FEM: elmer writer, make use of new unit schema FEM: mm, N

src/Mod/Fem/femsolver/elmer/writer.py

@@ -54,12 +54,6 @@ _ELMERGRID_OFORMAT = "2"
 _SOLID_PREFIX = "Solid"
 
 
-# TODO constants and units
-# should be only one system for all solver and not in each solver
-# https://forum.freecadweb.org/viewtopic.php?t=47895
-# https://forum.freecadweb.org/viewtopic.php?t=48451
-
-
 def _getAllSubObjects(obj):
     s = ["Solid" + str(i + 1) for i in range(len(obj.Shape.Solids))]
     s.extend(("Face" + str(i + 1) for i in range(len(obj.Shape.Faces))))
@@ -101,6 +95,19 @@ class Writer(object):
         self._writeStartinfo()
 
     def _handleUnits(self):
+        # TODO constants and units
+        # should be only one system for all solver and not in each solver
+        # https://forum.freecadweb.org/viewtopic.php?t=47895
+        # https://forum.freecadweb.org/viewtopic.php?t=48451
+        # https://forum.freecadweb.org/viewtopic.php?f=10&t=48642
+        # The FreeCAD unit schema is only used to determine the schema number
+        # all definition are done here ATM
+        # keep in mind a unit schema might not be consistent:
+        # Length could be mm and Area could be m2 and Volume could be cm3
+        # as long as only the seven base units are retrieved from a unit schema
+        # the units are consistent
+        # TODO retrieve the seven base units from FreeCAD unit schema
+        # instead of hard coding them here for a second once
         self.unit_schema = 0
         self.unit_system = {  # standard FreeCAD Base units = unit schema 0
             "L": "mm",
@@ -132,7 +139,22 @@ class Writer(object):
                 "N": "mol",
                 "J": "cd",
             }
-        elif self.unit_schema > 1:
+        elif self.unit_schema == 8:
+            # see also unit comment in calculix writer
+            Console.PrintMessage(
+                "The FEM unit schema mm/N/s is used. "
+                "Elmer sif-file writing is done in FEM-units.\n"
+            )
+            self.unit_system = {
+                "L": "mm",
+                "M": "t",
+                "T": "s",
+                "I": "A",
+                "O": "K",
+                "N": "mol",
+                "J": "cd",
+            }
+        elif self.unit_schema > 1 and self.unit_schema != 8:
             Console.PrintMessage(
                 "Unit schema: {} not supported by Elmer writer. "
                 "The FreeCAD standard unit schema mm/kg/s is used. "