From 9e1470a06d2dee9430f38be5d52da1637bcd888b Mon Sep 17 00:00:00 2001
From: Vuko Vukcevic <v.vukcevic@wikki.co.uk>
Date: Thu, 11 Apr 2019 17:38:28 +0200
Subject: [PATCH] Robustness improvement in donorBasedLayeredOverlapFringe

Looking at bounding box of the connected region to determine whether we are
going in the right direction.
---
 .../donorBasedLayeredOverlapFringe.C          | 36 +++++++++++++++++--
 .../donorBasedLayeredOverlapFringe.H          |  7 ++++
 2 files changed, 40 insertions(+), 3 deletions(-)

diff --git a/src/overset/oversetMesh/oversetFringe/donorBasedLayeredOverlapFringe/donorBasedLayeredOverlapFringe.C b/src/overset/oversetMesh/oversetFringe/donorBasedLayeredOverlapFringe/donorBasedLayeredOverlapFringe.C
index e7afc6bb4..b05563034 100644
--- a/src/overset/oversetMesh/oversetFringe/donorBasedLayeredOverlapFringe/donorBasedLayeredOverlapFringe.C
+++ b/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)
@@ -372,9 +376,14 @@ void Foam::donorBasedLayeredOverlapFringe::calcAddressing() const
 
                         if
                         (
-                            faceCentreToRegionCentreDist
-                          - donorCentreToRegionCentreDist
-                          < distTol_
+                            // 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
@@ -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;
+    }
 }
 
 
diff --git a/src/overset/oversetMesh/oversetFringe/donorBasedLayeredOverlapFringe/donorBasedLayeredOverlapFringe.H b/src/overset/oversetMesh/oversetFringe/donorBasedLayeredOverlapFringe/donorBasedLayeredOverlapFringe.H
index 2cdd2aed8..21e4cf5b1 100644
--- a/src/overset/oversetMesh/oversetFringe/donorBasedLayeredOverlapFringe/donorBasedLayeredOverlapFringe.H
+++ b/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.