Diffuse waves on submerged thin shells

A statistical energy method is proposed for the calculation of the acoustic power and radiation pattern shed from diffusely vibrating thin-walled submerged shells. It is presumed that, at frequencies below coincidence where flexural waves cannot efficiently radiate into the fluid, radiation is dominated by the weakly fluid-coupled longitudinal and shear waves, which couple to the fluid by means of curvature and the Poisson effect. Assumed equipartition of acoustic energy amongst flexural, shear and extensional modes, and eikonal approximation calculations of the radiation rate from each mode type results in estimates for the diffuse radiation rate from a submerged shell. These rates are found to be largely independent of details of the structure and are very small, with loss tangents (Im{ω}/Re{ω}) of the order of 10^–4. This is contrasted with the much larger loss tangents which are obtained at frequencies above coincidence.