JOURNAL OF AEROSPACE SCIENCE AND RESEARCH
Year:2009 | Volume:2 | Issue:2|Papers Count:8

One of the required maneuvers of remote sensing satellites is the pointing or reorientation maneuver of its body axes toward a reference direction. This maneuver can be accomplished using control torques from a tri-axes reaction wheel mechanism with an appropriate control law. The satellite attitude governing equations are usually categorized as multivariable nonlinear coupled system, which makes the design of a control law complicated.In this article the Receding Horizon Control (RHC) idea is utilized to design an optimal control policy through a step by step linearization approach. Where in each step the nonlinear equations are locally linearized around the current state to form a linear quadratic regulator (LQR) problem, for which the required optimal feedback control matrix can be determined by solution of the Ricatti equation. This approach of solution leads to a closed loop control that brings about some robustness against environmental and or system disturbances present in a typical satellite system.

In this research a fatigue life model is introduced which is in good agreement with fatigue life behaviors of tested composite coupons for different loading condition. In order to show the conformity of this model with fatigue life behavior of composites, fatigue life data of different composite was used to show this conformity between the model and data for different on-axis and off-axis loading and various stress ratios. Also, it was shown that this model has appropriate behavior for all three regions of fatigue life for composite coupons. This model can predict fatigue life for tension-tension, tension-compression and compression-compression loadings.

In this study in order to predict the flow behavior, a numerical simulation in the tubular combustion chamber with a wall jet is used.For this purpose, in order to analyze the flow field based on the experimental results, the method of finite volume with non-staggered grids is used and acceptable compliance with the available experimental results. The flow is considered to be three-dimensional, steady, turbulent, incompressible, viscous, two - phase and the turbulence models used include RNG (K-ε) model. The results indicate the presence of strong circulating area in dome region in non-reaction mode. With the chemical interactions, density of flow is increased and as the size of combustion chamber is constant the increase in density leads to increase of central speed. As a result, the circulating area in dome region is almost eliminated. Also changes in rate of swirl air flow will result in increase of circulating flow in the primary area of combustion chamber.Increase of air to fuel ratio rises the magnitude of velocities and profile of uniform in output. Finally, the optimum sauter mean diameter and fuel spray angle is obtained.

A system of flight control should be used by the aerospace launch vehicle (ALV) for reaching to injection point in the orbit. ALV is a dynamic system which is described by mathematical terms which include imprecise dynamic ALV causes controller efficiency to become low, and steady state error is created.Specified cases lead to divergence. In comparison with other control systems, application of the PID controller is the most important advantage of it.Especially PID controllers are useful when there is no specific mathematical model and analytic methods are not utilizable. In this project, using of controller is proposed according to output results of guidance command along the vehicle path. For non-linear system, six degree of freedom ALV equation and considering single stage reaching orbit, also specific initial conditions, and PID controller is designed by the use of genetic algorithm.

In this paper, the divergent part of a two dimension nozzle of an intermittent blow-down hypersonic wind tunnel capable for maximum Mach number of 7 is designed. The real gas and viscous effects are taken into account in determination of nozzle contour. Finally, by using Foelsch method as an analytical method for designing hypersonic nozzle contour, a CFD code has been presented and the results of this code are attached.

It is of great significance to assure the compatibility between aircraft engine and frame within the basic design and prior to model fabrication and costly experiments. The main purpose of this research was the evaluation of flight path main sections and imposed restrictions in the compatibility of engine and frame. Results show methods to decrease take- off run, noise level, etc., identified through an analytical approach.

In this paper the design of an attitude control system with reaction jet is studied for a kind of vertical launch flying vehicle. The design process covers the components of the control system and the compensators. The attitude control system controls the roll, pitch and yaw angles for a few seconds after the vertical launch. The system design is based on the desired time schedule and the maximum required pitch rate of the flying vehicle during the initial maneuver in the vertical plane. The compensators are designed based on the desired performance criteria as defined within the text. Finally the designed control system and controllers are evaluated using a variable mass 6DOF flight simulation utilizing the full nonlinear equations of motion and considering the saturation of control signals.

In this paper, a moving mesh concept originally introduced to model the general motion of a two-dimensional body is improved. The solution domain is divided into two zones. The first zone, with a circular boundary, includes the moving body and is intended to facilitate the vibrational rotation of the body. This zone is meshed by triangular elements which displace rigidly with the body. The proposed approach suggests replacing the triangular elements in the most exterior layer of the first zone by square ones which reduces their number by half. Present grid configuration also allows the number of nodal points and elements to remain constant. In order to demonstrate the effectiveness of the present method, unsteady and compressible form of the Euler equations are solved for flow over a moving body. The performance of the method is verified by several sample problems and comparing the results with existing numerical and experimental analyses in the literature.