surfaceInterpolation::makeWeight: improve handling of very small faces

If division by the face area might cause an overflow use the cell-face distances
directly to calculate the weights.

src/finiteVolume/fvMesh/fvPatches/constraint/cyclic/cyclicFvPatch.C

@@ -2,7 +2,7 @@
   =========                 |
   \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
    \\    /   O peration     | Website:  https://openfoam.org
-    \\  /    A nd           | Copyright (C) 2011-2018 OpenFOAM Foundation
+    \\  /    A nd           | Copyright (C) 2011-2019 OpenFOAM Foundation
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
 License
@@ -43,15 +43,30 @@ void Foam::cyclicFvPatch::makeWeights(scalarField& w) const
 {
     const cyclicFvPatch& nbrPatch = neighbFvPatch();
 
-    const scalarField deltas(nf()&coupledFvPatch::delta());
-    const scalarField nbrDeltas(nbrPatch.nf()&nbrPatch.coupledFvPatch::delta());
+    const vectorField delta(coupledFvPatch::delta());
+    const vectorField nbrDelta(nbrPatch.coupledFvPatch::delta());
 
-    forAll(deltas, facei)
+    const scalarField nfDelta(nf() & delta);
+    const scalarField nbrNfDelta(nbrPatch.nf() & nbrDelta);
+
+    forAll(delta, facei)
     {
-        scalar di = deltas[facei];
-        scalar dni = nbrDeltas[facei];
+        const scalar ndoi = nfDelta[facei];
+        const scalar ndni = nbrNfDelta[facei];
+        const scalar ndi = ndoi + ndni;
 
-        w[facei] = dni/(di + dni);
+        if (ndni/vGreat < ndi)
+        {
+            w[facei] = ndni/ndi;
+        }
+        else
+        {
+            const scalar doi = mag(delta[facei]);
+            const scalar dni = mag(nbrDelta[facei]);
+            const scalar di = doi + dni;
+
+            w[facei] = dni/di;
+        }
     }
 }
 

src/finiteVolume/fvMesh/fvPatches/constraint/processor/processorFvPatch.C

@@ -2,7 +2,7 @@
   =========                 |
   \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
    \\    /   O peration     | Website:  https://openfoam.org
-    \\  /    A nd           | Copyright (C) 2011-2018 OpenFOAM Foundation
+    \\  /    A nd           | Copyright (C) 2011-2019 OpenFOAM Foundation
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
 License
@@ -42,20 +42,44 @@ void Foam::processorFvPatch::makeWeights(scalarField& w) const
 {
     if (Pstream::parRun())
     {
+        const vectorField delta(coupledFvPatch::delta());
+
         // The face normals point in the opposite direction on the other side
-        scalarField neighbFaceCentresCn
+        const vectorField nbrDelta
+        (
+            procPolyPatch_.neighbFaceCentres()
+          - procPolyPatch_.neighbFaceCellCentres()
+        );
+
+        const scalarField nfDelta(nf() & delta);
+
+        const scalarField nbrNfDelta
         (
             (
                 procPolyPatch_.neighbFaceAreas()
                /(mag(procPolyPatch_.neighbFaceAreas()) + vSmall)
-            )
-          & (
-              procPolyPatch_.neighbFaceCentres()
-            - procPolyPatch_.neighbFaceCellCentres())
+            ) & nbrDelta
         );
 
-        w = neighbFaceCentresCn
-           /((nf()&coupledFvPatch::delta()) + neighbFaceCentresCn);
+        forAll(delta, facei)
+        {
+            const scalar ndoi = nfDelta[facei];
+            const scalar ndni = nbrNfDelta[facei];
+            const scalar ndi = ndoi + ndni;
+
+            if (ndni/vGreat < ndi)
+            {
+                w[facei] = ndni/ndi;
+            }
+            else
+            {
+                const scalar doi = mag(delta[facei]);
+                const scalar dni = mag(nbrDelta[facei]);
+                const scalar di = doi + dni;
+
+                w[facei] = dni/di;
+            }
+        }
     }
     else
     {

src/finiteVolume/interpolation/surfaceInterpolation/surfaceInterpolation/surfaceInterpolation.C

@@ -2,7 +2,7 @@
   =========                 |
   \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
    \\    /   O peration     | Website:  https://openfoam.org
-    \\  /    A nd           | Copyright (C) 2011-2018 OpenFOAM Foundation
+    \\  /    A nd           | Copyright (C) 2011-2019 OpenFOAM Foundation
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
 License
@@ -178,9 +178,22 @@ void Foam::surfaceInterpolation::makeWeights() const
         // 90 deg and the dot-product will be positive.  For invalid
         // meshes (d & s <= 0), this will stabilise the calculation
         // but the result will be poor.
-        scalar SfdOwn = mag(Sf[facei] & (Cf[facei] - C[owner[facei]]));
-        scalar SfdNei = mag(Sf[facei] & (C[neighbour[facei]] - Cf[facei]));
-        w[facei] = SfdNei/(SfdOwn + SfdNei);
+        const scalar SfdOwn = mag(Sf[facei]&(Cf[facei] - C[owner[facei]]));
+        const scalar SfdNei = mag(Sf[facei]&(C[neighbour[facei]] - Cf[facei]));
+        const scalar SfdOwnNei = SfdOwn + SfdNei;
+
+        if (SfdNei/vGreat < SfdOwnNei)
+        {
+            w[facei] = SfdNei/SfdOwnNei;
+        }
+        else
+        {
+            const scalar dOwn = mag(Cf[facei] - C[owner[facei]]);
+            const scalar dNei = mag(C[neighbour[facei]] - Cf[facei]);
+            const scalar dOwnNei = dOwn + dNei;
+
+            w[facei] = dNei/dOwnNei;
+        }
     }
 
     surfaceScalarField::Boundary& wBf =