SUNTANS allows the specification of the velocity at the open boundaries in the file
boundaries.c. Boundary condition types on the velocity field can be specified in the pslg file
which sets the marker as described in Sections 3.1 and 3.2. The marker type
can be one of the following:
1 For closed boundaries.
2 For open or velocity-specified boundaries.
3 For open or stage-specified boundaries.
4 For no-slip boundary conditions.
1, then the velocity is set to 0 at those edges. If it is set to 2,
then the velocity is specified in the file boundaries.c by iterating over edges with marker=2.
If it is set to 3 then stage can be specified at the Voronoi cell center for the cell adjacent to this edge.
No-slip boundaries are specified by setting the marker to 4, where the velocity on the edge is specified by
updating phys->boundary_u, phys->boundary_v, and phys->boundary_w. No-slip conditions on top and bottom cells are
specified by setting CdB=-1 or CdT=-1, respectively. An example covering usage of type 2 boundary conditions, type
3 boundary conditions, and type 4 boundary conditions will be covered in turn.