[FEM] Elmer: fix flux equation

- the Flux solver must be executed before Heat and Electrostatic
- the analysis can have multiple Flux equations -> write a unique solver name to case.sif
- the Flux equation can currently only take 2 possible values. Therefore provide them as enum

src/Mod/Fem/femsolver/elmer/equations/electricforce.py

@@ -58,6 +58,9 @@ class Proxy(linear.Proxy, equationbase.ElectricforceProxy):
 
         obj.ExecSolver = SOLVER_EXEC_METHODS
         obj.ExecSolver = "After Timestep"
+        # Electrostatic has priority 10 and Electricforce needs
+        # the potential field calculated by Electrostatic
+        # therefore set priority to 5
         obj.Priority = 5
 
 

src/Mod/Fem/femsolver/elmer/equations/flux.py

@@ -34,6 +34,8 @@ from femtools import femutils
 from ... import equationbase
 from . import linear
 
+COEFFICIENTS = ["Heat Conductivity", "None"]
+VARIABLES = ["Potential", "Temperature"]
 
 def create(doc, name="Flux"):
     return femutils.createObject(
@@ -111,23 +113,28 @@ class Proxy(linear.Proxy, equationbase.FluxProxy):
             )
         )
         obj.addProperty(
-            "App::PropertyString",
+            "App::PropertyEnumeration",
             "FluxCoefficient",
             "Flux",
-            "Name of proportionality coefficient\nto compute the flux"
+            "Proportionality coefficient\nto compute the flux"
         )
         obj.addProperty(
-            "App::PropertyString",
+            "App::PropertyEnumeration",
             "FluxVariable",
             "Flux",
             "Variable name for flux calculation"
         )
 
-        obj.Priority = 5
         obj.CalculateFlux = True
         # set defaults according to the Elmer manual
-        obj.FluxCoefficient = "Temperature"
-        obj.FluxVariable = "Heat Conductivity"
+        obj.FluxCoefficient = COEFFICIENTS
+        obj.FluxCoefficient = "Heat Conductivity"
+        obj.FluxVariable = VARIABLES
+        obj.FluxVariable = "Temperature"
+        # Electrostatic has priority 10, Heat has 20 and Flux needs
+        # to be solved before these equations
+        # therefore set priority to 25
+        obj.Priority = 25
 
 
 class ViewProxy(linear.ViewProxy, equationbase.FluxViewProxy):

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

@@ -52,6 +52,7 @@ from femtools import membertools
 from .equations import elasticity
 from .equations import electricforce
 from .equations import flow
+from .equations import flux
 from .equations import heat
 
 
@@ -713,7 +714,7 @@ class Writer(object):
         # check if we need to update the equation
         self._updateFluxSolver(equation)
         # output the equation parameters
-        s["Equation"] = "Flux Solver"  # equation.Name
+        s["Equation"] = equation.Name
         s["Procedure"] = sifio.FileAttr("FluxSolver/FluxSolver")
         if equation.AverageWithinMaterials is True:
             s["Average Within Materials"] = equation.AverageWithinMaterials
@@ -799,13 +800,41 @@ class Writer(object):
                     "are a posteriori set to zero."
                 )
             )
+        tempFluxCoefficient = ""
+        if hasattr(equation, "FluxCoefficient"):
+            if equation.FluxCoefficient not in flux.COEFFICIENTS:
+                # was an App::PropertyString and changed to
+                # App::PropertyEnumeration
+                tempFluxCoefficient = equation.FluxCoefficient
+                equation.removeProperty("FluxCoefficient")
         if not hasattr(equation, "FluxCoefficient"):
             equation.addProperty(
-                "App::PropertyString",
+                "App::PropertyEnumeration",
                 "FluxCoefficient",
                 "Flux",
                 "Name of proportionality coefficient\nto compute the flux"
             )
+            equation.FluxCoefficient = flux.COEFFICIENTS
+            if tempFluxCoefficient:
+                equation.FluxCoefficient = tempFluxCoefficient
+            else:
+                equation.FluxCoefficient = "None"
+        tempFluxVariable = ""
+        if hasattr(equation, "FluxVariable"):
+            if equation.FluxVariable not in flux.VARIABLES:
+                # was an App::PropertyString and changed to
+                # App::PropertyEnumeration
+                tempFluxVariable = equation.FluxVariable
+                equation.removeProperty("FluxVariable")
+                equation.addProperty(
+                    "App::PropertyEnumeration",
+                    "FluxVariable",
+                    "Flux",
+                    "Variable name for flux calculation"
+                )
+                equation.FluxVariable = flux.VARIABLES
+                equation.FluxVariable = tempFluxVariable
+
 
     def _handleElectricforce(self):
         activeIn = []