Active vibration isolation and underwater sound radiation control

Abstract

Active vibration isolation and underwater sound radiation of structures are presented to investigate issues relevant to vibration control and far-field sound radiation of underwater structures. Finite element method (FEM) and boundary element method (BEM) are combined to model fluid–structure coupled systems. In the modeling of fluid–structure interaction, mode truncation and inertial coupling between fluid and structures are applied to sufficiently reduce model order. Moreover, the added mass matrix of fluid is modified to increase the accuracy of computation of natural frequencies of the coupled system. The modeling approach is presented especially for constructing time-domain models, which are inherently more suitable for exploring active control strategies than frequency-domain models for complicated and especially nonlinear systems. Adaptive control with two different weight updating algorithms is discussed. One is based on the local vibration and the other on the summed vibration. In the simulation example, a model of two degrees of freedom connected to a rigidly baffled plate with stiffeners is used to demonstrate the difference between active isolation of vibration and the suppression of far-field sound radiation, and it is demonstrated that suppression of summed vibration can result in smaller sound radiation than the suppression of local vibration only.