How to import a STEP geometry into EGS++

[physicsmed]

Hello everyone! I’m trying to simulate a geometry originally given as a .step file in EGS++. I used Gmsh to open the STEP file (with extension ".step") and generate a tetrahedral mesh (exported as .msh in ASCII format).

In my EGS++ input file, I’m defining the geometry like this:
`:start geometry definition:

:start geometry:
    library = egs_mesh
    name    = my_mesh
    file    = "my_geometry.msh"
:stop geometry:

:start geometry:
    name = bounding_box
    library = egs_box
    box size = 50 50 50
    :start media input:
        media = vacuum
    :stop media input:
:stop geometry:

:start geometry:
    library = egs_genvelope
    name = my_envelope
    base geometry = bounding_box
    inscribed geometries = my_mesh
:stop geometry:

simulation geometry = my_envelope

:stop geometry definition:
`
However, when I run egs_view filter.egsinp, I get a segmentation fault (core dumped). Sometimes I also see an error about “No matching stop delimiter.”
1- Is there a recommended workflow or common pitfalls when converting .step to .msh for EGS++? is there any other way to read directly my 3D geometry avoiding the conversion?
2- Could the crash be related to missing region definitions or an unbounded geometry?

[rtownson]

Using gmsh, you need to give each "physical volume" in the mesh a name, that will correspond to a material. It might look something like this at the top of the .msh file. If you know the physical volume IDs, you can type it manually, or you can use the GUI to do it.

$MeshFormat
      2 4.1 0 8
      3 $EndMeshFormat
      4 $PhysicalNames
      5 2
      6 3 89 "c552"
      7 3 90 "air"
      8 $EndPhysicalNames

For the following line, I suggest providing the full file path and removing the quotes. Just in case that's the issue.

file    = "my_geometry.msh"

[physicsmed]

Thank you for the reply!
I think the problem that in my mesh format I do not have the physicalNames, I think it is difficult to select each physical volume and give it a material name, because I have a complex geometry. I am wondering if there is a way to do that automatically by a software or any other tool?

This is few first lines from my msh file :

"$MeshFormat
4.1 0 8
$EndMeshFormat
$Entities
2376 3853 1588 43
1 4.25 21 1.6 0
2 4.25 21 5 0
3 4.25 27.5 5 0
4 4.25 27.5 1.6 0
5 4.25 22.65 7.945033519973779e-16 0 "

I can provide you my files in case you want to check them.

[mxxo]

@physicsmed if you're able to share your STEP and msh files that would be helpful.

[physicsmed]

The step and Mesh files, you can download them directly from this link, and Thanks in advance.
https://www.swisstransfer.com/d/4a3dda60-1647-44ad-a3bf-7bd16b67e3f7
@rtownson @mxxo

[mxxo]

@physicsmed just for completeness, would you also mind sharing your full egsinp inline here? Like Reid said I would also try removing the "s around the filename.

Programmatic import and assignment of Physical Groups based on STEP file labels should be possible using the Gmsh API. Here is a Python example that might be adaptable for your use case - I haven't tried it myself though: https://gitlab.onelab.info/gmsh/gmsh/-/blob/5aa1d110aa864b9017c8f5815bb0daa9dba5a41d/examples/api/step_assembly.py

But unless this is something you expect to do many times for different files, I might opt for doing it manually in Gmsh or semi-automatically using a Gmsh geo script. How many materials are present? You can use the Visibility tool to selectively show volume subsets of the full model (Tools->Visibility, Elementary Entities dropdown).

The msh file doesn't have any tetrahedrons yet, so it can't be used with egs_mesh in its current form - you can confirm this using Tools->Statistics, or Tools->Options->Mesh->Visibility and only check 3D Element Edges and 3D Element Faces.

Based on the error messages I'm getting during my attempts to mesh the STEP file, Gmsh is having trouble with the fine detail on some of the screws. Would it be an acceptable simplification for you to remove some of the screw detail, e.g. simplifying them to two cylinders, one for the head and one for the body?

If there's an interference check available in your CAD tool, that would also be worthwhile confirming there's no interference.