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 GMSH (default) and CadQuery meshing:

# GMSH backend (default) - 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

imprint

bool

True

Imprint shared surfaces

implicit_complement_material_tag

str

None

Void space material tag

Backend Selection:

Parameter

Type

Default

Description

meshing_backend

str

auto

"gmsh" or "cadquery". Auto-selected based on other arguments provided. Defaults to "cadquery" if no backend-specific args given.

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

angular_tolerance

float

0.1

Angular tolerance for tessellation

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) if unstructured_volumes is set

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()

See Also#

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