In this research, it is considered that the air cushion vehicle should not drift sideways for a good driving performance. A nonlinear state feedback control was proposed previously for the trajectory control of an air cushion vehicle. With this control law, the successful values of the propulsion forces could be calculated. However, the way how to realize these forces was not considered. In the present paper, an algorithm for the generation of these propulsion forces is proposed. An experimental system with a simple air cushion vehicle model is also constructed. Then, the validity of the proposed scheme is verified through several trajectory control experiments.
A genetic algorithm (GA) was applied to a maximum downrange problem of a space-plane to study its effectiveness as a solving tool of optimum path problems. It is generally impossible to obtain analytical solutions of optimal control problems in engineering because of the existence of many variables and constraints. Numerical methods, e. g., steepest descent method etc., however, can hardly find global minimums of such problems with strong nonlinearities. In such cases, to choose proper initial value is the essential matter, and it requires much experience and takes long time. Therefore, new methods searching for global optimum are widely developing, especially GA that can simultaneously search the solution space using many test solutions. Conventional methods of GA using bit notation, however, could not be applied to engineering problems, since which could only treat discrete numbers. Therefore we propose a new GA method using coefficients of a polynomial expansion to code genes of a chromosome, and then we can apply it to time continuous control problems. At first we used the method to solve a linear regulator problem to check accuracy and convergence of GA solutions, and next maximum downrange problem of space-plane.
The electric propulsion orbit transfer system for using the development of Solar Power Satellite (SPS) is evaluated from the point of view of energy investment. First, the energy cost of total SPS system is analyzed for the cases that the electric propulsion or the chemical propulsion is used as an orbit transfer system of SPS. Then, the minimum energy investment ratio in SPS to the total energy consumption on the earth in which the high levels of population and capital on the earth can be maintained is estimated by the evaluation model of SPS using World Dynamics. The simulation results show that about 12-18% reduction of energy investment ratio is possible in the case that the electric propulsion is used compared with in the case that the chemical propulsion is used as an orbit transfer system of SPS.
This paper considers dynamic analysis and control of a space robot at capturing a target. The computer simulation of this problem requires three phases: 1) dynamic motion analysis of link systems, 2) control problems of a manipulator, and 3) impulsive force analysis at a capture. Motion dynamics of free-floating link systems are formulated by Kane's equations. A resolved acceleration control is applied to determine control torque of a robot manipulator. Implicit equations associated with impulsive forces and velocity jumps in systems are utilized to analyze an intermittent motion. An order-n formulation, which efficiently solves dynamic equations of serial rigid body systems, is applied to a numerical computation method for the three phases. As numerical examples, a space robot with seven rigid bodies and a target satellite with three rigid bodies are considered. By specifying a motion path of an end-effector of the robot manipulator, the capture of the target satellite is simulated, and the impulsive forces at the capture is calculated.
Bow shock wave/turbulent boundary layer interaction regions induced by a blunt body have been experimentally investigated carefully. By selecting the displacement h, between a flat plate and a blunt body simulating Solid Rocket Booster (SRB), as the main parameter, the effects of the displacement on the flowfields are examined. Flowfields are visualized by use of the Schlieren method and oil flow technique, then surface pressure distributions are measured for various h, 5, 10, 15 and 20mm. For small h, the secondary separation with the primary separation is observed, and there exists a new weak separation downstream of the attachment line. On the contrary for large h, no secondary separation is observed, and the flow structure becomes much simple. The results show that the peak pressure is rapidly decreased as h is increased, also as apart from the centerline. Clearly the displacement affects the interaction region considerably.
Thruster assignment to generate ideal forces and torques is important for a chaser spacecraft approaching another spacecraft (a target spacecraft), for example, during rendezvous and docking operations. The thruster selection is more important in the proximity area of the target spacecraft where the chaser spacecraft controls both relative position and attitude. The conventional method is based on a table look-up. It is easy to execute (calculation time minimum) but tends to generate a wasteful pattern of thruster select. Two new methods based on fuzzy logic are proposed: one removes such wasteful patterns using fuzzy pattern matching and the other selects thrusters one by one while it reduces the residual control forces and torques with smaller fuel consumption using fuzzy inference. Numerical simulations are given to compare the conventional method, the proposed fuzzy methods and the linear programming (fuel minimum). The results show that the proposed fuzzy methods realize a thruster select logic with low fuel-consumption in allowable calculation time and that they provide a flexibility in the trade off between calculation time and fuel consumption.
This paper evaluates the accuracy of the quadrature formula for the logarithmic singular integral; ∫1-1√(1-ξ)/(1+ξ)f(ξ)ln|x-ξ|dξ, appeared in the numerical method of unsteady subsonic lifting surface. Its accuracy is estimated by the expansion method with the orthogonal polynomials relative to the weighting function √(1-ξ)/(1+ξ), on the assumption that the function f is a polynomial. This analysis shows that the precision degree of their n-points quadrature can not exceed n in general, and that it is not improved even if the control point x is set to that of Stark's quadrature formula.