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