PROPAGATION OF PLANE ACOUSTICAL WAVES IN WOOD AS A STOCHASTIC MEDIUM

The description of the propagation of sound waves in stochastic and non-linear media led to the formulation of non-linear and stochastic acoustics. Since in a stochastic medium the acoustic material constants are stochastic variables, it is necessary in such materials to describe sound waves by an appropriate stochastic differential equation. The structural analysis of wood has shown that it is a stochastic, anisotropic and non-homogeneous medium, and that the physical parameters relevant for wave propagation are stochastic variables with certain probability distributions. Many authors had simply supposed that these probability distributions are so narrow that it is sufficient to take only their mean values and to substitute them into a corresponding ''deterministic'' differential equation. It appears. however, that the stochastic character of the physical parameters of wood relevant for sound propagation in it greatly influences its acoustic properties. In this paper we investigate the propagation of a travelling plane sound wave in wood considered as a stochastic medium assuming that its wavenumber has a normal distribution.