I am looking to utilise symmetry with a magnetic fields simulation in order to reduce model complexity. The attached models are much simplified version of the actual design I am simulating, but are adequate to show my problem.
I have a simple coil, above which is positioned a permanent magnet assembly, comprising of 2 magnets in antisymmetry (one North up, one South up).
Attached are 3 models representing this simple setup. The first has no symmetry, the second has a single plane of symmetry and the third has symmetry in 2 planes.
The first 2 simulations are easily done using the coil geometry analysis node (and ensuing the length factor is given as 2 for the single plane symmetry version, so that the coil resistance is calculated correctly). The plots from the first 2 models also make perfect sense and are in agreement.
However, when I introduce a second symmetry plane, the results start to not make sense.
I have added a Perfect Magnetic Conductor boundary condition on the plane where the crossing field must be normal, and have introduced a mirror 3D dataset in order to get plots of the full cross section of the model. This mirror 3D dataset has the vector transformation set to antisymmetric, to account for the permanent magnet and coil antisymmetry in this plane).
The plots look OK, but I am a little concerned that the Fz in the coil has increased (having been very close to zero, basically a model rounding error) to about 0.21N. I am aware that force calculations are mesh dependant, but doubling the mesh densoty produces the same result, which makes me think there is something that needs adjusting somewhere... This force should be zero, theoretically.
Could this be because of an incorrect setup or boundary condition somewhere?
The attached Word doc shows images of the 3 models.
Any feedback greatly appreciated!
Mark