Navier-Stokes regularity in 3D
  This short proof shows that for smooth and sufficiently fast decaying initial data at infinity, the full incompressible Navier-Stokes solutions are eternal. The proof uses an orthogonal decomposition of the velocity field and some well-known vector calculus identities to establish a particular contradiction, which leads to a vanishing integral, which is the main integral that determines the evolution of enstrophy. As it is shown that enstrophy is non-increasing, it is well-know that the solutions stay regular at all times. 
Jussi Lindgren
physics.gen-ph