Fem: Add partial support for hexahedral elements - fixes FreeCAD#5698

Author: marioalexis84

src/Mod/Fem/femmesh/gmshtools.py

@@ -151,6 +151,17 @@ def __init__(self, gmsh_mesh_obj, analysis=None):
         else:
             self.HighOrderOptimize = "0"
 
+        # SubdivisionAlgorithm
+        algoSubdiv = self.mesh_obj.SubdivisionAlgorithm
+        if algoSubdiv == "All Quadrangles":
+            self.SubdivisionAlgorithm = "1"
+        elif algoSubdiv == "All Hexahedra":
+            self.SubdivisionAlgorithm = "2"
+        elif algoSubdiv == "Barycentric":
+            self.SubdivisionAlgorithm = "3"
+        else:
+            self.SubdivisionAlgorithm = "0"
+
         # mesh groups
         if self.mesh_obj.GroupsOfNodes is True:
             self.group_nodes_export = True
@@ -858,6 +869,15 @@ def write_geo(self):
         geo.write("Mesh.Algorithm3D = " + self.algorithm3D + ";\n")
         geo.write("\n")
 
+        geo.write("// subdivision algorithm\n")
+        geo.write("Mesh.SubdivisionAlgorithm = " + self.SubdivisionAlgorithm + ";\n")
+        geo.write("\n")
+
+        geo.write("// incomplete second order elements\n")
+        sec_order_inc = "1" if self.mesh_obj.SecondOrderIncomplete else "0"
+        geo.write("Mesh.SecondOrderIncomplete = " + sec_order_inc + ";\n")
+        geo.write("\n")
+
         geo.write("// meshing\n")
         # remove duplicate vertices
         # see https://forum.freecad.org/viewtopic.php?f=18&t=21571&start=20#p179443

src/Mod/Fem/femobjects/mesh_gmsh.py

@@ -73,6 +73,12 @@ class MeshGmsh(base_fempythonobject.BaseFemPythonObject):
         "Elastic",
         "Fast curving"
     ]
+    known_mesh_SubdivisionAlgorithms = [
+        "None",
+        "All Quadrangles",
+        "All Hexahedra",
+        "Barycentric"
+    ]
 
     def __init__(self, obj):
         super(MeshGmsh, self).__init__(obj)
@@ -305,3 +311,22 @@ def add_properties(self, obj):
                 "For each group create not only the elements but the nodes too."
             )
             obj.GroupsOfNodes = False
+
+        if not hasattr(obj, "SubdivisionAlgorithm"):
+            obj.addProperty(
+                "App::PropertyEnumeration",
+                "SubdivisionAlgorithm",
+                "FEM Gmsh Mesh Params",
+                "Mesh subdivision algorithm"
+            )
+            obj.SubdivisionAlgorithm = MeshGmsh.known_mesh_SubdivisionAlgorithms
+            obj.SubdivisionAlgorithm = "None"
+
+        if not hasattr(obj, "SecondOrderIncomplete"):
+            obj.addProperty(
+                "App::PropertyBool",
+                "SecondOrderIncomplete",
+                "FEM Gmsh Mesh Params",
+                "Create incomplete second order elements"
+            )
+            obj.SecondOrderIncomplete = False