Mesh Converter from ICEM

[adigh23]

Hi everyone,
I've been working on a set of Python scripts that enable converting ICEM CFD meshes (.msh) to Neko's .nmsh format and wanted to share them with the community for feedback and discussion.

Motivation

ICEM CFD is a widely used meshing tool, especially in industrial and reactor applications, but there doesn't seem to be a direct path from ICEM into Neko at the moment. The existing support leans heavily toward Gmsh, so users coming from an ICEM workflow are a bit left out. I thought it would be valuable to bridge that gap.

How It Works

The conversion pipeline is:

.msh (ICEM) → .rea → .re2 → .nmsh (via rea2nbin)

The first script, which handles the .msh to .rea conversion, was given by @vbaconnet . I then wrote a second script that converts from .rea to .re2. Both scripts are written in Python and rely on pyMech rather than Nek5000's own utilities. One of the main reasons for this approach is that certain Nek5000 tools have hardcoded element limits, which becomes a problem when working with very large meshes. The pyMech-based approach doesn't have that restriction. The scripts also handle periodic boundary conditions, which was an important requirement for my use case.

I am sharing the scripts below for review. It would be great if this ICEM mesh conversion support could also be added as a feature in Neko, so that users who rely on ICEM rather than Gmsh have a supported path into the Neko workflow.

Any feedback, suggestions, or comments are very welcome. Thanks!
mesh_to_rea.py
mshconvert.py
reatore2.py

[njansson]

Very nice! Fully agree would be great to add this feature to the repo.