[SCM] Gerris Flow Solver branch, upstream, updated. b3aa46814a06c9cb2912790b23916ffb44f1f203

[Stephane Popinet]

The following commit has been merged in the upstream branch:
commit 2a525fe14a1abbed508515dc9925d6297b0fe8f7
Author: Stephane Popinet <popinet at users.sf.net>
Date:   Tue Dec 9 08:50:56 2008 +1100

    New function gfs_center_minmod_gradient
    
    darcs-hash:20081208215056-d4795-99b764386d858e3276c921136436cc1d64071539.gz

diff --git a/src/advection.c b/src/advection.c
index d765f51..62ce407 100644
--- a/src/advection.c
+++ b/src/advection.c
@@ -914,6 +914,8 @@ void gfs_advection_params_write (GfsAdvectionParams * par, FILE * fp)
 	   "gfs_center_gradient" :
 	   par->gradient == gfs_center_van_leer_gradient ?
 	   "gfs_center_van_leer_gradient" :
+	   par->gradient == gfs_center_minmod_gradient ?
+	   "gfs_center_minmod_gradient" :
 	   "none",
 	   par->flux == gfs_face_advection_flux ?
 	   "gfs_face_advection_flux" :
@@ -987,6 +989,8 @@ void gfs_advection_params_read (GfsAdvectionParams * par, GtsFile * fp)
       par->gradient = gfs_center_gradient;
     else if (!strcmp (gradient, "gfs_center_van_leer_gradient"))
       par->gradient = gfs_center_van_leer_gradient;
+    else if (!strcmp (gradient, "gfs_center_minmod_gradient"))
+      par->gradient = gfs_center_minmod_gradient;
     else if (!strcmp (gradient, "none"))
       par->gradient = none;
     else if (fp->type != GTS_ERROR)
diff --git a/src/fluid.c b/src/fluid.c
index 3f152b5..0d83058 100644
--- a/src/fluid.c
+++ b/src/fluid.c
@@ -521,7 +521,7 @@ gdouble gfs_center_van_leer_gradient (FttCell * cell,
       v0 = GFS_VARIABLE (cell, v);
       v1 = neighbor_value (&f1, v, &x1);
       v2 = neighbor_value (&f2, v, &x2);
-      
+
       s1 = 2.*(v0 - v1);
       s2 = 2.*(v2 - v0);
 
@@ -538,7 +538,62 @@ gdouble gfs_center_van_leer_gradient (FttCell * cell,
   /* only one or no neighbors */
   return 0.;
 }
-					 
+
+static gdouble limiter (gdouble r, gdouble beta)
+{
+  gdouble v1 = MIN (r, beta), v2 = MIN (beta*r, 1.);
+  v1 = MAX (0., v1);
+  return MAX (v1, v2);
+}
+
+/**
+ * gfs_center_minmod_gradient:
+ * @cell: a #FttCell.
+ * @c: a component.
+ * @v: a #GfsVariable index.
+ *
+ * The gradient is normalized by the size of the cell and is limited
+ * using a minmod limiter.
+ *
+ * Returns: the value of the @c component of the gradient of variable @v
+ * at the center of the cell.  
+ */
+gdouble gfs_center_minmod_gradient (FttCell * cell,
+				    FttComponent c,
+				    guint v)
+{
+  FttDirection d = 2*c;
+  FttCellFace f1;
+  gdouble v0;
+
+  g_return_val_if_fail (cell != NULL, 0.);
+  g_return_val_if_fail (c < FTT_DIMENSION, 0.);
+
+  f1 = gfs_cell_face (cell, FTT_OPPOSITE_DIRECTION (d));
+  v0 = GFS_VARIABLE (cell, v);
+  if (f1.neighbor) {
+    FttCellFace f2 = gfs_cell_face (cell, d);
+    gdouble x1 = 1., v1;
+    
+    v1 = neighbor_value (&f1, v, &x1);
+    if (f2.neighbor) {
+      /* two neighbors */
+      gdouble x2 = 1., v2;
+      
+      v2 = neighbor_value (&f2, v, &x2);
+
+      gdouble g;
+      if (v0 == v1)
+	g = 0.;
+      else
+	g = limiter ((v2 - v0)*x1/((v0 - v1)*x2), 1.)*(v0 - v1)/x1;
+      return g;
+    }
+  }
+  /* only one or no neighbors */
+  return 0.;
+}
+
 /**
  * gfs_face_gradient:
  * @face: a #FttCellFace.
@@ -549,7 +604,10 @@ gdouble gfs_center_van_leer_gradient (FttCell * cell,
  * Set the value of @g as the gradient of variable @v on the
  * @face. The value returned is second order accurate in space and
  * conservative, in the sense that values at a coarse/fine cell
- * boundary are consistent.  
+ * boundary are consistent.
+ *
+ * The value of the gradient (normalised by the size of @face->cell)
+ * is given by: @g->b - @g->a*GFS_VARIABLE (@face->cell, @v).
  */
 void gfs_face_gradient (const FttCellFace * face,
 			GfsGradient * g,
diff --git a/src/fluid.h b/src/fluid.h
index 727a759..770eb88 100644
--- a/src/fluid.h
+++ b/src/fluid.h
@@ -116,6 +116,9 @@ void                  gfs_center_gradient_stencil   (FttCell * cell,
 gdouble               gfs_center_van_leer_gradient  (FttCell * cell,
 						     FttComponent c,
 						     guint v);
+gdouble               gfs_center_minmod_gradient    (FttCell * cell,
+						     FttComponent c,
+						     guint v);
 
 typedef struct _GfsGradient GfsGradient;
 

-- 
Gerris Flow Solver