Dynamic analysis of an annular cavity: Criteria for the selection of the modal basis

The study of the dynamic behavior of a structure coupled with a light fluid and excited by an external harmonic mechanical force needs a good understa nding of the interaction between the solid and the fluid. As the fluid is n ot directly excited, the dynamic response of the fluid in the cavity depend s only on the reciprocal influence of both media. This paper quantifies the fluid-structure interaction, as function of both the modal spatial coincid ence between the solid and the fluid, and the frequency coincidence of the natural frequencies of both media with respect to the excitation frequency of the force. A simple method of comparison is developed to investigate the optimal contents of the modal basis. This makes the dynamic response of th e cavity and the structure converge with a minimum number of modes. In orde r to address this problem, one has to develop criteria for defining the app ropriate modes for each basis. The theory has been applied to four cases an d the results show good agreement. Finally, some results are also compared with those obtained by a finite element model to demonstrate the usefulness of these criteria to find the optimal mesh size for both media. (C) 1999 A cademic Press.