ASA 129th Meeting - Washington, DC - 1995 May 30 .. Jun 06

5pUW10. Sound scattering by a fluid-filled cylindrical shell in water.

Gregory Kaduchak

Charles M. Loeffler

Appl. Res. Labs., Univ. of Texas, P.O. Box 8029, Austin, TX 78713-8029

Previous calculations and observations of backscattering by cylindrical shells in water usually involve shells which are either empty or subject to extremely light interior loading conditions such as air. Typical echo signatures display distinct contributions described by specular reflection and guided waves launched along the shell structure. The present research analyzes the backscattering effects as a consequence of filling the interior cavity with a higher impedance fluid such as water. Energy transferred into the cavity couples into radiation mechanisms which drastically increase the fine structure in the backscattering form function. Dispersion curves derived from full 3-D elasticity theory via the Watson transform methodology display a complicated mode structure which is a combination of the guided waves found on a cylindrical shell in vacuum and the normal modes of a fluid-filled cylindrical cavity satisfying rigid boundary conditions. The radiation damping of the associated curves yields insight into mechanisms of energy transfer to and from the internal cavity through the guided Lamb waves traveling along the shell. The cylindrical shells studied are excited by plane waves at normal incidence and have radius to thickness ratios of 5% and 10%.