Vibration of Containing Structures by Sound in the Contained Fluid

Abstract

A system which consists of a rigid rectangular box with one simply supported flexible wall is analyzed by numerical and statistical methods for the internal acoustostructural mode coupling factors and the corresponding modal average radiation efficiency. It is found that for subcritical frequencies, but above a frequency which corresponds to the lower limit for maximum proximate mode coupling, the radiation efficiency is equal to that of a baffled panel radiating into a free field. At supercritical frequencies a value of radiation efficiency half that of a freely radiating panel is found. Below the limiting frequency an approximate dependence upon (f/fc )3 is found experimentally in all cases. The same type of behavior has been observed with an internally excited, partically closed cylinder. The radiation efficiency of a clamped panel is calculated to be about 3 db greater than that of the simply supported panel at low frequencies. This factor falls to zero at the critical frequency and above. 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.