So by alternatively decomposing the stress tensor into isotropic and deviatoric parts, as usual in fluid dynamics: σ σ = − − [ p − − ( λ λ + 2 3 μ μ ) ( ∇ ∇ ⋅ ⋅ u ) ] I + μ μ ( ∇ ∇ u + ( ∇ ∇ u ) T − − 2 3 ( ∇ ∇ ⋅ ⋅ u ) I )