Ray acoustic fields of submerged thin elastic shells under on- and off-surface source excitation: The cylindrical prototype

Abstract

The ray-acoustic formulation developed previously for a thin elastic cylindrical shell [Felsen etal., J. Acoust. Soc. Am. 87, 554–569 (1990)] is subject to extensive numerical tests for both on- and off-surface sources, i.e., plane waves, which incidence may be normal or oblique to the axis of cylinder, and phased line sources located on or near the shell surface. The Fresnel transition function is employed to account for the saddle point-near-pole effect which arises when the incidence angle is close to the mode angle. As functions of frequency, the amplitude and phase of the pressure field are computed in the range of κa=2 to 50, where κ is the transverse component of the acoustic wavenumber and a is the shell radius, at particular observation angles; whereas the field pattern, parametrized by κa, is established along the azimuthal direction. The ray field agrees well with the reference solution (normal modes) in both cases. Furthermore, the constituent ray-acoustic components, especially shell-guided modes of different types such as compressional and shear waves, are also shown individually so as to identify their imprint on the total field, and the coupling coefficients for the supersonic leaky and subsonic trapped flexural waves are numerically compared, thus quantifying the excitation mechanisms of structural waves.