An investigation of the acoustic properties of vibrating finite cylinders

Abstract

To aid in the preliminary design, or in the trouble-shooting of acoustically radiating cylindrical structures, there exist few analytical approximations for finite length cylinders, or exact solutions for infinite length cylinders. In this work a flexible acoustic radiator model is implemented that can encompass a wide range of finite cylinder geometries subject to various modes of vibration. The boundary element method is applied to an integral form of the Helmholtz equation. The efficiency and accuracy of the analysis is enhanced by employing a quadratic isoparameteric element discretization of the radiating surface. Velocity profile inputs to the acoustic model include profiles generated from both rigid body and flexural motion types. Results from all of the velocity profiles examined in this work indicate strong radiating abilities for frequencies of vibration where the acoustic wavelength is less than approximately one-sixth the cylinder radius. In the low-frequency region, the effectiveness of the radiator is found to be related to the complexity of the applied velocity profile. The trends observed in the present numerical solutions agree well with those of previous work. An experimental verification of the modelling procedure has been carried out. In accordance with the modal analysis testing technique, velocity profiles were experimentally determined and used as boundary conditions to the numerical acoustic model. Measurements of the actual far-field acoustic pressure compare well with the results predicted from the numerical modelling.