Lamb and Creeping Waves Around Submerged Spherical Shells Resonantly Excited bySound Scattering. 2: Further Applications

摘要

Analysis is based on a methodology proposed that uses the three-dimensionalequations of dynamic elasticity to describe shell motions and to predict its sonar scattering cross section. This is valid at all frequencies, for shells of any thickness, (constant) curvature, and it accounts for their fluid-loaded condition. It is used to predict the cross sections, which are later interpreted on the basis of the various resonance features that manifest themselves in the frequency response. The spectral locations of the resonances depend on various types of elastic waves propagating along the shell, or in surrounding fluid. Exact plots are generated for phase velocities of these (lamb) waves always accounting for curvature and fluid-loading effects present on the shell, without appeals to plate waves or theories. Some dispersion plots were generated using the Donnell Shell-Theory approximation, which seems to yield accurate results up to the coincidence frequency. Aside from the broad resonance lobe present at the coincidence frequency, there is another high-frequency resonance lobe, due to a thickness-resonance response curve for a thin shell, around its coincidence frequency, serves to identify origins of the various types of observed resonance features and relate them to elastic and acoustic waves that propagate along the shell or outer fluid. Many computer-generated graphs are displayed to illustrate these points.