Energy-averaged method for ship mechanical noise prediction under kinematic excitation in the full frequency domain

Abstract

Mechanical noise plays a key role in ship acoustic performance design as an important component of underwater sound radiation. In this paper, a numerical method for predicting ship mechanical noise, energy-averaged method, is proposed considering coupling mechanism, numerical model and kinematic excitation in full frequencies. In the method, vibroacoustic BEM coupling equations are established by the equivalent generalized force converted from kinematic loads based on the energy-averaged method in low-mid frequencies, and the vibroacoustic transfer functions obtained by SEA are modified in high frequencies, which can reduce computational errors resulting from an offset of natural frequency between a numerical model and a real structure, kinematic loads with incomplete information, and pathological matrices. The accuracy and reliability of the energy-averaged method are verified by the hydroacoustic experiments. The simulated and experimental results are comprehensively evaluated by overall errors, correlation coefficients, and standard deviations. The errors between the simulation and the experiment are 0.75 dB, 0.51 dB, and 1.21 dB in different frequency regions for the shaker case, respectively, while those are 0.41 dB and 0.82 dB in the different diesel engine cases. Additionally, the phenomenon of acoustic cavity resonances cannot be neglected in low frequencies, and the acoustic cavity must be modelled to predict mechanical noise.