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# Re: [femm] Re: Incorrect force direction

- To: <femm@egroups.com>
- Subject: Re: [femm] Re: Incorrect force direction
- From: "Steven Stretz" <stretzsj@execpc.com>
- Date: Thu, 4 Jan 2001 21:25:07 -0600
- References: <5b.fefc9e5.27823eac@aol.com> <000901c07451$cd9c00e0$52e78ec6@ibmbn145hv> <3A534275.E66BF094@foster-miller.com> <000901c075ce$f329f5a0$a2e78ec6@ibmbn145hv> <003b01c07678$9f0609a0$d18ecfa9@Pstretzsj> <3A541506.F5A5126E@plix.com>

    I can't help you much. All of the work I do is 2D. I evaluated it several
    years ago so my opinions are dated. That's why I said I hope that the
    software had improved. Part of the problem with the 2D version was the way
    they tried to handle nonlinear properties of the materials and eddy
    currents. The material had to be broken up into "elements", called
    something else, which was more trouble than doing finite elements. AND, if
    I have to go through all that work why go with boundary elements.

    The program seemed to work for DC motors, magnets, far field and high
    frequency effects. If I were designing M.R.I. equipment I might like it.
    But I design electric induction machines. Bottom line, it might be a good,
    maybe great package for some things but not everything.

    If I had to recommend I would suggest Infolytica. They have been around a
    long time. I trust the theory and have faith in those working on it. The
    salesman has been calling me and is begging me to try it again and says it
    is much better than the version I tried. The other is Ansoft. I trust John
    Brauer who is one of the people that work on it's development. I have no
    comment on OPERA, and I think Magsoft is better at 2D and came out of the
    machines world, may not be as generally robust.

    Good luck and thanks.
    ----- Original Message -----
    From: "Dave Squires" <djsquires@plix.com>
    To: <femm@egroups.com>
    Sent: Thursday, January 04, 2001 12:15 AM
    Subject: Re: [femm] Re: Incorrect force direction

    > Steven,
    > I am evaluating Amperes right now. I have to say I think their
    > interface leaves a lot to be desired. It is a pain in the butt to enter
    > and define a problem. Geometry entry is not at all intuitive not to
    > mention boundary element definition. I told them already I don't
    > think the software is worth the $15,000 they are asking.
    > When did you evaluate and use it? It seems to me to be worth
    > about $2K-5K on the open market. I guess they don't have
    > any competition and charge the high price as a result.
    > Do you know of another 3D package that is worth the price charged?
    >
    > My gut feel so far is not to buy IES Amperes.
    >
    > Thanks,
    > Dave Squires
    >
    > Steven Stretz wrote:
    >
    > > Comparison is a very good idea however I have had such terrible luck
    with
    > > IES software I would not trust it any farther than I could throw the CD.
    > > Boundary elements are great for far field effects but historically their
    > > attempts at handling near fields, nonlinearities, induced currents, etc.
    has
    > > been at best questionable. I'll trust your judgement and hope the
    software
    > > has improved but be careful using it. I leased the software for a year
    and
    > > returned in after several months and asked for my money back, which I
    never
    > > received.
    > > ----- Original Message -----
    > > From: "Greg Watson" <gowatson@optusnet.com.au>
    > > To: <femm@egroups.com>
    > > Sent: Wednesday, January 03, 2001 3:48 PM
    > > Subject: Re: [femm] Re: Incorrect force direction
    > >
    > > > ----- Original Message -----
    > > > From: "David Meeker" <dmeeker@foster-miller.com>
    > > > To: <femm@egroups.com>
    > > > Sent: Thursday, January 04, 2001 1:47 AM
    > > > Subject: Re: [femm] Re: Incorrect force direction
    > > >
    > > >
    > > > > Anyhow, I modelled your problem on Amperes by IES, which is a rather
    > > expensive
    > > > > commercial 3-D magnetostatic solver based on boundary elements,
    rather
    > > than
    > > > finite
    > > > > elements. This ought to give a good idea of how things would run in
    a
    > > real
    > > > 3-D test
    > > > > rig, assuming everything is carefully aligned. I arbitrarily made
    the
    > > machine
    > > > 1"
    > > > > deep in the "into the page" direction, for the purposes of making a
    3-D
    > > > geometry. I
    > > > > chose a relatively fine density for the surface elements, and then
    set
    > > it to
    > > > > evaluate the forces on the magnet at a bunch of different axial
    > > positions.
    > > > What it
    > > > > predicts is that the centring force peaks when the front edge of the
    > > magnet is
    > > > just
    > > > > past the iron, with the centring force dropping to near zero when
    the
    > > magnet
    > > > is
    > > > > completely between the iron bars. femm predicts the same sort of
    > > behaviour,
    > > > except
    > > > > that femm predicts the peak force to be more like 15 Newton/inch,
    rather
    > > than
    > > > 9 N.
    > > > > The force from the 3-D geometry is smaller than in the 2-D model
    because
    > > some
    > > > of the
    > > > > magnet's flux leaks into the sides of the bars--this is an
    intrinsically
    > > 3-D
    > > > effect
    > > > > that can't be modelled by a 2-D solver.
    > > >
    > > > Hi David,
    > > >
    > > > Thanks for the effort.
    > > >
    > > > My concern was not that FEMM should report a large centring force but
    that
    > > a
    > > > program which I normally have found to be very realistic would report
    a
    > > > repulsive & not a centring force, no matter how fine the mesh or how
    much
    > > care I
    > > > took in making sure the geometry of the mesh and / or of the model
    didn't
    > > effect
    > > > the result.
    > > >
    > > > My duplication involved a round Neo, 4 on point right angle plastic
    guides
    > > hot
    > > > glued to the vertical faces of 2 right angle steel pieces (two guides
    per
    > > face,
    > > > 1 top, 1 bottom). Alignment isn't too critical. Although the plastic
    > > guides
    > > > aren't ideal, you can get a feel for the forces by the amount of
    effort
    > > needed
    > > > to roll the magnet back & forth between the guides.
    > > >
    > > > Greg
    > > >
    > > >
    > > >
    > > >
    >
    >
    >
    >

- Follow-Ups:
  - Re: [femm] FE magnetics commercial ware
    - From: David Meeker <dmeeker@foster-miller.com>

- References:
  - Re: [femm] Re: Incorrect force direction
    - From: dcm3c@aol.com
  - Re: [femm] Re: Incorrect force direction
    - From: "Greg Watson" <gowatson@optusnet.com.au>
  - Re: [femm] Re: Incorrect force direction
    - From: David Meeker <dmeeker@foster-miller.com>
  - Re: [femm] Re: Incorrect force direction
    - From: "Greg Watson" <gowatson@optusnet.com.au>
  - Re: [femm] Re: Incorrect force direction
    - From: "Steven Stretz" <stretzsj@execpc.com>
  - Re: [femm] Re: Incorrect force direction
    - From: Dave Squires <djsquires@plix.com>

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