Reference Geometry

Reference Geometry#

ReferenceGeometry

ReferenceGeometry class contains all geometrical related reference values.

ProjectedArea

Recipe for automatically computing a projected reference area.

Automatic projected reference area#

Assigning ProjectedArea to ReferenceGeometry.area records a recipe – which surfaces and which direction – instead of a number. The value is measured at submission and stored alongside the recipe, so the choice of surfaces survives into the uploaded simulation.json and remains inspectable in the web interface afterwards. Assigning a concrete area computed beforehand stores only the number, and the reasoning behind it is lost.

with fl.create_draft(new_run_from=geometry, face_grouping="faceId") as draft:
    body = fl.SurfaceSelector(name="body").match("*body*")
    wheels = fl.SurfaceSelector(name="wheels").match("*rim*")

    with fl.SI_unit_system:
        params = fl.SimulationParams(
            reference_geometry=fl.ReferenceGeometry(
                area=fl.ProjectedArea(
                    surfaces=[body, wheels],
                    direction="X",
                ),
            ),
            ...
        )

    # Submit inside the draft context: the measurement needs the tessellation.
    project.run_case(params=params)

The result is the silhouette union of the selected surfaces. Surfaces that overlap along the projection direction are counted once, not summed, and a surface named more than once – listed twice, or matched by several selectors – contributes once. There is no need to deduplicate before assigning.

Half-body domains: do not scale by hand

When the meshing settings use domain_type="half_body_positive_y" or "half_body_negative_y", the mesher builds the model trimmed at Y=0. The reference area is measured over that same half automatically, so the stored value already describes the model the solver sees.

Multiplying by 0.5 yourself is wrong in both directions: it double-halves a geometry that was uploaded as a full model, and it halves a geometry that was already just one half. Because the trim is derived from the finalized meshing settings, it is also correct either way – whether the uploaded geometry is a full model the mesher will cut, or already a single half.

Projecting along Y – the trim axis itself – is unaffected, since the cut plane is perpendicular to the view.

Note

The measurement rasterizes a silhouette and counts whole pixels, so the result carries a small discretization error – on the order of 0.1% at the default settings. Treat a difference of that size between two measurements of the same geometry as expected rather than as a defect.

See also