Understanding FEM_MeshRegion

[balrobs]

Playing with the FEM_MeshRegion command I saw a strange behaviour (bug?)
Steps to replicate:

1. draw an outer Draft_Rectangle -> Rectangle
2. draw an inner Draft_Rectangle -> Rectangle001
3. select Rectangle and Rectangle001 and use Part_BooleanFragments to create -> BooleanFragments
4. select BooleanFragments and use Part_CompoundFilter to create -> CompoundFilter
5. create a FEM_Analysis container -> Analysis
6. select CompoundFilter and use FEM_GmshFromShape to create -> FEMMeshGmsh
7. select FEMMeshGmsh and use FEM_MeshRegion, set a max element size (i.e. 100mm) and add one edge of Rectange001

The mesh refinement happens as expected at the selected edge

Screenshot_01.png (48.39 KiB) Viewed 875 times

Now change the steps slightly:

1. draw an outer Draft_Rectangle -> Rectangle002
2. draw four Draft_Lines to create the inner rectange -> Line, Line001, Line002, Line003
3. select Rectangle002, Line, Line001, Line002 and Line003 and use Part_BooleanFragments to create -> BooleanFragments001
4. select BooleanFragments001 and use Part_CompoundFilter to create -> CompoundFilter001
5. select CompoundFilter001 and use FEM_GmshFromShape to create -> FEMMeshGmsh001
6. select FEMMeshGmsh001 and use FEM_MeshRegion, set a max element size (i.e. 100mm) and add one edge of the inner rectangle (i.e. Line002)

As you can see the mesh refinement now happens not for the selected edge

Screenshot_02.png (35.23 KiB) Viewed 875 times

Here my FreeCAD info and my test file:

Code: Select all

OS: Windows 10 (10.0)
Word size of FreeCAD: 64-bit
Version: 0.20.27518 (Git)
Build type: Release
Python version: 3.8.12
Qt version: 5.12.9
Coin version: 4.0.0
OCC version: 7.5.3
Locale: German/Germany (de_DE)

[user1234]

Here my FreeCAD info

Which gmsh version are you using?

The question is, if the second is valid. It have 7 wires.

0.png (267.96 KiB) Viewed 826 times

Generally, gmsh need between i mesh region and a second defined region (also the default values), an extra empty region (3rd face in your case) for the transition.

1.png (280.77 KiB) Viewed 826 times

meshRegion_test_edit.FCStd

(29.22 KiB) Downloaded 25 times

Greetings
user1234

[balrobs]

Thanks user1234 for your answer

Which gmsh version are you using?

4.9.3

Generally, gmsh need between i mesh region and a second defined region (also the default values), an extra empty region (3rd face in your case) for the transition.

OK, now I start better understanding how mesh region works.
May I then ask you please if you know a way to create a mesh refinement around an edge or point geometry for a 2d mesh without first creating geometry regions in the model but controling both mesh size and refinement extension within the refinement object?
Something like this:

mesh_refinement_around_line_and_point.JPG (250.38 KiB) Viewed 766 times

Hope my request makes sense
Kind regards
balrobs

[user1234]

Something like this

I tried to archive that in more ways, but nothing works for me. Also the mesh region is sometimes pretty mysterious to me. Maybe someone other have a proper answer. Sorry.

Greetings
user1234

[balrobs]

I tried to archive that in more ways, but nothing works for me. Also the mesh region is sometimes pretty mysterious to me. Maybe someone other have a proper answer. Sorry.

Nevertheless, thank you very much
Basically I'm able to achieve my goal with Gsmh scripting but can't figure out how to do it in FreeCAD

Code: Select all

lc = 0.5;
Point(1) = {0.0, 0.0, 0.0, lc};
Point(2) = {5.0, 0.0, 0.0, lc};
Point(3) = {5.0, 5.0, 0.0, lc};
Point(4) = {0.0, 5.0, 0.0, lc};
Line(1) = {1, 2};
Line(2) = {2, 3};
Line(3) = {3, 4};
Line(4) = {4, 1};
Curve Loop(1) = {1, 2, 3, 4};
Plane Surface(1) = {1};
lc2 = 0.02;
Point(5) = {4.0, 4.0, 0.0, lc2};
Point{5} In Surface{1};
lc3 = 0.05;
Point(6) = {1.0, 1.0, 0.0, lc3};
Point(7) = {2.0, 4.0, 0.0, lc3};
Line(5) = {6, 7};
Line{5} In Surface{1};

gmsh.jpg (147 KiB) Viewed 700 times