Tehran, Iran

Amirkabir University of Technology , formerly called the Tehran Polytechnic, is a public research university located in Tehran, Iran. AUT is one of the most prestigious universities, and the first established technical university in Iran, referred to as "Mother of Industrial Universities".The university was first founded by Habib Nafisi in 1958 and then developed by Dr. Mohammad Ali Mojtahedi, during the reign of the Pahlavi dynasty. Originally named the Tehran Polytechnic, it began its activities with five engineering departments. Six months before the victory of 1979 Iranian Revolution, Tehran Polytechnic was renamed after the famed Iranian prime minister Amir Kabir . With its expansion, the university now boasts fifteen science and engineering departments, and two other affiliated centers, located in Bandar Abbas and Mahshahr. There are currently around 9,100 students enrolled in the undergraduate and graduate programs. AUT has 480 full-time academic faculty members and 550 administrative employees. This gives AUT the highest staff-to-student ratio among the country's universities. The executive branch consists of four departments which receive active participation from various councils in planning and administering affairs.AUT has signed mutual agreements with international universities for research and educational collaboration. There is a joint program between AUT and the University of Birmingham.AUT is one of the leading universities in E-Learning systems in Iran which has begun its activities in 2004.Amirkabir University is the pioneer of sustainable development in Iran and established the AUT's Office of Sustainability on July 2011. The activities of the Office of Sustainability contribute to AUT's campus by reducing energy consumption, costs, and emissions, and also student coursework, volunteer opportunities for students, as well as research and education academic activities on sustainable development. Wikipedia.

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Eynbeygui M.,Amirkabir University of Technology | Aghdam M.M.,Amirkabir University of Technology
Meccanica | Year: 2017

This paper deals with a two-dimensional generalized plane strain micro-mechanical model to simulate semi-coupled thermo-electro-elastic behavior of transversely polarized piezoelectric fibrous composites. The solution domain includes a representative volume element (RVE) consists of a long piezoelectric fiber surrounded by corresponding matrix in a square array arrangement. Fibers have orthotropic and/or transversely isotropic properties while are perfectly bonded to the isotropic matrix. In addition, the constituents are assumed to have linear thermo-electro-elastic behavior. The virtual form of equilibrium equations has been extended to cover the semi-coupled thermo-electro-elastic loading by using appropriate constitutive relations. The element-free Galerkin method is employed to discretize the governing equations in terms of three main primary variables including, displacements, electric potential and temperature. The performance of the present micro-mechanical study reveals close agreement compared with other techniques available in the literature. Based on the present study, ample results are addressed to provide an insight into the effects of the local fields, i.e. displacement, electric potential, electric field, and stress distributions within the RVE for the specific fiber volume fraction. © 2017 Springer Science+Business Media Dordrecht

Fakharan Z.,Amirkabir University of Technology | Naji L.,Amirkabir University of Technology
Journal of Alloys and Compounds | Year: 2017

This paper describes the effect of localized surface plasmon resonance (LSPR) in the non-fullerene bulk heterojunction polymer solar cells (BHJ PSCs) by incorporating Agx-TiO2 nanocomposites into the active layer. Four types of Agx-TiO2 nanocomposites with different contents of Ag and distinctly different crystallite size and great uniformity were synthesized to systematically probe their influences on photovoltaic performances of PSCs. The nanocomposites were studied using x-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and diffuse reflectance spectroscopy (DRS) and were compared with the corresponding data of pure TiO2. The crystallite size of Agx-TiO2 decreased as the Ag content of the nanocomposites increased. The effect of Agx-TiO2 on the chemical and optical properties of P3HT was studied using UV–Vis spectroscopy, photoluminescence (PL) spectroscopy and cyclic voltammetry (CV) technique. The electron-hole recombination rate and also the band gap of P3HT were significantly decreased in combination with Agx-TiO2. I–V characteristics of PSC devices improved significantly as the Ag content of the Agx-TiO2 nanocomposites increased. The best devices were found to have an open circuit voltage (VOC) of about 1 V and power conversion efficiency (PCE) of about three times higher than that obtained for TiO2-based devices, prepared at the same conditions. PCE of these devices was however about 28% lower than that of PCBM-based PSC devices fabricated in this work. The current study shed light on how plasmonic nanostructures of Agx-TiO2 influences light absorption, exciton generation, exciton dissociation and charge transport inside non-fullerene based PSC devices. © 2017 Elsevier B.V.

Barati M.R.,Amirkabir University of Technology
International Journal of Engineering Science | Year: 2017

In this paper, a general bi-Helmholtz nonlocal strain-gradient elasticity model is developed for wave dispersion analysis of porous double-nanobeam systems in thermal environments. The present model incorporates three scale coefficients to examine wave dispersion relations much accurately. Porosity-dependent material properties of inhomogeneous nanobeams are defined via a modified power-law function. Based on Hamilton's principle, the governing equations of double-nanobeam system on elastic substrate are obtained. Solving analytically these equations gives wave frequencies and phase velocities as a function of wave number. It is demonstrated that phase velocities of a nanoporous double-nanobeam system rely on the porosities, thermal loading, material gradation, nonlocal parameters, strain gradient parameter, interlayer springs, elastic substrate and wave number. © 2017 Elsevier Ltd

Saber-Samandari S.,Eastern Mediterranean University | Saber-Samandari S.,Amirkabir University of Technology
Materials Science and Engineering C | Year: 2017

Significant efforts have been made to develop a suitable biocompatible scaffold for bone tissue engineering. In this work, a chitosan-graft-poly(acrylic acid-co-acrylamide)/hydroxyapatite nanocomposite scaffold was synthesized through a novel multi-step route. The prepared scaffolds were characterized for crystallinity, morphology, elemental analysis, chemical bonds, and pores size in their structure. The mechanical properties (i.e. compressive strength and elastic modulus) of the scaffolds were examined. Further, the biocompatibility of scaffolds was determined by MTT assays on HUGU cells. The result of cell culture experiments demonstrated that the prepared scaffolds have good cytocompatibility without any cytotoxicity, and with the incorporation of hydroxyapatite in their structure improves cell viability and proliferation. Finally, celecoxib as a model drug was efficiently loaded into the prepared scaffolds because of the large specific surface area. The in vitro release of the drug displayed a biphasic pattern with a low initial burst and a sustained release of up to 14 days. Furthermore, different release kinetic models were employed for the description of the release process. The results suggested that the prepared cytocompatible and non-toxic nanocomposite scaffolds might be efficient implants and drug carriers in bone-tissue engineering. © 2017 Elsevier B.V.

Asadi H.,University of Alberta | Asadi H.,Amirkabir University of Technology | Souri M.,Shahrood University of Technology | Wang Q.,City University of Hong Kong
Composite Structures | Year: 2017

In this research, the aerothermoelastic behaviors of supersonic functionally graded carbon nanotube reinforced composite (FG-CNTRC) flat panels in thermal environments are scrutinized. The dynamic model of the FG-CNTRC flat panel is developed on the basis of the first-order shear deformation theory incorporating von Karman geometrical nonlinearity. The thermomechanical properties of carbon nanotubes and polymer matrix are assumed to be temperature-dependent. The aerodynamic pressure is calculated according to the first-order supersonic piston theory. Adopting the discrete singular convolution method, the equations of motion and boundary conditions are converted into a set of algebraic equations. Ample numerical results are presented to highlight the aerothermoelastic responses of the FG-CNTRC flat panel considering various influential parameters such as CNT volume fraction and distribution, boundary conditions, thermal environments, geometrical parameters and Mach number. The results reveal that CNT distribution and volume fraction play a key role in enhancing the aerothermoelastic responses of FG-CNTRC flat panels. It is also found that presence of the aerodynamic pressure plays an essential role not only in the onset of aerothermal buckling instability, but also in changing the vibration and buckling mode shapes of FG-CNTRC flat panels. © 2017 Elsevier Ltd

Khaleghi H.,Amirkabir University of Technology
Aerospace Science and Technology | Year: 2017

This paper reports on a numerical investigation of the radial penetration of injectors in a high-speed axial fan. Four annular injectors with different radial heights were placed over the casing and choke to stall unsteady computations were performed for each case. Results reveal that as long as the blade is “wall–stall” (i.e., stall is initiated from the tip), range extension is mostly due to injecting into the tip of the blade. If the injector is located close enough to the blade, however, increasing the radial penetration of the injector can provide considerable range extension by changing the rotor stalling mode from “wall–stall” to “blade–stall”. The rotor with zero tip clearance has been also studied in the current work. Results show that endwall injection can desensitize the compressor to the detrimental effects of the tip clearance. © 2017 Elsevier Masson SAS

Mohammadzadeh-Keleshteri M.,Amirkabir University of Technology | Asadi H.,Amirkabir University of Technology | Asadi H.,University of Alberta | Aghdam M.M.,Amirkabir University of Technology
Composite Structures | Year: 2017

The objective of this research is to scrutinize large amplitude vibration response of functionally graded carbon nanotube reinforced composite (FG-CNTRC) annular sector plates with surface-bonded piezoelectric layers. A nonlinear formulation is derived based on the first-order shear deformation theory (FSDT), von Karman geometrical nonlinearity along with the Hamilton principle. The distribution of electric potential through the thickness of the piezoelectric layers is simulated by a sinusoidal function. The closed circuit electrical boundary condition is taken into consideration for the top and bottom surfaces of the piezoelectric layers. The nonlinear dynamic equations, boundary conditions and Maxwell equation are discretized using the generalized differential quadrature method and direct iterative method is then employed to solve the nonlinear system of equations. The variation of nonlinear frequency versus the vibration amplitude is highlighted considering various influential parameters such as distribution and volume fraction of the CNTs, geometrical parameters, boundary conditions and the thickness of the piezoelectric layers. It is found that the dynamic responses of the CNTRC sector plate may be noticeably enhanced by adjusting values of the CNT volume fraction and distribution. The numerical results reveal that the increase in the nonlinear frequency descents at certain vibration amplitude owing to vibration mode redistribution. © 2017 Elsevier Ltd

Nasouri K.,Amirkabir University of Technology | Shoushtari A.M.,Amirkabir University of Technology
Composites Science and Technology | Year: 2017

Lightweight conductive multi-walled carbon nanotubes (MWCNTs)/polyvinyl alcohol (PVA) composite nanofibers were prepared by electrospinning process with an aim to investigate the potential of such nanofibers as an effective electromagnetic interference (EMI) shielding material. The influence of MWCNTs content, thickness, and frequency on the EMI shielding of conductive MWCNTs/PVA composite nanofiber has been investigated. These experiments were designed by response surface methodology (RSM) and quadratic model was used to calculation of the responses. The predicted responses were in good agreement with the experimental results according to RSM model. The RSM analysis confirmed that MWCNTs content and thickness were the main significant variables affecting the absorption shielding effectiveness. Moreover, the sample thickness has no significant influence on the reflection shielding effectiveness. The RSM model predicted the 31.5 dB value of the highest absorption with low reflection (8.8 dB) at conditions of 7.7 wt% MWCNTs content, 3 mm of the sample thickness, and 12 GHz of incident EM wave frequency. The obtained RSM results confirmed that the selected RSM model presented suitable performance for evaluating the involved variables and prediction of EMI shielding parameters. © 2017 Elsevier Ltd

Kamarian S.,Amirkabir University of Technology | Shakeri M.,Amirkabir University of Technology
Composites Part B: Engineering | Year: 2017

This paper deals with analysis and optimization of rectangular and skew composite plates with embedded Shape Memory Alloy (SMA) wires with respect to thermal buckling. The governing equations are derived based on First Order Shear Deformation Theory (FSDT) and the critical buckling temperatures are calculated using Generalized Differential Quadrature (GDQ) method. The influences of SMA volume fraction, lay-up orientation, pre-strain of SMA fibers, dependency of material properties on temperature, and geometrical parameters like skew angle on thermal buckling of the structure are examined. Results demonstrate that SMAs can play a significant role in delaying buckling when the structure is under thermal loads. Then, in the second part of results, optimization of shape memory alloy hybrid composite (SMAHC) plates is presented in order to maximize critical buckling temperatures. A four-layer composite plates with two SMA-reinforced layers is considered for the optimization problem in which the orientations of fibers are the optimization variables. As the critical buckling temperatures cannot be obtained through a closed-form solution, the optimization process takes a lot of time. Therefore, a powerful meta-heuristic algorithm called Firefly Algorithm (FA) is implemented to find the best answers. A comprehensive verification study is also performed to indicate the accuracy and efficiency of both GDQ solution and optimization process. © 2017

Sahmani S.,Amirkabir University of Technology | Aghdam M.M.,Amirkabir University of Technology
Composites Part B: Engineering | Year: 2017

The size-dependent radial buckling and postbuckling behavior of functionally graded cylindrical shells at nanoscale integrated with piezoelectric nanolayers is studied in this paper on the basis of nonlocal elasticity theory within the framework of exponential shear deformation shell theory to capture the influence of transverse shear deformation in a refined form. By introducing a new reference surface, the stretching-bending coupling terms due to unsymmetrical material characteristics related to the functionally graded substrate of nanoshell are removed. After that, with the aid of boundary layer of shell buckling, the non-classical partial nonlinear differential equations are constructed to describe the nonlocal instability of nanoscaled shells. Finally, a perturbation-based solution methodology is utilized to propose explicit expressions for the nonlocal equilibrium paths associated with the both prebuckling and postbuckling domains of hybrid functionally graded nanoshells subjected to the combination of hydrostatic pressure and lateral electric field. It is seen that the nonlocality size effect causes to reduce the critical hydrostatic pressure, but it leads to increase the associated shortening of the movable ends of hybrid functionally graded nanoshells. © 2017 Elsevier Ltd

Kabir M.-Z.,Amirkabir University of Technology | Tavousi Tehrani B.,Amirkabir University of Technology
Composite Structures | Year: 2017

In this paper, an analytical study on thermal, mechanical, and thermomechanical buckling and post-buckling of symmetric laminated composite plates reinforced with shape memory alloy (SMA) fibers are presented. The closed-form solution used in this study is developed based on the FSDT incorporated with the Von-Karman non-linear strains. The effect of SMA fibers is captured by adding a tensile recovery, stress term that determined using 1-D simplified Brinson's model, in the constitutive equations of the SMA composite plate. Galerkin technique is implemented for solving the nonlinear partial differential equations of motion to obtain buckling load and post-buckling path. The influence of several parameters such as SMA activation temperature, SMA fiber volume fraction, SMA pre-strain, biaxial ratio, etc., are studied in this work. Due to the generation of recovery force, significant improvement in buckling load is attained by increasing each of the SMA fiber volume fraction, activation temperature or SMA pre-strain. © 2017 Elsevier Ltd

Jafarinezhad M.R.,Islamic Azad University at Tehran | Eslami M.R.,Amirkabir University of Technology
Composite Structures | Year: 2017

This study deals with the response of an FGM annular plate under lateral thermal shock load. The equations of motion are obtained using the first order shear deformation plate theory. The governing equations are solved using the Laplace transformation and Galerkin finite element method. Finally, numerical inversion of the Laplace transform is carried out to obtain the results in real time domain. It is shown that coupling coefficient has a damping effect on the radial force resultant and deflection. © 2017 Elsevier Ltd

Dehghan M.,Amirkabir University of Technology | Abbaszadeh M.,Amirkabir University of Technology
Engineering Analysis with Boundary Elements | Year: 2017

The collocation technique based on the radial basis functions (RBFs) method is simple and efficient for solving a wide area of problems. But the mentioned technique is poor for solving problems that have shock (advection problems) or the discontinuous initial condition. The local RBFs collocation technique is a meshless method based on the strong form. The use of local collocation RBFs method overcomes the mentioned important issue. In the current paper, based on the proposed idea in Wang (2015) [54], we consider a linear combination of shape functions of local radial basis functions collocation method and moving Kriging interpolation technique. For showing the efficiency of new technique, some multi-dimensional problems such as Cahn-Hilliard, Swift-Hohenberg and phase field crystal equations have been chosen. Moreover, several test problems are given that show the acceptable accuracy and efficiency of the proposed scheme. © 2017 Elsevier Ltd

Bahmyari E.,Amirkabir University of Technology | Khedmati M.R.,Amirkabir University of Technology
Acta Mechanica | Year: 2017

A novel computational scheme called the Chaotic Radial Basis Function is presented in this paper for quantification of uncertainties in bending analysis of moderately thick plates with elastically restrained edges under lateral loading. The plate modulus of elasticity, the stiffness of the elastically restrained edges, and the lateral loading on the plate are considered as random processes and are represented by using the Karhunen–Loève expansion which is based on a linear combination of the eigenfunctions of the covariance function with uncorrelated random variables. These random variables which could have any types of probability measures constitute the random space of the stochastic problem. The proposed method relies on discretizing the random space by a set of properly distributed nodes and then employing a Galerkin-Chaotic Radial Basis Function scheme to derive the coupled deterministic set of equations governing the stochastic plate bending. The accuracy of the proposed method is investigated by comparing the results obtained by the method with those of the Monte Carlo method. It is seen that the presented method provides accurate results with a considerably less computational cost in comparison to the Monte Carlo simulation. Further, the effect of coefficients of variations of the plate module of elasticity, applied loading and the stiffness of the restrained edges as well as the influence of the correlation lengths, aspect ratio and the plate thickness are investigated on the statistics of the plate deflection. © 2017 Springer-Verlag Wien

Khaksar-e Oshagh M.,Amirkabir University of Technology | Shamsi M.,Amirkabir University of Technology
Mathematical Methods in the Applied Sciences | Year: 2017

In this paper, a computational technique based on the pseudo-spectral method is presented for the solution of the optimal control problem constrained with elliptic variational inequality. In fact, our aim in this paper is to present a direct approach for this class of optimal control problems. By using the pseudo-spectral method, the infinite dimensional mathematical programming with equilibrium constraint, which can be an equivalent form of the considered problem, is converted to a finite dimensional mathematical programming with complementarity constraint. Then, the finite dimensional problem can be solved by the well-developed methods. Finally, numerical examples are presented to show the validity and efficiency of the technique. © 2017 John Wiley & Sons, Ltd.

Ahmadi-Javid A.,Amirkabir University of Technology | Hooshangi-Tabrizi P.,Amirkabir University of Technology
Computers and Operations Research | Year: 2017

This paper addresses a ternary-integration scheduling problem that incorporates employee timetabling into the scheduling of machines and transporters in a job-shop environment with a finite number of heterogeneous transporters where the objective is to minimize the completion time of all jobs. The problem is first formulated as a mixed-integer linear programming model. Then, an Anarchic Society Optimization (ASO) algorithm is developed to solve large-sized instances of the problem. The formulation is used to solve small-sized instances and to evaluate the quality of the solutions obtained for instances with larger sizes. A comprehensive numerical study is carried out to assess the performance of the proposed ASO algorithm. The algorithm is compared with three alternative metaheuristic algorithms. It is also compared with several algorithms developed in the literature for the integrated scheduling of machines and transporters. Moreover, the algorithms are tested on a set of adapted benchmark instances for an integrated problem of machine scheduling and employee timetabling. The numerical analysis suggests that the ASO algorithm is both effective and efficient in solving large-sized instances of the proposed integrated job-shop scheduling problem. © 2017 Elsevier Ltd

Ebrahimi H.,Amirkabir University of Technology | Rahmani M.,Amirkabir University of Technology
International Journal of Hydrogen Energy | Year: 2017

The current work presents modeling and simulation of a membrane micro-fixed bed reactor to produce and separate hydrogen. In contrast to commonly hydrogen production in chemical looping reforming (CLR), hydrogen is produced here in a reduction cycle of chemical looping combustion without employing steam. After validating the model with experimental data found in the literature, the adapted mathematical model was employed to study the performance of membrane microreactor. The results show that employing membrane assisted chemical looping combustion for reduction cycle, not only separate the valuable hydrogen, but it also increases total hydrogen production. Two dimensional model shows that diffusion fluxes, both axial and radial are important in the microreactor. Temperature analysis shows that total hydrogen production is decreased by increasing temperature. By contrary, permeate flux passing through the membrane is increased at elevated temperatures. More hydrogen may be produced by using a membrane with higher permeability and employing a high surface to volume membrane microreactor. © 2016 Hydrogen Energy Publications LLC

Khosravi Bizhaem H.,Amirkabir University of Technology | Basirat Tabrizi H.,Amirkabir University of Technology
Powder Technology | Year: 2017

Gas-solid flow behavior in a pulsed fluidized bed was studied experimentally and numerically. Eulerian-Eulerian two-fluid model approach in conjunction with the kinetic theory of granular flow was used for simulation of dense gas-solid flow. The effect of pulsating flow with frequency range of 1 to 10 Hz for particle sizes of Geldart B and A/B group with variation of particle density was investigated. Model simulation results were compared reasonably well with researcher's findings and the experimental data. Time-averaged local pressure drop and solid volume fraction were obtained and the effect of various pulsation frequencies on the bed expansion ratio, solid volume fraction, voidage and solid axial velocity was discussed. By increasing the pulsation frequency up to 10 Hz, results show reduction in the bubble size, bed expansion ratio and pressure fluctuation. Time-averaged axial velocity and voidage have a flatter profile with increasing pulsation frequency. © 2017 Elsevier B.V.

Pichan M.,Amirkabir University of Technology | Rastegar H.,Amirkabir University of Technology | Monfared M.,Ferdowsi University of Mashhad
IEEE Transactions on Industrial Electronics | Year: 2017

Distributed generation (DG) has been considered as an alternative source of power generation, especially in stand-alone applications, where both single- and three-phase loads must be supplied with fixed amplitude and frequency sinusoidal voltages. Therefore, the presence of the neutral wire is inevitable. A four-leg inverter is a common solution to connect DGs to stand-alone loads as well as providing the neutral wire. In this paper, by considering a filter inductor in the fourth (neutral) leg of the four-leg inverter, a detailed model is presented, which illustrates a strong coupling among different phases. In order to remove this coupling effect, it is proposed to transform the quantities from the abc to the αβγ reference frame. Furthermore, based on the proposed decoupled model, a new deadbeat control scheme is proposed to provide balanced sinusoidal voltages at the output of the inverter. To confirm the effectiveness of the proposed modeling and control techniques, experimental results on a 3-kW setup with the digital-signal-processor-based digital controller are provided under various loading conditions, such as linear/nonlinear, balanced/unbalanced, and single-/three-phase loads. © 2017 IEEE.

Rezaei M.H.,Amirkabir University of Technology | Menhaj M.B.,Amirkabir University of Technology
IET Control Theory and Applications | Year: 2017

The stationary average consensus problem is studied for high-order multi-agent systems (MASs) under balanced directed networks. The objective is to bring the positions of agents to the average of their initial positions while allowing all the remaining states (e.g., velocity, acceleration, and higher-order states) to converge to zero. To this end, the authors propose two consensus protocols for high-order MASs in two cases: (i) state-feedback control, which assumes that each agent has access to its own states as well as the relative positions of its neighbours; and (ii) output-feedback control, where each agent measures only its own position and the relative positions of its neighbours. Two case studies are given to illustrate the advantages and effectiveness of the proposed protocols. In the first case study, a state-feedback controller is designed for consensus-based formation control of a team of vertical take-off and landing aircraft. In the second case study, an output-feedback consensus protocol is designed for a third-order MAS and compare it with a recent technique from the literature. © The Institution of Engineering and Technology 2016.

Mehri M.,Sharif University of Technology | Asadi H.,University of Alberta | Asadi H.,Amirkabir University of Technology | Kouchakzadeh M.A.,Sharif University of Technology
Computer Methods in Applied Mechanics and Engineering | Year: 2017

As a first endeavor, the aeroelastic responses of functionally graded carbon nanotube reinforced composite (FG-CNTRC) truncated conical curved panels subjected to aerodynamic load and axial compression are investigated. The nonlinear dynamic equations of FG-CNTRC conical curved panels are derived according to Green's strains and the Novozhilov nonlinear shell theory. The aerodynamic load is estimated in accordance with the quasi-steady Krumhaar's modified supersonic piston theory by taking into account the effect of the panel curvature. Matrix transform method along with the harmonic differential quadrature method (HDQM) are employed to solve the nonlinear equations of motion of the FG-CNTRC truncated conical curved panel. The advantage of the matrix transform method is that we only need to discretize the meridional direction. Effects of semi-vertex angle of the cone, subtended angle of the panel, boundary conditions, geometrical parameters, volume fraction and distribution of CNT, and Mach number on the aeroelastic characteristics of the FG-CNTRC conical curved panel are put into evidence via a set of parametric studies and pertinent conclusions are outlined. The results prove that the panels with different FG distributions have different critical dynamic pressure. It is found that the semi-vertex and subtended angles play a pivotal role in changing the critical circumferential mode number of the flutter instability. Besides, the research shows that the superb efficiency of proposed method with few grid points, which requires less CPU time, are attributed to the matrix transform method and the higher-order harmonic approximation function in the HDQM. © 2017 Elsevier B.V.

Dehghanbaghi N.,Amirkabir University of Technology | Sajadieh M.S.,Amirkabir University of Technology
Computers and Industrial Engineering | Year: 2017

In this paper, we consider the joint optimization of production, inventory, transportation and pricing policies in a multi-product two-stage supply chain. The products are complementary and their demands are not only dependent on their own price but also on their complementary product price. Mathematical model of the problem is presented in both centralized and decentralized supply chains. Exact algorithms are presented using mathematical and convexity analysis to solve mixed integer nonlinear models. Numerical studies show that the profit of centralized supply chain is more stable compared to decentralized supply chain when the dependency rate of products changes. © 2017 Elsevier Ltd

Karimi N.,Amirkabir University of Technology | Davoudpour H.,Amirkabir University of Technology
Computers and Operations Research | Year: 2017

This paper investigates scheduling of jobs with deadlines across a serial multi-factory supply chain which involves minimizing sum of total tardiness and total transportation costs. Jobs can be transported among factories and can be delivered to the customer in batches which have limited capacity. The aim of this optimization problem is threefold: (1) determining the number of batches, (2) assigning jobs to batches, and (3) scheduling the batches production and delivery in each factory. The proposed problem formulated as a mixed-integer linear program. Then the model's performance is analyzed and evaluated through two examples. Moreover, a knowledge-based imperialistic competitive algorithm (KBICA) is also presented to find an approximate optimum solution for the problem. Computational experiments of the proposed problem investigate the efficiency of the method through different sizes of the test problems. © 2016 Elsevier Ltd

Kowsari E.,Amirkabir University of Technology | Chirani M.R.,Amirkabir University of Technology
Carbon | Year: 2017

For the first time, we report on the preparation of highly effective electrolyte additive by combining graphene oxide (GO) covalently functionalized with ammonium-based ionic liquid in dye-sensitized solar cell (DSSC). GO was modified in two-step, first, with 1–6, hexamethylenediamine then, the products were reacting with alkyl-halide. The effects of GO- hexamethylene tributyl-ammonium iodide and GO-hexamethylene trimethyl-ammonium iodide as additives on the photovoltaic performance of DSSCs were studied to find the ideal characteristics for minimize the aggregation in ionic liquids based electrolytes. The investigation showed the addition of IL-functionalized GO forms a molecular bridge for electrons transfer in the ionic liquid based electrolyte that has a significant increase in photovoltaic density (Jsc) from 7.141 to 16.847 mA cm−2 more than twice. Under an optimized additive/electrolyte ratio of 4 wt%, the conversion efficiency of DSSCs was remarkably enhanced to 8.33% from initial 3.96% that of referenced ionic liquids-based device. Furthermore, based on these nanocomposite electrolytes, the resulting DSSCs exhibited better electron diffusion coefficient of I− and I3 − and ionic conductivity which improves Jsc. It is anticipated that this work may provide an effectual way to develop nanocomposite consisting of graphene derivatives as a great potential for practical application. © 2017 Elsevier Ltd

Ebrahimi F.,Imam Khomeini International University | Barati M.R.,Amirkabir University of Technology
Composite Structures | Year: 2017

This paper investigates damping vibration characteristics of hygro-thermally affected functionally graded (FG) viscoelastic nanobeams embedded in viscoelastic foundation based on nonlocal strain gradient elasticity theory. The modeling of nanobeam is carried out via a higher order refined beam theory which captures shear deformation influences needless of any shear correction factor. The viscoelastic foundation is consists of Winkler-Pasternak layer together with a viscous layer of infinite parallel dashpots. Power-law model is adopted to describe continuous variation of temperature-dependent material properties of FG nanobeam. The governing equations of nonlocal strain gradient viscoelastic nanobeam in the framework of refined beam theory are obtained using Hamilton's principle and solved implementing an analytical solution for different boundary conditions. To validate the presented model, the results are compared with those of elastic nanobeams. The effects of linear, shear and viscous layers of foundation, structural damping coefficient, hygro-thermal environment, nonlocal parameter, material characteristic parameter, power-law exponent, mode number, boundary conditions and slenderness ratio on the frequency response of viscoelastic FG nanobeams are investigated. © 2016

Omidi O.,University of Tennessee at Knoxville | Lotfi V.,Amirkabir University of Technology
Soil Dynamics and Earthquake Engineering | Year: 2017

Seismic nonlinear analysis of concrete arch dams is a topic having been extensively studied in the last two decades. Due to the existence of different joints within the body of arch dams, the discrete crack (DC) approach utilizing interface elements for the joints is the most realistic method. In fact, it could be the first step to assess the seismic safety of an arch dam. Furthermore, since the mass concrete blocks may crack due to severe ground excitations, a plastic–damage (PD) model well capturing stiffness degradation and permanent deformation due to tensile cracking and compressive crushing might be needed. In this study, a special finite element program called SNACS is developed based on the combined discrete crack and plastic–damage (DC–PD) technique. The dam–reservoir interaction as an important factor affecting the seismic response of arch dams is also treated by the Lagrangian–Eulerian formulation. The joints modeling strategy adopted herein is addressed first and then, a brief review of the plastic–damage model proposed by Lee and Fenves and extended herein to 3-D space is presented. Afterwards, the nonlinear seismic analysis of a typical thin arch dam is performed based on the combined approach and the response is compared with the results of each method. It is emphasized that employing the combined DC and PD models gives more reliable and consistent response in comparison with using DC or PD approaches applied alone. Therefore, the DC–PD technique could be considered as a major step toward a more accurate seismic safety evaluation of concrete arch dams. © 2017 Elsevier Ltd

Ghayempour S.,Amirkabir University of Technology | Montazer M.,Amirkabir University of Technology
Ultrasonics Sonochemistry | Year: 2017

Application of natural biopolymers for green and safe synthesis of zinc oxide nanoparticles on the textiles is a novel and interesting approach. The present study offers the use of natural biopolymer, Tragacanth gum, as the reducing, stabilizing and binding agent for in-situ synthesis of zinc oxide nanoparticles on the cotton fabric. Ultrasonic irradiation leads to clean and easy synthesis of zinc oxide nanoparticles in short-time at low-temperature. FESEM/EDX, XRD, FT-IR spectroscopy, DSC, photocatalytic activities and antimicrobial assay are used to characterize Tragacanth gum/zinc oxide nanoparticles coated cotton fabric. The analysis confirmed synthesis of star-like zinc oxide nanoparticles with hexagonal wurtzite structure on the cotton fabric with the average particle size of 62 nm. The finished cotton fabric showed a good photocatalytic activity on degradation of methylene blue and 100% antimicrobial properties with inhibition zone of 3.3 ± 0.1, 3.1 ± 0.1 and 3.0 ± 0.1 mm against Staphylococcus aureus, Escherichia coli and Candida albicans. © 2016 Elsevier B.V. All rights reserved.

Daryaei R.,Amirkabir University of Technology | Eslami A.,Amirkabir University of Technology
Soil Dynamics and Earthquake Engineering | Year: 2017

Explosive Compaction (EC) or Blast Densification (BD) has been commonly used as one of the deep soil improvement techniques to densify loose, saturated granular soils. Soil is compacted due to huge compression force of explosion in several depths and the corresponding liquefaction. Among soil characteristics, settlement is important since it is a fast and easy indicator of layer compaction degree. To measure settlement instrumentation can be used but they are expensive and susceptible to damage due to explosion. Predicting settlement using empirical equations is also another method, however, they cannot consider soil complex behavior and are consequently inaccurate. In this study, numerical approach has been used to evaluate settlement and excess pore water pressure (PWP) during and after explosion, using finite element software PLAXIS3D, in which the UBCSAND soil model has been employed to represent saturated sand. This model is capable of calculating PWP buildup due to dynamic loads such as earthquake and explosion. This method was calibrated and compared, using well-known case histories in the literature. Results of settlement from these cases, were compared with both empirical equations and measured site values. Pulses of PWP due to shock wave were also calculated by the model as well as PWP buildup until reaching liquefaction zone. Predictions from this approach were more accurate than empirical equations. Moreover, it was revealed that the rate of settlement and PWP dissipation is proportionate to soil's permeability. Thus, numerical approach can be confidently implemented to evaluate soil characteristics. © 2017

Khadangi E.,Amirkabir University of Technology | Bagheri A.,Amirkabir University of Technology
Computers in Human Behavior | Year: 2017

There are more important relationships based on users' behavior and the done activities than those of friendship in online social networks. Study of social behavior of users in these networks has many applications. Analyzing online social networks' activity graphs, as a better representation of users' social behavior, may open new perspectives for real applications such as finding important users. Although detecting these influential nodes based on their friendship relationships is studied a lot, finding important nodes using users' behavior and activates has not attracted much attention. In this work, we study users' importance in various Facebook activity networks including like, comment, post, share, and mixed, then compare gained rankings with those of the friendship network and conclude that users influence analysis in activity networks represents very different results. Afterwards, we propose new centrality measures that can present different rankings suitable for different applications, further to have the potential for simultaneous consideration of various activities in a multilayer network. Experimental results highlights the benefits of using the presented methods. To the best of our knowledge, our methods are the first and only proposed centrality measures that can present different rankings for various applications based on users' social behavior. © 2017 Elsevier Ltd

Karimi Z.,Amirkabir University of Technology | Ghidary S.S.,Amirkabir University of Technology
Neurocomputing | Year: 2017

Manifold-based semi-supervised classifiers have attracted increasing interest in recent years. However, they suffer from over learning of locality and cannot be applied to the point cloud sampled from a stratified space. This problem is resolved in this paper by using the fact that the smoothness assumption must be satisfied with the interior points of the manifolds and may be violated in the non-interior points. Distinction of interior and non-interior points is based on the behavior of graph Laplacian in the ϵ-neighborhood of the intersection points. First, this property was generalized to KNN graph representing the stratified space and then a new algorithm was proposed that penalizes the smoothness on the non-interior points of the manifolds by modifying the edge weights of the graph. Compared to some recent multi-manifold semi-supervised classifiers, the proposed method does not require neither knowing the dimensions of the manifolds nor large amount of unlabeled points to estimate the underling manifolds and does not assume similar properties for neighbors of all data points. Some experiments have been conducted in order to show that it improves the classification accuracy on a number of artificial and real benchmark data sets. © 2017 Elsevier B.V.

Saryazdi M.G.H.,Amirkabir University of Technology
Pramana - Journal of Physics | Year: 2017

Mathieu equation is a well-known ordinary differential equation in which the excitation term appears as the non-constant coefficient. The mathematical modelling of many dynamic systems leads to Mathieu equation. The determination of the locus of unstable zone is important for the control of dynamic systems. In this paper, the stable and unstable regions of Mathieu equation are determined for three cases of linear and nonlinear equations using the homotopy perturbation method. The effect of nonlinearity is examined in the unstable zone. The results show that the transition curves of linear Mathieu equation depend on the frequency of the excitation term. However, for nonlinear equations, the curves depend also on initial conditions. In addition, increasing the amplitude of response leads to an increase in the unstable zone.

Hybrid nanocomposites based on high-density polyethylene (HDPE)/poly (ethylene-co-vinyl alcohol) (EVOH)/clay were prepared and fully characterized. Morphological (WAXS and TEM), calorimetric (DSC), and dynamic mechanical thermal (DMTA) analyses were applied to investigate potential of nanocomposites as barrier against oxygen. Co-existence of ingredients of different nature, i.e. HDPE (general-purpose non-polar component), EVOH (engineering polar component with excellent barrier properties), nanoclay (planar one-dimensional mineral barrier nanofiller), and maleated HDPE (PE-g-MA) as coupling agent, brings about serious intricacies in view of interaction between existing phases. Conceptual/experimental analysis was performed to explore the interdependence between microstructure and oxygen barrierity of HDPE/EVOH/clay nanocomposites through the lens of interaction state in the system. Morphological measurements confirmed formation of an intercalated nanostructure, while investigations on complex viscosity, storage modulus, permeability, thermo-mechanical properties, and nanoclay interlayer galleries were all indicative of dependence of nanocomposites' properties on molecular interactions. The performance of nanocomposite sheets as oxygen barriers was mechanistically explained. © 2017 Walter de Gruyter GmbH, Berlin/Boston 2017.

Moattari M.,Amirkabir University of Technology | Sattari-Far I.,Amirkabir University of Technology
Theoretical and Applied Fracture Mechanics | Year: 2017

Engineering structures may have significant lower crack-tip constraint compared with those in the standard fracture toughness test specimens. This paper considers a methodology to extend the application of fracture toughness master curve approach for structures with low crack-tip constraint. This is conducted by considering the Q-parameter as a suitable crack-tip constraint parameter, and study its effects on the reference temperature T 0 in the master curve approach. The experimental fracture toughness data from the literature as well as supplemental experiments are used for this purpose. The relation between Q and T 0 is investigated by using numerical analyses of experiments covering various types of geometry, loading condition, thickness and crack depth. The effects of loading amplitudes and material properties on the relation between Q and T 0 are also studied. Based on this study, a relationship between Q and T 0 is derived and experimentally verified. It is shown that the proposed relationship has a considerable ability to predict the apparent fracture toughness behavior in the ductile to brittle region of complex structures without need of conducting additional experimental fracture toughness tests. © 2017 Elsevier Ltd.

Taghizadeh H.,Sahand University of Technology | Tafazzoli-Shadpour M.,Amirkabir University of Technology
Journal of the Mechanical Behavior of Biomedical Materials | Year: 2017

Arterial wall tissues are sensitive to their mechanical surroundings and remodel their structure and mechanical properties when subjected to mechanical stimuli such as increased arterial pressure. Such remodeling is evident in hypertension and aging. Aging is characterized by stiffening of the artery wall which is assigned to disturbed elastin function and increased collagen content. To better understand and provide new insight on microstructural changes induced by aging, the lamellar model of the aortic media was utilized to characterize and compare wall structure and mechanical behavior of the young and old human thoracic aortic samples. Such model regards arterial media as two sets of alternating concentric layers, namely sheets of elastin and interlamellar layers. Histological and biaxial tests were performed and microstructural features and stress–strain curves of media were evaluated in young and old age groups. Then using optimization algorithms and hyperelastic constitutive equations the stress–strain curves of layers were evaluated for both age groups. Results indicated slight elevation in the volume fraction of interlamellar layer among old subjects most probably due to age related collagen deposition. Aging indicated substantial stiffening of interlamellar layers accompanied by noticeable softening of elastic lamellae. The general significant stiffening of old samples were attributed to both increase of volume fraction of interlamellar layers and earlier recruitment of collagen fibers during load bearing due to functional loss of elastin within wall lamellae. Mechanical characterization of lamellar structure of wall media is beneficial in study of arterial remodeling in response to alternated mechanical environment in aging and clinical conditions through coupling of wall microstructure and mechanical behavior. © 2016 Elsevier Ltd

Elhami S.,Amirkabir University of Technology | Razfar M.R.,Amirkabir University of Technology
International Journal of Advanced Manufacturing Technology | Year: 2017

Electrochemical discharge machining (ECDM) is a cost-effective machining process used to shape non-conductive materials such as glass and ceramics. The process can overcome poor machinability of hard and brittle materials. Different types of physical phenomena can be added to the ECDM components to improve the machining efficiency. As the main target of this paper, ultrasonic vibration was integrated to the cathode of the ECDM process (UAECDM), which resulted in vibration concentration only to the machining zone. In order to design the experimental configuration, modal analysis was used. Machining speed was the main output of this investigation. Gas film and electric discharge were two main physical phenomena during ECDM. The thickness of gas film, location, and pattern of discharges were determined, experimentally. Also, current signal was a useful tool that could record significant details of involved mechanisms and phenomena during machining. Images of gas film showed that the application of ultrasonic vibration decreased the thickness of gas film by 65%. In addition, the vibration amplitude of 10 μm created the most uniform current signal, which had a considerable effect on the material removal rate (MRR). Results showed that all levels of vibration amplitude increased the machining speed during discharge and hydrodynamic regimes of the machining process. © 2017 Springer-Verlag London

Shamisa A.,University of Tehran | Karrari M.,Amirkabir University of Technology
IET Generation, Transmission and Distribution | Year: 2017

In this study, a novel technique for fast transient stability limit assessment is proposed. In the proposed method, first the whole power system is approximated with a single machine equivalent model independent of the type and location of the fault, and its parameters are identified using on-line measured data. Next, a graphical index based on transient energy approach is presented for the transient stability limit. The proposed method is tested on a real 247-machine power network to all devices in service, and the load flow matched with real recorded data. Simulation studies show very promising results. Furthermore, they show that the defined stability index can be evaluated immediately after the fault clearing and can be accurately estimated even if does not exist any prior knowledge about the operating condition. This new method can be used for preventive security assessment in smart power systems. The results show that the proposed graphical stability limit can be used accurately as a measure for 'distance to critical clearing time' of relays. © 2016 The Institution of Engineering and Technology.

Ebrahimi M.,Amirkabir University of Technology | Jahangirian A.,Amirkabir University of Technology
Scientia Iranica | Year: 2015

An efficient parallel strategy is presented for optimization of the aerodynamic shapes using Genetic Algorithm (GA). The method is a hybrid Parallel Genetic Algorithm (PGA) that combines a multi-population PGA and master-slave PGA using Message Passing Interface. GA parameters are firstly tuned according to the fact that subpopulations evolve independently. The effect of the number of sub-population on the computational time is investigated. Finally, a new strategy is presented based on the load balancing that aims to decrease the idle time of the processors. The algorithm is used for optimization of a transonic airfoil. An unstructured grid finite volume ow solver is utilized for objective function evaluations. For the considered class of problems, the suggested Hierarchical Parallel Genetic Algorithm (HPGA) results in more than 30% reduction in optimization time in comparison to regular master-slave PGA. A semi-liner speed-up is also obtained which indicates that the model is suited for modern cluster work stations. © 2015 Sharif University of Technology. All rights reserved.

Hamedi G.H.,Guilan University | Moghadas Nejad F.,Amirkabir University of Technology
Journal of Materials in Civil Engineering | Year: 2017

This study is an attempt to identify the effective mix design and thermodynamic parameters for the moisture damage of hot mix asphalt. In the present study, 24 different combinations of asphalt mixtures were made and evaluated using three types of aggregates with different mineralogical composition, two types of asphalt binders, and three types of additives. The components of surface-free energy of asphalt binders and aggregates are measured to provide thermodynamic parameters using the Wilhelmy Plate and Universal Sorption Device, respectively. To determine the performance of moisture sensitivity, environmental conditions simulation according to the modified Lottman test was used, and an indirect tensile strength test has been conducted on asphalt mixtures. The results of statistical analysis presented show that the free energy of cohesion, free energy of asphalt binder-aggregate adhesion, specific surface area of aggregates, and asphalt binder film thickness on the aggregate surface have a direct impact, and the debonding energy of the system and permeability of the asphalt mixture have a reverse impact on asphalt mixture strength against the moisture damage. © 2016 American Society of Civil Engineers.

Akbari M.,Amirkabir University of Technology | Akbari M.,University of Oklahoma
Journal of Petroleum Science and Engineering | Year: 2017

Acid fracturing is one of the applicable methods to stimulate oil and gas wells and increase the production rate in a carbonate reservoir. Acid fracture conductivity is an important parameter for the designing a fracture job. The amount of rock dissolved, fracture surface etching patterns, rock strength, and closure stress impact the resulting acid fracture conductivity. A model of acid fracture conductivity must accurately anticipate the fracture conductivity under closure stress. The rock strength affects substantially the fracture conductivity. A serious challenge of recent studies has been to predict the behaviour of different formations under various closure stresses. This study developed a robust intelligent model based on genetic algorithm to precisely predict the fracture conductivity by incorporating experimental data from various formations, whereby resulted in a good match between the model predictions and the experimental data. The effect of rock strength was investigated on the fracture conductivity under various closure stresses. The results show the rock strength plays a significant role when anticipating fracture conductivity, as various formations have behaved differently under different closure stresses. Furthermore, due to the complexity of rock behaviour at high closure stress, the results showed that as the closure stress increased the precision of all predictive correlations decreased considerably. Therefore, the fracture conductivity must be anticipated cautiously at high closure stresses by various predictive correlation particularly, in soft formation. © 2017 Elsevier B.V.

Gaminian H.,Amirkabir University of Technology | Montazer M.,Amirkabir University of Technology
Journal of Photochemistry and Photobiology A: Chemistry | Year: 2017

Polyester fabric were prepared with sensitized madder/TiO2 nano particles along with hydrolysis of polyester fabric in a one single-step processing by using sonochemical technique producing self-cleaning and hydrophilic properties under visible light. Moreover, central composite design (CCD) based on response surface methodology (RSM) has been used to design the experiments with three variables on the self- cleaning and water drop adsorption time of treated fabrics. The statistical analysis also recommended the optimum conditions for the polyester fabric treatment through the experimental results. Further, the tensile properties, bending length and dimensional stability of treated fabric were investigated in the optimum processing conditions. Also, the naonparicles were characterized by field emission scanning electron microscopy (FESEM), EDX and XRD spectroscopy. Fabrics treated with madder/TiO2 nanoparticles showed superior self-cleaning properties toward degradation of Methylene Blue under visible light in comparison to bare TiO2-treated polyester fabric. Madder can be described as a safe sensitizer for nano TiO2 in photo degradation of organic contaminates as a replacement for most costly and hazardous heavy metals in order to produce self-cleaning textile in practical application such as automotive, upholstery and garment industry. © 2016 Elsevier B.V.

Namin F.A.,Amirkabir University of Technology
Conference on Millimeter-Wave and Terahertz Technologies, MMWaTT | Year: 2017

The optical properties of arrays of plasmonic nanoparticles (NPs) been the subject of extensive research in recent years. Plasmonic NPs with dimensions much smaller than the incident wavelength display a resonant behavior where the electromagnetic (EM) fields are strongly enhanced and highly confined to the surface of the NP. This property of plasmonic NPs is of great interest in numerous applications. Most theoretical studies have utilized spherical NPs. This is due to the fact that scattering behavior of spheres can be studied analytically. In a recent paper, it was shown that by using spheroidal NPs, it is possible to tune the resonance frequency. However, the response of such structures is highly polarization dependent. In this paper, we propose how it is possible to overcome this polarization dependence using a new unit cell geometry. © 2016 IEEE.

Ebrahimi F.,Imam Khomeini International University | Barati M.R.,Amirkabir University of Technology
Composite Structures | Year: 2017

This paper investigates buckling characteristics of a curved functionally graded (FG) nanobeam based on nonlocal strain gradient elasticity theory accounting the stress for not only the nonlocal stress field but also the strain gradients stress field. The modeling of nanobeam is carried out via a higher order refined beam theory which captures shear deformation influences needless of any shear correction factor. Power-law model is adopted to describe continuous variation of material properties of curved FG nanobeam. The governing equations of nonlocal strain gradient curved FG nanobeam in the framework of refined hyperbolic beam model are obtained using Hamilton's principle and solved implementing an analytical solution for simply-supported and clamped boundary conditions. To validate the present model, the results are compared with those of straight FG nanobeams by extending the radius of nanobeam to infinity. The effects of nonlocal parameter, length scale parameter, power-law exponent, boundary conditions and slenderness ratio on the buckling response of curved FG nanobeams are investigated. © 2016 Elsevier Ltd

Kiani Y.,Shahrekord University | Eslami M.R.,Amirkabir University of Technology
European Journal of Mechanics, A/Solids | Year: 2017

Thermoelastic analysis of an isotropic homogeneous layer within the framework of Lord-Shulman theory of generalized thermoelasticty is performed in this research. Two coupled partial differential equations, namely; the energy and equation of motion are established. The energy equation is kept in its original nonlinear form and the assumption made in previous investigations to linearize the energy equation is not established in the present work. The two coupled equations are presented in terms of axial displacement and temperature change. These equations are then transformed into a dimensionless presentation and discretised via the generalized differential quadrature method. The resulting equations are traced in time by means of the well-known β− Newmark time marching scheme and solved iteratively at each time step. After validating the proposed approach and solution method for the case of thermally linear, a set of parametric studies are carried out to explore the effects of thermal shock magnitude, relaxation time, and the coupling parameter. It is shown that thermally nonlinear theory governs when thermal shock is severe, relaxation time is large, or coupling parameter is large. © 2016

Mahdavi S.,Amirkabir University of Technology | Shiri M.E.,Amirkabir University of Technology | Rahnamayan S.,University of Ontario Institute of Technology
Information Sciences | Year: 2015

Metaheuristic algorithms are extensively recognized as effective approaches for solving high-dimensional optimization problems. These algorithms provide effective tools with important applications in business, engineering, economics, and science. This paper surveys state-of-the-art metaheuristic algorithms and their current applications in the field of large-scale global optimization. The paper mainly covers the fundamental algorithmic frameworks such as decomposition and non-decomposition methods. More than 200 papers are carefully reviewed to prepare the current comprehensive survey. © 2014 Elsevier Inc.

Shariyat M.,K. N. Toosi University of Technology | Asemi K.,Amirkabir University of Technology
Composites Part B: Engineering | Year: 2014

In the present paper, shear buckling analysis of the orthotropic heterogeneous FGM plates is investigated for the first time. Moreover, influence of the Winkler-type elastic foundation is considered. The material properties are assumed to have in-plane orthotropy and transverse heterogeneity. The most accurate approach, i.e., the three-dimensional elasticity is employed instead of using the approximate plate theories. In contrast to all of the available displacement-based buckling analyses that have employed C0-continuous commercial finite element codes or semi-analytical methods, present formulations are C2-continuous due to using the proposed 3D cubic B-spline element. Results are derived based on principle of minimum potential energy and a non-linear finite element procedure utilizing a Galerkin-type 3D cubic B-spline solution algorithm. Buckling loads are detected based on a generalized geometric stiffness concept. In this regard, effects of both the prebuckling and buckling states are considered. To present a better imagination and more detailed discussions, details of the buckling mode shapes and the foundation interaction are discussed for plates with simply-supported edges. In addition, the more practical free and clamped edge conditions are also considered. © 2013 Elsevier Ltd. All rights reserved.

Mohammadi S.,Amirkabir University of Technology | Mirsalim M.,Amirkabir University of Technology | Mirsalim M.,St. Mary's University
IEEE Transactions on Magnetics | Year: 2014

Analytical models have been demonstrated to be effective tools in the analysis of electromagnetic devices by providing fast, yet accurate solutions. In this paper, a comprehensive analytical framework for double-rotor radial-flux air-cored permanent-magnet (PM) machines is developed whereby the average as well as the torque ripples, back-electromotive force (EMF) waveforms, air-gap flux density distribution, and a number of other characteristics regarding the design of the machine are predicted. Also, closed-form expressions for inductances of the stator coils are analytically derived. All machine parameters and material properties including iron saturation are considered in the model. Moreover, an algorithm in order to optimally design the thicknesses of the rotor yokes based on the utilized steel is presented. Finally, genetic optimizations regarding the enhancement of the produced torque and back-EMF are performed. It is also shown that the results obtained from the proposed model match well with those issued from finite element method. © 1965-2012 IEEE.

Mohammadi S.,Amirkabir University of Technology | Mirsalim M.,Amirkabir University of Technology | Mirsalim M.,St. Mary's University
IET Electric Power Applications | Year: 2013

Analytical models are widely utilised in the study and performance prediction of electric machines by providing fast, yet accurate solutions. By combining conventional magnetic equivalent circuit techniques with Faraday's and Ampere's laws, an analytical model for double-sided permanent-magnet radial-flux eddy-current couplers is presented that can easily handle complex geometries. The proposed approach is also capable of taking the three-dimensional (3D) impacts into account. The characteristics and design considerations are also studied for a surface-mounted permanent-magnet structure. Moreover, the 2D and 3D finite-element methods are employed to verify the results, as well as transient study of the device under two different scenarios. Finally, sensitivity analysis is carried out to investigate the influence of the design variables on the characteristics of the coupler, which provides valuable information in the current and future studies of such devices. © The Institution of Engineering and Technology 2013.

Akbari Torkestani J.,Islamic Azad University of Arak | Meybodi M.R.,Amirkabir University of Technology
Computers and Electrical Engineering | Year: 2011

Performance of ad hoc networks dramatically declines as network grows. Cluster formation in which the network hosts are hierarchically partitioned into several autonomous non-overlapping groups, based on proximity, is a promising approach to alleviate the scalability problem of ad hoc networks. In this paper, we propose a localized learning automata-based clustering algorithm for wireless ad hoc networks. The proposed clustering method is a fully distributed algorithm in which each host chooses its cluster-head based solely on local information received from neighboring hosts. The proposed algorithm can be independently localized at each host. This results in a significantly reduction in message overhead of algorithm, and allows cluster maintenance can be locally performed only where it is required. To show the performance of proposed algorithm, obtained results are compared with those of several existing clustering methods in terms of the number of clusters, control message overhead, clustering time, and load standard deviation. © 2011 Elsevier Ltd. All rights reserved.

Mozaffari A.,Babol Noshirvani University of Technology | Gorji-Bandpy M.,Babol Noshirvani University of Technology | Samadian P.,Product Control Section | Rastgar R.,Amirkabir University of Technology | Rezania Kolaei A.,University of Aalborg
Swarm and Evolutionary Computation | Year: 2013

Optimizing and controlling of complex engineering systems is a phenomenon that has attracted an incremental interest of numerous scientists. Until now, a variety of intelligent optimizing and controlling techniques such as neural networks, fuzzy logic, game theory, support vector machines and stochastic algorithms were proposed to facilitate controlling of the engineering systems. In this study, an extended version of mutable smart bee algorithm (MSBA) called Pareto based mutable smart bee (PBMSB) is inspired to cope with multi-objective problems. Besides, a set of benchmark problems and four well-known Pareto based optimizing algorithms i.e. multi-objective bee algorithm (MOBA), multi-objective particle swarm optimization (MOPSO) algorithm, non-dominated sorting genetic algorithm (NSGA-II), and strength Pareto evolutionary algorithm (SPEA 2) are utilized to confirm the acceptable performance of the proposed method. In order to find the maximum exploration potentials, these techniques are equipped with an external archive. These archives aid the methods to record all of the non-dominated solutions. Eventually, the proposed method and generalized regression neural network (GRNN) are simultaneously used to optimize the major parameters of an irreversible thermal engine. In order to direct the PBMSB to explore deliberate spaces within the solution domain, a reference point obtained from finite time thermodynamic (FTT) approach, is utilized in the optimization. The outcome results show the acceptable performance of the proposed method to optimize complex real-life engineering systems. © 2012 Elsevier B.V. All rights reserved.

Akbari Torkestani J.,Islamic Azad University of Arak | Meybodi M.R.,Amirkabir University of Technology
Journal of Network and Computer Applications | Year: 2011

Recently, several studies have been conducted to design mobility-based multicast routing protocols for wireless mobile ad hoc networks (MANET). These protocols assume that the mobility parameters of the network are fixed, and so they cannot perform well under real MANET scenarios in which the mobility parameters of the hosts vary over time at random. Finding the optimal solution to the multicast routing problem is incredibly hard, if the mobility parameters are assumed to be random variables. This becomes more difficult when the probability distribution function of these random variables is assumed to be unknown. In this paper, we propose a weighted multicast routing algorithm for MANET in which the mobility parameters are supposed to be random variables with unknown distribution. In this method, the multicast routing problem is first transformed into an equivalent stochastic Steiner tree problem in which the random weight associated with a communication link is its expected duration time. Then, a learning automata-based algorithm is proposed for solving the proxy Steiner tree problem. The aim of the proposed algorithm is to find the most stable multicast route (with the maximum duration) against the host mobility. Experimental results confirm the superiority of the proposed method over the best existing mobility-based multicast routing protocols in terms of the packet delivery ratio, multicast route lifetime, control message overhead, and end-to-end delay. © 2010 Elsevier Ltd. All rights reserved.

Akbari Torkestani J.,Islamic Azad University of Arak | Meybodi M.R.,Amirkabir University of Technology
Information Sciences | Year: 2012

Finding the minimum weight connected dominating set (MCDS) in an arbitrary graph is an NP-hard problem and several heuristics and approximation methods have been proposed to solve it. Forwarding the messages along the virtual backbone induced by the connected dominating set (CDS) significantly reduces the routing overhead as well as the power consumption by reducing the routing nodes to the backbone nodes. This paper first defines the stochastic MCDS problem where the probability distribution function (PDF) of the random weight associated with the graph vertices is unknown. Then, it presents several learning automata-based algorithms (Algorithms 1-6) to solve the stochastic MCDS problem. Taking advantage of learning automata, the proposed algorithms significantly reduce the number of samples that must be taken from the graph to construct the MCDS. It is proved that by the proper choice of the learning rate, the probability of finding the MCDS is close enough to unity. The standard sampling method (SSM) is the baseline with which we compare the performance of the proposed algorithms. Experimental results show that Algorithm 6 significantly outperforms the SSM and the other proposed algorithms in terms of the sampling rate. © 2012 Elsevier Inc. All rights reserved.

Mostafaei H.,Islamic Azad University at Urmia | Meybodi M.R.,Amirkabir University of Technology
Wireless Personal Communications | Year: 2013

In wireless sensor networks, when each target is covered by multiple sensors, we can schedule sensor nodes to monitor deployed targets in order to improve lifetime of network. In this paper, we propose an efficient scheduling method based on learning automata, in which each node is equipped with a learning automaton, which helps the node to select its proper state (active or sleep), at any given time. To study the performance of the proposed method, computer simulations are conducted. Results of these simulations show that the proposed scheduling method can better prolong the lifetime of the network in comparison to similar existing methods. © 2012 Springer Science+Business Media New York.

Mohammadi S.,Amirkabir University of Technology | Mirsalim M.,Amirkabir University of Technology | Mirsalim M.,St. Mary's University | Vaez-Zadeh S.,University of Tehran
IEEE Transactions on Energy Conversion | Year: 2014

Analytical models play an important role in the design of electromagnetic devices by providing computationally efficient solutions. In this paper, by combining magnetic equivalent circuit approaches and Faraday's and Ampere's laws, a model for radial-flux eddy-current couplers is developed, which can easily handle complex geometries as well as account for iron saturation, all material properties, and three-dimensional (3-D) parameters. The characteristics and the design considerations of a surface-mounted permanent-magnet structure are presented. Also, a procedure aimed at an optimal design of the yoke thicknesses is utilized. Moreover, 2-D and 3-D finite-element methods are employed in the analyses and evaluation of the model. Finally, sensitivity analysis is performed to explore the impacts of the machine parameters on the device performance. © 2013 IEEE.

Mohammadi S.,Amirkabir University of Technology | Mirsalim M.,Amirkabir University of Technology | Mirsalim M.,St. Mary's University
Electric Power Systems Research | Year: 2014

It is essential for engineers to improve overall performance of electromagnetic devices. In this paper, single/multi-objective design optimization of double-sided permanent-magnet radial-flux eddy-current couplers is carried out. To this end, an analytical model of such devices is developed by combining conventional magnetic equivalent circuit techniques with Faraday's and Ampere's laws. The model is capable of easily dealing with complex geometries and material properties such as iron saturation and the PM characteristics as well as the associated design constraints so that the designs that are more realistic can be achieved. A genetic algorithm that enjoys a flexible objective function is finally adopted to find the optimal machine parameters. Finite-element method is also employed to verify the results. © 2013 Elsevier B.V.

Akbari Torkestani J.,Islamic Azad University of Arak | Meybodi M.R.,Amirkabir University of Technology
Cluster Computing | Year: 2011

In the last decade, numerous efforts have been devoted to design efficient algorithms for clustering the wireless mobile ad-hoc networks (MANET) considering the network mobility characteristics. However, in existing algorithms, it is assumed that the mobility parameters of the networks are fixed, while they are stochastic and vary with time indeed. Therefore, the proposed clustering algorithms do not scale well in realistic MANETs, where the mobility parameters of the hosts freely and randomly change at any time. Finding the optimal solution to the cluster formation problem is incredibly difficult, if we assume that the movement direction and mobility speed of the hosts are random variables. This becomes harder when the probability distribution function of these random variables is assumed to be unknown. In this paper, we propose a learning automata-based weighted cluster formation algorithm called MCFA in which the mobility parameters of the hosts are assumed to be random variables with unknown distributions. In the proposed clustering algorithm, the expected relative mobility of each host with respect to all its neighbors is estimated by sampling its mobility parameters in various epochs. MCFA is a fully distributed algorithm in which each mobile independently chooses the neighboring host with the minimum expected relative mobility as its cluster-head. This is done based solely on the local information each host receives from its neighbors and the hosts need not to be synchronized. The experimental results show the superiority of MCFA over the best existing mobility-based clustering algorithms in terms of the number of clusters, cluster lifetime, reaffiliation rate, and control message overhead. © 2011 Springer Science+Business Media, LLC.

Akbari Torkestani J.,Islamic Azad University of Arak | Meybodi M.R.,Amirkabir University of Technology | Meybodi M.R.,Institute for Studies in Theoretical Physics and Mathematics IPM
Applied Soft Computing Journal | Year: 2011

Due to the hardness of solving the minimum spanning tree (MST) problem in stochastic environments, the stochastic MST (SMST) problem has not received the attention it merits, specifically when the probability distribution function (PDF) of the edge weight is not a priori known. In this paper, we first propose a learning automata-based sampling algorithm (Algorithm 1) to solve the MST problem in stochastic graphs where the PDF of the edge weight is assumed to be unknown. At each stage of the proposed algorithm, a set of learning automata is randomly activated and determines the graph edges that must be sampled in that stage. As the proposed algorithm proceeds, the sampling process focuses on the spanning tree with the minimum expected weight. Therefore, the proposed sampling method is capable of decreasing the rate of unnecessary samplings and shortening the time required for finding the SMST. The convergence of this algorithm is theoretically proved and it is shown that by a proper choice of the learning rate the spanning tree with the minimum expected weight can be found with a probability close enough to unity. Numerical results show that Algorithm 1 outperforms the standard sampling method. Selecting a proper learning rate is the most challenging issue in learning automata theory by which a good trade off can be achieved between the cost and efficiency of algorithm. To improve the efficiency (i.e., the convergence speed and convergence rate) of Algorithm 1, we also propose four methods to adjust the learning rate in Algorithm 1 and the resultant algorithms are called as Algorithm 2 through Algorithm 5. In these algorithms, the probabilistic distribution parameters of the edge weight are taken into consideration for adjusting the learning rate. Simulation experiments show the superiority of Algorithm 5 over the others. To show the efficiency of Algorithm 5, its results are compared with those of the multiple edge sensitivity method (MESM). The obtained results show that Algorithm 5 performs better than MESM both in terms of the running time and sampling rate. © 2010 Elsevier B.V. All rights reserved.

Jannati M.,Amirkabir University of Technology | Hosseinian S.H.,Amirkabir University of Technology | Vahidi B.,Amirkabir University of Technology | Li G.-J.,Shanghai JiaoTong University
Renewable and Sustainable Energy Reviews | Year: 2014

As the wind power capacity increases, the effect of wind power fluctuations on the system stability becomes more significant. Despite its high costs, utilizing energy storage resources such as batteries is inevitable in the smoothing process of wind power fluctuations. In a wind power plant, the place where batteries are located has considerable direct effect on their required capacity and thus on the initial investment cost. Therefore, in this paper a suitable configuration which significantly reduces the batteries investment cost is proposed and then the wind power fluctuation of a large wind power plant connected to a smart distribution grid is smoothed. Additionally, existing configurations for installing batteries in large wind power plants are investigated. The proposed configuration utilizes smart parks as aggregated storage resources in load side and an aggregated battery energy storage system with limited capacity in plant side as well. Therefore, in addition to accurate smoothing of wind power fluctuations, the energy storage investment cost is reduced significantly utilizing the proposed configuration. Simulation studies in MATLAB software package are carried out to verify the performance of the proposed approach. © 2013 Published by Elsevier Ltd.

Faghihi F.,Amirkabir University of Technology | Mohammadi N.,Amirkabir University of Technology | Hazendonk P.,University of Lethbridge
Macromolecules | Year: 2011

The glass transition behavior of emulsion polymerized butyl acrylate (BA)-methyl methacrylate (MMA) copolymers was related to their microstructural features. Broad transition regions composed of two distinct peaks were observed in both DMA and DSC measurements of copolymers with various comonomer compositions indicating dynamic and microstructural heterogeneity. This was further investigated using 2D WISE experiment. Nanophase segregation within the copolymers was inferred from detailed analysis of their local dynamic behavior. The length scale of segregation was calculated to be 7.4 nm by 13C NMR spin diffusion experiment. A modeling procedure was also developed to extract the distribution of comonomers compositions within the samples from heat flow first-derivative data. Bimodal comonomer composition distributions were extracted in accordance with their glass transition behavior. © 2011 American Chemical Society.

Behzadnia A.,Amirkabir University of Technology | Montazer M.,Islamic Azad University at Tehran | Rad M.M.,Shahid Beheshti University of Medical Sciences
Ultrasonics Sonochemistry | Year: 2015

In this study, N-doped ZnO/TiO2 core-shell nanocomposite was successfully sonosynthesized and sonofabricated on wool fabric through a facile one-step method under ambient pressure and low temperature (75-80 °C) as a novel photo-catalyst nanocomposite on textile material. The differences between crystalline phase transformation of conventional and ultrasound synthesized N-ZnO/TiO2 has been compared. The influence of different zinc acetate and titanium isopropoxide precursors in the formation of nanocomposite was studied and optimized through response surface methodology. The photocatalytic activity of the sonofabricated catalyst on the wool fabric surface was evaluated through decomposition of Methylene Blue as a model compound under sunlight irradiation. Also, N-doped ZnO/TiO2 nanocomposite sonosynthesized on wool fabric led to photo bleaching of wool fabric due to decomposition of the naturally occurred pigments under daylight irradiation. Further, yellowness index, antibacterial and antifungal activity against Escherichia coli, Staphylococcus aureus and Candida albicans, cell viability, char residual, alkali solubility, mechanical properties and water drop absorption time on the treated wool fabrics were evaluated. Also, the acid solubility of the synthesized nanopowder obtained from sonobath after treatment was characterized in acetic acid indicating higher acid resistance on N-doped ZnO/TiO2 nanocomposite. © 2015 Elsevier B.V. All rights reserved.

Pacheco-Torgal F.,University of Minho | Abdollahnejad Z.,University of Minho | Camoes A.F.,University of Minho | Jamshidi M.,Amirkabir University of Technology | Ding Y.,Dalian University of Technology
Construction and Building Materials | Year: 2012

The alkali activation of alumino-silicate materials is a complex chemical process evolving dissolution of raw materials, transportation or orientation and polycondensation of the reaction products. Publications on the field of alkali-activated binders, state that this new material is likely to have high potential to become an alternative to Portland cement. While some authors state that the durability of these materials constitutes the most important advantage over Portland cement others argue that it's an unproven issue. This paper presents a review of the literature about the durability of alkali-activated binders. The subjects of this paper are resistance to acid attack, alkali-silica reaction, corrosion of steel reinforcement, resistance to high temperatures and to fire, resistance to freeze-thaw. Special attention is given to the case of efflorescences, an aspect that was received very little concern although it is a very important one. © 2011 Elsevier Ltd. All rights reserved.

Tavana N.R.,Amirkabir University of Technology | Weihrauch K.,University of Hagen
Logical Methods in Computer Science | Year: 2011

We introduce a new type of generalized Turing machines (GTMs), which are intended as a tool for the mathematician who studies computability in Analysis. In a single tape cell a GTM can store a symbol, a real number, a continuous real function or a probability measure, for example. The model is based on TTE, the representation approach for computable analysis. As a main result we prove that the functions that are computable via given representations are closed under GTM programming. This generalizes the well known fact that these functions are closed under composition. The theorem allows to speak about objects themselves instead of names in algorithms and proofs. By using GTMs for specifying algorithms, many proofs become more rigorous and also simpler and more transparent since the GTM model is very simple and allows to apply well-known techniques from Turing machine theory. We also show how finite or infinite sequences as names can be replaced by sets (generalized representations) on which computability is already defined via representations. This allows further simplification of proofs. All of this is done for multi-functions, which are essential in Computable Analysis, and multirepresentations, which often allow more elegant formulations. As a byproduct we show that the computable functions on finite and infinite sequences of symbols are closed under programming with GTMs. We conclude with examples of application. © N. R. Tavana and K. Weihrauch.

Saeedi M.,Amirkabir University of Technology | Wille R.,University of Bremen | Drechsler R.,University of Bremen
Quantum Information Processing | Year: 2011

While a couple of impressive quantum technologies have been proposed, they have several intrinsic limitations which must be considered by circuit designers to produce realizable circuits. Limited interaction distance between gate qubits is one of the most common limitations. In this paper, we suggest extensions of the existing synthesis flow aimed to realize circuits for quantum architectures with linear nearest neighbor interaction. To this end, a template matching optimization, an exact synthesis approach, and two reordering strategies are introduced. The proposed methods are combined as an integrated synthesis flow. Experiments show that by using the suggested flow, quantum cost can be improved by more than 50% on average. © 2010 Springer Science+Business Media, LLC.

Taghavi I.,Amirkabir University of Technology | Taghavi I.,University of Illinois at Urbana - Champaign | Kaatuzian H.,Amirkabir University of Technology | Leburton J.-P.,University of Illinois at Urbana - Champaign
Applied Physics Letters | Year: 2012

A detailed rate-equation-based model is developed to study carrier transport effects on optical and electrical characteristics of the multiple quantum well heterojunction bipolar transistor laser in time-domain. Simulation results extracted using numerical techniques in small-signal regime predict significant enhancement in device optical bandwidth when multiple quantum wells are used. Cavity length and base width are also modified to optimize the optoelectronic performances of the device. An optical bandwidth of ≈60 GHz is achieved in the case of 5 quantum wells each of 70 Å widths and a cavity length of 200 μm. © 2012 American Institute of Physics.

Akbari Torkestani J.,Islamic Azad University at Tehran | Meybodi M.R.,Amirkabir University of Technology | Meybodi M.R.,Institute for Studies in Theoretical Physics and Mathematics IPM
Computer Networks | Year: 2010

In wireless ad hoc networks, due to the dynamic topology changes, multi hop communications and strict resource limitations, routing becomes the most challenging issue, and broadcasting is a common approach which is used to alleviate the routing problem. Global flooding is a straightforward broadcasting method which is used in almost all existing topology-based routing protocols and suffers from the notorious broadcast storm problem. The connected dominating set (CDS) formation is a promising approach for reducing the broadcast routing overhead in which the messages are forwarded along the virtual backbone induced by the CDS. In this paper, we propose an intelligent backbone formation algorithm based on distributed learning automata (DLA) in which a near optimal solution to the minimum CDS problem is found. Sending along this virtual backbone alleviates the broadcast storm problem as the number of hosts responsible for broadcast routing is reduced to the number of hosts in backbone. The proposed algorithm can be also used in multicast routing protocols, where the only multicast group members need to be dominated by the CDS. In this paper, the worst case running time and message complexity of the proposed backbone formation algorithm to find a 1 / (1 - ε) optimal size backbone are computed. It is shown that by a proper choice of the learning rate of the proposed algorithm, a trade-off between the running time and message complexity of algorithm with the backbone size can be made. The simulation results show that the proposed algorithm significantly outperforms the existing CDS-based backbone formation algorithms in terms of the network backbone size, and its message overhead is only slightly more than the least cost algorithm. © 2009 Elsevier B.V. All rights reserved.

Pazuki G.,Amirkabir University of Technology | Seyfi Kakhki S.,Seyfi Trading Company
Journal of Molecular Liquids | Year: 2013

To model partition coefficients of Penicillin G Acylase in polymer-salt aqueous two-phase systems (ATPS), a hybrid GMDH neural network is presented on the basis of original GMDH approach. We performed two major amendments to the structure of original approach in order to enhance the model complexity and power to trace high order of non-linearity. An extensive data set observed by Pazuki et al. is examined by original GMDH approach and hybrid GMDH neural network model. Compared to results generated by original GMDH approach and UNIFAC-FV model, hybrid model stands out with a noticeable superiority in tracking data trend. Average Absolute Deviation percent (AAD%) of proposed hybrid model is 4.04% which indicates a superior accuracy in comparison with those of original GMDH approach and UNIFAC-FV model with AADs% of 6.91% and 5.58%. Copyright © 2013. All rights reserved.

Yousefi N.,Hong Kong University of Science and Technology | Gudarzi M.M.,Amirkabir University of Technology | Zheng Q.,Hong Kong University of Science and Technology | Aboutalebi S.H.,Hong Kong University of Science and Technology | And 2 more authors.
Journal of Materials Chemistry | Year: 2012

Polyurethane (PU)-based composite films containing highly aligned graphene sheets are produced through an environmentally benign process. An aqueous liquid crystalline dispersion of graphene oxide (GO) is in situ reduced in PU, resulting in a fine dispersion and a high degree of orientation of graphene sheets. The PU particles are adsorbed onto the surface of the reduced graphene oxide (rGO), and the rGO sheets with a large aspect ratio of over 10000 tend to self-align during the film formation when the graphene content is high enough, say more than 2 wt%. The resulting composites show excellent electrical conductivity with an extremely low percolation threshold of 0.078 vol%, which is considered one of the lowest values ever reported for polymer composites containing graphene. The electrical conductivity of the composites with high graphene contents presents significant anisotropy due to the preferential formation of conductive networks along the in-plane direction, another proof of the existence of the self-aligned, layered structure. © 2012 The Royal Society of Chemistry.

Ovesy H.R.,Amirkabir University of Technology | Fazilati J.,Aerospace Rresearch Institute
Computers and Structures | Year: 2012

In the current paper, it is the first time that a dynamic stability analysis of moderately thick cylindrical panels made from FG materials is conducted by employing finite strip formulations based on a Reddy-type third order shear deformation theory (HSDT). Two versions of finite strip methods (FSM), namely semi-analytical and B-spline methods are developed. The mechanical properties of FGM are assumed to change in thickness direction according to a power-law function. The temperature effects are ignored. The strain terms are expressed in terms of the Koiter-Sanders theory of shallow shells. In order to demonstrate the capabilities of the developed methods in predicting parametric behavior of the subject structures, some representative results are obtained and compared with those in the literature wherever available. © 2012 Civil-Comp Ltd. and Elsevier Ltd. All rights reserved.

Nazari A.G.,Islamic Azad University at Tehran | Mozafari M.,Amirkabir University of Technology
Advanced Powder Technology | Year: 2012

In this study, structural features of alumina-titanium diboride nanocomposite (Al 2O 3-TiB 2) were simulated from the mixture of titanium dioxide, boric acid and pure aluminum as raw materials via mechanochemical process using the optimized artificial neural network. The phase transformation and structural evolutions during the mechanochemical process were characterized using X-ray powder diffractometry (XRD). For better understanding the refining crystallite size and amorphization phenomena during the milling, XRD data were modeled and simulated by artificial neural network (ANN). An ANN consisting of three layers of neurons was trained using a back-propagation learning rule. Also, the ANN was optimized by Taguchi method. Additionally, the crystallite size, interplanar distance, amorphization degree and lattice strain were compared for the simulated values and experimental results. © 2011 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.

Montazer M.,Amirkabir University of Technology | Pakdel E.,Islamic Azad University at Tehran | Moghadam M.B.,Allame Tabatabaee University
Colloids and Surfaces A: Physicochemical and Engineering Aspects | Year: 2011

One of the main problems of wool as an important proteinous fiber is low resistance against alkali media. Finding a way to solve this problem without any influences on other fiber characteristics is still a matter of research. Using nano particles on textile materials is a new approach to produce novel properties. Here, nano titanium dioxide (NTO) particles along with butane tetra carboxylic acid (BTCA) were sonicated in the ultra sound bath and applied as a nano colloid on the wool fabric. BTCA played different roles as wool cross-linker, a polyanionic agent, and stabilizer for nano TiO2. Various concentrations of NTO and BTCA were applied through impregnation of the fabric in ultrasonic bath followed by curing. The resistance of fabrics against alkali was assessed by solubility in sodium hydroxide and the hydrophilicity monitored by the water drop absorption time and the contact angle before and after UV irradiation. Interestingly, the alkali solubility of the nano TiO2 treated wool fabrics reduced while the fabric became more hydrophilic. This fact was shown by the testing results and is thoroughly discussed in the article. The response surface methodology (RSM) was also applied to find the optimum conditions for the wool fabric treatment. © 2010 Elsevier B.V.

Montazer M.,Amirkabir University of Technology | Pakdel E.,Islamic Azad University at Tehran
Journal of the Textile Institute | Year: 2011

Wool is a textile material that is valued for its strength, warmth, water resistance, and texture. But this natural fiber of the protein keratin lacks the stain resistance of synthetic fabrics and is also generally susceptible to harsh processing conditions. In this study, raw and oxidized wool fabrics were treated with nano titanium dioxide (TiO2) powder in an ultrasonic bath. These particles were linked to the wool surface by butane tetra carboxylic acid and also sodium hypophosphite was used as a catalyst. The photo-catalytic activity of TiO2 nanoparticles deposited on the wool fabrics was followed by the degradation of Acid Blue 113 as a stain and also determined by the degradation rate of food stains such as coffee, tea, and fruit juice under the ultraviolet rays. The results showed that increasing the amount of nano TiO2 leads to improved degradation of stains on the treated fabric. © 2011 The Textile Institute.

Niknam T.,Shiraz University of Technology | Firouzi B.B.,Islamic Azad University at Marvdasht | Mojarrad H.D.,Amirkabir University of Technology
Expert Systems with Applications | Year: 2011

Reduce fossil fuel resources; increasing established new power generation unit costs; and ever growing demand for electric energy necessitate optimal economic dispatch (ED) in today's electric power systems. Modern heuristic optimization techniques have been given much attention by many researchers due to their ability to find an almost global optimal solution for ED problems. One of the recently proposed evolutionary algorithms is the Shuffled Frog Leaping Algorithm (SFLA). In the original SFLA, every frog updates its position according to the best solution, because of the influence of the local best solution, every frog will constringe about the local best solution quickly. In this paper a new method is proposed to modify the worst frog's position. This proposed approach is called Modified Shuffle Frog Leaping Algorithm (MSFLA). Also, in order to improve the algorithm's stability and the ability to search the global optimum, a Chaotic Local Search (CLS) is used to get rid of the local optima. The proposed algorithm, called Chaotic Modified Shuffled Frog Leaping Algorithm (CMSFLA), is used to solve the ED problem considering the valve-point loading effects, multi-fuel and prohibited operating zones. The proposed algorithm is tested on different sample systems and its results are compared with other methods. © 2010 Elsevier Ltd. All rights reserved.

Norouzi M.,Islamic Azad University at Tehran | Zare Y.,Islamic Azad University at Tehran | Kiany P.,Amirkabir University of Technology
Polymer Reviews | Year: 2015

Along with the rising trend of stringent fire safety regulations, demands for reduction in the fire hazard caused by highly combustible materials such as textiles and polymers have become a matter of significant importance. Therefore, numerous attempts have been made to improve the flame retardation of textiles for a variety of applications. The present paper aims to review the recent developments in the flame retardant nanocomposites of natural and synthetic textile polymers. We survey the application of different nanoparticles or a combination of nanoparticles and conventional flame retardants. Furthermore, a comprehensive discussion on mechanisms and optimized conditions of flame retardation and thermal stability is presented. © 2015 Copyright © Taylor & Francis Group, LLC.

Jalal M.,Islamic Azad University at Tehran | Ramezanianpour A.A.,Amirkabir University of Technology
Composites Part B: Engineering | Year: 2012

Enhancement of strength and ductility is the main reason for the extensive use of fiber reinforced polymer (FRP) jackets to provide external confinement to reinforced concrete columns especially in seismic areas. Therefore, numerous researches have been carried out in order to provide a better description of the behavior of FRP-confined concrete for practical design purposes. This study presents a new approach to obtain strength enhancement of concrete cylinders confined with carbon fiber reinforced polymer (CFRP) composites by applying artificial neural networks (ANNs). The proposed ANN model is based on experimental results collected from literature. It represents the ultimate strength of concrete cylinders after CFRP confinement which is also given in explicit form in terms of geometrical and mechanical parameters. The accuracy of the proposed ANN model is quite satisfactory as compared to experimental results. Moreover the results of proposed ANN model are compared with five important theoretical models proposed by researchers so far and considered to be in good agreement. © 2011 Elsevier Ltd. All rights reserved.

Khodaii A.,Amirkabir University of Technology | Kazemi Tehrani H.,Islamic Azad University at Tehran | Haghshenas H.F.,Amirkabir University of Technology
Construction and Building Materials | Year: 2012

Beneficial effects of using hydrated lime to reduce moisture susceptibility of Hot Mix Asphalts are well recognized and widely used in industry. In present study, the effect of varying percentages of hydrated lime (from 0% to 2%) on the moisture susceptibility of warm mix asphalt was evaluated. Based on the obtained results it was shown that increasing hydrated lime content reduces the moisture susceptibility of dense graded warm mix asphalt. However, 80% of tensile strength ratio was reached without utilization of hydrated lime in some prepared samples with gap grading, using polymer modified bitumen. © 2012 Elsevier Ltd. All rights reserved.

Khodaii A.,Amirkabir University of Technology | Haghshenas H.F.,Amirkabir University of Technology | Kazemi Tehrani H.,Islamic Azad University at Tehran
Construction and Building Materials | Year: 2012

Response surface methodology was employed to evaluate the effect of lime content and grading on the dry and saturated indirect tensile strength as well as Tensile Strength Ratio of hot mix asphalt. The statistical significance of linear, quadratic and interactive terms of these factors were examined and second order polynomial models were successfully fitted to the experiment data. It was shown that maximum Tensile Strength Ratio was achieved at 1% lime content and with grading containing most coarse aggregate. It was further concluded that decreasing the aggregate size and increase in mastic asphalt would increase the stripping potential of hot mixes asphalt. © 2012 Elsevier Ltd. All rights reserved.

Montazer M.,Amirkabir University of Technology | Alimohammadi F.,Islamic Azad University at Tehran | Shamei A.,Islamic Azad University at Tehran | Rahimi M.K.,Islamic Azad University at Tehran
Carbohydrate Polymers | Year: 2012

This study introduces a new green method synthesis of silver nanoparticles on the cotton fabric surface through using Tollens' reagent. In this approach, silver nitrate (AgNO3) was transformed to Ag2O followed by an aqueous solution with ammonia; subsequently, silver nanoparticles were synthesized on the cotton fabric directly. The main objective of this research was to successfully employ the reducing and stabilizing features of cellulose to synthesize nano silver. Accordingly, the antibacterial efficiency was evaluated against two common pathogenic bacteria: S. aureus and E. coli. Additionally, the color variation on the cotton fabric and durability of the antibacterial properties on the fabric were assessed and reported. The Raman spectra, CHN elemental analysis, SEM images, XRD patterns, and EDS spectrum were employed to characterize the treated cotton fabrics. The treated fabrics demonstrated an excellent antibacterial activity against the mentioned bacteria. A slight decrease in the antibacterial feature of the cotton fabrics was observed after successive washings. However, an efficient antibacterial activity remained on the fabrics. © 2011 Elsevier Ltd. All rights reserved.

Montazer M.,Amirkabir University of Technology | Pakdel E.,Islamic Azad University at Tehran
Journal of Photochemistry and Photobiology C: Photochemistry Reviews | Year: 2011

The consumption of titanium dioxide in today's world is on the increase. As the most popular nano substance, TiO 2 is used in various industries notably in the textile industry. More and more recently, through a synergistic combination of photocatalytic features of nanoparticles, fabrics with novel properties are produced. Self-cleaning and stability against UV rays as well as chemical media, to name but a few, are among new prominent properties, obtained on textiles. A common subject reported in most studies has been the diverse approaches to immobilize the nanoparticles on the surface of fabrics. Wool is among common textile materials that have undergone numerous processes to be modified. This review intends to bring to light different aspects of application of nano titanium dioxide in the textile industry especially on wool, and also presents a concise overview on the rigorous pieces of research conducted in this realm. © 2011 Elsevier B.V.

Ghanbari S.,Islamic Azad University at Tehran | Mahboubi F.,Amirkabir University of Technology
Materials and Design | Year: 2011

Ni matrix-Al particle composite coating was adopted via sediment co-deposition (SCD) method on the zincate coated aluminum substrate. Surface morphology was investigated by scanning electron microscopy (SEM). The electrochemical behavior of the coatings was studied by polarization potentiodynamic test in 3.5. wt.% sodium chloride using a three electrode open cell. The effect of the electroplating parameters on the Al co-deposition was studied. Maximum of 22. wt.% Al particles were deposited in the coating. It was found that the zincate coating plays an important role in improving the nickel layer adherent. Furthermore, incorporation of aluminum particles in Ni matrix refined the Ni crystal coatings. However, polarization curves shifted to negative potentials and corrosion rate is decreased. © 2010 Elsevier Ltd.

Dolatzadeh F.,Amirkabir University of Technology | Moradian S.,Amirkabir University of Technology | Jalili M.M.,Islamic Azad University at Tehran
Corrosion Science | Year: 2011

Various organosilane-treated SiO2 nanoparticles were dispersed in a 2-pack polyurethane coating. The influence of surface modification and silica content on the electrochemical behaviour of the resultant nanocoatings was investigated. Electrochemical impedance spectroscopy (EIS) and open circuit potential (OCP) variations were examined. The surface chemistry of nanoparticles and its effect on the resultant nanocoating morphology were also studied utilising FTIR, and TEM analyses. The results reveal that the presence of more hydrophobic groups and longer-lengthed hydrophobic chains on the surface of nanoparticles, greatly improves the interfacial interactions at the polymer/filler interfaces resulting in a better corrosion performance. © 2011 Elsevier Ltd.

Hashemi B.,Shiraz University of Technology | Dehghan M.,Amirkabir University of Technology
Mathematical and Computer Modelling | Year: 2012

This note tries to propose an efficient method for obtaining outer estimations for the so-called united solution set of the interval Lyapunov matrix equation AX+XA T=F, where A and F are known real interval matrices while X is the unknown matrix; all of dimension n×n. We first explore the equation in the more general setting of AE-solution sets, and show that only a small part of Shary's results on the AE-solution sets of interval linear systems can be generalized to the interval Lyapunov matrix equation. Then, we propose our modification of Krawczyk operator which enables us to reduce the computational complexity of obtaining an outer estimation for the united solution set to cubic, provided that the midpoint of A is diagonalizable. © 2011 Elsevier Ltd.

Tabasi O.,Amirkabir University of Technology | Falamaki C.,Amirkabir University of Technology | Khalaj Z.,Iran National Institute of Genetic Engineering and Biotechnology
Colloids and Surfaces B: Biointerfaces | Year: 2012

The present work concerns a preliminary step in the production of anticancer drug loaded porous silicon (PSi) for targeted-drug-delivery applications. A successful procedure for the covalent attachment of folic acid, polyethylene glycol (PEG) and doxorubicin to hydrophilic mesoporous silicon layers is presented. A systematic approach has been followed to obtain the optimal composition of the N,N'-dicyclohexylcarbodiimide (DCC)/N-hydroxysuccimide (NHS) in dimethylsulfoxide (DMSO) solution for the surface activation process of the undecylenic acid (UD) grafted molecules to take place with minimal undesired byproduct formation. The effect of reactant concentration and kind of solvent (aqueous or DMSO) on the attachment of folic acid to the activated PSi layer has been investigated. The covalent attachment of the doxorubicin molecules to the PSi layer functionalized with folic acid and PEG is discussed. The drug release kinetics as a function of pH has been studied. The functionalized PSi particles show a high cytotoxicity compared to the equivalent amount of free drug. Cell toxicity tests show clearly that the incorporation of folate molecules increases substantially the toxicity of the loaded PSi particles. Accordingly this new functionalized PSi may be considered a proper candidate for targeted drug delivery. © 2012 Elsevier B.V.

Sajadieh M.S.,Amirkabir University of Technology | Thorstenson A.,University of Aarhus
Computers and Operations Research | Year: 2014

We investigate four sourcing models with respect to either cooperative or non-cooperative planning strategies and either sole or dual sourcing. A two-stage supply chain is considered. It involves a single buyer and either one or two supplier(s)/vendor(s). At the buyer, the product is consumed at a constant rate and an (r, Q) inventory control policy is used for replenishments. The delivery lead time from the vendors is stochastic. The cost function comprises five elements: inventory holding costs for buyer and vendors, backorder costs and ordering costs for the buyer, and setup costs for the vendors. The objective is to minimize total system costs incurred at the buyer and the vendors. As there is no overall dominating combined sourcing strategy, a major finding is that determining the best strategy requires a detailed analysis. However, when total system costs are taken into account, dual sourcing does not appear as beneficial as sometimes claimed in the literature on order splitting. © 2013 Elsevier Ltd. All rights reserved.

Jahanshahi M.,Islamic Azad University at Tehran | Dehghan M.,Amirkabir University of Technology | Meybodi M.R.,Amirkabir University of Technology
Applied Intelligence | Year: 2013

Multicast routing is a crucial issue in wireless networks in which the same content should be delivered to a group of recipients simultaneously. Multicast is also considered as a key service for audio and video applications as well as data dissemination protocols over the last-mile backhaul Internet connectivity provided by multi-channel multi-radio wireless mesh networks (MCMR WMNs). The multicast problem is essentially related to a channel assignment strategy which determines the most suitable channel-radio associations. However, channel assignment brings about its own complications and hence, solving the multicast problem in MCMR WMNs will be more complicated than that of traditional networks. This problem has been proved to be NP-hard. In the major prior art multicast protocols developed for these networks, channel assignment and multicast routing are considered as two separate sub-problems to be solved sequentially. The work in this article is targeted at promoting the adoption of learning automata for joint channel assignment and multicast routing problem in MCMR WMNs. In the proposed scheme named LAMR, contrary to the existing methods, these two sub-problems will be solved conjointly. Experimental results demonstrate that LAMR outperforms the LCA and MCM proposed by Zeng et al. (IEEE Trans. Parallel. Distrib. Syst. 21(1):86-99, 2010) as well as the genetic algorithm-, tabu search-, and simulated annealing-based methods by Cheng and Yang (Int. J. Appl. Soft Comput. 11(2):1953-1964, 2011) in terms of achieved throughput, end-to-end delay, average packet delivery ratio, and multicast tree total cost. © 2012 Springer Science+Business Media, LLC.

Hajmohammadi M.R.,Amirkabir University of Technology | Salimpour M.R.,Isfahan University of Technology | Saber M.,Islamic Azad University at Tehran | Campo A.,University of Texas at San Antonio
Energy Conversion and Management | Year: 2013

Maintaining the peak temperature of a heat source under an allowable level has always been a major concern for engineers engaged in the design of cooling systems for electronic equipment. The primary goal of this paper is to examine the advantages and/or disadvantages of placing a conductive thick plate as a heat transfer interface between a heat source and a cold flowing fluid. In such arrangement, the heat source is cooled under the thick plate instead of being cooled in direct contact with the cooling fluid. It is demonstrated that the thick plate can significantly improve the heat transfer between the heat source and the cooling fluid by way of conducting the heat current in an optimal manner. The two most attractive advantages of this method are that no additional pumping power and no extra heat transfer surface area, that is quite different from fins (extended surfaces). Unlike related archival papers in the literature, the present paper allows open spaces toward optimization. The objective is to minimize the maximum temperature, the 'hot spot'. Detailed analytical expressions are presented and a numerical analysis is carried out on the conservation equations based on the SIMPLEC algorithm. It is categorically proved that there exists an optimal thickness of the thick plate, which minimizes the peak temperature. Also, it is shown that the efficiency of the optimized plate on minimizing the target peak temperature depends upon the Reynolds number of the fluid flow and the material thermal conductivity. © 2013 Elsevier Ltd. All rights reserved.

Doagou-Mojarrad H.,Amirkabir University of Technology | Gharehpetian G.B.,Amirkabir University of Technology | Rastegar H.,Amirkabir University of Technology | Olamaei J.,Islamic Azad University at Tehran
Energy | Year: 2013

This paper presents an interactive fuzzy satisfying method, which is based on Hybrid Modified Shuffled Frog Leaping Algorithm, and should solve the problem of the Multi-objective optimal placement and sizing of DG (distributed generation) units in the distribution network. Minimizing total electrical energy losses, total electrical energy cost and total pollutant emissions produced are the objective functions in this problem.Also, the improvement of the voltage profile is considered as a constraint in determining the optimal placement. In the proposed method, the objective functions are modeled with fuzzy sets. The multi-objective problem is transformed into a mini-max problem, which is then handled by the proposed evolutionary algorithm.Finally, the proposed algorithm is tested on a 69-bus distribution test system based on technical, economical and environmental protection considerations. The simulation results illustrate the good performance and applicability of the proposed method. © 2013 Elsevier Ltd.

Mohammadi M.,Islamic Azad University at Tehran | Hosseinian S.H.,Amirkabir University of Technology | Gharehpetian G.B.,Amirkabir University of Technology
Solar Energy | Year: 2012

This study presents an optimized design of microgrid (MG) in distribution systems with multiple distributed generation (DG) units under different market policies such as pool/hybrid electricity market. Proposed microgrid includes various energy sources such as photovoltaic array and wind turbine with energy storage devices such as battery bank. In this study, microgrid is considered as independent power producer company (IPP) in power system. Price of selling/buying power in on-peak or off-peak for MG, DG and upstream power system (DISCO) under pool/bilateral/hybrid electricity market are different. In this study, particle swarm optimization (PSO) algorithm has been implemented for the optimization of the microgrid cost. The costs include capital cost, replacement cost, operation and maintenance costs and production cost for microgrid and DGs. Then, an objective function to maximize total net present worth (NPW) is presented. PSO approach is employed to obtain the minimum cost of microgrid, during interconnected operation by optimizing the production of local DGs and power exchanges with the main distribution grid. The optimization algorithm is applied to a typical LV network operating under different market policies. © 2011 Elsevier Ltd.

Montazer M.,Amirkabir University of Technology | Alimohammadi F.,Islamic Azad University at Tehran | Shamei A.,Amirkabir University of Technology | Rahimi M.K.,Islamic Azad University at Tehran
Colloids and Surfaces B: Biointerfaces | Year: 2012

Colloidal nano silver was applied on the surface of cotton fabric and stabilized using 1,2,3,4-butanetetracarboxylic acid (BTCA). The two properties of antimicrobial activity and resistance against creasing were imparted to the samples of fabric as a result of the treatment with silver nano colloid and BTCA. The antimicrobial property of samples was evaluated using two pathogenic bacteria including Escherichia coli and Staphylococcus aureus as outstanding barometers in this field. The durability of applied nanoparticles, color variation, wettability and wrinkle recovery angle of the treated samples were investigated employing related credible standards. The presence of nano silver particles on the surface of treated cotton fabric was proved using EDS spectrum as well as the SEM images. Furthermore, the creation of cross-links was confirmed by the means of both ATR-FTIR and Raman spectra. In conclusion, it was observed that BTCA plays a prominent role in stabilizing silver nanoparticle. Besides, Wettability and winkle recovery angle of finished samples decreased and increased, respectively. In addition, it is noteworthy that no obvious color variation was observed. © 2011 Elsevier B.V.

Montazer M.,Amirkabir University of Technology | Malekzadeh S.B.,Islamic Azad University at Tehran
Journal of Polymer Research | Year: 2012

A new method for production of nylon nanofibers with antibacterial properties containing silver nanoparticles (nylon nanofibers/Ag NPs) is introduced via in situ synthesis of nano-silver by reduction of silver nitrate in the polymer solution prior to electrospinning. The properties of the electrospinning solutions and the structures of the electrospun fibers were studied using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDAX), UV-vis spectrophotometer and reflection spectrophotometer. Further, the antibacterial properties of the nanofibers were investigated against Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive) bacteria. Interestingly, an antibacterial properties has been found on nylon 6 nanofibers while the nylon nanofibers/Ag NPs showed excellent antibacterial activities against both tested bacteria. The produced nylon nanofibers/Ag NPs can be a good candidate for biomedical applications, water and air filtration. © 2012 Springer Science+Business Media B.V.

Mohammadi M.,Islamic Azad University at Tehran | Hosseinian S.H.,Amirkabir University of Technology | Gharehpetian G.B.,Amirkabir University of Technology
International Journal of Electrical Power and Energy Systems | Year: 2012

In this paper an optimized design of micro-grid (MG) in a distribution system based on combination of photovoltaic array, fuel cell and battery bank with multiple DG units under hybrid electricity market model has been presented and so the results has been compared with results of pool electricity market. In this research, GA-based optimization method is used to obtain optimum power and price of the MG. Then, an objective function based on the total net present worth is considered and GA is employed to obtain the maximum net present worth of the MG, during interconnected operation by optimizing the production of local DGs and power exchanges with the main distribution grid. © 2011 Elsevier Ltd. All rights reserved.

Parvinzadeh Gashti M.,Islamic Azad University at Tehran | Moradian S.,Amirkabir University of Technology
Journal of Applied Polymer Science | Year: 2012

Polyethylene terephthalate (PET)-based nanocomposites containing three differently modified clays were prepared by melt compounding. The influence of type of clay on disperseability, thermal, and dyeing properties of the resultant nanocomposite was investigated by various analytic techniques, namely, X-ray diffraction, optical microscopy (OPM), differential scanning calorimetry, thermal gravimetric analysis, dynamical mechanical thermal analysis, contact angle measurement (CAM), reflectance spectroscopy, and light fastness. OPM images illustrated formation of large-sized spherulites in pure PET, while only small-sized crystals appeared in PET/clay nanocomposites. Decreased glass transition temperatures for all PET/clay nanocomposites indicate that the amorphous regions of such composites become mobile at lower temperatures than those in pure PET. CAMs on the resultant PET composites demonstrated that the wettability of such composites depends on hydrophilicity of the nanoclay particles. Copyright © 2012 Wiley Periodicals, Inc.

Gorji M.,Islamic Azad University at Tehran | Jeddi A.A.A.,Amirkabir University of Technology | Gharehaghaji A.A.,Amirkabir University of Technology
Journal of Applied Polymer Science | Year: 2012

Electrospun nanofibrous webs are important in nanotechnology applications due to their high surface area and interconnected porosity. In this study, the effect of electrospinning duration on some physical and mechanical properties of polyurethane (PU) electrospun webs is investigated for potential applications such as protective clothing and membranes. The results show that the thickness and weight of webs and subsequently their tensile strength increase linearly with the electrospinning duration. Air permeability of nanofibrous webs decrease and hydrostatic pressure increases nonlinearly while water vapor permeability remains constant. This work shows that air permeability of PU webs follows Fick's law of diffusion. Some regression models have been proposed to describe electrospun membranes behavior. The results of this investigation indicate that this new generation of nanofibrous materials has a good potential for application as membrane in protective clothing. Copyright © 2012 Wiley Periodicals, Inc.

Malvandi A.,Amirkabir University of Technology | Hedayati F.,Islamic Azad University at Neyshabur | Ganji D.D.,Babol Noshirvani University of Technology
Powder Technology | Year: 2014

Unsteady two-dimensional stagnation point flow of a nanofluid over a stretching sheet is investigated numerically. In contrast to the conventional no-slip condition at the surface, Navier's slip condition has been applied. The behavior of the nanofluid was investigated for three different nanoparticles in the water-base fluid, namely copper, alumina and titania. Employing the similarity variables, the governing partial differential equations including continuity, momentum and energy have been reduced to ordinary ones and solved via Runge-Kutta-Fehlberg scheme. It was shown that a dual solution exists for negative values of the unsteadiness parameter A and, as it increases, the skin friction Cfr grows but the heat transfer rate Nur takes a decreasing trend. The results also indicated that, unlike the stretching parameter ε, increasing in the values of the slip parameter λ widen the ranges of the unsteadiness parameter A for which the solution exists. Furthermore, it was found that an increase in both ε and λ intensifies the heat transfer rate. © 2013 Elsevier B.V.

Haeri H.,Islamic Azad University at Tehran | Shahriar K.,Amirkabir University of Technology | Marji M.F.,University of Yazd | Moarefvand P.,Amirkabir University of Technology
International Journal of Rock Mechanics and Mining Sciences | Year: 2014

The pre-cracked disk specimens (Brazilian disks containing single and double cracks in the middle part of the disk) of rock-like materials were experimentally tested under compressive line loading. The specimens were prepared from Portland Pozzolana Cement (PPC), fine sands and water. The failure load of the pre-cracked disks was measured, showing the decreasing effects of the cracks and their orientation on the final failure load. The breakage process of the disks was studied by inserting single and double cracks with different inclination angles. It was observed that wing cracks are produced at the first stage of loading, and start their propagation toward the direction of compressive line loading. The same specimens were numerically simulated by an indirect boundary element method known as the displacement discontinuity method. Finally, a numerical simulation was conducted to study the effect of crack length and its orientation on the cracks coalescence and breakage path. © 2014 Elsevier Ltd.

Akhavan Sadr F.,Islamic Azad University at Tehran | Montazer M.,Amirkabir University of Technology
Ultrasonics Sonochemistry | Year: 2014

Here, titanium dioxide nanoparticles (NPs) were sonosynthesized and loaded simultaneously onto the cotton fabric. Titanium tetra isopropoxide (TTIP) was used as precursor and ultrasonic irradiation was utilized as a tool for synthesis of TiO2 in low temperature with anatase structure and loading nanoparticles onto the cotton fabric. TiO2 loaded cotton fabric was characterized by XRD, FE-SEM, EDS, and XRF. Moreover, several properties of the treated cotton fabrics such as self-cleaning, UV protection, washing durability, and tensile strength were studied. The effect of variables, including TTIP concentration and sonication time, was investigated based on central composite design (CCD) and response surface methodology (RSM). The results confirmed formation of anatase TiO2 nanoparticles with 3-6 nm crystalline size loaded onto the cotton fabric at low temperature (75 C) that led to good self-cleaning and UV-protection properties. The excellent UV-protection rating of the treated fabric maintained even after 25 home launderings indicating an excellent washing durability. Interestingly, sonochemical method had no negative influence on the cotton fabric structure. The statistical analysis indicated significant effect of both TTIP concentration and sonication time on the content of the loaded TiO2 on the fiber and self-cleaning properties of the fabric. © 2013 Elsevier B.V. All rights reserved.

Badrnezhad R.,Amirkabir University of Technology | Mirza B.,Islamic Azad University at Tehran
Journal of Industrial and Engineering Chemistry | Year: 2014

Precise modeling flux decline under various operating parameters in cross-flow ultrafiltration (UF) of oily wastewaters and afterward, employing an appropriate optimization algorithm in order to optimize operating parameters involved in the process model result in attaining desired permeate flux, is of fundamental great interest from an economical and technical point of view. Accordingly, this current research proposed a hybrid process modeling and optimization based on computational intelligence paradigms where the combination of artificial neural network (ANN) and genetic algorithm (GA) meets the challenge of specified-objective based on two steps: first the development of bio-inspired approach based on ANN, trained, validated and tested successfully with experimental data collected during the polyacrylonitrile (PAN) UF process to treat the oily wastewater of Tehran refinery in a laboratory scale in which the model received feed temperature (T), feed pH, trans-membrane pressure (TMP), cross-flow velocity (CFV), and filtration time as inputs; and gave permeate flux as an output. Subsequently, the 5-dimensional input space of the ANN model portraying process input variables was optimized by applying GA, with a view to realizing maximum or minimum process output variable. The results obtained validate the estimates of the ANN-GA technique with a good accuracy. Finally, the relative importance of the controllable operation factors on flux decline is determined by applying the various correlation statistic techniques. According to the result of the sensitivity analysis based on the correlation coefficient, the filtration time was the most significant one, followed by T, CFV, feed pH and TMP. © 2013 The Korean Society of Industrial and Engineering Chemistry.

Alizadeh M.,Shiraz University of Technology | Paydar M.H.,Shiraz University | Sharifian Jazi F.,Amirkabir University of Technology
Composites Part B: Engineering | Year: 2013

Nanostructured Al/B 4C composites with an average grain size of 151 nm were successfully fabricated in the form of sheets, by using accumulative roll bonding (ARB) process. Furthermore, monolithic Al (without B 4C particles) also was processed by the same method for comparison. The microstructure of the composites, evaluated by optical and scanning electron microscopy, revealed the properly distributed B 4C particles in the Al matrix. The grain size of the Al matrix, after the final ARB cycle, is studied using Williamson-Hall analysis of X-ray diffraction (XRD) pattern of the deformed sample. Mechanical properties of the specimens were investigated by tensile and hardness tests. The tensile strength and microhardness of the processed samples increased with increasing the number of ARB cycle. Whereas, the elongation dropped abruptly at the first cycle; afterwards, it remained nearly constant in the monolithic samples and increased slightly in the composites. © 2012 Published by Elsevier Ltd.

Asadi S.,Amirkabir University of Technology | Hadavandi E.,Amirkabir University of Technology | Mehmanpazir F.,Islamic Azad University at Tehran | Nakhostin M.M.,Islamic Azad University at Tehran
Knowledge-Based Systems | Year: 2012

Artificial Intelligence models (AI) which computerize human reasoning has found a challenging test bed for various paradigms in many areas including financial time series prediction. Extensive researches have resulted in numerous financial applications using AI models. Since stock investment is a major investment activity, Lack of accurate information and comprehensive knowledge would result in some certain loss of investment. Hence, stock market prediction has always been a subject of interest for most investors and professional analysts. Stock market prediction is a challenging problem because uncertainties are always involved in the market movements. This paper proposes a hybrid intelligent model for stock exchange index prediction. The proposed model is a combination of data preprocessing methods, genetic algorithms and Levenberg-Marquardt (LM) algorithm for learning feed forward neural networks. Actually it evolves neural network initial weights for tuning with LM algorithm by using genetic algorithm. We also use data pre-processing methods such as data transformation and input variables selection for improving the accuracy of the model. The capability of the proposed method is tested by applying it for predicting some stock exchange indices used in the literature. The results show that the proposed approach is able to cope with the fluctuations of stock market values and also yields good prediction accuracy. So it can be used to model complex relationships between inputs and outputs or to find data patterns while performing financial prediction. © 2012 Elsevier B.V. All rights reserved.

Amid A.,Islamic Azad University at Tehran | Ghodsypour S.H.,Amirkabir University of Technology | O'Brien C.,University of Nottingham
International Journal of Production Economics | Year: 2011

Supplier selection is one of the most important activities of purchasing departments. This importance is increased even more by new strategies in a supply chain. Supplier selection is a multi-criteria decision making problem in which criteria have different relative importance. In practice, for supplier selection problems, many input information are not known precisely. The fuzzy set theories can be employed due to the presence of vagueness and imprecision of information. A weighted maxmin fuzzy model is developed to handle effectively the vagueness of input data and different weights of criteria in this problem. Due to this model, the achievement level of objective functions matches the relative importance of the objective functions. In this paper, an analytic hierarchy process (AHP) is used to determine the weights of criteria. The proposed model can help the decision maker (DM) to find out the appropriate order to each supplier, and allows the purchasing manager(s) to manage supply chain performance on cost, quality and service. The model is explained by an illustrative example. © 2010 Elsevier B.V. All rights reserved.

Montazer M.,Amirkabir University of Technology | Pakdel E.,Islamic Azad University at Tehran
Photochemistry and Photobiology | Year: 2010

Wool is the most important animal fiber used in textile industries, but its photostability is very low. Scientists have searched for new ways to increase the photostability of wool. As TiO2 nano particles have features suitable for new applications, the UV-blocking power of nano TiO2 may be used for protecting fabrics against UV rays. Treatment of wool with TiO 2 can be effective for controlling photodegradation. This study focused on protecting wool fabric against UV rays using nano TiO2. To this end, oxidized and raw wool were treated with citric acid as the cross-linking agent and different concentrations of nano TiO2. The whiteness and yellowness of wool fabric samples were reported. XRD patterns proved the existence of TiO2 nano-particles on the wool surface. Finally, the results revealed that nano TiO2 is a suitable UV absorber on wool fabric and its effect depends on concentration. © 2010 The American Society of Photobiology.

Amirkabir University of Technology and National Science Foundation | Date: 2015-05-26

The embodiments herein provide a self-excited contact less Hybrid Electromagnetic Braking (HEB) system provided with a both Permanent Magnetic (PM) type ECB and electrically excited windings type ECB. The HEB system has an Eddy Current Brake (ECB) and a Regenerative Brake (RB) with two outer rotors and a common internal stator. The rotor assembly of the RB is coupled to the same shaft on which the ECB rotor is mounted. The RB collects an input mechanical power from the shaft to supply electrical power to ECB windings through a power electronic interface module. A controller measures the system conditions to send a control signal to the power electronic interface module to control a power flow from RB to ECB. The ECB and RB develops two braking torques on the shaft to initiate a braking action in the vehicle.

Seifvand N.,Amirkabir University of Technology | Kowsari E.,Amirkabir University of Technology
RSC Advances | Year: 2015

We are reporting a well-designed nanostructured composite, consisting of titanium dioxide (TiO2) and cobalt (Co) imidazole (Im) complex functionalized graphene oxide (FGO). The Co-Im complex was attached on the GO by covalent bonding of Im with the graphene functional groups. The films were characterized by XRD, XPS, TEM, UV-vis, FTIR and Raman spectroscopy in order to subsequently prove the evidence of hybridization of GO with the Co-Im complex. The band gap calculated for the TiO2 thin film was 3.10 eV, 2.96 eV for TiO2/GO and 2.776 eV for TiO2/FGO. Experimental results confirmed high-percentage deterioration of NOx (51%) and CO (46%). The photodegradation experiments revealed a significant photocatalytic character of TiO2, physical adsorption of GO, and the affinity of cobalt to undergo complex formation with pollutant gases. The TiO2/FGO composite increases air pollutant degradation by nearly three times that of the bare TiO2 thin film. © The Royal Society of Chemistry.

Fazilati J.,Amirkabir University of Technology | Ovesy H.R.,Amirkabir University of Technology
Composite Structures | Year: 2012

The dynamic instability of moderately thick laminated cylindrical shell panels having internal cutouts is studied by using the developed finite strip methods (FSM). The effects of perforations are investigated using a negative stiffness modeling approach. Good accuracy in the results is achieved. © 2011 Elsevier Ltd.

Asadi Z.S.,Amirkabir University of Technology | Mahboubi F.,Amirkabir University of Technology
Materials and Design | Year: 2012

The main aim of this work was to investigate the effect of the sample geometry on properties of the conventional plasma nitrided (CPN) and active screen plasma nitrided (ASPN) steel. Sample assemblies consisting of rectangular grooved steel blocks with different groove dimensions of 2, 4, 6, 8 and 10 (W)×40 (H)×20 (L)mm3 and AISI 4340 steel plates (substrates) with dimensions of 10×40×60mm3, to serve as groove cover, were prepared. The sample assemblies were conventional and active screen plasma nitrided under the gas mixture of 75%N2+25%H2, at temperatures of 500°C and 540°C, pressure of 4torr, for 5h. Properties of the nitrided substrates were investigated by evaluating compound layer thickness, case depth, phase composition and hardness profile. Results of the experiments showed that the thickness of the compound layer, hardness and nitrided case depth increased with increasing the width of the groove for both methods. Also, in each sample, nitrogen atoms penetrated more deeply in the regions of the groove closer to the edge. Hallow cathode effect occurred at the sample with 2mm width groove, in the CPN method, leading to the overheating of the sample. In ASPN, the hardness and the nitrided case depth are lower in comparison with CPN. The surface morphology of the CPN treated samples consists of cauliflower shape surface nitrides while the surface of the AS plasma nitrided samples are covered by the hexagonal particles with uniform distribution. © 2011 Elsevier Ltd.

Habibi A.,Amirkabir University of Technology | Ketabchi M.,Amirkabir University of Technology
Materials and Design | Year: 2012

The pure copper sample was severely plastically deformed by 8-pass equal channel angular rolling process. The thermal stability of processed copper was investigated by measuring the development of microhardness at isochronal annealing temperature. According to variation in microhardness, the recrystallization temperature of pure copper after 8 pass of equal channel angular rolling process was 230 °C. The influence of post-annealing on microstructure, mechanical and electrical properties of the 8-pass processed copper was investigated. Scanning electron microscopy micrographs and X-ray diffraction peak broadening analysis have demonstrated that grain size decreased with post-annealing, which is the reason for the increase in strength of the copper specimen. The electrical conductivity of sample increased after post-annealing because of the rearrangement of dislocations. © 2011.

Pourgharibshahi A.,Amirkabir University of Technology | Taghikhany T.,Amirkabir University of Technology
Journal of Constructional Steel Research | Year: 2012

One of the objectives in performance-based earthquake engineering is to quantify the seismic reliability of a structure due to future random earthquakes at a designated site. For that purpose, two performance evaluation processes that do incorporate the effect of aleatory and epistemic uncertainties are illustrated and used in order to calculate the reliability of different height Special Moment Resisting frames through two probabilistic-based measures. These two measures are the confidence levels for satisfying the desired performance levels at given hazard levels and mean annual frequency of exceeding a specified structural capacity. Analytical models are employed including panel zone and a comprehensive model for structural components that not only include strength and stiffness degradation in back bone curve, but also incorporate gradual deterioration of strength and stiffness under cyclic loading. Incremental dynamic analysis is then utilized to assess the structural dynamic behavior of the frames and to generate required data for performance based evaluations. This research is intended to contribute to the progress in improvement of the performance knowledge on seismic design and evaluation of special steel moment resisting frame structures. © 2011 Elsevier Ltd. All rights reserved.

Bodaghi M.,Amirkabir University of Technology | Shakeri M.,Amirkabir University of Technology
Composite Structures | Year: 2012

In this article, the free vibration and dynamic response of simply supported functionally graded piezoelectric cylindrical panel impacted by time-dependent blast pulses are analytically investigated. Using Hamilton's principle, the equations of motion based on the first-order shear deformation theory are derived. Also, Maxwell's electricity equation is taken as one of the governing equations. Three sets of electric surface conditions including closed circuit and two mixtures of closed and open circuit surface conditions are considered. By introducing an analytical approach and using the Fourier series expansions, the Laplace transform and Laplace inverse method, the solution of unknown variables are obtained in the real time domain based on a combination of system frequencies. Finally, the effects of various electric surface conditions, geometric parameters and the material power law index on the free vibration and transient response of functionally graded piezoelectric cylindrical panels subjected to various impulsive loads are examined in detail. © 2012 Elsevier Ltd.

Hatami F.,Research Institute of Petroleum Industry RIPI | Rahai A.,Amirkabir University of Technology
Journal of Constructional Steel Research | Year: 2012

In this study, nonlinear behavior of steel shear walls (SSW) and composite steel shear wall reinforced with carbon fibers (CSSW) was investigated. Experimental and numerical studies were carried out to evaluate the effects of fiber content/angle and panel width on the properties of these walls. Results showed that wider panel widths enhance the behavior of both the SSW and CSSW. Higher fiber contents increase energy absorption, stiffness, over-strength and capacity, but decrease ductility values. It was concluded that fiber polymer has a more dominant effect on thin SSWs. The effect of fiber angle on the behavior of the CSSW was also studied and a few equations, relating fiber angle to properties, were suggested. © 2011 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.

Moattar M.H.,Amirkabir University of Technology | Homayounpour M.M.,Amirkabir University of Technology
Speech Communication | Year: 2012

Speaker indexing or diarization is an important task in audio processing and retrieval. Speaker diarization is the process of labeling a speech signal with labels corresponding to the identity of speakers. This paper includes a comprehensive review on the evolution of the technology and different approaches in speaker indexing and tries to offer a fully detailed discussion on these approaches and their contributions. This paper reviews the most common features for speaker diarization in addition to the most important approaches for speech activity detection (SAD) in diarization frameworks. Two main tasks of speaker indexing are speaker segmentation and speaker clustering. This paper includes a separate review on the approaches proposed for these subtasks. However, speaker diarization systems which combine the two tasks in a unified framework are also introduced in this paper. Another discussion concerns the approaches for online speaker indexing which has fundamental differences with traditional offline approaches. Other parts of this paper include an introduction on the most common performance measures and evaluation datasets. To conclude this paper, a complete framework for speaker indexing is proposed, which is aimed to be domain independent and parameter free and applicable for both online and offline applications. © 2012 Elsevier B.V. All rights reserved.

Khoshnoudian F.,Amirkabir University of Technology | Kashani M.M.B.,Amirkabir University of Technology
Journal of Constructional Steel Research | Year: 2012

According to the previous researches, conventional nonlinear static procedure (NSP), which is limited to single mode response, cannot predict the seismic demands of tall buildings with reliable accuracy. To estimate the seismic demands in upper stories for tall buildings the effects of higher modes should be included. In the recent years, developing traditional pushover analysis to consider the effects of higher modes conducted researchers to propose several methods, such as N2, MPA and MMPA procedures, that have a specific approach to estimate seismic demands of structures but the accuracy of them is doubtable for estimating of hinge plastic rotations. Recently consecutive modal pushover (CMP) procedure was proposed to consider the effects of higher modes with acceptable accuracy especially in prediction of hinge plastic rotations. The CMP procedure was limited to include two or three modes, and use of higher modes might cause some inaccuracy at results of upper stories. In CMP procedure, estimation of modal participating factors is important and choosing inadequate modes may cause large errors. In this paper some changes have been applied to the CMP procedure to improve accuracy of the results and the modified method is proposed and named modified consecutive modal pushover (MCMP) procedure. In this modified method the contribution of mode is used of effective modal participating mass ratio. The comparison of MCMP procedure to exact values derived by nonlinear response history analysis (NL-RHA) demonstrated the reliable predictions and it can overcome the limitations of traditional pushover analysis. © 2011 Elsevier Ltd. All rights reserved.

Ramezanianpour A.A.,Amirkabir University of Technology | Bahrami Jovein H.,Amirkabir University of Technology
Construction and Building Materials | Year: 2012

Durability of concrete is an important issue for predicting the service life of concrete structures. Recently, the properties of metakaolin as high-quality pozzolanic materials are investigated by several researchers. It is not widely produced and used due to the lack of adequate experiments on this material in the Middle East. Local kaolin with high kaolinite content was thermally treated by a special furnace at 800°C and 60 min burning time to produce metakaolin. This study investigates the performance of concrete mixtures containing local metakaolin in terms of compressive strength, water penetration, sorptivity, salt ponding, Rapid Chloride Permeability Test (RCPT) and electrical resistivity at 7, 28, 90 and 180 days. In addition, microstructure of the cement pastes incorporating metakaolin was studied by XRD and SEM tests. The percentages of metakaolin that replace PC in this research are 0%, 10%, 12.5% and 15% by mass. The water/binder (w/b) ratios are 0.35, 0.4 and 0.5 having a constant total binder content of 400 kg/m 3. Results show that concrete incorporating metakaolin had higher compressive strength and metakaolin enhanced the durability of concretes and reduced the chloride diffusion. An exponential relationship between chloride permeability and compressive strength of concrete is exhibited. A significant linear relationship was found between Rapid Chloride Permeability Test and salt ponding test results. © 2011 Elsevier Ltd. All rights reserved.

Ovesy H.R.,Amirkabir University of Technology | Taghizadeh M.,Amirkabir University of Technology | Kharazi M.,Sahand University of Technology
Composite Structures | Year: 2012

The compressive post-buckling behavior of composite laminates containing embedded delamination with arbitrary shape is investigated analytically. For modeling the embedded delamination, the laminate is divided into three smaller regions. The higher order shear deformation theory is implemented and the formulation is based on the Rayleigh-Ritz approximation technique by the application of the simple/complete polynomial series for each region. The nonlinear equilibrium equations, which are achieved through the application of the principle of Minimum Potential Energy, are solved by employing the Newton-Raphson iterative procedure. Some interesting results are obtained and compared with those achieved by the finite element method of analysis using ANSYS commercial software. A good agreement is seen to exist between the results. This is while for a given level of accuracy in the results, ANSYS requires a markedly larger number of degrees of freedom compared to that needed by the developed method. Moreover, a considerable reduction in the load carrying capacity of laminate is noticed due to the presence of delamination. © 2011 Elsevier Ltd.

Ovesy H.R.,Amirkabir University of Technology | Fazilati J.,Amirkabir University of Technology
Composite Structures | Year: 2012

A Reddy type, third order shear deformation theory of plates is applied to the development of two versions of finite strip method (FSM), namely semi-analytical and spline methods, to predict the behavior of the moderately thick plates containing cutouts. The internal cutouts are modeled based on two different modeling approaches, and the effects of cutouts on the buckling critical stresses as well as natural frequencies are investigated. © 2011 Elsevier Ltd.

Shahabadi S.I.S.,Amirkabir University of Technology | Garmabi H.,Amirkabir University of Technology
Journal of Reinforced Plastics and Composites | Year: 2012

Water-assisted melt-intercalation process is a relatively new method for nanocomposite production. Technical challenges notwithstanding, this process is capable of bringing forth good results and promising advantages. Having used this process, we produced composites in a twin-screw extruder. The aim of this study was to find, through a designed set of experiments, the conditions that result in producing nanocomposites. In this study, the main focus of our characterization phase was on rheological behavior. We then used mechanical testing, X-ray diffraction, and atomic force microscopy for verification purposes. The results obtained from these techniques were manifold; therefore, we used response surface method to present them intelligibly. After examining different modifiers, we concluded that chain length, packing density, and cation exchange selectivity are important parameters for choosing proper modifier type. Plus, as has been reported by other groups, this process was found to be mainly diffusion-controlled rather than shear-controlled. © The Author(s) 2012 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav.

Nasrollahi V.,Amirkabir University of Technology | Arezoo B.,Amirkabir University of Technology
Materials and Design | Year: 2012

The springback phenomenon has a significant role in precision sheet metal bending. Traditionally, the designers obtain the values for springback for different materials and bending parameters from handbook tables or springback graphs. However these tables or graphs cannot be used for perforated components which are parts with holes on the bending surfaces. This paper presents the results of research in wipe bending for perforated components. In the present research the influence of process variables such as hole type, number of holes, the ratio of hole width to sheet width, die radius and pad force on springback are discussed. Some experiments are carried out on HSLA360 and St12 materials which show that the presence of holes on the bending area can affect the springback considerably. These experiments are also simulated by finite element method. The results of the finite element model used, compared with experiments show the reliability of the proposed model. These results are also used as the training data for two artificial neural networks. The first network is used for one type of hole and the second one for three types of holes. After testing both networks the results show that the latter is more accurate to predict the springback. © 2011 Elsevier Ltd.

Fallah A.,Amirkabir University of Technology | Aghdam M.M.,Amirkabir University of Technology
Composites Part B: Engineering | Year: 2012

In this paper, thermo-mechanical buckling and nonlinear free vibration analysis of functionally graded (FG) beams on nonlinear elastic foundation are investigated. Nonlinear governing partial differential equation (PDE) of motion is derived based on Euler-Bernoulli assumptions together with Von Karman strain-displacement relation. Based on the Galerkin's decomposition method, the nonlinear PDE governing equation is reduced to a nonlinear ordinary differential equation (ODE). He's variational method is employed to obtain a simple and efficient approximate closed form solution for the resulted nonlinear ODE. Comparison between results of the present work and those available in literature shows accuracy of the presented expressions. Some new results for the thermo-mechanical buckling and nonlinear free vibration analysis of the FG beams such as the effects of vibration amplitude, material inhomogeneity, nonlinear elastic foundation, boundary conditions, geometric parameter and thermal loading are presented to be used in future references. © 2011 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.

Mortazavi A.,Amirkabir University of Technology | Molladavoodi H.,Amirkabir University of Technology
Engineering Fracture Mechanics | Year: 2012

The excavation of underground openings generally causes damage to the rock in the vicinity of the openings. The dominant causes of irreversible rock deformations are damage process and plastic flow. Most of the existing elastic-plastic models employed in the analysis and design of rock structures only consider the plastic flow and ignore the full damage process. The common approach used to model the rock failure, does not model the rock realistically and often the important issues such as stiffness degradation, softening, and significant differences in rock response under tensile and compressive loadings are ignored. Therefore, developments of realistic damage models are essential in the design process of rock structures. In this paper, the basic concepts of continuum damage mechanics are outlined. Then, a more clear and accurate definition of the damage function is established. In the definition of rock damage function, many authors considered only the tensile stress condition. Since quasi brittle materials such as rock degrade under tensile and compressive stress fields, separate tensile and compressive damage functions are introduced. The proposed damage functions are formulated in the framework of a damage model which was coded and implemented into a commercial code. Accordingly, the developed algorithm was applied to the simulation of brittle rocks behavior. Using field measurements from the AECL's (Atomic Energy of Canada Limited) Mine-by Experiment tunnel, the new developed damage model was calibrated and validated for its ability to reproduce the shape and size of excavation damage zone (EDZ) around the Mine-by test tunnel. © 2012 Elsevier Ltd.

Tatari M.,Isfahan University of Technology | Dehghan M.,Amirkabir University of Technology
JVC/Journal of Vibration and Control | Year: 2012

In this work, multi-point boundary value problems are considered. These problems have important roles in the modelling of various problems in physics and engineering. Although numerous works have been carried out on the existence and uniqueness to the solution of these problems, the numerical or analytical methods are not established for solving them. In this paper the well-known He's variational iteration method is applied for solving the multi-point boundary value problems. The method is modified and the results are shown using some test problems. These results show the efficiency of the new approach. © 2011 The Author(s).

Khedmati M.R.,Amirkabir University of Technology | Nazari M.,Amirkabir University of Technology
Marine Structures | Year: 2012

This paper presents the results of a numerical investigation into the structural behaviour of preloaded tubular members under lateral impact loads by means of finite element method. The lateral load represents a statically modelled impact from collision between tubular member and a solid rectangular indenter. Three different kinds of end conditions have been applied to the model and the effects of boundary conditions are investigated. Also, the effect of preloading on the buckling strength as well as the ultimate strength for laterally impacted tubes is assessed and it will be shown that preloading and position of applying force directly affect these strengths. In other words, by increasing in the amount of preloading, ultimate strength reduces and member tends to collapse under lower amounts of loads. The influence of the position of applying lateral load has also been addressed and relevant results will be discussed. In order to verify the performance of numerical model, the results have been examined against an available experimental test. © 2011 Elsevier Ltd.

Dehghani M.,Amirkabir University of Technology | Nikravesh S.K.Y.,Amirkabir University of Technology
International Journal of Electrical Power and Energy Systems | Year: 2011

The aim of this paper is to design nonlinear decentralized controllers for multi-machine power systems. The design procedure is based on H ∞ control theory and consists of two parts. First, the feedback linearization technique is used. Then, a robust controller is designed using the linear matrix inequalities (LMI) approach. The controller has two blocks. One, is a nonlinear function of some local measurable signals such as the generator active and reactive powers, the rotor speed and the armature current. The other block is a PID controller. The linear H ∞ theory is used to tune the PID parameters. The method results in a controller which is easy for implementing in practice. The performance of the controller is tested on a sample multi-machine power system model. Simulation results show the effectiveness, robustness and good performance of the proposed controller. © 2011 Elsevier Ltd. All rights reserved.

Ebrahimi J.,Amirkabir University of Technology | Hosseinian S.H.,Amirkabir University of Technology | Gharehpetian G.B.,Amirkabir University of Technology
IEEE Transactions on Power Systems | Year: 2011

A new evolutionary algorithm known as the shuffled frog leaping algorithm is presented in this paper, to solve the unit commitment (UC) problem. This integer-coded algorithm has been developed to minimize the total energy dispatch cost over the scheduling horizon while all of the constraints should be satisfied. In addition, minimum up/down-time constraints have been directly coded not using the penalty function method. The proposed algorithm has been applied to ten up to 100 generating units, considering one-day and seven-day scheduling periods. The most important merit of the proposed method is its high convergence speed. The simulation results of the proposed algorithm have been compared with the results of algorithms such as Lagrangian relaxation, genetic algorithm, particle swarm optimization, and bacterial foraging. The comparison results testify to the efficiency of the proposed method. © 2010 IEEE.

Mousavi S.M.,Amirkabir University of Technology | Abyaneh H.A.,Amirkabir University of Technology
IEEE Transactions on Power Systems | Year: 2011

This paper presents a comprehensive approach to probabilistic characterization of aggregated load pattern of low-voltage consumers. Different from previous methods, consumer load patterns obtained from load survey are converted to empirical cumulative density functions. The functions are then used to address stochastic nature of load pattern in any given point of distribution network. The proposed approach is adopted to investigate the effect of load models on the characterization of aggregated load patterns. In addition, a goodness-of-fit analysis has been carried out to show that the load models can significantly affect the accuracy of aggregated load modeling. It is demonstrated that the constant power (real and reactive) load model which is normally adopted in most distribution network management studies may lead to misleading results compared to the actual network. Case studies are presented and discussed with reference to a real distribution network. The results verify that the proposed method is accurate and flexible, and the voltage-dependent load model is the most promising solution for the aggregated load modeling. © 2010 IEEE.

Tabatabaei S.M.,Amirkabir University of Technology | Vahidi B.,Amirkabir University of Technology
Electric Power Systems Research | Year: 2011

This paper proposes a novel methodology for the optimal location and sizing of shunt capacitors in radial distribution systems. This method is based on a fuzzy decision making which using a new evolutionary method. The capacitor placement optimization problem includes: minimizing the cost of peak power, reducing energy loss and improving voltage profile. The installation node is selected by the fuzzy reasoning supported by the fuzzy set theory in a step by step procedure. Also an evolutionary algorithm known as bacteria foraging algorithm (BFA) is utilized in solving the objective multivariable optimization problem and the optimal node for capacitor placement is determined. The proposed approach is applied to 34-bus distribution system as a test study and the results are compared with previous method. The results show that this method provides more economic solution by reducing power losses, energy loss, total required capacitive compensation and show a good improvement in nodes voltage to be in the requested range. Comparison between the proposed method in this paper and similar methods in other research works shows the effectiveness of the proposed method for solving optimum capacitor planning problem. © 2010 Elsevier B.V.

Hosseinzadeh S.A.A.,Amirkabir University of Technology | Tehranizadeh M.,Amirkabir University of Technology
Journal of Constructional Steel Research | Year: 2012

The nonlinear behavior of steel plate shear walls (SPSWs) with stiffened large rectangular openings used as windows or doors in buildings is studied. A number of SPSWs with and without openings are numerically analyzed, and the results are utilized (a) to characterize the behavior of SPSWs with the openings, (b) to study the effects of various opening features as well as size of local boundary elements (LBE) around the opening and thickness of infill plates on either side of the opening and (c) to investigate the changes in the system strength, stiffness and ductility due to the introduction of the openings. Results show that the procedure addressed by AISC Design Guide 20 for design of beams above and below the opening level is not perfect. Use of thicker or thinner infill plates or weaker profiles for the LBE can alter the yielding sequence in the system. Notably, the type, location and geometry of stiffened openings are not influential themselves on the system strength, although different LBE sizes required for different openings may have some effects. The introduction of stiffened openings in different SPSWs increases both the ultimate strength and stiffness, while somewhat decreases the ductility ratio. © 2012 Elsevier Ltd. All rights reserved.

Bayat M.,Amirkabir University of Technology | Aghdam M.M.,Amirkabir University of Technology
Composites Part B: Engineering | Year: 2012

In this study, a generalized plane strain micromechanical model is presented to obtain micro-stress/strain fields within the unidirectional (UD) hollow fiber reinforced composites. In addition, the thermally induced residual stresses during cooling down process, overall elastic properties and energy absorption capability of hollow reinforced composite are studied. The representative volume element (RVE) of the composite consists of a quarter of the fiber surrounded by matrix to represent the real composite with repeating square array of fibers. Fully bonded fiber-matrix interface condition is considered and the displacement continuity and traction reciprocity are properly imposed to the interface. The cubic serendipity shape functions are used to convert the solution domain to a proper rectangular domain. A Least-squares based differential quadrature element method (DQEM) is used to obtain solutions for the governing partial differential equations of the problem. Results of the presented method for various stress and displacement components and thermal residual stresses show excellent agreement with finite element analysis. Furthermore, predicted overall properties also show good agreement with other available analytical and finite element results. Moreover, results also revealed that the presented model can provide highly accurate predictions with a few number of elements and grid points within each element. © 2011 Elsevier Ltd. All rights reserved.

Golzar K.,Amirkabir University of Technology | Jalali-Arani A.,Amirkabir University of Technology | Nematollahi M.,Amirkabir University of Technology
Construction and Building Materials | Year: 2012

Improving bitumen properties by using polymeric materials such as ethylene butyl acrylate, styrene-ethylene-butylene-styrene, ethylene vinyl acetate and styrene-butadiene-styrene has been reported by the researchers. To avoid practical measuring difficulties, Artificial Neural Network has been employed to predict the properties. The presented study, by employing practical data obtained by the researchers and using MATLAB program, has suggested models to predict physical-mechanical properties of modified bitumen. In the process, an appropriate architecture has been obtained to predict each of desirable properties by using try and error method. Comparing the model results with experimental data showed the high acceptability of the suggested models. © 2012 Elsevier Ltd. All rights reserved.

Majidpour M.,Amirkabir University of Technology
Journal of Engineering and Technology Management - JET-M | Year: 2016

This paper highlights distinctive features of technological catch-up in complex product systems (CoPS). This paper contrasts catch-up trends in CoPS with trends in mass-market commodity goods, such as those produced in South Korea. Developing countries are lagging behind in many CoPS areas and technological catch-up in CoPS industries is a very challenging process. This paper argues that due to specific technological and market regimes, the dominant model of technological catch-up in CoPS is based on path-following catch-up. Stage-skipping catch-up is only possible in minor technologies and path-creating catch-up is almost impossible in CoPS industry. © 2016 Elsevier B.V.

Yasavol N.,Tarbiat Modares University | Mahboubi F.,Amirkabir University of Technology
Materials and Design | Year: 2012

Plasma nitriding is a surface treatment process, which is widely used to improve wear, fatigue and corrosion resistance of the industrial parts. Nevertheless, corrosion resistance can be enhanced by oxidizing of the nitrided components. This paper considers the duplex treatment of plasma nitriding and post-oxidizing of AISI 4130 low alloy steel. After plasma nitriding, the post-oxidizing treatment was done in the various gas mixtures of O2/H2 and temperatures. The treated samples were characterized using metallographic techniques, XRD, SEM, micro-hardness and potentiodynamic test. The X-ray diffraction confirmed the development of gamma prime and epsilon iron nitride phases during the nitriding, and hematite (Fe2O3) and magnetite (Fe3O4) phases under the oxidizing process. The sample oxidized under O2/H2 volume ratio of 1/3 showed the best corrosion resistance, which is attributed to the formation of an almost single phase magnetite oxide layer on the top of the compound layer. © 2012.

Abdullah A.,Amirkabir University of Technology | Malaki M.,Amirkabir University of Technology | Eskandari A.,Amirkabir University of Technology
Materials and Design | Year: 2012

Residual stresses exist in all manufacturing processes which use heat and/or force such as casting, forming, machining and welding. Sometimes they cause decrease in strength and life of components especially under dynamic loads and vibration conditions. To improve fatigue strength, a number of post treatment operations are being used such as grinding, shot peening, re-melting and heat treatment. Ultrasonic peening is a newly developed method for the improvement of fatigue strength of, mainly, welded joints and structures. By employing this process, geometry of weld toe can be modified for reducing the stress concentration. In addition, elimination of tensile residual stresses, exertion of compressive residual stresses and closing of cracks, voids and cavities are expected, too. The extra advantage of this technology is its application on massive and large structures which cannot be treated by other procedures. For investigating the effect of ultrasonic peening on stainless steel-304 welded parts, a series of experiments were designed and implemented. Ultrasonic peening is mostly used as a mechanical surface treatment method in the automotive and aerospace industries. However, this paper comprises the results of experimental fatigue strength tests along with metallography, micro hardness and corrosion resistance tests of welded pieces with and without processing by ultrasonic peening. Experiments proved that under post treatment by ultrasonic peening, a better mechanical and corrosion resistance is achieved. © 2012.

Kenevisi M.S.,Amirkabir University of Technology | Mousavi Khoie S.M.,Amirkabir University of Technology
Materials and Design | Year: 2012

Transient Liquid Phase (TLP) bonding of two dissimilar alloys Al7075 and Ti-6Al-4V has been done at 500°C under 5×10-4torr. Cu was electrodeposited on Al7075 and Ti-6Al-4V surfaces, 50μm thick Sn-4Ag-3.5Bi film was used as interlayer and bonding process was carried out at several bonding times. The microstructure of the diffusion bonded joints was evaluated by Light Optical Microscopy (LOM), Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS). The eutectic and intermetallic compounds formation along Al7075 grain boundaries and Ti/Al interface such as θ(Al2Cu), TiAl and Ti3Al were responsible for joint formation at the aluminum and titanium interfaces. Microhardness and shear strength tests were used to investigate the mechanical properties of the bonds. Hardness of the joints increased with increasing bonding time which can be attributed to the intermetallics formation at the interface. The study showed that the highest bond strength was 36MPa which was obtained for the samples joined for 60min. © 2012 Elsevier Ltd.

Safarzadegan Gilan S.,Amirkabir University of Technology | Bahrami Jovein H.,Amirkabir University of Technology | Ramezanianpour A.A.,Amirkabir University of Technology
Construction and Building Materials | Year: 2012

This paper develops a hybrid support vector regression (SVR) - particle swarm optimization (PSO) model to predict the compressive strength (CS) and rapid chloride penetration test (RCPT) results of concretes containing metakaolin. The predictive accuracy of SVR models is highly dependent on their learning parameters. Therefore, PSO is exploited to seek the optimal hyper-parameters for SVR in order to improve its generalization capability. Moreover, a SVR-based sequential forward feature selection algorithm is proposed to disclose the most dominant input variables for the prediction of CS and RCPT results. The performance of the hybrid model is compared with the well-known system modeling method of adaptive neural-fuzzy inference system (ANFIS) by using 100 data samples with 25 different mix proportions established by experiments. The results show that the hybrid model has strong potential to predict material properties with high degree of accuracy and robustness. © 2012 Elsevier Ltd. All rights reserved.

Mirzaei D.,Amirkabir University of Technology | Dehghan M.,Amirkabir University of Technology
CMES - Computer Modeling in Engineering and Sciences | Year: 2011

The meshless local Petrov-Galerkin (MLPG) method with an efficient technique to deal with the time variable are used to solve the heat conduction problem in this paper. The MLPG is a meshless method which is (mostly) based on the moving least squares (MLS) scheme to approximate the trial space. In this paper the MLS is used for approximation in both time and space domains, and we avoid using the time difference discretization or Laplace transform method to overcome the time variable. The technique is applied for continuously nonhomogeneous functionally graded materials (FGM) in a finite strip and a hallow cylinder. This idea can be easily extended to all MLS based methods such as the element free Galerkin (EFG), the local boundary integral equation (LBIE) and etc. © 2011 Tech Science Press.

Ramezanzadeh B.,Amirkabir University of Technology | Attar M.M.,Amirkabir University of Technology
Progress in Organic Coatings | Year: 2011

The mechanical and viscoelastic properties of an epoxy-polyamide coating containing nano and micro sized ZnO particles were studied. The nanocomposites were prepared at different loadings of the nano sized ZnO particles. The composites were also prepared using micro sized ZnO particles at different lambdas (lambda (λ) = PVC/CPVC). The optical properties of each nanocomposite were studied by UV-vis technique. Dynamic mechanical thermal analysis (DMTA) and micro-Vickers were used to investigate the mechanical properties of the composites. The viscoelastic properties of the composites were studied by a tensile test. The fracture morphologies of the composites were studied by a scanning electron microscope (SEM). An increase in Tg together with a decrease in cross-linking density of the composites was obtained when the coating was reinforced with the micro sized ZnO particles. On the other hand, the Tg and cross-linking density of the composites were decreased using nano sized ZnO particles. It was also found that, the Young's modulus and the fracture energy of the coating were decreased using micro and nano sized ZnO particles. The greater toughness as well as fracture energy of the composite was obtained when it was reinforced with the nano sized ZnO particles. The curing behavior of the epoxy coating was affected in the presence of the micro and nano sized ZnO particles. © 2011 Elsevier B.V.

Ramezanzadeh B.,Amirkabir University of Technology | Attar M.M.,Amirkabir University of Technology
Progress in Organic Coatings | Year: 2011

The effects of micro and nano sized ZnO particles on the corrosion resistance and hydrolytic degradation of an epoxy coating were studied. Different analytical techniques including scanning electron microscope (SEM), electrochemical impedance spectroscopy (EIS), dynamic thermal mechanical analysis (DMTA) and nano-indentation were utilized to evaluate the hydrolytic degradation as well as the corrosion resistance of the coatings in exposure to 3.5 wt% NaCl solution. It was found that the epoxy coating resistance against corrosive electrolyte was significantly improved using nano and micro sized ZnO particles. The corrosion resistance of the nanocomposite was considerably greater than the one reinforced with the micro-ZnO particles. Moreover, the resistance of the coating reinforced with the nano sized particles against hydrolytic degradation in exposure to the corrosive electrolyte was considerably greater than the one reinforced with the micro sized particles. Decrease in both nano hardness and cross-linking density of the epoxy coating reinforced with nanoparticles after exposure to the corrosive electrolyte were considerably lower than the blank sample and the sample reinforced with the micro sized ZnO particles. Using nano sized particles the coating adhesion loss decreased. © 2011 Elsevier B.V.

Lotfi A.,Shahid Beheshti University | Dehghan M.,Amirkabir University of Technology | Yousefi S.A.,Shahid Beheshti University
Computers and Mathematics with Applications | Year: 2011

This paper presents a numerical method for solving a class of fractional optimal control problems (FOCPs). The fractional derivative in these problems is in the Caputo sense. The method is based upon the Legendre orthonormal polynomial basis. The operational matrices of fractional Riemann-Liouville integration and multiplication, along with the Lagrange multiplier method for the constrained extremum are considered. By this method, the given optimization problem reduces to the problem of solving a system of algebraic equations. By solving this system, we achieve the solution of the FOCP. Illustrative examples are included to demonstrate the validity and applicability of the new technique. © 2011 Elsevier Ltd. All rights reserved.

Saadatmandi A.,University of Kashan | Dehghan M.,Amirkabir University of Technology
Computers and Mathematics with Applications | Year: 2011

Fractional differentials provide more accurate models of systems under consideration. In this paper, approximation techniques based on the shifted Legendre-tau idea are presented to solve a class of initial-boundary value problems for the fractional diffusion equations with variable coefficients on a finite domain. The fractional derivatives are described in the Caputo sense. The technique is derived by expanding the required approximate solution as the elements of shifted Legendre polynomials. Using the operational matrix of the fractional derivative the problem can be reduced to a set of linear algebraic equations. From the computational point of view, the solution obtained by this method is in excellent agreement with those obtained by previous work in the literature and also it is efficient to use. © 2011 Elsevier Ltd. All rights reserved.

Vahidkhah K.,Amirkabir University of Technology | Fatouraee N.,Amirkabir University of Technology
International Journal for Numerical Methods in Biomedical Engineering | Year: 2012

Because of their deformability and tendency to form aggregates, red blood cells (RBCs) immensely affect the hydrodynamic properties of blood flow in microcirculation. In this paper, RBCs' two-dimensional deformation and motion in Poiseuille flow and in a stenosed arteriole is numerically investigated by the immersed boundary-lattice Boltzmann method. The RBCs are modeled as suspended capsules of fluid in plasma flow. A neo-Hookean elastic model with bending resistance is utilized for the RBC membrane. Also, the suspending plasma is modeled as an incompressible Newtonian fluid. To take the effects of aggregation and dissociation of RBCs into account, intercellular interaction is modeled by the Morse potential. The effects of essential parameters namely, mechanical resistance of the RBC membrane, plasma viscous forces, and cell membrane adhesion strength on RBC behavior are presented. Motions and deformations of RBCs in a stenosis and the effects of the stenosed zone on the behavior of cell aggregates were also simulated and analyzed in this study. © 2011 John Wiley and Sons, Ltd.

Kowsari E.,Amirkabir University of Technology | Faraghi G.,Malek-Ashtar University of Technology
Materials Research Bulletin | Year: 2010

Flower-like Y2O3 nano-/microstructured phosphors without metal activators have successfully been fabricated by an ionic liquid (IL)-assisted method involving temperature (600 8C) annealing. In this paper, the effect of IL concentration on themorphology of the product has been investigated. The IL plays a crucial role in the formation of various morphologies of Y2O3. The structural and morphological features of the obtained samples have been characterized by means of X-ray powder diffraction (XRD) analysis, photoluminescence spectra (PL), Fourier-transform infrared (FT-IR) spectra and X-ray photoelectron spectra (XPS). The photoluminescence spectra of the products exhibit an intense bluish-white emission (ranging from 405 to 430 nm and centered at 418 nm). The luminescent mechanisms have been ascribed to the carbon impurities in the Y 2O3 host. The effect of the ILs cation and the counter anions on the Y2O3 morphology of these nanostructures was studied experimentally. It was observed that Y2O3 morphology and PL of these nanostructures were strongly influenced by the type of cation and anion. As the length of the subsidiary chain of cation section of IL (imidaziole ione) reduces, the thickness of the nano-sheets increases. It is expected that the present method may easily be extended to similar nano-/microstructures of other oxide materials. Such investigations are currently underway. © 2010 Elsevier Ltd. All rights reserved.

Zare Y.,Amirkabir University of Technology | Garmabi H.,Amirkabir University of Technology
Applied Surface Science | Year: 2014

In this paper, the adhesion at the interface between two nanofillers (montmorillonite and CaCO3) and a polymer matrix (PP) in a ternary polymer nanocomposite is analyzed by modeling of mechanical properties. Also, Sato-Furukawa model is simpli.ed for calculation of tensile modulus in the ternary nanocomposites. Moreover, linear and quadratic models are well examined for yield strength of the ternary samples. A good agreement is observed between the experimental results and the predictions, which validate the current modeling for a ternary system. Although the present ternary samples contain a high content of nanoparticles, the theoretically obtained parameters by several models confirm the existence of a good interfacial adhesion between both nano.llers and PP matrix. Additionally, all studied models demonstrate the largest level of interfacial bonding in samples containing 4 wt% of MMT and different CaCO3 contents (2-20 wt%). © 2014 Elsevier B.V. All rights reserved.

Jalal M.,Amirkabir University of Technology | Fathi M.,Razi University | Farzad M.,Islamic Azad University at Shahrood
Mechanics of Materials | Year: 2013

In the present study, strength enhancement and durability-related characteristics along with rheological, thermal and microstructural properties of high strength self compacting concrete (HSSCC) containing nano TiO 2 and industrial waste ash namely as fly ash (FA) have been investigated. With this respect, Portland cement was replaced by up to 15 wt% waste ash and up to 5 wt% TiO2 nanoparticles and the properties of HSSCC specimens were measured. It was found that with the aim of energy saving and recycling of waste materials, addition of FA as a natural pozzolan can improve the rheological, mechanical and durability properties of concrete at higher ages. TiO2 nanoparticles as a partial replacement of cement up to 4 wt% could accelerate C-S-H gel formation as a result of increased crystalline Ca(OH)2 amount at the early age of hydration and hence improve the microstructure of concrete leading to improved durability-related properties and strength enhancement of the concrete. Several empirical relationships for predicting flexural and split tensile strength of concrete based on compressive strength for HSSCC containing FA and nano TiO2 at different ages have been obtained. Finally, an energy-based assessment of strength enhancement of nano-containing concrete has been presented. © 2013 Elsevier Ltd. All rights reserved.

Esfahani S.E.,Islamic Azad University at South Tehran | Kiani Y.,Amirkabir University of Technology | Eslami M.R.,Amirkabir University of Technology
International Journal of Mechanical Sciences | Year: 2013

In the present study, thermal buckling and post-buckling analysis of Functionally Graded Material (FGM) Timoshenko beams resting on a non-linear elastic foundation are examined. Thermal and mechanical properties of the FGM media are considered to be functions of both temperature and position. Theory of Timoshenko beam combined with von-Karman's strain-displacement relations are applied in virtual work principle to obtain the system of non-linear equilibrium equations. Different types of boundary conditions such as clamped, simply supported, and rolled edges are assumed for edge supports. Generalized Differential Quadrature Method (GDQM) is employed to discrete the equilibrium equations in space domain. Post-buckling equilibrium paths are depicted for different values of the power law index, non-linear elastic foundation parameters, boundary conditions, thermal loading type, and slenderness ratio. It is found that depending on the boundary conditions and the type of thermal loading, the response of the structure may be of the bifurcation-type or unique stable path. © 2013 Elsevier Ltd.

Hosseinzadeh A.,Amirkabir University of Technology | Reza A.M.,University of Wisconsin - Milwaukee
IEEE Transactions on Systems, Man, and Cybernetics, Part B: Cybernetics | Year: 2012

A classifier combining strategy, virtual voting by random projection (VVRP), is presented. VVRP takes advantage from the bounded distortion incurred by random projection in order to improve accuracies of stable classifiers like discriminant analysis (DA) where existing classifier combining strategies are known to be failed. It uses the distortion to virtually generate different training sets from the total available training samples in a way that does not have the potential for overfitting. Then, a majority voting combines the base learners trained on these versions of the original problem. VVRP is very simple and just needs determining a proper dimensionality for the versions, an often very easy task. It is shown to be stable in a very large region of the hyperplane constructed by the dimensionality and the number of the versions. VVRP improves the best state-of-the-art DA algorithms in both small and large sample size problems in various classification fields. © 2012 IEEE.

Sadeghi H.,Amirkabir University of Technology | Kardan A.A.,Amirkabir University of Technology
Computers in Human Behavior | Year: 2015

The benefits of computer-supported collaborative learning are well established. To apply this learning strategy, at the initial step learners must be assigned to best collaborative groups. It is a crucial task, because group-mates of each student have major impacts on his/her learning during the collaboration period. In the literature, various approaches have been offered to tackle this problem. However, they suffered from failure to meet all the problem requirements and/or non-optimal solutions and/or very long process time. This study discloses how the problem and all of its requirements can be efficaciously formulated through a binary integer programming approach to construct a linear model which is optimally solvable in a reasonable time. The concept of justice in the context of learner group formation is also introduced and we expose how it can be quantified and applied to the model. For the experiments, 35 undergraduate learners experience collaborative learning through an online course forum for a semester. The performance of the new method was evaluated and compared with results obtained from random grouping and two other greedy and heuristic techniques in terms of four indicators: execution time of the group formation task, mean deviation of the achieved solutions from the optimal, mean student satisfaction with the learning experience, and mean learner new acquired knowledge from collaborative learning. Finding revealed that though the new method was not as fast as the heuristic ones, it generated an optimum solution in a reasonably short time. Results also indicated that the learners were more satisfied and performed better when they were grouped via the suggested method. © 2015 Elsevier Ltd. All rights reserved.

Tavasoli A.,Amirkabir University of Technology
ISA transactions | Year: 2012

Optimum coordination of individual brakes and front/rear steering subsystems is presented. The integrated control strategy consists of three modules. A coordinated high-level control determines the body forces/moment required to achieve vehicle motion objectives. The body forces/moment are allocated to braking and steering subsystems through an intermediate unit, which integrates available subsystems based on phase plane notion in an optimal manner. To this end, an optimization problem including several equality and inequality constraints is defined and solved analytically, such that a real-time implementation can be realized without the use of numeric optimization software. A low-level slip-ratio controller works to generate the desired longitudinal forces at small longitudinal slip-ratios, while averting wheel locking at large slip-ratios. The efficiency of the suggested approach is demonstrated through computer simulations. Copyright © 2012 ISA. Published by Elsevier Ltd. All rights reserved.

Mahmoodi N.M.,Iran Institute for Color Science and Technology | Hayati B.,Amirkabir University of Technology | Arami M.,Amirkabir University of Technology | Lan C.,University of Ottawa
Desalination | Year: 2011

In this paper, the adsorption of Acid Black 26 (AB26), Acid Green 25 (AG25) and Acid Blue 7 (AB7) onto Pine Cone (PC) was investigated in aqueous solution. Surface study of PC was investigated using Fourier transform infrared (FTIR) and scanning electron microscopy (SEM). The effect of operational parameters such as adsorbent dosage, dye concentration, inorganic anion (salt), pH and temperature onto dye removal was studied. The intraparticle diffusion model, the pseudo-first order and the pseudo-second order were used to describe the kinetics data. Equilibrium isotherms were analyzed using Langmuir, Freundlich and Tempkin adsorption models. Thermodynamic parameters of dye adsorption were obtained. The experimental data fitted well to the pseudo-second order kinetics model for dyes. The results indicated that isotherm data of AB26 and AG25 followed Langmuir isotherm and isotherm data of AB7 followed Freundlich isotherm models. The thermodynamic data indicated that the adsorption was endothermic process. Dye desorption studies in aqueous solution at pH 12 showed that maximum desorption of 93%, 97% and 94.5% were achieved for AB26, AG25 and AB7, respectively. It can be concluded that PC could be effectively employed as an effective biosorbent for the removal of dyes. © 2010 Elsevier B.V.

Kamali A.,Amirkabir University of Technology | Fatemi Ghomi S.M.T.,Amirkabir University of Technology | Jolai F.,University of Tehran
Computers and Mathematics with Applications | Year: 2011

Supply chain management is concerned with the coordination of different parts of the production system. Companies have realized that they must closely collaborate with the suppliers of their strategic components or products. Recently, developing integrated inventory models for the supplier selection problem has attracted a significant amount of attention amongst researchers. In these models some incentives are required from the vendors to motivate the buyer to change his (her) policies to the policy which is optimal for the entire system. Quantity discount policies are used as common incentives in the literature. However, the literature on this problem does not incorporate quantity discount into the coordination model. This paper develops a multi-objective mixed integer nonlinear programming model to coordinate the system of a single buyer and multiple vendors under an all-unit quantity discount policy for the vendors. Due to the complexity of the problem two well known meta-heuristic algorithms are proposed to solve the problem. An illustrative example is given to show the behavior of the model. Results obtained from solving the sample problems show good performance of the proposed algorithms in finding the optimal solutions. © 2011 Elsevier Ltd. All rights reserved.

Dehghan M.,Amirkabir University of Technology | Fakhar-Izadi F.,Amirkabir University of Technology
Mathematical and Computer Modelling | Year: 2011

Ostrovsky equation (modified Korteweg-de Vries equation) is used for modeling of a weakly nonlinear surface and internal waves in a rotating ocean. The Ostrovsky equation is a nonlinear partial differential equation and also is complicated due to a nonlinear integral operator as well as spatial and temporal derivatives. In this paper we propose a numerical scheme for solving this equation. Our numerical method is based on a collocation method with three different bases such as B-spline, Fourier and Chebyshev. A numerical comparison of these schemes is also provided by three examples. © 2011 Elsevier Ltd.

Eslahchi M.R.,Tarbiat Modares University | Dehghan M.,Amirkabir University of Technology
Computers and Mathematics with Applications | Year: 2011

In this research first we explicitly obtain the relation between the coefficients of the Taylor series and Jacobi polynomial expansions. Then we present a new method for computing classical operational matrices (derivative, integral and product) for general Jacobi orthogonal functions (polynomial and rational). This method can be used for many classes of orthogonal functions. © 2011 Elsevier Ltd. All rights reserved.

Jamshidi M.,Building Research Institute, Egypt | Ramezanianpour A.A.,Amirkabir University of Technology
Construction and Building Materials | Year: 2011

Asbestos fibers have been used in cement based materials to improve tensile strength and controlling crack formation and propagation. Asbestos-cement sheets are produced by the Hatschek technique in a number of developing countries. Due to the health and safety issues in the asbestos products, attempts have been made to substitute other fibers using the Hatschek system for cement sheets. The quality and homogeneity of the products depend on the type of fibers and varies substantially in the Hatschek system during production. In this investigation acrylic and glass fibers in separate and hybrid forms were used for manufacture of flat and corrugated sheets. Higher strength and ductility were obtained for the sheets containing glass fibers. Performance was even better when hybrid system of acrylic and glass fibers was used. The hybrid system was used for production of fiber-cement sheets in factory. This system is proposed as an appropriate alternative for substituting asbestos in the Hatschek process. © 2010 Elsevier Ltd. All rights reserved.

Ejtemaei M.,Amirkabir University of Technology | Gharabaghi M.,University of Tehran | Irannajad M.,Amirkabir University of Technology
Advances in Colloid and Interface Science | Year: 2014

In recent years, extraction of zinc from low-grade mining tailings of oxidized zinc has been a matter of discussion. This is a material which can be processed by flotation and acid-leaching methods. Owing to the similarities in the physicochemical and surface chemistry of the constituent minerals, separation of zinc oxide minerals from their gangues by flotation is an extremely complex process. It appears that selective leaching is a promising method for the beneficiation of this type of ore. However, with the high consumption of leaching acid, the treatment of low-grade oxidized zinc ores by hydrometallurgical methods is expensive and complex. Hence, it is best to pre-concentrate low-grade oxidized zinc by flotation and then to employ hydrometallurgical methods. This paper presents a critical review on the zinc oxide mineral flotation technique. In this paper, the various flotation methods of zinc oxide minerals which have been proposed in the literature have been detailed with the aim of identifying the important factors involved in the flotation process. The various aspects of recovery of zinc from these minerals are also dealt with here. The literature indicates that the collector type, sulfidizing agent, pH regulator, depressants and dispersants types, temperature, solid pulp concentration, and desliming are important parameters in the process. The range and optimum values of these parameters, as also the adsorption mechanism, together with the resultant flotation of the zinc oxide minerals reported in the literature are summarized and highlighted in the paper. This review presents a comprehensive scientific guide to the effectiveness of flotation strategy. © 2013 Elsevier B.V.

Dehghani K.,Amirkabir University of Technology | Mazinani M.,Amirkabir University of Technology
Materials and Manufacturing Processes | Year: 2011

In the present work, a nanostructured layer was formed on the surface of pure copper via friction stir processing (FSP). The surface nanostructuring can be of significant importance in terms of surface-dependent properties such as fatigue, wear, coating, and even corrosion. During FSP, the applied rotating and traverse speeds were 1600rpm and 50mm/min, respectively. The results show that a nanograin layer of about 90μm thick, having the grain size of 50-200nm, was formed on the surface of pure copper. The nanostructured layer was then characterized using atomic force microscopy (AFM), field emission scanning electron microscopy (FESEM), as well as scanning electron microscopy (SEM). The microhardness of nanograin layer (175Hv) was about three times that of the base material (60Hv). Copyright © Taylor & Francis Group, LLC.

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.

Behnam B.,Amirkabir University of Technology
Structural Design of Tall and Special Buildings | Year: 2016

Post-earthquake fires (PEF) may result in a catastrophe in urban regions even worse than the earthquake itself. Most urban structures are not designed to resist two subsequent extreme loads such as earthquake and fire. Thus, these types of structures are too weak when subjected to the PEF loads. On the other hand, it is well understood that irregular building structures are more susceptible to sustain earthquake damage than regular buildings. Investigating irregular buildings can therefore be more important when there is a high possibility of PEF. While there are various irregularities, here, vertical irregularity is considered. The study is performed on one irregular seven-story tall moment-resisting steel frame designed based on the American Society of Civil Engineers code. The frame is firstly subjected to an earthquake load with the peak ground acceleration of 0.35 g and then is exposed to a generalized exponential fire curve. To make a comparison between the results, the PEF analysis is also performed for the regular frame. The results show that there is a marked difference between the PEF of the regular frame with that of the irregular frame. In addition, two types of failure—local and global—were observed during the analysis, where the local collapse is related to the deflection of beams, and the global collapse is pertained to the considerable movement of the columns. It is observed during the analysis that the irregular frames are more susceptible to collapse globally. Copyright © 2015 John Wiley & Sons, Ltd. Copyright © 2015 John Wiley & Sons, Ltd.

Rahimian M.,Islamic Azad University at Semnan | Parvin N.,Amirkabir University of Technology | Ehsani N.,Malek-Ashtar University of Technology
Materials and Design | Year: 2011

Aluminum matrix composite is one of the most conventional types of metal matrix composites. This paper deals with the effect of production parameters on wear resistance of Al-Al2O3 composites. Alumina powder with a particle size of 12, 3 and 48μ and pure aluminum powder with particle size of 30μ were used. The amount of added alumina powder was up to 20%. Ball milling was utilized to blend the powders. The range of sintering temperature and time were 500, 550 and 600°C and 30, 45, 60 and 90min respectively. It was found that increasing sintering temperature results in increasing density, hardness and wear resistance and homogenization of the microstructure. However at certain sintering temperatures and time, considerable grain growth and reduction of hardness value occurred, leading to the degradation of wear resistance. The results showed that at high alumina content, relative density of the composite increases. However, after raising the particle size of alumina, relative density initially increases and then drops to lower values. Increasing weight percent of alumina powder leads to higher hardness and consequently improves the wear resistance of Al-Al2O3 composite. The use of fine alumina particles has a similar effect on hardness and the wear resistance. Finally, a finer grain size was observed, at high amount and low size of the reinforcement particle. © 2010 Elsevier Ltd.

Fakhari V.,Amirkabir University of Technology | Ohadi A.,Amirkabir University of Technology | Yousefian P.,Amirkabir University of Technology
Composite Structures | Year: 2011

In the present study, finite element formulation based on higher order shear deformation plate theory is developed to analyze nonlinear natural frequencies, time and frequency responses of functionally graded plate with surface-bonded piezoelectric layers under thermal, electrical and mechanical loads. The von Karman nonlinear strain-displacement relationship is used to account for the large deflection of the plate. The material properties of functionally graded material (FGM) are assumed temperature-dependent. The temperature field has uniform distribution over the plate surface and varies in the thickness direction. The considered electric field only has non-zero-valued component Ez. Numerical results are presented to study effects of FGM volume fraction exponent, applied voltage in piezoelectric layers, thermal load and vibration amplitude on nonlinear natural frequencies and time response of FGM plate with integrated piezoelectric layers. In addition, nonlinear frequency response diagrams of the plate are presented and effects of different parameters such as FGM volume fraction exponent, temperature gradient, and piezoelectric voltage are investigated. © 2011 Elsevier Ltd.

Nekoubin N.,Amirkabir University of Technology
International Journal of Thermal Sciences | Year: 2016

In this study, the conjugate conduction-convection heat transfer in the thermally developing region of a parallel plate microchannel with the constant heat flux at the walls is investigated. The flow is forced to move by applying the pressure difference and is assumed to be fully developed. Moreover, the effects of electrical double layer (EDL) with low zeta potential on the fluid flow and on the temperature field are taken into account. To do so, an analytical/numerical method is proposed to solve the energy equation in a single domain formulation. The energy equation is split and a series solution based on the variational calculus is employed to determine the temperature field. The effects of various parameters such as Peclet number, non-dimensional wall thickness, thermal conductivity ratio, and the zeta potential are studied in details. The obtained results show that the increasing of zeta potential decreases the heat transfer rate. Moreover, the Nusselt number has a non-monotonic behavior when the wall thickness varies. © 2016 Elsevier Masson SAS

Mehrara A.,Amirkabir University of Technology | Khodaii A.,Amirkabir University of Technology
Journal of Materials in Civil Engineering | Year: 2011

A closer look at a number of researches carried out on the stripping potential of asphalt mixtures shows that there is no global agreement on a comprehensive procedure for evaluation of the moisture sensitivity of these mixtures. Therefore, an attempt was made to assess moisture sensitivity and its interaction with permanent deformation through performing a dynamic creep test on coarse graded and dense graded asphalt mixtures in different environmental and loading conditions, using a UTM25 loading machine. In the next step, test results were interpreted by using a newly developed three-stage creep model. According to the results, the coarse graded mixtures have lower moisture sensitivity and could better resist permanent deformations than the dense graded mixtures. Based on the creep models, low stress levels cannot appropriately show the behavior of asphalt specimens. It was also concluded that, at higher temperatures, asphalt mixtures might become more sensitive to temperature than moisture. © 2011 ASCE.

Ahmadlou M.,Amirkabir University of Technology | Ahmadlou M.,Dynamic Brain Research Office | Adeli H.,Ohio State University | Adeli A.,Ohio State University
International Journal of Psychophysiology | Year: 2012

EEGs of the frontal brain of patients diagnosed with major depressive disorder (MDD) have been investigated in recent years using linear methods but not based on nonlinear methods. This paper presents an investigation of the frontal brain of MDD patients using the wavelet-chaos methodology and Katz's and Higuchi's fractal dimensions (KFD and HFD) as measures of nonlinearity and complexity. EEGs of the frontal brain of healthy adults and MDD patients are decomposed into 5 EEG sub-bands employing a wavelet filter bank, and the FDs of the band-limited as well as those of their 5 sub-bands are computed. Then, using the ANOVA statistical test, HFDs and KFDs of the left and right frontal lobes in EEG full-band and sub-bands of MDD and healthy groups are compared in order to discover the FDs showing the most meaningful differences between the two groups. Finally, the discovered FDs are used as input to a classifier, enhanced probabilistic neural network (EPNN), to discriminate the MDD from healthy EEGs. The results of HFD show higher complexity of left, right and overall frontal lobes of the brain of MDD compared with non-MDD in beta and gamma sub-bands. Moreover, it is observed that HFD of the beta band is more discriminative than HFD of the gamma band for discriminating MDD and non-MDD participants, while the KFD did not show any meaningful difference. A high accuracy of 91.3% is achieved for classification of MDD and non-MDD EEGs based on HFDs of left, right, and overall frontal brain beta sub-band. The findings of this research, however, should be considered tentative because of limited data available to the authors. © 2012 Elsevier B.V.

Miandoabchi E.,Institute for Trade Studies and Research | Daneshzand F.,Amirkabir University of Technology | Szeto W.Y.,University of Hong Kong | Zanjirani Farahani R.,Kingston University
Computers and Operations Research | Year: 2013

This paper addresses the problem of designing urban road networks in a multi-objective decision making framework. Given a base network with only two-way links, and the candidate lane addition and link construction projects, the problem is to find the optimal combination of one-way and two-way links, the optimal selection of network capacity expansion projects, and the optimal lane allocations on two-way links to optimize the reserve capacity of the network, and two new travel time related performance measures. The problem is considered in two variations; in the first scenario, two-way links may have different numbers of lanes in each direction and in the second scenario, two-way links must have equal number of lanes in each direction. The proposed variations are formulated as mixed-integer programming problems with equilibrium constraints. A hybrid genetic algorithm, an evolutionary simulated annealing, and a hybrid artificial bee colony algorithm are proposed to solve these two new problems. A new measure is also proposed to evaluate the effectiveness of the three algorithms. Computational results for both problems are presented. © 2013 Elsevier Ltd.

Nekahi A.,Amirkabir University of Technology | Firoozi S.,Amirkabir University of Technology
Materials Research Bulletin | Year: 2011

Preparation of titanium diboride (TiB 2) nanoparticles was carried out by volume combustion synthesis. TiO 2, B 2O 3 and elemental Mg were mixed with 0-60% salt mixture of KCl, NaCl and CaCl 2 with increment of 15% as a low melting temperature diluent. Compressed samples were synthesized in a tubular furnace at a constant heating rate under argon atmosphere. Thermal analysis of the process showed that the addition of the low melting temperature salts mixture led to a significant decrease in ignition and combustion temperatures. Synthesized samples were then leached by nitric and hydrochloric acids to remove impurities. The samples were examined by XRD, SEM and DLS analysis. The results showed the formation of fine deagglomerated particles with the addition of the salts mixture. The results revealed that 45% salts mixture had the smallest average particle size of about 90 nm. © 2011 Elsevier Ltd. All rights reserved.

Tajeddini V.,Amirkabir University of Technology | Ohadi A.,Amirkabir University of Technology | Sadighi M.,Amirkabir University of Technology
International Journal of Mechanical Sciences | Year: 2011

This paper describes a study of three-dimensional free vibration analysis of thick circular and annular isotropic and functionally graded (FG) plates with variable thickness along the radial direction, resting on Pasternak foundation. The formulation is based on the linear, small strain and exact elasticity theory. Plates with different boundary conditions are considered and the material properties of the FG plate are assumed to vary continuously through the thickness according to power law. The kinematic and the potential energy of the platefoundation system are formulated and the polynomial-Ritz method is used to solve the eigenvalue problem. Convergence and comparison studies are done to demonstrate the correctness and accuracy of the present method. With respect to geometric parameters, elastic coefficients of foundation and different boundary conditions some new results are reported which may be used as benchmark solutions for future researches. © 2011 Elsevier Ltd. All rights reserved.

Edrissi M.,Amirkabir University of Technology | Norouzbeigi R.,Amirkabir University of Technology
Journal of Materials Science: Materials in Electronics | Year: 2011

Deer horn-like and spherical nanoparticles of ZnO have been prepared via microwave heating (MWH) of Bis (2-pyridinethiol N-oxide) Zinc (II) [BPTZ] complex. The product was characterized by XRD, SEM, LLS, BET, FTIR and chemical analysis. The 2 3 factorial and the Taguchi L 4 designs were used for factors effect estimation and determination of optimum conditions for spherical ZnO nanoparticle synthesis. The three main factors considered were power of microwave, temperature of pyrolysis and time of thermal decomposition. The time of pyrolysis had the most influence on the average particle size and the size distribution of product. The average particle size for the spherical ZnO at optimum conditions was found to be 16 nm and the particle range was 16 ± 13 nm. © 2010 Springer Science+Business Media, LLC.

Barati E.,Malek-Ashtar University of Technology | Alizadeh Y.,Amirkabir University of Technology
Fatigue and Fracture of Engineering Materials and Structures | Year: 2011

The main purpose of the paper is to propose a numerical method for evaluation of J-integral in plates made of functionally graded materials (FGM) with sharp and blunt V-notches under Mode I loading. The material properties have been assumed to be varied exponentially along the specimen width (notch direction). Using the proposed method, the effect of material gradient on the J-integral for two cases of sharp and blunt V-notches has been studied. The results have shown that in FGMs with sharp V-notches, the J-integral is not proportional to. So, the parameter J L is path dependent. It has been observed that the material gradient has larger effect on the J-integral in sharp V-notch compared with that in blunt V-notch. © 2011 Blackwell Publishing Ltd.

Saadatmandi A.,University of Kashan | Dehghan M.,Amirkabir University of Technology
JVC/Journal of Vibration and Control | Year: 2011

A numerical method for solving the linear and non-linear fractional integro-differential equations of Volterra type is presented. The fractional derivative is described in the Caputo sense. The method is based upon Legendre approximations. The properties of Legendre polynomials together with the Gaussian integration method are utilized to reduce the fractional integro-differential equations to the solution of algebraic equations. Illustrative examples are included to demonstrate the validity and applicability of the presented technique and a comparison is made with existing results. © The Author(s) 2011 Reprints and permissions.

Asgari M.,Amirkabir University of Technology | Akhlaghi M.,Amirkabir University of Technology
European Journal of Mechanics, A/Solids | Year: 2011

In this paper, natural frequencies characteristics of a thick hollow cylinder with finite length made of two-dimensional functionally graded material (2D-FGM) based on three-dimensional equations of elasticity is considered. The axisymmetric conditions are assumed for the 2D-FGM cylinder. The material properties of the cylinder are varied in the radial and axial directions with power law functions. Effects of volume fraction distribution and FGM configuration on the natural frequencies of a simply supported cylinder are analyzed. Also, the effects of length and thickness of the cylinder are considered for different material distribution profiles. Three-dimensional equations of motion are used and the eigen value problem is developed based on direct variational method. Finite element method with graded material characteristics within each element of the structure is used for solution. The study shows that the 2D-FGM cylinder exhibit interesting frequency characteristics when the constituent volume fractions and its configuration are varied. © 2010 Elsevier Masson SAS. All rights reserved.

Momeni A.,Amirkabir University of Technology | Dehghani K.,Amirkabir University of Technology
Materials Science and Engineering A | Year: 2011

The hot deformation characteristics of the 2205 duplex stainless steel were analyzed using constitutive equations and processing maps. The hot compression tests were performed at temperature range of 950-1200°C and strain rate of 0.001-1s-1. Flow stress was modeled by the constitutive equation of hyperbolic sine function. However, the stress exponent and strain rate sensitivity were different at low and high deformation temperatures where austenite and ferrite are dominant, respectively. It was recognized that strain at the peak point of flow curve increases with the Zener-Hollomon parameter, Z, at low temperature deformation while at high temperature deformation it actually decreases with Z. The power dissipation map, instability map and processing map were developed for the typical strain of 0.3. It was realized that dynamic restoration mechanisms could efficiently hinder the occurrence of flow instability at low and medium strain rates. Otherwise, the increase in strain rate at low and high temperatures could increase the risk of flow instability. © 2010 Elsevier B.V.

Pouranvari M.,Islamic Azad University at Dezful | Marashi S.P.H.,Amirkabir University of Technology
Science and Technology of Welding and Joining | Year: 2011

One of the most important issues in resistance spot welding of three-sheet stack joints is the insufficient growth of the weld nugget, which may cause problems in places needing larger weld nuggets (i.e. sheet/sheet interface). In this paper, the effect of sheet thickness on the pattern of weld nugget development during resistance spot welding of three-steel sheets of equal thickness is studied. Results showed that there is a critical sheet thickness of 1.5 mm at which the fusion zone size at the sheet/sheet interface is nearly equal to the fusion zone size at the geometrical centre of the joint. Increasing the sheet thickness beyond the critical size causes a shift in the location of weld nugget formation from the geometrical centre to the sheet/sheet interfaces. Below the critical sheet thickness, the weld nugget growth in the geometrical centre of the joint is higher than that in the sheet/sheet interface. © 2011 Institute of Materials, Minerals and Mining.

Fakhari V.,Amirkabir University of Technology | Ohadi A.,Amirkabir University of Technology
JVC/Journal of Vibration and Control | Year: 2011

In this paper, large amplitude vibration control of functionally graded material (FGM) plates under thermal gradient and transverse mechanical loads using integrated piezoelectric sensor/actuator layers is investigated. In this regard, finite element formulation based on higher order shear deformation plate theory is developed. The von Karman nonlinear strain-displacement relationship is used to account for the large deflection of the plate. The material properties of FGM are assumed to be temperature-dependent and graded in the thickness direction according to a simple power law distribution in terms of the volume fractions of the constituents. The temperature field is assumed to be constant in the plane and varied only in the thickness direction of the plate. In order to control the large amplitude vibration of the plate, two control algorithms are employed: classical displacement-velocity feedback control and robust H2 control. Also, the uncertainty which arises from external disturbances (low-frequency sine-wave sensor noise and high-frequency Gaussian white sensor noise) is considered. Active control of both the static deflection due to thermal gradient and dynamic oscillation is studied. Numerical results are presented to investigate the effectiveness of the mentioned control algorithms to control nonlinear vibration and thermally induced deflection of the FGM plate. Also, robustness of the controllers in the face of sensor noise is investigated. Effects of the design parameters on performance of each controller are studied and finally, the two control methods are compared. © 2010 The Author(s).

Dehghan M.,Amirkabir University of Technology | Hajarian M.,Amirkabir University of Technology
JVC/Journal of Vibration and Control | Year: 2011

This note proposes an iterative method to solve the Sylvester matrix equation AY + YB = C over a reflexive matrix Y which has wide applications in many systems and control applications. Analysis of convergence shows that the proposed iterative method converges to the reflexive solution for any initial reflexive matrix. Finally, a numerical example confirms the theoretical results and shows that the method works reliably. © The Author(s) 2010.

Nazari A.,Islamic Azad University at Sāveh | Jamshid Aghazadeh Mohandesi,Amirkabir University of Technology | Riahi S.,Islamic Azad University at Sāveh
International Journal of Damage Mechanics | Year: 2011

Fracture toughness of functionally graded steels in crack divider configuration has been modeled. By utilizing plain carbon and austenitic stainless steel slices with different heights and arrangements as electroslag remelting electrodes, functionally graded steels were produced. The fracture toughness of the functionally graded steels in crack divider configuration was found to depend on the type, volume fraction, and position of containing phases. According to the area under stress-strain curve of each layer in the functionally graded composites, a mathematical model has been presented to predict fracture toughness of functionally graded steels using the rule of mixtures. There is a good agreement between experimental results and those acquired from the analytical model. Also a modification method has been proposed for better predicting the fracture toughness of the composites. The modification was performed so that the position of each layer could be contributed to the modeling. The results show that after modification, the agreement between experimental and analytical results is better than the situation in which no modification was applied. © The Author(s), 2010.

Hejazi I.,Amirkabir University of Technology | Sharif F.,Amirkabir University of Technology | Garmabi H.,Amirkabir University of Technology
Materials and Design | Year: 2011

Polypropylene/Ethylene-Propylene-Diene-Monomer (PP/EPDM) blends are well known for having a combination of favourable mechanical properties. In this paper, addition of organoclay to PP/EPDM to make PP/EPDM nanocomposites with enhanced mechanical properties is studied. PP/EPDM/organoclay nanocomposites were prepared using a lab scale twin-screw extruder. Maleic anhydride grafted polypropylene (PP-g-MA) was used to enhance the intercalation/exfoliation process and to create good adhesion at the polymer/polymer and polymer/filler interfaces. Taguchi method was employed to deign the experiments and optimize material and processing parameters for optimized mechanical properties. Organoclay (NC) and compatibilizer content were selected as material parameters and the main processing variables were feeding rate and average shear rate (RPM). X-ray diffraction (XRD), Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM) were used to study the microstructure of the nanocomposites samples. It was observed that NC content and shear rate in extruder improved the tensile strength and modulus. Another important result was the insignificant effect of NC content on impact strength while increasing shear rate first increased and then decreased the impact strength. © 2011 Elsevier Ltd.

Amirbayat J.,Amirkabir University of Technology
International Journal of Clothing Science and Technology | Year: 2011

Purpose: The purpose of this paper is to provide an estimation of safe fabric length during automatic vertical feeding of fabrics into work stations. Design/methodology/approach: The analysis is based on the application of the energy method and taking advantage of dimensionless groups. Findings: Limits of the safe maximum force and length are obtained for a fabric of known properties and given friction coefficient between the fabric and supporting bed. Originality/value: The paper demonstrates how to calculate the buckling force of a horizontally positioned fabric where the weight cannot be neglected and how to calculate the maximum length of such a fabric which can be pushed into a work station without buckling. © Emerald Group Publishing Limited.

Kabir M.Z.,Amirkabir University of Technology | Nazari A.,Amirkabir University of Technology
Journal of Constructional Steel Research | Year: 2011

Inclusion of various defects, e.g. imperfection or notches, in cylinders during their service life is expected and identifying of the load bearing capacity of the structure in the presence of those imperfection and damages are necessary. In the present paper, the plastic buckling of notched cylinders is studied experimentally and numerically for various groups of the cylinder dimensions. The study focuses on influences of various characteristics of notches, such as orientation, position and notch length on the buckling capacity of the cylindrical shells. In this direction, the amount of absorbed internal strain energy affected by inserting notch is calculated and compared with intact ones. © 2011 Elsevier Ltd. All rights reserved.

Yazdchi K.,University of Twente | Salehi M.,Amirkabir University of Technology
Composites Part A: Applied Science and Manufacturing | Year: 2011

Based on the new simplified 3D Representative Volume Element (RVE) for a wavy carbon nanotube (CNT), an analytical model has been developed to study the stress transfer in single-walled carbon nanotube (SWCNT) reinforced polymer composites. The model is capable of predicting axial as well as interfacial shear stresses along a wavy CNT embedded in a matrix. Based on the pullout modeling technique, the effects of waviness, aspect ratio, CNT diameter, volume fraction, Poisson's ratio and matrix modulus on axial and interfacial shear stresses have also been analyzed in details. The results of the analytical model are in good agreements when compared with the corresponding results for straight CNTs. © 2011 Elsevier Ltd. All rights reserved.

Norouzbeigi R.,Amirkabir University of Technology | Edrissi M.,Amirkabir University of Technology
Journal of the American Ceramic Society | Year: 2011

Nano alumina powders have been synthesized by combustion method using eight new fuels. The effectiveness of key process factors on the production of nanoparticles was investigated and optimized using Taguchi L16 array design. The products were characterized by XRD, BET, TGA, EDX, FESEM, and TEM analyses. Results demonstrated that the nano-structured aluminum oxide powders had crystal sizes between 7.2 and 13 nm and specific surface areas between 21.0 and 70.0 m2/g. The synthesis of γ-alumina was modified to achieve higher specific surface area (122.6 m2/g). A nano-network of powders which was woven by alumina nano-fibers was successfully fabricated by the modification route. The length and diameter of fibers were about 160 and 10 nm, respectively. © 2011 The American Ceramic Society.

Bagherizadeh E.,Amirkabir University of Technology | Kiani Y.,Amirkabir University of Technology | Eslami M.R.,Amirkabir University of Technology
Composite Structures | Year: 2011

In this study, the mechanical buckling of functionally graded material cylindrical shell that is embedded in an outer elastic medium and subjected to combined axial and radial compressive loads is investigated. The material properties are assumed to vary smoothly through the shell thickness according to a power law distribution of the volume fraction of constituent materials. Theoretical formulations are presented based on a higher-order shear deformation shell theory (HSDT) considering the transverse shear strains. Using the nonlinear strain-displacement relations of FGMs cylindrical shells, the governing equations are derived. The elastic foundation is modelled by two parameters Pasternak model, which is obtained by adding a shear layer to the Winkler model. The boundary condition is considered to be simply-supported. The novelty of the present work is to achieve the closed-form solutions for the critical mechanical buckling loads of the FGM cylindrical shells surrounded by elastic medium. The effects of shell geometry, the volume fraction exponent, and the foundation parameters on the critical buckling load are investigated. The numerical results reveal that the elastic foundation has significant effect on the critical buckling load. © 2011 Elsevier Ltd.

Kowsari E.,Amirkabir University of Technology | Ghezelbash M.R.,Amirkabir University of Technology
Materials Letters | Year: 2011

A hydrothermal method has been employed to prepare cactus-like zincoxysulfide ZnOxS1-x nanostructures with the assistance of a dicationic task-specific ionic liquid (TSIL), [mim]{(CH)2} 3[imm](SCN)2. To the best of our knowledge, this is the first time that this TSIL with the SCN anion has been used in place of conventional reagents as a source of S to prepare a ZnOxS 1-x nanostructure. The photocatalytic activities of the ZnO xS1-x nanostructures have been compared using UV and visible lights. BET results showed that the surface areas and photocatalytic activities of cactus-like zincoxysulfide ZnOxS1-x nanostructures were higher than those of other samples. ZnOxS 1-x nanostructures with cactus-like morphology exhibited a significant enhancement of photocatalytic activity toward the degradation of methyl orange (MO) as compared to other samples, as revealed by photoluminescence measurements. This could be attributed to enhanced oxygen vacancies and crystallite defects formed as a result of substitution of S 2- in the lattice of ZnO. © 2011 Elsevier B.V. All rights reserved.

Hajikazemi M.,Amirkabir University of Technology | Sadr M.H.,Amirkabir University of Technology
International Journal of Solids and Structures | Year: 2014

In this paper, stiffness reduction of general symmetric laminates containing a uniform distribution of matrix cracks in a single orientation is analyzed. An admissible stress field is considered, which satisfies equilibrium and all the boundary and continuity conditions. This stress field has been used in conjunction with the principle of minimum complementary energy to get the effective stiffness matrix of a cracked general symmetric laminate. Natural boundary conditions have been derived from the variational principle to overcome the limitations of the existing variational methods on the analysis of general symmetric laminates. Therefore, the capability of analyzing cracked symmetric laminates using the variational approach has been enhanced significantly. It has been shown that the method provides a rigorous lower bound for the stiffness matrix of a cracked laminate, which is very important for practical applications. Results derived from the developed method for the properties of the cracked laminates showed an excellent agreement with experimental data and with those obtained from McCartney's stress transfer model. The differences of the developed model with McCartney's model are discussed in detail. It can be emphasized that the current approach is simpler than McCartney's model, which needs an averaging procedure to obtain the governing equations. Moreover, it has been shown that the existing variational models are special cases of the current formulation. © 2014 Published by Elsevier Ltd. All rights reserved.

Mousavi S.J.,Amirkabir University of Technology | Shourian M.,Amirkabir University of Technology
Water Resources Research | Year: 2010

Global optimization models in many problems suffer from high computational costs due to the need for performing high-fidelity simulation models for objective function evaluations. Metamodeling is a useful approach to dealing with this problem in which a fast surrogate model replaces the detailed simulation model. However, training of the surrogate model needs enough input-output data which in case of absence of observed data, each of them must be obtained by running the simulation model and may still cause computational difficulties. In this paper a new metamodeling approach called adaptive sequentially space filling (ASSF) is presented by which the regions in the search space that need more training data are sequentially identified and the process of design of experiments is performed adaptively. Performance of the ASSF approach is tested against a benchmark function optimization problem and optimum basin-scale water allocation problems, in which the MODSIM river basin decision support system is approximated. Results show the ASSF model with fewer actual function evaluations is able to find comparable solutions to other metamodeling techniques using random sampling and evolution control strategies. Copyright 2010 by the American Geophysical Union.

Javadi M.,Amirkabir University of Technology | Sharifzadeh M.,Amirkabir University of Technology | Shahriar K.,Amirkabir University of Technology
Journal of Hydrology | Year: 2010

Fractures in rock mass are the main flow paths and introduce as a most important attribute in rock mass hydraulic behavior. The non-linear fluid flow through rock fractures was studied in this paper. Computational domain of an artificial three-dimensional fracture is generated and used for CFD simulations. Both laminar and turbulent flow simulations were performed for a wide range of flow rates. Also, a new non-linear fluid flow formulation was developed on the basis of some geometrical and kinematical assumptions for fracture and fluid flow, respectively. Based on comparison between simulation results and developed formulation, a new geometrical model has been proposed for non-linear fluid flow through rough fractures, which suggests a polynomial expression, like Forchheimer law, to describe the dependence of pressure drop on flow rate. Finally, this model has been evaluated with experimental results of a fracture with different geometries. The results show that the predicted pressure drop for turbulent flow simulation was roughly 3-17% more than those for laminar one at the Reynolds number of 4.5-89.5, respectively. Moreover, a good accuracy was found between the proposed model and turbulent flow simulation results. These findings may prove useful for computational studies of flows through real rock fractures, or inclusions in simulators for large-scale flow in fractured rocks. © 2010 Elsevier B.V.

Raiesdana S.,Islamic Azad University at Qazvin | Goplayegani S.M.H.,Amirkabir University of Technology
Neurocomputing | Year: 2013

This paper explores a computational dynamic solution for epileptic seizure control. A neuronal model of epileptiform activity which is driving to periodicity, simulating seizures, is chaotified via two chaos anti-control algorithms. Anti-control of some in vivo measurements is also put to test. The perspective is that in an epileptic disorder, a transition of the state of the neuronal system from being chaotic to being patho-physiologically periodic can cause this dynamical disorder. The aim is to retrieve the chaotic state which was running before the seizure start. Based on identifying loss regions for period orbits in the state space, the first control method acts by avoiding the system trajectories entrance into the defined loss regions. On the other hand, the second method, based on intra-attractor (orbit) control concept, is an attempt to steer trajectories to the unstable manifold of a target unstable period orbit solution embedded within the system dynamic. The presented anti-control methods make use of a novel strategy to model chaotic time series' return map with radial basis function to improve the estimation of the dynamics under investigation. Our results show that both methods are successful in driving the model's dynamical activity away from the periodic direction while the second one seems to be faster and more efficient. Moreover, testing both methods on some hippocampal recordings of epileptized rats yields fairly acceptable results in dynamic modulation. This opens ways for further online experimental stimulations based on chaos concept. © 2013 Elsevier B.V.

Zare Y.,Amirkabir University of Technology
Waste Management | Year: 2013

Currently, the growing consumption of polymer products creates the large quantities of waste materials resulting in public concern in the environment and people life. Nanotechnology is assumed the important technology in the current century. Recently, many researchers have tried to develop this new science for polymer recycling. In this article, the application of different nanofillers in the recycled polymers such as PET, PP, HDPE, PVC, etc. and the attributed composites and blends is studied. The morphological, mechanical, rheological and thermal properties of prepared nanocomposites as well as the future challenges are extensively discussed. The present article determines the current status of nanotechnology in the polymer recycling which guide the future studies in this attractive field. © 2012 Elsevier Ltd.

Anani Y.,Sharif University of Technology | Alizadeh Y.,Amirkabir University of Technology
Materials and Design | Year: 2011

This paper proposes a new visco-hyperelastic constitutive law for modeling the finite-deformation strain rate-dependent behavior of foams as compressible elastomers. The proposed model is based on a phenomenological Zener model, which consists of a hyperelastic equilibrium spring and a Maxwell element parallel to it. The hyperelastic equilibrium spring describes the steady state response. The Maxwell element, which captures the rate-dependency behavior, consists of a nonlinear viscous damper connected in series to a hyperelastic intermediate spring. The nonlinear damper controls the rate-dependency of the Maxwell element. Some strain energy potential functions are proposed for the two hyperelastic springs. compressibility effect in strain energy is described by entering the third invariant of deformation gradient tensor into strain energy functions. A history integral method has been used to develop a constitutive equation for modeling the behavior of the foams. The applied history integral method is based on the Kaye-BKZ theory. The material constant parameters, appeared in the formulation, have been determined with the aid of available uniaxial tensile experimental tests for a specific material. © 2010 Elsevier Ltd.

Momeni A.,Amirkabir University of Technology | Dehghani K.,Amirkabir University of Technology
Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science | Year: 2011

Hot compression tests were conducted in a temperature range of 1173 K to 1323 K (900 °C to 1050 °C) and strain rates of 0.001 seconds -1 to 1 second-1 to investigate the hot deformation behavior of the austenitic stainless steel type 1.4563. The results showed that hot deformation at low temperatures, i.e., 1173 K to 1223 K (900 °C to 950°C), and at low and medium strain rates, i.e., 0.001 seconds-1 to 0.1 seconds-1, results in the dynamic formation of worm-like precipitates on existing grain boundaries. This in turn led to the restriction or even inhibition of dynamic recrystallization. However, at higher temperatures and strain rates when either the time frame for dynamic precipitation was too short or the driving force was low, dynamic recrystallization occurred readily. Furthermore, at low strain rates and high temperatures, there was no sign of particles, but the interactions between solute atoms and mobile dislocations made the flow curves serrated. The strain rate sensitivity was determined and found to change from 0.1 to 0.16 for a temperature increase from 1173 K to 1323 K (900 °C to 1050 °C). The variations of mean flow stress with strain rate and temperature were analyzed. The calculated apparent activation energy for the material was approximately 406 kJ/mol. The hyperbolic sine function correlated the Zener-Hollomon parameter and flow stress successfully at intermediate stress levels. However, at low levels of flow stress a power-law equation and at high stresses an exponential equation well fitted the experimental data. © 2010 The Minerals, Metals & Materials Society and ASM International.

Fallah A.,Amirkabir University of Technology | Fallah A.,Sharif University of Technology | Aghdam M.M.,Amirkabir University of Technology
European Journal of Mechanics, A/Solids | Year: 2011

In this study, simple analytical expressions are presented for large amplitude free vibration and post-buckling analysis of functionally graded beams rest on nonlinear elastic foundation subjected to axial force. Euler-Bernoulli assumptions together with Von Karman's strain-displacement relation are employed to derive the governing partial differential equation of motion. Furthermore, the elastic foundation contains shearing layer and cubic nonlinearity. He's variational method is employed to obtain the approximate closed form solution of the nonlinear governing equation. Comparison between results of the present work and those available in literature shows the accuracy of this method. Some new results for the nonlinear natural frequencies and buckling load of the FG beams such as the effect of vibration amplitude, elastic coefficients of foundation, axial force, and material inhomogenity are presented for future references. © 2011 Elsevier Masson SAS. All rights reserved.

Ramezanzadeh B.,Amirkabir University of Technology | Attar M.M.,Amirkabir University of Technology
Materials Chemistry and Physics | Year: 2011

Epoxy nanocomposites containing different contents of Nano-ZnO particles were prepared. The nanocomposites were exposed to 3.5 wt% NaCl solution up to 60 days. Mechanical properties of the nanocomposites (before and after exposure to NaCl solution) were studied by dynamic mechanical thermal analysis (DMTA) and nano-indentation techniques. Fourier transform infrared spectroscopy (FTIR) was utilized to investigate hydrolytic degradation of coatings. Corrosion resistance of the composites was studied by an electrochemical impedance spectroscopy (EIS). Results showed that blank sample was severely deteriorated after exposure to corrosive electrolyte. Corrosion resistance of the epoxy coating was significantly improved using nanoparticles. The cross-linking density and indentation hardness of the blank sample were significantly decreased after exposure to corrosive electrolyte. Results showed that nanoparticles could significantly improve coating resistance against hydrolytic degradation. Results revealed that decrease in cross-linking density and indentation hardness of the epoxy coatings containing 3.5 and 5 wt% nanoparticles were not significant. Decrease in adhesion loss was also obtained using nanoparticles. © 2011 Elsevier B.V. All rights reserved.

Asadi H.,Amirkabir University of Technology | Aghdam M.M.,Amirkabir University of Technology
International Journal of Mechanical Sciences | Year: 2014

In this study, large amplitude vibration and post-buckling analysis of variable cross-section laminated composite beams with symmetric and asymmetric lay-ups resting on nonlinear elastic foundation is investigated using the generalized differential quadrature (GDQ) method. Geometric nonlinearity of von-Karman type is considered. Various combinations of boundary conditions including free edges are considered. Furthermore, elastic foundation consists of shearing layer, linear and cubic nonlinearity. Natural frequencies are obtained for the nonlinear problem using the Picard iterative method. Results for linear and nonlinear analyses of uniform laminated beams are validated with the available data in the open literature, which show close agreement. Moreover, some new results are also presented for the nonlinear natural frequencies and buckling load of the non-uniform laminated composite beams to study effects of vibration amplitude, elastic coefficients of foundation, axial force, boundary conditions and variation of cross-section. © 2013 Elsevier Ltd.

Hajikazemi M.,Amirkabir University of Technology | Sadr M.H.,Amirkabir University of Technology
International Journal of Solids and Structures | Year: 2014

The present research work presents a variational approach for stress analysis in a general symmetric laminate, having a uniform distribution of ply cracks in a single orientation, subject to general in-plane loading. Using the principle of minimum complementary energy, an optimal admissible stress field is derived that satisfies equilibrium, boundary and traction continuity conditions. Natural boundary conditions have been derived from the variational principle to overcome the limitations of the existing methodology on the analysis of general symmetric laminates. Thus, a systematic way to formulate boundary value problem for general symmetric laminates containing many cracked and un-cracked plies has been derived, and appropriate mathematical tools can then be employed to solve them. The obtained results are in excellent agreement with the available results in the literature. In the field of matrix cracks analysis for symmetric laminates, the present formulation is the most complete variational model developed so far. © 2013 Elsevier Ltd. All rights reserved.

Zamani Ketek Lahijania Y.,Amirkabir University of Technology | Mohseni M.,Amirkabir University of Technology | Bastani S.,Institute for Colorants
Tribology International | Year: 2014

This work describes the mechanical behavior of different nanocomposite films containing non-treated and silane treated nanosilica loaded into a UV cured urethane acrylate resin. Nanoindentation, nanoscratch, micro-hardness and dynamic mechanical thermal analysis were utilized to assess the coatings. It was demonstrated that the surface treated nanoparticles had stronger interfacial interaction with the polymeric matrix and had improved storage modulus. Nanoindentation and microindentation results suggested that a homogenous reinforced structure was formed in the bulk and surface of hybrid coatings filled with treated nanosilica. This resulted in films with high abrasion resistance. © 2013 Elsevier Ltd.

Mahmoodi N.M.,Iran Institute for Color Science and Technology | Salehi R.,Amirkabir University of Technology | Arami M.,Amirkabir University of Technology
Desalination | Year: 2011

This paper investigates the ability of activated carbon (AC) to adsorb two anionic dyes from colored wastewater in single and binary systems. Direct Blue 78 (DB78) and Direct Red 31 (DR31) were used as anionic dye models. The surface characteristics of AC were investigated using fourier transform infrared (FTIR) and scanning electron microscopy (SEM). The effects of AC dosage, initial dye concentration and salt on dye removal were investigated at 25°C. The kinetic and isotherm of dye adsorption were studied. Adsorption kinetic of dyes was studied in single and binary systems and rate sorption was found to conform to pseudo - second order kinetic model. The isotherm data of dyes in single and binary systems followed Langmuir isotherm. The maximum adsorption capacity (Q 0) of DB78 and DR31 was 76.92mg/g and 111mg/g for single system and 76.92mg/g and 125mg/g for binary system, respectively. Results indicated that AC could be used as an adsorbent to remove the anionic dyes from single and binary pollutants systems. © 2011 Elsevier B.V.

Nasseri R.,Amirkabir University of Technology | Mohammadi N.,Amirkabir University of Technology
Carbohydrate Polymers | Year: 2014

A comparative performance study of cellulose whiskers (CW) and starch nanoparticles (SN) on plasticized starch (PS) reinforcement has been presented. In order to study the involved surface phenomena, CW and SN were extracted through acid hydrolysis using sulfuric acid to fulfill the similar surface groups and interactions. CW-filled and SN-filled nanocomposites were then prepared with relatively identical process to alleviate the effect of fabrication method for better comparison of CW and SN performance on PS reinforcement. Morphology of nanoparticles and their dispersion state in the corresponding nanocomposites were investigated by transmission electron microscopy and field emission scanning electron microscopy, respectively. X-ray diffraction was used for crystallography of nanocomposites and established the transcrystallization only in CW-filled nanocomposites. Nanocomposites comprising quasi-spherical SNs showed higher reinforcement in dynamic mechanical tests compared to the corresponding nanocomposites containing rod-like CWs, which were attributed to more efficient filler/filler and filler/matrix interactions originated from hydrogen bonding in SN-filled nanocomposites. © 2014 Elsevier Ltd.

Montazer M.,Amirkabir University of Technology | Seifollahzadeh S.,Amirkabir University of Technology
Coloration Technology | Year: 2011

This research aims to enhance the self-cleaning properties of fibre-blended fabric using surface pretreatment prior to the application of titanium dioxide nanoparticles. To this end, the polyester/wool fabric was modified, in that the wool fibres were oxidised with potassium permanganate and the polyester fibres were hydrolysed with lipase before nano processing. Butane tetracarboxylic acid was also used to enhance the adsorption of the nanoparticles and also to stabilise them on the fabric surface. The self-cleaning properties of the fabric were examined through staining of the fabric with CI Basic Blue 9 and then discolouring by exposing to ultraviolet and daylight irradiation. Some other properties of the treated fabrics, such as water drop absorption, crease recovery angle and bending were investigated and are discussed in detail. The colour changes of different samples indicated an appropriate discoloration on the titanium dioxide-treated fabrics after ultraviolet and daylight irradiation. Overall, the surface pretreatment of the wool and polyester fibres improved the self-cleaning properties of the fabric significantly. © 2011 The Authors. Coloration Technology © 2011 Society of Dyers and Colourists.

Kowsari E.,Amirkabir University of Technology
Journal of Nanoparticle Research | Year: 2011

Nanosheet-based microspheres of ZnO with hierarchical structures, hollow prism, and coralline-like ZnO nanostructures were successfully prepared by ultrasonic irradiation in acidic ionic liquids (AILs). The hollow spherical is made up of many thin petals, the thickness of which is only about 90 nm. In the presence of AIL2, the one prepared at a frequency of 40 kHz is a mixture of nanofibers with diameters ranging from less than 30 nm to about 100 nm. ZnO nanostructure (with AIL1) reveals lozenge-shape hollow prism structures. The products were hollow prism structure covered with some nanometric-size nanoparticles. The average size of the nanoparticles is in the range of 40-80 nm. It is found that the ultrasonic irradiation time, ultrasonic frequency, and the AILs influence the growth mechanism and optical properties of ZnO nanostructures. Producing Zno nanostructures by different traditional methods (e.g., hydrothermal method) requires basic media. These methods are not economical and environmentally friendly in many industrial processes. In so doing, a critical problem has been the point that, normally, a high concentration of base causes reactor metal corrosion. This is a simple and low-cost method, which can be expected to be applied in industry in the future. Also, importantly, the structures synthesized in this experiment can indicate a new way to construct nanodevices by self-organization in one step. © 2011 Springer Science+Business Media B.V.

Dastjerdi R.,Amirkabir University of Technology | Montazer M.,Amirkabir University of Technology
Colloids and Surfaces B: Biointerfaces | Year: 2011

Due to the opposite surface charge of TiO 2 and silver nano-particles, at around neutral pH, it is expected that the interaction between these particles and cross-linkable polysiloxane (XPs) resin and thus their final properties would be affected by their processing technique. This paper has focused on the effect of processing design on the interaction, surface orientation and final properties of surface nano-colloidal functionalization. The results disclosed the key role of the applied process on the properties of the treated fabrics which have been well discussed through the modeling of this effect on orientations of nanoparticles on the surface. The developed models are interestingly verified by various characterizations. Applying a premixed TiO 2/XPs colloid as an after treatment on Ag treated samples caused more enhanced stain photo-degradability and UV protection properties, while the reduction of enhanced hydrophobicity, washing durability, and stain-repellency were observed as compared to applying Ag/XPs premixed colloid on TiO 2. The role of processing on XPs stabilizing efficiency and its co-photo-catalytic function on TiO 2 nanoparticles has been concluded and deeply discussed. The appropriate processing design can be tailored in order to accomplish desirable hydrophilicity/hydrophobicity with a granted bioactivity. The results reveal that ideal bioactivity, stain photo-degradability, self-cleaning, UV protection, anti-staining properties, and washing durability can be achieved by applying a mixture of silver and XPs as an after-treatment on TiO 2 treated fabrics. © 2011 Elsevier B.V.

Hassanzadeh T.,Islamic Azad University at Qazvin | Meybodi M.R.,Amirkabir University of Technology
AISP 2012 - 16th CSI International Symposium on Artificial Intelligence and Signal Processing | Year: 2012

Data clustering is a common technique for data analysis and is used in many fields, including data mining, pattern recognition and image analysis. K-means clustering is a common and simple approach for data clustering but this method has some limitation such as local optimal convergence and initial point sensibility. Firefly algorithm is a swarm based algorithm that use for solving optimization problems. This paper presents a new approach to using firefly algorithm to cluster data. It is shown how firefly algorithm can be used to find the centroid of the user specified number of clusters. The algorithm then extended to use k-means clustering to refined centroids and clusters. This new hybrid algorithm called K-FA. The experimental results showed the accuracy and capability of proposed algorithm to data clustering. © 2012 IEEE.

Hosseinabadi Farahani M.,University of Tehran | Hosseini L.,Amirkabir University of Technology
International Journal of Advanced Manufacturing Technology | Year: 2013

This paper considers the single machine scheduling problem with a new version of time-dependent processing times. The processing time of a job is defined as a piecewise linear function of its start time. It is preferred that the processing of each job be started at a specific time which means that processing the job before or after that time implies additional effort to accomplish the job. The job-processing time is a nonmonotonic function of its start time. The increasing rate of processing times is job independent and the objective is to minimize the cycle time. We show that the optimal schedule is V shaped and propose an optimal polynomial time algorithm for the problem. © 2012 Springer-Verlag London Limited.

Behnamian J.,Amirkabir University of Technology | Fatemi Ghomi S.M.T.,Amirkabir University of Technology
Information Sciences | Year: 2013

Traditionally centralized manufacturing planning, scheduling, and control mechanisms are being found to be insufficiently flexible to respond to highly dynamic variations in the market requirements. In order to be competitive in today's rapidly changing business world, organizations have shifted from a centralized to a decentralized structure in many areas of decision making. Distributed scheduling is an approach that enables local decision makers to create schedules that consider local objectives and constraints within the boundaries of the overall system objectives. In this paper, we assumed that production takes place in several factories, which may be geographically distributed in different locations, in order to take advantage from the trend of globalization. In this approach, the factories that are available to process the jobs have different speeds in which each factory has parallel identical machine. The optimization criterion is the minimization of the maximum completion time or makespan among the factories. After proposing mixed integer linear programming model for the problem, we developed a heuristic and genetic algorithm. For the proposed genetic algorithm, at first, to represent the solutions, we suggested a new encoding scheme, and then proposed a local search based on the theorem developed in the paper. Finally, we compare the obtained solutions using the lower bound developed in this paper. The results show the proposed algorithms to be very efficient for different structures of instances. © 2012 Elsevier Inc. All rights reserved.

Bakhshi B.,Amirkabir University of Technology | Khorsandi S.,Amirkabir University of Technology
International Journal of Communication Systems | Year: 2013

Channel assignment in multichannel multiradio wireless mesh networks is a powerful resource management tool to exploit available multiple channels. Channels can be allocated either statically on the basis of long-term steady state behavior of traffic or dynamically according to actual traffic demands. It is a common belief that dynamic schemes provide better performance; however, these two broad classes of channel allocation schemes have not been compared in detail. In this paper, we quantify the achievable performance gain and fairness improvement through an optimal dynamic channel allocation scheme. We develop optimal algorithms for a dynamic and three static schemes using mixed integer linear programming and compare them in the context of QoS provisioning, where network performance is measured in terms of acceptance rate of QoS sensitive traffic demands. Our extensive simulations show that static schemes should optimize channel allocation for long-term traffic pattern and maintain max-min fairness to achieve acceptable performances. Although the dynamic and max-min fair static schemes accomplish the same fairness, the dynamic channel allocation outperforms the static scheme about 10% in most cases. In heavily overloaded regimes, especially when network resources are scarce, both have comparable performances, and the max-min fair scheme is preferred because it incurs less overhead. Copyright © 2011 John Wiley & Sons, Ltd.

Salarirad M.M.,Amirkabir University of Technology | Behnamfard A.,Amirkabir University of Technology
Hydrometallurgy | Year: 2011

In carbon-in-pulp and carbon-in-leach circuits, among different organic and inorganic compounds present in the gold cyanide solution, flotation reagents play the main role in the fouling of activated carbon. In this study the effects of different types and variable concentrations of flotation and dewatering reagents on the kinetics of gold sorption onto granular activated carbon (GAC) were evaluated on the basis of kinetic rate constant (i.e.; k value) of an empirical rate equation. The lower the k value, the greater is the fouling effect. It was observed that the k value rapidly decreases by increasing the concentration of collectors including potassium isobutyl xanthate (PIBX) and potassium ethyl xanthate (PEX) up to 20 mg/L and at higher concentrations, the k value gradually leveled off to 53 h - 1 for PIBX, which is 46% lower than the 99 h - 1 for PEX. At low concentrations (i.e.; up to 15 mg/L) of methyl isobutyl carbinol, the k value gradually reduced and at higher concentrations, the decrease is found to be more pronounced. The fouling effect of flocculant was negligible and it would be even insignificant at high concentrations. The combinational effect of flotation reagents on the kinetic activity of GAC towards gold sorption was synergistically better. The cumulative adsorption of flotation reagents onto GAC in a continuous circuit within 28 days resulted in 40% decrease of k value, although it was still above admissible limit of 80-100 h - 1. © 2011 Elsevier B.V. All rights reserved.

Dilamian M.,Islamic Azad University at South Tehran | Montazer M.,Amirkabir University of Technology | Masoumi J.,Shahid Beheshti University
Carbohydrate Polymers | Year: 2013

Here, antimicrobial nanofibrous membranes were produced by electrospinning of chitosan/poly(ethylene oxide) (PEO) solution in the presence of poly(hexamethylene biguanide) hydrochloride (PHMB). The influence of PHMB on the electrospinnability and antimicrobial properties of chitosan/PEO nanofibers were studied. Further, viscosity of the solutions as well as morphology of the nanofibrous structures were investigated. Results revealed that incorporation of PHMB in chitosan/PEO solutions led to decrease in the zero-shear rate viscosity up to 20%. Moreover, increasing PHMB from 0.5 mM to 1 mM led to formation of thinner fibers with diameters ranging from 240 nm to 60 nm, respectively. Fourier transform infrared (FT-IR) spectrums indicated the functional groups of chitosan, PEO and PHMB in nanofibrous structure. Differential scanning calorimetry (DSC) thermograms indicated interaction of PHMB with PEO and chitosan through alteration in the thermal behavior of the nanofibers. Inhibition of the bacteria growth for both Escherichia coli and Staphylococcus aureus were achieved on the PHMB loaded nanofibers. Also, a burst release of PHMB from mats has been observed in the first hour. These findings suggest that there is a great potential in fabrication of biomaterials with incorporation of PHMB using electrospinning. © 2013 Elsevier Ltd. All rights reserved.

Neghlani P.K.,Amirkabir University of Technology | Rafizadeh M.,Amirkabir University of Technology | Taromi F.A.,Amirkabir University of Technology
Journal of Hazardous Materials | Year: 2011

Polyacrylonitrile nanofibers (PAN-nFs) were produced using the electrospinning method. Subsequently, the electrospun fibers were modified by diethylenetriamine to produce aminated polyacrylonitrile (APAN) nanofibers. Finally, the adsorbability of copper ions on the surface of the nanofibers was examined in an aqueous solution. Attenuated total internal reflection (ATIR) analysis confirmed the surface amination of the produced PAN-nFs. The grafting yield was calculated by the gravimetric method. The optimum condition was determined to yield the maximum grafting of amine groups to PAN with no losses in sample flexibility. Atomic absorption spectroscopy (AAS) was used to measure the copper ion concentration in the solution. Results indicate that the adsorption process in nanofibers is three times faster in comparison with microfibers. Moreover, the pH effect was studied based on the adsorption behavior of copper ions on the APAN nanofibers. In addition, thermodynamic parameters were calculated, revealing that the process was endothermic and demonstrating that randomness increased at the solid-solution interface during the process. The obtained enthalpy value indicates that the chelation of copper ions among the aminated polyacrylonitrile can be regarded as a chemical adsorption process. The adsorption data fit well with the Langmuir isotherm. The saturation adsorption capacity obtained from the Langmuir model for Cu(II) ions was 116.522. mg/g which is five times more than the reported value for APAN microfibers [S. Deng, R. Bai, J.P. Chen, Aminated polyacrylonitrile fibers for lead and copper removal, Langmuir,19 (2003)5058-5064]. Analysis using atomic force microscopy (AFM) showed that the surface roughness increased upon adsorption of the metal ion. Scanning electron microscopy (SEM) examination demonstrated that there were no cracks or sign of degradation on the surface after amination. © 2010 Elsevier B.V.

Khishvand M.,Amirkabir University of Technology | Khamehchi E.,Amirkabir University of Technology
Industrial and Engineering Chemistry Research | Year: 2012

Gas lift allocation can be modeled as a nonlinear programming problem in which adjusting optimum gas injection rates and compressor pressure maximize the oil rate or other objective functions. This study describes a nonlinear programming approach to maximize daily cash flow of some gas-lifted wells in an uncertain condition for oil price. First, some solution points of each well are obtained by employing a production simulation software. Then, by use of nonlinear optimization, a model is developed for gas lift performance in each well. Then these functions are used to develop a model under capacity, pressure and other real constraints for the cash flow of production from these wells. Oil price is assumed as a triangle risk function in this model. Results show a significant increase in cash flow in comparison with old case due to appropriate gas injection parameters. Sensitivity analysis on this problem shows that oil price, compression cost and water-oil ratio variations should be considered in the long term optimization. © 2012 American Chemical Society.

Harifi T.,Amirkabir University of Technology | Montazer M.,Amirkabir University of Technology
Ultrasonics Sonochemistry | Year: 2015

Abstract High intensity ultrasound was used for the synthesis and simultaneous deposition of TiO2:Fe3O4:Ag nanocomposites on polyester surface providing a feasible route for imparting magnetic and enhanced antibacterial and self-cleaning activities with controllable hydrophilicity/hydrophobicity at low temperature. Synergistic impact of sonochemistry and physical effects of ultrasound originating from implosive collapse of bubbles were responsible for the formation and adsorption of nanomaterials on the fabric surface during ultrasound irradiation. The increase in photocatalytic activity of TiO2 was obtained attributing to the co-operation of iron oxide and silver nanoparticles nucleated on TiO2 surface boosting the electron-hole pair separation and prolonging their recombination rate. The process was further optimized in terms of reagents concentrations including Fe2+/TiO2 and Ag/TiO2 molar ratios using central composite design in order to achieve the best self-cleaning property of the treated fabric. The magnetic measurements indicated the super-paramagnetic behavior of the treated fabric with saturation magnetization of 4.5 (emu/g). Findings suggest the potential of the proposed facial method in producing an intelligent fabric with durable multi-functional activities that can be suitable for various applications including medical, military, bio-separation, bio-sensors, magneto graphic printing, magnetic screens and magnetic filters. © 2015 Elsevier B.V.

Behnamfard A.,Amirkabir University of Technology | Salarirad M.M.,Amirkabir University of Technology | Veglio F.,University of L'Aquila
Waste Management | Year: 2013

A novel hydrometallurgical process was proposed for selective recovery of Cu, Ag, Au and Pd from waste printed circuit boards (PCBs). More than 99% of copper content was dissolved by using two consecutive sulfuric acid leaching steps in the presence of H2O2 as oxidizing agents. The solid residue of 2nd leaching step was treated by acidic thiourea in the presence of ferric iron as oxidizing agent and 85.76% Au and 71.36% Ag dissolution was achieved. The precipitation of Au and Ag from acidic thiourea leachate was investigated by using different amounts of sodium borohydride (SBH) as a reducing agent. The leaching of Pd and remained gold from the solid reside of 3rd leaching step was performed in NaClO-HCl-H2O2 leaching system and the effect of different parameters was investigated. The leaching of Pd and specially Au increased by increasing the NaClO concentration up to 10V% and any further increasing the NaClO concentration has a negligible effect. The leaching of Pd and Au increased by increasing the HCl concentration from 2.5 to 5M. The leaching of Pd and Au were endothermic and raising the temperature had a positive effect on leaching efficiency. The kinetics of Pd leaching was quite fast and after 30min complete leaching of Pd was achieved, while the leaching of Au need a longer contact time. The best conditions for leaching of Pd and Au in NaClO-HCl-H2O2 leaching system were determined to be 5M HCl, 1V% H2O2, 10V% NaClO at 336K for 3h with a solid/liquid ratio of 1/10. 100% of Pd and Au of what was in the chloride leachate were precipitated by using 2g/L SBH. Finally, a process flow sheet for the recovery of Cu, Ag, Au and Pd from PCB was proposed. © 2013 Elsevier Ltd.

Mardani A.,Amirkabir University of Technology | Tabejamaat S.,Amirkabir University of Technology
International Journal of Hydrogen Energy | Year: 2010

Energy crises and the preservation of the global environment are placed man in a dilemma. To deal with these problems, finding new sources of fuel and developing efficient and environmentally friendly energy utilization technologies are essential. Hydrogen containing fuels and combustion under condition of the moderate or intense low-oxygen dilution (MILD) are good choices to replace the traditional ones. In this numerical study, the turbulent non-premixed CH4+H2 jet flame issuing into a hot and diluted co-flow air is considered to emulate the combustion of hydrogen containing fuels under MILD conditions. This flame is related to the experimental condition of Dally et al. [Proc. Combust. Inst. 29 (2002) 1147-1154]. In general, the modelling is carried out using the EDC model, to describe turbulence-chemistry interaction, and the DRM-22 reduced mechanism and the GRI2.11 full mechanism to represent the chemical reactions of H 2/methane jet flame. The effect of hydrogen content of fuel on flame structure for two co-flow oxygen levels is studied by considering three fuel mixtures, 5%H2+95%CH4, 10%H2+90%CH4 and 20% H2+80%CH4(by mass). In this study, distribution of species concentrations, mixture fraction, strain rate, flame entrainment, turbulent kinetic energy decay and temperature are investigated. Results show that the hydrogen addition to methane leads to improve mixing, increase in turbulent kinetic energy decay along the flame axis, increase in flame entrainment, higher reaction intensities and increase in mixture ignitability and rate of heat release. © 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.

Nagheeby M.,Amirkabir University of Technology | Kolahdoozan M.,Amirkabir University of Technology
International Journal of Environmental Science and Technology | Year: 2010

Oil spills is one of the most important hazards in the estuarine and coastal water. In recent decades, engineers try to predict the status of oil slick to manage the pollution spreading. The prediction of oil slick transport is carried out mainly by means of numerical models. In the current study, the development and application of a two-phase fluid flow model to simulate oil transport in the marine environment are presented. Different transport and fate processes are included in the developed model. The model consists of the Lagrangian method for the advection process, the Random Walk technique for horizontal diffusion process and the empirical equations for the fate processes. The major forces for driving oil particles are fluid current, wind speed and turbulent flow. Therefore, the multi-component hydrocarbon method has been included to the developed model in order to predict fate processes. As prediction of particle velocity components is of major importance for oil slick advection, therefore the binomial interpolation procedure has been chosen for the particle velocity components computations. In addition, shoreline boundary condition is included in the developed model to simulate shore response to oil slick transport near the beaches. The results of the model applications are compared with the analytical solutions, experimental measurements and other numerical models cited in literature. Comparisons of different sets of results represent the capability of developed model to predict the oil slick transport. In addition, the developed model is tested for two oil spill cases in the Persian Gulf. © IRSEN, CEERS, IAU.

Naderi B.,Amirkabir University of Technology | Ruiz R.,Polytechnic University of Valencia
Computers and Operations Research | Year: 2010

This paper studies a new generalization of the regular permutation flowshop scheduling problem (PFSP) referred to as the distributed permutation flowshop scheduling problem or DPFSP. Under this generalization, we assume that there are a total of F identical factories or shops, each one with m machines disposed in series. A set of n available jobs have to be distributed among the F factories and then a processing sequence has to be derived for the jobs assigned to each factory. The optimization criterion is the minimization of the maximum completion time or makespan among the factories. This production setting is necessary in today's decentralized and globalized economy where several production centers might be available for a firm. We characterize the DPFSP and propose six different alternative mixed integer linear programming (MILP) models that are carefully and statistically analyzed for performance. We also propose two simple factory assignment rules together with 14 heuristics based on dispatching rules, effective constructive heuristics and variable neighborhood descent methods. A comprehensive computational and statistical analysis is conducted in order to analyze the performance of the proposed methods. © 2009 Elsevier Ltd. All rights reserved.

Naderi B.,Amirkabir University of Technology | Ruiz R.,Polytechnic University of Valencia | Zandieh M.,Shahid Beheshti University
Computers and Operations Research | Year: 2010

This paper deals with a realistic variant of flowshop scheduling, namely the hybrid flexible flowshop. A hybrid flowshop mixes the characteristics of regular flowshops and parallel machine problems by considering stages with parallel machines instead of having one single machine per stage. We also investigate the flexible version where stage skipping might occur, i.e., not all stages must be visited by all jobs. Lastly, we also consider job sequence dependent setup times per stage. The optimization criterion considered is makespan minimization. While many approaches for hybrid flowshops have been proposed, hybrid flexible flowshops have been rarely studied. The situation is even worse with the addition of sequence dependent setups. In this study, we propose two advanced algorithms that specifically deal with the flexible and setup characteristics of this problem. The first algorithm is a dynamic dispatching rule heuristic, and the second is an iterated local search metaheuristic. The proposed algorithms are evaluated by comparison against seven other high performing existing algorithms. The statistically sound results support the idea that the proposed algorithms are very competitive for the studied problem. © 2009 Elsevier Ltd. All rights reserved.

Agah S.M.,Amirkabir University of Technology | Abyaneh H.A.,Amirkabir University of Technology
IEEE Transactions on Power Delivery | Year: 2011

This paper presents a methodology to quantify the benefit of the distribution transformer life extension brought about by customer-owned distributed-generation (DG) units. The proposed methodology is applied to a realistic distribution system with various scenarios, including different penetration levels and combinations of the DG technologies. A number of realistic distribution transformers are then used to demonstrate the results. The results show the distribution transformer loss-of-life variation, as a function of the DG penetration level, presenting a monotonically decreasing characteristic which saturates after a certain penetration level. Regarding DG technologies, it should be noted that remarkable reduction is achieved in loss-of-life rates of the examined transformers for all of the proposed scenarios. However, the extent of the reduction largely depends on the production pattern of the DG unit. As revealed by the results, the microturbine emerges as the most promising technology in the life extension of distribution transformers. © 2011 IEEE.

Tavakoli M.R.B.,Amirkabir University of Technology | Vahidi B.,Amirkabir University of Technology
IEEE Transactions on Power Delivery | Year: 2011

In this paper, by creating a 3-D model of power-line equipment and lightning leader progression models, an alternate procedure for calculating the shielding failure rate (SFR) of transmission lines is presented. The stepping nature of lightning downward leader is modeled according to field observations with the use of discrete line charges approaching the earth. A simplified self-consistent model for an upward connecting leader is also adopted to find the position of lightning incidence to the transmission line. The required electric field in an environment is computed by using the charge simulation method. A comparison has been made between the SFR calculated by proposed method and the values calculated by conventional electrogeometrical model. In addition, different previously proposed incidence criteria are implemented and compared. Some comparisons are also made between the calculated SFR and available field data for selected overhead lines. © 2010 IEEE.

Behnam B.,Amirkabir University of Technology
International Journal of Civil Engineering | Year: 2016

Observations and investigations have proved that using traditional fire curves such as standard fire curves and natural fire curves should be limited to small/ medium compartments. In addition, when using the traditional fire curves, a uniform temperature is assumed throughout the compartment. However, for large open compartments, assuming uniform temperature is not compatible with real fires. To overcome this limitation, a nonuniform fire method named as travelling fire is employed as an alternative. A study is performed here on a seismicdamaged large plan three-story reinforced concrete structure designed to meet the life safety level of performance when exposed to a travelling fire. To draw a comparison, the structural fire analysis is also performed using the traditional methods. The results show a notable difference— while the fire resistance based on the travelling fire is around 91 min, it is around 140 min when based on a uniform temperature. This shows that the structure studied is more susceptible to failure when subjected to the nonuniform fire than the uniform fire. © Iran University of Science and Technology 2016.

Forough S.A.,Amirkabir University of Technology | Nejad F.M.,Amirkabir University of Technology | Khodaii A.,Amirkabir University of Technology
Construction and Building Materials | Year: 2014

Several temperature shifting techniques have been proposed for construction of relaxation modulus master curve of asphalt mixes using the time-temperature superposition principal; however, it is not clear which one works better than the others. Therefore, the main objective of this study was to compare the relative ability of five common temperature shifting techniques, i.e. Numerical, Log-Linear, Williams-Landel-Ferry (WLF), Modified Kaelble, and Arrhenius, to construct the relaxation modulus master curve for dense graded asphalt mixtures. For this purpose, 72 cylindrical asphalt mixture specimens containing crushed stone aggregates with 60/70 penetration asphalt binder were fabricated using two different aggregate gradations, two binder contents, two air void levels, and three aging conditions with three replicates for each experimental combination. Direct tension relaxation modulus tests were conducted on the specimens at four different temperatures using the trapezoidal loading pattern at a low level of strain. The tensile relaxation modulus master curves of all the specimens were constructed using the Generalized Logistic Sigmoidal Model for the five shifting techniques. Finally, both the graphical and statistical comparisons were made among the temperature shift factors resulted by the mentioned techniques, and the best fit between the measured and predicted data was found for the Numerical technique, followed by Arrhenius, Williams-Landel-Ferry (WLF), Modified Kaelble, and Log-Linear methods respectively. © 2013 Elsevier Ltd. All rights reserved.

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.

Asasian N.,Amirkabir University of Technology | Kaghazchi T.,Amirkabir University of Technology | Soleimani M.,Amirkabir University of Technology
Journal of Industrial and Engineering Chemistry | Year: 2012

Following the previous work (Kaghazchi et al., 2010 [11]), dealing with applying a combination of two kinds of agricultural wastes to produce a new adsorbent, this study is dedicated to investigate the details of mercury adsorption process from aquatic medium by this adsorbent. So the Mix-ZC activated carbon (the sample prepared by chemical activation of a mixture of pistachio-nut shells and licorice residues impregnated with zinc chloride) was selected for doing a series of batch adsorption experiments on it. Equilibrium isotherms, such as Freundlich, Langmuir, Dubinin-Redushkevich and Temkin have been tested. Kinetic studies based on Lagergren first-order, pseudo-second-order rate expressions and intra-particle diffusion studies have been done. The mechanisms of mercury adsorption onto this adsorbent under the operating conditions were also studied. © 2011 The Korean Society of Industrial and Engineering Chemistry.

Gudarzi M.M.,Amirkabir University of Technology | Sharif F.,Amirkabir University of Technology
Journal of Colloid and Interface Science | Year: 2012

A novel and environmentally friendly method based on mixing of colloidal polymer particles and graphene sheets has been developed. It is found that colloidal polymers can be employed to stabilize graphene oxide (GO) sheets during reduction to graphene. Adsorption of polymer particles at the surface of graphene layers seems to be underlying mechanism of stabilization of graphene sheets. Surface polarity of the polymer particles is crucial for the successful stabilization of graphene layers. Presence of colloidal particles at the surface of graphene prohibits restacking and agglomeration of nanolayers, resulting in fine dispersion of graphene throughout the polymeric matrix. Formation of strong bond between polar segments of the polymer chain and oxygen groups of graphene sheets generates a strong interface improving final properties of the composites. Inclusion of merely 2. wt% of graphene into an acrylic resin resulted in an increase of 522% and 242% in modulus and hardness, respectively. © 2011 Elsevier Inc.

Soroush A.,Amirkabir University of Technology | Ferdowsi B.,Amirkabir University of Technology
Powder Technology | Year: 2011

Discrete element modeling is employed to investigate the micromechanics of two granular assemblies subjected to constant-volume cyclic loading. For this purpose, two assemblies of spherical particles are modeled at the same confining pressure but with two different void ratios. The cyclic behaviors of the assemblies are inspected and the micromechanical parameters and their variations during cyclic loading are carefully observed and analyzed. The evolution of contact force networks with the progression of the loading cycles confirms that the contact force networks are hysteretic and their formation depends on the previous strain conditions of the assemblies. The distributions of the contact normals and their normal forces are also investigated to obtain a quantitative insight of the changes in the contact force networks. The probability distributions of the normal and tangential forces during cyclic loading are similar to the results of previous experimental studies that were conducted on two-dimensional specimens of granular materials. In addition, variations of the fabric tensors, which were calculated for strong contacts, are studied to trace the changes of the structural anisotropy of the specimens. The results suggest that the structural anisotropy of the specimens increases dramatically when they approach the state of liquefaction and that the degree of anisotropy is more profound in the strong contacts. Finally, the displacements of the particles during specific loading cycles are calculated to determine the relation between the movements of the particles and the changes in the macro-scale behavior of the two assemblies. The results of this study elaborate the origin of liquefaction phenomena with respect to the microstructure of the granular soils, showing the role of different mode of contacts failure in micro-scale (sliding and rolling) on the overall observed behavior of granular soils with two different relative densities, moreover the importance of strong and weak contacts in cyclic constant-volume loading of the media. It also emphasizes on the variation of structural anisotropy in undrained cyclic loading of granular media and its relationship with common soil behavior in macro-scale during liquefaction failure. © 2011 Elsevier B.V.

Hosseinzadeh S.A.A.,Golestan University | Tehranizadeh M.,Amirkabir University of Technology
Journal of Constructional Steel Research | Year: 2014

The overall behavior of steel plate shear wall (SPSW) dual systems comprises the contributions of the infill plate tension field and boundary frame moment resisting actions. In the literature, a moment frame acting as SPSW boundaries (SPSW boundary frame) is treated as the same frame acting alone (bare frame). However, due to an interaction effect between the infill wall and the boundary frame, the actual behavior of SPSW boundary frame is different from the behavior of the same bare frame. In the present paper, a number of code designed single and multi-story SPSWs and the corresponding bare frames are numerically analyzed (a) to study the influence of infill walls on the behavior of boundary frames and (b) to evaluate the effectiveness of infill walls. Results show that the presence of infill walls can significantly improve the performance of moment-resisting frame systems, especially for multi-story ones, in terms of strength, stiffness, ductility and energy dissipation capability. In turn, the better performance of the SPSW system than the corresponding bare frame is not only due to the contribution of the infill wall, but also due to the improvement in the performance of the frame resulted from the wall-frame interaction. © 2014 Elsevier Ltd.

Farahnakian M.,Amirkabir University of Technology | Razfar M.R.,Amirkabir University of Technology
Materials and Manufacturing Processes | Year: 2014

Several methods such as plasma enhanced turning (PET) and ultrasonic-aided turning (UAT) have been introduced to assist conventional turning (CT) in order to overcome the difficulties of hard turning. There exist extensive experimental researches which have shown the feasibility of PET and UAT in hard turning. This paper investigates the cutting force and surface roughness in hybrid plasma and UAT hybird turning (HYT) on the AISI 4140 hardened steel. The studied parameters are turning parameters (cutting speed, feeding rate, and depth of cut), tool material, plasma, and ultrasonic parameters. For this purpose, a model was developed to relate current of plasma to the material removal temperature. The plasma and ultrasonic equipment were installed on the lathe, then hybrid ultrasonic and plasma aided machining was applied on AISI 4140 hardened steel for experiment using Taguchi design. Results showed the reduction of cutting forces in hybrid machining in comparison with CT, PET, and UAT; and depending on cutting conditions, workpiece surface roughness can be improved in hybrid machining in comparison with CT, PET, and UAT. © 2014 Taylor & Francis Group, LLC.

Ovesy H.R.,Amirkabir University of Technology | Fazilati J.,Astronautics Research Institute
Composite Structures | Year: 2014

The parametric instability regions of laminated composite plate and cylindrical shells subjected to non-uniform in-plane axial end-loadings are studied. The static as well as varying parts of the end-loading assumed to vary according to parabolic distribution in the width of the panel. The dynamic instability of panels has been investigated by using a developed finite strip method (FSM). The problem has been formulated on the basis of principle of virtual work. The effects of loading distribution as well as boundary conditions and static loading on the instability regions of load frequency are studied by applying Bolotin's first order approximation. In order to demonstrate the capabilities of the developed formulations and methods in predicting the structural parametric dynamic behavior, some representative results are obtained and compared with those in the literature wherever available. © 2013 Elsevier Ltd.

Sahmani S.,Amirkabir University of Technology | Bahrami M.,Amirkabir University of Technology | Ansari R.,Guilan University
Composite Structures | Year: 2014

The prime aim of the current study is to predict the free vibration behavior of third-order shear deformable nanobeams in the vicinity of postbuckling configuration and in the presence of surface effects which includes surface elasticity, residual surface stress and surface inertia. To accomplish this end, Gurtin-Murdoch elasticity theory within the framework of third-order shear deformation beam theory is employed. In order to satisfy the balance conditions between the bulk and surfaces of nanobeam, a cubic distribution is considered for the normal stress through the thickness. By using Hamilton's principle, the non-classical governing differential equations of motion including von Karman geometric nonlinearity are derived. After using generalized differential quadrature (GDQ) method to discretize the governing equations on the basis of Chebyshev-Gauss-Lobatto grid points, the pseudo-arc length continuation technique is utilized to solve the eigenvalue problem. The natural frequencies of nanobeam corresponding to the both prebuckling and postbuckling domains are obtained for various buckling mode shapes based on the numerical solution strategy. It is demonstrated that in the prebuckling domain of the first vibration mode shape, increasing of beam thickness leads to lower natural frequency for all types of boundary conditions, but this behavior becomes reverse in the postbuckling domain. © 2014 Elsevier Ltd.

Yazdanpanah R.,Amirkabir University of Technology | Mirsalim M.,Amirkabir University of Technology
IEEE Transactions on Magnetics | Year: 2014

Analytical approaches could be very useful in the design and analysis of electromagnetic devices. This paper is concerned with the design and analysis of an axial-flux wound-excitation eddy-current brake, for which a subdomain-based analytical approach is developed, whereby performance characteristics and design considerations of the device are evaluated. The practical constraints of the proposed structure are discussed and 3-D finite-element analysis (FEA) is employed in the analyses as well as validation of the implemented model. Moreover, a parametric analysis is performed, which provides valuable information regarding the design of the device. In addition, the extracted closed-form expressions for the brake characteristics can be used in the design of the associated control systems. Finally, a prototype has been manufactured whose results agree well with those discussions issued from FEA as well as the proposed model. © 1965-2012 IEEE.

Shariati S.R.P.,Amirkabir University of Technology | Bonakdarpour B.,Amirkabir University of Technology | Zare N.,Amirkabir University of Technology | Ashtiani F.Z.,Amirkabir University of Technology
Bioresource Technology | Year: 2011

The use of membrane sequencing batch reactors, operated at HRT of 8, 16 and 24. h, was considered for the treatment of a synthetic petroleum wastewater. Increase in HRT resulted in statistically significant decrease in MLSS. Removal efficiencies higher than 97% were found for the three model hydrocarbon pollutants at all HRTs, with air stripping making a small contribution to overall removal. Particle size distribution (PSD) and microscopic analysis showed reduction in the protozoan populations in the activated sludge with decreasing HRT. PSD analysis also showed a higher proportion of larger and smaller sized particles at the lowest HRT. The rate of membrane fouling was found to increase with decreasing HRT; SMP, especially carbohydrate SMP, and mixed liquor apparent viscosity also showed a pronounced increase with decreasing HRT, whereas the concentration of EPS and its components decreased. FTIR analysis identified organic compounds as the main component of membrane pore fouling. © 2011 Elsevier Ltd.

Kaghazchi T.,Amirkabir University of Technology | ShamsiJazeyi H.,Amirkabir University of Technology
Journal of Industrial and Engineering Chemistry | Year: 2011

In this study, activated carbon was treated using a gaseous by-product produced by the reaction of nitric acid and activated carbon. To determine the effectiveness of this treatment for enhancing the Hg(II) removal capacity of activated carbons, several batch experiments have been conducted for two different commercial activated carbons at different pH values, temperatures, and initial concentrations. In addition, Iodine number, BET surface area, total and micro-pore volume, as well as pH pzc amounts of treated and untreated samples were compared to determine the effects of this treatment on the porous structure and surface charge of activated carbons. After this modification, a decrease in porous characteristic and an increase in the surface acidity of activated carbons were observed. Hg(II) speciation for experimental conditions in this work showed that molecular species including HgCl 2, HgClOH, and Hg(OH) 2 are generally present in the solution. Additionally, thermodynamic calculations indicated that the Hg(II) removal using the modified activated carbons in this work is an endothermic process with increase in the entropy of the system. The positive entropy change was described by the chemisorption mechanisms during which some released species from the surface into the aqueous phase may increase the degree of freedom. © 2011 The Korean Society of Industrial and Engineering Chemistry.

Ahmad R.R.,Amirkabir University of Technology
Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science | Year: 2013

Stiffened plate buckles in different modes, including web/flange buckling, torsional buckling, plate buckling, and interactions of them. Generally, interactions of different buckling modes in stiffened plates are ignored and elastic buckling analysis of each mode is treated separately. In some design codes, to cope with interactions of different buckling modes, the influence of adjacent elements are considered as rotational springs. The main aim of this study is to compare literature- and rule-based expressions to assess the elastic buckling strength of T-bar stiffened plates and to identify the applicability of selected expressions for certain conditions. Different buckling modes and their interactions are investigated, and critical Euler stresses are evaluated. Upon comparison with given expressions and the finite element method, it is found that some of the proposed expressions are not applicable in certain conditions. © IMechE 2012.

Khamei A.A.,Amirkabir University of Technology | Dehghani K.,Amirkabir University of Technology
Journal of Alloys and Compounds | Year: 2010

A model was developed to predict the hot deformation behavior of Ni60 wt%-Ti40 wt% alloy. In these regard, the hot compression tests were carried out at the temperatures from 950 °C to 1050 °C and at the strain rates of 0.001 s-1 to 0.35 s-1. The experimental data were then used to determine the constants of developed constitutive equations. The developed model can be represented by Zener-Hollomon parameter in a hyperbolic sinusoidal equation form. The predicted stress-strain curves are in a very good agreement with those obtained experimentally, both illustrating the occurrence of dynamic recrystallization. Also, in both cases, the peak and steady-state stresses raised with decreasing temperature and increasing strain rate. The very good agreement between the measured and predicted results indicates the high accuracy of developed model and established constitutive equations in predicting and analyzing the hot deformation behavior of Ni60 wt%-Ti40 wt%. © 2009.

Talebi H.A.,Amirkabir University of Technology | Khorasani K.,Concordia University at Montréal
IEEE Transactions on Control Systems Technology | Year: 2013

The problem of fault detection and isolation/identification (FDI) of nonlinear systems using neural networks is considered in this paper. The proposed FDI approach employs recurrent neural network-based observers for simultaneously detecting, isolating and identifying the severity of actuator faults in presence of disturbances and uncertainties in the model and sensory measurements. The neural network weights are updated based on a modified dynamic backpropagation scheme. The proposed FDI scheme does not rely on the availability of full state measurements. In most works in the literature the fault function acts as an additive term on the actuator, whereas in this work the fault acts as a multiplicative term. This will make the formal stability and convergence analysis of the overall FDI scheme nontrivial and challenging. Our stability analysis considers the presence of plant and sensor uncertainties through the use of Lyapunov's direct method with no restrictive assumptions on the system and/or the FDI algorithm. The performance of our proposed FDI approach is evaluated through simulations that are performed for two case studies, namely FDI of 1) reaction wheel type actuators that are commonly utilized in the attitude control subsystem (ACS) of a satellite and 2) actuators in a two-link flexible joint manipulator. © 1993-2012 IEEE.

Hamta N.,Amirkabir University of Technology | Fatemi Ghomi S.M.T.,Amirkabir University of Technology | Jolai F.,University of Tehran | Akbarpour Shirazi M.,Amirkabir University of Technology
International Journal of Production Economics | Year: 2013

This paper addresses multi-objective (MO) optimization of a single-model assembly line balancing problem (ALBP) where the operation times of tasks are unknown variables and the only known information is the lower and upper bounds for operation time of each task. Three objectives are simultaneously considered as follows: (1) minimizing the cycle time, (2) minimizing the total equipment cost, and (3) minimizing the smoothness index. In order to reflect the real industrial settings adequately, it is assumed that the task time is dependent on worker(s) (or machine(s)) learning for the same or similar activity and sequence-dependent setup time exists between tasks. Finding an optimal solution for this complicated problem especially for large-sized problems in reasonable computational time is cumbersome. Therefore, we propose a new solution method based on the combination of particle swarm optimization (PSO) algorithm with variable neighborhood search (VNS) to solve the problem. The performance of the proposed hybrid algorithm is examined over several test problems in terms of solution quality and running time. Comparison with an existing multi-objective evolutionary computation method in the literature shows the superior efficiency of our proposed PSO/VNS algorithm. © 2012 Elsevier B.V. All rights reserved.

Kiani Y.,Amirkabir University of Technology | Eslami M.R.,Amirkabir University of Technology
Acta Mechanica | Year: 2013

Thermal buckling analysis of a transversely graded circular plate attached to a centric partial elastic foundation is studied, analytically. Thermomechanical properties of the circular plate are distributed across the thickness based on a power law function. The governing equations of the plate are obtained by means of the classical plate theory. A conventional Winkler-type foundation is assumed to be in contact with the plate which acts in compression as well as in tension. Proper boundary conditions are chosen after pre-buckling analysis of the plate, and stability equations are established via the adjacent equilibrium criterion. To analyze the thermal stability problem, the plate is divided into two sections, a foundation-less domain and an in-contact region. An exact procedure is presented to accurately predict the critical buckling temperature as well as the buckled configuration of the plate. Analysis of various involved parameters including the Winkler parameter, foundation radius, power law index, and loading type is presented. It is concluded that while the loading is symmetric, in many cases, the buckled configuration of the plate is asymmetric. © Springer-Verlag Wien 2013.

Rezvan A.T.,Amirkabir University of Technology | Gharneh N.S.,Amirkabir University of Technology | Gharehpetian G.B.,Amirkabir University of Technology
Energy and Buildings | Year: 2013

This paper presents a method to determine the optimum capacity of distributed generation technologies for buildings. The Combined Heat and Power (CHP) unit has both absorption and electric chiller for cooling loads, and a supplementary boiler for heating loads. The demand is uncertain in the model. The underlying uncertainty is modeled using probabilistic theory. In this method, the expected value of the objective function is evaluated using numerical approaches. A simulation based optimization method is presented which can estimate the cost of system operation and find the appropriate design by means of stochastic programming. The effect of minimum economic turn-down of the facilities is also discussed in this paper. The optimum capacity of distributed generation technologies has a great effect on the cost of the building. Therefore, the proposed method is applied for a hospital in Iran as a case study. The results show that the optimum capacities of CHP and absorption chiller decreases and the capacities of the electric chiller and boiler rise by an increase in demand uncertainty. In addition, the appropriate minimum economic turn-down of facilities has a considerable effect on the overall system cost. © 2012 Elsevier B.V.

Alijani F.,Amirkabir University of Technology | Amabili M.,McGill University | Karagiozis K.,McGill University | Bakhtiari-Nejad F.,Amirkabir University of Technology
Journal of Sound and Vibration | Year: 2011

Nonlinear forced vibrations of FGM doubly curved shallow shells with a rectangular base are investigated. Donnell's nonlinear shallow-shell theory is used and the shell is assumed to be simply supported with movable edges. The equations of motion are reduced using the Galerkin method to a system of infinite nonlinear ordinary differential equations with quadratic and cubic nonlinearities. Using the multiple scales method, primary and subharmonic resonance responses of FGM shells are fully discussed and the effect of volume fraction exponent on the internal resonance conditions, softening/hardening behavior and bifurcations of the shallow shell when the excitation frequency is (i) near the fundamental frequency and (ii) near two times the fundamental frequency is shown. Moreover, using a code based on arclength continuation method, a bifurcation analysis is carried out for a special case with two-to-one internal resonance between the first and second doubly symmetric modes with respect to the panel's center (ω13≈2ω11). Bifurcation diagrams and Poincar maps are obtained through direct time integration of the equations of motion and chaotic regions are shown by calculating Lyapunov exponents and Lyapunov dimension. © 2010 Elsevier Ltd.

Dehghani H.,Amirkabir University of Technology | Ataee-pour M.,Amirkabir University of Technology
Resources Policy | Year: 2012

Minig projects are complex businesses that demand constant risk assessment. This is because several kinds of uncertainties influence the value of a mine project, typically. These uncertainties may be classified as exploration uncertainties, economic uncertainties and engineering uncertainties. The evaluation of a mine project under these uncertainties is a complicated job, which may lead to making a wrong decision by managers and stockholders. Therefore, at first, the engineers must recognize the mining uncertainties before carrying out the project evaluation. The economic uncertainties are the most important factors, which may affect the project evaluation. Among the mentioned uncertainties, the operating cost uncertainty is an important and effective factor, which is ignored to a certain extent.This research uses the binomial tree technique to compute the net present value of the Cayeli copper mine under three scenarios: (1) assuming certainty for both price and operating costs, (2) assuming uncertainty for metal price and certainty for operating costs and (3) assuming uncertainty for both price and operating costs. It is concluded that the mine evaluation suggests greater net present value when uncertainty is considered for both price and operating costs. © 2012 Elsevier Ltd.

Tavasoli A.,Amirkabir University of Technology | Naraghi M.,Amirkabir University of Technology
Asian Journal of Control | Year: 2013

Nonlinear vehicle control allocation is achieved by distributing the control task to tire forces with nonlinear saturation constraints. The overall vehicle control is accomplished by developing a hierarchical scheme. First, a high-level sliding mode control with adaptive gain is considered to obtain the body force/moment for stable vehicle motion. The proposed controller only requires online adaptation of control gains without acquiring the knowledge of upper-bounds on system uncertainties. Then, optimal distribution of tire forces (ODF) with nonlinear saturation constraints is considered. The high-level control objectives are mapped to individual tire forces by formulating a nonlinear optimization problem. The interior-point (IP) method is adopted for a nonlinear programming task at each time step. Evaluation of the overall system is accomplished by simulation testing with a nine-degrees-of-freedom vehicle nonlinear model. Comparison with a well-recognized control system shows the effect of saturation constrained ODF (SCODF) on improving vehicle handling and stability. © 2012 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society.

Safargholi F.,Amirkabir University of Technology
International Journal of Electrical and Computer Engineering | Year: 2014

Farhad Safargholi was born in Iran on January 19, 1990. He received the Engineering degree from the Bu-Ali Sina University, Hamadan, Iran, in 2012, where he is currently working toward the Master degree in Amirkabir University of Technology (AUT), Tehran, Iran. His research interests focus on power electronics, modulation strategies, FACTS, load flow and harmonic distortion of power system. To reduce the high harmonic components at the main power supply current and to improve the input voltage distortion for matrix converter, design of input filters characteristics for matrix converter system is very important. Also, the input filter can be applied to the near unity power factor operation at the input side. It can be used to improve the power quality of the input current. This paper represents a direct space vector modulation (SVM) method and introduces switching patterns for SVM method and then design of input filter to compensate the power factor is analyzed. Simulation results with inductive load (RL) and Permanent-magnet synchronous motor (PMSM) are shown to validate the effectiveness of the proposed method. Copyright © 2014 Institute of Advanced Engineering and Science. All rights reserved.

Bank Tavakoli M.R.,Amirkabir University of Technology | Vahidi B.,Amirkabir University of Technology
International Journal of Electrical Power and Energy Systems | Year: 2010

In this paper a simulation ground is designed to track the lightning path from cloud to the striking point on high voltage overhead line (OHL) structures. By using this simulation method, the strikes to towers, phase wires, ground wires and earth is counted. The method also reveals the property of strokes attaching the phase wires like their path, their peak current and their distance from earth in final jump. The simulation environment consists of two towers, ground wires, phase wires and earth comprising a full span. The downward lightning leader is simulated based on field observations by stepping line charges coming down. The inception of upward leader is tested in each step movement to find the target striking point. Using this method, lightning performance of an OHL is investigated and the number of strikes as well as highest lightning current attaching the phase wires is extracted. The results, yield by proposed method, are also compared with the existing methods of OHL lightning performance analysis. © 2010 Elsevier Ltd.

Habashi H.R.,Amirkabir University of Technology | Alinia M.M.,Amirkabir University of Technology
Journal of Constructional Steel Research | Year: 2010

The nonlinear response of steel plate shear wall (SPSW) dual systems under lateral loading with regard to the interaction between the infill plates and frame members is studied. A number of SPSWs are numerically analyzed and the results are utilized to discuss (a) the influence of infill plates on the behavior of frames and (b) to evaluate their degree of effectiveness in resisting lateral loads. Results show that SPSWs designed according to design codes should have desirable sequences of yielding and that plastic deformations should primarily be provided by the infill plates. It is illustrated that the infill plates are very effective in the initial stages of loading (up to the drift angle of 1% ) and absorb substantial part of storey shear. However, once diagonal yield zones develop in the infill plates, they begin to lose their effectiveness; and when yield zones spread throughout the wall, additional applied loads are essentially carried by the frame members. © 2009 Elsevier Ltd. All rights reserved.

Mobasheri R.,University of Sussex | Peng Z.,University of Sussex | Mirsalim S.M.,Amirkabir University of Technology
International Journal of Heat and Fluid Flow | Year: 2012

An Advanced CFD simulation has been carried out in order to explore the combined effects of pilot-, post- and multiple-fuel injection strategies and EGR on engine performance and emission formation in a heavy duty DI-diesel engine. An improved version of the ECFM-3Z combustion model has been applied coupled with advanced models for NOx and soot formation. The model was validated with experimental data achieved from a Caterpillar 3401 DI diesel engine and good agreement between predicted and measured in-cylinder pressure, heat release rate, NOx and soot emissions was obtained. The optimizations were conducted separately for different split injection cases without pilot injection and then, for various multiple injection cases. Totally, three factors were considered for the injection optimization, which included EGR rate, the separation between main injection and post-injection and the amount of injected fuel in each pulse. For the multiple injection cases, two more factors (including double and triple injections during main injection) were also added. Results show that using pilot injection accompanied with an optimized main injection has a significant beneficial effect on combustion process so that it could form a separate 2nd stage of heat release which could reduce the maximum combustion temperature, which leads to the reduction of the NOx formation. In addition, it has found that injecting adequate fuel in post-injection at an appropriate EGR allows significant soot reduction without a NOx penalty rate. © 2011 Elsevier Inc.

Dehghan M.,Amirkabir University of Technology | Fakhar-Izadi F.,Amirkabir University of Technology
International Journal for Numerical Methods in Biomedical Engineering | Year: 2011

In this paper we present two pseudospectral methods based on Fourier series and rational Chebyshev functions for solving the Nagumo equation. In each of the two presented methods the problem is reduced to a system of ordinary differential equations that is solved by the leapfrog difference scheme and the fourth-order Runge-Kutta method, respectively. We compare the numerical solutions with the exact solution to validate the numerical methods. Numerically comparing of the two methods also will be considered. © 2009 John Wiley & Sons, Ltd.

Dehghan M.,Amirkabir University of Technology | Salehi R.,Amirkabir University of Technology
Computational Mechanics | Year: 2011

The radial basis function (RBF) collocation methods for the numerical solution of partial differential equation have been popular in recent years because of their advantage. For instance, they are inherently meshless, integration free and highly accurate. In this article we study the RBF solution of Eikonal equation using boundary knot method and analog equation method. The boundary knot method (BKM) is a meshless boundary-type radial basis function collocation technique. In contrast with the method of fundamental solution (MFS), the BKM uses the non-singular general solution instead of the singular fundamental solution to obtain the homogeneous solution. Similar to MFS, the RBF is employed to approximate the particular solution via the dual reciprocity principle. In the current paper, we applied the idea of analog equation method (AEM). According to AEM, the nonlinear governing operator is replaced by an equivalent nonhomogeneous linear one with known fundamental solution and under the same boundary conditions. Finally numerical results and discussions are presented to show the validity and efficiency of the proposed method. © 2010 Springer-Verlag.

Aghajani Bazzazi A.,Amirkabir University of Technology | Osanloo M.,Amirkabir University of Technology | Karimi B.,Amirkabir University of Technology
Expert Systems with Applications | Year: 2011

In multiple attribute decision making (MADM) problem, a decision maker (DM) has to choose the best alternative that satisfies the evaluation criteria among a set of candidate solutions. It is generally hard to find an alternative that meets all the criteria simultaneously, so a good compromise solution is preferred. The VIKOR method was developed for multi-criteria optimization of complex systems. This method focuses on ranking and selecting from a set of alternatives in the presence of conflicting criteria. It introduces the multi-criteria ranking index based on the particular measure of "closeness" to the "ideal" solution. To deal with the uncertainty and vagueness from humans' subjective perception and experience in decision process, this paper presents an evaluation model based on deterministic data, fuzzy numbers, interval numbers and linguistic terms. Combination of analytic hierarchy process (AHP) and entropy method was applied for attribute weighting in this proposed MADM method. To demonstrate the potential of the methodology, the proposed method is used for surface mine equipment selection problems. © 2010 Elsevier Ltd. All rights reserved.

Boloori Arabani A.R.,Amirkabir University of Technology | Fatemi Ghomi S.M.T.,Amirkabir University of Technology | Zandieh M.,Shahid Beheshti University
Expert Systems with Applications | Year: 2011

Cross-docking is an approach in inventory management which can reduce inventories, lead times and customer response time. In this strategy, products and shipments are unloaded from inbound trucks, sorted and categorized based on their characteristics, moved and loaded onto outbound trucks for delivery to demand points in a distribution network. The important fact is that, the items are stored in the inventory for a period which is primarily less than the actual time allocated to keep these items in a typical warehouse. Therefore, total cost and space requirement for inventory can be cut down. One of the most important targets in such systems is to establish coordination between the performance of inbound and outbound trucks in that these trucks can be scheduled, and the product items can be allocated to trucks effectively. This paper addresses some meta-heuristics to find the best sequence of inbound and outbound trucks, so that the objective, minimizing the total operation time called makespan, can be satisfied. Furthermore, not only the efficiency and capability of the algorithms' parameters are assessed and analyzed by some performance measures, but also these meta-heuristics are compared with each other in order to find out the set of homogeneous algorithms among all proposed algorithms. By this analysis, it can be shown that the suitability of these meta-heuristics is quite sensible especially for the cross-docking systems with large sizes in which a high volume of inbound or outbound trucks transmit the product items. © 2010 Elsevier Ltd. All rights reserved.

Keshavarz E.,Islamic Azad University at Sirjan | Khorram E.,Amirkabir University of Technology
Computers and Industrial Engineering | Year: 2011

In this paper, a fuzzy bi-criteria transportation problem is studied. Here, the model concentrates on two criteria: total delivery time and total profit of transportation. The delivery times on links are fuzzy intervals with increasing linear membership functions, whereas the total delivery time on the network is a fuzzy interval with a decreasing linear membership function. On the other hand, the transporting profits on links are fuzzy intervals with decreasing linear membership functions and the total profit of transportation is a fuzzy number with an increasing linear membership function. Supplies and demands are deterministic numbers. A nonlinear programming model considers the problem using the max-min criterion suggested by Bellman and Zadeh. We show that the problem can be simplified into two bi-level programming problems, which are solved very conveniently. A proposed efficient algorithm based on parametric linear programming solves the bi-level problems. To explain the algorithm two illustrative examples are provided, systematically. © 2011 Elsevier Ltd. All rights reserved.

Shamsi M.,Amirkabir University of Technology
Optimal Control Applications and Methods | Year: 2011

In the present contribution, a modified Legendre pseudospectral scheme for accurate and efficient solution of bang-bang optimal control problems is investigated. In this scheme control and state functions are considered as piecewise constant and piecewise continuous polynomials, respectively, and the switching points are also taken as decision variables. Furthermore, for simplicity in discretization, the integral formulation of the dynamical equations is considered. Thereby, the problem is converted into a mathematical programming problem which can be solved by the well-developed parameter optimization algorithms. The main advantages of the present method are that: (i) it obtains good results even by using a small number of collocation points and the rate of convergence is high; (ii) the switching times can be captured accurately; and (iii) the wrongly chosen number of switching points can be detected by the results of the method. These are illustrated through a numerical implementation of the method on three examples and the efficiency of the method is reported. © 2010 John Wiley & Sons, Ltd.

Behnamian J.,Amirkabir University of Technology | Zandieh M.,Shahid Beheshti University
Expert Systems with Applications | Year: 2011

Recently introduced colonial competitive algorithm (CCA) has shown its excellent capability on different optimization problems. The aim of this paper is to propose a discrete version of this method to determine a schedule that minimizes sum of the linear earliness and quadratic tardiness in the hybrid flowshops scheduling problem with simultaneously considering effects of sequence-dependent setup times and limited waiting time. In other word we assume that the waiting time for each job between two consecutive stages cannot be greater than a given upper bound. Also for this problem, a mixed integer program is formulated. Computational results are presented to evaluate the performance of the proposed algorithms for problems with different structures. © 2011 Elsevier Ltd. All rights reserved.

Moghadas Nejad F.,Amirkabir University of Technology | Zakeri H.,Amirkabir University of Technology
Expert Systems with Applications | Year: 2011

The research presented in this article is aimed at the development of an automated imaging system for distress detection and isolation in asphalt pavement distress obtained from pavement image acquisition system (PIAS). This article focuses on comparing the discriminating power of several multi-resolution texture analysis techniques using wavelet, ridgelet, and curvelet-based texture descriptors. The approach consists of four steps: Image collection, segmentation of regions of interest (ROI), extraction of the most discriminative texture features, creation of a classifier that automatically identifies the pavement distress, and storage. Tests comparing the wavelet, ridgelet, and curvelet texture features indicated that curvelet-based signatures outperform all other multi-resolution techniques for pothole distress, yielding accuracy rates in the 97.9%. Ridgelet-based signatures outperform all other multi-resolution techniques for cracking distress, yielding accuracy rates in the 93.6-96.4% rate. © 2010 Elsevier Ltd. All rights reserved.

Jaberipour M.,Amirkabir University of Technology | Khorram E.,Amirkabir University of Technology
Engineering Optimization | Year: 2011

In general design optimization problems, it is usually assumed that the design variables are continuous. However, many practical problems in engineering design require considering the design variables as integer or discrete values. The presence of discrete and integer variables along with continuous variables adds to the complexity of the optimization problem. Very few of the existing methods can yield a globally optimal solution when the objective functions are non-convex and non-differentiable. This article presents a mixed-discrete harmony search approach for solving these nonlinear optimization problems which contain integer, discrete and continuous variables. Some engineering design examples are also presented to demonstrate the effectiveness of the proposed method. © 2011 Taylor & Francis.

Ghanbari A.,Amirkabir University of Technology | Bahrami M.,Amirkabir University of Technology
Journal of Intelligent and Robotic Systems: Theory and Applications | Year: 2011

Swimming microrobots can exhibit high levels of performance to move freely in the human body fluids to fulfill risky biomedical operations by mimicking microorganisms. Many researchers have proposed micro swimming methods for viscous flows based on flagellar motion. Here, a novel swimming microrobot inspired by ciliated microorganisms based on artificial cilia is introduced. The hydrodynamic model is developed and performance parameters such as propulsive force, propulsive velocity and efficiency of the microrobot are computed. The velocity and efficiency dependence on design parameters of microrobot is evaluated. The proposed micro swimming concept offers appropriate efficiency, thrust, speed and maneuverability. It is shown that the introduced swimming microrobot can reach a maximum speed 4.5 mm/s and efficiency of 40%. The proposed microrobot has the potential to be utilized in both viscous and turbulent body flows. © 2011 Springer Science+Business Media B.V.

Nejad F.M.,Amirkabir University of Technology | Zakeri H.,Amirkabir University of Technology
Expert Systems with Applications | Year: 2011

Quantification of pavement crack data is one of the most important criteria in determining optimum pavement maintenance strategies. Recently, multi-resolution analysis such as wavelet decompositions provides very good multi-resolution analytical tools for different scales of pavement analysis and distresses classification. This paper present an automatic diagnosis system for detecting and classification pavement crack distress based on Wavelet-Radon Transform (WR) and Dynamic Neural Network (DNN) threshold selection. The algorithm of the proposed system consists of a combination of feature extraction using WR and classification using the neural network technique. The proposed WR + DNN system performance is compared with static neural network (SNN). In test stage; proposed method was applied to the pavement images database to evaluate the system performance. The correct classification rate (CCR) of proposed system is over 99%. This research demonstrated that the WR + DNN method can be used efficiently for fast automatic pavement distress detection and classification. The details of the image processing technique and the characteristic of system are also described in this paper. © 2011 Published by Elsevier Ltd.

Javanbakht M.,Amirkabir University of Technology | Moein M.M.,Amirkabir University of Technology | Akbari-adergani B.,Food and Drug Laboratory Research Center
Journal of Chromatography B: Analytical Technologies in the Biomedical and Life Sciences | Year: 2012

The applicability of an on-line solid phase extraction method using molecularly imprinted monolithic column was developed for the assay of tramadol (TRD) in urine and plasma samples. The monolithic column was prepared by using TRD as the template, methacrylic acid (MAA) as the functional monomer, ethylene glycol dimethacrylate (EGDMA) as the cross-linker and chloroform as the porogen with in situ molecular imprinting polymerization technique. Various parameters affecting the extraction efficiency of the monolithic column were evaluated. Chromatographic analysis of TRD after on-line clean-up of samples was performed by reversed-phase HPLC on an ACE column with ultraviolet detection at 218. nm. The present work was successfully applied for automated simple analysis of TRD in urine and plasma samples with high recoveries between 90.5-93.1% and 93.3-96.0%, respectively. The results revealed that in concentration up to 500. ng/mL of dextromethorphan (DEX), timolol (TMO) and O-desmethyltramadol (M1), the recoveries were not reduced more than 4.3% and 4.0% for plasma and urine samples, respectively. The limit of detection (S/N=3) and limit of quantification (S/N=10) for TRD in urine samples were 0.03. ng/mL and 0.10. ng/mL, and in plasma samples were 0.3 and 1.0. ng/mL, respectively. Inter-column precision of the assays (n=3) for urine and plasma samples at the 100. ng/mL TRD level were 4.0% and 4.2%, respectively. © 2012.

Kia M.R.,Amirkabir University of Technology | Noshad H.,Amirkabir University of Technology
Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms | Year: 2015

Multiple scattering of protons through a target is explained by a set of coupled stochastic differential equations. The motion of protons in matter is calculated by analytical random sampling from Moliere and Landau probability density functions (PDF). To satisfy the Vavilov theory, the moments for energy distribution of a 49.1 MeV proton beam in aluminum target are obtained. The skewness for the PDF of energy demonstrates that the energy distribution of protons in thin thickness becomes a Landau function, whereas, by increasing the thickness of the target it does not follow a Gaussian function completely. Afterwards, the depth-dose distributions are calculated for a 60 MeV proton beam traversing soft tissue and for a 160 MeV proton beam travelling through water. The results prove that when elastic scattering is taken into account, the Bragg-peak position is decreased, while the dose deposited in the Bragg region is increased. The results obtained in this article are benchmarked by comparison of our results with the experimental data reported in the literature. © 2015 Elsevier B.V. All rights reserved.

Ahmadlou M.,Amirkabir University of Technology | Adeli H.,Ohio State University | Adeli A.,Ohio State University
Clinical EEG and Neuroscience | Year: 2012

This article presents a new methodology for investigation of the organization of the overall and hemispheric brain network of patients with attention-deficit hyperactivity disorder (ADHD) using theoretical analysis of a weighted graph with the goal of discovering how the brain topology is affected in such patients. The synchronization measure used is the nonlinear fuzzy synchronization likelihood (FSL) developed by the authors recently. Recent evidence indicates a normal neocortex has a small-world (SW) network with a balance between local structure and global structure characteristics. Such a network results in optimal balance between segregation and integration which is essential for high synchronizabilty and fast information transmission in a complex network. The SW network is characterized by the coexistence of dense clustering of connections (C) and short path lengths (L) among the network units. The results of investigation of C show the local structure of functional left-hemisphere brain networks of ADHD diverges from that of non-ADHD which is recognizable in the delta electroencephalograph (EEG) sub-band. Also, the results of investigation for L show the global structure of functional left-hemisphere brain networks of ADHD diverges from that of non-ADHD which is observable in the delta EEG sub-band. It is concluded that the changes in left-hemisphere brain's structure of ADHD from that of the non-ADHD are so much that L and C can distinguish the ADHD brain from the non-ADHD brain in the delta EEG sub-band. © 2012 EEG and Clinical Neuroscience Society.

Afrooz K.,Amirkabir University of Technology | Abdipour A.,Amirkabir University of Technology
IEEE Transactions on Electromagnetic Compatibility | Year: 2012

In this paper, an unconditionally stable finite-difference time-domain algorithm is presented for analysis of lossy nonuniform multiconductor transmission line (MTL). The results of the proposed algorithm are confirmed by those of the Leap-Frog algorithm. The unconditionally stable algorithm alone cannot decrease the time consumption, especially when the MTL is excited by modulated signals. The complex phasor transformation approach is used to separate the modulating signal from the carrier signal when an MTL is excited by a modulated signal. A new set of equations is generated using this approach. The new equations are based on the modulating signal, and the carrier signal is eliminated in these equations. The derived equations are solved by Leap-Frog algorithm, and the results confirm the accuracy of these equations. Finally, the proposed equations are solved by the unconditionally stable algorithm at several temporal step sizes. The results indicate that this method has much lower CPU time compared with the conventional method and also has a very good accuracy. © 2012 IEEE.

Ghashochi Bargh H.,Amirkabir University of Technology | Sadr M.H.,Amirkabir University of Technology
Meccanica | Year: 2012

The paper illustrates the application of the particle swarm optimization (PSO) algorithm to the lay-up design of symmetrically laminated composite plates for maximization of fundamental frequency. The design variables are the fiber orientation angles, edge conditions and plate length/width ratios. The formulation is based on the classical laminated plate theory (CLPT), and the method of analysis is the semi-analytical finite strip approach which has been developed on the basis of full energy methods. The performance of the PSO is also compared with the simple genetic algorithm and shows the good efficiency of the PSO algorithm. To check the validity, the obtained results are compared with those available in the literature and some other stacking sequences, wherever possible. © 2011 Springer Science+Business Media B.V.

Shalmani F.M.,Amirkabir University of Technology | Halladj R.,Amirkabir University of Technology | Askari S.,Amirkabir University of Technology
Powder Technology | Year: 2012

Microwave synthesis has been shown to dramatically enhance the reaction rate of many zeolite syntheses. In this study, crystals of nanosized SAPO-34 molecular sieves were synthesized by using microwave-assisted hydrothermal heating with different synthesis conditions to elucidate the effect of these contributing factors on the SAPO-34 formation, in terms of the size and morphology of crystals. All samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and thermal gravimetric analysis (TGA). It was found that microwave-assisted hydrothermal heating was required to obtain fully crystalline SAPO-34 crystals. The hydrothermal heating time played a crucial role in the shape and size control of nanosized SAPO-34 crystals, while the aging time had a negligible effect. The smaller pure SAPO-34 crystals were formed when using a higher concentrated solution as the initial gel. Smaller crystals were produced at higher microwave power, whereas the crystal morphology was found to be independent of the microwave power levels. The crystal size and morphology of SAPO-34 could be controlled by microwave irradiation time and an optimum microwave irradiation time for the preparation of nanosized SAPO-34 crystals was found. © 2012 Elsevier B.V.

Askari S.,Amirkabir University of Technology | Halladj R.,Amirkabir University of Technology
Ultrasonics Sonochemistry | Year: 2012

Synthesis of SAPO-34 nanocrystals which has been recently considered as a challenging task was successfully performed by sonochemical method using TEAOH as structure directing agent (SDA). The products were characterized by XRD, SEM, EDX, BET and TGA. The average crystal size of the final product prepared sonochemically is 50 nm that is much smaller than that of synthesized under hydrothermal condition and the morphology of the crystals changes from uniform spherical nanoparticles to spherical aggregates of cube type SAPO-34 crystals respectively. In the case of sample synthesized sonochemically with aid of hydrothermal condition, the surface area is significantly upper than that of obtained by the conventional static hydrothermal technology with almost the same crystallinity. SAPO-34 framework synthesized by just ultrasonic treatment is unstable and a significant part of SAPO-34 nanocrystals is transformed to the dense phase of AlPO 4 structure, i.e., Cristobalite. Contrary to hydrothermal method that at least 24 h of the synthesis time is required to obtain fully crystalline SAPO-34, sonochemical-assisted hydrothermal synthesis of samples leads to form fully crystalline SAPO-34 crystals taking only 1.5 h. In a sonochemical process, a huge density of energy for crystallization is provided by the collapse of bubbles which formed by ultrasonic waves. The fact that small SONO-SAPO-34 crystals could be prepared by the sonochemical method suggests a high nucleation density in the early stages of synthesis and slow crystal growth after nucleation. © 2011 Elsevier B.V. All rights reserved.

Rahbar-Ranji A.,Amirkabir University of Technology
Ocean Engineering | Year: 2012

Corrosion is one of the time dependent detrimental phenomena which reduces strength of structures and leads to catastrophic failures. All rules and regulations concerning strength of corroded plates are based on uniform thickness reduction. To estimate residual strength of corroded structures, typically a much higher level of accuracy is required, since, the actual corroded plate has irregular surfaces. There is little study on strength analysis of corroded plate with irregular surfaces especially as a function of corrosion parameters. It is the main aim of present work to study ultimate strength of corroded steel plates with irregular surfaces under in-plane compression. Nonlinear finite element method is employed to determine ultimate strength of corroded steel plates with irregular surfaces. Comparing the results with ultimate strength of corroded plates with uniform thickness, a reduction factor is introduced. Having done this, ultimate strength of corroded plates could be evaluated easily as a function of corrosion conditions. © 2012 Elsevier Ltd.

Azadi M.,Islamic Azad University at Qazvin | Mir Mohammad Hosseini S.M.,Amirkabir University of Technology
Tunnelling and Underground Space Technology | Year: 2010

The liquefaction of soils under earthquake loadings has always been a main concern for geotechnical engineering practices. As an earthquake causes the ground to liquefy, the effective stress and hence the shear strength of the soil decreases sharply, and large deformations happen in the area. This phenomenon occurs only rarely when the liquefaction occurs at a large depth. However, deformations increase extensively when this layer is located in shallow depths near the ground level. In this case super structures and also underground structures may be severely damaged. The tunnels which are constructed in this layer may be affected by the liquefaction as well. In this condition the liquefaction may cause settlement in the ground, deformation in the tunnel shield, buoyancy in the underground buildings, reduction in bearing capacity and increases in lateral spread and pore pressures. In this paper the FLAC software has been used to model the pore pressure changes during earthquakes that lead to soil liquefaction. The studies thus far have been focused on the impact of the soil liquefaction on the tunnels constructed in this area. According to the studies, the buoyancy and uplifting forces due to liquefaction have major effects on the behavior of underground structures. Increasing the soil parameters such as friction angle and damping ratio causes the liquefaction effects on the tunnel to decrease, and increasing the geometric parameters such as tunnel diameter and location depth causes these effects to increase. © 2009 Elsevier Ltd. All rights reserved.

Heydarpour Y.,Amirkabir University of Technology | Aghdam M.M.,Amirkabir University of Technology | Malekzadeh P.,Persian Gulf University
Composite Structures | Year: 2014

The influences of centrifugal and Coriolis forces on the free vibration behavior of rotating carbon nanotube reinforced composite (CNTRC) truncated conical shells are examined. The material properties of functionally graded carbon nanotube-reinforced composites (FG-CNTRCs) are assumed to be graded in the thickness direction and are estimated through a micromechanical model. The governing equations are derived based on the first-order shear deformation theory (FSDT) of shells using Hamilton's principle. The initial mechanical stresses are obtained by solving the dynamic equilibrium equations. The differential quadrature method (DQM) is adopted to discretize the equations of motion and the related boundary conditions. After demonstrating the convergence and accuracy of the presented approach, the effects of angular velocity, Coriolis acceleration, geometrical parameters, type of distribution and volume fractions of carbon nanotubes on the frequency parameters of the CNTRC truncated conical shells are studied. The results reveal that the influences of the type of carbon nanotube distribution and its volume fraction on the frequency parameters depend on the semi vertex angle and angular velocity of the shells and the frequency parameters of the shell with FG asymmetric carbon nanotube distribution can become greater than those of the case with FG symmetric distribution ones. © 2014 Elsevier Ltd.

Dariushi S.,Amirkabir University of Technology | Sadighi M.,Amirkabir University of Technology
Composite Structures | Year: 2014

The paper presents a geometrically nonlinear sandwich panel theory for orthotropic sandwich beams in which the large deformation of face sheets and core is considered. The equations are derived based on high order sandwich panel theory in which the Green strain and the second Piola-Kirchhoff stress tensor are used. Nonlinear equations for a simply supported beam are derived using Ritz method in conjunction with minimum potential energy principle. The resulted set of equations is solved by the Newton-Raphson iterative technique. The results of numerical computation for beams in three point bending are presented and compared with experiments as well as with some other available results. Also simplification was used to obtain the results of linear model and in parametric studies the effect of geometric parameters on difference between results of linear and nonlinear models are discussed.Some experimental tests on sandwich beams with glass/epoxy face sheets and soft polymeric cores were performed. The experimental results of specimens with different arrangement support the claims which were based on analytical predictions about similarities and differences between linear and nonlinear models. In all cases good agreement is obtained between the nonlinear analytical predictions and experimental results. © 2013 Elsevier Ltd.

Bahrami M.,Amirkabir University of Technology | Dehghani K.,Amirkabir University of Technology | Besharati Givi M.K.,University of Tehran
Materials and Design | Year: 2014

The main object of the present study is to investigate the effect of nano-sized SiC particle on the mechanical properties of the friction stir welding (FSW) joints. Prior to FSW, nano-sized SiC particles were incorporated into the joint line. A combination of three rotational speeds and three traveling speeds were applied. Microstructural evaluation using optical microscopy (OM) and scanning electron microscopy (SEM) revealed a banded structure consisting of particle-rich and particle-free regions in stir zone (SZ). The joints fabricated with rotational speed of 1250. rpm and traveling speeds of 40 and 50. mm/min, exhibited the highest mechanical properties. Owing to the presence of SiC nano-particles, at 1250. rpm and 40. mm/min, ultimate tensile strength (UTS) and percentage of elongation were improved by 31% and 76.1%, respectively. Significant increase in UTS and percentage of elongation were attributed to the pinning effect and increased nucleation sites associated with SiC nano-particles. Moreover, reinforcement particles resulted in breaking of primary grains. On the other hand, at 1250. rpm and 40. mm/min, SiC-included specimen showed superior ductility to SiC-free specimen. The fracture morphologies were in good agreement with corresponding ductility results. © 2013 Elsevier Ltd.

Darvazi A.R.,Amirkabir University of Technology | Iranmanesh M.,Amirkabir University of Technology
Materials and Design | Year: 2014

This paper presents a thermo-mechanical model to predict the thermal histories and the longitudinal residual stress difference at two sides of the butting surfaces using a factor named advancing retreating factor. This model allows taking into account of frictional heating dependent on both the temperature and the velocity of the tool, as well as heat generation due to plastic deformation dependent on temperature. The mechanical loads caused by the tool are added to the model for the mechanical analysis and the uncoupled thermo-mechanically equations are solved using a nonlinear finite element code ABAQUS. The numerical results showed that the longitudinal residual tensile stresses are asymmetrically distributed at different sides of the weld line due to the effect of the unsymmetrical temperature distribution and the tool forces. The calculated results have good agreement with experimental data that are presented in the literature. © 2013 Elsevier Ltd.

Niknam H.,Amirkabir University of Technology | Aghdam M.M.,Amirkabir University of Technology
Composite Structures | Year: 2014

In this paper, an attempt is made to obtain a closed form solution for both natural frequency and buckling load of nonlocal FG beams resting on nonlinear elastic foundation. Implementing Eringen's nonlocal elasticity theory, the effect of nonlocality is introduced into the Euler-Bernoulli beam theory to obtain the nonlinear governing partial differential equation. Application of the Galerkin technique to the governing equation leads to a nonlinear ODE in the time-domain. Finally, natural frequency of the FG nano beam is obtained using He's variational method. It is shown that considering the nonlocal effects decreases the buckling load as well as natural frequency. Results also reveal that effects of nonlocal parameters on fully clamped beams are more than other types of boundary conditions. Moreover, it is shown that the effect of nonlocality decreases by increasing length of the beam. © 2014 Elsevier Ltd.

Hashemikia S.,Amirkabir University of Technology | Montazer M.,Amirkabir University of Technology
Applied Catalysis A: General | Year: 2012

Nowadays, introducing a textile with multi-functional properties is in a central point of research also application of nano particles can be helpful to reach this goal. Here, nano TiO 2, citric acid and sodium hypophosphite applied on the cotton/polyester knitted fabric to obtain divers features on the fabric. The results revealed an excellent performance of the treatment on diverse properties of the fabric including flame retardancy, anti-pilling, hydrophilicity, self-cleaning, antibacterial and UV protection properties. Increasing the concentration of CA enhanced both the photoactive properties and washing fastness of the TiO 2 treated fabrics. Thermal behaviors of the treated fabrics displayed flame retardant characteristics with high char residue. Also the treated fabrics indicated the higher bioactivity and hydrophilicity with considerable lower pilling rate. This paper revealed a simple method on application of inorganic catalysts with friendly cross-linking agent to introduce multi-functional properties in the blended fiber yarns with knitted structure. © 2012 Elsevier B.V. All rights reserved.

Salehi M.,Amirkabir University of Technology | Farnoush H.,University of Kashan | Mohandesi J.A.,Amirkabir University of Technology
Materials and Design | Year: 2014

Functionally graded materials are one of the most promising candidates among advanced materials. However, some challenges still exist in its fabrication methods. The current study aims to produce functionally-graded bulk Al-SiC nanocomposites by a novel multistep friction stir processing (FSP) for the first time. The SiC nanoparticles were packed into a groove on the 6061 aluminum plate and FSP was performed by using a tool with pin length of 6. mm. Subsequently, FSP was reapplied on another groove by using a tool with a shorter pin length of 3.2. mm. The desirable distribution of SiC nanoparticles in the matrix was confirmed by scanning electron and atomic force microscopes. The composition of graded sample was changed continuously from 18 to 0. wt% SiC along the thickness. Accordingly, the microhardness profile showed a maximum of 160. Hv in the enriched zone which is 3.2 times higher than the hardness of the particle-depleted zone. However, a constant hardness value of 135. Hv was obtained along the thickness of homogenous sample which is 15% lower than that of superficial layer in graded sample. Moreover, the hardness values were linearly correlated with the inverse of interparticle spacing. © 2014 Elsevier Ltd.

Dehghan M.,Amirkabir University of Technology | Basirat Tabrizi H.,Amirkabir University of Technology
Powder Technology | Year: 2012

Motion of particles in a dilute turbulent boundary layer, near a flat wall is simulated numerically. Eulerian-Eulerian two-way coupled model is used. Closures for the particulate-phase equations are derived from the kinetic theory of granular flow. One equation model is used to model turbulence in the gas-phase. Effects of inertial parameters of solid-phase such as flow density, material density, particle diameter and free stream velocity are investigated. Furthermore, effects of granular temperature and particulate viscosity on motion of particles are discussed. Simulation results are compared with available numerical and experimental results. Results show that the granular temperature and solid-phase viscosity have a noticeable effect on simulation accuracy especially near the wall. Results are closer to experimental results when implementing the inlet granular temperature which is equal to area-weighted average of granular temperature in the boundary layer. Non-dimensional velocity profiles of solid-phase have a general trend and their dependence on location and free stream velocity is found very weak. © 2012 Elsevier B.V..

Saadat-Monfared A.,Amirkabir University of Technology | Mohseni M.,Amirkabir University of Technology | Tabatabaei M.H.,Iran Polymer And Petrochemical Institute
Colloids and Surfaces A: Physicochemical and Engineering Aspects | Year: 2012

The present work reports the influence of nano-cerium oxide particles on UV resistance of a polyurethane lacquer. Particles were initially stabilized in 3-phosphonopropyl based stabilizer and dispersed in a polyacrylate resin, followed by mixing with polyisocayanate hardener to obtain nanocomposite films. Static and dynamic light scattering and small angle neutron scattering techniques were employed to study the stabilization of particles embedded in nanocomposites. It was shown that a monolayer of stabilizer was grafted at the surface of nano-cerium oxide out of which uniformly distributed mono-disperse particles in the films were prepared. Films were then subjected to 700. h of accelerated artificial weathering. Their optical performances were then accessed by UV-vis spectroscopy. Clear coats containing nano-ceria showed less deterioration in UV exposure test compared to the blank polyurethane film. Samples loaded with 1.44% (w/w) of nano-ceria absorbed 92.5% of incident UV light in UV-B region and 67% of UV light in UV-A region. However, after 700. h exposure to UV radiation, films could absorb 80% of UV-B and 50% of UV-A, showing the brilliant efficacy of this nanoparticle to act as UV absorber. © 2012 Elsevier B.V.

Sahmani S.,Amirkabir University of Technology | Bahrami M.,Amirkabir University of Technology | Ansari R.,Guilan University
Composite Structures | Year: 2014

In the present investigation, a numerical analysis is conducted to predict size-dependent nonlinear free vibration characteristics of third-order shear deformable microbeams made of functionally graded materials (FGMs). For this purpose, the modified strain gradient elasticity theory and von Karman geometric nonlinearity are implemented into the classical third-order shear deformation beam theory to develop a nonclassical higher-order beam model including three additional length scale parameters to capture size effect efficiently. It is assumed that the material properties of the FGM microbeams are evaluated by the Mori-Tanaka homogenization technique. On the basis of the Hamilton's principle, the size-dependent nonlinear governing differential equations of motion and associated boundary conditions are derived and then discretized along various end supports by employing generalized differential quadrature (GDQ) method. A direct iterative process corresponding to both positive and negative deflection cycles is adopted. Secondly, a parametric study is performed to demonstrate the influences of the values of dimensionless length scale parameter, material property gradient index and length to thickness aspect ratio on the linear and nonlinear natural frequencies of FGM microbeams. © 2013 Elsevier Ltd.

Heidary H.,Mapna Group | Kermani M.J.,Amirkabir University of Technology
International Communications in Heat and Mass Transfer | Year: 2012

In this paper heat transfer and flow field analysis in a wavy channel linked to a porous Gas Diffusion Layer (GDL) is numerically studied. The domain is very similar to our earlier computations of proton exchange membrane fuel cells (see Khakbaz-Baboli and Kermani (2008)). The fluid temperature at the channel inlet (T in) is taken less than that of the walls (T w). The governing equations are numerically solved in the domain by the control volume approach based on the SIMPLE technique (1972). A wide spectrum of numerical studies is performed over a range of Reynolds number Re H: 100≤Re H≤1000, wave number β: 0≤β≤10, the wave amplitude α: 0≤α≤0.3 and Darcy number Da: 0.1≤Da≤0.001. Simulations show that heat transfer in channels can enhance up to 100%, depending on the duct α, β and flow Re H. Computations show excellent agreement with the literature. The present work can provide helpful guidelines to the manufactures of the compact heat exchangers. © 2011 Elsevier Ltd.

Asiaban S.,Amirkabir University of Technology | Moradian S.,Amirkabir University of Technology
Dyes and Pigments | Year: 2012

Polypropylene has many advantages over other polymeric fibers such as high tensile strength, good abrasion resistance, high chemical resistance and very competitive price. However, the use of polypropylene fiber is restricted by the lack of affinity of conventional dyestuffs for this fiber. Many attempts have been made to improve the dyeability of polypropylene by various techniques. It must however, be noted that enhanced dyeability of polypropylene should not adversely impair its other properties, in particular its mechanical properties. To this end, in the present investigation, a mixture experimental design was used in order to attain an optimal region of proportions of three components namely polypropylene (PP), maleated polypropylene (polypropylene grafted with maleic anhydride (MAH-PP) as a compatibilizing agent) and polyamide 6 (PA6); where enhanced dyeability as well as retained mechanical properties would be achieved. Additionally, in order to analyze the morphology of the blends, differential scanning calorimetry (DSC) and scanning electron microscopy (SEM) were used. Finally, in order to evaluate effect of each component on fastness properties of the blends, wash, rub and light fastnesses were determined by the corresponding standard test methods. © 2011 Elsevier Ltd. All rights reserved.

Rashiddadash P.,Amirkabir University of Technology | Ramezanianpour A.A.,Amirkabir University of Technology | Mahdikhani M.,Imam Khomeini International University
Construction and Building Materials | Year: 2014

Fiber reinforced concrete (FRC) has been widely used due to its advantages over plain concrete. It can be an appropriate material for the repair of structures in a variety of situations. However there is a weak zone between fibers and paste in fiber reinforced concretes and this weak zone is full of porosity, especially in hybrid fiber reinforced concretes. Therefore, using of pozzolanic materials is required to reduce the porosity. Pumice and kaolin are two pozzolanic materials that have been found abundantly in some regions of the world. In this paper, the mechanical properties of concretes containing various amounts of the pozzolanic materials and steel and polypropylene fibers are investigated. At the first step of this paper, the flexural and impact resistance tests were carried out to choose the optimum percentage of steel and polypropylene fibers. Results showed that hybrid fiber reinforced concrete with 0.75% steel fibers and 0.25% polypropylene fibers had higher toughness indexes, modulus of rupture and impact resistance than other hybrid mixtures. Afterward, compressive strength and flexural tests on hybrid fiber reinforced concretes containing pumice and metakaolin were carried. Results showed that, metakaolin with highest substitution of cement had the best performance of mechanical properties of concrete. Moreover, this pozzolan caused increasing in compressive strength in comparison with control mixture. However, replacing pumice into the specimens had negative effect on the mechanical properties results. © 2013 Elsevier Ltd. All rights reserved.

Alizadeh-Sh M.,Amirkabir University of Technology | Marashi S.P.H.,Amirkabir University of Technology | Pouranvari M.,Islamic Azad University at Dezful
Materials and Design | Year: 2014

The paper aims at investigating the process-microstructure-performance relationship in resistance spot welding of AISI 430 ferritic stainless steel. The phase transformations which occur during weld thermal cycle were analyzed in details, based on the physical metallurgy of welding of the ferritic stainless steels. It was found that the microstructure of the fusion zone and the heat affected zone is influenced by different phenomena including grain growth, martensite formation and carbide precipitation. The effects of welding cycle on the mechanical properties of the spot welds in terms of peak load, energy absorption and failure mode are discussed. © 2013 Elsevier Ltd.

Javadi Y.,Islamic Azad University at Semnan | Sadeghi S.,Amirkabir University of Technology | Najafabadi M.A.,Amirkabir University of Technology
Materials and Design | Year: 2014

The main goal of this study is optimization of residual stresses produced by friction stir welding (FSW) of 5086 aluminum plates. Taguchi method is employed as statistical design of experiment (DOE) to optimize welding parameters including feed rate, rotational speed, pin diameter and shoulder diameter. The optimization process depends on effect of the welding parameters on longitudinal residual stress, which is measured by employing ultrasonic technique. The ultrasonic measurement method is based on acoustoelasticity law, which describes the relation between acoustic waves and internal stresses of the material. In this study, the ultrasonic stress measurement is fulfilled by using longitudinal critically refracted (LCR) waves which are longitudinal ultrasonic waves propagated parallel to the surface within an effective depth. The ultrasonic stress measurement results are also verified by employing the hole-drilling standard technique. By using statistical analysis of variance (ANOVA), it has been concluded that the most significant effect on the longitudinal residual stress peak is related to the feed rate while the pin and shoulder diameter have no dominant effect. The rotational speed variation leads to changing the welding heat input which affects on the residual stress considerably. © 2013 Elsevier Ltd.

Fallah H.,Amirkabir University of Technology
International Journal of Bifurcation and Chaos | Year: 2016

Pancreatic beta-cells produce insulin to regularize the blood glucose level. Bursting is important in beta cells due to its relation to the release of insulin. Pernarowski model is a simple polynomial model of beta-cell activities indicating bursting oscillations in these cells. This paper presents bursting behaviors of symmetric type in this model. In addition, it is shown that the current system exhibits the phenomenon of period doubling cascades of canards which is a route to chaos. Canards are also observed symmetrically near folds of slow manifold which results in a chaotic transition between n and n + 1 spikes symmetric bursting. Furthermore, mixed-mode oscillations (MMOs) and combination of symmetric bursting together with MMOs are illustrated during the transition between symmetric bursting and continuous spiking. © 2016 World Scientific Publishing Company.

Hemati F.,Amirkabir University of Technology | Garmabi H.,Amirkabir University of Technology
Canadian Journal of Chemical Engineering | Year: 2011

Nanocomposites of LDPE/LLDPE/nanoclay have been prepared using a lab-scale co-rotating twin screw extruder. Using XRD, tensile testing, AFM, TGA, effects of some material properties and one processing parameter on mechanical and thermal properties of the prepared nanocomposites were evaluated. Tensile properties indicated that all the prepared nanocomposites exhibited a significant improvement in elastic modulus and toughness compared to pristine LDPE/LLDPE blends of the same composition. Thermal stability of nanocomposites in the air and nitrogen atmosphere was improved. XRD patterns and AFM micrographs showed semi-exfoliated and intercalated microstructures for the prepared nanocomposites with different orders of mixing. © 2010 Canadian Society for Chemical Engineering.

Ataeefard M.,Iran Institute for Color Science and Technology | Moradian S.,Amirkabir University of Technology
Polymer - Plastics Technology and Engineering | Year: 2011

The effects of clays as nanoscale fillers have been rarely addressed. Influence of the amount of organoclay (ranging between 1 and 10 wt.%) on the nanocomposites structure, i.e., intercalated or exfoliated, and on the enhancement of mechanical, rheological and morphological properties of polypropylene (PP) nanocomposites was studied in this work. The fundamental material characterization was conducted using XRD, SEM, TEM, DSC, POM,DMTA as well as RMS. Overall mechanical properties determined by tensile tests showed improvements. DSC andPOMresults demonstrated decrease of nanocomposites crystallinity. XRD and TEM Showed intercalate/ exfoliate structures in the resultant nanocomposites. © Taylor & Francis Group, LLC.

Bahrami M.,Amirkabir University of Technology | Besharati Givi M.K.,University of Tehran | Dehghani K.,Amirkabir University of Technology | Parvin N.,Amirkabir University of Technology
Materials and Design | Year: 2014

The main purpose of this research is to investigate the influence of pin geometry on the macrostructure, microstructure and mechanical properties of the friction stir welds, reinforced with SiC nano-particles. Toward this end, friction stir welding (FSW) conducted using five geometrically different pin tools. Other welding parameters were remained unchanged. Microstructural evaluation using optical microscopy (OM) and scanning electron microscopy (SEM) revealed a banded structure consisting of particle-rich and particle-free regions in stir zone (SZ). The most uniform particle distribution was found in the case of using threaded tapered pin tool. On the other hand, it was discovered that the reinforcements had severely accumulated in the SZ of specimen friction stir welded (FSWed) with four-flute cylindrical pin tool. Moreover, threaded tapered and four-flute cylindrical specimens showed the highest and the lowest microhardness, respectively. In spite of four-flute cylindrical specimen, other specimens failed in base metal during tensile testing. Besides, the highest ultimate tensile strength (UTS) was recorded for the specimen FSWed with triangular pin tool. Fracture surface of tensile specimens were also studied employing SEM technique. © 2013 Elsevier Ltd.

Khajeh A.,Islamic Azad University at Birjand | Modarress H.,Amirkabir University of Technology
Journal of Hazardous Materials | Year: 2010

A quantitative structure property relationship (QSPR) study was performed to develop a model for prediction of flash point of esters based on a diverse set of 95 components. The most five important descriptors were selected from a set of 1124 descriptors to build the QSPR model by means of a genetic function approximation (GFA). For considering the nonlinear behavior of these molecular descriptors, adaptive neuro-fuzzy inference system (ANFIS) method was used. The ANFIS and GFA squared correlation coefficient for testing set was 0.969 and 0.965, respectively. The results obtained showed the ability of developed GFA and ANFIS for prediction of flash point of esters. © 2010 Elsevier B.V.

Rahai A.,Amirkabir University of Technology | Akbarpour H.,Amirkabir University of Technology
Composite Structures | Year: 2014

This paper presents the results of an experimental study on rectangular RC columns strengthened with carbon fiber-reinforced polymer (CFRP) composites under axial load and biaxial bending moment. A total of 8 large-scale RC columns with rectangular cross-section were cast and tested under bi-eccentric compressive loading up to failure. In this investigation, several parameters like CFRP thickness of one, two, three, and four layers, fiber orientations of ±45°, 0°, 90° and their combination, and eccentricities in the direction of both weak and main axis were studied. The effects of these parameters on the moment-curvature relationship, and load-longitudinal displacement relationship were investigated. In general, increasing longitudinal layers rather than transverse layers led to a greater load carrying and displacement capacity of the specimens, because of the overall behavior of RC wall-like columns. The results of these experimental and numerical studies showed a great improvement on the strength and ductility of confined RC columns. © 2013 Elsevier Ltd.

Asadi H.,Amirkabir University of Technology | Kiani Y.,Amirkabir University of Technology | Shakeri M.,Amirkabir University of Technology | Eslami M.R.,Amirkabir University of Technology
Composite Structures | Year: 2014

Post-buckling behavior of Shape Memory Alloy (SMA) hybrid composite laminated beams under uniform heating is investigated in this paper. Properties of the constituents are temperature-dependent. The von-Karman type of geometrical non-linearity suitable for small strains and moderate rotations is taken into account. Displacement field through the beam obeys the kinematics of first order shear deformation theory of Timoshenko. To model the SMA fibers, the one-dimensional thermomechanical constitutive law proposed earlier by Brinson (1993) [1], is implemented. These basic assumptions are incorporated with the static version of virtual displacements to extract the nonlinear governing equations of the beam. The resulting system of nonlinear equations are uncoupled and solved analytically. Closed-form expressions are presented to trace the deflection-temperature as well as bending moment-temperature and end-shortening force-temperature in heating process. After validating the proposed approach, various parametric studies are performed to study the influence of lay-up, SMA volume fraction, SMA prestrain, boundary condition, and thickness of the layer in which SMA fibers are embedded. Fascinating results are extracted due to the recovery stress of SMA fibers. © 2013 Elsevier Ltd.

Moein M.M.,Amirkabir University of Technology | Javanbakht M.,Amirkabir University of Technology | Akbari-adergani B.,Food and Drug Laboratory Research Center
Journal of Chromatography B: Analytical Technologies in the Biomedical and Life Sciences | Year: 2011

In this paper, a novel method is described for automated determination of dextromethorphan in biological fluids using molecularly imprinted solid-phase extraction (MISPE) as a sample clean-up technique combined with high performance liquid chromatography (HPLC). The water-compatible molecularly imprinted polymers (MIPs) were prepared using methacrylic acid as functional monomer, ethylene glycol dimethacrylate as cross-linker, chloroform as porogen and dextromethorphan as template molecule. These imprinted polymers were used as solid-phase extraction sorbent for the extraction of dextromethorphan from human plasma samples. Various parameters affecting the extraction efficiency of the MIP cartridges were evaluated. The high selectivity of the sorbent coupled to the high performance liquid chromatographic system permitted a simple and rapid analysis of this drug in plasma samples with limits of detection (LOD) and quantification (LOQ) of 0.12 ng/mL and 0.35 ng/mL, respectively. The MIP selectivity was evaluated by analyzing of the dextromethorphan in presence of several substances with similar molecular structures and properties. Results from the HPLC analyses showed that the recoveries of dextromethorphan using MIP cartridges from human plasma samples in the range of 1-50 ng/mL were higher than 87%. © 2011 Elsevier B.V.

Sedighi A.,Amirkabir University of Technology | Vafadust M.,Amirkabir University of Technology
Expert Systems with Applications | Year: 2011

This paper provides a new and fast method for segmentation and recognition of characters in license plate images. For this purpose, various methods have been proposed in literature. However, most of them suffer from: sensitivity to non-uniform illumination distribution, existence of shade in license plate, license plate color and the need for receiving an exact image of the license plate. In the proposed algorithm, non-uniform illumination and noise are reduced by a Gaussian lowpass filter and also by an innovational Laplacian-like transform and characters are segmented by a set of indigenous and relative features. To be prepared for recognition, the segmented characters are normalized by a local algorithm. Two feed-forward neural networks with back-propagation learning method are employed for character recognition. The principal component analysis (PCA) is used to decrease input data and, consequently, computational complexity. The proposed algorithm does not necessarily need an exact plate image and can receive a band from the vehicle original image as an input, which includes the plate. Our proposed method is completely robust to the disturbances such as non-uniform brightness distribution on the various positions of a license plate image and the plate color. In order to evaluate our algorithm, we applied it on a database including 120 vehicle images with different backgrounds, plate colors, brightness distributions, distances and viewing angles. The results confirm the robustness of the proposed method against severe imaging conditions. © 2011 Published by Elsevier Ltd.

Pashmforoush F.,Amirkabir University of Technology | Rahimi A.,Amirkabir University of Technology
Applied Optics | Year: 2015

BK7 is an optical glass extensively used in lens manufacturing. In this work, magnetic abrasive finishing (MAF) method was utilized for finishing of this hard-to-machine material and the effect of various process parameters on surface roughness was investigated using response surface methodology. The best surface roughness value achieved was 23 nm. Among various finishing parameters, the abrasive size was found to be the most significant parameter followed by machining gap, magnetic particles size, rotational speed, and percentage weight of binding agent. Also, the mechanisms of material removal were studied by using atomic force microscopy (AFM). The AFM observations revealed that both microcutting and microfracture mechanisms might exist during MAF of brittle materials depending on the finishing conditions. © 2015 Optical Society of America.

Sohrabi M.,Amirkabir University of Technology
Radiation Protection Dosimetry | Year: 2015

A 'Universal Radiation Protection System' (URPS) is proposed in this paper with a novel philosophy, concept and methodology. It applies a 'Standardised Integrated Dose System' (SIDS) based on health risk limits for workers and public, no matter where they live in the world. The URPS assigns equal radiation health risk limit to an individual by integrating doses from national natural background (NBG) radiation and from man-made sources. For public, the SIDS integrates doses from planned exposure situations within a dose limit (e.g. 1 mSv y-1) on top of the mean national NBG dose in a country. For workers, the SIDS integrates within a dose limit (e.g. 20 mSv y-1) of occupational dose and doses from mean national NBG and from planned exposure situations as a member of public within the public dose limit. A panorama overview and the rationale in support of the URPS are presented and discussed with a hope to ignite further thoughts and ideas towards establishing the URPS for universal use. © The Author 2015. Publish