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

[Dave Squires <djsquires@xxxxxxxx>]

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@xxxx, harti@xxxx 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
>
>
>
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