Modal coupling in the vibro-acoustic responses of submerged spherical-cylindrical-spherical shells stiffened by ribs and plates

This article presents a modal decomposition method for the analysis of radiated sound power of coupled shell structures submerged in infinite heavy fluid. This method provides greater physical insight into the self- and mutual-modal radiations of the in-vacuo modes. The corresponding cross-modal radiation efficiency is defined and formulated to analyze the mechanism of the energy transfer among the structural modes. A fully coupled finite element/boundary element model is developed for a simplified submarine hull, which is composed of a coupled sphericalcylindrical-spherical shell and a series of ring stiffeners and bulkheads. The interactions of different circumferential modes of the hull are examined. Modal coupling among the n = 1 grouped modes (including rigid body modes) is carried out to reveal the cross-modal coupling characteristics of the modes in the axial direction. In addition to the cross-modal radiation efficiencies, modal sound directivity is employed to show the physical mechanism of the modal coupling. The effects of apparent relative mass on the modal coupling are also investigated.