Low frequency noise reducing structures using passive and active damping methods

Abstract

Acoustic attenuation of lightweight structures is one way of lowering payload cost of launch vehicles. This paper describes results of a study to determine the effectiveness of high structural damping to reduce low frequency noise. Both passive and active damping techniques were examined. Passive damping was achieved using a surface bonded constrained layer damping treatment and active damping was achieved with surface bonded piezoceramic wafers and a closed-loop controller. The paper discusses the analytical models used to predict noise reduction of a large flat panel and show comparisons with test data. Finite element models using NASTRAN and vibro-acoustic models using SYSNOISE were used to predict noise reduction. A test bed made of a large flat composite panel mounted as one wall of a very stiff six-sided enclosure was constructed. The enclosure and panel was placed in an acoustic chamber and subjected to a high acoustic environment.