Structural vibration reduction achieved by lightweight porous layers through the near-field damping effect: A technical summary

Properly designed porous materials can provide damping equivalent to conventional viscoelastic dampers by the dissipation of the evanescent wave energy in the vibrating structure's acoustical near-field. At the same time, these materials possess advantages such as light weight and effective sound absorption. Thus, there are potential benefits with respect to cost and weight saving in automotive and aerospace applications by using porous layers as multi-functional noise and vibration control solutions. The intention in this article is to provide a concise summary of the methods and major findings previously presented in an extensive set of publications and conference presentations. In that work, porous media, such as fibers and foams, were designed to serve as treatments for various vibrating structures to examine their damping effectiveness. Both analytical modeling and numerical simulation based on finite element methods were involved depending on the complexity of the structure. Specifically, a Fourier transform-based computational method was introduced as the key step to allow accurate prediction of a panel's spatial response. The analytical model was further developed into an efficient software toolbox, so that parametric studies could be conducted to identify the optimal properties for a porous layer to provide the maximum damping within a target frequency region, based on which near-field damping design concepts are summarized. Key findings include the observation that the addition of bulk elasticity to the solid phase of the porous medium improves damping performance compared to equivalent limp treatments.