فهرست مطالب

Scientia Iranica
Volume:18 Issue: 2, 2011

  • Transactions B: Mechanical Engineering
  • تاریخ انتشار: 1390/05/01
  • تعداد عناوین: 8
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  • A. Jafarian, F. Roshanghalb, M.H. Saidi, F. Imanimehr Page 205
    The objective of the present work is to compare the performance of the regenerator of pulse tube refrigerators at low and high frequencies. The hydrodynamic and thermal behavior of the regenerator is investigated in this respect. To consider the system performance, a system of conservation equations including two energy equations for the regenerator as a porous media is employed. The present model considers one-dimensional, periodic, unsteady, compressible flow in the regenerator. The conservation equations are transformed by implementing the volumetric average scheme. The method of harmonic approximation is employed to derive an analytical solution. To explore the system performance, net energy flow and entropy generation minimization techniques are applied, in order to calculate the regenerator first and second law efficiencies. The effects of geometry and operating key parameters on the regenerator performance are considered as well.
  • M. Mohammadi Pirouz, M. Farhadi, K. Sedighi, H. Nemati, E. Fattahi Page 213
    Conjugate heat transfer in a rectangular channel with lower and upper wall-mounted obstacles is investigated using the Lattice Boltzmann Method (LBM). Laminar and incompressible flow of fluid circulating through the channel is assumed. The simulations are performed at. Studies are carried out for flow, with Reynolds numbers ranging from 200 to 1000, thermal diffusivity ratios (10, 100 and 1000) and the distance between obstacles, which are prescribed as multiples of obstacle width. A uniform heat flux through the base of obstacles is assumed. Results show that LBM is suitable for the study of heat transfer in conjugate problems. Results indicate that increase of thermal diffusivity yields to the removal of a higher quantity of energy from obstacle faces. Results also show that reducing the distance between obstacles makes the flow deviate and accelerate in the vicinity of faces, and causes an increase in the rate of convective heat transfer from obstacles.
  • F. Cheraghpour, S.A.A. Moosavian, A. Nahvi Page 222
    In this paper, a new Multi-Aspect Grasp (MAG) performance index is presented for evaluating grasp quality during an object manipulation task. The position of grasp points, the configuration of cooperative manipulators, and the kinetic aspects of manipulating arms and the grasped object are considered in the MAG index. The MAG index is used to evaluate the candidate points to choose the best grasp point and to select the most effective branch of the inverse kinematics solution, with respect to the given task. Simulation results, which are validated with analytical solutions, show the merits of the proposed index. According to these results, the MAG index indicates that in planar object manipulation tasks without rotation, the best grasp point is the object center of the mass, which is physically meaningful.
  • M. Mehravaran, S. Kazemzadeh Hannani Page 231
    Recently, a hybrid Lattice Boltzmann Level Set Method (LBLSM) for two-phase incompressible fluids with large density differences, in cases of negligible or a priori known pressure gradients, has been proposed. In the present work, the mentioned LBLSM method is extended to take into account pressure gradient effects. The lattice Boltzmann method is used for calculating velocities, the interface is captured by the level set function, and the surface tension is replaced by an equivalent body force. The method can be applied to simulate two-phase fluid flows with density ratios up to 1000 and viscosity ratios up to 100. In order to validate the method, the evolution and merging of rising bubbles were investigated, and the results are in agreement with other numerical or experimental results.
  • M.R. Soltani, M. Farahani, M.H. Asgari Kaji Page 241
    An experimental study was carried out on an axisymmetric supersonic inlet with external compression. The scope of this study was to investigate the general characteristics of the inlet buzz under various design and off-design conditions. The model was equipped with accurate and high frequency pressure sensors and the tests were conducted at Mach numbers varying from 1.8 to 2.5, at various angles of attack, and at different mass flow rates. Shadowgraph flow visualization, together with a high speed camera, was used to capture the external shock structure in front of the inlet. Frequencies of buzz were obtained from both the shadowgraph pictures and analysis of the pressure data. The amplitude of the shock wave motion was measured from the visualization pictures, too. The results show that for low mass flow rates, buzz frequency is almost independent of Mach number, while at a higher mass flow rate, the frequency of the shock oscillation increases with Mach number. Further, for each free stream Mach number, as the mass flow rate decreased, the amplitude of the shock movement grew, but its frequency decreased.
  • M. Kadkhodayan, F. Moayyedian Page 250
    Based on the two-dimensional plane stress wrinkling model of an elastic–plastic annular plate and a bifurcation functional from Hill’s general theory of uniqueness in polar coordinates, the critical conditions for the elastic and plastic wrinkling of the flange of a circular blank during the deep-drawing process are obtained to improve previous results of the literature. The influence of a blank-holder on wrinkling and on the number of waves generated can also be quantitatively predicted. A closed-form solution for the critical drawing stress is developed, based on the Tresca yield criterion, along with the assumption of perfectly plastic material. A nonlinear plastic stress field and the deformation theory of plasticity are used. It is demonstrated that using the large deflection theory for a strain tensor with neglecting nonlinear terms has the same result as the small deflection theory.
  • H. Nejat Pishkenari, S.H. Mahboobi, A. Alasty Page 261
    Differential Evolution (DE) and Genetic Algorithms (GA) are population based search algorithms that come under the category of evolutionary optimization techniques. In the present study, these evolutionary methods have been utilized to conduct the optimum design of a fuzzy controller for mobile robot trajectory tracking. Comparison between their performances has also been conducted. In this paper, we will present a fuzzy controller to the problem of mobile robot path tracking for a CEDRA rescue robot. After designing the fuzzy tracking controller, the membership functions will be optimized by evolutionary algorithms in order to obtain more acceptable results.
  • Y. Chen, B. Li Page 268
    Triangular Intuitionistic Fuzzy Numbers (TIFNs) express more abundant and flexible information than Triangular Fuzzy Numbers (TFNs). The main purpose of this paper is to propose a Dynamic Multi-Attribute Decision Making (DMADM) model on the basis of TIFNs, to solve the DMADM problem, where all the decision information takes the form of TIFNs. A new distance measure between two TIFNs is developed to aid in determining attribute weights, using the entropy method. An aggregation operator, the weighted arithmetic averaging operator on TIFNs (TIFN-WAA), is presented to aggregate the decision information with TIFNs. Finally, the effectiveness and applicability of the proposed DMADM model, as well as analysis of comparison with another model, are illustrated with an investment example.