NOISE TRANSMISSION BY VISCOELASTIC SANDWICH PANELS

摘要

This report presents an analytical study on low frequency noise transmission into rectangular enclosures by viscoelastic sandwich panels. The dimensions of these panels are typical of aircraft fuselage skin constructions. The report demonstrates that these panels can effect significant noise reduction. The' anal¬ysis considers two limiting cases of the core stiffness:(1) soft compressible cores with dilatational modes included and (2) hard incompressible cores with dilatational modes neglected. Sandwich panels with soft viscoelastic cores exhibit noise transmission characteristics similar to those of double wall elastic panels except in the frequency range where dilatational modes occur (300 to 600 Hz). At these frequencies noise can be reduced by as much as 30 dB more with viscoelas¬tic panels. Sandwich constructions with hard cores show significant noise reduc¬tion advantage over the elastic panels for the whole frequency range considered in this study (0 to 1000 Hz). Numerical results contained in this report include response and noise transmission characteristics of elastic and viscoelastic panels for several geometric and material parameter configurations.