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# Re: [femm] Re: FEMM simulations errors ??

- To: femm@yahoogroups.com
- Subject: Re: [femm] Re: FEMM simulations errors ??
- From: Dave Squires <djsquires@plix.com>
- Date: Wed, 13 Jun 2001 11:37:53 -0700
- References: <9g63qg+lvf8@eGroups.com>

    David,
    I don't think I quite agree with your explanation.
    If the two magnets are locked together and held
    in the position shown you then have a

    Net force = +B*Q +(-B*Q) = 0

    if embedded in a uniform field. Isn't that correct?

    Dave Squires

    David Meeker wrote:

    > --- 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
    >
    >
    >
    > Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/

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