Vibrations of a framed cylindrical shell submerged in and filled with acoustic fluids: Spectral solution

Abstract

A spectral solution to the problem of radiation from a submerged cylindrical shell stiffened by circumferential frames is presented. The model assumes ‘diaphragm’ are modeled as discrete rings, arbitrary in number and placement within the shell. In addition, the analysis allows for the shell to be filled with, and submerged in, different acoustic fluids. Fluid loading on the shell is computed as if the finite shell response was periodically extended to infinity along a cylindrical baffle. In contrast the far field radiation associated with the shell vibrations is obtained by embedding it in an infinite cylindrical rigid baffle. The analysis is illustrated for a thin steel shell in water, stiffened with an array of discrete frames and driven by a radially oriented point force. Calculations of the drive point response of the shell and the attenuation rate of vibrations with axial distance from the drive are presented showing the effects of fluid loading and the framing array. In addition the axial wavenumber spectrum of the near field pressure is computed as a function of stand off distance from the shell with and without frames. The subsonic components of the spectrum are shown to be dominated by exponentially decaying (evanescent) flexural waves while the supersonic, or radiating components exhibit only geometric spreading.