Glossary
Terms used throughout this manual, in one place.
A — magnetic vector potential
The scalar quantity Nabla actually solves for at every mesh node in a 2D magnetic problem (the out-of-plane component of the vector potential). Flux density B is derived from it (B = curl A), which is why Dirichlet boundary conditions are expressed as a fixed value of A rather than of B directly.
Axisymmetric
A problem type for parts that are solids of revolution around an axis (a solenoid, a linear
motor's round cross-section) modelled as a 2D slice in (r, z) instead of
(x, y). See Solving — problem types.
B, H, μ
B is magnetic flux density (tesla), H is magnetic field strength (A/m), and permeability μ is the ratio between them (B = μH). Air and most non-magnetic materials have a constant μ; iron and other soft-magnetic materials have a nonlinear, saturating B-H curve, which is why solving a model with iron regions takes several nonlinear iterations instead of one linear solve. See Regions & materials — B-H curves.
Coenergy
The energy-like quantity Nabla differentiates with respect to position (or angle) to get a force or torque, chosen because it stays well-defined through magnetic saturation where energy alone does not. You will not set anything called "coenergy" yourself; it underlies the force and torque results.
Demagnetisation (demag)
The risk that a permanent magnet is pushed, by an opposing field or by heat, past the "knee" of its own B-H curve and permanently loses strength. Nabla's Demag Risk result shows how close each magnet element came to that knee during a solve. See Post-processing — demag risk.
Eggshell method
How Nabla computes the net force or torque on a region: a thin weighted shell of elements just outside the region's own boundary, rather than the boundary itself, which keeps the result stable on the coarser elements a practical mesh actually has. See Post-processing — forces.
MPC — multi-point constraint
A constraint that ties several mesh degrees of freedom together with weights, rather than fixing one value outright. Nabla uses this to enforce periodic, anti-periodic and sliding-band boundary conditions between two boundaries whose mesh nodes do not line up one-to-one. See Boundary conditions — the sliding band.
MTPA / MTPV
Maximum Torque Per Ampere and Maximum Torque Per Volt: the current (or voltage) angle that gets the most torque out of a synchronous machine for a given current magnitude (MTPA, used below base speed) or a given voltage limit (MTPV, used in the field-weakening region above base speed). See the machine performance-analysis chapter.
Reluctivity
The reciprocal of permeability, 1/μ. Nabla's nonlinear solver works in terms of reluctivity because that is the quantity that appears linearly in the stiffness matrix; you will mostly meet the word in log lines about nonlinear convergence.
Sliding band
The narrow ring (or line, for a linear mover) of elements at the interface between a moving part and a stationary one. Nabla never moves the mesh itself: it re-solves the constraint across this band at the mover's new position on every time step, which is what lets a rotor spin without remeshing. See Boundary conditions — the sliding band.
Slip
For an induction machine, the fractional difference between the rotating field's synchronous speed and the rotor's actual mechanical speed. Zero slip means no induced rotor current and no torque; slip is what makes an induction motor an induction motor.
Steinmetz coefficients
The exponents and constant in the empirical iron-loss formula (loss ∝ k fαBβ) that turns a simulated flux waveform into a watts-per-kilogram estimate for a given core material. See Regions & materials — iron-loss coefficients.