Iranian Journal of Mechanical Engineering Transactions of ISME
Year:2001 | Volume:2 | Issue:1|Papers Count:5

In this paper, main objectives of Z-SAT attitude control system are described. Orbit of the satellite is circle, near polar, and about 700 km. above the surface of the Earth. A combination of gravity-gradient and magnetorquing stabilization methods is used to control attitude of the satellite. Using a detailed analysis on Keplerian and main perturbation forces, orbital dynamics of the satellite is developed.Proper configuration is designed to take the advantages of gravity-gradient torque. Deployable mechanism of control boom, and the optimum deployment attitude to deploy it are determined.Several algorithms are depicted to implement different attitude maneuvers, such as changing the rate and direction of rotation, and deliberation. Results of simulations show effectiveness of the stabilization method.

This paper describes the power spectral density matrix of manipulator tip displacement to stochastic excitation of the base. The dynamic equations for an articulated manipulator subjected to a vertically stochastic excitation are derived by Lagrangian method. Then the equations are linearized with respect to a small displacement in a fixed configuration.Sensitivity of the power spectral density of tip motion to the manipulator configuration and structural damping are investigated. Finally, simulation results are presented for a 2R Planner robot manipulator under vertical base excitation

This paper is concerned with the stability characteristics of gas-lubricated plane journal bearings systems during acceleration periods. The paper first establishes a theoretical analysis for the transient response of gas-lubricated journal bearing system. The stability margin which is expressed in terms of critical speed is obtained by the time - marching solution of the equation of motion of the journal coupled with the time-transient Reynolds equation. For this purpose, the compressible Reynolds equation is formulated as an initial value problem via Galarkin's finite element method. It is found that the effect of aspect ratio is more pronounced at low compressibility numbers and also an increase in the value of aspect ratio decreases the minimum value of stability threshold speed as well as zone of infinite stability.

Based on a two dimensional buckling modeling of an elastic -plastic annular plate and the well - known energy method, the critical conditions for the elastic and plastic wrinkling of the flange during the deep drawing with a blank-holder are studied. The blank-holder is considered to apply a uniform constant force. Using this model, first the critical stress for elastic and plastic wrinkling is obtained. Then the influences of the blank and die geometries and the blank-holder force on the critical stress in relation to wrinkling are discussed. Finally the optimum blank-holder force in relation to the plastic wrinkling in both theoretical and experimental approaches is obtained.

Heat transfer correlations for flow over tube bank are used to simulate heat transfer coefficient at any location in arrays of pin fin with variable cross section. The fin profile is assumed to be correlated with temperature of the fin and is controlled by a profile parameter. The resulting differential equation for temperature distribution in the fin arrays is integrated analytically. The relation between the volume per unit base area and the fin effectiveness is obtained in terms of an integral with the important optimization parameter being the tip temperature of the fin. The results are reported in dimension less form which is suitable for parametric study, design analysis and the fin optimization.