Global weak solutions of PDEs for compressible media: A compactness criterion to cover new physical situations

This short paper is an introduction of the memoir recently written by the two authors (see [D.Bresch., P.–E. Jabin, arXiv:1507.04629, (2015)]) which concerns the resolution of two longstanding problems: Global existence of weak solutions for compressible Navier-Stokes equations with thermodynamically unstable pressure and with anisotropic stress tensor. We focus here on a Stokes-like system which can for instance model flows in a compressible tissue in biology or in a compressible porous media in petroleum engineering. This allows us to explain, on a simpler but still relevant and important system, the tools recently introduced by the authors and to discuss the important results that have been obtained on the compressible Navier–Stokes equations. It is finally a real pleasure to dedicate this paper to G. Metivier for his 65’s Birthday. The article will appear in the corresponding special issue, Springer INdAM-Series, Eds F. Colombini, D. Del Santos, D. Lannes (2016).