No.710 R D Institute,CSSC,Yichang 44300,China
An analytical method is proposed to study the far-field acoustic characteristics of a finite harmonic vibrating cylinder close to the free surface. Firstly, based on the Image method, the influence of free liquid level is taken into account with a hypothetical virtual source. Then, combined with the Graf’s addition theorem, the sound pressure items of virtual and real sources are combined and converted into wavenumber domain to obtain a simple expression of sound pressure. Finally, the important index, the far-field radiated sound pressure, can be obtained by the Stationary phase method. Two kinds of mathematical physical models are established to deeply research the mechanism of acoustic scattering between the free surface and the structural surface. The results show that the influence of free liquid level can be summarized as the acoustic dipole, which has significant influence on the calculated results of radiated and scattered sound, but there are phase differences that can not be ignored except for similar propagation laws. The scattered sound pressure decreases at a fixed rate with increasing number of times, and the attenuation rate is proportional to the submergence depth of the cylindrical shell, but inversely proportional to the excitation frequency of the resonance vibration on the shell surface.