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Tabatabaei M.,Islamic Azad University at Khomeinishahr
Control Engineering and Applied Informatics | Year: 2016

In this paper, an analytical method for designing Proportional-Integral-Derivative (PID) controllers based on Laguerre orthonormal functions is presented. The PID controller parameters are calculated after matching the first three coefficients of Laguerre series of the open loop gain with the ideal one. To reach this goal, the plant, the PID controller and the ideal open loop gain transfer functions are represented in terms of their corresponding Laguerre series. The pole of the Laguerre basis function could be appropriately selected to assure the closed loop stability. Moreover, the optimum value of this parameter is determined to reach the best fitting to the desired step response considering the control signal constraint. The simulation results and the experimental tests on a DC servomotor system are given to show the effectiveness of the proposed method.

Shojaeian S.,Islamic Azad University at Tehran | Soltani J.,Islamic Azad University at Khomeinishahr | Soltani J.,Isfahan University of Technology | Arab Markadeh G.,Shahrekord University
IEEE Transactions on Power Systems | Year: 2012

In this paper, damping of the low frequency oscillations of multi-machine multi-UPFC power systems is investigated based on adaptive input-output feedback linearization control (AIFLC) approach. Considering a three-phase symmetrical fault, ignoring the subtransient states of the synchronous machines, the nonlinear state equations of the system are derived in order to obtain the UPFC reference control signals as well as the system parameters estimation laws. The stability of the system controller is proved by Lyapunov theory. Moreover using the six reduced order model of synchronous machine, some simulation results are presented in order to verify the validity and effectiveness of the proposed control approach. © 1969-2012 IEEE.

Latifi M.,Islamic Azad University at Khomeinishahr | Farhatnia F.,Islamic Azad University at Khomeinishahr | Kadkhodaei M.,Isfahan University of Technology
European Journal of Mechanics, A/Solids | Year: 2013

In this paper, the buckling problem of thin rectangular functionally graded plates subjected to proportional biaxial compressive loadings with arbitrary edge supports is investigated. Classical plate theory (CPT) based on the physical neutral plane is applied to derive the stability equations. Mechanical properties of the FGM plate are assumed to vary continuously along its thickness according to a power law function. The displacement function is considered to be in the form of a double Fourier series whose derivatives are determined using Stokes' transformation. The advantage of this method is capability of considering any possible combination of boundary conditions with no necessity to be satisfied in the Fourier series. To give generality to the problem, the plate is assumed to be elastically restrained by means of rotational and translational springs at the four edges. Numerical examples are presented, and the effects of the plate aspect ratio, the FGM power index, and the loading proportionality factor on the buckling load of an FGM plate with different usual boundary conditions are studied. The present results are compared with those have been previously reported by other analytical and numerical methods, and very good agreement is seen between the findings indicating validity and accuracy of the proposed approach in the buckling analysis of FGM plates. © 2013 Elsevier Masson SAS. All rights reserved.

Moradi-Dastjerdi R.,Islamic Azad University at Khomeinishahr | Foroutan M.,Razi University | Pourasghar A.,Razi University
Materials and Design | Year: 2013

In this paper, dynamic analysis of nanocomposite cylinders reinforced by single-walled carbon nanotubes (SWCNTs) subjected to an impact load was carried out by a mesh-free method. Free vibration and stress wave propagation analysis of carbon nanotube reinforced composite (CNTRC) cylinders are presented. In this simulation, an axisymmetric model is used. Four types of distributions of the aligned carbon nanotubes (CNTs) are considered; uniform and three kinds of functionally graded (FG) distributions along the radial direction of cylinder. Material properties are estimated by a micro mechanical model. In the meshfree analysis, moving least squares (MLSs) shape functions are used for approximation of displacement field in the weak form of motion equation and the transformation method was used for the imposition of essential boundary conditions. Effects of the kind of distribution and volume fractions of carbon nanotubes and cylinder thickness on the natural frequencies and stress wave propagation of CNTRC cylinders are investigated. Results obtained for this analysis were compared with FEM and previous published work and good agreement was seen between them © 2012 Elsevier Ltd.

Foroutan M.,Razi University | Moradi-Dastjerdi R.,Islamic Azad University at Khomeinishahr
Acta Mechanica | Year: 2011

In this paper, dynamic analysis of functionally graded material cylinders is carried out under an impact load. In this analysis, MLS shape functions are used for the approximation of the displacement field in the weak form of motion equation and essential boundary conditions are imposed by the transformation method. The resulting set of differential equations is solved using central difference approximation. The mechanical properties of the cylinders are assumed to be variable in the radial direction. Effects of the geometrical dimensions of the cylinders and the exponent of material volume fraction on the natural frequencies are investigated by the proposed model and FEM. Then the response of the cylinders to an impact load is determined by the proposed model, and effects of the above-mentioned parameters on the stress wave propagation is investigated. © 2011 Springer-Verlag.

Isfahani A.H.,Islamic Azad University at Khomeinishahr
IEEE Transactions on Magnetics | Year: 2010

The aim of this work is to present an accurate analytical model of a double-sided air-core linear permanent-magnet motor with segmented permanent-magnet poles. The thrust average as well as thrust ripple is precisely predicted by proposed model. Back-electromotive force and flux density distribution of the motor are also determined by this method. The finite-element method is then chosen to verify the modeling results. Finally, pole dimensions are optimized using the proposed model and the genetic algorithm, where thrust mean and thrust ripple are considered as the optimization aims. This model provides the analytical framework for design optimization of double-sided air-core permanent-magnet linear synchronous motors with segmented poles regarding more motor parameters and objectives. © 2010 IEEE.

Jazi S.R.,Islamic Azad University at Khomeinishahr | Farhatnia F.,Islamic Azad University at Khomeinishahr
Advanced Materials Research | Year: 2012

In this paper, buckling analysis of functionally graded super-elliptical plates is investigated by pb-2 Ritz method. The governing equation is derived based on classical plate theory (CLP). Since closed form solution of buckling differential equation is not available under various boundary conditions, pb-2 Ritz method (energy method) is applied to calculate non-dimensional buckling load. Total potential energy is given as summation of strain energy and work done by applied in-plane compression load. In order to obtain the buckling load, pb-2 Ritz method is applied corresponding to different peripheral supports (Clamped and Simply Supported) are used in the present study. The plates are assumed to have isotropic, two-constituent material distribution through the thickness and the modulus of elasticity of the plate is assumed to vary according to a power-law distribution in terms of the volume fractions of the constituents. Variation of buckling non-dimensional parameter is considered with respect to various powers of super-elliptic, FGM power law index and aspect ratio.

Hemmat Esfe M.,Islamic Azad University at Khomeinishahr
Journal of Thermal Analysis and Calorimetry | Year: 2016

In this article, thermal conductivity of ethylene glycol–water-based TiO2 nanofluids has been modeled by artificial neural network. For this purpose, thermal conductivity of nanofluids with volume fractions of 0.2–1 % has been collected in temperatures of 30–70 °C. These data were modeled by artificial neural networks. So two common types of neural networks were used, and the results were compared with each other. One of these networks was multilayer perceptron, and the other one was radial basis approximation. Finally, an experimental relationship was suggested for calculating thermal conductivity of this nanofluid and the results were compared with the results of radial basis neural network. This comparison shows that neural networks are very powerful in modeling the nanofluids experimental data and are able to follow the patterns of these data with a high precision. © 2016 Akadémiai Kiadó, Budapest, Hungary

Sanjari E.,Islamic Azad University at Khomeinishahr
Thermochimica Acta | Year: 2013

Accurate liquid-vapor pressure prediction is fundamental to develop equations of state to simulate, evaluate and optimize chemical processes. The accuracy of vapor pressure calculations is essential because it is used as a basis to calculate the acentric factor, thermal and equilibrium properties. In this study, a new accurate equation for calculate the vapor pressure of pure substances as a function of reduced temperature and critical pressure is presented by using Marquardt-Levenberg algorithm which minimize the sum of the squared differences between the values of the observed and predicted values of the dependent variables. Vapor pressures have been calculated with presented substance-dependent equation and compared with the data reported in data compilation for 75 pure substances for more than 15,000 data points, and the overall average absolute percentage deviation is only 0.091%. The accuracy of obtained model has been compared to the mostly used equations and the comparison indicates that the proposed method provide more accurate results than other methods used in this work. © 2013 Elsevier B.V.

Toghraie D.,Islamic Azad University at Khomeinishahr
Physica E: Low-Dimensional Systems and Nanostructures | Year: 2016

In this study, a numerical method for simulation of flow boiling through subcooled jet on a hot surface with 800 °C has been presented. Volume fraction (VOF) has been used to simulate boiling heat transfer and investigation of the quench phenomena through fluid jet on a hot horizontal surface. Simulation has been done in a fixed Tsub=55 °C, Re=5000 to Re=50,000 and also in different Tsub=Tsat−Tf between 10 °C and 95 °C. The effect of fluid jet velocity and subcooled temperature on the rewetting temperature, wet zone propagation, cooling rate and maximum heat flux has been investigated. The results of this study show that by increasing the velocity of fluid jet of water, convective heat transfer coefficient at stagnation point increases. More ever, by decreasing the temperature of the fluid jet, convective heat transfer coefficient increases. © 2016 Elsevier B.V.

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