snappyHexMesh: Automatically remove zero-sized patches

All patches are preserved if the 'keepPatches' option is set true.
Patch contributed by Mattijs Janssens

applications/utilities/mesh/generation/snappyHexMesh/snappyHexMesh.C

@@ -57,6 +57,7 @@ Description
 #include "MeshedSurface.H"
 #include "globalIndex.H"
 #include "IOmanip.H"
+#include "fvMeshTools.H"
 
 using namespace Foam;
 
@@ -571,6 +572,73 @@ scalar getMergeDistance(const polyMesh& mesh, const scalar mergeTol)
 }
 
 
+void removeZeroSizedPatches(fvMesh& mesh)
+{
+    // Remove any zero-sized ones. Assumes
+    // - processor patches are already only there if needed
+    // - all other patches are available on all processors
+    // - but coupled ones might still be needed, even if zero-size
+    //   (e.g. processorCyclic)
+    // See also logic in createPatch.
+    const polyBoundaryMesh& pbm = mesh.boundaryMesh();
+
+    labelList oldToNew(pbm.size(), -1);
+    label newPatchi = 0;
+    forAll(pbm, patchi)
+    {
+        const polyPatch& pp = pbm[patchi];
+
+        if (!isA<processorPolyPatch>(pp))
+        {
+            if
+            (
+                isA<coupledPolyPatch>(pp)
+             || returnReduce(pp.size(), sumOp<label>())
+            )
+            {
+                // Coupled (and unknown size) or uncoupled and used
+                oldToNew[patchi] = newPatchi++;
+            }
+        }
+    }
+
+    forAll(pbm, patchi)
+    {
+        const polyPatch& pp = pbm[patchi];
+
+        if (isA<processorPolyPatch>(pp))
+        {
+            oldToNew[patchi] = newPatchi++;
+        }
+    }
+
+
+    const label nKeepPatches = newPatchi;
+
+    // Shuffle unused ones to end
+    if (nKeepPatches != pbm.size())
+    {
+        Info<< endl
+            << "Removing zero-sized patches:" << endl << incrIndent;
+
+        forAll(oldToNew, patchi)
+        {
+            if (oldToNew[patchi] == -1)
+            {
+                Info<< indent << pbm[patchi].name()
+                    << " type " << pbm[patchi].type()
+                    << " at position " << patchi << endl;
+                oldToNew[patchi] = newPatchi++;
+            }
+        }
+        Info<< decrIndent;
+
+        fvMeshTools::reorderPatches(mesh, oldToNew, nKeepPatches, true);
+        Info<< endl;
+    }
+}
+
+
 // Write mesh and additional information
 void writeMesh
 (
@@ -812,6 +880,8 @@ int main(int argc, char *argv[])
         readScalar(meshDict.lookup("mergeTolerance"))
     );
 
+    const Switch keepPatches(meshDict.lookupOrDefault("keepPatches", false));
+
 
 
     // Read decomposePar dictionary
@@ -1351,6 +1421,12 @@ int main(int argc, char *argv[])
             motionDict
         );
 
+
+        if (!keepPatches && !wantSnap && !wantLayers)
+        {
+            removeZeroSizedPatches(mesh);
+        }
+
         writeMesh
         (
             "Refined mesh",
@@ -1392,6 +1468,11 @@ int main(int argc, char *argv[])
             snapParams
         );
 
+        if (!keepPatches && !wantLayers)
+        {
+            removeZeroSizedPatches(mesh);
+        }
+
         writeMesh
         (
             "Snapped mesh",
@@ -1438,6 +1519,11 @@ int main(int argc, char *argv[])
             distributor
         );
 
+        if (!keepPatches)
+        {
+            removeZeroSizedPatches(mesh);
+        }
+
         writeMesh
         (
             "Layer mesh",

applications/utilities/mesh/generation/snappyHexMesh/snappyHexMeshDict

@@ -26,6 +26,11 @@ addLayers       false;
 //singleRegionName false;
 
 
+//Optional: preserve all generated patches. Default is to remove
+//          zero-sized patches.
+//keepPatches true;
+
+
 // Geometry. Definition of all surfaces. All surfaces are of class
 // searchableSurface.
 // Surfaces are used