DAGMC Export Surface or Volume Mesh

Coreform Cubit
#1

Hello, does the DAGMC export feature only export a surface mesh? Im trying to run mesh tallies on OpenMC and when I use DAGMC export it is only exporting the surface mesh not my tetmesh.

Thanks

#2

Hi @thallam,
yes the DAGMC export does only export the surface meshes.

So you would need the tetmesh for OpenMC in the .h5m?

#3

Correct, I believe for the unstructured mesh tallies for openmc it requires a volumetric tetmesh so openmc can tally the data onto the mesh. As I understand there are two ways to utilize unstructured meshes in openmc. The first being the .h5m and moab and the other is .e and libmesh. I have tried the libmesh way but im running into errors on writing the data to the exodus mesh but I cant utilize the moab way because cubit is exporting the surfaces only.

#4

Do you know how the data structure for the mesh should be in the .h5m?

#5

The way I typically get an unstructured mesh for my mesh tallies in openmc is to create the volumetric mesh in Cubit, then export it to exodus, then use the MOAB mbconvert command line utility (available thru conda or however you want to get moab) to convert it to h5m, which is then suitable for OpenMC. If you mesh the surface of your volume using the same mesh settings as you did for the DAGMC export, then use the tetmesh feature in cubit, you can get an unstructured mesh that perfectly aligns with the geometry used for neutron transport, which can be nice.

#6

The problem is my professor is trying to get cubit from Sandia since we are doing government funded research but we haven’t gotten the program yet so I am just using coreform cubit learn which has a max export limit of 50k elements which is way to low for my needs. I am trying to currently save the cubit model as a .cub and use mbconvert to convert to a .h5m file but when I do this the material assignments are not preserved. when I open the model back up in coreform cubit the bloacks and material assignments are still there so I’m thinking it might be a moab convertion problem. But when using pymoab I can’t read any tags so I’m lost.