Vibroacoustic noise estimation of a combined elastic submarine-propeller system subjected to the self-propulsion conditions

The radiated sound from an underwater structure is primarily due to the flow about the body and vibrations of the body, whether the exciting mechanism is the propulsion system, external flow, or any mechanical component. The current study covers a particular instance of the complete acoustic radiation problem that the structure-borne noise radiated from a combined system of submarine model and its elastic propeller is investigated by considering the self-propulsion conditions. The selected models for the application are the DARPA-SUBOFF submarine and INSEAN E1617 propeller. The analysis procedure involves adopting a set of numerical methods to capture different aspects of the problem. Accordingly, the unsteady computational fluid dynamics (CFD-URANSE) is applied to express the propeller excitation, the finite element analysis is adopted to represent the dynamic characteristics of the combined elastic system, and the boundary element method is employed to assess the radiated noise resulting from the structural vibrations. The dynamic response of the elastic system, hence the fluid-structure, are described in the modal space, and the acoustic radiation is computed as the superposition of modal noise components. In the application, the low-frequency band 10-250 Hz is spanned and the noise prediction, in terms of sound pressure level, is presented as directivity patterns and surface distributions. The influence of flexibility of propeller blades is also assessed through a comparison with the results obtained for rigid propeller.