Vibroacoustic optimization of skin damped structures for noise reduction

Abstract

Most of the time the widely used passive treatments are designed to obtain the highest achievable damping. Although this might be satisfactory from a vibrational point of view the approach is not optimal for noise reduction. The idea is illustrated in the case study of a plate on which polymer/aluminum thin patches have been bonded. The system acoustic pressure and structure displacement equations are transformed into a single integro differential one governing the plate displacement. The solution is then expanded into a series of resonance modes. These modes are estimated using a perturbation expansion with respect to the fluid/solid density ratio. Numerically, in vacuo resonance modes are firstly computed using a viscoelastic incompressible 3D FE program together with a Newton-type iterative method and a sparse complex matrix solver implementing ARPACK. Radiation modal impedances are then computed to ponderate the in vacuo solution. The numerical model has been experimentally validated. Its specificity lies in the separate computation of three damping components: thermoelastic, skin and acoustic damping, this last one being caused by the fluid/structure coupling. Finally an optimization process determines an optimal system configuration to achieve the lowest acoustic damping while obtaining the highest viscoelastic damping.