Resonant response of complex shell structures

Resonances of shell structures play a prominent role in determining their acoustic characteristics. Among the most important of such characteristics are radiated noise, scattering, and self-noise levels. The nature of the structural resonances, for example the number of modes within a particular frequency band or the overall spatial dependence of the response, determines the importance of these phenomena in various contexts and what steps may be taken to modify their acoustic impact. In the past, knowledge of the resonant response of highly idealized systems has been used to guide the development of quiet platforms. The results of a scale model investigation of the effects of increased complexity on the nature of the resonances of submerged shell structures are reported. Effects presented here are flexural Bloch mode resonances, localized resonances resulting from structural irregularity, and the effects of non-axisymmetry on these phenomena. The implications of these results on acoustic design and the development of systems is discussed.