Effects of non-axisymmetric structures on vibro-acoustic signatures of a submerged vessel subject to propeller forces

Wave localization effects of concentrated mass in a cylindrical shell at high frequencies have been proved to increase the sound radiation of the shell, but the effects of non-axisymmetric substructures on the low-frequency vibro-acoustic responses of a propeller-shafting-hull system are more complicated due to the strong coupling between the propulsion system and the hull. To investigate the influences of the non-axisymmetric substructures on the structural and acoustic behaviors of submerged vessels, fully coupled finite element/boundary element models are developed for vessels with/without added mass and keel. The propeller-shafting system is connected to the pressure hull of the vessel through an irregularly shaped foundation. Large-scale underwater vibro-acoustic experiments are performed, and the numerical solutions are verified by the experimental results. The physical insight into the effects of the substructures on the acoustic responses of the propeller-shafting-hull system are discussed by examining the normal velocity distribution of the hull in the wavenumber space and the modal contributions of the modes of the substructures to the vibro-acoustic responses of the system. A passive control method is proposed to efficiently suppress the structural and acoustic responses of the system under both axial and lateral propeller excitations.