Navier-Stokes equation with spectrally truncated advection
= Navier-Stokes equation with spectrally truncated advection
Replacing the advecting <velocity> by a fixed finite Stokes projection $P_Nu$ makes the three-dimensional nonlinearity controlled by $\lambda_N^{1/4}|u|\|v\|\|w\|$. This yields global existence and uniqueness at the weak <energy> level.