THERMODYNAMIC CONSTRAINTS ON VISCOELASTIC MODELS FOR WAVE ABSORBING MATERIALS

The present paper analyses models describing wave absorbing materials from a thermodynamic point of view. This study deals with harmonic pla ne wave propagation through a viscoelastic homogeneous medium at the m acroscopic scale. The dynamic behaviour of the studied medium is model led using two distinct complex functions related to the bulk and to th e density, respectively. It is shown that the complex density function results from viscous body forces. This paper aims to discuss the ther modynamic constraints on these acoustic models for a general one-dimen sional (1D)-harmonic plane wave system. The dynamic intrinsic dissipat ion of the studied viscoelastic medium is defined and evaluated. Using the second law of thermodynamics, conditions are found to define cons istent functions modelling the dissipative effects. The classical rigi d open porous model used to describe many sound absorbing media is tak en as an example for such a harmonic viscoelastic model. It demonstrat es that the main dissipative phenomenon can be described using a compl ex density function. (C) 1998 Elsevier Science Ltd. All rights reserve d.