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# Re: [FEMM] Thrust Bearing AC analysis

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- Subject: Re: [FEMM] Thrust Bearing AC analysis
- From: David Meeker <dmeeker@ieee.org>
- Date: Tue, 03 Feb 2004 10:10:07 -0500
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`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

``

- References:
  - [FEMM] Thrust Bearing AC analysis
    - From: "Nathan Brown" <nathanbrown@snet.net>

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