The constitutive equations (Equation 3-60) can easily become unstable if discretized using the Galerkin finite element method (Ref. 2). Stabilized finite element methods are usually necessary in order to obtain physical solutions. The streamline diffusion method is used for the equations for the elastic stress tensor.

The theory about stabilization of the momentum equations Equation 3-56–Equation 3-57 is found in Numerical Stability — Stabilization Techniques for Fluid Flow.