Analysis on near-field vibroacoustic characteristics of the underwater cylindrical shells with WNFS

The surface vibration velocities and near-field pressure of the underwater cylindrical shell, which are excited by external force, were calculated using wave propagation method. In fact, the main goal is to explore the measures to suppress vibration of structure and near-field radiation noise. The wave number frequency spectrum method that combined the vibration wave number with the frequency domain method can be applied for the analysis of wave propagation in shell structures; based on the method and calculated results, the wave propagation spatial characteristics of vibration and near-field acoustic radiation of the underwater cylindrical shell were also analyzed. It is shown that there are three waves in cylindrical shell: flexural wave, shear wave, and extended wave; the first two belong to transversal wave, while the last belongs to longitudinal wave, and the wave propagation directions and velocities are all obtained. Near-field radiation sound waves are more complex than in surface acoustic field. In isotropic solid medium, wave numbers of the same type of waves at one frequency are the same. In order to reduce the vibration and noise, the dampers should be installed in the direction of wave propagation, and the types of dampers are determined by the wave propagation velocities. This work will give some guidelines for vibration and noise reduction of this kind of shells.