Reiko Koganei

Optimization of a Semi-Active Shock Absorber for Aircraft Landing Gear

We propose an optimization method for a semi-active shock absorber for use in aircraft landing gear, in order to handle variations in the maximum vertical acceleration of an aircraft during landing caused by the variation of the aircraft mass due to the variations in the number of passengers, and the amounts of cargo and fuel. In this optimization, the maximum vertical acceleration of an aircraft is set as an objective function to be minimized. Design variables searched in the first step of this optimization are discrete orifice areas formed by the outer surface of a hollow metering pin and a hole in the semi-active shock absorber. The design variable searched in the second step is a compensating orifice area which is controlled based on the mass variation. Using the optimum target orifice area obtained in the second step, we optimally determine a practical orifice area that is controlled by a stepping motor. The optimizations for a passive shock absorber and for semi-active shock absorbers with target and practical orifice areas indicate that the semi-active shock absorbers can handle aircraft mass variation much better than the optimum passive shock absorber. Furthermore, the robustness of the optimum practical orifice area controlled by a stepping motor is shown via simulation.© 2003 ASME

The Elucidation of Mechanism of Local Sound Pressure Increase Phenomenon

Payloads of satellite are exposed on the severe acoustic environment at the process of lift-off and supersonic zone of a launcher. This acoustic environment excites the payload in high pressure and broad frequency band of random acoustical excitation, which may cause serious damage to the structures or instruments of the spacecraft inside. Space instruments are designed and verified to the acoustic environment by ground reverberant acoustic chamber in order to specify random vibration level at component interface and to verify the payloads are working in function and the structure does not have structural damage. The present load sound pressure specification assumes that the sound pressure interior fairing is uniformly distributed. In spacecraft system acoustic tests, local pressure increase occurs in the narrow gap between spacecraft primal structure and components facing toward the fairing wall. This acoustical environment load to the components differs from that the components were tested alone and the flight acoustic environment may not be actually simulated in the ground testing. It is important to clarify the mechanism of sound pressure increase in the narrow gap in order to predict the level of sound pressure increase. In this study, we focus to the investigation of the mechanism by basic experiment including acoustic testing and vibration modal survey. It is clarified that the main reason of the phenomenon is dominated by the acoustic cavity on the appropriate boundary condition rather than structure vibration. And more, we predict the frequency at which the sound pressure increase at the narrow gap and compare analysis results with experiment results by using Boundary Element Method (BEM).Copyright

Sound Vibration Analysis at the Time of an Artificial Satellite Launch

In spacecraft system acoustic tests, one often sees local pressure increase in the narrow gap between spacecraft primal structures and components facing toward the fairing wall. This acoustical environment load to the components differs from that the components are tested alone and the flight acoustic environment may not be actually simulated in the ground testing. In this paper, in order to clarify the mechanism and evaluate this pressure increase, basic experiment including acoustic testing and vibration modal survey are employed. It is found that the main reason of the phenomenon is dominated by the acoustic cavity on the appropriate boundary condition rather than structure vibration. Boundary element method is used to analize the phenomenon and comparison of analysis and experiment results are carried out. The analytical and experimental results agree well. Furthermore, it is understood that the phenomenon of local sound pressure level increase is dominated by the acoustical standing wave mode (1, 1) which can be predicted by the presented methods.