ELASTODYNAMICS OF DEFORMABLE POROUS-MEDIA

The centre of mass (u(m)) and internal (u(i)) motions are taken as the field variables in porous media. They are respectively the fields ass ociated with total linear momentum flux and relative acceleration of s olid and fluid constituents. The pairs (u(m), 0) and (0, u(i)) are the natural modes of vibrations of porous media. The first mode represent s motion of porous medium as a whole, i.e. there is no relative motion of the constituents, while in the second mode one constituent moves w ith respect to another in such a manner that the medium is at rest. In terms of these field variables a complete set of balance equations an d boundary conditions is developed, which shows the compatibility of n ew fields with dynamic measurements. It is shown that material points in a pore-continuum undergo stretching as well as rotation about their own axis (or spinning). The centre-of-mass field is the measure of st retch and the internal field is the measure of spin. The existence of spin in continuum is postulated in polar field theories. In the presen t framework it appears naturally.