FEM: examples, added capacitance two balls example

src/Mod/Fem/CMakeLists.txt

@@ -55,6 +55,7 @@ SET(FemExamples_SRCS
     femexamples/constraint_tie.py
     femexamples/constraint_transform_beam_hinged.py
     femexamples/examplesgui.py
+    femexamples/equation_electrostatics_capacitance_two_balls.py
     femexamples/manager.py
     femexamples/material_multiple_bendingbeam_fiveboxes.py
     femexamples/material_multiple_bendingbeam_fivefaces.py
@@ -74,6 +75,7 @@ SET(FemExampleMeshes_SRCS
     femexamples/meshes/mesh_boxes_2_vertikal_tetra10.py
     femexamples/meshes/mesh_canticcx_hexa20.py
     femexamples/meshes/mesh_canticcx_tetra10.py
+    femexamples/meshes/mesh_capacitance_two_balls_tetra10.py
     femexamples/meshes/mesh_constraint_tie_tetra10.py
     femexamples/meshes/mesh_contact_box_halfcylinder_tetra10.py
     femexamples/meshes/mesh_contact_tube_tube_tria3.py

src/Mod/Fem/femexamples/equation_electrostatics_capacitance_two_balls.py

@@ -0,0 +1,170 @@
+# ***************************************************************************
+# *   Copyright (c) 2020 Sudhanshu Dubey <sudhanshu.thethunder@gmail.com>   *
+# *                                                                         *
+# *   This file is part of the FreeCAD CAx development system.              *
+# *                                                                         *
+# *   This program is free software; you can redistribute it and/or modify  *
+# *   it under the terms of the GNU Lesser General Public License (LGPL)    *
+# *   as published by the Free Software Foundation; either version 2 of     *
+# *   the License, or (at your option) any later version.                   *
+# *   for detail see the LICENCE text file.                                 *
+# *                                                                         *
+# *   This program is distributed in the hope that it will be useful,       *
+# *   but WITHOUT ANY WARRANTY; without even the implied warranty of        *
+# *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the         *
+# *   GNU Library General Public License for more details.                  *
+# *                                                                         *
+# *   You should have received a copy of the GNU Library General Public     *
+# *   License along with this program; if not, write to the Free Software   *
+# *   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  *
+# *   USA                                                                   *
+# *                                                                         *
+# ***************************************************************************
+
+# to run the example use:
+"""
+from femexamples.equation_electrostatics_capacitance_two_balls import setup
+setup()
+"""
+# Electrostatics equation in FreeCAD FEM-Elmer
+# https://forum.freecadweb.org/viewtopic.php?f=18&t=41488&start=90#p412047
+
+import FreeCAD
+from FreeCAD import Rotation
+from FreeCAD import Vector
+
+import Fem
+import ObjectsFem
+
+mesh_name = "Mesh"  # needs to be Mesh to work with unit tests
+
+
+def init_doc(doc=None):
+    if doc is None:
+        doc = FreeCAD.newDocument()
+    return doc
+
+
+def get_information():
+    info = {"name": "Electrostatics Capacitance Two Balls",
+            "meshtype": "solid",
+            "meshelement": "Tet10",
+            "constraints": ["electrostatic potential"],
+            "solvers": ["elmer"],
+            "material": "fluid",
+            "equation": "electrostatic"
+            }
+    return info
+
+
+def setup(doc=None, solvertype="elmer"):
+    # setup base model
+
+    if doc is None:
+        doc = init_doc()
+
+    # geometry object
+    # name is important because the other method in this module use obj name
+    small_sphere1 = doc.addObject("Part::Sphere", "Small_Sphere1")
+    small_sphere1.Placement = FreeCAD.Placement(Vector(-1000, 0, 0), Rotation(Vector(0, 0, 1), 0))
+    small_sphere1.Radius = '500 mm'
+
+    small_sphere2 = doc.addObject("Part::Sphere", "Small_Sphere2")
+    small_sphere2.Placement = FreeCAD.Placement(Vector(1000, 0, 0), Rotation(Vector(0, 0, 1), 0))
+    small_sphere2.Radius = '500 mm'
+
+    fusion = doc.addObject("Part::MultiFuse", "Fusion")
+    fusion.Shapes = [small_sphere1, small_sphere2]
+
+    large_sphere = doc.addObject("Part::Sphere", "Large_Sphere")
+    large_sphere.Radius = '5000 mm'
+
+    geom_obj = doc.addObject("Part::Cut", "Cut")
+    geom_obj.Base = large_sphere
+    geom_obj.Tool = fusion
+    doc.recompute()
+
+    if FreeCAD.GuiUp:
+        geom_obj.ViewObject.Transparency = 75
+        geom_obj.ViewObject.Document.activeView().viewAxonometric()
+        geom_obj.ViewObject.Document.activeView().fitAll()
+
+    # analysis
+    analysis = ObjectsFem.makeAnalysis(doc, "Analysis")
+
+    # solver
+    if solvertype == "elmer":
+        solver_object = analysis.addObject(ObjectsFem.makeSolverElmer(doc, "SolverElmer"))[0]
+        eq_electrostatic = ObjectsFem.makeEquationElectrostatic(doc, solver_object)
+        eq_electrostatic.CalculateCapacitanceMatrix = True
+        eq_electrostatic.CalculateElectricEnergy = True
+        eq_electrostatic.CalculateElectricField = True
+    else:
+        FreeCAD.Console.PrintWarning(
+            "Not known or not supported solver type: {}. "
+            "No solver object was created.\n".format(solvertype)
+        )
+
+    # material
+    material_object = analysis.addObject(
+        ObjectsFem.makeMaterialFluid(doc, "FemMaterial")
+    )[0]
+    mat = material_object.Material
+    mat["Name"] = "Air-Generic"
+    mat["Density"] = "1.20 kg/m^3"
+    mat["KinematicViscosity"] = "15.11 mm^2/s"
+    mat["VolumetricThermalExpansionCoefficient"] = "0.00 µm/m/K"
+    mat["ThermalConductivity"] = "0.03 W/m/K"
+    mat["ThermalExpansionCoefficient"] = "0.0034/K"
+    mat["SpecificHeat"] = "1.00 J/kg/K"
+    mat["RelativePermittivity"] = "1.00"
+    material_object.Material = mat
+
+    # 1st potential_constraint
+    constraint_elect_pot0 = analysis.addObject(
+        ObjectsFem.makeConstraintElectrostaticPotential(doc))[0]
+    constraint_elect_pot0.References = [(geom_obj, "Face1")]
+    constraint_elect_pot0.ElectricInfinity = True
+
+    # 2nd potential_constraint
+    constraint_elect_pot1 = analysis.addObject(
+        ObjectsFem.makeConstraintElectrostaticPotential(doc))[0]
+    constraint_elect_pot1.References = [(geom_obj, "Face2")]
+    constraint_elect_pot1.CapacitanceBody = 1
+    constraint_elect_pot1.CapacitanceBodyEnabled = True
+
+    # 3rd potential_constraint
+    constraint_elect_pot2 = analysis.addObject(
+        ObjectsFem.makeConstraintElectrostaticPotential(doc))[0]
+    constraint_elect_pot2.References = [(geom_obj, "Face3")]
+    constraint_elect_pot2.CapacitanceBody = 2
+    constraint_elect_pot2.CapacitanceBodyEnabled = True
+
+    # constant vacuum permittivity
+    const_vaccum_permittivity = analysis.addObject(
+        ObjectsFem.makeConstantVacuumPermittivity(doc))[0]
+    const_vaccum_permittivity.VacuumPermittivity = '1 F/m'
+
+    # mesh
+    from .meshes.mesh_capacitance_two_balls_tetra10 import create_nodes, create_elements
+    fem_mesh = Fem.FemMesh()
+    control = create_nodes(fem_mesh)
+    if not control:
+        FreeCAD.Console.PrintError("Error on creating nodes.\n")
+    control = create_elements(fem_mesh)
+    if not control:
+        FreeCAD.Console.PrintError("Error on creating elements.\n")
+    femmesh_obj = analysis.addObject(
+        ObjectsFem.makeMeshGmsh(doc, mesh_name)
+    )[0]
+    femmesh_obj.FemMesh = fem_mesh
+    femmesh_obj.Part = geom_obj
+    femmesh_obj.SecondOrderLinear = False
+
+    # mesh_region
+    mesh_region = ObjectsFem.makeMeshRegion(doc, femmesh_obj)
+    mesh_region.CharacteristicLength = '300 mm'
+    mesh_region.References = [(geom_obj, "Face2"), (geom_obj, "Face3")]
+
+    doc.recompute()
+    return doc