Numerical study on vibration characteristics of the underwater partially fluid-filled cylindrical shell

Abstract

The structural finite element coupled with acoustic finite element method is employed to study the vibration characteristics of an underwater partially water-filled cylindrical shell. Taking the underwater cylindrical shell without internal fluid for example, the natural frequency and vibration response of the shell are calculated with the numerical method. The analytical results of the model are also presented to illustrate the accuracy of the numerical method. Then by changing the depth of the internal fluid, the effects of internal fluid on the vibration characteristics of the underwater shells are analyzed. And the effects of the direction and location of the applied loads on the sound radiation as well as the forced vibration are discussed. The results show that the internal liquid has influences on the vibration characteristics and the sound radiation of the system, which leads to complicated mode shapes for the partial interaction between the internal liquid with the shell. When the depth of the internal liquid increases, the natural frequency of the coupled structure decreases, and the vibration mode becomes irregular. For the forced vibration, the response is maximum when radial excitation is applied at a location where the shell isn’t coupled to the internal fluid. The peak of the curve shifts to the lower frequency as the depth of the internal liquid increases.