Acoustic scattering from fluid-loaded elastic shells: A Gaussian beam approach

A new method is described for computing the acoustic far field scattered by a submerged smooth elastic thin shell. The total field is split into a sum of specular and leaky wave contributions. The latter arise from weakly radiating membrane waves that propagate globally over the structure, and are the focus of this work. The scattered leaky wave field is expressed, via a surface Helmholtz integral, as the sum of integrals along a finite number of Gaussian beams. The integral on each beam is then approximated as a line integral along the central ray of the beam. Finally, the far-field contribution from each line integral is reduced to a sum of stationary phase contributions. The derived asymptotic expression for the leaky wave field is uniformly valid for all observation directions. Difficulties associated with caustics and two-point ray tracing do not arise in the present formalism. A test of the method for a spherical shell shows that the numerical results agree well with the exact solution and the pure ray solution for kfa> 10, where kf is the fluid wave number.