Observable‐based hybrid ray‐mode‐resonance system parametrization of acoustic scattering by a finite submerged steel plate

Abstract

Numerical finite difference data for pulse scattering by a submerged steel plate of finite width, when processed in the slowness‐time domain [J. R. Fricke and A. B. Baggeroer, J. Acoust. Soc. Am. Suppl. 1 88, S51 (1990)], reveals distinct features related to the longitudinal and flexural modes in the plate, their excitation by, and conversion to, edge‐diffracted fields in the fluid, and other wave‐oriented observables. By an observable‐based parametrization (OBP), the problem is phrased here systematically and phenomenologically in terms of ray fields, traveling mode fields, edge coupling matrices, resonances, etc., to build up a self‐consistent OBP system format for quantitative prediction. Determination of the elements in the coupling matrices poses a set of canonical problems that can be addressed analytically under highly simplified conditions but must generally be done numerically or by experiment. For the very specialized case of a thin plate under heavy fluid loading, the plate supports only one subsonic wave, and single‐edge diffraction has been evaluated analytically [D. C. Crighton and D. Innes, Philos. Trans. R. Soc. London Ser. A 312, 291–341 (1984)]. This solution has been employed in the OBP algorithm to synthesize and compute the far‐field acoustic response to on‐plate line force excitation of a finite strip. The result is compared with a differently synthesized solution by Crighton. [Work supported by ONR.]