Grid refinement

In order to adjust the refinement of the mesh, the user can call m_af_core::af_adjust_refinement(). Each call will increase or decrease the refinement level at any location by at most one level. An example from advection.f90 is shown below:

The last argument specifies that refinement within a distance of N cells of the box's boundary should also trigger refinement in neighboring boxes. After refinement, information about the changes is returned through the refine_info argument. The argument ref_routine is a user-supplied subroutine that will be called for each relevant box (boxes covered with multiple layers of refinement don't matter). For each cell of a box, the subroutine should set a refinement flag. The options are:

• af_do_ref: Extra refinement is required
• af_rm_ref: The current refinement can be removed
• af_keep_ref: The current refinement should stay

An example from advection.f90 is shown below.

 
  subroutine refine_routine(box, cell_flags)
    type(box_t), intent(in) :: box
    integer, intent(out)      :: cell_flags(DTIMES(box%n_cell))
    real(dp)                  :: diff
    integer                   :: IJK, nc
 
    nc   = box%n_cell
 
    do kji_do(1,nc)
#if NDIM == 1
       diff = abs(box%dr(1) * (box%cc(i+1, i_phi) + &
            box%cc(i-1, i_phi) - 2 * box%cc(i, i_phi)))
#elif NDIM == 2
       diff = abs(box%dr(1) * (box%cc(i+1, j, i_phi) + &
            box%cc(i-1, j, i_phi) - 2 * box%cc(i, j, i_phi)) + &
            box%dr(2) * (box%cc(i, j+1, i_phi) + &
            box%cc(i, j-1, i_phi) - 2 * box%cc(i, j, i_phi)))
#elif NDIM == 3
       diff = abs(box%dr(1) * (box%cc(i+1, j, k, i_phi) + &
            box%cc(i-1, j, k, i_phi) - 2 * box%cc(i, j, k, i_phi)) + &
            box%dr(2) * (box%cc(i, j+1, k, i_phi) + &
            box%cc(i, j-1, k, i_phi) - 2 * box%cc(i, j, k, i_phi)) + &
            box%dr(3) * (box%cc(i, j, k+1, i_phi) + &
            box%cc(i, j, k-1, i_phi) - 2 * box%cc(i, j, k, i_phi)))
#endif
 
       if (box%lvl < 2 .or. diff > 2.0e-3_dp .and. box%lvl < 5) then
          cell_flags(ijk) = af_do_ref
       else if (diff < 0.1_dp * 2.0e-3_dp) then
          cell_flags(ijk) = af_rm_ref
       else
          cell_flags(ijk) = af_keep_ref
       end if
    end do; close_do
  end subroutine refine_routine

If any of the cells is marked for refinement, all the cells will be refined. Refinement will only be removed if all cells are marked for removal, and if the parent is not marked for refinement.

Prolongation after refinement

After the mesh has been refined, there will typically be new boxes, and some boxes will have been removed. A user can specify prolongation, restriction and boundary conditions routines for a cell-centered variable with the m_af_core::af_set_cc_methods routine, after which restriction and prolongation is automatically performed.