ENH: overset: Initial release of overset capability.

Adds overset discretisation to selected physics:
- diffusion : overLaplacianDyMFoam
- incompressible steady : overSimpleFoam
- incompressible transient : overPimpleDyMFoam
- compressible transient: overRhoPimpleDyMFoam
- two-phase VOF: overInterDyMFoam

The overset method chosen is a parallel, fully implicit implementation
whereby the interpolation (from donor to acceptor) is inserted as an
adapted discretisation on the donor cells, such that the resulting matrix
can be solved using the standard linear solvers.

Above solvers come with a set of tutorials, showing how to create and set-up
simple simulations from scratch.

src/meshTools/AMIInterpolation/GAMG/interfaceFields/cyclicACMIGAMGInterfaceField/cyclicACMIGAMGInterfaceField.C

@@ -93,6 +93,7 @@ Foam::cyclicACMIGAMGInterfaceField::~cyclicACMIGAMGInterfaceField()
 void Foam::cyclicACMIGAMGInterfaceField::updateInterfaceMatrix
 (
     scalarField& result,
+    const bool add,
     const scalarField& psiInternal,
     const scalarField& coeffs,
     const direction cmpt,
@@ -117,12 +118,7 @@ void Foam::cyclicACMIGAMGInterfaceField::updateInterfaceMatrix
         pnf = cyclicACMIInterface_.neighbPatch().AMI().interpolateToTarget(pnf);
     }
 
-    const labelUList& faceCells = cyclicACMIInterface_.faceCells();
-
-    forAll(faceCells, elemI)
-    {
-        result[faceCells[elemI]] -= coeffs[elemI]*pnf[elemI];
-    }
+    this->addToInternalField(result, !add, coeffs, pnf);
 }
 
 

src/meshTools/AMIInterpolation/GAMG/interfaceFields/cyclicACMIGAMGInterfaceField/cyclicACMIGAMGInterfaceField.H

@@ -120,6 +120,7 @@ public:
             virtual void updateInterfaceMatrix
             (
                 scalarField& result,
+                const bool add,
                 const scalarField& psiInternal,
                 const scalarField& coeffs,
                 const direction cmpt,

src/meshTools/AMIInterpolation/GAMG/interfaceFields/cyclicAMIGAMGInterfaceField/cyclicAMIGAMGInterfaceField.C

@@ -93,6 +93,7 @@ Foam::cyclicAMIGAMGInterfaceField::~cyclicAMIGAMGInterfaceField()
 void Foam::cyclicAMIGAMGInterfaceField::updateInterfaceMatrix
 (
     scalarField& result,
+    const bool add,
     const scalarField& psiInternal,
     const scalarField& coeffs,
     const direction cmpt,
@@ -117,12 +118,7 @@ void Foam::cyclicAMIGAMGInterfaceField::updateInterfaceMatrix
         pnf = cyclicAMIInterface_.neighbPatch().AMI().interpolateToTarget(pnf);
     }
 
-    const labelUList& faceCells = cyclicAMIInterface_.faceCells();
-
-    forAll(faceCells, elemI)
-    {
-        result[faceCells[elemI]] -= coeffs[elemI]*pnf[elemI];
-    }
+    this->addToInternalField(result, !add, coeffs, pnf);
 }
 
 

src/meshTools/AMIInterpolation/GAMG/interfaceFields/cyclicAMIGAMGInterfaceField/cyclicAMIGAMGInterfaceField.H

@@ -119,6 +119,7 @@ public:
             virtual void updateInterfaceMatrix
             (
                 scalarField& result,
+                const bool add,
                 const scalarField& psiInternal,
                 const scalarField& coeffs,
                 const direction cmpt,

src/meshTools/regionCoupled/GAMG/interfaceFields/regionCoupledGAMGInterfaceField/regionCoupledGAMGInterfaceField.H

@@ -112,6 +112,7 @@ public:
             virtual void updateInterfaceMatrix
             (
                 scalarField&,
+                const bool add,
                 const scalarField&,
                 const scalarField&,
                 const direction,

src/meshTools/regionCoupled/GAMG/interfaceFields/regionCoupledGAMGInterfaceField/regionCoupledWallGAMGInterfaceField.H

@@ -113,6 +113,7 @@ public:
             virtual void updateInterfaceMatrix
             (
                 scalarField&,
+                const bool add,
                 const scalarField&,
                 const scalarField&,
                 const direction,