Numerical details

• For discretization in space, the Finite Element Method (FEM) is used, using default continuous Galerkin elements of order 2 (for each component of the velocity) and 1 (for the scalar pressure). In the code, they are repectively defined as dolfin.VectorElement("CG", self.mesh.ufl_cell(), 2) and dolfin.VectorElement("CG", self.mesh.ufl_cell(), 1).

• For the time integration, a linear multistep semi-implicit method is used (the nonlinear term is extrapolated with a second-order Adams–Bashforth scheme, while the viscous term is treated implicitly).

• The equations are implemented using a perturbation formulation:

  • the field $v(x,t)$ is decomposed as $v(x,t) = V(x) + v'(x, t)$,
  • $V(x)$ is computed first,
  • then, we can compute the time evolution of $v'(x,t)$.

• To some extent, the toolbox aims at making the equations, numerical integration schemes and solvers replaceable by user-defined ones.