Vibration and radiation characteristics of partially submerged plates

While studying the underwater acoustic radiation problem, the fluid is usually assumed to be infinite; yet, most marine structures are only partially submerged in water, suggesting that the free surface effect should not be ignored. In this paper, the free surface effect is simulated with an anti-symmetric plane set. The vibration and sound radiation characteristics of partially submerged cantilever plates are analyzed by employing the finite element method combined with the indirect boundary element method. The natural frequencies and mode shapes of the cantilever plate at different immersion depths are first obtained and compared with the actual data, which validates the proposed method. Then, the half-immersed plate's vibro-acoustic characteristics are calculated, on which the impact of different load positions and immersion depths is discussed as well. It is observed that the natural frequency of the immersed plate decreases with the increase of the immersion depth. Also, the load position would influence the sound power level of the plate, and the exact influence is related to the frequency. Plus, the plate's sound power level increases with the increase of the immersion depth, and the peak of acoustic radiation power curve tend to move toward low frequency range as the immersion depth rises.