Islamic Azad University at Ahar
Ahar, Iran
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Aliha M.R.M.,Iran University of Science and Technology | Razmi A.,Islamic Azad University at Ahar
Engineering Fracture Mechanics | Year: 2017

In this contribution, low temperature crack growth resistance of Warm Mix Asphalt (WMA) mixtures reinforced with two types of fiber, namely natural Jute fiber and synthetic Polyolefin-Aramid (FORTA) fiber is investigated experimentally. Using semi-circular bend (SCB) specimen, the influence of different fiber weight percentages (0.3%, 0.5% and 0.7%) and test temperatures (0°, −10° and −20 °C) on mixed mode I + II fracture toughness values (i.e. KIc and KIIc) are studied. It was shown that both fibers can increase in general the fracture resistance of WMA concrete relative to the control mixture. Moreover, modes I and II fracture toughness and effective fracture toughness (Keff) values are increased by decreasing the test temperature or increasing the fiber content. The FORTA fiber provided better crack growth resistance characteristics than the Jute fiber for the WMA mixtures. The effects of both natural and synthetic fibers on enhancing the performance of the tested WMA mixtures was more pronounced for dominantly pure mode I loading case. © 2017 Elsevier Ltd

A robust method is proposed for optimal design of electrically separated two-stage thermoelectric refrigeration systems based on chemical reaction optimization algorithm (CRO). In order to investigate the performance of the proposed method, a full computer code was developed and different test cases were solved by it to show the accuracy and efficiency of the method. Cooling capacity and coefficient of performance of the refrigeration system are considered as objective functions of the optimization process. The effects of the joint thermal resistance at the interface of the two stages on objective functions in all of the case studies also were studied and sensitivity analysis of COP and cooling capacity of the system to this parameter is conducted. The obtained results were compared to those obtained by literature approaches. The outlined results showed improvement of the objective functions using the CRO method in comparison to the results of the genetic algorithm previously used for optimization of the considered refrigeration system. The obtained results of the paper showed that the CRO algorithm can be successfully employed for optimal design of electrically separated two-stage thermoelectric refrigeration system. © 2017 Elsevier Ltd

Safari A.,Islamic Azad University at Ahar | Shayeghi H.,University of Mohaghegh
Expert Systems with Applications | Year: 2011

In this paper, iteration particle swarm optimization (IPSO) has been applied to determine the feasible optimal solution of the economic load dispatch (ELD) problem considering various generator constraints. Many realistic constraints, such as ramp rate limits, generation limitation, prohibited operating zone, transmission loss and nonlinear cost functions are all considered for practical operation. The performance of the classical particle swarm optimization (CPSO) greatly depends on its parameters, and it often suffers the problem of being trapped in local optima. A new index named, Iteration Best, is incorporated in CPSO to enrich the searching behavior, solution quality and to avoid being trapped into local optimum. Two test power systems, including 6 and 15 unit generating, are applied to compare the performance of the proposed algorithm with PSO, chaotic PSO, hybrid GAPSO, self organizing hierarchical PSO (SOH-PSO) methods. The numerical results affirmed the robustness and proficiency of proposed approach over other existing methods. © 2010 Elsevier Ltd. All rights reserved.

Ahmadivand A.,Islamic Azad University at Ahar
Optics and Laser Technology | Year: 2014

In this work, a broadband efficient hybrid Photonic-Plasmonic polarization beam splitter (HPPPBS) based on metal-silica-silicon interactions is proposed and investigated numerically. This device contains two silicon (Si) nanofibers with specific examined dimensions, a silica (SiO2) waveguide and a straight chain of Au nanoshells which is encompassed by silica host. All of the mentioned fibers and waveguide are deposited on a Mg2F crystal host. It is shown that this structure is working properly at near infrared region (NIR), specifically at telecommunication wavelength (λ≈1550 nm). Furthermore, relevant optical characteristics have been examined and studied, thoroughly. The quality of polarization splitting is demonstrated for both transverse electric (TE) and magnetic (TM) modes in separate figures. Simulation results corroborate that the sensitivity and accuracy of the superstructure during polarization dividing and light propagating are noticeable in comparison to analogous devices. Finite-difference time-domain method (FDTD-M) is utilized to examine the optical properties of the presenting structure. © 2013 Elsevier Ltd.

Aghababa M.P.,Islamic Azad University at Ahar
Nonlinear Dynamics | Year: 2014

The electromechanical gyrostat is a fourth-order nonautonomous system that exhibits very rich behavior such as chaos. In recent years, synchronization of nonautonomous chaotic systems has found many useful applications in nonlinear science and engineering fields. On the other hand, it is well known that the finite-time control techniques demonstrate good robustness and disturbance rejection properties. This paper studies the potential application of the finite-time control techniques for synchronization of nonautonomous chaotic electromechanical gyrostat systems in finite time. It is assumed that all the parameters of both drive and response systems are unknown parameters in advance. Moreover, the effects of dead-zone nonlinearities in the control inputs are also taken into account. Some adaptive controllers are introduced to synchronize two gyrostat systems in different scenarios within a given finite-time. Two illustrative examples are presented to demonstrate the efficiency and robustness of the proposed finite-time synchronization strategy. © 2013 Springer Science+Business Media Dordrecht.

Aghababa M.P.,Islamic Azad University at Ahar
Journal of Computational and Nonlinear Dynamics | Year: 2014

The problem of stabilization of nonlinear fractional systems in spite of system uncertainties is investigated in this paper. First, a proper fractional derivative type sliding manifold with desired stability and convergence properties is designed. Then, the fractional stability theory is adopted to derive a robust sliding control law to force the system trajectories to attain the proposed sliding manifold and remain on it evermore. The existence of the sliding motion is mathematically proven. Furthermore, the sign function in the control input, which is responsible to the being of harmful chattering, is transferred into the fractional derivative of the control input. Therefore, the resulted control input becomes smooth and free of the chattering. Some numerical simulations are presented to illustrate the efficient performance of the proposed chattering-free fractional variable structure controller. Copyright © 2014 by ASME.

Kourehli S.S.,Islamic Azad University at Ahar
International Journal of Structural Stability and Dynamics | Year: 2015

This paper presents a novel approach for structural damage detection and estimation using incomplete noisy modal data and artificial neural network (ANN). A feed-forward back propagation network is proposed for estimating the structural damage location and severity. Incomplete modal data is used in the dynamic analysis of damaged structures by the condensed finite element model and as input parameters to the neural network for damage identification. In all cases, the first two natural modes were used for the training process. The present method is applied to three examples consisting of a simply supported beam, three-story plane frame, and spring-mass system. Also, the effect of the discrepancy in mass and stiffness between the finite element model and the actual tested dynamic system has been investigated. The results demonstrated the accuracy and efficiency of the proposed method using incomplete modal data, which may be noisy or noise-free. © World Scientific Publishing Company.

Aghababa M.P.,Islamic Azad University at Ahar
Chinese Physics B | Year: 2011

In this paper, the problem of the finite-time synchronization of two uncertain chaotic gyros is discussed. The parameters of both the master and the slave gyros are assumed to be unknown in advance. The effects of model uncertainties and input nonlinearities are also taken into account. An appropriate adaptation law is proposed to tackle the gyros' unknown parameters. Based on the adaptation law and the finite-time control technique, proper control laws are introduced to ensure that the trajectories of the slave gyro converge to the trajectories of the master gyro in a given finite time. Simulation results show the applicability and the efficiency of the proposed finite-time controller. © 2011 Chinese Physical Society and IOP Publishing Ltd.

Aghababa M.P.,Islamic Azad University at Ahar
Transactions of the Institute of Measurement and Control | Year: 2014

This paper deals with the problem of robust control of uncertain non-integer-order non-linear complex systems in finite time. First, a novel fractional-order integral-type switching manifold is introduced. Then, the fractional-order stability theory is used to prove the finite time stability of the resulting sliding mode dynamics in a given finite time. Afterward, using the variable structure control theory, a novel robust non-integer control law is proposed to guarantee the convergence of the system trajectories to the prescribed sliding manifold within a given finite time. Simulation results reveal that the proposed fractional variable structure controller works well for finite-time chaos suppression of fractional-order hyperchaotic Chen and chaotic Lorenz systems with system uncertainties. © The Author(s) 2013.

Hadidi A.,Islamic Azad University at Ahar | Nazari A.,Islamic Azad University at Ahar
Applied Thermal Engineering | Year: 2013

Cost minimization of Shell-and-tube heat exchangers is a key objective. Traditional design approaches besides being time consuming, do not guarantee the reach of an economically optimal solution. So, in this research, a new shell and tube heat exchanger optimization design approach is developed based on biogeography-based optimization (BBO) algorithm. The BBO algorithm has some good features in reaching to the global minimum in comparison to other evolutionary algorithms. In this study BBO technique has been applied to minimize the total cost of the equipment including capital investment and the sum of discounted annual energy expenditures related to pumping of shell and tube heat exchanger by varying various design variables such as tube length, tube outer diameter, pitch size, baffle spacing, etc. Based on proposed method, a full computer code was developed for optimal design of shell and tube heat exchangers and three different test cases are solved by it to demonstrate the effectiveness and accuracy of the proposed algorithm. Finally the results are compared to those obtained by literature approaches up to the present. The obtained results indicate that the BBO algorithm can be successfully applied for optimal design of shell and tube heat exchangers. © 2012 Elsevier Ltd. All rights reserved.

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