THE EFFECT OF SUBSTRUCTURES ON THE ACOUSTIC RADIATION FROM AXISYMMETRICAL SHELLS OF FINITE-LENGTH

A modal-based method is developed to analyze the acoustic radiation of shells of finite length with internal substructures subjected to time -harmonic loads. In this method, a variational principle is used to de termine the relationship between the distribution of velocity and pres sure over the surface of the shell, and Lagrange multipliers are used to account for the interaction forces from the substructure motion. To identify the dominant physical characteristics of the fluid/shell/sub structure response, a singularity decomposition is introduced. This de composition uses the singular points of the response in complex wave-n umber space that are closest to the real axis. The response contributi ons from these singular points are found to be highly fluctuating, yet analytically simple functions of frequency. The remaining or residual response is a slowly varying function of frequency. To reduce computa tional effort, the singularity decomposition is combined with a freque ncy window method. The method is demonstrated for a cylindrical shell with elastic, hemispherical endcaps and internal circular panels. The effects of the substructure are illustrated by comparing the response of the shell/substructure system with corresponding results for an emp ty shell. It is shown that the substructures can significantly alter t he near- and far-field acoustic response.