DAGMC unstructured mesh tallies¶
DAGMC supports several advanced mesh tally options including tetrahedral mesh tallies (tetmeshes) and kernel density estimator tallies. Both options require an unstructured mesh.
Mesh production workflow¶
Cubit can be used to generate the unstructured meshes needed for tallies. To do so, use the following steps.
Load the geometry you wish to mesh into Cubit.
Use the mesh tools to produce the meshes you want.
Save the file as a .cub file. Remember to check the “Use Legacy .cub file Format” option in Cubit.
mbconvertexecutable to convert from the Cubit format to a faceted .h5m file that DAGMC can use.
Here is an example of how to use
$ mbconvert mesh.cub mesh.h5m
One can immediately view this mesh, by using
mbconvert to convert to vtk:
$ mbconvert mesh.h5m mesh.vtk
Tetrahedral mesh tallies¶
Currently the tetmesh tally option is only available in DAG-MCNP5/6, but there are plans to expand this to all the codes that DAGMC currently supports.
Once you have used the above instructions to produce one or more meshes in .h5m
format, you must specify to MCNP that your tally is a tetmesh tally. This is
done by putting special keywords on the tally comment (FC) line. For example,
adding the following lines to an MCNP input file would tell MCNP that tally 4 is
a tetmesh tally, that the input mesh file is
mesh.h5m, and the results
should be stored in
fmesh4:n geom=dag fc4 dagmc type=unstr_track inp=mesh.h5m out=mesh_out.h5m
Other standard MCNP options can also be used, such as energy bins:
fmesh4:n geom=dag emesh=1.0 2.0 15.0 fc4 dagmc type=unstr_track inp=mesh.h5m out=mesh_out.h5m
Or tally multipliers:
fmesh4:p geom=dag fc4 dagmc type=unstr_track inp=mesh.h5m out=mesh_out.h5m fm4 -1 0 -5 -6
$ mbconvert mesh_out.h5m mesh_out.vtk
Kernel density estimator tallies¶
The kernel density estimator tallies are a suite of tallies that allow scoring to be done using the vertices of a tetmesh or add additional mesh-based scoring such as collision estimator tallies. The theoretical details behind KDE tallies can be found in Kerry Dunn’s Ph.D. thesis.
To call a KDE collision tally, use:
fmesh4:p geom=dag fc4 dagmc type=kde_coll inp=mesh.h5m out=mesh_out.h5m hx=0.198 hy=0.0663 hz=0.0662
To call a KDE track length tally, use:
fmesh4:p geom=dag fc4 dagmc type=kde_track inp=mesh.h5m out=mesh_out.h5m hx=0.198 hy=0.0663 hz=0.0662
To call a KDE subtrack tally, use:
fmesh4:p geom=dag fc4 dagmc type=kde_subtrack inp=mesh.h5m out=mesh_out.h5m hx=0.1042 hy=0.0833 hz=0.0833 hx=0.1042 hy=0.0833 hz=0.0833 subtracks=3 seed=11699913