These days, we have many opportunities to launch small satellites as a piggyback payload. Faced with this situation, in this study, we deal with 3-axis attitude control of a small satellite equipped with a DGVSCMG (Double-Gimbal Variable-Speed Control Moment Gyro). Unlike conventional single-gimbal CMGs, only one DGVSCMG can attain 3-axis attitude control. This saves an inner space of a satellite and reserves an extra space for other missions. Satellite dynamics is described by a nonlinear differential equation. To avoid difficulties coming from this nonlinearity, we modeled its dynamics as an LPV (Linear Parameter-Varying) system and applied a GS (Gain-Scheduled) controller to this model. Compared with a conventional method, it is shown that the control performance has been improved.
Low-speed wind tunnel tests were performed to investigate aerodynamic effects induced by delta-shaped vortex generators installed on the upper surface of a trailing-edge flap. The vortex generator was applied to control the flow field around the trailing-edge flap where the flow was separated from the hinge line of the trailing-edge flap. The test results showed that the vortex generators increase the lift coefficient and the lift-to-drag ratio when the trailing-edge flap deflects to 30degrees. The leading-edge separation vortices formed from the delta-shaped vortex generators suppressed the flow separation on the trailing-edge flap. The height of the vortex generator geometrically changes depending on the trailing-edge flap deflection angles. Therefore, when the trailing-edge flap is not deflected such as cruise flight condition where the flow field is dominated by the attached flow, the vortex generator does not impose a penalty on the aerodynamic performance.
The purpose of this paper is to understand characteristics of flow around I-beam, which is designed based on structural point of view. The flow is investigated by analyzing the influence of angle-of-attack on the vortex-shedding frequencies and the flow structures. To achieve this purpose, two-dimensional flow around circular cylinder, square cylinder and I-beam is calculated and proper orthogonal decomposition is applied to the results to extract flow structures. The results show that the cavity of I-beam has impacts on the flow and the flow becomes complicated especially at 45°.
Although CFD tools are necessary for aerodynamic design, it is still time consuming and this is one of the big problems. In order to shorten the computational time, a fast CFD code “FaSTAR” has been developed. We combined two acceleration techniques. One is a convergence acceleration technique such as the multigrid method. A coarse-grid generation method using octree data of the Cartesian grid is proposed. This method is simple and it can generate high-quality coarse grids. The other is a programing technique such as data structure improvement and performance tuning. We demonstrate the high-speed performance of the code for aerodynamic computation of a standard aircraft model, NASA-CRM. The computational time is less than one hour using 10 million cells and 100 CPU cores. It is found that the multigrid method is beneficial for large-scale problems.
The mechanism of the helicopter rotor whirl instability in the forward flight is investigated by the parametric resonance analysis. By comparing the system natural frequencies with the frequency components of the aerodynamic forces that are observed in the SH-60K simulation, it is shown that the particular frequency components might cause the parametric resonance. By applying the aerodynamic forces with the particular frequencies to the right-hand side of the equations of motion, the method of the variation of constants is used to evaluate the parametric resonance. These results show that the parametric resonance between the backward whirl mode and the scissor mode makes the SH-60K whirl mode unstable. In order to suppress the whirl instability, the reduction of the rotor rotational speed or the stiffening of the rotor support structure is considered to be effective.
We investigate the effect of flight experience on pilot rating in linearized lateral-directional motions with pre-specified various flying qualities for Dutch-roll and roll modes using a ground fixed simulator. Our experiment, which was conducted with three categorized testees (professors, juniors, and freshmen belonging to Aviation course of Department of Aeronautics and Astronautics at Tokai Univ.), shows that flight experience affects pilot rating, and this consequently leads to different pilot rating for the same flying qualities.
Development of small satellites (50kg or less) is undergoing all over the world. Regardless its size, any satellite has to be tested for space environment. Various environment tests, such as vibration, vacuum, low and high temperature are necessary. Especially, shock test is one of the most difficult tests. The shock test needs to satisfy the SRS (shock response spectrum) requirement imposed by the launcher. If the SRS obtained in the test does not exceed the SRS requirement level, the test is invalid. At the same time, the SRS level as low as possible while satisfying the requirement is desired to protect the satellite from the overstress. SRS obtained by an air-gun type shock machine was analyzed using a commercial finite element code (LS-DYNA) to investigate the SRS at low frequencies, 100 to 300Hz, which is very difficult to control in the actual test. The analysis showed that controlling the friction of the slide table is effective to change the slope of SRS at the low frequencies. The lower the friction, the higher slope of SRS is obtained.