Modeling of acoustical properties of limp fibrous materials.

摘要

In this work, theoretical models have been developed for predicting the acoustical properties of fibrous materials when exposed to airborne sound as well as their energy dissipation characteristics when the materials are coupled with vibrating structures. A limp porous material model based on Biot's theory is presented first; it was used to predict the acoustical properties specifically for porous materials having bulk frame stiffnesses relatively small compared to that of air. Then, a transfer matrix method for modeling layered systems is described. That technique was combined with the limp porous material model to predict the acoustical properties of layered acoustical systems featuring layers of fibrous materials. The results of the theoretical predictions have been verified experimentally.;The development of two flow resistivity models is also described. The first flow resistivity model is a semi-empirical formulation that links the acoustical properties of a fibrous material to the microscopic material parameters which can be controlled in manufacturing processes. The second flow resistivity model is a physically-based model which explicitly takes the fiber radius distribution of each fiber component comprising the bulk material into account. The limp model was combined with the flow resistivity models to conduct various optimizations of the acoustical properties of fibrous materials. The results of those optimizations were also confirmed by measurement.;Finally, the damping effects of fibrous materials on vibrating structures were investigated by combining a modal analysis approach and the equivalent fluid representation of the fibrous materials. The damping effects of fibrous materials on structural vibration were demonstrated experimentally by using fibrous layers attached to an aluminum panel, and optimizations of the energy dissipation within fibrous materials attached to vibrating structures were conducted.;The theoretical models developed in the present work provide the tools for designing optimum fibrous materials and acoustical systems that give the best acoustical properties or the highest possible energy dissipating efficiencies. Appropriate use of these tools will reduce the present reliance on experimental measurements of material properties.