Regions & materials

Telling Nabla what each enclosed area of your drawing actually is.

Regions

A region is a physical area of the model — a slice of iron, a coil slot, the surrounding air. Arm Add Regions in the Model Tree and click once inside a closed shape boundary; Nabla drops a region marker there and works out the enclosed area for you, so the boundary just has to be closed, not explicitly selected edge by edge. Double-click a region (in the tree or on the canvas) to open Region Properties:

Region Name and a Color swatch for the canvas;
Material Properties — density, electrical conductivity, and either an isotropic mu or, with Anisotropic ticked, separate mu (ortho) / mu (norm) values and a direction angle (see Anisotropic permeability below), or a Catalog Material picked from the library (see the material library);
Iron Loss — the Steinmetz coefficients described in Iron-loss coefficients;
Magnetization and Current — Current Density (MA/m²) for a region that is itself an imposed current source (independent of any coil), plus Coercivity and direction of magnetization for a permanent-magnet region;
Set Coil — attach this region to a coil and pick which way its current flows: In (into the page) or Out (out of the page). A coil's two sides — the "go" slot and the "return" slot — are two regions each set to the same coil with opposite directions (see Coils & circuits);
Selected Motion — which motion zone this region belongs to, or (auto) to infer it from the zone's geometry;
Mesh Properties — a mesh size for this region only, overriding the model's default (see Meshing — mesh size).

Air has no special flag: an empty region is simply one nothing was assigned to (unit permeability, negligible conductivity). You do not need to mark a region as air deliberately.

Region Properties edits every currently selected region at once, not just the one you double-clicked — select a dozen slot regions and set Catalog Material once rather than region by region. The one field this does not apply to is Region Name: with more than one region selected it shows "n/a Multiple Regions Selected" and is left alone, because renaming does apply to the whole selection if you use it anyway (typing a name and pressing Enter with several regions selected gives all of them that same name — there is no uniqueness check, so duplicate region names are allowed but rarely what you want).

A region marker is auto-named Region N from an incrementing counter when placed. Deleting a marker (select it, press Delete) removes only the marker and its assignment — the enclosed area itself is not explicitly re-flagged as air, so a pocket that loses its only region marker is left out of the mesh or merged into a neighbouring region rather than becoming air automatically. Two markers dropped in the same enclosed area are not rejected, so re-triangulation quietly resolves to whichever assignment last touched that area — avoid it rather than relying on it.

Holes

A hole is a pure geometry marker, not a physical material: it tells the mesher "this enclosed area is excluded, do not mesh it" — the correct tool for a cavity or an area you are deliberately leaving out of the simulation. Placed exactly like a region: arm Add Holes and click inside a closed boundary; Ctrl+click an existing hole marker to select it.

The material library

Nabla ships a library of materials as CSV files grouped into folders (soft-magnetic steels, permanent magnets, and so on); each folder becomes a group in the Catalog Material picker inside Region Properties, browsable by group. A material record carries a B-H curve, an optional measured iron-loss table, a display colour, and — for hard-magnetic (permanent magnet) materials — the additional data described below. Picking one from the combo applies it to every currently selected region immediately.

Editing the library itself (adding a material, changing a curve, deleting one), like using the shipped library on a region, is free on every tier. A material you create yourself is saved into its own user_materials group, alongside the built-in ones. There is no search or filter box in the picker — with a large library, browsing by group is the only way to find a material by name.

Renaming is restricted to the user_materials group, but deleting is not: the Delete button removes whichever material is currently selected in the library, built-in or not, and it deletes that material's CSV file from disk immediately, with no separate confirmation for a built-in entry. Be deliberate about what is selected before pressing it — recovering a deleted built-in material means reinstalling or re-adding it by hand.

B-H curves

Double-click a material's name in the library to open its curve editor: a table of (H, B) points plotted live, with buttons to add or remove rows. A material only counts as having a usable nonlinear curve once it has at least two points with both H and B above zero; short of that, Nabla treats it as a plain linear material using its stored mu instead. The same editor also holds an optional measured iron-loss table (frequency, B, loss in W/kg) used to fit the Steinmetz coefficients below, and, for magnet materials, a per-temperature demagnetization-knee table used for the demag-risk result — see Post-processing — demag risk.

Hard-magnet (permanent magnet) data

A magnet material's editable data beyond its curve is three numbers: Br (residual flux density, T), Hc (coercivity), and a display mu. Br and Hc are the two you actually edit; Nabla keeps the linear hard-magnet relationship Br = μ·μ₀·Hc self-consistent by recomputing mu from whichever of Br/Hc you last changed. Assigning a magnet material to a region carries its coercivity across automatically (scaled from A/m to the kA/m the Region Properties field expects); editing the catalog material afterwards updates every region already assigned to it, so you do not have to revisit each magnet region by hand after a material tweak.

A magnet region also needs its own DOM (deg°) field — direction of magnetization, measured in degrees from the global X axis — set per region, next to Coercivity. There is no radial/tangential preset, so for a ring of magnets (an inset or surface-mount PMSM rotor) you set each pole's DOM by hand to the angle appropriate for its position — the parametric machine modules (see Machines) do this for you when they build a magnet rotor.

Anisotropic permeability

For laminated or otherwise directional materials, tick Anisotropic in Region Properties instead of using a single isotropic mu: set mu (ortho) and mu (norm) for the permeability along and across the material's principal (lamination) axis, and Mu Direction angle for that axis's angle from the global X direction. This is an alternative to a nonlinear catalog material, not a combination of the two — a region is either anisotropic-linear or governed by a B-H curve, never both at once.

Iron-loss coefficients

Region Properties' Iron Loss section implements the Steinmetz model W_Fe = K_h·f·B^α + K_e·f²·B² — hysteresis plus eddy-current loss density from frequency and peak flux density. Tick Enable Iron Loss and either type in K_h, α and K_e yourself or, if the assigned material carries a measured loss table, press Fit Curve to fit them automatically from that data. A fit updates only this region's coefficients; it does not rewrite the material file, so different regions sharing one catalog material can still fit independently if their operating points differ. See Post-processing — losses for how the result is reported once you solve.