Acoustic Harmonic and Transient Response of Fluid - Shells of Revolution.

This study deals with the harmonic and transient response of fluid loaded shells of revolution. A general approach is presented to evaluate the vibratory response and pressure field of fluid loaded shells of revolution which are excited by mechanical forces or acoustic incident waves. The approach is based on the use of an in vacuo modal expansion of the velocity of the shell and the mechanical or pressure excitation. The acoustic pressure on the vibrator is expressed as a modal expansion in which each modal pressure is a sum of modal velocities combined with self- and interaction modal radiation impulse responses. A new internal source density method is developed for calculating the acoustic self and interaction radiation impedance and impulse responses. A set of algebraic equations is developed for computing the vibratory response of fluid loaded shells of revolution which are excited by harmonic forces. These equations include modal coupling via the use of mode dependent mechanical impedances and acoustic impedances. These frequency dependent coupled equations are solved by using the matrix inverse method. A time dependent in vacuo modal vector method is developed to compute the transient response of fluid loaded shells of revolution. A set of time dependent coupled convolution integral equations is developed for the case of elastic spherical shells. A second set of general coupled convolution integral equations is then developed for the general case of fluid loaded shells of revolution. These equations are based on the use of acoustic self- and interaction modal radiation impulse responses. Both sets of coupled convolution integral equations are solved by the marching forward in time technique. Several numerical results are presented to illustrate the methods and determine the characteristics of acoustic radiation and scattering from fluid loaded shells of revolution. The source density distributions and acoustic modal radiation impedances of shells of revolution are presented. The velocity response and associated pressure are also presented to illustrate the characteristics of modal coupling for vibrating shells of revolution. Finally, the acoustic transient interaction of an incident acoustic wave and an elastic shell of revolution is illustrated through several examples.