FEM Ferromagnet Mesh API¶

1. What it is and when to use it¶

Object mesh policy is owned by the object: every magnetic object carries its own recipe (PerObjectMeshRecipe) that overrides study-level defaults. This is the “per-object mesh config” layer of the three-layer FEM mesh doctrine (universe → object → shared solver mesh).

Mode selection:

Impact on the simulation: the object recipe controls local gradient resolution (exchange, domain walls, interfaces) independently per object; the final mesh remains one conforming shared-domain mesh.

2. Physical and mathematical explanation¶

An authoring layer, not a physical model. The object recipe selects the discrete space locally for that object; cross-object consistency is provided by the shared solver mesh. Size the elements with respect to the exchange length:

where \(A\) — exchange stiffness (\(\mathrm{J\,m^{-1}}\)), \(M_s\) — saturation magnetization (\(\mathrm{A\,m^{-1}}\)).

3. Example — complete Python script¶

# %% Object-owned mesh policy overview
import fullmag as fm

nm = 1.0e-9

study = fm.study("ferromagnet_mesh_api_example")
study.engine("fem")
study.device("cpu", precision="double")
study.mode("strict")

study.universe(mode="manual", size=(800 * nm, 400 * nm, 300 * nm))
study.universe.mesh(
    minimum_element_size=8 * nm,
    maximum_element_size=80 * nm,
    maximum_element_growth_rate=1.5,
    grading="geometric",
)

film = study.geometry(fm.Box(300 * nm, 100 * nm, 5 * nm), name="film")
film.Ms = 800.0e3
film.Aex = 13.0e-12
film.alpha = 0.02
film.m = fm.texture.uniform(1.0, 0.0, 0.0)

# Ordinary unstructured policy:
film.mesh(minimum_element_size=2.5 * nm, maximum_element_size=5 * nm, order=1)
# ...or explicit thin-film topology:
# film.mesh.thin_film(layers=4, topology="tetrahedral", maximum_element_size=5 * nm)

study.exchange()
study.demag(model="airbox", variant="robin")
study.build_domain_mesh()
study.stages.add_relax(stage_id="equilibrium", tolT=1.0e-6)

4. Exact API¶

Three authoring levels:

1. Ordinary — object.mesh(**kwargs): sizes, order, quality, boundary layers (Free-Tetrahedral API).

2. Topology helper — object.mesh.thin_film(...): tetrahedral or prismatic through the thickness (Thin-Film Tetrahedral API, Swept-Prism API).

3. Advanced — a direct PerObjectMeshRecipe: full control of strategy, ordered operations, size fields, and swept controls.

Every mode has its own command, required companion fields, and capability boundary; disallowed combinations end in validation errors, never in silent replacement.

ProblemIR mapping: the object recipe (PerObjectMeshRecipe) is the canonical representation; the study supplies only lowest-precedence defaults.

5. How to set it in Control Room¶

Model Explorer
└── Objects
    └── <object>
        └── Mesh            → selection kind: object.mesh

The Object Mesh Policy inspector (ObjectMeshPolicyPanel.tsx) groups all authoring levels: size presets, element size parameters, thin-film strategy, interface/edge refinement, backend parameters, advanced JSON, and the Quality/History tabs. Full description: FEM Object Mesh Panel.

6. Backend support¶

7. Limitations and known pitfalls¶

• An object recipe does not create a separate mesh — the final solver mesh is one conforming mesh; cross-object conflicts are resolved by build policy.

• Study-level defaults have the lowest precedence against object recipes.

8. Scientific bibliography¶

1. C. Geuzaine and J.-F. Remacle, “Gmsh,” Int. J. Numer. Methods Eng. 79, 1309–1331 (2009).

9. Source-code index¶

Source-code index¶

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