Regularity of coupled two-dimensional nonlinear Fokker-Planck and   Navier-Stokes systems
  We consider systems of particles coupled with fluids. The particles are described by the evolution of their density, and the fluid is described by the Navier-Stokes equations. The particles add stress to the fluid and the fluid carries and deforms the particles. Because the particles perform rapid random motion, we assume that the density of particles is carried by a time average of the fluid velocity. The resulting coupled system is shown to have smooth solutions at all values of parameters, in two spatial dimensions. 
Peter Constantin, Charles Fefferman, Edriss Titi, Arghir Zarnescu