Analysis of sound transmission through flexible panel/frame walls

Low frequency sound transmission through flexible walls is an important vehicle noise control problem, particularly for aircraft interior noise. The coupled structural/acoustic problem for spatially periodic wall structures is solved using a two-scale perturbation expansion based on the scale separation between panel size and acoustic wavelength, and an averaging procedure applied over the rapidly varying (panel) scale. A composite solution is formed from a smoothed global solution and a periodic local solution that accounts for the detailed panel motions. The panel subsystems appeared in an averaged sense in the global solution through transfer functions, obtained from the local solution for distributed frame loadings and acoustic boundary conditions. Walls composed of identical panel subsystems, each containing several different panels, attached to a flexible frame can be analyzed. Solutions are presented for a model problem involving sound transmission through a panel/frame wall, and compared with the exact solution to assess the accuracy of the perturbation method. A promising noise reduction concept is Alternate Resonance Tuning (ART), in which adjacent wall panels are tuned to resonate alternately above and below the frequency to be attenuated, with the resulting out-of-phase motion producing acoustic cancellation. A sound transmission problem is solved to illustrate ART for an idealized flexible panel frame wall. Noise reduction by ART is demonstrated by using two panels with different resonant frequencies in each subsystem.

Duke Scholars

Author Donald B. Bliss Thomas Lord Department of Mechanical Engineering and Materia ...