An inversion approach based on multiple-aspect resonance analysis of finite cylindrical shells in water

Abstract

Inverse scattering of fluid-loaded, elastic, thin-walled cylindrical shells is addressed by multiple-aspect resonance analysis. A set of aspect-dependent acoustic phenomena is selected from membrane wave and resonance scattering theories, which are expected to be backscattered by fluid-filled or empty thin-walled shells and to give rise to resonance phenomena in the ka range (1,50). The features selected are from spatial axial modes, and Lamb-type, Scholte–Stoneley, and shear helical waves. The last three wave families are significant only over a small range of target aspects near broadside, with the width of this range depending on shell properties. Approximate equations are formulated relating resonance behavior in the aspect-frequency domain, to target parameters such as shell outer radius, thickness, length, and material. The inverse methodology is validated on experimental data from a steel cylindrical shell with flat end-caps, filled with air or water and suspended in the water column. The target was continuously rotated on the plane of its longitudinal axis while insonified by broadband pulses. Good agreement between theory and experiment encourages the extension of the approach to more complex scatterers for classification purposes. [Work partially supported by EC (MAST DEO project).]