Published 12 issues per year
ISSN Print: 0040-2508
ISSN Online: 1943-6009
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Equation of State in the Set of Acoustics Equations for a Moving Non-Uniform Medium
ABSTRACT
A broad class of devices for the diagnostics of substances and materials are based on the use of wave processes in non-uniform media. The need to increase the volume of primary information stimulates combined application of electromagnetic and acoustic waves. The mathematical formalism of acoustic waves has much in common with that of electromagnetic waves, however its development lags behind noticeably, which must be taken into account in the design of combined diagnostic systems.
The set of acoustic equations is based on the general equations of hydrodynamics. Presently a number of approaches [1-6] are used to derive such sets. However, they all have a feature in common, namely that the continuity equation and the equation of motion are constructed for a fixed volume, whereas the equation of state is constructed for a fixed mass, and hence the equation set is not designed to describe a single object. The transition to one object is not complex. In a number of simple applications it is done automatically in the process of transformations, or it can be accomplished at final stages of the analysis. Problems of greater complexity, like propagation of acoustic waves through a non-uniform moving medium, require that such a transformation should be performed at the very beginning. It is based on the energy and matter conservation laws that should be applied to a volume fixed in space and bounded by walls transparent for the transport of matter and energy. It is less suitable to use other conservation laws because the interrelations of the quantities involved are established quite simply in terms of energy. In this paper a derivation of the equation of state is considered for a volume fixed with respect to a reference frame. The full-scale derivation of this equation along with other essential relations can be represented in paper [7].