Effects of internal acoustic coupling on the response of a base-excited hollow structure

Abstract

Traditionally, structural dynamic simulation predictions for hollow structures do not include internal acoustic volumes. This is the case for two reasons. First, it can be difficult to create a volume mesh of complicated internal cavities, and this additional volume would drastically increase the size of the model. Second, it is often blindly assumed that acoustic coupling is not important for structures with anything but thin walls. However, if the structural and acoustic modes are compatible, that is, the modes have similar frequencies and shapes, then the interaction between the structure and the enclosed acoustic volume will occur and can have an effect on structural response. The magnitude of this coupling effect is demonstrated here by examining the structural response predictions for a finite element model of a hollow structure with and without the acoustic volume in place. When a base excitation is applied at a frequency and location to excite compatible modes, the response predictions are seen to be drastically different if the acoustic volume is included. The frequency response results of the coupled finite element simulations will be compared with those of the classic two degree of freedom dynamic vibration absorber, showing the effect of frequency ratio and damping on the structural response.