Usage and Examples

This module is very basic, mainly involving the VolumeMesh class. The usage of this libary will be illustrated through examples, and further details can be found in the other sections. The full examples are given in the samples folder. We show the examples in Python, but as the module is built from C++, it should be a direct translation if needed. Refer to classes for more information.

Mesh Structure

The mesh is composed of three main parts: vertices, elements, and marked faces. We group elements and marked faces with element and face sets, respectively. We may want to assign attributes or conditions onto these element or face sets. This is accomplished by creating a JSON file. For example,

{
    "Element Sets": [
        {
            "index": 0,
            "attribute": "air"
        }
    ],
    "Face Sets": [
        {
            "index": 0,
            "boundary": "PEC"
        },
        {
            "index": 1,
            "boundary": "ABC"
        }
    ],
    "Hybrid Mesh": {
        "enable": true,
        "holes": [
            [0, 0, 0], [7, -7, 0]
        ]
    }
}

These three main sections must be present in the JSON file for it to be read properly. Currently, the supported boundary conditions are

[0] PEC (Perfect Electric Conductor)
[1] PMC (Perfect Magnetic Conductor)
[2] ABC (Absorbing Boundary Condition)
[3] PML (Perfectly Matched Layer)
[4] None
[5] None
[6] None
[7] NCB (Perfect Magnetic Conductor)

Loading

This example shows how to load a EXODUS (.g) mesh file and access its information.

import Geometry as geo

mesh_path = "../mesh/Cylinder.g"
json_path = "../mesh/Cylinder.json"

mesh = geo.VolumeMesh.from_exodus(mesh_path)
mesh.apply_config(json_path)
print(mesh.info)
print()

print("Vertex Array:")
print(mesh.vertices)
print()

print("Vertex Indices of Element Set 0:")
print(mesh.elem_set(0))
print()

print("Face Indices of Face Set 0:")
print(mesh.face_set(0))
print()

print("Element Operations:")
elem = mesh.element(0)
print("Volume:", elem.volume())
for face_num in range(4):
    print(f"Face {face_num}:")
    print(elem.face(face_num))
    print("Area:", elem.face(face_num).normal().norm() / 2)
print()

print("Element Set 0 Attribute:", mesh.get_elem_set_attribute(0))
print("Face Set 0 Boundary Condition:",  mesh.get_face_set_bc(0))
print()

Exporting STLs

Following from there, we can also export mesh data. We can export all the elements as faces, or specific face sets.

BC = geo.BoundaryCondition # Shorthand

mesh.save_exodus("CylinderVolume") # Export EXODUS (.g) file.
mesh.extract_surfaces().save_stl("CylinderBoundary") # Export STL file.
# Only export the ABC Boundary.
mesh.extract_surfaces(mesh.face_sets_with_bc(BC.ABC)).save_stl("CylinderABC")

Hybrid Mesh Generation

To utilize the hybrid mesh generation functionality, we need only call a few functions.

mesh = geo.VolumeMesh.from_exodus(mesh_path)
config = mesh.apply_config(json_path) # Get the config data.

BC = geo.BoundaryCondition # Shorthand

# Generate the grid mesh with each cube's side being 1.4.
# Ignore ABC face sets when generating the regular mesh.
hybrid = mesh.create_hybrid_mesh(1.4, mesh.face_sets_with_bc(BC.ABC))
hybrid.export_exodus("HybridCylinder")

hybrid_surfs = hybrid.extractSurfaces()
hybrid_surfs.save_stl("InnerCylinderPEC", inner.face_sets_with_bc(BC.PEC))
hybrid_surfs.save_stl("InnerCylinderNCB", inner.face_sets_with_bc(BC.NCB))

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Usage and Examples

Mesh Structure

Loading

Exporting STLs

Hybrid Mesh Generation

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