Computation of volume fractions on a variable-resolution grid

This test case is similar to fractions.c but with a refined band in the middle.

#include "fractions.h"

The refinement band is defined by this function.

int main()
  origin (-0.5, -0.5);
  init_grid (16);

  refine (level == 4 && fabs (x) < 0.25);

We use a circle of radius 0.3 and initialise the fractions.

  vertex scalar φ[];
  scalar c[];
  c.refine = c.prolongation = fraction_refine;
  face vector s[];
    φ[] = sq(0.3) - sq(x) - sq(y);
  fractions (φ, c, s);

Output the reconstruced facets and cells.

  output_facets (c, stdout, s);
  output_facets (c, stderr);
  FILE * fp = fopen ("cells", "w");
  output_cells (fp);
  fclose (fp);

Finally, we reconstruct the interface and display the reconstructed facets only in the “halo cells”. This is a check of the consistency of the boundary conditions applied to n and α.

  vector n[];
  scalar α[];
  reconstruction (c, n, α);
  coord p[2];
  for (int l = 0; l < depth(); l++)
    foreach_halo (prolongation, l) 
      foreach_child() {
        coord m = {n.x[],n.y[]};
	if (facets (c[], m, α[], p) == 2)
	  fprintf (stderr, "halo %g %g\nhalo %g %g\nhalo\n", 
		   x + p[0].x*Δ, y + p[0].y*Δ, 
		   x + p[1].x*Δ, y + p[1].y*Δ);

This gives this figure where “exact” uses c and s, “VOF” uses only c and “halo” is the halo cell reconstuction.

Exact and VOF-reconstucted interface

Exact and VOF-reconstucted interface