AN IMPEDANCE/MOBILITY CONDENSATION METHOD FOR PRELIMINARYVIBRO-ACOUSTIC ANALYSIS

摘要

Equipment mounted on spacecraft structural panels aresubject to high levels of vibration during lift-off. Thesevibrations result mainly from the acoustic loadsoriginated by the propulsion system of the launcher.Hence, acoustic loads on the payloads inside the fairingare random and broadband in nature. Early knowledgeof the random vibration environment is of crucialimportance during development phases. At present,simple design formulas, that include only theequipment mass, are used for this purpose. However,these formulas do not capture the physical reality of thephenomena involved, they are rather a product ofconservatively enveloping available measurements.This results in excessive mechanical over-design andvibration over-testing of subsystems, equipment andcomponents, with significant penalties in terms of costand weight.This paper summarizes the development of an accurateand simple procedure to specify the random vibrationsresulting from the acoustic environment. This isaccomplished by a physical analysis of the acousticexcitation of mounting panels and the coupled panel-equipmentmotion with the identification of the mainparameters. The acoustic field is described with rigidscattering analysis taking into account the jointacceptance, while the structural response is synthesizedby means of the impedance/mobility technique as acondensation methodology.The method has been validated against detaileddynamic and coupled structural-acoustic responsepredictions obtained with Finite and BoundaryElements codes. Correlates reasonably well with thedetailed predictions and a more realistic and lessconservative representation of the environment isobserved than what is specified by current standards.