Robustness improvement in donorBasedLayeredOverlapFringe

Looking at bounding box of the connected region to determine whether we are
going in the right direction.

src/overset/oversetMesh/oversetFringe/donorBasedLayeredOverlapFringe/donorBasedLayeredOverlapFringe.C

@@ -331,6 +331,10 @@ void Foam::donorBasedLayeredOverlapFringe::calcAddressing() const
             const unallocLabelList& owner = mesh.faceOwner();
             const unallocLabelList& neighbour = mesh.faceNeighbour();
 
+            // Get bounding box of this region for additional check when marking
+            // acceptors
+            const boundBox& bb = allRegions[regionID].globalBounds();
+
             // Mark cells that are eligible to be acceptors (not donors)
             boolList eligibleCells(mesh.nCells(), true);
             forAllConstIter (labelHashSet, donors, iter)
@@ -371,11 +375,16 @@ void Foam::donorBasedLayeredOverlapFringe::calcAddressing() const
                             mag(faceCentre - centrePoint);
 
                         if
+                        (
+                            // First, distance based criterium
                             (
                                 faceCentreToRegionCentreDist
                               - donorCentreToRegionCentreDist
                               < distTol_
                             )
+                            // Second, bounding box based criterium
+                         && (bb.contains(faceCentre))
+                        )
                         {
                             // Face is closer to the centre point than cell: we
                             // are moving in the right direction. Mark the face
@@ -681,6 +690,27 @@ Foam::donorBasedLayeredOverlapFringe::donorBasedLayeredOverlapFringe
             << "The number should be greater than 0."
             << abort(FatalError);
     }
+
+    // Recommendation: use at least two layers in order to avoid going defining
+    // acceptors on the wrong side and filling in the whole region with holes
+    if (nLayers_ == 1)
+    {
+        WarningIn 
+        (
+            "donorBasedLayeredOverlapFringe::"
+            "donorBasedLayeredOverlapFringe\n"
+            "(\n"
+            "    const fvMesh& mesh,\n"
+            "    const oversetRegion& region,\n"
+            "    const dictionary& dict\n"
+            ")"
+        )   << "It is recommended to use at least 2 layers (nLayers = 2) in"
+            << " order to avoid defining acceptor cells on the wrong side"
+            << " of the region."
+            << nl
+            << "Be sure to check the fringe layer for this region."
+            << endl;
+    }
 }
 
 

src/overset/oversetMesh/oversetFringe/donorBasedLayeredOverlapFringe/donorBasedLayeredOverlapFringe.H

@@ -37,6 +37,13 @@ Description
     each other (e.g. 10:1 cell ratio, where the finer cells are found on the
     background mesh will probably be problematic to correctly set-up).
 
+    Note: based on distance tolerance (see distTol_ member), specified number of
+    layers and the bounding box of the connected donor region, it is possible
+    that acceptors end also on the wrong side (from the region centre as opposed
+    to towards the region centre). I do all I can to prevent this by looking at
+    the bounding box and hinting that at least 2 layers should be used. Be sure
+    to check the overset assembly for this region using calcOverset utility.
+
 Author
     Vuko Vukcevic, Wikki Ltd.  All rights reserved.