Abstract:

This paper considers the damping of waves propagating in high porosity (97%) open-cell foams which are fully saturated by a viscous fluid. The technique of homogenization is applied on two spatial scales to the fluid-foam system. The resulting equations are found to be those of Biot [M. A. Biot, J. Acoust. Soc. Am. 28, 168--178 (1956)] but reduce to the simpler form given by Chase [D. M. Chase, J. Acoust. Soc. Am. 65, 1--8 (1979)] when particular properties of the solid foam matrix are taken into consideration. A number of important material parameters are identified, and of particular significance is the measure of drag between the solid and fluid components. The results of numerical fluid flow experiments are used to obtain estimates of the damping coefficient. Comparisons are made with measurements of the steady state and frequency-dependent damping coefficients, which are determined using specially constructed experimental rigs. [Published with the permission of the Contoller of Her Britannic Majesty's Stationary Office.]