Coil Group¶

Scalar field that gives each separate conductor body of an excitation coil a distinct integer label. A single CoilSpecification can cover several disconnected bodies at once (for example all coil sides of one phase of a polyphase winding); this coefficient shows which body a cell belongs to. See Coil Groups.

Registered name: "Coil Group".

Per-cell value:

Cell location	Value
Inside body \(k\) of some `CoilSpecification`	non-negative integer \(k = 0, 1, \dots\)
Outside every coil	NaN

The numbering restarts at 0 for each CoilSpecification, so two cells with the same label belong to the same body only when they belong to the same coil specification. To tell different coils apart, combine this coefficient with Coil Index.

The NaN outside-coil value renders as the configured NaN colour in ParaView, so coil cells stand out visually against the rest of the mesh without needing a threshold filter.

This coefficient is primarily an inspection aid — useful for checking that a marker really covers the bodies you intended, or for driving per-body logic in custom post-processing.

Example: IPM-motor stator¶

Figure 1: Coil Group on the 24-slot stator of the IEEJ IPM benchmark. Each of the three phases is one CoilSpecification whose marker covers 8 disjoint sub-coils, so the field takes values \(0, 1, \dots, 7\) inside the conductors. The surrounding air domain is not covered by any coil and is rendered in ParaView's NaN colour (green here).

The figure comes from an IEEJ IPM motor benchmark whose three phase specs collapse the 24 winding bodies into three regex markers — see Coil Groups:

coil = CoilSpecification(
    f"Coil::{phase}",
    Vol(rf"Coil::[+-]{phase}::.*"),     # 8 disjoint sub-coils → groups 0..7
    CoilTopologyOpen(
        Bnd(rf"Coil::[+-]{phase}::.*::In"),
        Bnd(rf"Coil::[+-]{phase}::.*::Out"),
    ),
    CoilTypeStranded(turns_per_coil),
    CoilExcitationCurrent(current=cff_sin),
    reverse_direction=Vol(rf"Coil::\-{phase}::.*"),
)

Because the labels are per-spec local, a sub-coil in phase U with the same label as one in phase V will share its colour. To distinguish phases at a glance, combine Coil Group with Coil Index.