VIBRATION OF CONTAINING STRUCTURES BY SOUND IN CONTAINED FLUID

A system which consists of a rigid rectangular box with one simply-supported flexible wall is analysed by numerical and statistical methods for the internal acousto-structural mode coupling factors and the corresponding modal average radiation efficiency. A lower limiting frequency is found above which the subcritical radiation efficiency is equal to that of a baffled panel radiating into free-field conditions but below which the radiation efficiency falls below the free-field values. This limit is important practically in the cases of small box volumes and gases of high sound speed. At supercritical frequencies, a value of radiation efficiency half that of a freely radiating panel is found. Measurements have confirmed the existence of the lower limiting frequency. It has also been observed in the case of a cylinder. Corrections to the normal statistical energy response and radiation equations are presented which take into account the fact that it may not be assumed, purely on the basis of modal density ratio considerations, that many acoustic modes couple with an individual structural mode. © 1969.