Excitation of finite and infinite length cylindrical shells by internal sound fields

Abstract

Cylindrical shells, such as industrial piping system components, are efficiently excited by broadband internal noise at discrete frequencies below the ring frequency. Two types of excitation are recognized: finite length pipe resonances that are visible in short pipes, and coincident excitation that has been studied for long or anechoically terminated pipes. Both mechanisms occur to varying degrees in pipes of any length, and both require that the acoustic and structural wavenumbers be closely (or exactly) matched. Because ducts possess an infinite number of potential coincidence frequencies, coincidence transmission (i.e., precisely matched wavenumbers) is dominant in pipes. In the limit for long shells, both mechanisms are damping controlled and approach the same levels. Experimental data for short and intermediate shells show that coincidence transmission (“infinite shell”) can be the sole cause of vibration over wide frequency bands where the density of resonant modes is low. A simple theory is used to predict the frequency and amplitude of response peaks caused by both mechanisms. [Work supported by NSF.]