Modern Perspectives in Applied Mathematics: Theory and Numerics of PDEs

Existence of global weak solutions to Navier-Stokes-Fokker-Planck systems

Endre Süli

University of Oxford

The lecture will survey recent developments concerning the existence of global-in-time weak solutions to a general class of coupled microscopic-macroscopic bead-spring chain models that arise in the kinetic theory of dilute solutions of polymeric liquids with noninteracting polymer chains. The class of models involves the unsteady incompressible Navier-Stokes equations in a bounded domain for the velocity and the pressure of the fluid, with an elastic extra-stress tensor appearing on the right-hand side of the momentum equation. The extra-stress tensor stems from the random movement of the polymer chains and is defined by the Kramers expression through the associated probability density function that satisfies a Fokker-Planck type parabolic equation, a crucial feature of which is the presence of a centre-of-mass diffusion term. The proof of the existence of global weak solutions relies on an entropy estimate and various weak compactness techniques.

The lecture is based on a series of recent papers with John W. Barrett (Imperial College London).