Reproducible FreeCAD Workspace with CFD Capability

This project aims to ease the environment setup for FreeCAD CfdOF workbench.

Basically it's a nix-shell configuration of a FreeCAD environment with CfdOF installed.

By the time I finished this project, I found preCICE adapters and solvers packaged with the Nix package manager which has a simliar goal(reproducibility). That's a flakes repository for NixOS.

How to use

1. Install nix. Follow the instruction of your distro. Or you can follow the instructions by nix official.
   • For Arch users, simply pacman -Sy nix, and enable nix-daemon service.
2. Change working directory to here, the repository.
3. Open a new shell with nix-shell freecad-cfd.nix. Packages are built in this step. This is the way to launch an interactive shell, and normally the packages are built only once.
4. In the new shell, install CfdOF plugin by executing the script install-mod-cfdof.sh
   • this script pins the module's git revision, making it reproducible
5. Run mkdir -p freecad-state/{home,userdata,temp} to create the folders for FreeCAD data. Read shellHook variable in freecad-cfd.nix and cmd.sh for more details.
6. (Optional) In console, run freecad -t TestCfdOF, and it will test the workbench.
7. In console, run freecad, and enjoy your journey.
8. (Optional) To further test the environment, you need to load a demo from CfdOF, and run the calculation.
   • In some cases, testing a single demo cannot ensure everything works.
9. Later you don't need to run the steps above again if you want to launch FreeCAD directly, just change directory here and execute start-cfd.sh. The script will pass the arguments to FreeCAD.

How it works

• FreeCAD version is pinned with nixpkgs release.
  • Config path is changed with environment variables.
    • Warning: NEVER hard code ANY path in FreeCAD settings.
• OpenFOAM and related components which are not maintained in nixpkgs are built through local package definitions.
  • Versions are pinned by pinning source code version.
  • cfmesh-cfdof and hisa don't have versioned source code, and their code packages are relatively small, so the code packages are bundled.
• CfdOF's version is pinned by git commit hash.
• nixgl is used to make UI working.

Build time

My building platform: EPYC 7D12(1.1GHz, 32 core 64 threads) with 128G RAM.

• FreeCAD: about 10 minutes
• OpenFOAM: around 50 minutes, it looks not fully parallel
• cfmesh-cfdof: the scripts build it sequentially, about 15 minutes
• hisa: the scripts build it sequentially, about 14 minutes
• parmetis and scotch are rebuilt for their dynamic linking libraries, and these shouldn't take long time to build

The rest packages are provided by nixpkgs prebuilts.

Q&A

Why does FreeCAD need a rebuild?

As of FreeCAD 0.21.2, the FEM workbench has a bug that prevents correct detection of solvers in system path. If you don't need this patch or don't want to rebuild, just comment out freecad-patched and uncomment pkgs.freecad in freecad-cfd.nix.

Credits

• CfdOF
• AUR openfoam-org
• AUR openfoam-com
• AUR scotch
• AUR parmetis-git

License

This project is licensed under the MIT license. The license doesn't apply to the bundled source code zips(cfmesh, hisa), which are licensed under GPL3.