Numerical prediction of propeller excited acoustic response of submarine structure based on CFD, FEM and BEM

Abstract

A mesh-less Refined Integral Algorithm (RIA) of Boundary Element Method (BEM) is proposed to accurately solve the Helmholtz Integral Equation (HIE). The convergence behavior and the practicability of the method are validated. Computational Fluid Dynamics (CFD), Finite Element Method (FEM) and RIA are used to predict the propeller excited underwater noise of the submarine hull structure. Firstly the propeller and submarine's flows are independently validated, then the self propulsion of the “submarine+propeller” system is simulated via CFD and the balanced point of the system is determined as well as the self propulsion factors. Secondly, the transient response of the “submarine + propeller” system is analyzed at the balanced point, and the propeller thrust and torque excitations are calculated. Thirdly the thrust and the torque excitations of the propeller are loaded on the submarine, respectively, to calculate the acoustic response, and the sound power and the main peak frequencies are obtained. Results show that: (1) the thrust mainly excites the submarine axial mode and the high frequency area appears at the two conical-type ends, while the torque mainly excites the circumferential mode and the high frequency area appears at the broadside of the cylindrical section, but with rather smaller sound power and radiation efficiency than the former, (2) the main sound source appears at BPF and 2BPF and comes from the harmonic propeller excitations. So, the main attention should be paid on the thrust excitation control for the sound reduction of the propeller excited submarine structure.