Finished writing first version of donorBasedLayeredOverlap fringe

Note: did not attempt to compile yet, let alone test it

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

@@ -27,6 +27,7 @@ License
 #include "faceCellsFringe.H"
 #include "oversetRegion.H"
 #include "addToRunTimeSelectionTable.H"
+#include "syncTools.H"
 
 // * * * * * * * * * * * * * * Static Data Members * * * * * * * * * * * * * //
 
@@ -41,11 +42,22 @@ namespace Foam
     );
 }
 
+
+const Foam::debug::tolerancesSwitch
+Foam::donorBasedLayeredOverlapFringe::distTol_
+(
+    "donorBasedLayeredOverlapDistanceTolerance"
+    0.0
+);
+
+
 // * * * * * * * * * * * * * Private Member Functions  * * * * * * * * * * * //
 
 void Foam::donorBasedLayeredOverlapFringe::calcAddressing() const
 {
-    if (acceptorsPtr_)
+    // Make sure that either acceptorsPtr is unnalocated or if it is allocated,
+    // that it is empty
+    if (acceptorsPtr_ && !acceptorsPtr_->empty())
     {
         FatalErrorIn
         (
@@ -54,52 +66,438 @@ void Foam::donorBasedLayeredOverlapFringe::calcAddressing() const
             << abort(FatalError);
     }
 
-    // Get reference to region cell zone
+    // Get list of all overset regions
-    const cellZone& rcz = region().zone();
+    const PtrList<oversetRegion>& allRegions =
+        this->region().overset().regions();
 
-    // Make a hash set to collect acceptor points
+    // Loop through all connected regions and check whether the fringe overlap
-    // Note: 2 patches connecting at the corner may create a duplicate,
+    // has been found for all of them
-    // which is filtered on insertion
+    bool allFringesReady = true;
-    labelHashSet acceptorSet;
+    forAll (connectedRegionIDs_, crI)
-
-    // Find patches and mark cells
-    forAll (patchNames_, nameI)
     {
-        const polyPatchID curFringePatch
+        // Get ID of this region
-        (
+        const label& regionID = connectedRegionIDs_[crI];
-            patchNames_[nameI],
-            mesh().boundaryMesh()
-        );
 
-        if (!curFringePatch.active())
+        // Get the overset region
+        const oversetRegion& region = allRegions[regionID];
+
+        // Get the fringe algorithm from the region
+        const oversetFringe& fringe = region.fringe();
+
+        // If this is not faceCells fringe, issue a Warning. This fringe
+        // selection algorithm is intended to work only with faceCells fringe on
+        // the other side. VV, 9/Apr/2019
+        if (!isA<faceCellsFringe>(fringe))
         {
-            FatalErrorIn
+            WarningIn
             (
-                "void donorBasedLayeredOverlapFringe::calcAddressing() const"
+                "void Foam::donorBasedLayeredOverlapFringe::"
-            )   << "Fringe patch " << patchNames_[nameI]
+                "updateIteration(donorAcceptorList&) const"
-                << " cannot be found"
+            )   << "donorBasedLayeredOverlap fringe is designed to work"
-                << abort(FatalError);
+                << " with faceCells fringe as a connected region fringe."
+                << nl
+                << "Connected overset region " << region.name()
+                << " has " << fringe.type() " fringe type. "
+                << nl
+                << "Proceed with care!"
+                << endl;
         }
 
-        const unallocLabelList& curFaceCells =
+        // Update flag collecting whether all connected regions found the
-            mesh().boundaryMesh()[curFringePatch.index()].donorBasedLayeredOverlap();
+        // overlap
-
+        allFringesReady &= fringe.foundSuitableOverlap();
-        forAll (curFaceCells, fcI)
-        {
-            // Check if cell is in region zone
-            if (rcz.whichCell(curFaceCells[fcI]) > -1)
-            {
-                // Found acceptor
-                acceptorSet.insert(curFaceCells[fcI]);
-            }
-        }
     }
 
-    // Collect acceptors
+    // Sets containing all acceptors and all holes for all connected regions
-    acceptorsPtr_ = new labelList(acceptorSet.sortedToc());
+    labelHashSet allAcceptors(0.02*mesh.nCells());
+    labelHashSet allFringeHoles(0.02*mesh.nCells());
 
-    // Holes are empty for this fringe
+    if (allFringesReady)
-    fringeHolesPtr_ = new labelList();
+    {
+        // Loop through connected regions
+        forAll (connectedRegionIDs_, crI)
+        {
+            // Get ID of this region
+            const label& regionID = connectedRegionIDs_[crI];
+
+            // Get fringe of the connected region
+            const oversetFringe& fringe = allRegions[regionID].fringe();
+
+            // The fringe should be finalized, which means we may take a const
+            // reference to its final donor acceptors
+            const donorAcceptorList& crDonorAcceptorPairs =
+                fringe.finalDonorAcceptors();
+
+            // Hash set containing donors
+            labelHashSet donors(6*crDonorAcceptorPairs.size());
+
+            // Initialize centre of the donors of this connected region in order
+            // to search in a given direction
+            vector centrePoint(vector::zero);
+
+            // Loop through all donor/acceptors
+            forAll (crDonorAcceptorPairs, daI)
+            {
+                // Get this donor/acceptor pair
+                const donorAcceptor& daPair = crDonorAcceptorPairs[daI];
+
+                // Check whether all donors have been found
+                if (!daPair.donorFound())
+                {
+                    FatalErrorIn
+                    (
+                        "donorBasedLayeredOverlapFringe::"
+                        "updateIteration(donorAcceptorList&) const"
+                    )   << "Donor not found for donor/acceptor pair " << daI
+                        << nl
+                        << "Donor/acceptor data: " << daPair
+                        << nl
+                        << "In connected region: " << allRegions[regionID].name()
+                        << abort(FatalError);
+                }
+
+                // Mark donors on my processor from this connected region. Note
+                // that the check has been made in constructor to make sure that
+                // this region is the only donor region for the connected region
+                if (daPair.donorProcNo() == Pstream::myProcNo())
+                {
+                    // Get donor index
+                    const label& dI = daPair.donorCell();
+
+                    // Insert donor into the hash set
+                    if (donors.insert(dI))
+                    {
+                        // Donor has been inserted (not previously found in the
+                        // hash set), add donor point to centre point (the
+                        // centre point will be calculated later on as
+                        // arithmetic mean)
+                        centrePoint += daPair.donorPoint();
+                    }
+
+                    // Loop through extended donor cells
+                    donorAcceptor::DynamicLabelList& extDonors =
+                        daPair.extendedDonorCells();
+                    donorAcceptor::DynamicPointList& extDonorPoints =
+                        daPair.extendedDonorPoints();
+
+                    forAll (extDonors, i)
+                    {
+                        // Get donor index
+                        const label& edI = extDonors[i];
+
+                        // Inser extended donor into the hash set
+                        if (donors.insert(edI))
+                        {
+                            // Donor has been inserted (not previously found in
+                            // the hash set), add extended donor point as well
+                            centrePoint += extDonorPoints[i];
+                        }
+                    } // End for all extended donors
+                } // End if this donor is on my processor
+            } // End for all (master) donor cells
+
+            // Use the centre point as specified by the user if it was specified
+            // (if the regionCentrePoints_ list is not empty). This avoids
+            // parallel communication as well.
+            if (!regionCentrePoints_.empty())
+            {
+                // Use specified centre point, discarding the data we calculated
+                // above
+                centrePoint = regionCentrePoints_[crI];
+            }
+            else
+            {
+                // User did not specify centre points and the centre point holds
+                // the sum of all the points. Reduce the data
+                reduce(centrePoint, sumOp<vector>());
+                nUniqueDonors = returnReduce(donors.size(), sumOp<label>());
+
+                // Calculate the final centre point by finding the arithmetic mean
+                centrePoint /= nUniqueDonors;
+            }
+
+            // We now have a collection of all donors for this connected region
+            // and the centre point to move to. Let's collect the acceptors
+            labelHashSet acceptors(donors.size()); // Reasonable size estimate
+
+            // Get necessary mesh data (from polyMesh/primitiveMesh)
+            const polyMesh& mesh = this->mesh();
+            const vectorField& cc = mesh.cellCentres();
+            const vectorField& fc = mesh.faceCentres();
+            const cellList& meshCells = mesh.cells();
+            const unallocLabelList& owner = mesh.faceOwner();
+            const unallocLabelList& neighbour = mesh.faceNeighbour();
+
+            // Mark cells that are eligible to be acceptors (not donors)
+            boolList eligibleCells(mesh.nCells(), true);
+            forAllConstIter (labelHashSet, donors, iter)
+            {
+                eligibleCells[iter.key()] = false;
+            }
+
+            // Loop nLayers away from initial donors
+            for (label i = 0; i < nLayers_; ++i)
+            {
+                // Face markup for propagation
+                boolList propagateFace(mesh.nFaces(), false);
+
+                // Loop through all donors and mark faces that are pointing
+                // towards the centre point and have an eligible neighbour
+                forAllConstIter (labelHashSet, donors, iter)
+                {
+                    // Get the cell index and the cell
+                    const label& cellI = iter.key();
+                    const label& cell = meshCells[cellI];
+
+                    // Get cell centre of this donor and calculate distance to
+                    // centre point
+                    const vector& donorCentre = cc[cellI];
+                    const scalar donorCentreToRegionCentreDist =
+                        mag(donorCentre - centrePoint);
+
+                    // Loop through all faces of the cell
+                    forAll (cFaces, i)
+                    {
+                        // Get face index (global)
+                        const label& faceI = cFaces[i];
+
+                        // Get face centre and calculate distance to centre
+                        // point
+                        const vector& faceCentre = fc[faceI];
+                        const scalar faceCentreToRegionCentreDist =
+                            mag(faceCentre - centrePoint);
+
+                        if
+                        (
+                            faceCentreToRegionCentreDist
+                          - donorCentreToRegionCentreDist
+                          < distTol_
+                        )
+                        {
+                            // Face is closer to the centre point than cell: we
+                            // are moving in the right direction. Mark the face
+                            propagateFace[faceI] = true;
+                        }
+                    } // End for all faces of the cell
+                } // End for all donor cells
+
+                // Sync the face list across processor boundaries
+                syncTools::syncFaceList
+                (
+                    mesh,
+                    propagateFace,
+                    orOp<bool>(),
+                    false
+                );
+
+                // Loop through all faces and append acceptors
+                for (label faceI = 0; faceI < mesh.nInternalFaces(); ++faceI)
+                {
+                    if (propagateFace[faceI])
+                    {
+                        // Face is marked, select owner or neighbour
+                        const label& own = owner[faceI];
+                        const label& nei = neighbour[faceI];
+
+                        // Either owner or neighbour may be eligible, not both
+                        if (eligibleCells[own])
+                        {
+                            // Owner cell is not a donor, insert it
+                            acceptors.insert(own);
+
+                            // Mark as ineligible
+                            eligibleCells[own] = false;
+                        }
+                        else if (eligibleCells[nei])
+                        {
+                            // Neighbour cell is not a donor, insert it
+                            acceptors.insert(nei);
+
+                            // Mark as ineligible
+                            eligibleCells[nei] = false;
+                        }
+                    }
+                }
+
+                // Loop through boundary faces
+                for
+                (
+                    label faceI = mesh.nInternalFaces();
+                    faceI < mesh.nFaces();
+                  ++faceI
+                )
+                {
+                    if (propagateFace[faceI])
+                    {
+                        // Face is marked, select owner if this is the right
+                        // side. Neighbour handled on the other side
+                        const label& own = owner[faceI];
+
+                        if (eligibleCells[own])
+                        {
+                            // Face cell is not a donor, insert it
+                            acceptors.insert(own);
+
+                            // Mark as ineligible
+                            eligibleCells[own] = false;
+                        }
+                    }
+                }
+
+                // Special treatment for last iteration
+                if (i == nLayers_ - 1)
+                {
+                    // This is not the last iteration, transfer acceptors into
+                    // donors
+                    donors.transfer(acceptors);
+
+                    // Resize acceptors list
+                    acceptors.resize(donors.size());
+                }
+            } // End for specified number of layers
+
+            // At this point, we have the final set of acceptors and we marked
+            // all cells that are ineligible (either donor or acceptor). The
+            // remaining thing to do is to mark the interior holes
+
+            // Create a hash set containing fringe holes, initialized with
+            // acceptors in order to avoid having special conditions in the loop
+            // below for the first pass
+            labelHashSet fringeHoles(10*acceptors.size());
+
+            // Collect holes until there are no holes to collect
+            label nAddedHoles;
+            do
+            {
+                // Reset number of newly added holes
+                nAddedHoles = 0;
+
+                // Face markup for propagation
+                boolList propagateFace(mesh.nFaces(), false);
+
+                // Loop through all acceptors and mark faces that are pointing
+                // towards the centre point and have eligible neighbour (not an
+                // acceptor or donor)
+                forAllConstIter (labelHashSet, fringeHoles, iter)
+                {
+                    // Get the cell index and the cell
+                    const label& cellI = iter.key();
+                    const label& cell = meshCells[cellI];
+
+                    // Note: there's no need to check for the distance here
+                    // because there's always at least one "buffer" layer
+                    // towards the outer side that consists of donors, which are
+                    // marked as ineligible at the beginning
+
+                    // Loop through all faces of the cell and mark all of them
+                    // for propagation
+                    forAll (cFaces, i)
+                    {
+                        propagateFace[cFaces[i]] = true;
+                    }
+                }
+
+                // Sync the face list across processor boundaries
+                syncTools::syncFaceList
+                (
+                    mesh,
+                    propagateFace,
+                    orOp<bool>(),
+                    false
+                );
+
+                // Loop through all faces and append interior holes
+                for (label faceI = 0; faceI < mesh.nInternalFaces(); ++faceI)
+                {
+                    if (propagateFace[faceI])
+                    {
+                        // Face is marked, select owner or neighbour
+                        const label& own = owner[faceI];
+                        const label& nei = neighbour[faceI];
+
+                        // Either owner or neighbour may be eligible, not both
+                        if (eligibleCells[own])
+                        {
+                            // Owner cell is not a hole (or an acceptor in the
+                            // first iteration), insert it
+                            if (fringeHoles.insert(own))
+                            {
+                                // Count number of added holes in this iteration
+                                ++nAddedHoles;
+                            }
+
+                            // Mark as ineligible
+                            eligibleCells[own] = false;
+                        }
+                        else if (eligibleCells[nei])
+                        {
+                            // Neighbour cell is not a hole (or an acceptor in
+                            // the first iteration), insert it
+                            if (fringeHoles.insert(nei))
+                            {
+                                // Count number of added holes in this iteration
+                                ++nAddedHoles;
+                            }
+
+                            // Mark as ineligible
+                            eligibleCells[nei] = false;
+                        }
+                    }
+                }
+
+                // Loop through boundary faces
+                for
+                (
+                    label faceI = mesh.nInternalFaces();
+                    faceI < mesh.nFaces();
+                  ++faceI
+                )
+                {
+                    if (propagateFace[faceI])
+                    {
+                        // Face is marked, select owner if this is the right
+                        // side. Neighbour handled on the other side
+                        const label& own = owner[faceI];
+
+                        if (eligibleCells[own])
+                        {
+                            // Face cell is not a hole (or an acceptor in the
+                            // first iteration), inser it
+                            if (fringeHoles.insert(own))
+                            {
+                                ++nAddedHoles;
+                            }
+
+                            // Mark as ineligible
+                            eligibleCells[own] = false;
+                        }
+                    }
+                }
+
+                // We moved one layer "inside" the fringe. Keep going until
+                // there are no more holes to add
+
+            } while (nAddedHoles != 0);
+
+            // Finally, we have collected all the fringe holes and acceptors
+            // from this connected region. Append them to the global sets
+            allAcceptors += acceptors;
+            allFringeHoles += fringeHoles;
+
+        } // End for all connected regions
+
+        // Set acceptors and holes from the data for all regions
+        acceptorsPtr_ = new labelList(allAcceptors.sortedToc());
+        fringeHolesPtr_ = new labelList(allFringeHoles.sortedToc());
+    }
+    else
+    {
+        // Connected fringes are not ready, allocate empty lists for acceptors
+        // and holes, which will be deleted when asked for again from the
+        // iterative procedure (see candidateAcceptors() and fringeHoles())
+        acceptorsPtr_ = new labelList(0);
+        holesPtr_ = new labelList(0);
+    }
 }
 
 
@@ -132,6 +530,25 @@ Foam::donorBasedLayeredOverlapFringe::donorBasedLayeredOverlapFringe
     acceptorsPtr_(nullptr),
     finalDonorAcceptorsPtr_(nullptr)
 {
+    // Sanity check number of layers: must be greater than 0
+    if (nLayers_ < 1)
+    {
+        FatalIOErrorIn
+        (
+            "donorBasedLayeredOverlapFringe::"
+            "donorBasedLayeredOverlapFringe\n"
+            "(\n"
+            "    const fvMesh& mesh,\n"
+            "    const oversetRegion& region,\n"
+            "    const dictionary& dict\n"
+            ")",
+            dict
+        )   << "Invalid number of layers specified, nLayers = " nLayers_
+            << nl
+            << "The number should be greater than 0."
+            << abort(FatalError);
+    }
+
     // Read names of connected regions
     const wordList connectedRegionNames(dict.lookup("connectedRegions"));
 
@@ -150,10 +567,10 @@ Foam::donorBasedLayeredOverlapFringe::donorBasedLayeredOverlapFringe
     }
 
     // Loop through all regions and check whether the overlap has been found
-    forAll (connectedRegion_, crI)
+    forAll (connectedRegionNames, crI)
     {
         // Get name of this connected region
-        const word& crName = connectedRegion_[crI];
+        const word& crName = connectedRegionNames[crI];
 
         // Find this region in the list of all regions
         const label regionID = findIndex(allRegions, crName);
@@ -176,13 +593,51 @@ Foam::donorBasedLayeredOverlapFringe::donorBasedLayeredOverlapFringe
 
         // Collect the region index in the list
         connectedRegionIDs_[crI] = regionID;
+
+        // Sanity check: if the specified connected donor region has more than 1
+        // donor regions, this fringe algorithm is attempted to be used for
+        // something that's not intended. Issue an error
+        if (allRegions[regionID].donorRegions().size() != 1)
+        {
+            FatalErrorIn
+            (
+                "donorBasedLayeredOverlapFringe::"
+                "donorBasedLayeredOverlapFringe\n"
+                "(\n"
+                "    const fvMesh& mesh,\n"
+                "    const oversetRegion& region,\n"
+                "    const dictionary& dict\n"
+                ")"
+            )   << "Region " << crName << " specified as connected region, but"
+                << " that region has "
+                << allRegions[regionID].donorRegions().size() << " donor regions."
+                << abort(FatalError);
+        }
+
+        // Sanity check whether the donor region of connected region is actually
+        // this region
+        if (regionID != this->region().index())
+        {
+            FatalErrorIn
+            (
+                "donorBasedLayeredOverlapFringe::"
+                "donorBasedLayeredOverlapFringe\n"
+                "(\n"
+                "    const fvMesh& mesh,\n"
+                "    const oversetRegion& region,\n"
+                "    const dictionary& dict\n"
+                ")"
+            )   << "The donor region of region " << crName
+                << " should be only region " << this->region().name()
+                << abort(FatalError);
+        }
     }
 
     // Sanity check: number of (optionally) specified centre points must be
     // equal to the number of connected regions
     if
     (
-        regionCentrePoints_.size()
+        !regionCentrePoints_.empty()
      && (regionCentrePoints_.size() != connectedRegionIDs_.size())
     )
     {
@@ -207,6 +662,33 @@ Foam::donorBasedLayeredOverlapFringe::donorBasedLayeredOverlapFringe
             << " make sure to specify centre points for all connected regions."
             << abort(FatalError);
     }
+
+    // Sanity check: if the user has specified centre points, dynamic mesh
+    // simulations may be problematic. Issue a warning
+    if
+    (
+        !regionCentrePoints_.empty()
+     && isA<dynamicFvMesh>(this->mesh())
+    )
+    {
+        WarningIn
+        (
+            "donorBasedLayeredOverlapFringe::"
+            "donorBasedLayeredOverlapFringe\n"
+            "(\n"
+            "    const fvMesh& mesh,\n"
+            "    const oversetRegion& region,\n"
+            "    const dictionary& dict\n"
+            ")"
+        )   << "You have specified regionCentrePoints for a dynamic mesh"
+            << " simulation."
+            << nl
+            << "Make sure that the centre points always remain in/near the"
+            << " centre of donors in connected regions!"
+            << nl
+            << "Proceed with care!"
+            << endl;
+    }
 }
 
 
@@ -232,98 +714,23 @@ bool Foam::donorBasedLayeredOverlapFringe::updateIteration
     {
         FatalErrorIn
         (
-            "donorBasedLayeredOverlapFringe::updateIteration(donorAcceptorList&"
+            "donorBasedLayeredOverlapFringe::"
+            "updateIteration(donorAcceptorList&) const"
         )   << "finalDonorAcceptorPtr_ already allocated. Something went "
             << "wrong with the iteration procedure (flag was not updated)."
             << nl << "This should not happen for donorBasedLayeredOverlapFringe."
             << abort(FatalError);
     }
 
-    // Get list of all overset regions
+    // Allocate the list by reusing the argument list
-    const PtrList<oversetRegion>& allRegions =
+    finalDonorAcceptorsPtr_ = new donorAcceptorList
-        this->region().overset().regions();
+    (
+        donorAcceptorRegionData,
+        true
+    );
 
-    // Loop through all connected regions and check whether the fringe overlap
+    // Set the flag to true and return
-    // has been found for all of them
+    updateSuitableOverlapFlag(true);
-    bool allFringesReady = true;
-    forAll (connectedRegionIDs_, crI)
-    {
-        // Get ID of this region
-        const label& regionID = connectedRegionIDs_[crI];
-
-        // Get the overset region
-        const oversetRegion& region = allRegions[regionID];
-
-        // Get the fringe algorithm from the region
-        const oversetFringe& fringe = region.fringe();
-
-        // If this is not faceCells fringe, issue a Warning. This fringe
-        // selection algorithm is intended to work only with faceCells fringe on
-        // the other side. VV, 9/Apr/2019
-        if (!isA<faceCellsFringe>(fringe))
-        {
-            WarningIn
-            (
-                "void Foam::donorBasedLayeredOverlapFringe::"
-                "calcAddressing() const"
-            )   << "donorBasedLayeredOverlap fringe is designed to work"
-                << " with faceCells fringe as a connected region fringe."
-                << nl
-                << "Connected overset region " << region.name()
-                << " has " << fringe.type() " fringe type. "
-                << nl
-                << "Proceed with care!"
-                << endl;
-        }
-
-        // Update flag collecting whether all connected regions found the
-        // overlap
-        allFringesReady &= fringe.foundSuitableOverlap();
-    }
-
-    if (allFringesReady)
-    {
-        // Loop through connected regions
-        forAll (connectedRegionIDs_, crI)
-        {
-            // Get ID of this region
-            const label& regionID = connectedRegionIDs_[crI];
-
-            // Get fringe of the connected region
-            const oversetFringe& fringe = allRegions[regionID].fringe();
-
-            // The fringe should be finalized, which means we may take a const
-            // reference to its final donor acceptors
-            const donorAcceptorList& crDonorAcceptorPairs =
-                fringe.finalDonorAcceptors();
-
-            // Sanity check the validity of donor
-
-            // Mark donors on my processor from this connected region
-
-            // Calculate the centre for this connected region if it isn't
-            // specified
-
-            // Mark all future acceptors by moving towards the centre using
-            // face-neighbour walk nLayers times
-
-            // Now that the acceptors are marked, mark all remaining holes
-
-        }
-
-        // Allocate the list by reusing the argument list
-        finalDonorAcceptorsPtr_ = new donorAcceptorList
-        (
-            donorAcceptorRegionData,
-            true
-        );
-
-        // Set the flag to true and return
-        updateSuitableOverlapFlag(true);
-
-        return foundSuitableOverlap();
-    } // else connected fringes are not ready yet, foundSuitableOverlap flag is
-      // alraedy false, so there's nothing to do
 
     return foundSuitablaOverlap();
 }
@@ -335,6 +742,16 @@ const Foam::labelList& Foam::donorBasedLayeredOverlapFringe::fringeHoles() const
     {
         calcAddressing();
     }
+    else if (fringeHolesPtr_->empty())
+    {
+        // Fringe holes pointer is empty, delete both acceptorPtr_ and
+        // fringeHolesPtr_ and calculate addressing. Since this fringe strategy
+        // depends on other fringes, we need to have a special control in the
+        // iterative algorithm that will start only when all the others are done
+        // See calcAddressing() for details
+        deleteDemandDrivenData(fringeHolesPtr_);
+        deleteDemandDrivenData(acceptorsPtr_);
+    }
 
     return *fringeHolesPtr_;
 }
@@ -346,6 +763,16 @@ const Foam::labelList& Foam::donorBasedLayeredOverlapFringe::candidateAcceptors(
     {
         calcAddressing();
     }
+    else if (acceptorsPtr_->empty())
+    {
+        // Acceptors pointer is empty, delete both acceptorPtr_ and
+        // fringeHolesPtr_ and calculate addressing. Since this fringe strategy
+        // depends on other fringes, we need to have a special control in the
+        // iterative algorithm that will start only when all the others are done
+        // See calcAddressing() for details
+        deleteDemandDrivenData(fringeHolesPtr_);
+        deleteDemandDrivenData(acceptorsPtr_);
+    }
 
     return *acceptorsPtr_;
 }

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

@@ -29,13 +29,13 @@ Description
     until the final donor/acceptor assembly has been performed for all regions
     whose donor region is this region. Then, all donors are collected and the
     acceptors are cells neighbouring the donors nLayers towards the interior.
-    Interior is defined either by a user-specified point or as a centre of
+    Interior is defined either by user-specified points for each region or as a
-    volume of the donor cells.
+    centre of volume of the donor cells in particular region.
 
     This fringe algorithm is intended to be used along with the faceCells fringe
     on the other side, where the cell sizes are not significantly different from
-    each other (e.g. 10:1 cell ratio will probably be problematic to correctly
+    each other (e.g. 10:1 cell ratio, where the finer cells are found on the
-    set-up).
+    background mesh will probably be problematic to correctly set-up).
 
 Author
     Vuko Vukcevic, Wikki Ltd.  All rights reserved.
@@ -72,8 +72,8 @@ class donorBasedLayeredOverlapFringe
 
         //- Optional list of points representing a rough estimate of the centre
         //  for each underlying connected region. If these are not provided, the
-        //  centre is calculated as the centre of volume of all donors for a
+        //  centre is calculated as the centre of all donors for a given
-        //  given connected region
+        //  connected region
         pointList regionCentrePoints_;
 
         //- How many layers to move away from connected region donors to define
@@ -90,6 +90,13 @@ class donorBasedLayeredOverlapFringe
         mutable donorAcceptorList* finalDonorAcceptorsPtr_;
 
 
+    // Private static data
+
+        //- Distance tolerance to determine propagation direction. Note:
+        //  absolute value, default = 0. Might be useful is some strange cases
+        static const debug::tolerancesSwitch distTol_;
+
+
     // Private Member Functions
 
         //- Disallow default bitwise copy construct