Recently, the lattice gas method has been widely used to simulate fluid motions. Many researchers have computed the velocity fields of various flows by this method, and have already confirmed that the results agree well with the experiments. However, the pressure field has not been examined. In this paper, in order to verify the pressure field of the lattice gas method, we will present a method to compute the pressure field, and apply it to a flow around a plate and that around a rotating wing which is a model of the Weis-Fogh mechanism. The drag and the lift coefficients obtained by this method agree reasonably well with experimental values, and the validity of the pressure fields by the lattice gas method was confirmed.
Transfer function zeros of active control systems are studied for a two dimensional typical airfoil in an in-compressible flow. Both steady and unsteady aerodynamics are used for the modeling of the dynamics. Sensor location which gives us a minimum phase transfer function is examined over the airfoil area between the leading edge and the hinge line of the tailing edge control surface. Three types of zeros exist in the transfer function with an unsteady aerodynamic modeling. It is shown that the zeros corresponding to the ones derived from the steady aerodynamics determine an upper and lower boundaries of the flight velocity through which the transfer function changes its phase characteristics. The zeros that are originally contained in the unsteady aerodynamic modeling do not contribute to the phase change. However, two other zeros that are generated through the modeling determine a front boundary of the sensor location. It is to be noted in flutter control systems that a zero always exists near the critical pole and the transfer function shows a situation of near pole-zero cancellation around the flutter point.
Surface and back pressures, and three aerodynamic force components for two models of reentry vehicle: the cocoon type and the pan type, were measured at three transonic flow speeds: Mach number of 0.6, 0.7 and 0.8. Schlieren photographs were also taken to visualize the flow pattern. Comparing the results of force measurement with those calculated from measured pressure distributions, reasonable agreement was obtained. The Euler equations were also solved for a case with attack angle of 0 deg and Mach number of 0.8. In spite of good agreement on pressure distribution along the forward part of model, there was some discrepancy in back pressure between numerical calculation and experiment, which produced difference in drag coefficient. When the back pressure was then replaced by the experimental data, reasonable agreement of drag coefficient was obtained between them. As a result, it turned out that the pan type was more appropriate as a reentry vehicle than the cocoon type.
A new method which combines H∞ control with eigenstructure assignment is proposed and applied to the vibration control of flexible structures. One of the features on H∞ control is that the design requirements are given in frequency domain, and H∞ control is useful for application to the flexible structures which strongly require the robust stability. However, it is difficult for H∞ control to attain the requirements of response properties in the time domain. So in this paper, the 2-steps approach is proposed, that is, as a first step the full state feedback control law is designed to satisfy the good response using eigenstructure assignment, and in the next the robust state estimator holding its performance is solved via H∞ filter problem. Proposed method is applied to the vibration control of flexible structures, and it is demonstrated that the designed control law has good performance and robust stability using analysis and experiments.
This paper discusses the next generation global satellite system which follows NAVSTAR/GPS and supplies the services of mobile communications as well as position determination for all kinds of mobile vehicles. The service area of the system proposed here is not global in the first stage of the operation because several geosynchronous satellites are used as the means of navigation and radio communication in the limited area. A constellation of five geosynchronous satellites is dealt with to evaluate the performance in terms of the coverage and the navigation accuracy.
This paper provides a new design method to stabilize an open-loop system containing time-varying uncertainties, which occur in either the input matrix or the output matrix as well as in the state matrix. The method is based on eigen-value assignment, in which the closed-loop system may be attained by output feedback controller with low order dynamic compensator because of permitting the relaxation of the closed-loop eigenvalue assignment. A sufficient condition for the closed-loop system to be exponentially stable is given. Moreover, we clarify the relation between the robustness of closed-loop stability and the order of compensator. To demonstrate the effectiveness of the result, designs of lateral autopilot system of a missile are shown.
This paper concerns the horizontal tail volume of T-tail equipped on PAR-WIG vehicles, capable of OGE flight. There are few previous papers, available to the author, showing explicitly the following facts. First, the tail-volume ratio is excessively larger than conventional airplanes. Second, what are the main factors having influence on the first fact for the said vehicles. Third, how different are the role of the said main factors between OGE and IGE flights. This paper satisfies these points.
A ram accelerator is a device which can launch a heavy payload using a chemical energy release induced by shock waves. The operation principle is pretty silimar to that of a ramjet. Detailed operation mechanisms are now intensively under investigation.