DAGMC H5M Files

DAGMC H5M Files#

The primary output format. Creates triangular surface meshes for use with DAGMC-enabled transport codes (OpenMC, MCNP, FLUKA, etc.).

Basic Export#

import cadquery as cq
from cad_to_dagmc import CadToDagmc

assembly = cq.Assembly()
assembly.add(cq.Workplane("XY").sphere(10), name="sphere")

model = CadToDagmc()
model.add_cadquery_object(assembly, material_tags=["tungsten"])

model.export_dagmc_h5m_file(
    filename="dagmc.h5m",
    min_mesh_size=0.5,
    max_mesh_size=10.0,
)

With Different Backends#

Choose between h5py (default) and pymoab backends:

import cadquery as cq
from cad_to_dagmc import CadToDagmc

sphere1 = cq.Workplane().sphere(5)
sphere2 = cq.Workplane().moveTo(10, 0).sphere(2)

assembly = cq.Assembly()
assembly.add(sphere1)
assembly.add(sphere2)

model = CadToDagmc()
model.add_cadquery_object(cadquery_object=assembly, material_tags=["mat1", "mat2"])

# Export using h5py backend (default, no MOAB needed)
model.export_dagmc_h5m_file(
    filename="dagmc_h5py.h5m",
    h5m_backend="h5py",
)

# Export using pymoab backend (requires MOAB installation)
model.export_dagmc_h5m_file(
    filename="dagmc_pymoab.h5m",
    h5m_backend="pymoab",
)

With Meshing Backends#

Choose between the cad-to-dagmc-mesher (default), GMSH and CadQuery meshing:

# cad-to-dagmc-mesher backend (default) - surface and volume meshing
model.export_dagmc_h5m_file(
    filename="dagmc.h5m",
    meshing_backend="cad-to-dagmc-mesher",
    tolerance=0.01,
    angular_tolerance=0.2,
)

# GMSH backend - full control over mesh parameters
model.export_dagmc_h5m_file(
    filename="dagmc.h5m",
    meshing_backend="gmsh",
    min_mesh_size=0.5,
    max_mesh_size=10.0,
    mesh_algorithm=1,
)

# CadQuery backend - simpler, uses CadQuery's tessellation
model.export_dagmc_h5m_file(
    filename="dagmc.h5m",
    meshing_backend="cadquery",
    tolerance=0.1,
    angular_tolerance=0.1,
)

API Reference#

`export_dagmc_h5m_file()`#

Common Parameters:

Parameter	Type	Default	Description
`filename`	str	“dagmc.h5m”	Output file path
`scale_factor`	float	1.0	Geometry scale factor. See the note below on how it affects the units of the linear mesh sizing parameters
`imprint`	bool or int	True	Imprint shared surfaces. An int limits the imprint to that many threads
`implicit_complement_material_tag`	str	None	Void space material tag

Backend Selection:

Parameter	Type	Default	Description
`meshing_backend`	str	auto	`"cad-to-dagmc-mesher"`, `"gmsh"` or `"cadquery"`. Auto-selected from the other arguments provided. Defaults to `"cad-to-dagmc-mesher"` when no backend-specific arguments are given, falling back to `"cadquery"` if cad-to-dagmc-mesher is not installed.
`h5m_backend`	str	“h5py”	`"h5py"` or `"pymoab"` for writing h5m files

GMSH Backend Parameters:

These parameters only apply when using meshing_backend="gmsh" (or when auto-selected):

Parameter	Type	Default	Description
`min_mesh_size`	float	None	Minimum mesh element size
`max_mesh_size`	float	None	Maximum mesh element size
`mesh_algorithm`	int	1	GMSH meshing algorithm (1-10)
`method`	str	“file”	CAD transfer method: `"file"` or `"in memory"`
`set_size`	dict	None	Per-volume mesh sizes. Keys can be volume IDs (int) or material tag names (str).
`unstructured_volumes`	list	None	Volume IDs (int) or material tags (str) for conformal volume mesh
`umesh_filename`	str	“umesh.vtk”	Output filename for unstructured volume mesh

CadQuery Backend Parameters:

These parameters only apply when using meshing_backend="cadquery":

Parameter	Type	Default	Description
`tolerance`	float	0.1	Linear tolerance for tessellation, in scaled-geometry units
`angular_tolerance`	float	0.1	Angular tolerance for tessellation

cad-to-dagmc-mesher Backend Parameters:

These parameters only apply when using meshing_backend="cad-to-dagmc-mesher":

Parameter	Type	Default	Description
`tolerance`	float	0.01	Linear tolerance for the surface mesh, in scaled-geometry units
`angular_tolerance`	float	0.2	Angular tolerance for the surface mesh
`tet_volumes`	Iterable[str]	None	Material tag names of the volumes to fill with tetrahedra
`target_edge_length`	float	None	Target tetrahedron edge length, in scaled-geometry units
`umesh_filename`	str	“umesh.vtk”	Output filename for unstructured volume mesh

Important

scale_factor and the units of linear mesh sizes. All the linear mesh sizing parameters are in the units of the scaled geometry, so the same number means the same deflection on the output mesh whichever backend you use:

Backend	Linear sizing parameters
`gmsh`	`min_mesh_size`, `max_mesh_size`, `set_size`
`cad-to-dagmc-mesher`	`tolerance`, `target_edge_length`
`cadquery`	`tolerance`

A consequence is that the defaults get finer as scale_factor grows. This matters most for the cad-to-dagmc-mesher tolerance default of 0.01: with scale_factor=100 (metres to centimetres) that is a 0.1 mm deflection, which on a large model can generate a huge number of facets and exhaust memory. Scale the tolerance with the geometry, for example tolerance=0.5 (5 mm) for a metre-scale model exported with scale_factor=100.

angular_tolerance is an angle and is unaffected by scale_factor.

Note

Before this behaviour was made consistent, the cadquery backend interpreted tolerance in the units of the unscaled geometry, because it tessellates first and scales the resulting vertices afterwards. If you used that backend with a scale_factor other than 1.0, the same tolerance value now produces a mesh scale_factor times finer than it used to; multiply your old tolerance by scale_factor to get the previous mesh density. A warning is raised to flag this.

tet_volumes and target_edge_length must be given together to write a volume mesh.

Warning

Do not mix GMSH and CadQuery backend parameters in the same call. If you provide parameters from both backends without explicitly setting meshing_backend, an error will be raised.

Returns:

str - Path to the created h5m file
Or tuple[str, str] - (h5m_path, vtk_path) when a volume mesh is also written, which is when unstructured_volumes is set on the GMSH backend, or when tet_volumes and target_edge_length are set on the cad-to-dagmc-mesher backend

Using in OpenMC#

Load the DAGMC geometry in OpenMC:

import openmc

# Define materials (names must match material tags)
tungsten = openmc.Material(name="tungsten")
tungsten.add_element("W", 1.0)
tungsten.set_density("g/cm3", 19.3)

steel = openmc.Material(name="steel")
steel.add_element("Fe", 1.0)
steel.set_density("g/cm3", 7.8)

materials = openmc.Materials([tungsten, steel])

# Load the DAGMC geometry
dag_universe = openmc.DAGMCUniverse(filename="dagmc.h5m")
geometry = openmc.Geometry(root=dag_universe.bounded_universe())

# Set up settings
settings = openmc.Settings()
settings.batches = 10
settings.particles = 1000
settings.run_mode = "fixed source"

model = openmc.Model(geometry=geometry, materials=materials, settings=settings)
model.run()

DAGMC H5M Files

Contents

DAGMC H5M Files#

Basic Export#

With Different Backends#

With Meshing Backends#

API Reference#

`export_dagmc_h5m_file()`#

Using in OpenMC#

See Also#

DAGMC H5M Files

Contents

DAGMC H5M Files#

Basic Export#

With Different Backends#

With Meshing Backends#

API Reference#

export_dagmc_h5m_file()#

Using in OpenMC#

See Also#

`export_dagmc_h5m_file()`#