FEM: solver CalculiX: add geometrical nonlinear analysis

src/Mod/Fem/FemInputWriterCcx.py

@@ -225,8 +225,12 @@ def write_step_begin(self, f):
         f.write('\n***********************************************************\n')
         f.write('** One step is needed to run the mechanical analysis of FreeCAD\n')
         f.write('** written by {} function\n'.format(sys._getframe().f_code.co_name))
-        f.write('*STEP\n')
-        f.write('*STATIC\n')
+        static_frequency_step = '*STEP'
+        if self.solver_obj.GeometricalNonlinearity == "nonlinear" and self.analysis_type == 'static':
+            static_frequency_step += ', NLGEOM'   # https://www.comsol.com/blogs/what-is-geometric-nonlinearity/
+        elif self.solver_obj.GeometricalNonlinearity == "nonlinear" and self.analysis_type == 'frequency':
+            print('Analysis type frequency and geometrical nonlinear analyis are not allowed together, linear is used instead!')
+        f.write(static_frequency_step + '\n')
 
     def write_constraints_fixed(self, f):
         f.write('\n***********************************************************\n')

src/Mod/Fem/FemToolsCcx.py

@@ -35,6 +35,7 @@
 class FemToolsCcx(FemTools.FemTools):
 
     known_analysis_types = ["static", "frequency"]
+    known_geom_nonlinear_types = ["linear", "nonlinear"]
     finished = QtCore.Signal(int)
 
     ## The constructor

src/Mod/Fem/_FemSolverCalculix.py

@@ -50,6 +50,15 @@ def __init__(self, obj):
         analysis_type = fem_prefs.GetInt("AnalysisType", 0)
         obj.AnalysisType = FemToolsCcx.FemToolsCcx.known_analysis_types[analysis_type]
 
+        known_geom_nonlinear_types = ["linear", "nonlinear"]
+        obj.addProperty("App::PropertyEnumeration", "GeometricalNonlinearity", "Fem", "Type of geometrical nonlinearity")
+        obj.GeometricalNonlinearity = known_geom_nonlinear_types
+        geom = ccx_prefs.GetBool("NonlinearGeometry", False)
+        if geom is True:
+            obj.GeometricalNonlinearity = known_geom_nonlinear_types[1]  # nonlinear
+        else:
+            obj.GeometricalNonlinearity = known_geom_nonlinear_types[0]  # linear
+
         obj.addProperty("App::PropertyIntegerConstraint", "NumberOfEigenmodes", "Fem", "Number of modes for frequency calculations")
         noe = fem_prefs.GetInt("NumberOfEigenmodes", 10)
         obj.NumberOfEigenmodes = (noe, 1, 100, 1)