This paper describes the design and evaluation of an aerodynamic force balance within ms-order test time. A cross-beam strain gauge force balance, which is compact and easy to extend to multi-component measurement, was developed. The balance was designed to have simple vibration characteristics with simple and high stiffness configuration. An experimental modal analysis method and finite element analysis method were applied to evaluate vibration characteristics of the balance. This balance was used for drag force measurement with a hemisphere model in a free piston shock tunnel with a test time of approximately 1 ms. A signal recovery technique based on frequency domain de-convolution, which improves time resolution of the force measurement is also described. Measured drag force coefficient agreed well with the predicted theoretical value.
With a minimal set of three Euler angles, the attitude motion of a spacecraft is exactly described as a nonlinear, multiple input/multiple output, and cross-coupled system. In this work, the attitude motion equations are viewed as two blocks, a kinematics block and a dynamics block. Based on Lyapunov stability theory and backstepping technique, a new controller is derived from the nonlinear equations. The approach is then extended to a nonlinear attitude tracking case. Moreover, in practical attitude control, usually the moments of inertia are uncertain in value, but always positive. For this case, an adaptive nonlinear controller is developed. The effectiveness of the presented controllers is verified by simulation.
Flow-fields around the basic SSTO-rocket configurations are numerically simulated by the Reynolds-averaged Navier-Stokes (RANS) computations. Simulations of the Apollo-like configuration is first carried out, where the results are compared with NASA experiments and the prediction ability of the RANS simulation is discussed. The angle of attack of the freestream ranges from 0° to 180° and the freestream Mach number ranges from 0.7 to 2.0. Computed aerodynamic coefficients for the Apollo-like configuration agree well with the experiments under a wide range of flow conditions. The flow simulations around the slender Apollo-type configuration are carried out next and the results are compared with the experiments. Computed aerodynamic coefficients also agree well with the experiments. Flow-fields are dominated by the three-dimensional massively separated flow, which should be captured for accurate aerodynamic prediction. Grid refinement effects on the computed aerodynamic coefficients are investigated comprehensively.
The oscillation of a circular cylinder in a uniform flow is not only one of the basic subjects of fluid dynamics, but is also a very important problem in fluids engineering. In the present paper, the cross-flow and in-line vibrations of a two-dimensional circular cylinder were studied numerically. Both the forced and free vibrations were examined. Vortex shedding became synchronized with the forced cross-flow vibration at a frequency close to that of the Strouhal number of a stationary cylinder. With forced in-line vibration, vortex shedding began to synchronize with the frequency and also one half that of a circular cylinder at a higher vibration rate. With free vibration, the cross-flow vibration was excited when the natural frequency of the cylinder was near the stationary Strouhal number, and in-line vibration was observed near the natural frequency at around twice the stationary Strouhal number.
A micro-piggyback satellite, “μ-LabSat”, was launched by an H-IIA rocket on 14 December 2002. μ-LabSat is a bias momentum micro-satellite with two wheels, a configuration that is not normally capable of three-axis attitude maneuvers. This paper describes an algorithm that has been developed to enable such maneuvers and presents the results of its evaluation by numerical simulation and in-orbit experiment.
An optimal guidance law derived by solving the minimum-acceleration problem has been reported for control of a lunar lander. In our past work, the guidance law was proved to enable vertical/soft landing. However, it was not robust against disturbance because there was a constraint condition relative to initial conditions in order to satisfy optimality. Therefore, if the constraint is not satisfied, the lunar lander must be controlled to track the reference trajectory generated by the optimal guidance law in order to be robust against disturbance. The control system makes the landing system complex and fuel consumption is increased in comparison to a guidance law without tracking control. Consequently, this study restructures the optimal control problem as a minimum-jerk problem to solve it. Jerk is a physical quantity defined as the time derivative of acceleration. The new optimal guidance law obtained has no constraints on the initial conditions. The results of computer simulation confirm the usefulness of the proposed guidance law.
Detailed magneto-hydrodynamic (MHD) simulations of plasma flows in an inductively coupled plasma (ICP) heater are performed with air as the working gas. The plasma flows are numerically solved by the axisymmetric Navier-Stokes equations coupled with Park’s two-temperature models and Dunn-Kang’s chemical kinetic models to take into account the thermal and chemical non-equilibrium, while induction heating in plasmas is incorporated by solving the time-averaged MHD induction equations. Computations are done by changing the operating conditions such as the input power and the background pressure to examine how the plasma properties and the wall heat fluxes inside the discharge chamber depend on these parameters. Numerical results are compared with those of spectroscopic measurement. Good agreement is obtained in the downstream region where the flow is in local thermal equilibrium, however, qualitative discrepancy of electronic temperature between the theory and the experiment is found in the discharge chamber where Joule heating is significant.