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Femmesh2mesh doesn't approximate 2nd order elements #15815

Open goatchurchprime opened 3 months ago

goatchurchprime commented 3 months ago

Is there an existing issue for this?

Problem description

Gmsh can make second order elements used by some FEM packages that are quartic triangular splines. The current implementation ( https://github.com/FreeCAD/FreeCAD/blob/main/src/Mod/Fem/femmesh/femmesh2mesh.py ) of the FemMesh2Mesh feature ( https://wiki.freecad.org/FEM_FemMesh2Mesh ) ignores their shape.

I have a Macro femoder2tomesh.zip that can subdivide and plot them to a better tolerance, as seen in this image where the subdivision has been set to 4.

image

(Unfortunately it doesn't implement quad elements, as has recently been added: https://github.com/FreeCAD/FreeCAD/issues/15644 )

My Macro can also add an App::PropertyLink parameter to point back to the source FemMesh, as well as an App::PropertyIntegerList to state which mesh triangles came from which FemMesh elements. This is necessary when the mesh is used for other manufacturing processes (eg carbon fibre filament winding) in order to map back any properties calculated on the Mesh triangles back onto the FemMesh for simulation.

This feature would require a pop-up window to set the options and the subdivision factor. Since there is already a request for a pop-up window to set the deformation scale factor ( https://github.com/FreeCAD/FreeCAD/issues/11301 ), these features could all be combined.

Full version info

v0.21.2 and most recent

Subproject(s) affected?

FEM

Anything else?

femorder2torus.zip

Code of Conduct

FEA-eng commented 3 months ago

Any help with FEM is welcome. Are you able to send a PR to implement your macro with a simple pop-up window or will you need some support with this?

goatchurchprime commented 3 months ago

I can do, but it'll need some quality control first. Where do I look for a an example of a feature that has a good quality pop-up that I can model this on?

FEA-eng commented 3 months ago

Where do I look for a an example of a feature that has a good quality pop-up that I can model this on?

As I've mentioned in that issue about missing scale factor in GUI, I would base this pop-up on the one of the Part ShapeFromShape tool. That's the file: https://github.com/FreeCAD/FreeCAD/blob/74e5c3fafba7b0307c6b75e57ef648baae32f971/src/Mod/Part/Gui/ShapeFromMesh.ui