Acoustic and elastic wave scattering from elliptic-cylindrical shells

Abstract

An acoustic scattering formulation has been derived from a modification of the extended boundary integral method (null-field approach) developed for elastic wave scattering from infinite cylindrical shells of arbitrary shape. Thin shell theory is assumed to describe the motion of the scatterer. Acoustic and elastic p-p wave scattering calculations are presented for elliptic-cylindrical shells of different materials and eccentricities. At low frequencies, the scattering by an elliptical shell in a fluid is dominated by the bending resonances. At higher frequencies, the acoustic scattering is strongly dependent on the angle of incidence, material characteristics, and the predominately extensional structural resonances. In an elastic material, resonant modal responses of the shell were found to increase mode conversion of dilatational waves into shear waves. By comparison with elasticity theory for shells and by extrapolations from thin and thick plate theories, the limitations of the thin shell theory are shown to be material dependent. The present method is used to re-examine examples of backscatter from elliptic-cylindrical shells reported in other studies.