FEM CalculiX 2D mechanical analyses (plane stress, plane strain and axisymmetric) #12562

FEA-eng · 2024-02-23T09:38:07Z

resolves #10864

This PR implements 2D mechanical analyses (plane stress, plane strain and axisymmetric) with CalculiX.

Usage:

Prepare the model in the same way as for analysis with shells - surface geometry and thickness defined. The geometry has to lie on the XY plane (and on the right side of the Y axis for axisymmetric).
Apply constraints to the edges of the model. Just don't use the fixed boundary condition since CalculiX doesn't support it in 2D at the moment (it may change in the next versions). Use the displacement boundary condition instead - X and Y translation and Z rotation are available for this type of analysis.
Switch Model Space in CalculiX solver settings from the default 3D to plane stress, plane strain or axisymmetric and run the analysis.

marioalexis84

Tested and works correctly.
Just some comments about duplicate code.
In my opinion, it would be enough to remove the duplicate code in write_femelement_geometry.py; The other functions can remain as they are, in any case, in the future I plan to extend the C++ writing function to avoid systematic editing of the already written file.

marioalexis84 · 2024-02-23T16:49:53Z

src/Mod/Fem/femmesh/meshtools.py

+    f.truncate()
+    f.close()
+def plane_stress(
+    fileName
+):
+    # replace shell elements with plane stress elements
+    f = open(fileName, "r+")
+    lines = f.readlines()
+    f.seek(0)
+    for line in lines:
+        if line.find("S3") != -1:
+            line = line.replace("S3", "CPS3")
+        if line.find("S6") != -1:
+            line = line.replace("S6", "CPS6")
+        if line.find("S4") != -1:
+            line = line.replace("S4", "CPS4")     
+        f.write(line)
+
+    f.truncate()
+    f.close()
+def plane_strain(
+    fileName
+):
+    # replace shell elements with plane strain elements
+    f = open(fileName, "r+")
+    lines = f.readlines()
+    f.seek(0)
+    for line in lines:
+        if line.find("S3") != -1:
+            line = line.replace("S3", "CPE3")
+        if line.find("S6") != -1:
+            line = line.replace("S6", "CPE6")
+        if line.find("S4") != -1:
+            line = line.replace("S4", "CPE4")      
+        f.write(line)
+
+    f.truncate()
+    f.close()
+def axisymmetric(
+    fileName
+):
+    # replace shell elements with axisymmetric elements
+    f = open(fileName, "r+")
+    lines = f.readlines()
+    f.seek(0)
+    for line in lines:
+        if line.find("S3") != -1:
+            line = line.replace("S3", "CAX3")
+        if line.find("S6") != -1:
+            line = line.replace("S6", "CAX6")
+        if line.find("S4") != -1:
+            line = line.replace("S4", "CAX4")    
+        f.write(line)
+


These functions plus beam_reduced_integration could be compacted into a single function that takes the appropriate parameters or use a base function that does the replacement and then called inside the others.

marioalexis84 · 2024-02-23T17:05:08Z

src/Mod/Fem/femsolver/calculix/write_femelement_geometry.py

+                if ccxwriter.solver_obj.ModelSpace == "3D":
+                    shellth_obj = matgeoset["shellthickness_obj"]
+                    section_def = "*SHELL SECTION, {}{}\n".format(elsetdef, material)
+                    thickness = shellth_obj.Thickness.getValueAs("mm").Value
+                    section_geo = "{:.13G}\n".format(thickness)
+                    f.write(section_def)
+                    f.write(section_geo)
+                else:
+                    shellth_obj = matgeoset["shellthickness_obj"]
+                    section_def = "*SOLID SECTION, {}{}\n".format(elsetdef, material)
+                    thickness = shellth_obj.Thickness.getValueAs("mm").Value
+                    section_geo = "{:.13G}\n".format(thickness)
+                    f.write(section_def)
+                    f.write(section_geo)    


It is better not to repeat code in the if-else block. Move duplicate code out of conditional block.

marioalexis84 · 2024-02-23T17:09:03Z

src/Mod/Fem/femsolver/calculix/write_mesh.py

+
+        # Use 2D elements if model space is not set to 3D
+        if ccxwriter.solver_obj.ModelSpace == "plane stress":
+            meshtools.plane_stress(ccxwriter.femmesh_file)
+        if ccxwriter.solver_obj.ModelSpace == "plane strain":
+            meshtools.plane_strain(ccxwriter.femmesh_file)
+        if ccxwriter.solver_obj.ModelSpace == "axisymmetric":
+            meshtools.axisymmetric(ccxwriter.femmesh_file)
+


Note that by properly adapting the functions in meshtools.py, these conditionals could be replaced by a call to a single function.

marioalexis84 · 2024-02-23T17:09:27Z

src/Mod/Fem/femsolver/calculix/write_mesh.py

+        # Use 2D elements if model space is not set to 3D
+        if ccxwriter.solver_obj.ModelSpace == "plane stress":
+            meshtools.plane_stress(ccxwriter.femmesh_file)
+        if ccxwriter.solver_obj.ModelSpace == "plane strain":
+            meshtools.plane_strain(ccxwriter.femmesh_file)
+        if ccxwriter.solver_obj.ModelSpace == "axisymmetric":
+            meshtools.axisymmetric(ccxwriter.femmesh_file)
+


FEA-eng · 2024-02-23T18:20:58Z

In my opinion, it would be enough to remove the duplicate code in write_femelement_geometry.py; The other functions can remain as they are, in any case, in the future I plan to extend the C++ writing function to avoid systematic editing of the already written file.

Ok, done. Thank you for reviewing. So it can be merged ?

FEA-eng · 2024-02-24T11:27:13Z

@chennes Can you merge it ?

FEA-eng · 2024-02-26T20:08:09Z

@chennes The required tests passed. Some other tests failed but apparently because of Part Design Helix:

Traceback (most recent call last):
  File "/Users/runner/work/FreeCAD/FreeCAD/.conda/freecad/opt/freecad/Mod/PartDesign/PartDesignTests/TestHelix.py", line 126, in testRectangle
    self.assertAlmostEqual(helix.Shape.Volume, 1178.0961742825648,places=5)
AssertionError: 1178.0962040829334 != 1178.0961742825648 within 5 places (2.980036856570223e-05 difference)

So it shouldn't be related to the PR.

use the wires of the computed face instead of the selected ones.

FEA-eng added 4 commits February 23, 2024 10:03

Update meshtools.py

5c769a5

Update solver.py

f9e762c

Update write_femelement_geometry.py

37667ef

Update write_mesh.py

58bc616

github-actions bot added the WB FEM Related to the FEM Workbench label Feb 23, 2024

marioalexis84 reviewed Feb 23, 2024

View reviewed changes

Update write_femelement_geometry.py

d0548de

marioalexis84 approved these changes Feb 23, 2024

View reviewed changes

Merge branch 'main' into fem_2d_analyses

94682cc

chennes self-assigned this Feb 26, 2024

FlachyJoe referenced this pull request Feb 26, 2024

PartDesign_Helix: use computed wires

d7a95b4

use the wires of the computed face instead of the selected ones.

Merge branch 'main' into fem_2d_analyses

d9a05a1

chennes merged commit 7eae061 into FreeCAD:main Mar 2, 2024
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FEM CalculiX 2D mechanical analyses (plane stress, plane strain and axisymmetric) #12562

FEM CalculiX 2D mechanical analyses (plane stress, plane strain and axisymmetric) #12562

FEA-eng commented Feb 23, 2024

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FEA-eng commented Feb 23, 2024

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FEA-eng commented Feb 26, 2024

FEM CalculiX 2D mechanical analyses (plane stress, plane strain and axisymmetric) #12562

FEM CalculiX 2D mechanical analyses (plane stress, plane strain and axisymmetric) #12562

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FEA-eng commented Feb 26, 2024