ASA 126th Meeting Denver 1993 October 4-8

4pSA1. Convolution formulation of leaky wave contributions to scattering by plates and by cylinders and shells of variable curvature.

P. L. Marston

Appl. Res. Lab., Univ. of Texas, Austin, TX 78713-8029 and Phys. Dept., Washington State Univ., Pullman, WA 99164-2814

A novel high-frequency formulation is investigated that approximates the leaky wave amplitude at the scatterer in terms of a spatial convolution of the local incident wave pressure and a one-sided line response function h(s(greater than or equal to)0)=-j(alpha) exp(-(alpha)s+ik[sub l]s). Here, s is the propagation distance along the flat or curved surface, (alpha) is the reciprocal of the attenuation length, k[sub l] the real part of the wave number, and j=1 for equal fluid loading on both sides of a plate but j=2 for one-sided fluid loading of a shell or for Rayleigh waves on a solid. Application to plane waves incident on cylindrical surfaces (empty shell or solid) of slowly varying curvature yields the following far-field amplitude from a leaky ray propagating a distance S on the surface: p[sub l]=-2(alpha)p[sub inc](2(pi)a[sub 1]a[sub 2]/ kr)[sup 1/2] exp(-(alpha)S+i(pi)/4+i(eta)), where a[sub 1] and a[sub 2] are the radii of curvature at the launching and detachment regions and (eta) is a geometrical phase accumulation. When a[sub 1]=a[sub 2], the coupling coefficient G[sub l] for a circular cylinder derived previously is recovered. The result can be modified to situations where (alpha) varies weakly with curvature. [Work supported by ARL:UTIR&D Program and by ONR.]