Similarities between Various Lamb Waves in Submerged Spherical Shells, and Rayleigh Waves in Elastic Spheres and Flat Half-Spaces
NAVAL OCEANOGRAPHIC AND ATMOSPHERIC RESEARCH LAB STENNIS SPACE CENTER MS
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A variety of resonance features are studied in the back-scattering cross sections BSCS of an air-filled metal spherical shell submerged in water and insonified by a plane cw sound wave. Rayleigh R and whispering gallery WG waves were originally investigated for vibrational purposes for flat half-spaces in contact with vacuum. Lamb waves were originally studied in flat plates also in contact with vacuum. These old findings are generalized to the cases of an elastic spherical shell o.d.i.d.2a2b fluid-loaded on both surfaces, and excited by an incident plane wave. The various leaky-type Lamb waves present in the shell are shown to reduce to the earlier RWG waves as a much 1 much b and p sub f approaches 0. The manner in which each one of the various shell waves manifests itself in the various frequency bands of the shells BSCS as perceived by a remote sensor is also studied. Dispersion plots for the various phase velocities of the various waves are displayed in very wide i.e., 0ka500 bands, and a number of analogies between Lamb and RWG waves are obtained as the submerged shell becomes a solid sphere b much a, and vice versa bora. The fluid loadings, the finite thickness, and the curvatures of the structure all generate novel types of waves in the shell that manifest their effects in its BSCS that could have never emerged from earlier models that ignored these effects, and which are analyzed here.