Per-Volume Mesh Sizing

Per-Volume Mesh Sizing#

Control mesh density for different volumes using the set_size parameter. This allows finer meshes where detail is needed and coarser meshes elsewhere.

Note

Per-volume mesh sizing only works with the GMSH backend. The CadQuery backend ignores set_size.

Basic Usage#

Specify mesh sizes for specific volumes:

import cadquery as cq
from cad_to_dagmc import CadToDagmc

coarse_box = cq.Workplane().box(1, 1, 2)
fine_box = cq.Workplane().moveTo(1, 0.5).box(1, 1, 1.5)
default_box = cq.Workplane().moveTo(2, 1).box(1, 1, 1)

assembly = cq.Assembly()
assembly.add(coarse_box, name="coarse")
assembly.add(fine_box, name="fine")
assembly.add(default_box, name="global")

model = CadToDagmc()
model.add_cadquery_object(assembly, material_tags="assembly_names")

# Check available material tags
print("Material tags:", model.material_tags)
# Output: Material tags: ['coarse', 'fine', 'global']

model.export_dagmc_h5m_file(
    filename="different_resolution_meshes.h5m",
    min_mesh_size=0.01,
    max_mesh_size=10,
    set_size={
        "coarse": 0.9,  # Coarse mesh for this volume
        "fine": 0.1,    # Fine mesh for this volume
        # "global" not specified - uses min/max only
    },
)

Specifying Volumes#

By Material Tag Name#

Use material tag names (recommended):

set_size={
    "fuel": 0.5,      # All volumes with "fuel" tag
    "coolant": 2.0,   # All volumes with "coolant" tag
}

By Volume ID#

Use integer volume IDs:

set_size={
    1: 0.5,  # Volume 1
    2: 5.0,  # Volume 2
    3: 1.0,  # Volume 3
}

Mixed#

Combine both approaches:

set_size={
    1: 0.5,           # Volume 1 specifically
    "coolant": 2.0,   # All coolant volumes
}

How It Works#

  1. Volumes not in set_size use min_mesh_size and max_mesh_size only

  2. Volumes in set_size get their specified target size

  3. Material tag names are resolved to all volumes with that tag

  4. The mesh size applies to all surfaces of the volume

Complete Example#

import cadquery as cq
from cad_to_dagmc import CadToDagmc

# Create geometry with different mesh requirements
shield_inner = cq.Workplane("XY").sphere(5)
shield_outer = cq.Workplane("XY").sphere(10).cut(cq.Workplane("XY").sphere(5))
casing = cq.Workplane("XY").box(25, 25, 25).cut(cq.Workplane("XY").sphere(10))

assembly = cq.Assembly()
assembly.add(shield_inner, name="shield_inner")
assembly.add(shield_outer, name="shield_outer")
assembly.add(casing, name="casing")

model = CadToDagmc()
model.add_cadquery_object(assembly, material_tags="assembly_names")

# Fine mesh on inner shield (where neutrons interact most)
# Coarse mesh on casing (less important)
# Default mesh on outer shield
model.export_dagmc_h5m_file(
    filename="shielding.h5m",
    min_mesh_size=0.1,
    max_mesh_size=5.0,
    set_size={
        "shield_inner": 0.2,  # Fine mesh
        "casing": 3.0,        # Coarse mesh
        # "shield_outer" uses global min/max
    },
)

Using with Volume Meshes#

set_size also works with volume mesh export:

import cadquery as cq
from cad_to_dagmc import CadToDagmc

coarse_box = cq.Workplane().box(1, 1, 2)
fine_box = cq.Workplane().moveTo(1, 0.5).box(1, 1, 1.5)
default_box = cq.Workplane().moveTo(2, 1).box(1, 1, 1)

assembly = cq.Assembly()
assembly.add(coarse_box, name="coarse")
assembly.add(fine_box, name="fine")
assembly.add(default_box, name="global")

model = CadToDagmc()
model.add_cadquery_object(assembly, material_tags="assembly_names")

# GMSH mesh file with per-volume sizing
model.export_gmsh_mesh_file(
    filename="different_resolution_meshes.msh",
    dimensions=2,
    min_mesh_size=0.01,
    max_mesh_size=10,
    set_size={
        "coarse": 0.9,
        "fine": 0.1,
    },
)

Tips#

Tip

Finding volume IDs: If using volume IDs instead of tag names, the order depends on how volumes were added. Using material tag names is more robust.

Tip

Checking tags: After adding geometry, check model.material_tags to see available tag names:

model = CadToDagmc()
model.add_cadquery_object(assembly, material_tags="assembly_names")
print(model.material_tags)

See Also#

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