The Use of Poro-Elastic Finite Elements to Model the Structural Damping Effect of Fibrous Acoustical Treatments

Recently, new models for limp, fibrous sound absorbing materials have been proposed and verified. It has also been shown that these models may be used to optimize the sound absorption and barrier performance of layered acoustical systems. During that work, it was noticed that layers of fibrous materials can, under some circumstances, provide significant damping when they are applied to panel structures. It has since been shown that that structural damping effect may be predicted analytically by using a modal expansion procedure. The latter approach, however, can only conveniently be applied in circumstances when the vibrating structure has a simple shape and boundary conditions. Thus, in the work reported here it was of interest to demonstrate that the damping effect created by fibrous materials could also be predicted by using a finite element procedure. Successful application of the finite element method would then allow the damping effect of fibrous materials on arbitrarily shaped vibrating bodies to be studied. The poro-elastic finite element model that was used here to model the fibrous material has been described extensively elsewhere. That model has now been incorporated into a software package known as SAFE (Structural Acoustic Finite Element), an analysis module of the finite/boundary element package, COMET/Acoustics. The SAFE package was used to make the calculations reported here. The detailed objectives of the present work were first to duplicate analytical structural damping predictions by using a finite element approach, and thus to verify the earlier predictions. Secondly, it was desired to gain experience with modeling limp, fibrous materials by using SAFE. Finally, it was of interest to begin to optimize the acoustical behavior of acoustical materials by using numerical tools, and to examine the impact of these materials on the structural vibration of automotive panels, for example