Noise Control of an Acoustic Cavity Coupled with a Vibrating Plate Treated with a Spatially Varying Constrained Viscoelastic Layer.

摘要

Viscoelastic layers have long been recognized as an effective means of reducing the structural vibrations that can generate undesirably high pressure levels in a coupled acoustic cavity. Constraining the viscoelastic layer increases the effectiveness of the viscoelastic layer by adding transverse shear as a dissipation mechanism in the system. It is proposed in this dissertation to replace the traditionally homogeneous core of a constrained damping layer treatment by a non-homogeneous viscoelastic material in order to further improve the effectiveness of the treatment. A finite element model is developed to simulate the vibrations of plates treated with a non-homogeneous constrained layer treatment using Reissner- Mindlin plate theory. The predictions of the model are validated against the predictions of a commercially available finite element package (NASTRAN). The model of the plate/constraining layer treatment is then coupled with a finite element model of a coupled acoustic cavity. The integrated model is exercised to consider different material combinations and geometric layouts of the nonhomogeneous damping treatment in order to determine general guidelines for producing the largest reduction in sound pressure levels inside an acoustic cavity that is being driven by a flexible boundary. The predictions of the integrated finite element model are validated through experimental and numerical work. Close agreements are found between theoretical predictions and experimental results. Generally, it is found that damping treatments with stiffer outer perimeters and softer cores are more effective in attenuating the sound pressure levels in the acoustic cavity than other configurations of the non-homogeneous treatment. The theoretical and experimental techniques developed in this dissertation present invaluable tools for the design and performance predictions of plates treated with spatially varying damping treatments and coupled with acoustic cavities.