Structural-acoustic sensitivity analysis of propulsion system parameters for a coupled FE/BE model of a submarine

An important cause of low frequency submarine noise is rotation of the propeller in a nonuniform wake, resulting in fluctuations in the thrust. The propeller transmits forces to the submarine hull via the propeller shaft and the fluid, as well as directly radiating sound. The forces excite hull resonances, leading to high sound radiation levels at the natural frequencies of the hull and the propeller shafting system. The axial forces that are transmitted to the hull via the shaft can be addressed by a vibration attenuation device known as a resonance changer (RC). The RC is implemented in the propulsion system. For optimisation of the RC parameters, a simplified model of a submarine hull has been developed, where the structure is represented using finite elements and the fluid domain is represented using boundary elements, respectively. Gradient based optimisation techniques have been used and a sensitivity analysis based on the adjoint operator has been implemented.