Gmsh error: Unknown element type for UNV export (MSH type 15)

[bernd]

According this http://www.manpagez.com/info/gmsh/gmsh- ... msh_63.php the "MSH elm-type 15" is a 1-node point.

[joha2]

result: the mesh generation failes:

Code: Select all

Warning : Unknown element type for UNV export (MSH type 15) - output file might be invalid
Warning : Unknown element type for UNV export (MSH type 15) - output file might be invalid
Warning : Unknown element type for UNV export (MSH type 15) - output file might be invalid
Warning : Unknown element type for UNV export (MSH type 15) - output file might be invalid
Warning : Unknown element type for UNV export (MSH type 15) - output file might be invalid
Warning : Unknown element type for UNV export (MSH type 15) - output file might be invalid
Warning : Unknown element type for UNV export (MSH type 15) - output file might be invalid
Warning : Unknown element type for UNV export (MSH type 15) - output file might be invalid
Warning : Unknown element type for UNV export (MSH type 15) - output file might be invalid
Warning : Unknown element type for UNV export (MSH type 15) - output file might be invalid
Warning : Unknown element type for UNV export (MSH type 15) - output file might be invalid
Warning : Unknown element type for UNV export (MSH type 15) - output file might be invalid

Hey guys,

I observed this behaviour, too. This occured when I used bleeding edge versions of gmsh, i.e., 4.x. But nevertheless in my case I never observed any problems with the mesh in FreeCAD itself. I thought, it is just an incompatibility in gmsh where single node elements are created and the UNV export - which is necessary for the communication with FreeCAD - cannot "write them out". At the end of the day the MSH type 15 elements are not exported, but the UNV file can be read into FreeCAD anyway.

Best wishes
Johannes

[bernd]

... I thought, it is just an incompatibility in gmsh where single node elements are created and the UNV export - which is necessary for the communication with FreeCAD - cannot "write them out". At the end of the day the MSH type 15 elements are not exported ...

This leads to the question, "What is a single node element?" In my FEM understanding there are nodes and element made from nodes, but What is a node element and why do we have node elements in out meshes?

[Jee-Bee]

I can imagine that they are handy for springs masses etc


mass at some point from a object with spings tied to the object or so.

[joha2]

... I thought, it is just an incompatibility in gmsh where single node elements are created and the UNV export - which is necessary for the communication with FreeCAD - cannot "write them out". At the end of the day the MSH type 15 elements are not exported ...

This leads to the question, "What is a single node element?" In my FEM understanding there are nodes and element made from nodes, but What is a node element and why do we have node elements in out meshes?

Maybe we should investigate some of the meshes which lead to this output and check from the BREP file which geometry could cause such a behaviour by exporting into another format instead of UNV. A good starting point would be to modify the shape2mesh.geo file and see whether the type 15 can be exported into another format instead of throwing an error.

[bernd]

good idea johannes, another possibility would be a post to gmsh mailing list.

[joha2]

good idea johannes, another possibility would be a post to gmsh mailing list.

I investigated what I wrote yesterday and it seems that the node 15 elements are just the vertices from the geometry. I generated a fusion object by fusing together sphere, cube, torus, cone and meshed it with gmsh 4.3.0. As expected the "Unknown element type for UNV export" error appeared again, but the mesh was generated. So I used the shape2geo file and changed Mesh.Format from 2 (UNV) to 1 (MSH).

From http://gmsh.info/doc/texinfo/gmsh.html#MSH-file-format it is easy to extract the type 15 elements, which are - as already pointed out - single nodes. These were first written into a text file and then imported back via the point clouds module into FreeCAD to be shown in the geometry.

So it seems first that these single nodes are just intersection points of the geometry and that the element type 15 is just not supported by UNV, as presumed.

Who defined the UNV format? And do we know whether it is properly implemented in gmsh?

Best wishes
Johannes

[bernd]

might be because geo file includes Mesh.SaveAll option ... http://gmsh.info//doc/texinfo/gmsh.html ... cal-groups ?

[joha2]

might be because geo file includes Mesh.SaveAll option ... http://gmsh.info//doc/texinfo/gmsh.html ... cal-groups ?

Setting Mesh.SaveAll = 0; does not change anything. The error message remains.

[bernd]

we should find away to surpress this warning. We get dozens of posts in this regard ...