14. Fundamental Studies on Underwater Sound Radiated from a Vibrating Ship Hull

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Recent development of underwater acoustic devices causes a need to study the underwater sound radiated from a ship. Such underwater sound has, two subjects, one is pure radiation due to the ship hull vibration excited by the engine and the other is scattering due to the ship hull vibration excited by incident acoustic wave. In the present report, first we discuss the mutual coupled interaction between the ship hull vibration and the surrounding acoustic field including the effect of free water surface under time harmonic exciting force. Then we introduce the reciprocal theorem of velocity potential, and expand the theorem into the reciprocity of sound radiation and scattering problem. Secondly, we discuss an analytical approach in order to study the fundamental characteristics of the sound from the ship, solving a 2-dimensional semi-submerged circular cylindrical shell. Thirdly, we discuss a numerical approach in order to study the sound properties from the arbitrary hull shape, proposing a method of numerical analysis with F. E. M, for the vibration of structure and B. E. M. for the sound in a fluid. As an numerical example, we calculate the problem of the 2-dimentional circular shell, compare the numerical solutions with the analytical approach, and show a good agreement between them. Then we demonstrate the reciprocity between the radiation and the scattering sound problem.
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