Axisymmetric¶

Axisymmetric solves the r-z half-plane of a model that is symmetric about an axis, so a rotationally symmetric part such as a coil or a tubular actuator solves as a 2D problem. You author the full 3D model, and the frame sections it for the 2D solve. See Frames for what a frame decides.

import femforge as ff

config = ff.SimulationConfig(
    frame=ff.Axisymmetric(axis=ff.Axis.Z),
    mesh=ff.MeshConfig(step="models/tubular.step", global_mesh_size=0.5 * ff.U.mm),
    domain=ff.DomainConfig(
        materials=[ff.materials.Air(), ff.materials.N52()],
        tags=[
            ff.EntityTag(
                selector={ff.TagKey.MAGNETIZATION: "N"},
                conditions=[ff.Magnetization(direction=ff.Direction(0, 0, 1))],
            ),
            ff.EntityTag(selector={ff.TagKey.NAME: "mover"}, conditions=[ff.ForceComponent(label="mover")]),
        ],
    ),
)

print(config.frame.label, config.solved_physics())

Fields¶

femforge stores radial as its unit part perpendicular to the axis and rejects a radial parallel to the axis. With radial=None, the half-plane faces the world axis least aligned with the symmetry axis, X first: Axis.Z maps the authored X to the radial direction, and Axis.Y leaves the coordinates as authored. An unset radial is left out of the serialized config, so it adds nothing to the run identity.

For an axis that does not pass through the origin, give it an origin:

import femforge as ff

frame = ff.Axisymmetric(
    axis=ff.Axis(origin=ff.Vec3(10, 0, 0), direction=ff.Direction(0, 0, 1)),
    radial=ff.Direction(0, 1, 0),
)

print(frame.label, frame.plane)

Axisymmetric.plane is the SolvePlane that rule picks: the authored origin of the section and the authored directions of its +X (radial) and +Y (axis). The section and the workbench's expansion both read it.

How femforge sections the model¶

The driver converts the STEP in its first stage, prepare_geometry, through Axisymmetric.prepare_geometry:

1. It builds the parametric geometry when the config has one, else it reads the authored STEP.
2. import_tagged_step imports the STEP as tagged parts, one per named solid. Every body needs a key=value name, and a STEP that holds only faces is rejected: author the 3D model and let the frame section it.
3. axisymmetric_cross_section places the parts in the solve frame through plane, then intersects each solid with the X >= 0 half of the Z = 0 plane. Each face keeps its solid's tags and color.
4. It writes the section to geometry.step in the run directory, and the mesher meshes it in 2D.

The section raises when a solid does not reach the half-plane, and when a section reaches X < 0, which Elmer's axisymmetric solve would reject silently. The mesher names each body's edge on the symmetry axis <BODY>__AXIS, and magnetostatics pins the potential to zero there.

cross_section_3D is the 3D counterpart for pictures: it cuts away a quarter wedge and keeps the tags.

Physics¶

The solved stack runs in the Axi Symmetric coordinate system. Authored physics.overrides must integrate per radian too, so customize the physics after you set the frame.

Conditions¶

Results¶

Results come back in the solve frame: a vector's Y component is the axial one and its X component the radial one. Elmer integrates per radian in its 2D symmetric coordinate systems, and femforge converts only the typed force and torque fields to full-revolution totals:

Result.axial_force takes an axis in the authored frame:

The workbench field viewer shows the section as solved, mirrors it into the full plane, or revolves it around the axis back into the authored frame.

Limits¶

• Only magnetostatics and heat conduction have an axisymmetric form.
• An axisymmetric run computes no torque.
• femforge sections one half-plane and does not check that the model is symmetric.
• Every solid must cross the half-plane; a part off to the side of the section raises.