step_to_h5m

Please note that this tool will likely change its name soon.

This is intended to be a python package heavily inspired by Paramak, and borrowing a lot from its namesake: https://github.com/fusion-energy/step_to_h5m). It's "raison d'etre" is to enable a link between the online CAD-tool onShape and the neutron transport code OpenMC.

We will use cadQuery and its links to OCCT to enable import and imprinting/merging algorithms.

The code structure we intend is a main class Assembly which contains the geometry in terms of a set of volumes. We then use gmsh to generate a surface mesh which may be used by OpenMC through DAGMC/MOAB (i.e. .h5m-files)

To install/set up in a virtual python environment

replace <name> with an arbitrary name for your virtual environment

1. Clone the github repository as you'd normally do
2. In the directory where you want your environment to reside do: python -m venv <name>
3. Activate the environment: source <name>/bin/activate
4. install the requirements: pip install -r requirements.txt
5. Build and install moab (if not already installed). The moab team relies on conda for standard installation but are working on a pip-based solution. Once that is done moab would simply be added to the requirements-file instead.
6. Clone the moab code-repository: e.g. git clone git@bitbucket.org:fathomteam/moab.git
7. Configure and build the code: mkdir build; cd build; cmake .. -DENABLE_PYMOAB=1; make; make install

Run a test case:

The follwing code-snippet can now be run to explore the capabilities of Assembly/step_to_h5m

  import assembly as ab
  a=ab.Assembly()
  a.stp_files=["file.step"]
  a.import_stp_files()
  a.export_brep('file.brep')
  a.brep_to_h5m(brep_filename='file.brep',min_mesh_size=0.1, max_mesh_size=10, samples=20)

N.b. the last 3 parameters to brep_to_h5m are simply echoing their default values, and uses the default mesher: gmsh. Their significance is that all curves are sampled by 20 points, but limits the generated mesh-elements to be within the size range [min_mesh_size,max_mesh_size]. This procedure will in turn call OCP and gmsh to produce a mesh with merged surfaces in the output file "dagmc.h5m"

The other available meshing backend is the stl-export from CadQuery (accessible by setting backend='stl') which uses the parameters stl_tol and stl_ang_tol to set meshing quality.

The export_brep-step may be omitted, in which case a temporary file will be written.