ENH: add blockMeshDict "mergeType" keyword (#1589)

- enumerated values are (points | topology) which can be optionally
  specified in the blockMeshDict. Default is 'topology'.

  If the command-line option `blockMesh -merge-points` is specified,
  this has absolute priority over any blockMeshDict entry.

STYLE: changed blockMesh "-blockTopology" option to "-write-obj"

- this is more specific to what it does. Potentially wish to add a
  "-write-vtk" option in the future.

TUT: adjust tutorials to use preferred or necessary merge strategies:

  * channel395DFSEM - topology
  * nozzleFlow2D - points
  * pipeCyclic - points

applications/utilities/mesh/generation/blockMesh/blockMesh.C

@@ -43,11 +43,11 @@ Usage
     \b blockMesh [OPTION]
 
     Options:
-      - \par -blockTopology
+      - \par -write-obj
-        Write the topology as a set of edges in OBJ format and exit.
+        Write topology as a set of edges in OBJ format and exit.
 
-      - \par -merge-geometric
+      - \par -merge-points
-        Use geometric instead of topological merging
+        Merge points instead of default topological merge
 
       - \par -region \<name\>
         Specify alternative mesh region.
@@ -117,13 +117,15 @@ int main(int argc, char *argv[])
 
     argList::addBoolOption
     (
-        "blockTopology",
+        "write-obj",
         "Write block edges and centres as obj files and exit"
     );
+    argList::addOptionCompat("write-obj", {"blockTopology", 1912});
+
     argList::addBoolOption
     (
-        "merge-geometric",
+        "merge-points",
-        "Use geometric (point) merging instead of topological merging "
+        "Geometric (point) merging instead of topological merging "
         "(slower, fails with high-aspect cells. default for 1912 and earlier)",
         true  // mark as an advanced option
     );
@@ -157,12 +159,12 @@ int main(int argc, char *argv[])
     // Remove old files, unless disabled
     const bool removeOldFiles = !args.found("noClean");
 
-    // Topological merge, unless otherwise specified
+    // Default merge (topology), unless otherwise specified
-    blockMesh::mergeStrategy strategy(blockMesh::TOPOLOGICAL);
+    blockMesh::mergeStrategy strategy(blockMesh::DEFAULT_MERGE);
 
-    if (args.found("merge-geometric"))
+    if (args.found("merge-points"))
     {
-        strategy = blockMesh::GEOMETRIC;
+        strategy = blockMesh::MERGE_POINTS;
     }
 
     word regionName(polyMesh::defaultRegion);
@@ -217,11 +219,15 @@ int main(int argc, char *argv[])
     }
 
 
-    if (args.found("blockTopology"))
+    bool quickExit = false;
+
+    if (args.found("write-obj"))
     {
+        quickExit = true;
+
         Info<< nl;
 
-        // Write mesh as edges.
+        // Write mesh as edges
         {
             OFstream os(runTime.path()/"blockTopology.obj");
 
@@ -238,21 +244,21 @@ int main(int argc, char *argv[])
             Info<< "Writing block centres as obj format: "
                 << os.name().name() << endl;
 
-            const polyMesh& topo = blocks.topology();
+            for (const point& cc : blocks.topology().cellCentres())
-
-            for (const point& cc :  topo.cellCentres())
             {
                 os << "v " << cc.x() << ' ' << cc.y() << ' ' << cc.z() << nl;
             }
         }
+    }
 
+    if (quickExit)
+    {
         Info<< "\nEnd\n" << endl;
 
         return 0;
     }
 
 
-
     // Instance for resulting mesh
     if (useTime)
     {

src/mesh/blockMesh/blockMesh/blockMesh.C

@@ -37,13 +37,21 @@ namespace Foam
 }
 
 
+const Foam::Enum<Foam::blockMesh::mergeStrategy>
+Foam::blockMesh::strategyNames_
+({
+    { mergeStrategy::MERGE_TOPOLOGY, "topology" },
+    { mergeStrategy::MERGE_POINTS, "points" },
+});
+
+
 // * * * * * * * * * * * * * * * * Constructors  * * * * * * * * * * * * * * //
 
 Foam::blockMesh::blockMesh
 (
     const IOdictionary& dict,
     const word& regionName,
-    const mergeStrategy strategy
+    mergeStrategy strategy
 )
 :
     meshDict_(dict),
@@ -77,17 +85,24 @@ Foam::blockMesh::blockMesh
     vertices_(Foam::vertices(blockVertices_)),
     topologyPtr_(createTopology(meshDict_, regionName))
 {
-    // TODO - extend with Enum
+    // Command-line option has precedence over dictionary setting
 
-    bool useTopoMerge = (strategy == mergeStrategy::TOPOLOGICAL);
+    if (strategy == mergeStrategy::DEFAULT_MERGE)
-
-    if (meshDict_.getOrDefault("fastMerge", useTopoMerge))
     {
-        calcTopologicalMerge();
+        strategyNames_.readIfPresent("mergeType", meshDict_, strategy);
+
+        // Warn about fairly obscure old "fastMerge" option?
+    }
+
+    if (strategy == mergeStrategy::MERGE_POINTS)
+    {
+        // MERGE_POINTS
+        calcGeometricalMerge();
     }
     else
     {
-        calcGeometricalMerge();
+        // MERGE_TOPOLOGY
+        calcTopologicalMerge();
     }
 }
 
@@ -96,7 +111,7 @@ Foam::blockMesh::blockMesh
 
 bool Foam::blockMesh::valid() const
 {
-    return topologyPtr_.valid();
+    return bool(topologyPtr_);
 }
 
 
@@ -219,18 +234,14 @@ Foam::label Foam::blockMesh::numZonedBlocks() const
 
 void Foam::blockMesh::writeTopology(Ostream& os) const
 {
-    const pointField& pts = topology().points();
+    for (const point& p : topology().points())
-
-    for (const point& pt : pts)
     {
-        os << "v " << pt.x() << ' ' << pt.y() << ' ' << pt.z() << endl;
+        os << "v " << p.x() << ' ' << p.y() << ' ' << p.z() << nl;
     }
 
-    const edgeList& edges = topology().edges();
+    for (const edge& e : topology().edges())
-
-    for (const edge& e : edges)
     {
-        os << "l " << e.start() + 1 << ' ' << e.end() + 1 << endl;
+        os << "l " << e.start() + 1 << ' ' << e.end() + 1 << nl;
     }
 }
 

src/mesh/blockMesh/blockMesh/blockMesh.H

@@ -30,6 +30,23 @@ Class
 Description
     A multi-block mesh generator
 
+    Dictionary controls
+    \table
+        Property    | Description                           | Required | Default
+        scale       | Point scaling                         | no  | 1.0
+        vertices    |                                       | yes |
+        blocks      |                                       | yes |
+        edges       |                                       | no  |
+        faces       |                                       | no  |
+        boundary    | Boundary definition                   | no  |
+        patches     | Alternate version for "boundary"      | no  |
+        namedBlocks |                                       | no  |
+        namedVertices |                                     | no  |
+        mergeType   | Merging "points" or "topology"        | no  | topology
+        checkFaceCorrespondence |                           | no  | true
+        verbose     |                                       | no  | true
+    \endtable
+
 Note
     The vertices, cells and patches for filling the blocks are demand-driven.
 
@@ -45,6 +62,7 @@ SourceFiles
 #ifndef blockMesh_H
 #define blockMesh_H
 
+#include "Enum.H"
 #include "blockList.H"
 #include "searchableSurfaces.H"
 #include "polyMesh.H"
@@ -66,6 +84,27 @@ class blockMesh
 :
     public blockList
 {
+public:
+
+    // Data Types
+
+        //- The block merging strategy
+        enum mergeStrategy
+        {
+            DEFAULT_MERGE,  //!< Default (TOPOLOGY), not selectable
+            MERGE_TOPOLOGY, //!< "topology" merge by block topology (default)
+            MERGE_POINTS    //!< "points" merge by point geometry
+        };
+
+
+private:
+
+    // Static Data
+
+        //- Names corresponding to the mergeStrategy
+        static const Enum<mergeStrategy> strategyNames_;
+
+
     // Private Data
 
         //- Reference to mesh dictionary
@@ -179,18 +218,7 @@ class blockMesh
 
 public:
 
-    // Data Types
+    //- Runtime type information
-
-        //- The block merging strategy
-        enum mergeStrategy
-        {
-            TOPOLOGICAL,    //!< Merge using block topology
-            GEOMETRIC       //!< Merge using point geometry
-        };
-
-
-    // Static Data Members
-
     ClassName("blockMesh");
 
 
@@ -202,7 +230,7 @@ public:
         (
             const IOdictionary& dict,
             const word& regionName,
-            const mergeStrategy strategy = TOPOLOGICAL
+            mergeStrategy strategy = mergeStrategy::DEFAULT_MERGE
         );
 
 

src/mesh/blockMesh/blockMesh/blockMeshMergeGeometrical.C

@@ -55,7 +55,7 @@ void Foam::blockMesh::calcGeometricalMerge()
 
     if (verboseOutput)
     {
-        Info<< "Creating merge list.." << flush;
+        Info<< "Creating merge list (geometric search).." << flush;
     }
 
     // set unused to -1

src/mesh/blockMesh/blockMesh/blockMeshMergeTopological.C

@@ -328,7 +328,7 @@ void Foam::blockMesh::calcTopologicalMerge()
 
     if (verboseOutput)
     {
-        Info<< "Creating merge list with fast topological search.." << flush;
+        Info<< "Creating merge list (topological search).." << flush;
     }
 
     // Size merge list and initialize to -1

tutorials/incompressible/pimpleFoam/LES/channel395DFSEM/system/blockMeshDict

@@ -1,7 +1,7 @@
 /*--------------------------------*- C++ -*----------------------------------*\
 | =========                 |                                                 |
 | \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
-|  \\    /   O peration     | Version:  v1912                                 |
+|  \\    /   O peration     | Version:  v2006                                 |
 |   \\  /    A nd           | Website:  www.openfoam.com                      |
 |    \\/     M anipulation  |                                                 |
 \*---------------------------------------------------------------------------*/
@@ -14,7 +14,7 @@ FoamFile
 }
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
-fastMerge   true;   // Use fast topological search
+mergeType topology; // Point merging is very slow
 
 scale   1;
 

tutorials/incompressible/simpleFoam/pipeCyclic/system/blockMeshDict

@@ -1,7 +1,7 @@
 /*--------------------------------*- C++ -*----------------------------------*\
 | =========                 |                                                 |
 | \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
-|  \\    /   O peration     | Version:  v1912                                 |
+|  \\    /   O peration     | Version:  v2006                                 |
 |   \\  /    A nd           | Website:  www.openfoam.com                      |
 |    \\/     M anipulation  |                                                 |
 \*---------------------------------------------------------------------------*/
@@ -14,6 +14,8 @@ FoamFile
 }
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
+mergeType points;   // Merge points instead of topology
+
 scale   1;
 
 //- Half angle of wedge in degrees

tutorials/multiphase/interFoam/LES/nozzleFlow2D/system/blockMeshDict

@@ -1,7 +1,7 @@
 /*--------------------------------*- C++ -*----------------------------------*\
 | =========                 |                                                 |
 | \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
-|  \\    /   O peration     | Version:  v1912                                 |
+|  \\    /   O peration     | Version:  v2006                                 |
 |   \\  /    A nd           | Website:  www.openfoam.com                      |
 |    \\/     M anipulation  |                                                 |
 \*---------------------------------------------------------------------------*/
@@ -14,6 +14,8 @@ FoamFile
 }
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
+mergeType points;   // Merge points instead of topology
+
 scale   1e-6;
 
 vertices