I know that taking the scalar product of the harmonic (Laplacian) friction term with ##\underline u## is
$$\underline u \cdot [\nabla \cdot(A\nabla \underline u)] = \nabla \cdot (\underline u A \nabla \underline u) - A (\nabla \underline u )^2 $$
where ##\underline u = (u,v)## and ##A## is a...