Experimental investigation of the vibroacoustic response characteristics of rib-stiffened panels with simple and complex attachments.

摘要

This work experimentally investigates the critical vibroacoustic response characteristics of a class of lightweight structures representative of those used in communications satellites. Parametric trends are identified and contrasted for the structures loaded with simple (non-resonant) mass attachments and for complex (resonant) equipment attachments. Unlike related previous works where the attachments' mass was typically on the order of ten percent of the primary structure mass, in this investigation the maximum loaded structure mass is approximately ten times that of the underlying sandwich panel mass. The critical parameters investigated include the average system conductance, radiation efficiency and damping. The transition that the critical vibroacoustic parameters make when the loading is incrementally increased, from an unloaded uniform structure to the maximum loaded complex structure, are also assessed. Parameter trends for the average conductance and radiation efficiency show significant shifts when the attachment mass exceeds the underlying structure mass. The radiation efficiency and radiation coupling results collapse to two nominal radiation efficiency profiles, one for the attachment mass greater than the structure mass and one for the attachment mass less than the structure mass, which can be used to describe the structural acoustic coupling characteristics of all loaded panel configurations investigated. The internal loss factor results show the role that internal and radiation losses play in the total induced loss factor including the effects of both resonant and non-resonant attachments. For the unloaded and mass loaded panels the radiation losses play a significant role over much of the frequency spectrum especially near and above the critical frequency. With just a few equipment attachments the total loss characteristics change significantly showing that over much of the frequency spectrum the induced damping effects of the resonant attachments are the limiting loss mechanism. When the equipment loading exceeds the total underlying structure mass, the loss effects of the equipment completely dominate the total induced loss factor at all frequencies by approximately 10 to 20 dB. One of the recurring themes observed in the results of this investigation is the presence of irregularity in the parametric trends at mid-frequencies. With the structural in-homogeneity present in these loaded panels it is logical that there should be a cross-over frequency region where the modes dominating the response transition from global (the effects of the attachments and stiffeners more uniformly affect the vibration) to local (the non-homogeneous features only affect the local response). (Abstract shortened by UMI.)