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# Re: FEMM simulations errors ??

- To: femm@yahoogroups.com
- Subject: Re: FEMM simulations errors ??
- From: "David Meeker" <dcm3c@aol.com>
- Date: Tue, 12 Jun 2001 22:07:12 -0000
- In-reply-to: <9g609m+td2p@eGroups.com>
- User-agent: eGroups-EW/0.82

    --- In femm@y..., harti@h... wrote:
    > To explain it a bit more:
    >
    > Look at the posted GIF pic.
    >
    > I drew a clockwise red bouding box
    > at the additional 4 points in the air
    > which I placed additionally in the fem
    > model near the 2 runner magnets (called "runner stack")
    >
    > When I integrate it this way and use the "Force from Stress Tensor"
    > I get around +640 N/m into x-Direction,
    > but as you can see, the runner stack must move to the left side,
    > due to the reduced magnetic field at the left side, so the
    calculated
    > force is into the wrong direction !
    > So is this a FEMM error or do I still have to make the mesh still
    > finer ?
    > The dimensions are:
    > 2 neodym stator magnets 10 cm x 1 cm and 2 runner magnets
    > 3 cm x 1cm, 2 cm thick steel core as back flux core.

    The way that you have your arrangement configured, the magnets should
    be pushed to the right--femm is giving a reasonable answer.

    The way to see this is to think of each magnet as being composed of 2
    point poles of strength Q. For a N pole, the force on the pole is
    B*Q, where B is the flux density created by the stator permanent
    magnets. For a S pole, the force is -B*Q. When you look at it this
    way, you can see that the vertical force should be zero, and there
    should be a net horizontal force to the right. One reference for this
    trick is M. Lindeburg's "Engineer in Training Review Manual, 6th ed.,"
    1982.

    Dave Meeker
    --
    http://members.aol.com/_ht_a/dcm3c

- Follow-Ups:
  - RE: [femm] Re: FEMM simulations errors ??
    - From: "Adrian" <adrianw@solid-state-logic.com>
  - Re: [femm] Re: FEMM simulations errors ??
    - From: Dave Squires <djsquires@plix.com>

- References:
  - Re: FEMM simulations errors ??
    - From: harti@harti.com

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