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FEM: Add ccx capacitance two spheres example (#25117)

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* FEM: Update CMakeLists.txt

* FEM: add new ccx electrostatics example

* FEM: Update equation_electrostatics_capacitance_two_balls.py

* FEM: Update equation_electrostatics_capacitance_two_balls_ccx.py
This commit is contained in:
FEA-eng
2025-11-10 17:47:33 +01:00
committed by GitHub
parent 2d83e86f07
commit b038f4130c
3 changed files with 213 additions and 1 deletions
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1
src/Mod/Fem/CMakeLists.txt
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@@ -85,6 +85,7 @@ SET(FemExamples_SRCS
femexamples/elmer_nonguitutorial01_eigenvalue_of_elastic_beam.py
femexamples/equation_deformation_spring_elmer.py
femexamples/equation_electrostatics_capacitance_two_balls.py
femexamples/equation_electrostatics_capacitance_two_balls_ccx.py
femexamples/equation_electrostatics_electricforce_elmer_nongui6.py
femexamples/equation_flow_elmer_2D.py
femexamples/equation_flow_initial_elmer_2D.py

2
src/Mod/Fem/femexamples/equation_electrostatics_capacitance_two_balls.py
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@@ -39,7 +39,7 @@ def get_information():
return {
"name": "Electrostatics Capacitance Two Balls",
"meshtype": "solid",
"meshelement": "Tet10",
"meshelement": "Tet4",
"constraints": ["electrostatic potential"],
"solvers": ["elmer"],
"material": "fluid",

211
src/Mod/Fem/femexamples/equation_electrostatics_capacitance_two_balls_ccx.py Normal file
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@@ -0,0 +1,211 @@
# ***************************************************************************
# * Copyright (c) 2020 Sudhanshu Dubey <sudhanshu.thethunder@gmail.com> *
# * Copyright (c) 2021 Bernd Hahnebach <bernd@bimstatik.org> *
# * Copyright (c) 2025 Jakub Michalski <jakub.j.michalski@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 *
# * *
# ***************************************************************************
import sys
import FreeCAD
from FreeCAD import Rotation
from FreeCAD import Vector
import Fem
import ObjectsFem
from . import manager
from .manager import get_meshname
from .manager import init_doc
def get_information():
return {
"name": "Electrostatics Capacitance Two Balls CCX",
"meshtype": "solid",
"meshelement": "Tet4",
"constraints": ["electrostatic potential, electric charge density"],
"solvers": ["calculix"],
"material": "fluid",
"equations": ["electrostatic"],
}
def get_explanation(header=""):
return (
header
+ """
To run the example from Python console use:
from femexamples.equation_electrostatics_capacitance_two_balls_ccx import setup
setup()
See forum topic post for similar Elmer example:
https://forum.freecad.org/viewtopic.php?f=18&t=41488&start=90#p412047
Analytical solution - capacitance 6.68e-12 F
Source of analytical solution:
https://en.wikipedia.org/wiki/Capacitance#Capacitance_of_conductors_with_simple_shapes
To obtain capacitance in postprocessing:
- cut the sphere in half with Region Clip Filter to see the results inside
- calculate the potential difference (you can use the legend of the Potential field)
- divide the total applied charge (1e-9 C) by this potential difference
"""
)
def setup(doc=None, solvertype="calculix"):
# init FreeCAD document
if doc is None:
doc = init_doc()
# explanation object
# just keep the following line and change text string in get_explanation method
manager.add_explanation_obj(doc, get_explanation(manager.get_header(get_information())))
# geometric objects
small_sphere1 = doc.addObject("Part::Sphere", "Small_Sphere1")
small_sphere1.Placement = FreeCAD.Placement(Vector(-300, 0, 0), Rotation(Vector(0, 0, 1), 0))
small_sphere1.Radius = "100 mm"
small_sphere2 = doc.addObject("Part::Sphere", "Small_Sphere2")
small_sphere2.Placement = FreeCAD.Placement(Vector(300, 0, 0), Rotation(Vector(0, 0, 1), 0))
small_sphere2.Radius = "100 mm"
fusion = doc.addObject("Part::MultiFuse", "Fusion")
fusion.Shapes = [small_sphere1, small_sphere2]
large_sphere = doc.addObject("Part::Sphere", "Large_Sphere")
large_sphere.Radius = "1000 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")
if FreeCAD.GuiUp:
import FemGui
FemGui.setActiveAnalysis(analysis)
# solver
if solvertype == "calculix":
solver_obj = ObjectsFem.makeSolverCalculiX(doc, "SolverCalculiX")
solver_obj.AnalysisType = "electromagnetic"
solver_obj.ElectromagneticMode = "electrostatic"
analysis.addObject(solver_obj)
else:
FreeCAD.Console.PrintWarning(
"Unknown or unsupported solver type: {}. "
"No solver object was created.\n".format(solvertype)
)
# material
material_obj = ObjectsFem.makeMaterialFluid(doc, "Air")
mat = material_obj.Material
mat["Name"] = "Air"
mat["Density"] = "1.204 kg/m^3"
mat["ThermalConductivity"] = "0.02587 W/m/K"
mat["ThermalExpansionCoefficient"] = "3.43e-3 1/K"
mat["SpecificHeat"] = "1.01 kJ/kg/K"
mat["ElectricalConductivity"] = "1e-12 S/m"
mat["RelativePermeability"] = "1.0"
# mat["RelativePermittivity"] = "1.00059"
mat["RelativePermittivity"] = "1.0"
material_obj.Material = mat
material_obj.References = [(geom_obj, "Solid1")]
analysis.addObject(material_obj)
# constraint potential large sphere
name_pot1 = "ElectrostaticPotential1"
con_elect_pot1 = ObjectsFem.makeConstraintElectrostaticPotential(doc, name_pot1)
con_elect_pot1.References = [(geom_obj, "Face1")]
con_elect_pot1.Potential = "0.0 mV"
analysis.addObject(con_elect_pot1)
# constraint electric charge density small sphere 1
name_ch1 = "ElectricChargeDensity1"
con_elect_charge_dens1 = ObjectsFem.makeConstraintElectricChargeDensity(doc, name_ch1)
con_elect_charge_dens1.References = [(geom_obj, "Face2")]
con_elect_charge_dens1.Mode = "Interface"
con_elect_charge_dens1.InterfaceChargeDensity = "7.94e-9 C/m^2"
analysis.addObject(con_elect_charge_dens1)
# constraint electric charge density small sphere 2
name_ch2 = "ElectricChargeDensity2"
con_elect_charge_dens2 = ObjectsFem.makeConstraintElectricChargeDensity(doc, name_ch2)
con_elect_charge_dens2.References = [(geom_obj, "Face3")]
con_elect_charge_dens2.Mode = "Interface"
con_elect_charge_dens2.InterfaceChargeDensity = "-7.94e-9 C/m^2"
analysis.addObject(con_elect_charge_dens2)
# mesh
femmesh_obj = analysis.addObject(ObjectsFem.makeMeshGmsh(doc, get_meshname()))[0]
femmesh_obj.Shape = geom_obj
femmesh_obj.SecondOrderLinear = False
femmesh_obj.CharacteristicLengthMax = "50 mm"
femmesh_obj.ViewObject.Visibility = False
# mesh_region
mesh_region = ObjectsFem.makeMeshRegion(doc, femmesh_obj, name="MeshRegion")
mesh_region.CharacteristicLength = "20 mm"
mesh_region.References = [(geom_obj, "Face2"), (geom_obj, "Face3")]
mesh_region.ViewObject.Visibility = False
# generate the mesh
from femmesh import gmshtools
gmsh_mesh = gmshtools.GmshTools(femmesh_obj, analysis)
try:
error = gmsh_mesh.create_mesh()
except Exception:
error = sys.exc_info()[1]
FreeCAD.Console.PrintError(f"Unexpected error when creating mesh: {error}\n")
if error:
# try to create from existing rough 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.FemMesh = fem_mesh
doc.recompute()
return doc