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Re: [FEMM] Thrust Bearing AC analysis

Although the program can't yet do a combined DC+AC in a single analysis (magnetic bearings typically operate by imposing an AC "control" current on top of a DC "bias" current), one can get a transfer function for force/(control current) as a function of frequency (i.e. including effects of eddy currents/hysteresis). One would do this by looking at the frequency dependence of flux in the gap. The (force/current) transfer function will have more or less the same frequency dependence as the (flux density/current) transfer function for a point taken in the middle of one of the air gaps.

Dave.

Nathan Brown wrote:

I'm hoping that someone can give me some pointers for a 'simple' AC
analysis. I have many hours of FEMM experience solving DC magnetostatic
problems, but have yet to attempt an AC analysis.

Anyway, I'm trying to use FEMM to estimate the dynamic force capability of a
solid-core magnetic thrust bearing over a range of frequencies (up to 100
Hz). Before I get ahead of myself, will FEMM handle this type of analysis
(dynamic force calculation, considering eddy current generation within a
non-laminated block of material)?

At this point all I have is the FEMM model I used to determine the DC force
capacity of the thrust bearing. I did apply the electrical conductance
property to the core materials, but now I'm stuck. I'd greatly appreciate
any suggestions for how to proceed with the AC analysis.

I can provide further information if necessary.

Thanks!

Nathan Brown
nathanbrown@snet.net