فهرست مطالب

Mechanical Engineering Transactions of ISME - Volume:18 Issue: 2, Sep 2017

Iranian Journal of Mechanical Engineering Transactions of ISME
Volume:18 Issue: 2, Sep 2017

  • تاریخ انتشار: 1396/12/25
  • تعداد عناوین: 5
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  • Mostafa Varmazyar *, Mohammadreza Habibi, Arash Mohammadi Pages 5-22
    Various numerical boundary condition methods have been proposed to simulate various aspects of the no-slip wall condition using the Lattice Boltzmann Method. In this paper, a new boundary condition scheme is developed to model the no-slip wall condition in the presence of the body force term near the wall which is based on the Bennett extension. The error related to the new model is smaller than those of other boundary condition methods existing in the last studies. Based on the computational results, the body forces method which representing minimum error has been illustrated. Finally, the effect of the variation of diffusion coefficients on Rayleigh-Benard convection was studied. The critical Rayleigh number, which is obtained by current method, are in good agreement with the results calculated by the linear stability theory. It has been revealed that the proposed model is capable of computing the effect of high nonlinearity in the conservative equation in the presence of variable diffusion coefficients.
    Keywords: Lattice Boltzmann Method, Boundary Condition, Multi Relaxation Time, Variable Thermal Conductivity, Rayleigh, Benard Convection
  • Mohsen Jabbari *, Matin Mousavi, Mohammad Amin Kiani Pages 23-38
    In this paper, transient solution of two dimensional asymmetric thermal and mechanical stresses for a hollow cylinder made of piezoelectric material is developed. Transient temperature distribution, as function of radial and circumferential directions and time with general thermal boundary-conditions, is analytically obtained, using the method of separation of variables and generalized Bessel function. The results are the sum of transient and steady state solutions that depend upon the initial condition for temperature and heat source, respectively. The general form of thermal and mechanical boundary conditions is considered on the piezoelectric cylinder. Material properties of piezoelectric cylinder are the same along the thickness. A direct method is used to solve the Navier equations, using the Euler equation and complex Fourier series.
    Keywords: Transient, Thermoelasticity, Hollow Cylinder, Piezoelectric
  • Mojtaba Mahmoudi Monfared *, Reza Sourki, Reza Yaghoubi Pages 39-63
    The present paper deals with the mixed mode fracture analysis of a weakened orthotropic half-plane with multiple cracks propagation. The orthotropic half-plane contains Volterra type glide and climb edge dislocations. It is assumed that the medium is under in-plane loading conditions. The distributed dislocation technique is used to obtain integral equations for the dynamic problem of multiple smooth cracks which are located in an orthotropic half-plane. At first, with the help of Fourier transform the dislocation problem is solved and the stress fields are obtained. The integral equations are of Cauchy type singularity and are solved numerically to obtain the dislocation densities on the surface of several cracks to determine the dynamic stress intensity factors on the crack tips. Several numerical examples are solved to evaluate mode I and mode II dynamic stress intensity factors to show the effects of the orthotropy parameters, crack lengths, and crack speed on the dynamic stress intensity factors.
    Keywords: Mixed mode, Dynamic stress intensity factors, Multiple cracks, Distributed dislocation technique
  • Vahid Falahi, Hossein Mahbadi *, Mohammad Reza Eslami Pages 64-82
    In this paper, ratcheting behavior of beams subjected to mechanical cyclic loads at elevated temperature, using the rate dependent Chaboche unified viscoplastic model with combined kinematic and isotropic hardening theory of plasticity, is investigated. A precise and general numerical scheme, using the incremental method of solution, is developed to obtain the cyclic inelastic creep and plastic strains. Applying the numerical method to the governing equations obtained based on the mentioned unified model, cyclic behavior of the beam due to the combined plastic and creep strains are obtained. Effect of loading rate, creep time, and mean load on ratcheting response and stress amplitude of the beam due to the combination of axial and bending moments at elevated temperatures are obtained. It is shown that increasing the loading rate, results into decrease in ratcheting rate and increase in stress amplitude. Also, the ratcheting strain increases with increasing the creep time while the stress amplitude decreases. The results obtained using the applied method in this paper is verified with the experimental data given in the literature search.
    Keywords: Cyclic loading, Rate dependent plasticity, Viscoplasticity, Load controlled, Strain controlled
  • Maryam Khademi *, Ali Nikookar, Pooneh Khodabakhsh, Masoud Moadel Pages 83-95
    This research aims to predict PV output power by using different neuro-evolutionary methods. The proposed approach was evaluated by a data set, which was collected at 5-minute intervals in the photovoltaic laboratory of Niroo Research Institute of Iran (Tehran). The data has been divided into three intervals based on the amount of solar irradiation, and different neural networks were used for predicting each interval. NSGA II, a multi-objective optimization algorithm, has been applied to search an appropriate set of weights, which optimized the neural network with two or more conflicting objectives. The MLP-NSGA II algorithm provides better results with the Mean Square Error (MSE) and correlation coefficient (R2) of 0.01 and 0.98, respectively, in comparison with Linear Regression, MLP, and MLP-GA. By the way, obtained results show that the precision of prediction models would be improved by reducing input parameters’ time intervals.
    Keywords: PV output Power Predication, Multi, Objective Optimization Algorithms, Neural Network, NSGA II