Directional characteristics of conformal transducers on fluid loaded elastic shells

Abstract

A general analytic approach is presented to evaluate the directional characteristics of conformal velocity sources representing transducers on fluid loaded elastic shells. The sources/transducers are assumed to be structurally decoupled from the shell but are coupled to the shell via the fluid. The pressure field is expressed via superposition as the sum of the pressure field from the sources on a rigid shell plus the pressure field from the elastic shell assuming zero normal velocity for the sources. An in vacuo eigenvector expansion is used to describe the velocity field of the shell. The modal coefficients of the expansion for the shell are related shells via a set of linear algebraic equations to the modal coefficients of a different expansion for the surface pressure due to the sources on the rigid shell. Shadowing effects of the sources on the response of the shell are included in the formulation. Numerical results for the directional characteristics of specified circular velocity sources on rigid and elastic spherical shells are presented as a special case. The results illustrate the effects of diffraction and shell resonances on the directional characteristics of the sources in the low, mid, and high frequency regions. [Work supported by ONR.]