Elastic wave contributions in high-resolution acoustic images of fluid-filled, finite cylindrical shells in water

Abstract

Recent studies of plane wave scattering by finite, evacuated cylindrical shells at oblique incidence describe monostatic echo contributions from surface elastic waves. These waves follow helical paths along the shell’s surface and are guided back in the source direction after reflection from the cylinder truncation. The present research examines similar effects viewed in the time signature of a high-resolution acoustic imaging system. The experimental technique utilizes a narrow beam consisting of a short tone burst to probe a cylindrical shell along its axis of symmetry. The echo returns contain information which yields insight into local scattering processes at the impedance discontinuities of the finite scatterer. The cylindrical shell has a thickness-to-radius ratio h/a=5.5%. It is immersed in water and is subject to both exterior and interior fluid loading. Prominent artifacts are shown to coincide with near axial coincidence of the s0 and a0 Lamb waves. The echo contributions are extremely sensitive to the angle of incidence and interior fluid loading. By placing small ‘‘cuts’’ along the cylinder, it is possible to mimic the truncation effects for different scattering processes.