simulation results and experimental tests, shows that the results are improved by applying the proposed algorithm. This is the result of tuning the motors' torque and accuracy in a way that the highest DLCC can be achieved. © Springer Science+Business Media B.V. 2011.


Jalali Naini S.G.,Iran University of Science and Technology | Shafiee M.,University of Tehran
International Journal of Advanced Manufacturing Technology | Year: 2011

An upgrade action is a pre-sale procedure that brings the second-hand item to an improved functional state and effectively reduces its age. This action is usually costly and adds directly to the sale price of the second-hand product, but it improves the product reliability and can reduce the warranty servicing cost. In the present paper, we propose a decision model to determine the optimal price and upgrade strategy of a warranted second-hand product to maximize the dealer's expected profit. The objective function includes both demand and cost functions, where purchase price from an end user, upgrade cost, and warranty cost are involved. We illustrate our finding using real data on second-hand electric device. Also, a sensitivity analysis is conducted to evaluate the effect of model parameters on the optimal solution. © Springer-Verlag London Limited 2011.


Ashrafizadeh S.N.,Iran University of Science and Technology | Ameri Ghasrodashti A.,Tarbiat Modares University
Chemical Engineering Research and Design | Year: 2011

Miscible gas injection is generally used as one of the most efficient methods in the enhanced oil recovery. Minimum miscibility pressure (MMP) is an important parameter in the miscible gas injection projects, since local displacement efficiency in the reservoir media is highly dependent on the MMP. Therefore, an appropriate estimation of MMP would bring significant economic benefits. This paper presents a comparative study on five representative equations of state (EoSs) for predicting MMP using Parachor model together with the criterion of zero interfacial tension (IFT) at the miscibility conditions. The predicted MMP values are compared with the experimental data obtained from the most reliable measurement technique, so called slim tube method. Such a prediction would enables us to judge the accuracy of the results obtained from different equations of state as well as the capability of Parachor model to calculate the MMP. The results of predictions obtained for five oil-gas systems in this study reveal reliable MMP values within 5% of accuracy. © 2010 The Institution of Chemical Engineers.


Noroozi S.,Iran University of Science and Technology | Hashemabadi S.H.,Iran University of Science and Technology
Chemical Engineering Research and Design | Year: 2011

In this study the effect of inlet chamber design on de-oiling hydrocyclone efficiency has been investigated numerically with the aim of minimizing the energy loss. To this aim, effects of four different inlet chamber designs (exponential, conical, quadratic polynomial body profile and standard design) on efficiency have been considered. Algebraic slip mixture model and Reynolds Stress Model (RSM) have been employed for prediction of multiphase flow behavior and simulation of turbulent flow through the cyclone respectively. The simulation results for efficiency of standard design demonstrate a proper agreement with reported experimental data. The results show that the separation efficiency can be improved approximately 8% using exponential body shape. The recirculation eddies that exists in the upper section prevents inward radial flow, consequently the efficiency reduces; the simulations illustrate that inlet chamber shape affects on the size of these eddies. More recirculation in hydrocyclone inlet chamber with quadratic polynomial body profile causes minimum separation efficiency. © 2010 The Institution of Chemical Engineers.


Anbia M.,Iran University of Science and Technology | Parvin Z.,Iran University of Science and Technology
Chemical Engineering Research and Design | Year: 2011

Mesoporous carbon, CMK-3, was prepared using hexagonal Al-SBA-15 mesoporous silica, instead of SBA-15, as a template. The synthesized materials were examined via X-ray diffraction and N2-adsorption. The mesoporous carbon was studied for its adsorption of dibenzothiophene (DBT) from petroleum fuels. The performance of this adsorbent was compared with SBA-15 and Al-SBA-15, through which CMK-3 showed higher sulfur adsorption capabilities due to a larger mesopore volume and a higher specific surface area. The uptake capacity for DBT followed the order CMK-3>Al-SBA-15>SBA-15. The results confirmed the importance of the adsorbent pore size and its surface chemistry for the adsorption of DBT from liquid phase. Langmuir and Freundlich isotherm models were used to fit equilibrium data for CMK-3. The equilibrium data were best represented by the Langmuir isotherm. Kinetic studies were carried out and showed the sorption kinetics of dibenzothiophene was best described by a pseudo-second-order kinetic model. © 2010 The Institution of Chemical Engineers.


Anbia M.,Iran University of Science and Technology | Ghassemian Z.,Iran University of Science and Technology
Chemical Engineering Research and Design | Year: 2011

The present work elucidates an environmental friend by process for heavy metals removal from aqueous solutions using mesoporous silicate, containing zirconium and iron. The process comprises the three following steps: (1) synthesis and characterization of mesoporous silicate bed (the prepared adsorbent materials were characterized by powder X-ray diffraction, nitrogen isotherms, FTIR, TGA, and SEM). (2) Evaluation of the efficiency of this new adsorption bed for Cu and Cd removal from aqueous solutions. (3) Study of metal concentration (50-1000. ppm), stirring time (0.5-5. h) and pH (1.5-12) effects on the adsorption power using batch techniques. Results obtained indicate that under optimum conditions, pH in the vicinity of 5-6, Zr-M has the maximum adsorption capacity for both cations Cu and Cd. On the other hand, ZrFe-M1 containing a higher molar ratio of iron showed lower adsorption capacity for the cations Cu and Cd. © 2011 The Institution of Chemical Engineers.


Akbari T.,University of Tehran | Rahimikian A.,University of Tehran | Kazemi A.,Iran University of Science and Technology
Energy Conversion and Management | Year: 2011

This paper presents a multi-stage stochastic model for short-term transmission expansion planning considering the available transfer capability (ATC). The ATC can have a huge impact on the power market outcomes and the power system reliability. The transmission expansion planning (TEP) studies deal with many uncertainties, such as system load uncertainties that are considered in this paper. The Monte Carlo simulation method has been applied for generating different scenarios. A scenario reduction technique is used for reducing the number of scenarios. The objective is to minimize the sum of investment costs (IC) and the expected operation costs (OC). The solution technique is based on the benders decomposition algorithm. The N-1 contingency analysis is also done for the TEP problem. The proposed model is applied to the IEEE 24 bus reliability test system and the results are efficient and promising. © 2011 Elsevier Ltd. All rights reserved.


Hasheminejad S.M.,Iran University of Science and Technology | Rabbani V.,Iran University of Science and Technology
Archives of Acoustics | Year: 2015

The linear 3D piezoelasticity theory along with active damping control (ADC) strategy are applied for non-stationary vibroacoustic response suppression of a doubly fluid-loaded functionally graded piezolam-inated (FGPM) composite hollow cylinder of infinite length under general time-varying excitations. The control gain parameters are identified and tuned using Genetic Algorithm (GA) with a multi-objective performance index that constrains the key elasto-acoustic system parameters and control voltage. The uncontrolled and controlled time response histories due to a pair of equal and opposite impulsive ex-ternal point loads are calculated by means of Durbin's numerical inverse Laplace transform algorithm. Numerical simulations demonstrate the superior (good) performance of the GA-optimized distributed active damping control system in effective attenuation of sound pressure transients radiated into the in-ternal (external) acoustic space for two basic control configurations. Also, some interesting features of the transient fluid-structure interaction control problem are illustrated via proper 2D time domain images and animations of the 3D sound field. Limiting cases are considered and accuracy of the formulation is established with the aid of a commercial finite element package as well as comparisons with the current literature. Copyright © 2015 by PAN-IPPT.


Shirazi S.G.,Islamic Azad University at Qazvin | Mirzakuchaki S.,Iran University of Science and Technology
Applied Physics Letters | Year: 2011

Choosing a suitable doping level of channel relevant to channel diameter is considered for determining the carbon nanotube field effect transistors' performance which seem to be the best substitute of current transistor technology. For low diameter values of channel, the ratio of on/off current declines by increasing the doping level. But for higher diameter values, there is an optimum point of doping level in obtaining the highest on/off current ratio. For further verification, the variations of performance are justified by electron distribution function's changes on energy band diagram of these devices. The results are compared at two different gate fields. © 2011 American Institute of Physics.


Mashhadi S.,Iran University of Science and Technology
Security and Communication Networks | Year: 2016

A new multistage secret-sharing scheme based on the homogeneous linear feedback shift register is proposed. This scheme has few public outputs, a new simple construction, and different techniques for the reconstruction phase. Moreover, based on the semantic security of the underlying encryption scheme, we prove the computational security of our scheme in the standard model. © 2016 John Wiley & Sons, Ltd.


A new, efficient, one-pot multicomponent reaction for the synthesis of diazepine derivatives in excellent yields is described. The reactions of various 1,2-diamines, terminal alkynes, and an isocyanide take place in the presence of a catalytic amount of magnetically recoverable silica-supported superparamagnetic Fe3O4 nanoparticles in ethanol (as a green reaction medium) at ambient temperature. © 2013 Elsevier Ltd. All rights reserved.


Dekamin M.G.,Iran University of Science and Technology | Eslami M.,Iran University of Science and Technology | Maleki A.,Iran University of Science and Technology
Tetrahedron | Year: 2013

A wide variety of 2-amino-4H-chromene derivatives with diverse substituents on the 4H-chromene ring were efficiently prepared via one-pot, three-component reaction of an aromatic aldehyde, malononitrile (or ethyl cyanoacetate), and diverse enolizable C-H activated acidic compounds in the presence of low loading of potassium phthalimide-N-oxyl (POPINO), as a new organocatalyst, in aqueous media. This procedure is a clean, transition metal-free, and environmentally friendly approach to prepare different 2-amino-4H-chromen derivatives that offers many advantages including short reaction time, high to quantitative yields, low cost, and straightforward work-up. © 2012 Elsevier Ltd. All rights reserved.


Ayatollahi M.R.,Iran University of Science and Technology | Berto F.,University of Padua | Lazzarin P.,University of Padua
Carbon | Year: 2011

Brittle fracture of polycrystalline graphite is studied experimentally and theoretically using Brazilian disk specimens containing sharp and rounded-tip V-notches subjected to different degrees of loading mixity, ranging from pure mode I to pure mode II. The main purpose is twofold. First, to provide a new set of experimental results on fracture of V-notched graphite samples, with different values of loading mixities, V-notch angles and notch radii, which may be helpful for researchers because enlarges the very scarce available data; and second, to provide a fracture criterion for polycrystalline graphite under the above-mentioned conditions. The averaged value of the strain energy density over a well-defined volume is used to predict the static strength of the considered specimens. Good agreement is found between the experimentally obtained fracture loads and the theoretical predictions based on the constancy of the mean strain energy density over the material volume. © 2011 Elsevier Ltd. All rights reserved.


Maleknejad K.,Iran University of Science and Technology | Nedaiasl K.,Iran University of Science and Technology
Computers and Mathematics with Applications | Year: 2011

In this paper, the numerical solution of nonlinear Fredholm integral equations of the second kind is considered by two methods. The methods are developed by means of the Sinc approximation with the single exponential (SE) and double exponential (DE) transformations. These numerical methods combine a Sinc collocation method with the Newton iterative process that involves solving a nonlinear system of equations. We provide an error analysis for the methods. So far approximate solutions with polynomial convergence have been reported for this equation. These methods improve conventional results and achieve exponential convergence. Some numerical examples are given to confirm the accuracy and ease of implementation of the methods. © 2011 Elsevier Ltd. All rights reserved.


Nekoukar V.,Iran University of Science and Technology | Erfanian A.,Iran University of Science and Technology
Fuzzy Sets and Systems | Year: 2011

This paper presents a new adaptive terminal sliding mode tracking control design for a class of nonlinear systems using fuzzy logic system. The terminal sliding mode control (TSM) was developed to provide faster convergence and higher-precision control than the linear hyperplane-based sliding control. However, the original TSM encountered singularity problem with discontinuous control action. Moreover, a prior knowledge about the plant to be controlled is required. The proposed controller combines a continuous non-singular TSM with an adaptive learning algorithm and fuzzy logic system to estimate the dynamics of the controlled plant so that closed-loop stability and finite-time convergence of tracking errors can be guaranteed. The performance of the proposed control strategy is evaluated through the control of a two-link rigid robotic manipulator. Finally, the effectiveness of the proposed scheme is demonstrated through the control of the ankle and knee movements in paraplegic subjects using functional electrical stimulation. Simulation and experimental results verify that the proposed control strategy can achieve favorable control performance with regard to system parameter variations and external disturbances. © 2011 Elsevier B.V. All rights reserved.


Aghajani A.,Iran University of Science and Technology | Banas J.,Rzeszow University of Technology | Jalilian Y.,Iran University of Science and Technology
Computers and Mathematics with Applications | Year: 2011

In this paper we prove some results concerning the existence of solutions for a large class of nonlinear Volterra singular integral equations in the space C[0,1] consisting of real functions defined and continuous on the interval [0,1]. The main tool used in the proof is the concept of a measure of noncompactness. We also present some examples of nonlinear singular integral equations of Volterra type to show the efficiency of our results. Moreover, we compare our theory with the approach depending on the use of the theory of VolterraStieltjes integral equations. We also show that the results of the paper are applicable in the study of the so-called fractional integral equations which are recently intensively investigated and find numerous applications in describing some real world problems. © 2011 Elsevier Ltd. All rights reserved.


Golbabai A.,Iran University of Science and Technology | Sayevand K.,Iran University of Science and Technology
Computers and Mathematics with Applications | Year: 2011

This paper outlines a reliable strategy to use the homotopy perturbation method based on Jumarie's derivative for solving fractional differential equations. In this framework, compact structures of fourth-order fractional diffusion-wave equations are considered as prototype examples. Moreover, convergence of the proposed approach for these types of equations is investigated. Results show that the response expressions are Mittag-Leffler stable. © 2011 Elsevier Ltd. All rights reserved.


Rakhshanpouri S.,Iran University of Science and Technology | Rowshanzamir S.,Iran University of Science and Technology
Energy | Year: 2013

The most critical problems to overcome in the PEM (proton exchange membrane) fuel cell technology are the water management. In this work, a seven-layer theoretical model is proposed that includes anode and cathode inlet channels, anode and cathode GDLs (gas diffusion layers), CLs (catalyst layers), and the 117 Nation proton exchange membrane. The mathematical model is a one-dimensional, steady-state, isothermal and isobar to describe the water transport phenomena in PEMFC (proton exchange membrane fuel cell). A rationally chosen set of parameters are considered such as the humidity and the stoichiometry of the inlet gases, the porosity of GDL, and the membrane thickness. The results show that with sufficient levels of humidity, the water management would improve for larger porosities of GDLs or a thinner membrane, and the resistance and over voltage of the membrane can be reduced significantly as well. This model will help to select system parameters so that the fuel cell would not suffer from dehydration and flooding. Also, model predictions were successfully compared to theoretical I-V polarization curves presented by Chen et al. (2007) and Springer et al. (1991). © 2012 Elsevier Ltd.


Golbabai A.,Iran University of Science and Technology | Sayevand K.,Iran University of Science and Technology
Computers and Mathematics with Applications | Year: 2011

The homotopy perturbation method is applied to the generalized fourth-order fractional diffusionwave equations. The problem is formulated in the Caputo sense. Moreover, a reliable scheme for calculating nonlinear operators is proposed. The results reveal that the present method is very effective and convenient. © 2010 Elsevier Ltd. All rights reserved.


Ghavami S.,Iran University of Science and Technology | Abolhassani B.,Iran University of Science and Technology
International Journal of Communication Systems | Year: 2012

In this paper, a two-phase algorithm for the spectrum sensing and power/rate control of a secondary user (S-user) or cognitive radio is proposed. In the first phase, the primary base station (P-BS), which is conscious of both the number and the data rate of primary active users (P-user), broadcasts theitusage capacity percentage (UCP) of its cell. Since knowing only the UCP is not enough to guarantee that the total load (of P-users and S-users) is less than a maximum permissible load, the S-user must measure the total interference received from both the P-users and other S-users. In this direction, using both the UCP and measurement of the interference received from the P-users and the S-users by the S-user or secondary base station (S-BS), we mathematically derive an equation for issuing data transmission permission, which if it is held then the second phase of the algorithm: the transmit power/rate control starts. In this phase, the S-user and the S-BS look for feasible values for the transmit power level and transmission rate. If there are feasible values, it starts its transmission at these feasible transmit power and rate. Since both the location of the S-user and the channel condition vary in time, the whole algorithm is iterated periodically with a period faster than the coherence time of the channel. Furthermore, we consider the down link of the above system with cooperation among neighboring S-users to overcome fading channels and we investigate the amount of improvement in the reliability of the issuing data transmission permission. As well, we consider the uplink of the system with multiple antennas in the S-BS to investigate the improvement in the same parameter over spatially correlated and independent fading channels. Theoretical analysis is validated using computer simulations. Both theoretical analysis and computer simulations show that the proposed cooperative spectrum sensing algorithm performs properly at SNR = -5dB in flat Nakagami-m fading channels with m = 1 even in correlated fading channels. We also address the improvement of the reliability of the issuing data transmission permission in the uplink in case of using multiple antennas only in the S-BS. © 2011 John Wiley & Sons, Ltd.


Hedayati H.,Iran University of Science and Technology
Journal of Multiple-Valued Logic and Soft Computing | Year: 2011

The notion of implicative interval-valued intuitionistic fuzzy filter of a pseudo-BL algebra with respect to t-norm T and t-conorm S is introduced. The characteristic properties and connections are described. Also some natural equivalence relations and partitions defined on the set of implicative interval-valued intuitionistic (T, S)-fuzzy filters are analysed. © 2011 Old City Publishing, Inc.


Yildirim A.,Ege University | Saadatnia Z.,Iran University of Science and Technology | Askari H.,Iran University of Science and Technology
Mathematical and Computer Modelling | Year: 2011

In this paper, Hamiltonian Approach (HA) is applied to obtain the analytical approximate solution of the nonlinear oscillators with Rational and Irrational Elastic Terms. Periodic solutions are analytically verified and consequently the relationship between the natural frequency and the initial amplitude is obtained in an analytical form. A comparison of the period of oscillation and obtained solutions with the exact results illustrates that the Hamiltonian approach is very effective and quite accurate for nonlinear equations. © 2011 Elsevier Ltd.


Golbabai A.,Iran University of Science and Technology | Sayevand K.,Iran University of Science and Technology
Mathematical and Computer Modelling | Year: 2011

The fractional advection-dispersion equation (FADE) known as its non-local dispersion, is used in groundwater hydrology and has been proven to be a reliable tool to model the transport of passive tracers carried by fluid flow in a porous media. In this paper, compact structures of FADE are investigated by means of the homotopy perturbation method with consideration of a promising scheme to calculate nonlinear terms. The problems are formulated in the Jumarie sense. Analytical and numerical results are presented. © 2010 Elsevier Ltd.


Kazemimoghadam M.,Iran University of Science and Technology | Mohammadi T.,Iran University of Science and Technology
Desalination | Year: 2011

Zeolite hydroxysodalite (HS) was synthesized successfully by hydrothermal method using the natural kaolin. In the first step, kaolin has been calcined at 700°C to the metakaolinite phase. As a second step, the zeolitisation experiments have been carried out under hydrothermal conditions. The metakaolinite obtained has been reacted with NaOH solutions in autoclaves at 100°C. The crystal species were characterized by X-ray diffraction (XRD) patterns and morphology of the supports subjected to crystallization was characterized by Scanning electron microscopy (SEM). Performance of the hydrophilic Nano zeolite membranes during separation of water/Ethanol mixtures was evaluated. These membranes showed very high selectivity of water for water/Ethanol mixtures. Separation factor as high as 10,000 was obtained for ethanol feed concentration of 90%. Total mass flux was also obtained 0.959kg/m 2.h. © 2011 Elsevier B.V.


Abdoos M.,Iran University of Science and Technology | Mozayani N.,Iran University of Science and Technology | Bazzan A.L.C.,University of Porto
Engineering Applications of Artificial Intelligence | Year: 2013

Agent-based technologies are rapidly growing as a powerful tool for modelling and developing large-scale distributed systems. Recently, multi-agent systems are largely used for intelligent transportation systems modelling. Traffic signals control is a challenging issue in this area, especially in a large-scale urban network. In a large traffic network, where each agent represents a traffic signals controller, there are many entities interacting with each other and hence it is a complex system. An approach to reduce the complexity of such systems is using organisation-based multi-agent system. In this paper, we use an organisation called holonic multi-agent system (HMAS) to model a large traffic network. A traffic network containing fifty intersections is partitioned into a number of regions and holons are assigned to control each region. The holons are hierarchically arranged in two levels, intersection controller holons in the first level and region controller holons in the second level. We introduce holonic Q-learning to control the signals in both levels. The inter-level interactions between the holons in the two levels contribute to the learning process. Experimental results show that the holonic Q-learning prevents the network to be over-saturated while it causes less average delay time and higher flow rate. © 2013 Elsevier Ltd.


Gandomi A.H.,Tafresh University | Yang X.-S.,National Physical Laboratory United Kingdom | Alavi A.H.,Iran University of Science and Technology
Engineering with Computers | Year: 2013

In this study, a new metaheuristic optimization algorithm, called cuckoo search (CS), is introduced for solving structural optimization tasks. The new CS algorithm in combination with Lévy flights is first verified using a benchmark nonlinear constrained optimization problem. For the validation against structural engineering optimization problems, CS is subsequently applied to 13 design problems reported in the specialized literature. The performance of the CS algorithm is further compared with various algorithms representative of the state of the art in the area. The optimal solutions obtained by CS are mostly far better than the best solutions obtained by the existing methods. The unique search features used in CS and the implications for future research are finally discussed in detail. © 2011 Springer-Verlag London Limited.


Sanaye S.,Iran University of Science and Technology | Chahartaghi M.,Shahrood University of Technology | Asgari H.,Iran University of Science and Technology
Energy | Year: 2013

The Gas Engine driven Heat Pump (GEHP) operating cycle is a vapor compression refrigeration type which includes compressor, condenser, expansion valve, evaporator, and a gas engine to drive the compressor. In the present work, the dynamic modeling of GEHP system during startup in cooling mode is performed and variation of evaporator and condenser temperatures, shaft power consumed by compressor, engine fuel consumption, and primary energy ratio of system were determined at various time steps. The dynamic modeling included transient heat transfer equations for condenser and evaporator for computing the evaporator and condenser temperatures. These equations were solved using Runge-Kutta method. In order to validate dynamic modeling, the modeling output results were compared with the empirical results obtained for a GEHP system. The comparison of modeling results and the experimental measured values for various amounts of evaporator and condenser temperatures, cooling capacity, gas engine fuel consumption, shaft power consumed by compressor and primary energy ratio of system showed average difference values of 1.73°C, 1.26°C, 8.05%, 9.51%, 9.27% and 7.15% respectively. © 2013 Elsevier Ltd.


Bayati M.R.,Iran University of Science and Technology | Golestani-Fard F.,Iran University of Science and Technology | Moshfegh A.Z.,Sharif University of Technology
Materials Chemistry and Physics | Year: 2010

In this research, the effect of applied voltage and electrolyte concentration on structure, chemical composition, optical properties, and especially photo-catalytic activity of the TiO2 layers containing micro/nano-sized pores are discussed. TiO2 layers were synthesized by micro arc oxidation (MAO) process using different electrolyte concentrations and applied voltages. Surface structure of the layers was studied by scanning electron microscope (SEM); furthermore, energy dispersive spectrophotometry (EDS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) techniques were employed to determine phase structure and chemical composition of the layers. Photo-activity of the layers was also examined by measuring the decomposition rate of methylene blue on their surfaces. Band gap energy of the grown layers was also measured by a UV-vis spectrophotometer. It was found that there is a critical voltage at which electrical sparks begin to appear on the anode surface due to applying voltages higher than breakdown voltage of the surface gas layer. The critical voltage which was responsible for formation of structural pores decreased at higher concentrations of electrolyte. Meanwhile, surface pore size increased at higher applied voltages, or alternatively using electrolytes with higher concentrations. The layers contained the anatase and the rutile phases whose fractions varied with the synthesis parameters. It was also revealed that the band gap energy of the grown layers decreased with the applied voltage and electrolyte concentration. Moreover, the photo-catalytic performance of the layers synthesized at medium applied voltages was higher than that of the layers produced at lower or higher voltages. More than 90% of methylene blue solution was decomposed after 160 min UV irradiation on the layers produced in an electrolyte with a concentration of 10 g l-1. © 2009 Elsevier B.V. All rights reserved.


Amereh E.,Iran University of Science and Technology | Afshar S.,Iran University of Science and Technology
Materials Chemistry and Physics | Year: 2010

TiO2 was supported on a porous material, like NaX zeolite, by using sol-gel method and TiCl4 as precursor. SEM of synthesized samples shows that nano titanium species are located on the external surface of the zeolite. Nano titanium species bound to the framework through Ti-O-Si bonds were also observed by IR analysis. The XRD patterns show that the supported TiO2 are crystallized in anatase form, and the intensity of the X-ray diffraction peaks increased with increasing TiO2 loading. These materials are used as photocatalyst for the degradation of acetophenone and toluene to H2O and CO2. The effect of some factors such as the pH of the photodegradation reaction, time of UV irradiation and amounts of TiO2 loading and catalyst used was investigated. The results of this work show that as photocatalyst for the degradation of acetophenone and toluene, the nano titanium oxide based on NaX zeolite is superior over the nano titanium oxide powder alone. © 2009 Elsevier B.V. All rights reserved.


Sanaye S.,Iran University of Science and Technology | Shirazi A.,Iran University of Science and Technology
Energy and Buildings | Year: 2013

A major portion of electricity consumption in buildings in residential, administrative, and commercial sectors is related to air-conditioning (A/C) systems. To reduce and shift the electricity consumption of A/C systems from on-peak hours to off-peak hours, an ice thermal energy storage (ITES) can be utilized. In this paper, thermo-economic optimization of an ITES system was carried out for A/C applications. In order to consider the environmental aspects, a penalty cost was considered for CO2 emission. Applying the genetic algorithm optimization technique, the optimum values of system design parameters were obtained. The objective function included the capital and operational costs as well as the penalty cost due to CO2 emission, without and with costs associated with exergy destruction. The results indicated that, on average, the amount of electricity consumption and CO2 emission of ITES system were lower 9% and 9.8%, respectively, in comparison with those of a conventional system. Furthermore, the ITES extra capital cost could be paid back through savings in electricity cost in 3.43 years. © 2013 Elsevier B.V.


Kaveh A.,Iran University of Science and Technology | Ahmadi B.,Iran University of Science and Technology
Scientia Iranica | Year: 2013

In this paper, the Charged System Search (CSS) algorithm and the force method are used for the simultaneous analysis and design of structures. Supervisor agents are introduced for the optimization procedure to enhance the exploration ability of the CSS. The presented method is applied to the design and analysis of some planer and space structures. A new formulation is presented for the objective function, and the accuracy and efficiency of the presented approach is examined by comparing the resulting design parameters and structural weight with those of other methods from literature. © 2013 Sharif University of Technology.


Ayatollahi M.R.,Iran University of Science and Technology | Karimzadeh A.,Iran University of Science and Technology
International Journal of Fracture | Year: 2013

Effect of orthodontic bracket bonding-debonding on fracture toughness of human dental enamel was investigated by using nano-indentation test. For this purpose, some ceramic brackets were bonded by a dental adhesive on the buccal surface of sound human teeth enamel. All clinical requirements were considered for bracket bonding and sample preparation. After debonding of the brackets, the teeth were sectioned transverse to their longitudinal axes and from the middle of the bracket region to prepare the samples required for nano-indentation tests. The nanoindentation test was performed on both the enamel under bracket and the intact enamel. The values of fracture toughness of dental enamel in both regions were calculated from the analysis of nano-scale holes observed after the nano-indentation tests. A comparison between the results obtained from the two regions indicated that bracket bonding-debonding significantly decreased the fracture toughness of human dental enamel. © 2013 Springer Science+Business Media Dordrecht.


Kaveh A.,Iran University of Science and Technology | Nikaeen M.,Iran University of Science and Technology
International Journal of Civil Engineering | Year: 2013

In this research, the Charged System Search (CSS) and Enhanced Charged System Search (ECSS) algorithms are used to obtain the optimum design of irregular grillage systems with different spacing and various boundary conditions. The cross-sectional properties of the beams are selected as the design variables and the weight of structure is used as the objective function. The displacement limitations and permissible stress constraints are employed from LRFD-AISC and are considered in the formulation of the design problem. Furthermore, in obtaining the response of the grillage systems, the effect of warping is also taken into account. The comparison of the results shows that warping changes the beam spacing, and different boundary conditions have substantial effects on the optimum design of irregular grillage systems.


Dargahi V.,Iran University of Science and Technology | Dargahi S.,University of Tabriz
IET Power Electronics | Year: 2013

This study proposes a mathematical model for stacked multicell (SM) converters (SMCs), to be exploited in the analytic determination of the natural voltage balancing dynamics of the SMCs, that is, investigation of the start-up behaviour, dynamic response and natural voltage balancing phenomenon. The crux of the proposed strategy is based on the closed-form analytic solution derivation for the switching functions used in the switching of the SMCs operated under phase disposition (PD) and phase-shifted carrier (PSC) pulse-width modulation (PD-PSC-PWM) technique. Hence, the suggested approach develops an analytic solution for the Fourier series and associated Fourier coefficients pertinent to the switching functions of the SMCs by obtaining the switching instants of the PD-PSC-PWM modulator in terms of -Kapteyn series- when the frequency of the triangular carrier waveform (fc) and that of the sinusoidal reference waveform (fr) have an integer ratio, that is, fcfr -1 = k, kεN{double struck}. This strategy results into a model ('first-order differential equation based model') which can be readily developed for the SMCs with any number of levels expediting the investigation of their performance. Numeric computation results of the proposed analytic model for the SMCs and simulation results as well as measurements taken from an experimental set-up are presented in order to validate the suggested approach and derived model.©The Institution of Engineering and Technology 2013.


Hasheminejad S.M.,Iran University of Science and Technology | Aghabeigi M.,Iran University of Science and Technology
Journal of Sound and Vibration | Year: 2011

A semi-analytical mathematical model is developed to study the transient liquid sloshing characteristics in half-full horizontal cylindrical containers of elliptical cross section subjected to arbitrary lateral external acceleration. The problem solution is achieved by employing the linear potential theory in conjunction with conformal mapping, resulting in linear systems of ordinary differential equations which are truncated and then solved numerically by implementing Laplace transform technique followed by Durbins numerical inversion scheme. A ramp-step function is used to simulate the lateral acceleration excitation during an idealized turning maneuver. The effects of tank aspect ratio, excitation input time, and baffle configuration on the resultant sloshing characteristics are examined. Limiting cases are considered and good agreements with available analytic and numerical solutions as well as experimental data are obtained. © 2011 Elsevier Ltd. All rights reserved.


Oraizi H.,Iran University of Science and Technology | Sharifi A.-R.,Iran University of Science and Technology
IEEE Transactions on Microwave Theory and Techniques | Year: 2011

A general analysis and design procedure is developed for the asymmetrical multisection power divider with arbitrary power division ratio and arbitrary specifications of input and output impedance matching over any desired frequency bandwidth. The even- and odd-mode analysis, which was previously applied to the design of multisection Gysel power dividers, required that the unequal power division ratios be accompanied with appropriately proportional output impedances. This requirement is relaxed here. The equivalent circuits are first obtained for the divider and then their scattering parameters are determined. Some error functions are then constructed by the method of least squares. Their minimization determines the geometrical dimensions of the optimum divider. An approximate method based on the even and odd modes is developed for its initial design of the divider. Two examples of single- and double-section dividers are designed. Their frequency responses of isolation and transmission coefficients are obtained by the proposed method, HFSS software, fabrication, and measurement. They agree within the approximate assumptions. A two-section and two-way power divider is designed and fabricated by the proposed method for the case of unequal port impedances in the L-band. The measured isolation between the outputs is better than -22 dB in 44% of the band. © 2006 IEEE.


Hasheminejad S.M.,Iran University of Science and Technology | Mirzaei Y.,Iran University of Science and Technology
Journal of Sound and Vibration | Year: 2011

An exact three-dimensional elastodynamic analysis for describing the natural oscillations of a freely suspended, isotropic, and homogeneous elastic sphere with an eccentrically located inner spherical cavity is developed. The translational addition theorem for spherical vector wave functions is employed to impose the zero traction boundary conditions, leading to frequency equations in the form of exact determinantal equations involving spherical Bessel functions and Wigner 3j symbols. Extensive numerical calculations have been carried out for the first five clusters of eigenfrequencies associated with both the axisymmetric and non-axisymmetric spheroidal as well as toroidal oscillation modes for selected inner-outer radii ratios in a wide range of cavity eccentricities. Also, the corresponding three-dimensional deformed mode shapes are illustrated in vivid graphical forms for selected eccentricities. The numerical results describe the imperative influence of cavity eccentricity, mode type, and radii ratio on the vibrational characteristics of the hollow sphere. The existence of "multiple degeneracies" and the trigger of "frequency splitting" are demonstrated and discussed. The accuracy of solution is checked through appropriate convergence studies, and the validity of results is established with the aid of a commercial finite element package as well as by comparison with the data in the existing literature. © 2010 Elsevier Ltd. All rights reserved.


Naderpour H.,Semnan University | Kheyroddin A.,Semnan University | Amiri G.G.,Iran University of Science and Technology
Composite Structures | Year: 2010

Strengthening and retrofitting of concrete columns by wrapping and bonding FRP sheets has become an efficient technique in recent years. Considerable investigations have been carried out in the field of FRP-confined concrete and there are many proposed models that predict the compressive strength which are developed empirically by either doing regression analysis using existing test data or by a development based on the theory of plasticity. In the present study, a new approach is developed to obtain the FRP-confined compressive strength of concrete using a large number of experimental data by applying artificial neural networks. Having parameters used as input nodes in ANN modeling such as characteristics of concrete and FRP, the output node was FRP-confined compressive strength of concrete. The idealized neural network was employed to generate empirical charts and equations for use in design. The comparison of the new approach with existing empirical and experimental data shows good precision and accuracy of the developed ANN-based model in predicting the FRP-confined compressive strength of concrete. © 2010 Elsevier Ltd.


Barzinpour F.,Iran University of Science and Technology | Esmaeili V.,Iran University of Science and Technology
International Journal of Advanced Manufacturing Technology | Year: 2014

Thousands of victims and millions of affected people are consequences of natural disasters, every year. Therefore, it is essential to prepare a proper response program that considers early activities of disaster management. In urban areas, local organizations and municipal authorities are responsible for disaster-related operations such as providing emergency shelters, proper equipment, and relief supplies in order to reduce sufferings of survivors. In this paper, a new multi-objective mixed-integer linear programming model is developed for preparation planning phase of disaster management. The proposed model is inspired from a real case study of an urban district in Iran, which considers both humanitarian- and cost-based objectives in a goal-programming approach. Proactive damage estimation result of Risk Assessment tool for Diagnosis of Urban Areas against Seismic Disaster software is used as an input in order to allocate affected people to local emergency management facilities that should be established. The location allocation model is solved for both current municipal subregional zoning and a virtual zoning approach that creates auxiliary cells. Mathematical results show that the second approach can reduce logistic costs and increase total coverage simultaneously. In other words, using virtual zones would help the authorities create a better collaboration between neighboring local areas and as a result, efficiency of the decisions improves. © 2013 Springer-Verlag London.


Kalantar M.,Iran University of Science and Technology | Mousavi G. S.M.,Iran University of Science and Technology
Applied Energy | Year: 2010

This paper presents dynamic behavior and simulation results in a stand-alone hybrid power generation system of wind turbine, microturbine, solar array and battery storage. The hybrid system consists of a 195 kW wind turbine, an 85 kW solar array; a 230 kW microturbine and a 2.14 kAh lead acid battery pack optimized based on economic analysis using genetic algorithm (GA). At first, a developed Lyapunov model reference adaptive feedback linearization method accompanied by an indirect space vector control is applied for extraction of maximum energy from a variable speed wind power generation system. Then, a fuzzy logic controller is designed for the mentioned purpose and its performance is compared with the proposed adaptive controller. For meeting more load demands, the solar array is integrated with the wind turbine. In addition, the microturbine and the battery storage are combined with the wind and solar power generation system as a backup to satisfy the load demand under all conditions. A supervisory controller is designed in order to manage energy between the maximum energy captured from the wind turbine/solar arrays, and consumed energies of the load, dump load, battery state of charge (SOC), and generated energy by the microturbine. Dynamic modeling and simulation are accomplished using MATLAB Simulink™ 7.2. © 2010 Elsevier Ltd. All rights reserved.


Djavanroodi F.,Iran University of Science and Technology | Derogar A.,Iran University of Science and Technology
Materials and Design | Year: 2010

The forming limit diagram (FLD) is a useful concept for characterizing the formability of sheet metal. In this work, the formability, fracture mode and strain distribution during forming of Ti6Al4V titanium alloy and Al6061-T6 aluminum alloy sheets has been investigated experimentally using a special process of hydroforming deep drawing assisted by floating disc. The selected sheet material has been photo-girded for strain measurements. The effects of process parameters on FLD have been evaluated and simulated using ABAQUS/Standard. Hill-swift and NADDRG theoretical forming limit diagram models are used to specify fracture initiation in the finite element model (FEM) and it is shown that the Hill-swift model gives a better prediction. The simulated results are in good agreement with the experiment. © 2010 Elsevier Ltd.


Shokrieh M.M.,Iran University of Science and Technology | Rafiee R.,Iran University of Science and Technology
Composite Structures | Year: 2010

The main goal of this research is to study the tensile behavior of embedded short carbon nanotubes (CNTs) in a polymer matrix in presence of van der Waals (vdW) interaction as inter-phase region. A 3D finite element model of a unit cell consisting of capped carbon nanotubes, inter-phase and surrounding polymer is built. The unit cell is subjected to tensile load case to obtain longitudinal Young's modulus of the investigated cell. A parametric study is carried out to investigate the effect of CNT's length on reinforcement. It is observed that improvement in the Young's modulus of CNT-composite is negligible for lengths smaller than 100. nm and saturation takes place in larger lengths on the order of 10 μm. Furthermore, a comparison between results obtained for short carbon nanotubes and long carbon nanotube is presented. The efficient length of CNT in form of (10, 10) is obtained at the order of 10 μm. Finally, it was shown that direct use of micromechanics equations for short fibers will overestimate the stiffness. However, employing effective stiffness of equivalent fiber comprising of CNT and its inter-phase instead of high modulus of CNT will lead us to more appropriate results, which are in an acceptable agreement with conventional semi-empirical micromechanics equations. © 2010 Elsevier Ltd.


Pouretedal H.R.,Iran University of Science and Technology | Keshavarz M.H.,Iran University of Science and Technology
Journal of Alloys and Compounds | Year: 2010

In this work, Zn1-XCuXS and Zn1-XNi XS nanocomposites were synthesized by using a controlled coprecipitation. The nanocomposite materials were characterized by the use of UVVis spectra, atomic absorption spectroscopy, X-ray diffraction patterns, transmission electron microscopy image and BrunauerEmmettTeller method. For Zn1-XCuXS and Zn1-XNiXS nanoparticles, the X-ray diffraction patterns show the zinc-bland crystal structure. The blue shift in band-gap of ZnS was observed through incorporation of Cu2+ and Ni2+ ions. The Congo red photodegradation was performed to study the photoactivity of prepared nanocomposites under UVVis irradiation. The effect of dopant mole fraction, dosage of photocatalyst and pH of samples were considered on the decolorization rate of dye and photoactivity of nanocomposites. The maximum degradation of dye was obtained at pH 57. The Zn0.94Ni0.06S and Zn0.90Ni0.10S nanocomposites show the highest photoactivity. The influence of hydrogen peroxide and several anions were studied on the photoactivity of proposed catalysts. Also, the reproducibility of nanoparticles behavior as photocatalyst shows at least a four cycles of photodegradation process. © 2010 Elsevier B.V. All rights reserved.


Tavana N.R.,Iran University of Science and Technology | Shoulaie A.,Iran University of Science and Technology
IEEE Transactions on Magnetics | Year: 2010

In this paper, in order to achieve the sinusoidal back electromotive force (EMF) waveform in a permanent-magnet machine, which is closely related to its magnet shape, we have used magnet arc shaping technique. An analytical analysis based on Maxwell equations is proposed for calculating magnetic field and thrust/torque. Then the accuracy of the presented method in modeling of machine is verified by the finite-element method. Finally, a magnet shape design is carried out based on the analytical method to produce sine air-gap magnetic field. The results show an enhancement in optimized motor performance. © 2010 IEEE.


Kaveh A.,Iran University of Science and Technology | Talatahari S.,University of Tabriz
Journal of Constructional Steel Research | Year: 2010

Grillage systems are widely used in structures to cover large areas in bridge decks, ship hulls and floors. In this paper, the charged system search (CSS) algorithm is utilized to obtain the optimum design of grillage systems. This algorithm is inspired by the Coulomb and Gauss laws of electrostatics in physics and the governing laws of motion from Newtonian mechanics. The cross-sectional properties of beams are considered as the design variables. Comparison of the results with those of some previous studies shows the robustness of the new algorithm. © 2010 Elsevier Ltd. All rights reserved.


Abdollahzadeh E.,Iran University of Science and Technology
Journal of Pragmatics | Year: 2011

This rhetorical study investigated the employment of interpersonal metadiscourse in applied linguistics articles written in English by Anglo-American and Iranian academic writers. To this end, a representative sample of 60 conclusion sections written by the two groups of writers was selected as the corpus. The two groups of writers were compared in terms of their use of " hedges" , " emphatics" , and " attitude markers" in the extracts. The interpersonal categories were also broken down into subtypes depending on the linguistic items used, and analyzed for distribution in the conclusion sections. The functional-contextual analysis shows similarities and differences in the rhetorical behaviour of these authors in their use of interpersonal metadiscourse. There was a remarkable tendency by both writer groups towards hedging their propositions. Pronounced differences were mainly in the higher use of emphatics and attitude markers by Anglo-American authors. High certainty avoidance and abstinence from attitudinal language was noticeable amongst Iranian experts. The differences are attributed to the degree of rhetorical sensitivity to and awareness of audience, purpose, cultural leanings, and the proclivities of the disciplinary genre. The implications of this study can be helpful in academic writing, EFL writing instruction, and genre analysis. © 2010 Elsevier B.V.


Korayem M.H.,Iran University of Science and Technology | Taheri M.,Iran University of Science and Technology
Journal of Nanoparticle Research | Year: 2014

In this article, the modeling of various contact theories to be applied in the biomanipulation of different micro/nanoparticles based on the atomic force microscope has been studied, and the effect of adhesion force in different contact models on indentation depth and contact angle between tip and substrate has been explored for the target biological micro/nanoparticle. The contact models used in this research include the Hertz, JKR, DMT, BCP, COS, PT, and the SUN models. Also, the target particles comprise the biological micro/nanoparticles of DNA, yeast, platelet, and nanobacterium. Previous research works have investigated the contact models for the manipulation of non-biological gold micro/nanoparticles in the air environment. Since in a real biomanipulation situation, the biological micro/nanoparticles are displaced in biological environments; in this article, various contact theories for the biomanipulation of biological micro/nanoparticles in different biological environments have been modeled and compared for the first time. The results of modeling indicate that the use of Hertz contact model in analyzing the biomanipulation of biological nanoparticles is not appropriate, because it does not take the adhesion force into consideration and thus produces a significant error. Also, all the six contact models developed in this article show larger deformations for studied bionanoparticles in comparison to the gold nanoparticles, which can be justified with regards to the mechanical properties of gold. © 2013 Springer Science+Business Media Dordrecht.


Vahidinasab V.,Iran University of Science and Technology | Jadid S.,Iran University of Science and Technology
Electric Power Systems Research | Year: 2010

This paper presents a stochastic multiobjective model for self-scheduling of a power producer which participates in the day-ahead joint energy and reserves markets. The objective of a power producer is to compromise the conflicting objectives of payoff maximization and gaseous emissions minimization when committing its generation of thermal units. The proposed schedule will be used by the power producers to decide on emission quota arbitrage opportunities and for strategic bidding to the energy and reserves market. The paper analyzes a scenario-based multiobjective model in which random distributions, such as price forecasting inaccuracies as well as forced outage of generating units are modeled as scenarios tree using a combined fuzzy c-mean/Monte-Carlo simulation (FCM/MCS) method. With the above procedure the stochastic multiobjective self-scheduling problem is converted into corresponding deterministic problems. Then a multiobjective mathematical programming (MMP) approach based on ε-constraint method is implemented for each deterministic scenario. Piecewise linearized fuel and emission cost functions are applied for computational efficiency and the model is formulated as a mixed-integer programming (MIP) problem. Numerical simulations for a power producer with 21 thermal units are discussed to demonstrate the performance of the proposed approach in increasing expected payoffs by adjusting the emission quota arbitrage opportunities. © 2009 Elsevier B.V. All rights reserved.


Kalantar M.,Iran University of Science and Technology | Mousavi G. S.M.,Iran University of Science and Technology
Applied Energy | Year: 2010

In this paper, modeling, analysis, design, simulation and control of a single ended primary inductor converter (SEPIC) are discussed for renewable energy applications. Because the traditional control methods such as proportional-integral-derivative (PID) and classical half-cycle Posicast controllers based on feedforward are sensitive to noise and variations in natural frequency, a Posicast control with feedback structure is proposed and designed to reduce or rejection undesirable sensitivity greatly, to suppress measurement noise and to eliminate the overshoot in the output response. The SEPIC converter is modeled using average value modeling analysis. Dynamic modeling and simulation are accomplished using MATLAB Simulink™ 7.2. © 2010 Elsevier Ltd. All rights reserved.


Amini F.,Iran University of Science and Technology | Samani M.Z.,Iran University of Science and Technology
Computer-Aided Civil and Infrastructure Engineering | Year: 2014

This article presents a time varying wavelet-based pole assignment (WPA) method to control seismic vibrations in multi-degree of freedom (MDOF) structural systems. The discrete wavelet transform is used to determine the energy content over the frequency band of the response in real time. The frequency content was implemented in the Big Bang-Big Crunch algorithm to update the optimum values of the closed-loop poles of the structural system adaptively. To calculate optimum gain matrix, a robust pole placement algorithm was used. The gain matrix is calculated online based on response characteristic in real time and must not be calculated a priori (offline) choice. The WPA is tested on a 10-story structural system subject to several historical ground motions. It is observed that the WPA has advantages in some design problems. Numerical examples illustrate that the proposed approach reduces the displacement response of the structure in real time more than conventional linear quadratic regulator (LQR) controller. © 2014 Computer-Aided Civil and Infrastructure Engineering.


Mohammad Reza A.P.,Iran University of Science and Technology | Ali M.H.,University of South Carolina
Energy | Year: 2010

Voltage source inverter (VSI) can produce single and three-phase (3P) AC voltages from a constant or variable DC voltage. There are many ways to control the VSI output voltage. Each control way produces some harmonics at the VSI output voltage. The space vector pulse width modulation (SVPWM) may be more effective than other modulation methods, e.g. harmonic injection, phase shifting, multi career pulse width modulation, in decreasing the low order harmonics (LOH). Different switching strategies (SSs) of power electronic devices in SVPWM have some specific advantages and disadvantages with regard to one another. In this paper, a comparative study between different SVPWM SSs is carried out by considering some objective functions such as total harmonic distortion (THD), power and switching losses, the ratio of the harmonic components to the fundamental component, distortion factor (DF). It is also shown that by selecting an optimized and appropriate SS for SVPWM, the harmonic orders, which are the multiples of the frequency index (FI), are eliminated. Then, to investigate the impact of variations of the capacitors voltage and switching frequency on power quality criteria, the most appropriate and optimized SS is applied to a 3P three-level (3L) neutral-point-clamped (NPC) VSI to supply a 3P load.This paper also presents a novel and optimized SS and control approach for a 3L two-quadrant (2Q) chopper in NPC VSI superconducting magnetic energy storage (SMES). Using the proposed SS, the voltage of the VSI capacitors in SMES can be independently controlled; also, the minimum power and switching losses - as well as the proper convection - can be achieved using this same strategy. The simulation results indicate that when combined with a proportional-integral (PI) control approach the proposed SS can be easily implemented in the power networks and can balance and stabilize the multi-level VSIs' capacitor voltage level. The voltage variation of the capacitors in the steady state condition is less than (0.062%) which is 15 times better than the IEEE standard requirement (1%). To investigate the effectiveness and reliability of the proposed approach in stabilizing capacitor voltage, SMES performance using the presented approach is compared with that of SMES when the capacitors of the 3L VSI are replaced with equal and ideal voltage sources. This comparison is carried out from the power quality point of view and it is shown that the proposed SS with a PI controller is highly reliable. © 2010 Elsevier Ltd.


Faieghi M.,Islamic Azad University at Miyaneh | Jalali A.,Iran University of Science and Technology | Mashhadi S.K.E.D.M.,Iran University of Science and Technology
ISA Transactions | Year: 2014

The cruise control problem of high speed trains in the presence of unknown parameters and external disturbances is considered. In particular a Lyapunov-based robust adaptive controller is presented to achieve asymptotic tracking and disturbance rejection. The system under consideration is nonlinear, MIMO and non-minimum phase. To deal with the limitations arising from the unstable zero-dynamics we do an output redefinition such that the zero-dynamics with respect to new outputs becomes stable. Rigorous stability analyses are presented which establish the boundedness of all the internal states and simultaneously asymptotic stability of the tracking error dynamics. The results are presented for two common configurations of high speed trains, i.e. the DD and PPD designs, based on the multi-body model and are verified by several numerical simulations. © 2013 ISA.


Toshani H.,Iran University of Science and Technology | Farrokhi M.,Iran University of Science and Technology
Robotics and Autonomous Systems | Year: 2014

In this paper, an online adaptive strategy based on the Lyapunov stability theory is presented to solve the inverse kinematics of redundant manipulators. In the proposed approach, Radial Basis Function (RBF) Neural Networks (NNs) are employed to obtain the joint angles of the robot using the Cartesian coordinate of the end-effector. Quadratic Programming (QP) method is incorporated in the training algorithm of the NNs to satisfy the constraints of the problem such as the joint angle limits and obstacles in the workspace of the robot. For better initialization of the NNs' weights, fuzzy logic is employed. In this way, smaller errors for the initial position of the end-effector and feasibility of the joint angles can be obtained. The convergence of the NNs' weights and satisfaction of the constraints are guaranteed by employing an adaptive scheme that is based on the Lyapunov stability analysis and Kuhn-Tucker conditions, which is part of the QP to update the NNs' weights. In addition, obstacle avoidance is also considered in the proposed method. The simulations are carried out on the seven degrees-of-freedom PA-10 robot manipulator. The results show the effectiveness of the proposed approach in obtaining successful configurations of the robot while the solutions of the inverse kinematics are feasible. Moreover, a comparison with the recently reported methods in the literature shows advantages of the proposed method. © 2014 Elsevier B.V. All rights reserved.


Kaveh A.,Iran University of Science and Technology | Zolghadr A.,Iran University of Science and Technology
Advances in Engineering Software | Year: 2014

Structural optimization with frequency constraints is a challenging class of optimization problems characterized by highly non-linear and non-convex search spaces. When using a meta-heuristic algorithm to solve a problem of this kind, exploration/exploitation balance is a key feature to control the performance of the algorithm. An excessively exploitative algorithm might focus on certain areas of the search space ignoring the others. On the other hand, an algorithm that is too explorative overlooks high quality solutions as a result of not performing adequate local search. This paper compares nine multi-agent meta-heuristic algorithms for sizing and layout optimization of truss structures with frequency constraints. The variation of the diversity index during the optimization history is analyzed in order to inspect exploration/exploitation properties of each algorithm. It appears that there is a significant relationship between the algorithm efficiency and the evolution of the diversity index. © 2014 Elsevier Ltd. All rights reserved.


Taleizadeh A.A.,Iran University of Science and Technology | Taleizadeh A.A.,Raja University | Niaki S.T.A.,Sharif University of Technology | Aryanezhad M.-B.,Iran University of Science and Technology | Shafii N.,University of Porto
Information Sciences | Year: 2013

Multi-periodic inventory control problems are mainly studied by employing one of two assumptions. First, the continuous review, where depending on the inventory level, orders can happen at any time, and next the periodic review, where orders can only be placed at the beginning of each period. In this paper, we relax these assumptions and assume the times between two replenishments are independent random variables. For the problem at hand, the decision variables (the maximum inventory of several products) are of integer-type and there is a single space-constraint. While demands are treated as fuzzy numbers, a combination of back-order and lost-sales is considered for the shortages. We demonstrate the model of this problem is of an integer-nonlinear-programming type. A hybrid method of fuzzy simulation (FS) and genetic algorithm (GA) is proposed to solve this problem. The performance of the proposed method is then compared with the performance of an existing hybrid FS and simulated annealing (SA) algorithm through three numerical examples containing different numbers of products. Furthermore, the applicability of the proposed methodology along with a sensitivity analysis on its parameters is shown by numerical examples. The comparison results show that, at least for the numerical examples under consideration, the hybrid method of FS and GA shows better performance than the hybrid method of FS and SA. © 2012 Elsevier Inc. All rights reserved.


Maleki A.,Iran University of Science and Technology
Helvetica Chimica Acta | Year: 2014

A one-pot multicomponent synthesis of imidazo[1,2-a]pyridine derivatives by using pyridin-2-amines, aldehydes, and terminal alkynes in the presence of a catalytic amount of silica-supported iron oxide (Fe3O 4@SiO2) nanoparticles in refluxing EtOH in good-to-excellent yields is reported. Copyright © 2014 Verlag Helvetica Chimica Acta AG, Zürich.


Kazemy A.,Iran University of Science and Technology | Farrokhi M.,Iran University of Science and Technology
Asian Journal of Control | Year: 2013

The problem of robust absolute stability for time-delay Lur'e systems with parametric uncertainties is investigated in this paper. The nonlinear part of the Lur'e system is assumed to be both time-invariant and time-varying. The structure of uncertainty is a general case that includes norm-bounded uncertainty. Based on the Lyapunov-Krasovskii stability theory, some delay-dependent sufficient conditions for the robust absolute stability of the Lur'e system will be derived and expressed in the form of linear matrix inequalities (LMIs). These conditions reduce the conservativeness in computing the upper bound of the maximum allowed delay in many cases. Numerical examples are given to show that the proposed stability criteria are less conservative than those reported in the established literatures. © 2012 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society.


Hasheminejad S.M.,Iran University of Science and Technology | Rezaei S.,Iran University of Science and Technology | Shakeri R.,Iran University of Science and Technology
Thin-Walled Structures | Year: 2013

The elaborated method of eigenfunction expansion in elliptic coordinates is employed to obtain an exact time-domain series solution, involving products of angular and radial Mathieu functions, for the forced flexural vibrations of a thin elastic plate of elliptical planform. The plate is supported by a constant moduli two-parameter foundation, while elastically restrained against translation and rotation at its edge, and subjected to the combined action of uniform in-plane static edge forces and general arbitrary time-dependent transverse loads with arbitrary initial conditions. Numerical calculations are carried out for the displacement response of clamped or simply supported elliptical plates of selected aspect ratios in various practical loading configurations (i.e., an impulsive point load, a point force in circular motion, a uniformly distributed harmonic load, and a blast load), with or without an elastic foundation, while taking the effects of initial tension or compression below the buckling load into consideration. Limiting cases are considered and good agreements with available results as well as with the computations made by using a commercial finite element package are obtained. © 2012 Elsevier Ltd. All rights reserved.


Haghiri A.,Iran University of Science and Technology | Bidabadi M.,Iran University of Science and Technology
Fuel | Year: 2011

In this investigation, a theoretical study is performed to analyze the dynamic behavior of particles across flame propagation through a two-phase mixture consisting of micro-iron particles and air. In the first step for calculation of the particle velocity profile, the Lagrangian approach of particle motion is employed, and then thermophoretic, gravitational and buoyancy forces are taken into consideration. In order to simulate the temperature profile for the thermophoretic force, it is assumed that the flame structure consists of three zones: preheat, reaction, and post flame (burned). It should be noted that the radiative heat-transfer equation is employed to describe the thermal radiation exchanged between the burned zone and the preheat zone. In the resumption, a control volume above the leading edge of the combustion zone is considered and the change in the particle number density in this volume is obtained via the balance of particle mass fluxes passing through it. The results show that the induced thermal radiation plays a significant role in increasing the mixture temperature all over the preheat zone, and that the particle velocity profile and the concentration distribution of particles as a function of distance from the leading edge of the combustion zone also have considerable consistency with published experimental data. © 2011 Elsevier Ltd. All rights reserved.


Sedighian Kashi S.,Iran University of Science and Technology | Sharifi M.,Iran University of Science and Technology
IEEE Communications Surveys and Tutorials | Year: 2013

The combination of sensor and actor nodes in wireless sensor actor networks (WSANs) has created new challenges notably in coordination. In this paper, we survey, categorize, and bring into perspective existing researches on weak connectivity and its impacts on coordination ranging from a node failure to disability of actor nodes to communicate with other actors permanently. We present challenges in each category alongside existing provisions and approaches in the context of the proposed coordination-oriented connectivity categorization. Alongside explanation of general concepts for a communication generalist, we compare the proposed protocols using parameters related to weak connectivity and coordination. Powerful actors can help weaker sensors in many aspects such as routing and data forwarding and many sensors can help few actors in the regions that actors are sparsely deployed. Actors can carry, move and charge sensors while sensors can detect partitions of inter-actor network. Considering lessons learned from surveyed works, we show that actor and sensor nodes in a WSAN must cooperate to provide an integrated network when network connectivity is weak. © 1998-2012 IEEE.


Kaveh A.,Iran University of Science and Technology | Motie Share M.A.,University of Tehran | Moslehi M.,University of Tehran
Acta Mechanica | Year: 2013

An improved version of the charged system search (CSS) algorithm is introduced which is called magnetic charged system search (MCSS). In the new algorithm, magnetic forces are considered in addition to electrical forces, using the Biot-Savart law. Each charged particle (CP), as a search agent, exerts magnetic forces on other CPs based on the variation of its objective function value during its last movement and its distance between other CPs. This additional force provides useful information for the optimization process and enhances the performance of the CSS algorithm. The efficiency of the MCSS is examined by application of this algorithm to well-known mathematical benchmarks and three well-studied engineering design problems. The results are compared to those of the CSS, and the improvements are highlighted. © 2012 Springer-Verlag Wien.


Mosavi M.R.,Iran University of Science and Technology | Azarbad M.R.,Iran University of Science and Technology
AEU - International Journal of Electronics and Communications | Year: 2013

GPS positioning issue has been experienced a surge of interest for multipath mitigation in the past few years. Multipath disturbance is a challenging error in high precision GPS positioning particularly in kinematic mode where the moving receiver undergoes different multipath circumstances. Diverse hardware and software approaches have been implemented to reduce this error in both static and kinematic modes. We have proposed an algorithm to alleviate C/A code multipath in kinematic mode. Our proposed scheme falls into software group where wavelet transform (WT) has been used as the main basis. Of course, we have used stationary wavelet transform (SWT) as the key idea of our proposed method that makes it possible to investigate all frequency sub-bands. Consequently, it would be possible to extract multipath disturbance since it is considered to be a low frequency term. After applying SWT to double difference (DD) residuals, the multipath error is extracted and used to correct DD observations. In this paper, we have designed three experiments to study our proposed method efficiency under different conditions in comparison with existing algorithms. © 2013 Elsevier GmbH.


Soltanpour M.R.,Iran University of Science and Technology | Khooban M.H.,Islamic Azad University
Nonlinear Dynamics | Year: 2013

In this paper, an optimal fuzzy sliding mode controller is used for tracking the position of robot manipulator, is presented. In the proposed control, initially by using inverse dynamic method, the known sections of a robot manipulator's dynamic are eliminated. This elimination is done due to reduction over structured and unstructured uncertainties boundaries. In order to overcome against existing uncertainties for the tracking position of a robot manipulator, a classic sliding mode control is designed. The mathematical proof shows the closed-loop system in the presence of this controller has the global asymptotic stability. Then, by applying the rules that are obtained from the design of classic sliding mode control and TS fuzzy model, a fuzzy sliding mode control is designed that is free of undesirable phenomena of chattering. Eventually, by applying the PSO optimization algorithm, the existing membership functions are adjusted in the way that the error tracking robot manipulator position is converged toward zero. In order to illustrate the performance of the proposed controller, a two degree-of-freedom robot manipulator is used as the case study. The simulation results confirm desirable performance of optimal fuzzy sliding mode control. © 2013 Springer Science+Business Media Dordrecht.


Sanaye S.,Iran University of Science and Technology | Asgari H.,Iran University of Science and Technology
International Journal of Refrigeration | Year: 2013

The gas-engine driven air-to-water heat pump, type air conditioning system, is composed of two major thermodynamic cycles (including the vapor compression refrigeration cycle and the internal combustion gas engine cycle) as well as a refrigerant-water plate heat exchanger. The thermal modeling of gas engine driven air-to-water heat pump system with engine heat recovery heat exchangers was performed here for the heating mode of operation (in which it was required to model engine heat recovery heat exchanger). The modeling was performed using typical thermodynamic characteristics of system components, Artificial Neural Network and the multi-objective genetic algorithm optimization method. The comparison of modeling results with experimental ones showed average differences of 5.08%, 5.93%, 5.21%, 2.88% and 6.2% which shows acceptable agreement for operating pressure, gas engine fuel consumption, outlet water temperature, engine rotational speed, and system primary energy ratio. © 2013 Elsevier Ltd and IIR. All rights reserved.


Korayem M.H.,Iran University of Science and Technology | Shafei A.M.,Iran University of Science and Technology
Acta Astronautica | Year: 2013

The goal of this paper is to describe the application of Gibbs-Appell (G-A) formulation and the assumed modes method to the mathematical modeling of N-viscoelastic link manipulators. The paper's focus is on obtaining accurate and complete equations of motion which encompass the most related structural properties of lightweight elastic manipulators. In this study, two important damping mechanisms, namely, the structural viscoelasticity (Kelvin-Voigt) effect (as internal damping) and the viscous air effect (as external damping) have been considered. To include the effects of shear and rotational inertia, the assumption of Timoshenko beam (TB) theory (TBT) has been applied. Gravity, torsion, and longitudinal elongation effects have also been included in the formulations. To systematically derive the equations of motion and improve the computational efficiency, a recursive algorithm has been used in the modeling of the system. In this algorithm, all the mathematical operations are carried out by only 3 x 3 and 3 x 1 matrices. Finally, a computational simulation for a manipulator with two elastic links is performed in order to verify the proposed method. © 2012 Elsevier Ltd. All rights reserved.


Omidi E.,Iran University of Science and Technology | Korayem A.H.,Iran University of Science and Technology | Korayem M.H.,Iran University of Science and Technology
Precision Engineering | Year: 2013

This paper investigates the sensitivity of nanoparticle parameters in a robust controlled process, by a compatible nanomanipulation model consisting of all effective phenomena in nanoscale. The dynamic model of nanoparticle displacement utilizes the Lund-Grenoble (LuGre) friction model, since it demonstrates pre-slip displacement, friction delay, various forces of failure and the stick-slip movement, with respect to other presented models. Also, the interaction force between nanoparticle and AFM cantilever tip are modeled by using the Derjaguin model. Sliding mode control (SMC) approach is used to provide the desired substrate motion trajectory, despite the challenges in the piezoelectric substrate motion control, consisting of thermal drift, hysteresis, and other uncertainties. In this paper, the dynamic model of nanoparticle manipulation is expressed to determine the nanoparticle behavior for substrate movement with desired trajectory and the effect of pre-process selections of the result of the manipulation. Depending on obtained diagrams for parameters sensitivity, the prediction of manipulation result is more precise, and also this is effective on choosing of proper initial condition and parameter selection in pushing purposes. Finally, it can be used to adjust proper pushing time and input for an accurate and successful pushing and assembly. It also provides a real-time visualization during micro/nanomanipulation and increases complexity of the resulting created structures. © 2013 Elsevier Inc.


Vahedi Nouri B.,Bu - Ali Sina University | Fattahi P.,Bu - Ali Sina University | Ramezanian R.,Iran University of Science and Technology
International Journal of Production Research | Year: 2013

Job scheduling and maintenance activities scheduling are two important issues in production management, which are often addressed separately. In this paper, the non-permutation flow shop scheduling problem with learning effects and flexible maintenance activities is studied. Each machine has a number of preventive maintenance activities that should be finished within specific time intervals. The aim is to simultaneously determine the sequence of jobs and the finish time of maintenance activities for minimising the sum of tardiness costs and maintenance costs. A mixed integer linear programming model is proposed to formulate the problem. Owing to the high complexity of the problem, an improvement heuristic method and a hybrid meta-heuristic algorithm based on the simulated annealing algorithm and firefly algorithm is presented to find nearly optimal solutions for medium and large problems. To obtain better and more robust solutions, the Taguchi method is used in order to calibrate the hybrid algorithm parameters. Finally, the computational results are provided for evaluating the performance and effectiveness of the proposed solution approaches. © 2013 Taylor and Francis.


Mohamadi Monavar F.,Iran University of Science and Technology | Komjani N.,Iran University of Science and Technology
Progress in Electromagnetics Research | Year: 2011

In this paper, we present a novel approach for improving the bandwidth of a microstrip patch antenna using Jerusalem cross-shaped frequency selective surfaces (JC-FSSs) as an artificial magnetic ground plane. The invasive weed optimization (IWO) algorithm is employed to derive optimal dimensions of the patch antenna and JC-FSS element in order for the whole structure to work at 5.8 GHz with consideration of gain. For the most efficient design, the antenna and FSS ground plane are optimized together, rather than as separate components. Simulation results demonstrate that this optimum configuration (the microstrip patch antenna over the artificial magnetic ground plane) have a broad bandwidth of about 10.44%. This wide bandwidth is obtained while the thickness of the whole structure is limited to 0.1λ. Further more desirable radiation characteristics have been successfully realized for this structure. The radiation efficiency of the AMC antenna configuration was found to be greater than 85% over the entire bandwidth. In general by introducing this novel Jerusalem cross artificial magnetic conductor (JC-AMC) in lieu of the conventional perfect electric conductor (PEC) ground plane, the bandwidth enhancement of about 67% and a thinner and lighter weight design has been obtained. Sample antenna and EBG layer are also fabricated and tested, to verify the designs. It is shown that the simulation data in general agree with the measurement results for the patch antennas implemented with FSS ground plane.


Oraizi H.,Iran University of Science and Technology | Pazoki R.,Iran University of Science and Technology
IEEE Transactions on Antennas and Propagation | Year: 2011

The radiation pattern of aperture stacked patch (ASP) antennas is improved. In the proposed geometry, the patch shape is designed such that the effective propagation constant of the antenna is decreased and therefore pattern degradation due to higher order modes is eliminated. The results show that the operational bandwidth of the proposed structure is increased from 68% to 76% compared to the traditional ASP. © 2011 IEEE.


Rahmani B.,Iran University of Science and Technology | Markazi A.H.D.,Iran University of Science and Technology
IEEE Transactions on Control Systems Technology | Year: 2013

A new method for the design of network-based control systems, together with mathematical tools for closed-loop stability assessment, is proposed. In order to preserve the closed-loop stability under random network time delays, the variable selective control (VSC) methodology is introduced, which combines the idea of variable sampling control with the packet-based control methodologies. In the proposed method, event-driven sensors are employed, which sample the plant output just after a new control input signal is received by the actuator. The advantages are as follows: 1) the latest actual sampling period becomes equal to the most recent time delay, which is known by direct measurement; 2) better estimation of the actual plant states can be performed in the predictive controller; 3) less frequent and shorter packets need to be transferred through the network; and 4) the stability analysis becomes simpler and does not depend on variable-size matrices. In order to deal with packet dropout issue, a simple, yet effective, algorithm is adopted in the controller, where packet losses are considered as variable time delays. In light of this formulation, the networked control system can be considered as a switched linear system and, therefore, previously existing theoretical results are adopted for stability analysis of the VSC method. Simulation studies on a well-known benchmark problem demonstrate the effectiveness of the proposed method. © 1993-2012 IEEE.


Karimian R.,Iran University of Science and Technology | Oraizi H.,Iran University of Science and Technology | Fakhte S.,Iran University of Science and Technology | Farahani M.,Iran University of Science and Technology
IEEE Antennas and Wireless Propagation Letters | Year: 2013

A novel F-shaped microstrip slot antenna for WLAN and WiMAX multiple-input-multiple-output (MIMO) systems is presented. The proposed antenna structure consists of both open-ended and short-ended slots connected by a metal 'via' to a microstrip line. The open-ended slot is exploited to obtain resonant mode at 2.4 GHz, and three short-ended slots are aimed to obtain resonant modes at 3.5, 5.2, and 5.8 GHz, whose center frequencies can be adjust by the slot lengths. The parametric studies show that the center frequencies are independent of each other. A four-element array configuration of the proposed antenna for MIMO applications is also studied. The simulation and measurement results of reflection coefficient, mutual coupling, and radiation pattern are presented, which attest to the applicability of antenna. © 2002-2011 IEEE.


Kaveh A.,Iran University of Science and Technology | Bakhshpoori T.,Iran University of Science and Technology
Structural Design of Tall and Special Buildings | Year: 2013

In the last two decades, many researchers have implemented various kinds of meta-heuristic algorithms in order to overcome the complex nature of the optimum design of structures. In this paper, the optimum design of two-dimensional steel frames for discrete variables based on the Cuckoo Search (CS) algorithm is developed. The CS is one of the recently developed population-based algorithms inspired by the behavior of some cuckoo species in combination with the Lévy flight behavior of some birds and insects. The design algorithm is supposed to obtain minimum weight frame through suitable selection of sections from a standard set of steel sections such as the American Institute of Steel Construction (AISC) wide-flange (W) shapes. Strength constraints of AISC load and resistance factor design specification and displacement constraints are imposed on frames. In order to demonstrate the effectiveness and robustness of the CS, low-weight design and performance comparisons are made between the CS and other algorithms for some benchmark frames. Copyright © 2011 John Wiley & Sons, Ltd.


Hasheminejad S.M.,Iran University of Science and Technology | Ahamdi-Savadkoohi A.,Iran University of Science and Technology
Composite Structures | Year: 2010

The linear three-dimensional elasticity theory in conjunction with the powerful transfer matrix solution technique is employed to investigate the steady-state nonaxisymmetric sound radiation characteristics of an arbitrarily thick functionally graded hollow cylinder of infinite length subjected to arbitrary time-harmonic on-surface concentrated mechanical drives. A formal integral expression for the radiated pressure field in the frequency domain is obtained by utilizing the spatial Fourier transform along the shell axis and Fourier series expansion in the circumferential direction. The method of stationary phase is subsequently employed to evaluate the integral for an observation point in the far-field. The analytical results are illustrated with numerical examples in which water-submerged metal-ceramic FGM cylinders are driven by harmonic concentrated radial/transverse surface forces and circumferential moment. The far-field radiated pressure amplitudes and directivities are calculated and compared with those of equivalent bi-laminate hollow cylinders with comparable volume fractions of constituent materials. The effects of FGM material profile, cylinder thickness, excitation frequency and type on the radiated far-field are examined. Limiting cases are considered and the validity of results is established by comparison with the data in the existing literature as well as with the aid of a commercial finite element package. © 2009 Elsevier Ltd. All rights reserved.


Ayatollahi M.R.,Iran University of Science and Technology | Torabi A.R.,Iran University of Science and Technology
Materials and Design | Year: 2010

Two failure criteria are proposed in this paper for brittle fracture in rounded-tip V-shaped notches under pure mode I loading. One of these criteria is developed based on the mean stress criterion and the other based on the point stress criterion which both are well known failure criteria for investigating brittle fracture in elements containing a sharp crack or a sharp V-notch. To verify the validity of the proposed criteria, first the experimental data reported by other authors from three-point bend (TPB) and four-point bend (FPB) tests on PMMA at -60 °C and Alumina-7% Zirconia ceramic are used. Additionally, some new fracture tests are also carried out on the rounded-tip V-notched semi-circular bend (RV-SCB) specimens made of PMMA for various notch opening angles and different notch tip radii. A very good agreement is shown to exist between the results of the mean stress criterion and the experimental data. © 2009 Elsevier Ltd. All rights reserved.


Kaveh A.,Iran University of Science and Technology | Talatahari S.,University of Tabriz
Journal of Constructional Steel Research | Year: 2010

An optimum topology design algorithm based on the hybrid Big Bang-Big Crunch optimization (HBB-BC) method is developed for the Schwedler and ribbed domes. A simple procedure is defined to determine the Schwedler and ribbed dome configuration. This procedure includes calculating the joint coordinates and element constructions. The nonlinear response of the dome is considered during the optimization process. The effect of diagonal members on the results is investigated and the optimum results of Schwedler domes obtained by the HBB-BC method demonstrate the efficiency of these domes to cover large areas without intermediate supports. © 2009 Elsevier Ltd. All rights reserved.


Anbia M.,Iran University of Science and Technology | Hariri S.A.,Iran University of Science and Technology | Ashrafizadeh S.N.,Iran University of Science and Technology
Applied Surface Science | Year: 2010

Batch sorption experiments were carried out to remove dyes, methyl orange (MO), orange G (OG) and brilliant red X-3B (X-3B), from their aqueous solutions using a mesoporous silica SBA-3 as an adsorbent. The effect of surfactant template in SBA-3 on the removal of OG, MO and X-3B was investigated. Experiments were carried out to investigate the influence of contact time, initial concentration, pH, and adsorbent dosage on the adsorption performance. The adsorption results of anionic dyes on the uncalcined SBA-3 (noted as SBA-3) were compared with those of the calcined SBA-3 (noted as C-SBA-3). The uncalcined SBA-3 adsorbent has a large adsorption capacity and a strong affinity for the anionic dyes. Langmuir, Freundlich and Temkin isotherms were employed to model the experimental results, from which the Freundlich isotherm exhibited the most appropriate to predict the same. Freundlich isotherm exhibited the most appropriate to predict the experimental results. The kinetic data were also analyzed through pseudo-first-order and pseudo-second-order models. The pseudo-second-order kinetic model well depicted the kinetics of dyes adsorption on mesoporous SBA-3. © 2009 Elsevier B.V. All rights reserved.


Bayati M.R.,Iran University of Science and Technology | Moshfegh A.Z.,Sharif University of Technology | Golestani-Fard F.,Iran University of Science and Technology
Applied Surface Science | Year: 2010

V2O5-TiO2 layers with a sheet-like morphology were synthesized by micro arc oxidation process for the first time. Surface morphology and topography of the layers were investigated by scanning electron microscope (SEM) and atomic force microscope (AFM). Phase structure and chemical composition of the layers were also studied by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) techniques. It was revealed that the composite layers had a sheet-like structure average thickness of which was about 100 nm depending on the applied voltage. The layers consisted of anatase, rutile, and vanadium pentoxide phases fractions of which varied with the applied voltage. The optical properties of the layers were also examined employing a UV-vis spectrophotometer. It was found that the absorption edge of the grown composite layers shifted toward the visible wavelengths when compared to MAO-synthesized pure titania layers. The band gap energy of the composite layers was calculated as 2.58 eV. Furthermore, photo-catalytic performance of the layers was examined by measuring the decomposition rate of methylene blue under ultraviolet and visible irradiations. The results demonstrated that about 90% and 68% of methylene blue solution was decomposed after 120 min ultraviolet and visible irradiations over the composite layers, respectively. © 2009 Elsevier B.V. All rights reserved.


Hosseini-Hashemi Sh.,Iran University of Science and Technology | Rokni Damavandi Taher H.,University of British Columbia | Akhavan H.,Iran University of Science and Technology
Composite Structures | Year: 2010

This paper deals with free vibration analysis of radially functionally graded circular and annular sectorial thin plates of variable thickness, resting on the Pasternak elastic foundation. Differential quadrature method (DQM) is used to yield natural frequencies of the circular/annular sectorial plates under simply-supported and clamped boundary conditions on the basis of the classical plate theory (CPT). The inhomogeneity of the plate is characterized by taking exponential variation of Young's modulus and mass density of the material along the radial direction whereas Poisson's ratio is assumed to remain constant. The validity of the present solution is first examined by studying the convergence of the frequency parameters. Then, a comparison of results with those available in literature confirms the excellent accuracy of the present approach. Afterwards, the frequency parameters of the circular/annular sectorial thin plates with uniform, linear, and quadratic variations in thickness are computed for different boundary conditions and various values of the material inhomogeneity constants, sector angles, and inner to outer radius ratios. Crown Copyright © 2010.


Shokrieh M.M.,Iran University of Science and Technology | Rafiee R.,Iran University of Science and Technology
Materials and Design | Year: 2010

Analytical formulations are presented to predict the elastic moduli of graphene sheets and carbon nanotubes using a linkage between lattice molecular structure and equivalent discrete frame structure. The obtained results for a graphene sheet show an isotropic behavior, in contrast to limited molecular dynamic simulations. Young's modulus of CNT represents a high dependency of stiffness on tube thickness, while dependency on tube diameter is more tangible for smaller tube diameters. The presented closed-form solution provides an insight to evaluate finite element models constructed by beam elements. The results are in a good agreement with published data and experimental results. © 2009 Elsevier Ltd. All rights reserved.


Shokrieh M.M.,Iran University of Science and Technology | Rafiee R.,Iran University of Science and Technology
Composite Structures | Year: 2010

The longitudinal behavior of a carbon nanotube in a polymeric matrix is studied using a non-linear analysis on a full 3D multi-scale finite element model consisting of carbon nanotube, non-bonded interphase region and surrounding polymer. The bonding between carbon nanotube and its surrounding polymer is treated as van der Waals interactions. The results of simulation of carbon nanotube reinforced polymer implies on a non-linear stress-strain behavior. A comparison between finite element analysis results and the rule of mixture for conventional composites shows that the rule of mixture overestimates the result and cannot capture the scale difference between micro- and nano-scale. An equivalent fiber is developed to overcome this difficulty and corresponding longitudinal, transverse and shear moduli are calculated. The results reveal that the length of CNT affects the efficiency of reinforcement phenomenon. © 2009 Elsevier Ltd. All rights reserved.


Gandomi A.H.,Highest Prestige Scientific and Professional National Foundation | Alavi A.H.,Iran University of Science and Technology | Sahab M.G.,Tafresh University
Materials and Structures/Materiaux et Constructions | Year: 2010

This paper proposes a new approach for the formulation of compressive strength of carbon fiber reinforced plastic (CFRP) confined concrete cylinders using a promising variant of genetic programming (GP) namely, linear genetic programming (LGP). The LGP-based models are constructed using two different sets of input data. The first set of inputs comprises diameter of concrete cylinder, unconfined concrete strength, tensile strength of CFRP laminate and total thickness of utilized CFRP layers. The second set includes unconfined concrete strength and ultimate confinement pressure which are the most widely used parameters in the CFRP confinement existing models. The models are developed based on experimental results collected from the available literature. The results demonstrate that the LGP-based formulas are able to predict the ultimate compressive strength of concrete cylinders with an acceptable level of accuracy. The LGP results are also compared with several CFRP confinement models presented in the literature and found to be more accurate in nearly all of the cases. Moreover, the formulas evolved by LGP are quite short and simple and seem to be practical for use. A subsequent parametric study is also carried out and the trends of the results have been confirmed via some previous laboratory studies. © RILEM 2009.


Kaveh A.,Iran University of Science and Technology | Nasrollahi A.,Iran University of Science and Technology
Applied Soft Computing Journal | Year: 2014

In this paper, a performance-based optimal seismic design of steel frames is presented utilizing Charged System Search (CSS) optimization. This meta-heuristic optimization algorithm has been recently developed and employed in many optimization problems showing a high capability in structural optimization. Here, a pushover analysis method based on semi-rigid connection concept is employed as analysis and design method. Two numerical examples which have been previously considered in literature are studied and the results illustrate significant improvement in structural weight compared to the conventional design methods. The capabilities of the CSS are compared to those of the ACO and GA. © 2014 Elsevier B.V.


Shabestari S.G.,Iran University of Science and Technology | Malekan M.,Iran University of Science and Technology
Journal of Alloys and Compounds | Year: 2010

The effect of different amount of Al-5Ti-1B grain refiner on the macro and microstructural features and characteristic parameters of the cooling curve of 319 aluminum alloy were studied using thermal analysis. Important parameters in liquidus, eutectic Si and eutectic Cu-phase regions have been calculated using the first derivative cooling curves. The results indicated that, the solidification parameters such as nucleation and growth temperatures of various phases, undercooling temperatures, solidification range and total solidification time were affected by grain refining. Also, latent heat and fraction solid were determined for the different amount of grain refiner for 319 alloy. It has been found that the fraction solid is completed fast by addition of Al-5Ti-1B grain refiner. © 2009 Elsevier B.V. All rights reserved.


Ayatollahi M.R.,Iran University of Science and Technology | Khoramishad H.,Iran University of Science and Technology
International Journal of Pressure Vessels and Piping | Year: 2010

In this paper, the finite element method has been used to study the effect of soil weight on the stress intensity factors of an axially oriented semi-elliptical crack located on the inner surface of a buried pipe. The Burns and Richard model has been utilized to take into account the interaction between the soil and the pipe. The finite element results revealed that the cracks in a buried pipe are subjected to mixed mode loading. The mode I and mode II stress intensity factors depend on the circumferential location of internal crack. KI is always significantly larger than KII and is maximum when the internal crack is along the vertical direction. A comparison between the results of two-dimensional and three-dimensional cracks also signified that the two-dimensional analysis always represents more conservative results. Depending on the crack aspect ratio (a/c), the discrepancy between the results of two and three-dimensional analyses can be significant. © 2010 Elsevier Ltd.


Shokrieh M.M.,Iran University of Science and Technology | Mazloomi M.S.,Iran University of Science and Technology
Composite Structures | Year: 2010

This paper presents a new analytical method for calculation of the stiffness of two-dimensional tri-axial braided composites. A unit cell has been introduced as a representative cell of a braided composite and its components. The braided composite is considered as consisting of three layers. The first two layers represent braided tows and the third layer is the axial tow. Then, using rule of mixtures, mechanical properties of each layer are calculated. Next, using analytical relations, the undulation of representative layers of braided tows is calculated. Finally, using a volume averaging method, the total stiffness of the braided composite is calculated. The results are compared with those obtained from experimental methods and the effect of braided tows crimp on the stiffness of braided composites is examined. © 2010 Elsevier Ltd.


Ayatollahi M.R.,Iran University of Science and Technology | Torabi A.R.,Iran University of Science and Technology
Engineering Fracture Mechanics | Year: 2010

A criterion is proposed for brittle fracture analysis in rounded-tip V-notched components. This criterion, called RV-MTS, is developed based on the maximum tangential stress (MTS) criterion proposed earlier for investigating mixed mode brittle fracture in sharp cracks. Using the RV-MTS criterion, a set of fracture curves is presented based on the notch stress intensity factors (NSIFs) for predicting mixed mode and also pure mode II fracture toughness of rounded-tip V-notches. The criterion is also able to predict fracture initiation angles under mixed mode loading. The validity of the criterion is evaluated by several fracture tests performed on the rounded-tip V-notched Brazilian disc (RV-BD) specimens made of PMMA. A good agreement is shown to exist between the theoretical predictions and the experimental results for various notch opening angles and different notch radii. © 2010 Elsevier Ltd.


Shabestari S.G.,Iran University of Science and Technology | Ghanbari M.,Iran University of Science and Technology
Journal of Alloys and Compounds | Year: 2010

The effects of plastic deformation and semisolid forming on the iron and manganese-rich intermetallics in Al-8Si-3Cu-4Fe-2Mn alloys were investigated. High volume fraction of α-Al 15(Fe,Mn) 3Si 2 intermetallics were precipitated during melting and solidification of this alloy. The as-cast specimens were deformed plastically in rolling process to achieve 5-15% plastic deformation. Plastic deformation caused fragmentation of brittle intermetallics in Al-Si matrix because of their low formability and also produced α-Al spheroids after reheating in semisolid temperature due to recrystallization and partial melting (RAP) process. Microstructural investigations revealed that appropriate semisolid structure with α-Al sphericity of 93% and grain size of 64 μm was obtained after 10-15% plastic deformation of the samples and holding them in 580 °C for 15 min. Thixoforming process was performed in 580 °C up to 30% deformation on the prepared semisolid feedstocks, which caused re-distribution of the intermetallic particles in the final near net shape part. The mean equivalent diameter of iron-manganese bearing intermetallics decreased from 26-43 μm in the as-cast condition to 9-11 μm in the thixoformed samples. The aspect ratio also decreased from 1.7 in the as-cast condition to 1.2 in the thixoformed samples. Reduction of the mean diameter and aspect ratio of intermetallics and their good distribution after thixoforming process will improve tensile strength and formability of the alloy. © 2010 Elsevier B.V. All rights reserved.


Banijamali A.,Iran University of Science and Technology | Fazlpour B.,Iran University of Science and Technology
Astrophysics and Space Science | Year: 2012

Teleparallel gravity is an equivalent formulation of general relativity in which instead of the Ricci scalar R, one uses the torsion scalar T for the Lagrangian density. Recently teleparallel dark energy has been proposed by Geng et al. (in Phys. Lett. B 704, 384, 2011). They have added quintessence scalar field, allowing also a non-minimal coupling with gravity in the Lagrangian of teleparallel gravity and found that such a non-minimally coupled quintessence theory has a richer structure than the same one in the frame work of general relativity. In the present work we are interested in tachyonic teleparallel dark energy in which scalar field is responsible for dark energy in the frame work of torsion gravity. We find that such a non-minimally coupled tachyon gravity can realize the crossing of the phantom divide line for the effective equation of state. Using the numerical calculations we display such a behavior of the model explicitly. © 2012 Springer Science+Business Media B.V.


Talebitooti M.,Iran University of Science and Technology
Archive of Applied Mechanics | Year: 2013

This paper focuses on the free vibration analysis of thick, rotating laminated composite conical shells with different boundary conditions based on the three-dimensional theory, using the layerwise differential quadrature method (LW-DQM). The equations of motion are derived applying the Hamilton's principle. In order to accurately account for the thickness effects, the layerwise theory is used to discretize the equations of motion and the related boundary conditions through the thickness of the shells. Then, the equations of motion as well as the boundary condition equations are transformed into a set of algebraic equation applying the DQM in the meridional direction. This study demonstrates the applicability, accuracy, stability and the fast rate of convergence of the present method, for free vibration analyses of rotating thick laminated conical shells. The presented results are compared with those of other shell theories obtained using conventional methods and a special case where the angle of the conical shell approaches zero, that is, a cylindrical shell and excellent agreements are achieved. © 2012 Springer-Verlag Berlin Heidelberg.


Sanaye S.,Iran University of Science and Technology | Shirazi A.,Iran University of Science and Technology
International Journal of Refrigeration | Year: 2013

One method to reduce the peak electrical demand of air-conditioning (A/C) systems is incorporating an ice thermal energy storage (ITES) with the A/C system. In this paper, an ITES system was modeled for A/C applications and analyzed from energy, exergy, economic, and environmental aspects (4E analysis). Applying the genetic algorithm optimization technique, multi-objective optimization of the system was performed and the optimum values of system design parameters were obtained. The exergy efficiency and total cost rate were considered as objective functions. The performance of modeled ITES system was also compared with a conventional system. The results indicated that electricity consumption in ITES system was 10.9% lower than that of the conventional one. Furthermore, 0.659 × 106 kg of CO2 was prevented from emitting into the atmosphere in comparison with the conventional system. The extra capital cost associated with using ITES system was paid back with savings in electricity consumption in 3.39 years. © 2012 Elsevier Ltd and IIR. All rights reserved.


Bagheri A.,University of Pittsburgh | Amini F.,Iran University of Science and Technology
Structural Control and Health Monitoring | Year: 2013

A new methodology for optimal control of structures under uniform hazard earthquake excitation has been presented in this study. The proposed method for generation of uniform hazard earthquake accelerograms is based on the sets of ground motions developed for the SAC Steel Project. The proposed controller employs the decomposing capabilities of wavelet analysis on uniform hazard earthquake accelerograms and the ability of the pattern search method to optimize a cost function to control response of structure. The performance and effectiveness of the presented method are applied to both single degree of freedom and multiple degree of freedom systems for the response control of uniform hazard earthquake-excited systems. The results are compared with the linear quadratic regulator control algorithm; performance of the proposed control system has been found to be better than the linear quadratic regulator controller. Copyright © 2012 John Wiley & Sons, Ltd.


Ziaeinejad S.,Iran University of Science and Technology | Sangsefidi Y.,Iran University of Science and Technology | Pairodin Nabi H.,Iran University of Science and Technology | Shoulaie A.,Iran University of Science and Technology
IEEE Transactions on Power Electronics | Year: 2013

In this paper, the direct torque control (DTC) of symmetrical two-phase induction and synchronous motors using different structures of two-phase inverters including two-, three-, and four-leg inverters is studied. Essential equations for controlling both electromagnetic torque and the stator flux modulus are presented and switching tables are derived. Different inverter topologies are compared in terms of the control system operation in high-speed applications and maximum speed of the rotating field deliverable by the drive system. The performance of the DTC of two-phase induction and synchronous motors fed by different inverter topologies is evaluated and the correctness of presented theories is validated by experimental results. © 2012 IEEE.


Dashti R.,Iran University of Science and Technology | Yousefi S.,Tarbiat Modares University
Reliability Engineering and System Safety | Year: 2013

Asset management (AM) is composed of distribution system activities that lead to realize the system administration targets based on the stakeholders' benefits and correspondingly satisfying them. In this paper, asset management structure is represented and employing the AM structure, asset management processes are proposed. Furthermore, corresponding revisory actions are represented based on distribution asset wastages in order to structure a novel reliability based asset assessment model. The proposed model has been applied in a real distribution company, which provides 1 million customers with their requisite electrical energy. Crown Copyright © 2012 Publishedby Elsevier Ltd.All rights reserved.


Aliha M.R.M.,Iran University of Science and Technology | Ayatollahi M.R.,Iran University of Science and Technology
Theoretical and Applied Fracture Mechanics | Year: 2014

Fracture toughness of a white marble is studied experimentally using several cracked chevron notched Brazilian disc (CCNBD) specimens under pure mode I and pure mode II loading. Even in the presence of natural scatters in the test data, it was observed that the average mode II fracture toughness KIIc was considerably larger than that of mode I fracture toughness KIc such that the mean fracture toughness ratio (KIIc/KIc) was about 2. Using the generalized maximum tangential stress theory, the obtained mode II test results were estimated in terms of mode I fracture toughness data. The enhanced KIIc value in the CCNBD specimen could be related to the influence of very large negative T-stress value that exists in the mode II CCNBD specimens. The statistical analyses of test data were performed successfully to predict the Weibull parameters of mode II results in terms of mode I Weibull parameters. © 2013 Elsevier Ltd.


Shabannia R.,Iran University of Science and Technology
Journal of Materials Science: Materials in Electronics | Year: 2016

ZnO thin films were successfully produced on porous silicon (PS) substrates by a chemical bath deposition method. ZnO thin films were then annealed at 300, 500, and 700 °C for 20 min in nitrogen (N2) atmosphere. X-ray diffraction, field emission scanning electron microscopy (FESEM), and photoluminescence (PL) were utilized to investigate the effect of post-annealing temperature on the structural, optical, and electrical properties of ZnO thin films. The lattice constant, full width at half maximum, and strain (the grain size) of (0 0 2) peak of ZnO thin films decreased (increased) with increasing the annealing temperature, respectively. The FESEM images revealed that the ZnO thin films are compact array ZnO nanocolumns and were perpendicularly grown to the PS substrate. The biggest ratio of the PL intensity of UV emission to that of visible emission is observed from ZnO thin films annealed at 500 °C. The PL results of the ZnO thin films exhibit that the UV peak positions shift slightly toward lower wavelengths with increase of the annealing temperature. The current–voltage measurements demonstrate that the current level increases as the annealing temperature increases to 500 °C, and then decreases when the temperature further increases up to 700 °C. © 2016 Springer Science+Business Media New York


Rahimi R.,Iran University of Science and Technology | Kerdari H.,Islamic Azad University at Sāveh | Rabbani M.,Iran University of Science and Technology | Shafiee M.,Damghan University
Desalination | Year: 2011

Hollow zinc ferrite nanosphere was synthesized by a facile solvothermal method using ultrasonic waves. The prepared nanoparticles were employed for the removal of Congo Red (CR) in the wastewater treatment. X-ray diffraction (XRD) pattern of the ferrite sample is well in agreement with the standard pattern of the cubic structure. Scanning electron microscopy (SEM) image reveals that the resultant ferrite is nanoporous structurally and the average sizes of spheres and holes diameter were measured at 127.3 and 20.94nm, respectively. Structure of samples before and after wastewater treatment was investigated by FT-IR spectra. The magnetic properties of the hollow nanospheres were characterized on a vibrant sample magnetometer (VSM) with maximum saturation magnetization value of 76.2emu/g. UV-visible absorption spectroscopy was used to record the adsorption behavior. The maximum adsorption capacity of magnetic hollow nanospheres (0.02g) for CR in the concentration range (1-50mg L -1) studied, as calculated from the Langmuir isotherm model at 25°C and pH 6, was found to be 16.58mg g -1. © 2011 Elsevier B.V.


Torabi A.R.,University of Tehran | Ayatollahi M.R.,Iran University of Science and Technology
European Journal of Mechanics, A/Solids | Year: 2014

The aim of this research was to present a brittle fracture model for predicting the compressive failure load of engineering components weakened by V-notches with end holes (VO-notches). For this purpose, two well-known brittle fracture models in tension, namely the point stress (PS) and the mean stress (MS) were applied to the compressive stress field around the VO-notches and for each model a closed-form expression was obtained for the compressive mode I notch fracture toughness. In order to evaluate the validity of PS and MS criteria, the theoretical values of compressive notch fracture toughness were compared with the experimental results reported recently in literature dealing with fracture in fine-grained isostatic graphite plates containing V-notches with end holes subjected to pure compression. The results showed that while the MS model with a total discrepancy of 5% was an appropriate failure criterion, the PS model with about 86% accuracy could not predict the experimental results satisfactorily.©2013 Elsevier Masson SAS. All rights reserved.


Ayatollahi M.R.,Iran University of Science and Technology | Shadlou S.,Iran University of Science and Technology | Shokrieh M.M.,Iran University of Science and Technology
Engineering Fracture Mechanics | Year: 2011

The effects of multi-walled carbon nanotubes (MWNTs) on fracture behavior of epoxy under mixed mode I/II loading have been studied. A number of test specimens based on different contents of MWNTs were prepared and the fracture tests were carried out. The increase in fracture resistance of the nanocomposite depended on the mode mixity. To find the reason, the fracture mechanisms in different modes of fracture were studied by examination of the fracture surfaces. It was found that in addition to the mechanisms, which contribute in mode I fracture, some extra mechanisms participate in mixed mode and mode II loading. © 2011 Elsevier Ltd.


Ayatollahi M.R.,Iran University of Science and Technology | Mirsayar M.M.,Iran University of Science and Technology | Dehghany M.,Iran University of Science and Technology
Materials and Design | Year: 2011

The experimental technique of photoelasticity has been utilized for calculating bi-material notch stress intensities as well as the coefficients of higher order terms. Employing the equations of multi-parameter stress field allows data collection from a larger zone from the notch tip and makes the data collection from experiments more convenient. Moreover, the effects of higher order terms in the region near the notch tip are taken into account. For the photoelasticity experiments, a laboratory specimen known as the Brazilian disk with a central notch, consisting of Aluminum and Polycarbonate, has been utilized. Using this specimen, different mode mixities could be easily produced by changing the loading angle. The bi-material notch stress intensities and the first non-singular stress term (called I-stress) were then calculated for different test configurations. In order to utilize the advantages of whole-field photoelasticity and minimize the experimental errors, a large number of data points were substituted in the multi-parameter stress field equations. Then the resulting system of nonlinear equations was solved by employing an over-deterministic least squares method coupled with the Newton-Raphson algorithm. It has been shown that considering the I-stress term improves, to a large extent, the accuracy of the stress intensities calculated through the photoelasticity technique. Moreover, by reconstructing the isochromatic fringes, the effects of the I-stress term on the shape and size of these fringes around the notch tip were investigated for a 30° notch. Finally, the experimental photoelasticity results were compared with the corresponding values obtained from finite element analysis and a good correlation was observed. © 2011 Elsevier Ltd.


Kaveh A.,Iran University of Science and Technology | Farhoudi N.,K. N. Toosi University of Technology
Journal of Constructional Steel Research | Year: 2011

Meta-heuristic optimization algorithms have attracted many researchers in the last decade. Adjustment of different parameters of these algorithms is usually a time consuming task which is mostly done by a trial and error approach. In this study an index, namely convergence factor (CF), is introduced that can show the performance of these algorithms. CF of an algorithm provides an estimate of the suitability of the parameters being set and can also enforce the algorithm to adjust its parameters automatically according to a pre-defined CF. In this study GA, ACO, PSO and BB-BC algorithms are used for layout (topology plus sizing) optimization of steel braced frames. Numerical examples show these algorithms have some similarities in common that should be taken into account in solving optimization problems. © 2011 Elsevier Ltd. All rights reserved.


Ayatollahi M.R.,Iran University of Science and Technology | Aliha M.R.M.,Iran University of Science and Technology
Fatigue and Fracture of Engineering Materials and Structures | Year: 2011

The edge-cracked beam specimen subjected to anti-symmetric four-point bend (ASFPB) loading has been conventionally used in the past for investigating the pure mode II fracture experiments in many engineering materials. However, it is shown through finite element analysis that the ASFPB specimen sometimes fails to produce pure mode II conditions. For anti-symmetric loads applied close to the crack line, there are considerable effects from KI and T-stress in the ASFPB specimen. Pure mode II is provided only when the applied loads are sufficiently far from the crack plane. © 2011 Blackwell Publishing Ltd.


Farhadi S.,University of Kurdistan | Hosseini-Hashemi S.H.,Iran University of Science and Technology
JVC/Journal of Vibration and Control | Year: 2011

In the present work, active vibration suppression of moderately thick rectangular plates by means of piezoelectric actuators is investigated. Based on Lagrange energy method, a finite element formulation is presented for mathematical modeling of the system. Using modal controllability criterion, a simple method is offered for optimal placement of the piezoelectric actuator. For a cantilevered plate with specific characteristics, the optimal position of a piezoelectric patch is investigated. Then, for suppression of plate vibrations, an active damping controller is designed using modal velocity feedbacks. Numerical simulations are then performed for studying the performance of the designed controller. Presented simulations indicate the feasibility of vibration control of moderately thick plates by means of high voltage piezoelectric actuators. These simulations also show that, for a specific excitation force, the maximum required voltage for vibration suppression approaches to an asymptotic value as the values of modal feedback gains increase. This conclusion is of high importance in practical controller design. © The Author(s) 2011 Reprints and permissions.


Ayatollahi M.R.,Iran University of Science and Technology | Shadlou S.,Iran University of Science and Technology | Shokrieh M.M.,Iran University of Science and Technology
Composite Structures | Year: 2011

Multiscale modeling was presented for the nonlinear properties of polymer/single wall carbon nanotube (SWNT) nanocomposite under tensile, bending and torsional loading conditions. To predict the mechanical properties of both armchair and zigzag SWNTs, a finite element (FE) model based on the theory of molecular mechanics was used. For reducing the computational efforts, an equivalent cylindrical beam element was proposed, which has the unique advantage of describing the mechanical properties of SWNTs considering the nonlinearity of SWNT behavior. For a direct evaluation of the rigidities of the proposed equivalent beam, the data obtained through atomistic FE analyses of SWNT were fitted to six different equations, covering the three types of loading for both armchair and zigzag configurations. The proposed equivalent beam element was then used to build a cylindrical representative volume element (RVE) using which the effects of the interphase between SWNT and the polymer on the mechanical properties of RVE could be studied. It was found that while the interphase has a small effect on the nanocomposite stiffness, the ratio of (SWNT length)/(RVE length) dramatically affects the nanocomposite stiffness. © 2011 Elsevier Ltd.


Ayatollahi M.R.,Iran University of Science and Technology | Shadlou S.,Iran University of Science and Technology | Shokrieh M.M.,Iran University of Science and Technology
Materials and Design | Year: 2011

The effects of multi-walled carbon nanotubes (MWCNTs) on the mechanical properties of epoxy/MWCNT nano-composites were studied with emphasis on fracture toughness under bending and shear loading conditions. Several finite element (FE) analyses were performed to determine appropriate shear loading boundary conditions for a single-edge notch bend specimen (SENB) and an equation was derived for calculating the shear loading fracture toughness from the fracture load. It was seen that the increase in fracture toughness of nano-composite depends on the type of loading. That is to say, the presence of MWCNTs had a greater effect on fracture toughness of nano-composites under shear loading compared with normal loading. To study the fracture mechanisms, several scanning electron microscopy (SEM) pictures were taken from the fracture surfaces. A correlation was found between the characteristics of fracture surface and the mechanical behaviors observed in the fracture tests. © 2010 Elsevier Ltd.


Commercial centers are considered very important areas. Considering the huge volume of manpower and economic value of goods in these centers, this domain will assume higher importance. Possible accidents, such as fires in commercial centers can be occasion human, social, and economic catastrophic consequences. This study was an attempt to assess the safety level of Tehran's commercial centers and provide control measures to prevent possible accidents. To this end, the current state of Tehran's commercial is analyzed and available resources are identified. Then, safety indexes are extracted, some checklists are prepared, and the resources are accordingly assessed. For this purpose, the number of 48 commercial centers was selected. The results obtained from the assessment of resources indicate that the greatest gap belongs to the protection system against fire and buildings, respectively. This study proposes five alternatives for improving the safety of commercial centers, as follows: (a) implementing audit and evaluation system, (b) establishing reliability management system for fire fighting equipment, (c) monitoring and analyzing accidents and preparing GIS maps, (d) implementing 5S system in workplace and (e) establishing a reliability management system for safety trainings. Based on the results of this study, managers and other decision-makers in the area of urban planning and commercial centers can identify weak points in the system, improve their safety level, and, thereby, be effective in reducing the social and economic consequences of accidents. © 2016 Elsevier Ltd


Gheshlaghi B.,Islamic Azad University at Damavand | Hasheminejad S.M.,Iran University of Science and Technology
Applied Physics Letters | Year: 2012

The Timoshenko [S. S. Rao, Vibration of Continuous Systems (Wiley, New York, 2007)] beam model is used to derive the differential equations governing the free vibrations of thick nanowires (NWs) with dissipative surface stress effects. The natural frequencies are calculated as functions of NW length as well as thickness-to-length ratio, with the effects of dissipation, transverse shear deformation, and rotary inertia being included. The effects of latter two parameters are significant especially for higher modes of vibration and shorter NWs and are different from what is naively expected based on elementary mechanics for some specific dimensions. The results are also compared with the previous study using Euler-Bernoulli beam theory. © 2012 American Institute of Physics.


Nemati Hayati A.,Iran University of Science and Technology | Rezaie H.R.,Iran University of Science and Technology | Hosseinalipour S.M.,Iran University of Science and Technology
Materials Letters | Year: 2011

Poly(3-hydroxybutyrate)/nano-hydroxyapatite (PHB/nHA) composite scaffolds were fabricated via powder mixing, compression moulding, and particle leaching technique. The scaffolds had high porosity with interconnected porous architecture, a favorable structure for cell attachment and new bone tissue ingrowth. A homogeneous dispersion and a uniform distribution of HA nanoparticles in the polymer matrix were obtained. The scaffolds exhibited improved compressive modulus and compressive strength, which were all in the range of compressive modulus and compressive strength of cancellous bone. In addition, the use of toxic organic solvents was eliminated. Thus, the fabricated PHB/nHA composite scaffolds tend to be promising for application in bone tissue engineering. © 2010 Elsevier B.V.


Ayatollahi M.R.,Iran University of Science and Technology | Nejati M.,Iran University of Science and Technology
International Journal of Mechanical Sciences | Year: 2011

An overdeterministic method was used for calculating the Notch Stress Intensity Factors (NSIFs) as well as the coefficients of the higher order terms for structures containing sharp notches. The series solution of displacement fields around the notch tip was fitted to a large number of nodal displacements obtained from finite element analysis. An over-determined set of simultaneous linear equations was then derived and the nodal displacements reduced to a small set of unknown coefficients by employing the concept of the least-squares method. The efficiency of the proposed method was assessed through analyzing several notched specimens under pure mode I, pure mode II and mixed modes I/II loading. The accuracy of the NSIFs and the coefficients of higher order terms was evaluated by comparing them with the results available in the literature, or the results obtained by the boundary collocation method. While the presented method is simple, it yields very good results. © 2010 Elsevier Ltd. All rights reserved.


Assadi A.,Iran University of Science and Technology | Farshi B.,Iran University of Science and Technology
Physica E: Low-Dimensional Systems and Nanostructures | Year: 2011

In this article, explicit solution is presented for size and geometry dependent free vibration of curved nanostructures with consideration of surface properties. Additional surface elasticity, surface residual stress and also surface mass density are included in the study to generalize the existing classical theories. Considering the general presentation of the problem and regardless of the boundary conditions, the deviations of actual dynamic characteristics from classical theories for various geometries are found as new results. The modified natural frequencies of the structure are thus obtained and presented as normalized with respect to their corresponding conventional values. © 2010 Elsevier B.V. All rights reserved.


Rezaei F.,Iran University of Science and Technology | Javad Azhari S.,Iran University of Science and Technology
Microelectronics Journal | Year: 2011

This paper presents an ultra low voltage, high performance Operational Transconductance Amplifier (OTA) and its application to implement a tunable Gm-C filter. The proposed OTA uses a 0.5 V single supply and consumes 60 μw. Employing special CMFF and CMFB circuits has improved CMRR to 138 dB in DC. Using bulk driven input stage results in higher linearity such that by applying a 500 mvpp sine wave input signal at 2 MHz frequency in unity gain closed loop configuration, third harmonic distortion for output voltage is -46 dB and becomes -42.4 dB in open loop state for 820 mvpp output voltage at 2 MHz. DC gain of the OTA is 47 dB and its unity gain bandwidth is 17.8 MHz with 20 pF capacitance load due to both deliberately optimized design and special frequency compensation technique. The OTA has been used to realize a wide tunable Gm-C low-pass filter whose cutoff frequency is tunable from 1.4 to 6 MHz. Proposed OTA and filter have been simulated in 0.18 μm TSMC CMOS technology with Hspice. Monte Carlo and temperature dependent simulation results are included to forecast the mismatch and temperature effects after fabrication process. © 2011 Elsevier Ltd. All rights reserved.


Ayatollahi M.R.,Iran University of Science and Technology | Dehghany M.,Iran University of Science and Technology | Nejati M.,Iran University of Science and Technology
International Journal of Solids and Structures | Year: 2011

The effect of the first non-singular stress term on the fracture behavior of notched structures was investigated under symmetric geometry and loading conditions. According to the Williams series expansion, for a large domain of notch angles the non-singular stress terms of sharp notches are functions of complex eigenvalues and their corresponding complex coefficients. Hence, a new representation of stress field near the notch tip was developed in which the higher order terms are expressed as several explicit functions of real and imaginary parts of both the complex eigenvalues and their complex coefficients. A critical stress criterion was then applied to the new stress formulations to assess the influence of the first non-singular stress term on the apparent fracture toughness. Several finite element analyses were also performed on two laboratory specimens in order to show the effects of first non-singular term on the near field stress distribution of notched specimens. The results demonstrated that neglecting the first non-singular stress term could lead to significant errors in predicting the apparent fracture toughness of notched components. © 2011 Elsevier Ltd. All rights reserved.


Farhadi S.,University of Kurdistan | Hosseini-Hashemi S.H.,Iran University of Science and Technology
International Journal of Mechanical Sciences | Year: 2011

Aeroelastic behavior of a supersonic rotating rectangular plate in the air medium is studied. For simulating the plate structure, the Mindlin first-order shear deformation plate theory along with Von Karman nonlinear terms is employed. Air dynamic pressure is modeled using first-order piston theory. The plate is placed inside a rigid baffle to remove shock waves generated by plate rotation and provide a uniform flow passing over the plate. Nonlinear dimensionless generalized equations of motion are presented based on the Kane dynamic method. After linearization of the nonlinear equations of motion, effect of different parameters including plate aspect ratio, thickness ratio, hub radius ratio and dimensionless rotation speed on aeroelastic behavior of the system are investigated. Frequency locking and high frequency flutter phenomenon are observed in the numerical results. © 2011 Elsevier Ltd. All rights reserved.


Sargolzaei M.,Iran University of Science and Technology | Sargolzaei M.,Institute for Research in Fundamental Sciences | Lotfizadeh N.,Iran University of Science and Technology
Physical Review B - Condensed Matter and Materials Physics | Year: 2011

We have demonstrated the electronic structures and magnetic properties of single 3d transition metal (TM) atoms encapsulated in noble metal clusters with icosahedral symmetry in the framework of relativistic density functional theory. Orbital polarization corrections have been used to obtain an upper-estimation for orbital magnetic moments of all individual 3d atoms. The relativistic corrections are marginally affected the spin magnetic moments, whereas they induce significant orbital magnetism in TM@X12 icosahedra. It is found that a superatomic picture has to be taken into account in order to explain the spin and orbital magnetism induced in TM@X12 icosahedron based on the Hund's rules. © 2011 American Physical Society.


Assadi A.,Iran University of Science and Technology | Farshi B.,Iran University of Science and Technology
Physica E: Low-Dimensional Systems and Nanostructures | Year: 2011

In this article, analytical framework is developed for size dependent symmetric stability and self-instability of circular nanoplates including surface effects using modified Kirchhoff plate theory. The surrounding elastic medium is modeled as Winkler elastic foundation and its effect is comprehensively studied on self-instability problems. The derived explicit solutions contain Bessel functions with modified arguments reflecting the size dependency of the buckling loads. In order to check the results an inverse formulation is presented for effective Youngs modulus using the buckling loads to be verified by previous experimental results for nanowires. Several numerical examples are given for two types of materials with positive and negative surface properties to show the general trends of size dependencies. Some problems and limitations are explored for consistency of results with experiments and suggestions for future works. © 2011 Elsevier B.V. All rights reserved.


Tadjarodi A.,Iran University of Science and Technology | Imani M.,Iran University of Science and Technology
Materials Letters | Year: 2011

Cadmium oxide nanostructure was synthesized by calcining the obtained precursor of a mechanochemical reaction. The milling was carried out with cadmium nitrate tetrahydrate and acetamide reactants without any additives at room temperature. Resulting precursor was calcined at 450 °C for 2 h in a furnace. As a result of heating, the organic section of precursor was removed and cadmium oxide nanostructure was produced. The obtained compound from the mechanical milling (MM) technique possesses a cubic crystalline structure at nanoscale. XRD studies indicate that the obtained CdO has a cubic phase. Also, SEM and TEM images showed that the resulting material is composed of nanoparticles with the average diameter of 41 nm. The average size and standard deviation were calculated using a Microstructure Measurement program and a Minitab statistical software. © 2011 Elsevier B.V. All rights reserved.


Ghanbari B.,Iran University of Science and Technology
The Scientific World Journal | Year: 2014

We aim to study the convergence of the homotopy analysis method (HAM in short) for solving special nonlinear Volterra-Fredholm integrodifferential equations. The sufficient condition for the convergence of the method is briefly addressed. Some illustrative examples are also presented to demonstrate the validity and applicability of the technique. Comparison of the obtained results HAM with exact solution shows that the method is reliable and capable of providing analytic treatment for solving such equations. © 2014 Behzad Ghanbari.


Hosseini-Hashemi S.,Iran University of Science and Technology | Fadaee M.,Iran University of Science and Technology | Atashipour S.R.,Iran University of Science and Technology
International Journal of Mechanical Sciences | Year: 2011

An exact closed-form procedure is presented for free vibration analysis of moderately thick rectangular plates having two opposite edges simply supported (i.e. Lvy-type rectangular plates) based on the ReissnerMindlin plate theory. The material properties change continuously through the thickness of the plate, which can vary according to a power law distribution of the volume fraction of the constituents. By introducing some new potential and auxiliary functions, the displacement fields are analytically obtained for this plate configuration. Several comparison studies with analytical and numerical techniques reported in literature are carried out to establish the high accuracy and reliability of the solutions. Comprehensive benchmark results for natural frequencies of the functionally graded (FG) rectangular plates with six different combinations of boundary conditions (i.e. SSSSSSSCSCSCSCSFSSSFSFSF) are tabulated in dimensionless form for various values of aspect ratios, thickness to length ratios and the power law index. Due to the inherent features of the present exact closed-form solution, the present results will be a useful benchmark for evaluating the accuracy of other analytical and numerical methods, which will be developed by researchers in the future. © 2010 Elsevier Ltd. All rights reserved.


Hashemi S.H.,Iran University of Science and Technology | Samaei A.T.,Iran University of Science and Technology
Physica E: Low-Dimensional Systems and Nanostructures | Year: 2011

The present study proposes an analytical solution for the buckling analysis of rectangular nanoplates. In order to extract characteristic equations of the micro/nanoscale plate under in-plane load, the analysis procedure is based on the nonlocal Mindlin plate theory considering the small scale effects. The nonlocal Mindlin plate theory allows for small scale effects. The results show that buckling loads of biaxially compressed micro/nanoscale plate depend on the nonlocal parameter. In addition, the effects of small length scale on buckling loads are graphically presented for different geometrical parameters such as aspect ratios and loading factors. This study might be useful for the design of nanoelectronic devices such as atomic dust detectors and biological sensors. © 2011 Elsevier B.V. All rights reserved.


Ayatollahi M.R.,Iran University of Science and Technology | Torabi A.R.,University of Tehran
Materials Science and Engineering A | Year: 2011

The fracture load and the fracture initiation angle were experimentally measured for a V-notched specimen made of polycrystalline graphite under combined tensile-shear loading. The experimental results were obtained for several specimens with different notch angles and various notch tip radii. The experimental observations showed that for a constant notch tip radius, the fracture load in pure tensile loading conditions decreases as the notch angle increases. Moreover, for a constant notch angle, as the notch tip radius increases the fracture load in graphite specimens enhances in the entire domain between pure tensile and pure shear loading conditions. A recently developed failure criterion was then used to estimate the experimental values of the notch fracture resistance and the fracture initiation angle for the tested graphite specimens. The experimental results could be estimated very well by using the results of the proposed criterion. © 2011 Elsevier B.V.


Safkhani M.,Iran University of Science and Technology | Bagheri N.,Shahid Rajaee Teacher Training University | Naderi M.,Iran University of Science and Technology
International Journal of Medical Informatics | Year: 2014

Objective: In this paper we investigate the security level of a comprehensive RFID solution to enhance inpatient medication safety [2], named IS-RFID, which has been recently proposed by Peris-Lopez et al. Method: We analyses the security of the protocol against the known attacks in the context. The main target of this paper is to determine whether the new protocol provides the confidentiality property, which is expected to be provided by such a protocol. Results: It was found that IS-RFID has critical weaknesses. The presented security investigations show that a passive adversary can retrieve secret parameters of patient's tag in cost of O(216) off-line PRNG evaluations. Given the tag's secret parameters, any security claims are ruined. Conclusions: In this paper we presented an efficient passive secret disclosure attack which retrieves the main secret parameters related to the patient which shows that IS-RFID may put the patient safety on risk. The proposed attacking technique is in light of two vulnerabilities of the protocol: (1) the short length of the used PRNG, which is urged by the target technology, EPC C1 Gen2. [6]; (2) the message-generating mechanism utilizing PRNG was not carefully scrutinized. While the later point can be fixed by careful designing of the transferred messages between the protocol's party, the earlier point, i.e., the short length of the available PRNG for EPC C1 Gen2 tags, is a limitation which is forced by the technology. In addition, over the last years, schemes based solely on using simple operations or short PRNG (such as IS-RFID) have been shown to offer very low or no security at all. Recent advances in lightweight ciphers, such as PRESENT. [1] or Grain. [3], seem a much more appropriate solution rather than relying on short PRNGs. However, such solutions breaks the EPC C1 Gen2 compatibility. © 2013 Elsevier Ireland Ltd.


Etemad-Shahidi A.,Iran University of Science and Technology | Bali M.,Iran University of Science and Technology
Coastal Engineering | Year: 2012

The prediction of rubble mound breakwaters' stability is one of the most important issues in coastal and maritime engineering. The stability of breakwaters strongly depends on the wave height. Therefore, selection of an appropriate wave height parameter is very vital in the prediction of stability number. In this study, H50, the average of the 50 highest waves that reach the breakwater in its useful life, was used to predict the stability of the armor layer. First, H50 was used instead of the significant wave height in the most recent stability formulas. It was found that this modification yields more accurate results. Then, for further improvement of the results, two formulas were developed using model tree.To develop the new formulas, two experimental data sets of irregular waves were used. Results indicated that the proposed formulas are more accurate than the previous ones for the prediction of the stability parameter. Finally, the proposed formulas were applied to regular waves and a wide range of damage levels and it was seen that the developed formulas are applicable in these cases as well. © 2011 Elsevier B.V.


Daliri M.R.,Iran University of Science and Technology
Biomedical Signal Processing and Control | Year: 2013

In this paper, a new approach for the diagnosis of the subjects with Parkinson's disease (PD) from the healthy control subjects is proposed. This method uses the measurements of gait signals using the ground reaction forces under usual walking of the subjects. These measurements were computed using 8 sensors placed underneath of each foot. The absolute value of the difference between the force measurements were calculated for each sensor at each time and these signals went through a short-time Fourier transform (STFT) and several features were extracted from the spectrum of the signals. The histogram of these features was computed and the bin selection was performed using the feature discriminant ratio (FDR) method. Then the chi-square distance between the reduced histograms was computed and it formed a kernel for support vector machines (SVMs) for classification. The results on 93 subjects with PD and 73 healthy control subjects show that the proposed approach obtains an accuracy of 91.20% for the diagnosis of the PD using gait signals. © 2012 Elsevier Ltd.


Samaei A.T.,Iran University of Science and Technology | Abbasion S.,Empa - Swiss Federal Laboratories for Materials Science and Technology | Mirsayar M.M.,Iran University of Science and Technology
Mechanics Research Communications | Year: 2011

The effect of length scale on buckling behavior of a single-layer graphene sheet embedded in a Pasternak elastic medium is investigated using a nonlocal Mindlin plate theory. An explicit solution is extracted for the buckling loads of graphene sheet and the influence of the nonlocal parameter and aspect ratio on dimensionless buckling loads is presented. It is found that the nonlocal assumptions exhibit larger buckling loads and stiffness of elastic medium in comparison to classical plate theory. © 2011 Elsevier Ltd. All rights reserved.


Sedighy S.H.,Iran University of Science and Technology | Khalaj-Amirhosseini M.,Iran University of Science and Technology
Journal of Electromagnetic Waves and Applications | Year: 2011

In this paper, a new idea is proposed in order to modify the conventional Wilkinson power dividers for size reduction. The proposed structures contain Step Impedance Transmission Lines (SITLs) instead of the uniform ones, with reduced length at the design frequency. The impedance ratio of SITLs is considered variable and written as the total electrical length of the lines. With this additional design parameter and a higher degree of design freedom, the size of the dividers is reduced. One Wilkinson divider is designed and fabricated for operation at 1.00 GHz. The proposed Wilkinson power divider has a size reduction more than 55%. The measured results of the fabricated power dividers are in good agreement with the theoretical ones. © 2011 VSP.


Ramezani A.,Iran University of Science and Technology
Physica E: Low-Dimensional Systems and Nanostructures | Year: 2011

In this paper, the pull-in instability of electrostatically actuated nanotweezers considering the dispersion forces is studied using distributed and lumped parameter models. By analogy to nanoswitches, closed-form solutions are obtained for electrostatic nanotweezers. The distributed and lumped parameter modeling of the tweezer result, respectively, in two coupled nonlinear boundary value problems and two coupled nonlinear equations, which are solved numerically in the cases of electrostatic microtweezers, freestanding nanotweezers, and electrostatic nanotweezers. In each case, analytical and numerical solutions are obtained and compared with those of the corresponding switch. In addition, the results of the distributed and lumped parameter models are compared. The detachment length and minimum initial gap of nanotweezers are determined. © 2011 Elsevier B.V.


Mansoorbaghaei S.,Iran University of Science and Technology | Sadegh A.M.,City University of New York
International Journal of Solids and Structures | Year: 2011

In this paper, the impact of a thin-walled elastic spherical shell with an elastic barrier is investigated. Hertzian and Reissner (membrane-bending deformation) theories were employed for the deformation equations. Due to the complexity of the equations a linearization of the equations was proposed and a closed form solution of the problem was obtained. Newtonian method is applied in order to obtain the impact force and the time duration. The closed-form solution enables one to parametrically study the impact and the related quantities. Finally the results from the analytical solution are validated by the finite element method and also are compared with the results presented in Young (2003). The comparison of the results reveals a good agreement. It is concluded that the proposed closed-form solution can be used to parametrically assess the impact of elastic spherical shells to elastic half space. © 2011 Elsevier Ltd. All rights reserved.


Anbia M.,Iran University of Science and Technology | Fard S.E.M.,Iran University of Science and Technology
Sensors and Actuators, B: Chemical | Year: 2011

La3+ and K+ co-doped nanoporous TiO2-10 mol% SnO2 thin films have been prepared by sol-gel method with Pluronic P123 as the organic template on alumina substrates, and their humidity sensing properties have been investigated. It was found that the addition of rare earth ion La3+, alkali ion K+ and tri-block copolymer Pluronic P123 is beneficial for improving the humidity sensitive properties of the samples. The sensing behaviors of thin films were inspected at different sintering temperatures by constructing a humidity-impedance measuring system. It is found that nanoporous TiO2-SnO2 doped with 0.3 mol% La3+ and 50 mol% K+ sintered at 500 °C for 4 h shows the best humidity sensing properties. This thin film achieves a high sensitivity with the impedance changed five orders of magnitude from 109 Ω to 104 Ω with excellent linearity in the relative humidity (RH) range of 11-95% at 25 °C. The response and recovery time of this thin film are about 11 and 18 s, respectively. High sensitivity, narrow hysteresis loop, rapid response and recovery, prominent stability and good reproducibility are obtained. The effects of dopant content on humidity sensitivity have also been discussed in terms of segregation of rare earth ions at grain boundaries and granularity of crystals, and influence of K+ on the decrease in the intrinsic resistance of the materials and direct contribution to the conduction. © 2011 Elsevier B.V. All rights reserved.


Alavi A.H.,Iran University of Science and Technology | Ameri M.,Iran University of Science and Technology | Gandomi A.H.,Tafresh University | Mirzahosseini M.R.,Transportation Institute
Construction and Building Materials | Year: 2011

A high-precision model was derived to predict the flow number of dense asphalt mixtures using a novel hybrid method coupling genetic programming and simulated annealing, called GP/SA. The proposed constitutive model correlates the flow number of Marshall specimens with the percentages of filler, bitumen, voids in mineral aggregate, Marshall stability, and Marshall flow. The comprehensive experimental database used for the development of the model was established upon a series of uniaxial dynamic creep tests conducted in this study. Generalized regression neural network and multiple regression-based analyses were performed to benchmark the GP/SA model. The contributions of the variables affecting the flow number were evaluated through a sensitivity analysis. A subsequent parametric study was carried out and the trends of the results were confirmed with the results of the experimental study. The results indicate that the proposed GP/SA model is effectively capable of evaluating the flow number of asphalt mixtures. The derived model is remarkably straightforward and provides an analysis tool accessible to practicing engineers. © 2010 Elsevier Ltd. All rights reserved.


Ayatollahi M.R.,Iran University of Science and Technology | Nejati M.,Iran University of Science and Technology
Fatigue and Fracture of Engineering Materials and Structures | Year: 2011

An over-deterministic method has been employed for calculating the stress intensity factors (SIFs) as well as the coefficients of the higher-order terms in the Williams series expansions in cracked bodies, using the conventional finite element analysis. For a large number of nodes around the crack tip, an over-determined set of simultaneous linear equations is obtained, and using the fundamental concepts of the least-squares method, the coefficients of the Williams expansion can be calculated for pure mode I, pure mode II and mixed mode I/II conditions. A convergence study has been conducted to examine the effects of the number of nodes used, the number of terms in Williams expansion and the distance of the selected nodes from the crack tip, on the accuracy of the results. It is shown that the simple method presented in this paper, yields accurate results even for coarse finite element meshes or in the absence of singular elements. The accuracy of SIFs and the coefficients of higher-order terms are validated by using the available results in the literature. © 2010 Blackwell Publishing Ltd.


Ayatollahi M.R.,Iran University of Science and Technology | Nejati M.,Iran University of Science and Technology
Materials and Design | Year: 2011

A higher order representation of the stress field around the sharp notch has been utilized for calculating notch stress intensity factors (NSIFs) as well as the coefficients of higher order terms by the technique of photoelasticity. Adding the higher order terms to the singular term makes it possible to collect the data points from a larger zone, which helps to simplify the data collection from experiments. Moreover, the effects of higher order terms in the region near the notch tip are taken into account. To utilize the advantages of whole-field photoelasticity and minimize the experimental errors, a large number of data points have been employed and the overdeterministic least squares method combined with the Newton-Raphson method have been used to solve the resulting system of nonlinear equations. The NSIFs for a laboratory specimen called V-notched Brazilian disk (V-BD) were calculated for various notch angles under pure mode I, pure mode II and mixed mode I/II loading conditions. In addition to NSIFs, the coefficient of the first non-singular term of 30° notch was calculated experimentally and the effects of this term on the stress distribution in the vicinity of notch tip were investigated. A good correlation was observed between the experimental results and the numerical results obtained from finite element analysis. © 2010 Elsevier Ltd.


Farshi B.,Iran University of Science and Technology | Gheshmi S.,Iran University of Science and Technology | Miandoabchi E.,Iran University of Science and Technology
Materials and Design | Year: 2011

In this study warpage and shrinkage as defects in injection molding of plastic parts have been undertaken. MoldFlow software package has been used to simulate the molding experiments numerically. Plastic part used is an automotive ventiduct grid. The process optimization to minimize the above defects is carried out by sequential simplex method. Process design parameters are mold temperature, melt temperature, pressure switch-over, pack/holding pressure, packing time, and coolant inlet temperature. The output parameters aside from warpage and shrinkage consist of part weight, residual stresses, cycle time, and maximum bulk temperature. Results are correlated and interpreted with recommendations to be considered in such processes. © 2010 Elsevier Ltd.


Javidrad F.,Iran University of Science and Technology | Nouri R.,Iran University of Science and Technology
Composite Structures | Year: 2011

Designing a laminate based on its stiffness properties requires finding the optimum lamination stacking sequence to yield the required stiffness properties. The design variables to be considered are the number of layers and orientation angle of fibers in each layer group, which are treated as discrete-variables. The optimum lamination is then obtained by minimizing a cost function composed of the relative difference between the calculated effective stiffness properties and weight of trial laminate and the desired properties. This error minimization problem was solved using a modified simulated annealing heuristic method. The new simulated annealing implementation comprises a cooling procedure in which the temperature decrease relied adaptively on the objective function evolution. It is shown that the proposed method can give rise to an improvement in convergence speed. To achieve a further improvement in the performance of the method, simulated annealing parallelization implemented using the proposed cooling process. The main features of this algorithm are described and its encouraging results are presented. © 2010 Elsevier Ltd.


Ayatollahi M.R.,Iran University of Science and Technology | Aliha M.R.M.,Iran University of Science and Technology
Journal of the American Ceramic Society | Year: 2011

Mixed mode fracture resistance was analyzed for some previously tested ceramics using a three-parameter fracture criterion called the generalized maximum tangential stress (GMTS) criterion. For using this fracture criterion, the size of a critical distance from the crack tip was required. Therefore, an analytical model was suggested for determining the size of critical distance in terms of mode I fracture toughness and the tensile strength of ceramics. For some ceramics with reported grain size, the size of critical distance was found to be approximately 100 times the average grain size. The experimental results obtained from the cracked Brazilian disk specimen and reported in the literature for sialon, mullite, SiC, glass, sintered carbide, porcelain, zirconia, and alumina could be estimated very well when the GMTS fracture criterion was used. © 2010 The American Ceramic Society.


Habibpanah A.A.,Iran University of Science and Technology | Pourhashem S.,Iran University of Science and Technology | Sarpoolaky H.,Iran University of Science and Technology
Journal of the European Ceramic Society | Year: 2011

Titania-alumina composite membranes containing 10 and 20. mol% alumina were prepared by two different sol-gel methods; co-hydrolysis and separately peptized. The samples were characterized by different techniques. XRD results showed that for the composite membranes the anatase to rutile transformation temperature was increased by 200 and 300°C. According to specific surface area results, alumina effectively increased the specific surface area of composite membranes compared to pure titania membranes. Microstructure of composite supported membranes was considered by scanning electron microscopy and showed a crack-free layer with 1. μm thickness. The photocatalytic activity of composite samples showed that alumina addition up to an optimum amount can slightly affect the photocatalytic activity of titania. © 2011 Elsevier Ltd.


Hamidi A.G.,Iran University of Science and Technology | Arabi H.,Iran University of Science and Technology | Rastegari S.,Iran University of Science and Technology
International Journal of Refractory Metals and Hard Materials | Year: 2011

For manufacturing a heavy duty W-Cu composite, a porous tungsten skeleton is required; which later can be filled by molten copper via infiltration technique. The compression force usually up to 200 MPa can be provided by cold isostatic press (CIP) and the temperatures used for sintering the green compacts are more 2000 °C. However, in this research, high pressure within the range of 200 to 663 MPa was used to produce high density green specimens (60-80%) by CIP while sintering was carried out at a moderate temperature of 1550 °C. The tungsten skeletons were infiltrated with molten copper at 1300 °C. The reduction of sintering temperature from over 2000 °C to 1550 °C for a highly densified W-skeleton not only resulted into a successful production of W-Cu composites but also the obtained physical and mechanical properties of these composites are comparable to those obtained for lower compaction pressures and sintering temperature higher than 2000 °C. © 2010 Elsevier Ltd. All rights reserved.


Behzad S.,Iran University of Science and Technology
Optical and Quantum Electronics | Year: 2016

The full potential linearized augmented plane wave method with the generalized gradient approximation has been used to understand the electronic and optical properties of α-graphyne-like BN (α-BNyne) sheet. The total and partial density of states, electronic structure and optical constants for different light polarizations are obtained. The optical properties of α-BNyne are found to be strongly anisotropic. For electric field parallel to the α-BNyne sheet, strong optical adsorption and reflectivity are observed in the low-energy region, whiles for the electric field perpendicular to the α-BNyne sheet, the adsorption and reflectivity in the low-energy region are very weak. Also, the results of optical response property calculations show that α-BNyne sheet has broad spectral photoresponse. All of these properties indicate that α-BNyne is a new two-dimensional candidate for use in optoelectronic devices. © 2016, Springer Science+Business Media New York.


Ayatollahi M.R.,Iran University of Science and Technology | Aliha M.R.M.,Iran University of Science and Technology | Saghafi H.,Iran University of Science and Technology
Engineering Fracture Mechanics | Year: 2011

An edge cracked semi-circular specimen subjected to asymmetric three-point bend loading was suggested for investigating mixed mode fracture in brittle materials. Using finite element analysis, the crack parameters were obtained for various crack lengths and different locations of loading points. It was shown that by selecting appropriate positions for the loading points, full mode mixities from pure mode I to pure mode II could be achieved. Then, a series of fracture tests were conducted on PMMA using the proposed specimen. Very good agreement was found between the experimental results and those predicted from the generalized maximum tangential stress criterion. © 2010 Elsevier Ltd.


Hosseini-Hashemi S.,Iran University of Science and Technology | Fadaee M.,Iran University of Science and Technology | Atashipour S.R.,Iran University of Science and Technology
Composite Structures | Year: 2011

In this article, a new exact closed-form procedure is presented to solve free vibration analysis of functionally graded rectangular thick plates based on the Reddy's third-order shear deformation plate theory while the plate has two opposite edges simply supported (i.e., Lévy-type rectangular plates). The elasticity modulus and mass density of the plate are assumed to vary according to a power-law distribution in terms of the volume fractions of the constituents whereas Poisson's ratio is constant. Based on the present solution, five governing complicated partial differential equations of motion were exactly solved by introducing the auxiliary and potential functions and using the method of separation of variables. The validity and high accuracy of the present solutions are investigated by comparing some of the present results with their counterparts reported in literature and the 3-D finite element analysis. It is obvious that the present exact solution can accurately predict not only the out of plane, but also the in-plane modes of FG plate. Furthermore, a new eigenfrequency parameter is defined having its special own characteristics. Finally, the effects of boundary conditions, thickness to length ratio, aspect ratio and the power law index on the frequency parameter of the plate are presented. © 2010 .


Ahmadian H.,Iran University of Science and Technology | Azizi H.,Iran University of Science and Technology
JVC/Journal of Vibration and Control | Year: 2011

This paper deals with the stability of a beam subjected to thrust. The thrust acts upon the structure as a follower non-conservative force, thus the structure can lose its stability by flutter or divergence depending on the system parameters. The model consists of two beams interconnected by a nonlinear joint. The joint is a combination of linear and nonlinear springs and a damper. Follower force is assumed to be linearly distributed along the length of beam, so the governing equation has variable coefficients, so that only an approximate solution is possible. We divided the beam into a number of segments so that force distributions could be approximated as constants and then we used the method of multiple scales to obtain the analytical solution of the system. The flutter and divergence and post-critical behavior are then obtained. © 2011 The Author(s).


Shokrieh M.M.,Iran University of Science and Technology | Omidi M.J.,Iran University of Science and Technology
Composite Structures | Year: 2011

In this study, the strain rate effects on transverse tensile and compressive properties of unidirectional Glass fiber reinforced polymeric composites are investigated. To demonstrate strain rate effects, the tensile and compressive composite specimens with identical configuration are fabricated and tested to failure in the transverse direction at quasi-static strain rate of approximately 0.001s-1 and intermediate strain rates of 1-100s-1. The tensile and compressive tests are performed using a servo-hydraulic testing apparatus equipped with strain rate increasing mechanisms. For performing the practical tests, a jig and a fixture and other test supplies are designed and manufactured. The performance of the test jig is evaluated and showed that it is adequate for composites testing under tension and compression loads. The effects of strain rate on mechanical properties (maximum strength, modulus, and strain to failure) are considered. The characteristic results for the transverse properties indicate that damage evolution is strain-rate-dependent for the examined material. Also, a strain-rate-dependent empirical material model associated with different regression constants is proposed based on the experimental results obtained to characterize the rate dependent behavior of Glass/Epoxy composite material. © 2010 Elsevier Ltd.


Shahriari Y.,Iran University of Science and Technology | Erfanian A.,Iran University of Science and Technology
Neurocomputing | Year: 2013

The detection of the presence of the P300 in the electroencephalogram (EEG) is a challenging issue in P300-based brain-computer interface (BCI). The P300-based developed in this work allows a subject to communicate 1 of 36 symbols presented on a 6×6 matrix. When a target symbol is seen by the subject, unique event-related potential (ERP) characterized by P300 is elicited. Thus, in P300 speller, accurate detection of such distinct ERP provides faster and reliable communication. In this paper, a subspace-based spatial filter was employed to enhance the detection of the presence of the P300 in the EEG. The subspace-based filter was designed by maximizing the ratio between the brain signals synchronized with the target stimulus and that with the nontarget stimulus. The processing method was evaluated offline and online on the data obtained from five subjects. The results of offline studies showed that the average accuracies of 97.5% and 90.5% were achieved in P300 detection and character recognition, respectively. The average communication rate achieved was 17.13. bits/min with an average accuracy of 89.5% using 10 electrodes during online experiments. © 2013 Elsevier B.V.


Gheshlaghi B.,Iran University of Science and Technology | Hasheminejad S.M.,Iran University of Science and Technology
Composites Part B: Engineering | Year: 2011

The nonlinear flexural vibrations of micro- and nanobeams in presence of surface effects are studied within the framework of Euler-Bernoulli beam theory including the von Kármán geometric nonlinearity. Exact solution is obtained for the natural frequencies of a simply-supported nanobeam in terms of the Jacobi elliptic functions by using the free vibration modes of the corresponding linear problem. Numerical results include the normalized natural frequencies of vibration as functions of mode number, vibration amplitude, and nanobeam length and thickness. Also, the influence of surface effects on the system phase trajectory is considered. © 2011 Elsevier Ltd. All rights reserved.


Keshvari M.,Iran University of Science and Technology | Tayarani M.,Iran University of Science and Technology
Progress In Electromagnetics Research Letters | Year: 2011

A microstrip bandpass filter is presented based on Complementary Split Ring Resonators (CSRRs) and a pair of open-loop resonators that has a single pair of transmission zeros at finite frequencies that causes an improvement at skirt response. An equivalent circuit is introduced to make analysis and optimization faster. Finally a filter is designed using the proposed cell and the simulation results with both equivalent model and full wave analysis are in very good agreement. The filter was fabricated and the measurement result was also in good agreement with simulation results. Besides, the size of the designed filter is very small and it occupies an area less than 0.23λg × 0.16λg, where λg is the guided wavelength at the midband frequency.


Berto F.,University of Padua | Ayatollahi M.R.,Iran University of Science and Technology
Materials and Design | Year: 2011

The main purpose of this research is to re-analyse experimental results of fracture loads from blunt V-notched samples under mixed mode (I + II) loading considering different combinations of mode mixity ranging from pure modes I to II. The specimens are made of polymethyl-metacrylate (PMMA) and tested at room temperature. The suitability of fracture criterion based on the strain energy density (SED) when applied to these data is checked in the paper. Dealing with notched samples, characterized by different notch angles and notch root radii, the SED criterion used in combination with the concept of local mode I, valid in the proximity of the zone of crack nucleation, permits to provide a simple approximate but accurate equation for the SED in the control volume. This proposal unifies predictions for the experimental results obtained under modes I, II and mixed mode loading. © 2010 Elsevier Ltd.


Hamidi A.G.,Iran University of Science and Technology | Arabi H.,Iran University of Science and Technology | Rastegari S.,Iran University of Science and Technology
International Journal of Refractory Metals and Hard Materials | Year: 2011

Activated sintering of tungsten has been used to have infiltrable skeletons. For this purpose the effects of sintering temperature and activator amount were studied and appropriate production parameters were obtained. The results showed that by activated sintering, moderate sintering temperature such as 1400 °C can be used instead of conventional temperatures i.e. > 2000 °C. Activated sintering has the ability to produce fully open and interconnected porosities with desirable density that is ideal for infiltration. This method of production for infiltrated W-Cu composites has not been reported elsewhere. © 2011 Elsevier Ltd. All Rights reserved.


Yazdi M.,Iran University of Science and Technology | Komjani N.,Iran University of Science and Technology
Progress In Electromagnetics Research Letters | Year: 2011

In this paper, a planar microstrip UWB monopole antenna with a good band-rejection is presented. By using a pair of arc shaped parasitic elements around the patch, an excellent notched frequency band for rejecting the WLAN band (5-6 GHz) can be obtained. The arc shaped strips are parametrically studied and the effects of them on the radiation patterns and time domain behaviour of the UWB antenna are investigated.


Maleki A.,Iran University of Science and Technology | Rezayan A.H.,University of Tehran
Tetrahedron Letters | Year: 2014

A one-pot, three-component reaction for the synthesis of pyrido[2′,1′:2,3]imidazo[4,5-c]isoquinolines starting from 2-aminopyridines, phthalaldehyde, and trimethylsilyl cyanide in good to high yields is described. © 2014 Elsevier Ltd. All rights reserved.


Tootoonchian F.,Iran University of Science and Technology
IEEE Sensors Journal | Year: 2016

Resolvers are electromagnetic position sensors that are widely used in industrial applications. In this paper, a novel axial flux resolver with a simple solid rotor is introduced for the first time. The stator of the proposed resolver has a disk type structure with two-phase distributed windings as signal windings and a concentric winding as an excitation winding. The rotor is a disc with a simple structure. Its width is 20° without any winding, and thus, the proposed resolver has the advantages of variable reluctance resolvers for having no winding on rotor and also its manufacturing process is much simpler than that of variable reluctance resolvers. The performance analysis of the proposed structure is simulated and optimized using a 3D time stepping finite element method. Then, a prototype is constructed based on the optimized dimensions and tested. Good agreement between the simulation and the experimental results validates the success of the proposed resolver. © 2016 IEEE.


Shaeri M.H.,Iran University of Science and Technology | Saghafian H.,Iran University of Science and Technology | Shabestari S.G.,Iran University of Science and Technology
Materials and Design | Year: 2012

To improve mechanical properties specifically wear resistance and impact toughness of Cr-Mo steels, the specimen were subjected to austempering and martempering processes, and the results were compared with the common cycle used in industry (compressed air cooling). After the accomplishment of austenization process, the specimens were quenched in salt bath at 300 °C and 200 °C in austempering and martempering processes, respectively, for 2, 8, 30, and 120. min and then cooled down to room temperature in still air. Microstructure of the specimens was studied using optical microscopy (traditional black and white etching as well as color etching), scanning electron microscopy (SEM) as well as X-ray diffraction (XRD). Mechanical properties of the austempered and martempered specimens were investigated by measuring the hardness, impact toughness and wear resistance. Results shown that the samples austempered for 2. h have demonstrated the best impact toughness, while the samples martempered for 2. h have presented the highest values of wear resistance. In addition using salt bath instead of compressed air, leads to a better combination of wear resistance and toughness. © 2011 Elsevier Ltd.


Shokrieh M.M.,Iran University of Science and Technology | Heidari-Rarani M.,Iran University of Science and Technology | Ayatollahi M.R.,Iran University of Science and Technology
Materials and Design | Year: 2012

It is still questionable to think of delamination resistance of a double cantilever beam (DCB) as a material property independent of the specimen size and geometry. In this research, the effects of initial crack length and DCB specimen thickness on the mode I delamination resistance curve (R-curve) behavior of different unidirectional glass/epoxy DCB specimens are experimentally investigated. It is observed that the magnitudes of initiation and propagation delamination toughness (GIc-init and GIc-prop) as well as the fiber bridging length are constant in a specific range of the initial crack length to the DCB specimen thickness ratios of 8.5


Mirimani S.M.,Iran University of Science and Technology | Vahedi A.,Iran University of Science and Technology | Marignetti F.,University of Cassino and Southern Lazio
IEEE Transactions on Magnetics | Year: 2012

This paper studies the effects of static eccentricity on axial flux permanent-magnet machines (AFPMMs) using three-dimensional finite-element analysis (3-D FEA). Use of numerical modeling makes it possible to precisely study the eccentricity in these types of machines. The accuracy of the FEM model is validated using experimental measurement. To the best awareness of the authors, effects of static eccentricity in AFPMMs have not been studied before. Hence, a new definition for the static eccentricity factor (SEF) is presented and it is shown that the occurrence of static eccentricity is very high in these types of machines. A motor with different degrees of rotor eccentricity is simulated and the flux density distribution in the air gap and the total axial force between rotor and stator is obtained. In addition, unbalanced magnetic force (UMF) is calculated and it is mentioned that a steady torque is created by the forces. This study indicates that static eccentricity has noticeable effects on motor characteristics and can deteriorate the motor performances. © 2006 IEEE.


Najafi Kani E.,Semnan University | Allahverdi A.,Iran University of Science and Technology | Provis J.L.,University of Melbourne
Cement and Concrete Composites | Year: 2012

This paper addresses methods to reduce efflorescence in a geopolymer binder based on a pumice-type natural pozzolanic material from Taftan, Iran. Geopolymer pastes samples are analyzed for compressive strength and efflorescence formation after curing at 95% humidity for 28 days. To reduce the extent of efflorescence, Al-rich mineral admixtures such as metakaolin, ground granulated blast-furnace slag, and three types of calcium aluminate cements are incorporated into the dry binder at a range of concentrations. Hydrothermal curing at elevated temperatures also shows a positive effect in efflorescence reduction. Calcium aluminate cements show the greatest effect in efflorescence reduction, which is attributed to their dissolution in alkaline media releasing high amounts of alumina into the aluminosilicate geopolymer gel. These results confirm that it is possible to develop a more reliable geopolymer binder with improved properties either by adding a suitable amount of active alumina to precursors such as natural pozzolan, or by manipulating the curing conditions to enhance alumina release from less-reactive precursor phases. © 2011 Elsevier Ltd. All rights reserved.


Tolaminejad B.,Iran University of Science and Technology | Dehghani K.,University of Tehran
Materials and Design | Year: 2012

In the present research, equal channel angular extrusion (ECAE) of commercial purity aluminum (1070) was conducted using route BC. For ECAE processing a proper die set was designed and constructed. Electron backscatter diffraction (EBSD) and X-ray diffraction (XRD) analyses were used to evaluate the microstructure and texture of the extruded materials. The results reveal two distinct processing regimes: from 1 to 4 passes the microstructure evolves from elongated subgrains to a rather equiaxed array of ultrafine grains and from 4 to 8 passes there is no strict change in the average grain size. The boundary misorientation angle and the fraction of high-angle boundaries increase rapidly up to 4 passes and at a slower rate from 4 to 8 passes. Also, the variation of hardness and yield stress with number of extrusion was documented up to 8 passes. The present results showed that first ECAE pass has resulted in enhancement of mechanical properties more than four times over the annealed condition. Further ECAE processing has resulted in slight improvement. Based on two strengthening mechanisms, variations of the strength as a function of the pass numbers were related to the calculated dislocation densities and the average boundary spacing. © 2011 Elsevier Ltd.


Shokrieh M.M.,Iran University of Science and Technology | Mazloomi M.S.,Iran University of Science and Technology
Composite Structures | Year: 2012

The present paper represents a new analytical method for calculation of the stiffness of three-dimensional four-directional braided composites. In most previous works, the analytical approach had been largely neglected in the favor of the finite element model. Among those who have used the analytical model, the braided preform has been considered as made of one, or three, types of representative unit cells, while microscopic evidence of the microstructure of preforms reveals different configurations of the yarns in the interior, surface and corner regions of a braided preform. This paper presents a Multi-Unit Cell Model in which four kinds of unit cells, namely interior, interior surface, exterior surface and corner unit cells have been introduced as representative cells. Each type of unit cell in a braided composite possesses unique mechanical properties and has been considered as a uni-directional composite. Using rotation matrices, the angle between yarns and longitudinal direction has been incorporated in general coordinates of the model. Finally, using a volume averaging method, the total stiffness of the braided composite is calculated. The results are in good agreement with the available experimental data. The effect of braiding angle on the stiffness of braided composites is also examined. © 2011 Elsevier Ltd.


Ameri M.,Iran University of Science and Technology | Ameri M.,Transportation Institute | Behnood A.,Iran University of Science and Technology
Construction and Building Materials | Year: 2012

This paper aims to evaluate the effectiveness of steel slag as a substitute for virgin aggregates on mechanical properties of cold mix recycling asphalt pavement. For this purpose, gradation requirements of two types of Reclaimed Asphalt Pavement (RAP) materials in Cold In Place Recycling (CIR) mixes were modified. Mixtures' gradation requirements were satisfied by adding 20% and 10% of two types of new aggregates in accordance with Asphalt Institute CIR grading requirements. The results showed that the use of steel slag can enhance Marshall stability, resilient modulus, tensile strength, resistance to moisture damage and resistance to permanent deformation of CIR mixes. Use of anionic bitumen emulsion is recommended in preparing mixtures, because of its compatibility with them. © 2011 Elsevier Ltd. All rights reserved.


Ghoddousi P.,Iran University of Science and Technology | Javid A.A.S.,Iran University of Science and Technology
Materials and Structures/Materiaux et Constructions | Year: 2012

The experimental investigation on plastic shrinkage and plastic settlement for different selfconsolidating concrete (SCC) mixtures as repairing materials is presented. The concrete mixtures were placed on the surface of the concrete substrate slabs at different restraint degrees. Four different types of repairing materials such as plain SCC, SCC with silica fume (SF), SCC with latex and SF, and SCC with latex, SF and fiber were evaluated. The slabs included both reinforcement and without reinforcing bars. The tests involved measurement of concrete bleeding and evaporation rates, steel bar strains and crack characteristics. The results indicated that bleeding rate is not the only controlling factor, but restraint condition, configuration of steel bars and the concrete strain capacity are also affect plastic shrinkage and settlement behaviors significantly. Latex and fiber were found to be effective in reduction of cracks and concrete strains. Cracks did not develop on the surface of concrete containing latex and fiber. The results showed that if a slab is reinforced by one single bar (in each direction of the slab), at relatively large diameter as used in this study, it would not improve the plastic shrinkage behavior, although it causes plastic settlement cracking. © RILEM 2011.


Torabi A.R.,University of Tehran | Aliha M.R.M.,Iran University of Science and Technology
Engineering Solid Mechanics | Year: 2013

The aim of the present work was to develop a guideline for approving the railway axles made of C35 steel and containing surface and/or in-body defects after manufacturing. First, several through and part-through circular cracks were modeled on the surface and in the body of the axle at its critical cross-section. Then, the permissible size of such cracks was determined by using the fracture mechanics. To verify the validity of the guideline, the theoretical result for the semi-circular surface crack was compared with the allowable size prescribed by the international railway standard. A very good agreement was found to exist between the predicted and the standard values. © 2013 Growing Science Ltd. All rights reserved.


Mahmoodi M.,Iran University of Science and Technology | Sedighi M.,Iran University of Science and Technology | Tanner D.A.,University of Limerick
Materials and Design | Year: 2012

The layer removal technique and the X-ray diffraction method have been employed to evaluate the residual stresses through the thickness of aluminum alloy 5083 processed by equal channel angular rolling (ECAR). ECAR is a severe plastic deformation process that introduces shear deformation to sheet metals. The process has been completed on 2. mm thick strips passed three times through die channels in a continuous manner. In this work, the profile of residual stresses was quantitatively determined. It was observed that after the ECAR process, the residual stress magnitudes were changed from approximately zero in annealed condition up to half of the yield strength value of ECARed samples. The distribution of the residual stresses was found to be non-uniform through the thickness and the ECARed sample was compressive at the top surface while it was tensile at the bottom surface. © 2012 Elsevier Ltd.


Shokrieh M.M.,Iran University of Science and Technology | Kefayati A.R.,Iran University of Science and Technology | Chitsazzadeh M.,Iran University of Science and Technology
Materials and Design | Year: 2012

In this research, the effects of adding modified nanoclay (Cloisite 30B) on the mechanical properties (tensile, compression, flexural and fracture toughness) of epoxy polymer (ML-506) were investigated. Subsequently, the mechanical properties of polymer concrete (PC) made of nanoclay/epoxy were also studied. The nanoclay dispersion was achieved by sonication technique. Therefore, optimum sonication output power and time for achieving the highest d-spacing of nanoclay layers were obtained. The X-ray diffraction (XRD) results indicated that changing sonication output power and time during fabrication process did not have any remarkable effects on increasing the d-spacing of clay layers. In all production processes, the d-spacing was increased from 18.4. å to about 42. å and thus the intercalated nanocomposites were fabricated. In addition to XRD, the dispersion state and the d-spacing of nanoclay particles were observed using a transmission electron microscope (TEM). Also, the effects of various filler contents on the mechanical properties, i.e., tensile, compression, flexural and fracture toughness of nanocomposite were investigated. The results of mechanical testing showed that enhancement in the tensile and flexural moduli, compressive strength and fracture toughness were gained by 12.5%, 13.3%, 7.4% and 25.5% respectively. On the other hand, tensile and flexural strengths as well as strain to failure were decreased. Scanning electron microscope (SEM) was also used to study the fracture mechanism of nanocomposites. Finally, by adding the optimum amounts of nanoclay to the PC, its mechanical properties were compared with conventional ones. The results indicated that introduction of nanoclay into the PC did not improve tensile and flexural strengths although compression strength and fracture toughness were enhanced by 15.2% and 7.6% respectively. © 2012 Elsevier Ltd.


Ayatollahi M.R.,Iran University of Science and Technology | Akbardoost J.,Iran University of Science and Technology
Engineering Fracture Mechanics | Year: 2012

A new approach called the modified maximum tangential stress criterion has been developed for investigating size effects on mode I fracture toughness of quasi-brittle materials. This approach employs the maximum tangential stress criterion while accounting for the higher order term of Williams expansion A 3. Having assumed that the FPZ length changes with the specimen size, a formulation was suggested for expressing the variation of FPZ length versus the specimen size. Some experimental results reported for concrete and limestone were employed to assess the proposed criterion. It is shown that the proposed approach provides good estimates for the experimental data. © 2012 Elsevier Ltd.


Anbia M.,Iran University of Science and Technology | Mandegarzad S.,Iran University of Science and Technology
Journal of Alloys and Compounds | Year: 2012

The effect of mesoporous carbon CMK-3 as a support on Pt catalytic activities, dissociation of hydrogen molecules and enhanced hydrogen absorption on modified MIL-101 at ambient temperature have been studied. The isotherms of these unmodified and modified samples have been investigated using volumetric method at 298 K and the pressure ranging from 1 to 20 bar. These modification with Pt (20 wt%)/CMK-3 and carbon bridge, the hydrogen uptake was almost twice that of pristine sample. The storage capacity of modified MIL-101 at 20 bar and 298 K was found to be 1.34 wt% which is significantly improved as compared to the pure MIL-101, it is because of the Pt nanoparticles were uniformly distributed on the mesopores of CMK-3 support. Therefore Pt catalytic activities in dissociation of hydrogen molecules are improved leading to significant changes in hydrogen sorption properties at room temperature. Also The obtained composite is characterized by various techniques such as powder X-ray diffractometry, scanning electron microscopy, porosimetry by nitrogen adsorption and desorption and hydrogen adsorption. © 2012 Elsevier B.V.


Shokrieh M.M.,Iran University of Science and Technology | Akbari R S.,Iran University of Science and Technology
Journal of Composite Materials | Year: 2012

In this research, the process of slitting with an assumed residual stress distribution is simulated to calculate compliance functions of laminated composites. The primary aim of this article is to investigate different parameters influencing the calculation of compliance coefficients for laminated composites using a finite element model. First, using two- and three-dimensional finite element models, the process of slitting in isotropic materials for calculating the compliance coefficients is simulated. The results show a complete agreement between the two models. Also, the results of simulation show that in the modeling of slitting method for laminated composites, real slit width must be considered. That is because composite laminates are generally thin and slitting in these materials results in large slit width to thickness ratio. Finally, the developed simulation method is applied to calculate compliance coefficients for two carbon/epoxy- and glass/epoxy-laminated composites with quasi-isotropic and cross-ply lay-ups using a three-dimensional finite element modeling. For a better precision, a full three-dimensional model without symmetry assumption is considered. The presented method is capable of simulating slitting method in parts and specimens with complicated geometry as well as in orthotropic materials with any degree of orthotropy. © 2011 The Author(s).


Sedighi M.,Iran University of Science and Technology | Honarpisheh M.,Iran University of Science and Technology
Materials and Design | Year: 2012

Explosive welded multi-layers sheet metals are widely used in recent years. Evaluation of residual stresses of this new merging material is necessary for better understanding of its mechanical behavior. In this paper, incremental hole-drilling (IHD) is used to measure through-depth non-uniform residual stress gradient in explosive welded Al-Cu-Al multilayers. At first, the multilayer sheets at two different initial thicknesses were made by using explosive welding. Then, through-depth residual stress gradient was obtained with the IHD method. In addition, calibration coefficients have been obtained to evaluate the residual stress by using finite element method (FEM) analysis. Results show that multilayers surface is subjected to high tensile residual stress. Also there is an intense gradient of residual stress at the interface of multilayers. © 2011 Elsevier Ltd.


Honarpisheh M.,Iran University of Science and Technology | Asemabadi M.,Iran University of Science and Technology | Sedighi M.,Iran University of Science and Technology
Materials and Design | Year: 2012

In this study, an Al/Cu/Al multilayer sheet was fabricated by explosive welding process and the effects of annealing temperature on the interfacial properties of explosively bonded Al/Cu bimetal have been investigated. For this purpose, hardness changes along the thickness of the samples have been measured, and the thickness and type of intermetallic compounds formed at the joining interface have been explored by means of optical microscopy (OM), scanning electron microscopy (SEM) and also energy dispersive spectroscopy (EDS). The obtained results indicate that, with the increase of the annealing temperature, the thickness of intermetallic compounds has increased and the amount of hardness along the thickness of the joining interface has diminished. In the annealed sample at 400°C for 30min, it was observed that intermetallic layers have formed at the interface of Al/Cu bimetals. These layers consist of the intermetallic compounds AlCu3, Al2Cu and AlCu, and their thickness gets to about 5μm at some points. The examinations performed by the SEM, following the Vickers micro-hardness test, indicated the existence of a number of microcracks at the top and bottom interface of the sample annealed at 400°C. This shows the formation of brittle intermetallic compounds at the joining interface, and also indicates the low ductility of these compounds. © 2012 Elsevier Ltd.


Hasheminejad S.M.,Iran University of Science and Technology | Alaei-Varnosfaderani M.,Iran University of Science and Technology
Journal of Intelligent Material Systems and Structures | Year: 2012

The linear three-dimensional piezoelasticity theory in conjunction with the versatile transfer matrix approach is employed to investigate the steady-state nonaxisymmetric fluid-structure-coupled vibrations of an arbitrarily thick bilaminate simply supported hollow cylinder of finite length, composed of an inner layer of orthotropic functionally graded material perfectly bonded to an outer layer of radially/axially/circumferentially polarized functionally graded piezoceramic material. The cylinder is filled with a compressible nonviscous fluid and may be subjected to arbitrary time-harmonic on-surface mechanical drives. The analytical results are illustrated with numerical examples in which water-filled homogeneous PZT4-steel composite cylinders are driven by harmonic external concentrated or distributed radial surface loads. When the outer piezoelectric layer is operating in the receiving (sensing) mode, the frequency spectrums of the induced voltage, stress components, and on-axis acoustic pressure are calculated and discussed for the selected loading configurations. Also, when the piezolayer operates in the active vibration mode, the effects of polarization direction and number of control modes on the voltage required for partial or complete cancellation of the on-axis internal pressure are investigated. Limiting cases are considered, and the validity of results is established by comparison with the data in the existing literature as well as with the aid of a commercial finite element package. © 2012 The Author(s).


Abbasnia R.,Iran University of Science and Technology | Ahmadi R.,Iran University of Science and Technology | Ziaadiny H.,Iran University of Science and Technology
Composites Part B: Engineering | Year: 2012

Behavior of rectangular concrete columns confined with FRP composites depends on several parameters, including unconfined concrete strength, confinement level, aspect ratio of cross-section (defined as the depth/width of the cross-section), and the sharpness of the section corners. For modeling the cyclic stress-strain behavior of FRP-confined rectangular concrete columns, effect of column parameters on the cyclic behavior of these columns should be examined properly. In this paper, effects of unconfined concrete strength, confinement level and the aspect ratio of cross-section are studied. The test database includes 10 prisms from recent study of authors and 18 prisms from a new experiment. Results of tests show that some aspects of cyclic behavior of FRP-confined concrete prisms such as envelope curve and stress deterioration are unaffected by the considered parameters. Results also indicate that the plastic strain decreases as the unconfined concrete strength increases, but it is independent of the aspect ratio and the confinement level. While the reloading path in all specimens was almost linear, the unloading path was highly nonlinear and was affected by unconfined concrete strength. © 2011 Elsevier Ltd. All rights reserved.


Shokrieh M.M.,Iran University of Science and Technology | Safarabadi M.,Iran University of Science and Technology
Journal of Composite Materials | Year: 2012

In polymer composites, thermal residual stresses arise due to the mismatch of the thermal expansion coefficients of the fiber and matrix. Polymer composites generally consist of three phases: fiber, matrix, and the interphase. In this article, to study the effects of the interphase on residual stresses, a three-dimensional energy-based closed-form solution is developed. Residual stresses are assumed variable along longitudinal and radial directions, and two Airy stress functions are introduced. By considering the interphase region, in comparison with the perfect bonding conditions, thermal residual stresses decrease. The longitudinal residual stress distribution is sensitive to the interphase thickness. The maximum axial stress occurs at the fiber mid-length and decreases by increasing the interphase thickness. The maximum fiber-interphase and interphase-matrix interfacial shear stresses vary by increasing the interphase thickness, whereas their position is approximately unchanged. An increase in the interphase thickness leads to a decrease of the shear stress concentration factor near the fiber ends. For different magnitudes of bonding efficiency, the interfacial radial stresses are zero at the maximum fiber length. Although, the interphase region has a minor effect on the interfacial radial stresses, it has a significant effect on the maximum interfacial radial stresses at the fiber ends. © The Author(s) 2011.


Ahmadi R.,Iran University of Science and Technology
International Journal of Production Research | Year: 2016

Given a reward structure, this paper addresses an optimal replacement problem for complex multi-component systems. To maintain revenue stream resulting from system, the system is inspected according to a homogeneous Poisson process and certain actions are carried out in response to the system state. Decisions are based on a performance measure described by a Squared Bessel process. Given some assumption, we explore the inherent relation between the Squared Bessel process and an extended Gamma (EG) process. Since there are some flow of income and increasing costs due to inspections, the problem is to optimally stop processing the system and carrying out a renewal to maximize the reward functional. To this end, using the local characteristics of the EG process as a stopping criterion and the expected total discounted reward as a measure of policy, this paper aims at determining an optimal operating (stopping) time which truly balances both income and cost and so maximizes the expected discounted reward over a cycle. In support of the model a numerical example is provided to show feasibility of this programme in real application. Attention is restricted to perfect repair and inspection, but the paper provides the structure so that different scenarios can be explored. © 2016 Informa UK Limited, trading as Taylor & Francis Group


Shokrieh M.M.,Iran University of Science and Technology | Heidari-Rarani M.,Iran University of Science and Technology | Rahimi S.,Iran University of Science and Technology
Composite Structures | Year: 2012

Mode I delamination toughness (G Ic) of a laminated composite depends not only on the stacking sequence or indirectly coupling parameter of Dc=D122D11D22, but also on specimen geometrical ratios a 0/b and a 0/h. In this study, a non-uniformity ratio, β=(G Imax-G Iavg)/G Iavg%, is introduced to take into account the influence of above factors on the energy release rate distribution along the width of double cantilever beam (DCB) specimens simultaneously. Results show that the G Ic of multidirectional DCB specimens with 0°//0° crack interface and β<20% can be predicted by measuring the G Ic of the unidirectional plies with an error less than 10%. Moreover, a methodology is proposed to predict the maximum delamination toughness (G Imax) of multidirectional DCB specimens from β parameter without performing any experiments. With the present method, the effect of curved thumbnail shape of energy release rate along the delamination front is considered on the available closed-form relations for G I. © 2011 Elsevier Ltd.


Ara A.L.,Iran University of Science and Technology | Kazemi A.,Iran University of Science and Technology | Niaki S.A.N.,University of Toronto
Applied Energy | Year: 2011

This paper introduces a modified power flow model for Hybrid Flow Controller (HFC) as an energy flow controller. The existing power flow models for Hybrid Flow Controller are suitable only for conventional power flow analysis, and are not applicable for OPF and optimal location analysis of FACTS devices. In this paper, some modifications were applied to the existing models to promote the accuracy and improve their conformability on any power system and hence leading to a precise steady-state analysis. The modified model and the existing model are investigated using different IEEE test systems and the results are compared together. The optimization method is numerically solved using Matlab and General Algebraic Modelling System (GAMS) software environments. The solution procedure uses Mixed Integer Non-Linear Programming (MINLP) and Relaxed Mixed Integer Non-Linear Programming (RMINLP) to solve the optimal location and setting of HFC incorporated in OPF problem considering the total fuel cost, power losses, and the system loadability as objective functions for single objective optimization problem and improve the power system operation. © 2010 Elsevier Ltd.


Esmaili M.,Iran University of Science and Technology | Amjady N.,Semnan University | Shayanfar H.A.,Iran University of Science and Technology
Applied Energy | Year: 2011

Congestion management is a vital part of power system operations in recent deregulated electricity markets. However, after relieving congestion, power systems may be operated with a reduced voltage or transient stability margin because of hitting security limits or increasing the contribution of risky participants. Therefore, power system stability margins should be considered within the congestion management framework. The multi-objective congestion management provides not only more security but also more flexibility than single-objective methods. In this paper, a multi-objective congestion management framework is presented while simultaneously optimizing the competing objective functions of congestion management cost, voltage security, and dynamic security. The proposed multi-objective framework, called modified augmented ε-constraint method, is based on the augmented ε-constraint technique hybridized by the weighting method. The proposed framework generates candidate solutions for the multi-objective problem including only efficient Pareto surface enhancing the competitiveness and economic effectiveness of the power market. Besides, the relative importance of the objective functions is explicitly modeled in the proposed framework. Results of testing the proposed multi-objective congestion management method on the New-England test system are presented and compared with those of the previous single objective and multi-objective techniques in detail. These comparisons confirm the efficiency of the developed method. © 2010.


Khazali A.H.,Iran University of Science and Technology | Kalantar M.,Iran University of Science and Technology
International Journal of Electrical Power and Energy Systems | Year: 2011

This paper presents a harmony search algorithm for optimal reactive power dispatch (ORPD) problem. Optimal reactive power dispatch is a mixed integer, nonlinear optimization problem which includes both continuous and discrete control variables. The proposed algorithm is used to find the settings of control variables such as generator voltages, tap positions of tap changing transformers and the amount of reactive compensation devices to optimize a certain object. The objects are power transmission loss, voltage stability and voltage profile which are optimized separately. In the presented method, the inequality constraints are handled by penalty coefficients. The study is implemented on IEEE 30 and 57-bus systems and the results are compared with other evolutionary programs such as simple genetic algorithm (SGA) and particle swarm optimization (PSO) which have been used in the last decade and also other algorithms that have been developed in the recent years. © 2010 Elsevier Ltd. All rights reserved.


Sanaye S.,Iran University of Science and Technology | Dehghandokht M.,Iran University of Science and Technology
Applied Energy | Year: 2011

Parallel flow condenser (PFC), which is widely used in automobile air conditioning (AAC) industries, was modeled and optimized in this paper. A sample of designed and manufactured condenser of this type was modeled and tested. In the proposed physical model the condenser is divided into three regions of superheat, saturated (two-phase) and subcooled. The modeling results validated by comparison with the experimental data.In optimization section, the condenser heat transfer rate was maximized while its pressure drop was minimized applying genetic algorithm multi-objective optimization technique. A set of Pareto optimal solutions as well as the final optimal design point were presented for our case study.The optimum design parameters resulted in heat transfer rate increase for 7.1% and decrease in pressure drop for 96% in comparison with the corresponding manufactured operating parameters. © 2010 Elsevier Ltd.


Sarlak M.,Iran University of Science and Technology | Shahrtash S.M.,Iran University of Science and Technology
IET Generation, Transmission and Distribution | Year: 2011

In this study a new pattern recognition-based algorithm is presented for detecting high impedance faults (HIFs) in distribution networks with broken or unbroken conductors and distinguishing them from other similar phenomena such as capacitor bank switching, load switching, no-load transformer switching (through feeder switching), fault on adjacent feeders, insulator leakage current (ILC) and harmonic load. The proposed method has employed multi-resolution morphological gradient (MMG) for extraction of the time-based features from three half cycles of the post-disturbance current waveform. Then, according to these features, three multi-layer perceptron neural networks are trained. Finally, the outputs of these classifiers are combined using the average method. Applying the data for HIF, ILC and harmonic load from field tests and for other similar phenomena from simulations has shown high security and dependability of the proposed method. Also, a comparison between the features from the proposed MMG-based procedure and the features from discrete Fourier transform, discrete S-transform, discrete TT-transform and discrete wavelet transform is made in the feature space. © 2011The Institution of Engineering and Technology.


Hajabdollahi H.,Islamic Azad University at Zahedan | Tahani M.,Iran University of Science and Technology | Shojaee Fard M.H.,Iran University of Science and Technology
Applied Thermal Engineering | Year: 2011

Thermal modeling and optimal design of compact heat exchanger is presented in this paper. Fin pitch, fin height, cold stream flow length, no-flow length and hot stream flow length were considered as five design parameters. A CFD analysis coupled with artificial neural network was used to develop a relation between Colburn factor and Fanning friction factor for the triangle fin geometry with acceptable precision. Then, fast and elitist non-dominated sorting genetic algorithm (NSGA-II) was applied to obtain the maximum effectiveness and the minimum total pressure drop as two objective functions. The results of optimal designs were a set of multiple optimum solutions, called 'Pareto-optimal solutions'. It reveals that any geometrical changes which decrease the pressure drop in the optimum situation, lead to a decrease in the effectiveness and vice versa. Finally sensitivity analysis shows the increases of heat transfer surface area necessarily do not increases the pressure drop and it is case sensitive. © 2011 Elsevier Ltd. All rights reserved.


Peyghambarzadeh S.M.,Islamic Azad University at Mahshahr | Hashemabadi S.H.,Iran University of Science and Technology | Jamnani M.S.,Islamic Azad University at Mahshahr | Hoseini S.M.,Islamic Azad University at Mahshahr
Applied Thermal Engineering | Year: 2011

In this paper, forced convective heat transfer in a water based nanofluid has experimentally been compared to that of pure water in an automobile radiator. Five different concentrations of nanofluids in the range of 0.1-1 vol.% have been prepared by the addition of Al 2O 3 nanoparticles into the water. The test liquid flows through the radiator consisted of 34 vertical tubes with elliptical cross section and air makes a cross flow inside the tube bank with constant speed. Liquid flow rate has been changed in the range of 2-5 l/min to have the fully turbulent regime (9 × 10 3 < Re < 2.3 × 10 4). Additionally, the effect of fluid inlet temperature to the radiator on heat transfer coefficient has also been analyzed by varying the temperature in the range of 37-49 °C. Results demonstrate that increasing the fluid circulating rate can improve the heat transfer performance while the fluid inlet temperature to the radiator has trivial effects. Meanwhile, application of nanofluid with low concentrations can enhance heat transfer efficiency up to 45% in comparison with pure water. © 2011 Elsevier Ltd. All rights reserved.


Narimani E.,Iran University of Science and Technology | Shahhoseini S.,Iran University of Science and Technology
Applied Thermal Engineering | Year: 2011

Vane mist eliminators are among the most effective devices to separate liquid droplets from a gas flow. Separation efficiency of these devices is largely dependent on the gas velocity, vane spacing and vane turning angles. In this study the efficiency of this type of mist eliminator has been investigated, using computational fluid dynamic (CFD). In addition, a prediction model of the separation efficiency was obtained based on the response surface methodology. The simulation results showed that there was a conceivable dependency of separation efficiency on the gas velocity and geometrical parameters of vanes. The optimal values of these parameters were determined in order to achieve the maximum separation efficiency. © 2010 Elsevier Ltd. All rights reserved.


Heydari H.,Iran University of Science and Technology | Moghadasi A.H.,Iran University of Science and Technology
IEEE Transactions on Power Delivery | Year: 2011

This paper presents a positive approach in an optimized design of a combinatory unified power-quality conditioner (UPQC) and superconducting fault current limiters (SFCLs). This is based on a normalized simulated annealing algorithm compared with analytic hierarchy process objective optimization. The optimization algorithm for simultaneous optimization computes and produces three-dimensional alignments in Pareto front at the end of the optimization run. The results show that the SFCL can reduce the volt-ampere rating of the UPQC by limiting the fault current, thereby reducing the cost of UPQC installation. The aforementioned algorithm requires advanced numerical techniques for simulation studies by PSCAD/EMTDC on a sample distribution system for determining a global optimal combination of UPQC and SFCL by considering individual parameters and accounting for the constraints, which is the main motivation of this paper. This will result in a more thorough knowledge of scaling factors and the system quality mechanism which will enable the most efficient systems from the viewpoints of cost cutting, energy savings, and downsizing. © 2011 IEEE.


Bagheripoor M.,Iran University of Science and Technology | Bisadi H.,Iran University of Science and Technology
Applied Thermal Engineering | Year: 2011

A model for the study of hot strip rolling of aluminum alloys is proposed, and the approach is based on thermo-mechanical analysis using the Finite-Element Method (FEM). To assess the rolling behavior of materials during a pass, finite element program Abaqus/Explicit has been employed and the hot rolling process was modeled in three dimensions. The appropriate models for heat transfer mechanisms are considered and the temperature distribution along the rolled strip and the temperature variation during hot strip rolling process is predicted. The effects of various process parameters such as rolling speed, amount of thickness reduction, initial thickness of the strip and interface heat transfer coefficient are considered. To verify the validity of the model and predicted results, a multi-pass hot rolling program is used and a comparison is carried out between the predicted results by model with plant-recorded results. © 2011 Elsevier Ltd. All rights reserved.


Mohamadian S.,Iran University of Science and Technology | Shoulaie A.,Iran University of Science and Technology
IEEE Transactions on Power Delivery | Year: 2011

So far, various studies are carried out in the field of unbalance decomposition from harmonic distortion in three-phase systems, and several criteria are proposed to express the value of these two types of disturbances, separately. However, most of them do not comply with the standard definitions for the effective values of three-phase voltage and current. Furthermore, extensive investigations are not performed for the calculation of the decomposition factors in three-and four-wire three-phase systems. In this paper, sequence matrices are applied to phase and line voltage and current harmonics to calculate balanced and unbalanced components. Afterwards, according to IEEE Standard 14592010, new distinguishing factors are extracted for three-and four-wire installations. Also, a new index is introduced as total harmonic and unbalance distortion to have an overall consideration of the system disturbance. Finally, three illustrative examples are presented to show the ability of the proposed indices in evaluating unbalance and harmonic distortion in three-phase systems. © 2011 IEEE.


Alizadeh Pahlavani M.R.,Iran University of Science and Technology | Mohammadpour H.A.,Iran University of Science and Technology
Electric Power Systems Research | Year: 2011

In this paper, the impact of different gate-controlled series capacitor (GCSC) control methodologies on sub-synchronous resonance (SSR) problems of series capacitive compensated transmission lines is analyzed. The low-frequency power oscillation (LFPO) damping using GCSC also is studied. In these studies, the effect of the rating of the GCSC is also considered. Three different control methodologies are proposed: open loop, constant power, and Takagi-Sugeno (TS) fuzzy control. It is shown that the GCSC can damp both the SSR and LFPO using the constant power control (CPC) methodology. It is also shown that when the parameters of the CPC is optimized by the TS fuzzy controller, the third methodology can present a cost-effective solution for both the SSR and LFPO damping. In this work, the IEEE First Benchmark Model is employed, including a GCSC device, and the study is performed using MATLAB program. © 2010 Published by Elsevier B.V. All rights reserved.


Moeini R.,Iran University of Science and Technology | Afshar A.,Iran University of Science and Technology | Afshar M.H.,Iran University of Science and Technology
International Journal of Electrical Power and Energy Systems | Year: 2011

Real-time hydropower reservoir operation is a continuous decision-making process of determining the water level of a reservoir or the volume of water released from it. The hydropower operation is usually based on operating policies and rules defined and decided upon in strategic planning. This paper presents a fuzzy rule-based model for the operation of hydropower reservoirs. The proposed fuzzy rule-based model presents a set of suitable operating rules for release from the reservoir based on ideal or target storage levels. The model operates on an 'if-then' principle, in which the 'if' is a vector of fuzzy premises and the 'then' is a vector of fuzzy consequences. In this paper, reservoir storage, inflow, and period are used as premises and the release as the consequence. The steps involved in the development of the model include, construction of membership functions for the inflow, storage and the release, formulation of fuzzy rules, implication, aggregation and defuzzification. The required knowledge bases for the formulation of the fuzzy rules is obtained form a stochastic dynamic programming (SDP) model with a steady state policy. The proposed model is applied to the hydropower operation of "Dez" reservoir in Iran and the results are presented and compared with those of the SDP model. The results indicate the ability of the method to solve hydropower reservoir operation problems. © 2010 Elsevier Inc. All rights reserved.