Hybrid ray‐mode resonance system format for the acoustic response of submerged structures

Abstract

Many submerged structures of interest are comprised of elastic shells with attached loadings and/or substructures. In the midfrequency range, traveling waves in shell segments between loads, and also in substructures, may become important, whereas complex loadings as such may be better characterized in terms of their modal resonances. This motivates the formulation of a self‐consistent hybrid ray‐(traveling mode)‐resonance system that highlights the physical wave phenomena responsible for synthesizing the interactive fluid‐structure acoustic response. Such an observable‐based parametrization (OBP) generalizes the conventional approach based on modal resonances alone and reorganizes resonances compactly into propagators where these predominate. The OBP format for cw and transient excitation is illustrated on the example of an aperture‐coupled ring‐waveguide cavity in a rigid cylindrical baffle developed originally for electromagnetic radar scattering where the method was first applied [L.B. Felsen and G. Vecchi, IEEE Trans. Antennas Propag. (in press)]. Especially in the time domain, where successive early interactions are resolved by arrival times whereas later interactions are reconstituted as resonances, the ability of OBP to identify the physical observables is clearly evident. Similar behavior characterizes sound scattering from a submerged spherical elastic shell. [Work supported by ONR.]