Analytical Modeling of Active/Passive Smart Foam Noise Control Treatment in Aerospace Vehicles

Abstract

The smart foam noise control system is designed to reduce sound by a combination of the passive absorbing component of the poroelastic foam and the active component of the voltage-driven PVDF (polyvinylidene fluoride) film. In general, the passive foam works well in middle to high frequencies while the active component provides cancellation for low frequencies. In combining active and passive concepts, a hybrid noise control methodology is obtained which allows the control of noise over a wide frequency bandwidth. By adopting the vibration absorber concept for reactive vibration control of elastic structures, a smart foam system can be utilized as either a Distributed Active Vibration Absorber (DAVA) by attaching a mass plate on top of the foam, or a Distributed Vibration Absorber (DVA) device without the active PVDF component. In this paper a finite element modeling approach was developed for predicting the dynamics of the structure, the detailed solid and fluid dynamics inside the foam, and the active control performance obtained by the activation of the PVDF film. DAVA and DVA based noise control devices are also examined using this finite element approach on their vibration and acoustic reductions. In order to achieve this, a three-dimensional smart foam finite element model was developed. The foam finite element is based on Biot’s poroelasticity equations, where the solid and fluid fields are used to characterize frame vibrations and air flow components in the poroelastic foam. In addition, interface conditions are described for coupling multiple medium elements—panel, beam, membrane, acoustic and poroelastic foam in the smart foam system. For the active treatment, the feed forward open-loop control algorithm has been included to a two-dimensional (2D) smart system for implementing the active control for the smart foam system. Numerical predictions for smart foam, DVA and DAVA treatments for vibration reductions are presented and discussed.