فهرست مطالب

International Journal of Engineering
Volume:13 Issue: 4, Nov 2000

  • تاریخ انتشار: 1379/10/11
  • تعداد عناوین: 9
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  • Golnabi Pages 1-16
    Design and construction of a stable current supply with protection circuits are described. The reported circuit provides a high-stable and high-level current variable from 0.5-1.2 A with the protect ion circuits to prevent over load current, voltage and off-range temperature operation. A detailed analysis of the circuit parameters is given and the time behaviors of the load voltage/current and shut-off voltage/current are presented. Theoretical analysis shows a turn-on time of about 20 ns for the load current and a shut-off time of about 150 ns. The proposed scheme is verified both by simulation and by constructing a prototype. The prototype version of this circuit shows a good stability in load current, and the laser diode temperature can be monitored with an accuracy of about 1 degree. In addition, design and analysis of the current modulator and switching circuit s for laser diodes are reported. Modulation process and different modulation techniques are explained in detail. Drive circuits for positive and negative intensity modulation are presented. Transient analysis for the proposed drivers is performed by using PSPICE software and the results are reported here. Evaluation of the results indicates that the reported modulators can be used successfully for direct current modulations.
  • M. Jain, C. J. Singh Pages 17-22
    This investigation deals with transient analysis of cold standby system with n units. Chapman-Kolmogorov equations are developed for repair facility with two repairmen and solved by using matrix technique. Availability and reliability factors have been obtained with probability of the system. A particular case has also been discussed.
  • A. Baradaran Rahimi, A. Omehtalb Pages 23-34
    An approximate analytical solution is obtained for hypersonic flow past a slender elliptic cone using second-order perturbation techniques in spherical coordinate systems. The analysis is based on perturbations of hypersonic flow past a circular cone aligned with the free stream, the perturbations stemming from the small cross-section eccentricity. By means of hypersonic approximations for the basic cone problem, closed-form second-order approximate solutions for the perturbation equations are obtained within the framework of hypersonic small-disturbance theory. Results for the shock shape, shock-layer structure, and surface pressure are presented for all ranges of Mach number s, together with comparisons with experimental data. Also a complete vortical layer analysis is presented to prove the suitability of the surface boundary conditions.
  • M. Jahanmiri Pages 35-42
    To simulate the effect of free st ream turbulence on turbulent spot formation, experiments were conducted on the interaction of localized three-dimensional disturbances with the harmonic waves in a laminar boundary layer on a flat plate. Experiments conducted in three-dimensional diverging flow (but zero pressure gradient) show, while individually the disturbances decay downstream, their interaction leads to amplification of three-dimensional disturbance leading to formation of the turbulent spot. Also flow divergence show the least effect in the interaction process.
  • K. Mazaheri, A. Banai, S. A. Seyed, Reyhani Pages 43-54
    An adaptive unstructured grid generation scheme is introduced to use finite volume (FV) and finite element (FE) formulation to solve the heat equation with singular boundary conditions. Regular grids could not acheive accurate solution to this problem. The grid generation scheme uses an optimal time complexity frontal method for the automatic generation and delaunay triangulation of the grid points. The algorithm is incremental, so it is the most appropriate for an adaptive solver. Using adaptive grids, the solution is refined to get enough accuracy in all grid points. Two schemes are applied for the solution of the equations to show the flexibility of the adaptive grid scheme. First a cell-vertex finite volume formulation is used. Then, for the FE scheme, using linear shape functions, a set of linear equations are solved explicitly, with overrelaxation. A sequence of adaptation is applied and appropriate number of grid points are introduced in finite predetermined formats to the existent elements, till convergence in the solution is observed. A postprocess is used to smooth the distribution of the set of nodes. This procedure is applied to a few study cases to show that the method is convergent, and produces accurate solution even in the case of singular boundary conditions.
  • V. A. Mut, J. F. Postigo, R. O. Carelli, B. Kuchen Pages 55-64
    In this paper we present a robust hybrid motion/force controller for rigid robot manipulators. The main contribution of this paper is that the proposed hybrid control system is able to accomplish motion objectives in free directions and force objectives in constrained directions under parametric uncertainty both in robot dynamics and stiffness constraint constant. Also, the given scheme is proved globally stable in the sense that the control objectives are achieved asymptotically, when a signum function is used in the control law, though giving rise to chattering effects. To avoid this problem a saturation function is used. In this case the motion and force errors are proved to be bounded functions. Using the proposed control structure there is no need to measure the derivative of the interaction forces. Some simulation results are given to illustrate the control system performance.
  • J. Sadrekarimi Pages 65-72
    This paper explains the procedure and results of an experiment on the relationship between the unconfined compressive strength and percent weight loss due to freeze and thaw durability test of laboratory compacted soil-cement specimens. The tests were carried out on soil cement mixtures of 10 different soil types. It was shown that the percent weight loss due to freeze and thaw durability test (F&T) and the 28-day compressive strength (UCS) may be correlated with some error. However, using the graph given in this paper, the designer may estimate the percent weight loss with an error in the order of 2 percent. The 28-day UCS values are linearly correlated with the UCS values of the similar specimens subjected to the F & T durability tests with a regression factor of o.96.
  • A. A. Fakhimi, M. J. Moosavi Pages 73-80
    The conventional method to evaluate earthquake induced permanent deformations of slopes is the one proposed by Newmark. In this paper, permanent displacement of slopes is studied using a combination of distinct element and finite difference methods and the results of these numerical evaluations are compared with those of the Newmark''s approach. Several parameters involved, including peak ground acceleration, period of excitation, friction and cohesion of the sliding surface, are considered in this study. The results show that the period of excitation is an important parameter in finding the displacements of slopes. In addition, it is shown that in resonance condition, the permanent displacement of a slope, derived by Newmark''s method, can be twice the one predicted by the distinct element method. Finally, It is realized that, in frictional materials, permanent displacements of slopes obtained by the distinct element and Newmark''s methods are in better agreement compared with the corresponding results in cohesive materials.
  • M. Osanloo, M. Ataei Pages 81-89
    The Sungun copper deposit is located in about 40km north west of Ahar city in the east Azarbaigan province of Iran. The total geological ore deposit is estimated to be 740 million tons. In this study using all information from exploration and geotechnical studies of the area, final pit limits of Sungun copper deposit is designed by the 2-D Lerchs & Grossmann Algorithm. By this method, from 740 million tons of geological ore reserve, 411 million tons can be mined by open-pit method with overall stripping ratio of 2.14:1. Cut off grade is found to be 0.32% Cu. The average ore grade is found to be 0.665% Cu