NEAR-FIELD RAY ACOUSTIC RESPONSE OF SUBMERGED ELASTIC SPHERICAL-SHELLS

The presence of conspicuous penumbra regions in near-field wave scatte ring renders asymptotic treatment of ray integrals-by Fock's theory, f or instance-extremely involved, especially for elastic shell-fluid bou ndary conditions. A modified ray acoustic model that avoids these intr icacies as well as these associated with reflected-leaky wave transiti on regions has recently been proposed, and proved very accurate at mod erate and high frequencies for the thin cylindrical shell prototype [J . M. Ho, J. Acoust. Sec. Am. 96, 515-524 (1994)]. Following this appro ach, this paper discusses the ray synthesis of the on- and off-surface acoustic response of a submerged empty thin spherical shell insonifie d by an acoustic plane wave. In particular, the two spectral integrals that would yield the incident and reflected ray fields by saddle poin t reductions are combined into a single integral representing the modi fied geometrical acoustics field, which may be so rearranged that it i s merely the continuum form of the discrete (normal mode series) solut ion for the total field, thereby facilitating its numerical implementa tion. The complementary leaky compressional wave fields are described by spectral integrals characterizing multiple guided wave circumnaviga tions around the shell and are evaluated by residue calculus as usual. It is shown through extensive numerical results that, for the thin sp herical shell, the modified ray algorithm also accurately reconstructs the acoustic near field in the entire latitudinal domain provided ka greater than or equal to 1 or so (where k is the fluid acoustic wave n umber and a is the shell mean radius).