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Time- and Coordinate-Dependent Boundary Condition

Conductive cylinder in rotating magnetic field.

Problem type:

Plane problem of transient magnetics.

Geometry:

Conductive cylinder in rotating magnetic field

Given:

Relative magnetic permeability of air μ = 1;
Relative magnetic permeability of conductor μ = 1;
Conductivity of conductor σ = 6.3·107 S/m;
Magnitude of external field B0 = 1 T;
Number of poles 2p = 6;
Frequency f = 50 Hz.

Solution:

To specify rotating magnetic field on the outer boundary of the region, Bn = B0 sin (ωt - pφ), we apply the Dirichlet boundary condition, using the formula: A = cos (18000*t - 3*atan2 (y/x)) / 60

The coefficient A0 = 1/60 arises from consideration

Bn = (1/r)(∂A/∂φ) = A0p·sin(ωt - pφ) / r

and

A0 = B0·r/p

Due to periodicity of the problem, only half of the model is presented, and odd periodic boundary condition A1 = -A2 is applied on the cut. In fact, it would be enough to simulate just 60° sector of the model. In time domain, problem is simulated with automatic adaptive time step, up to 0.05 seconds (approx. 2.5 periods).

Results:
t = 0.0002 sec:
Conductive cylinder in rotating magnetic field simulation

t = 0.048 sec:
Induction motor Massive rotor eddy currents

t = 0.05 sec:
AC motor steel rotor eddies

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