Ray acoustic formulation of sound wave scattering from submerged cylindrical thin elastic shells with endcaps.

Abstract

Cylindrical shells with endcaps of various types are useful prototypes for a class of submerged elastic structures of current interest period. In the mid- and high-frequency ranges (ka≳3, where ‘‘a’’ is the radius of the cylinder), ray acoustics offers a physical-based methodology for computing the scattered signature. Restricted to thin shell dynamics, hemispherically capped cylinders are investigated by combining results from our previous studies of infinite cylindrical and full spherical shells [Felsen etal., J. Acoust. Soc. Am. 87, 554–569 (1990); J. M. Ho and L. B. Felsen, J. Acoust. Soc. Am. 88, 2389–2414 (1990)]. Rays from arbitrarily incident plane waves are traced to the cylinder and give rise there to geometrically reflected and phase matched shell guided supersonic wavefields, each with its own distinct trajectories. The surface guided fields follow helical paths on the cylindrical portion, which are smoothly matched to great circle paths on the hemispheres, and are turned back there toward the cylinder at a pitch-dependent caustic. The total field is synthesized by the sum of all possible ray paths, traversing the structure azimuthally and longitudinally, which reach the observer. Quantitative expressions are obtained by including ray field launching, detachment, and propagation coefficients. Attention is also given to conical endcaps and to conical sections with smoothly joined spherical caps. [Work supported by ONR.]