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# Re: [femm] Re: Incorrect force direction

- To: femm@egroups.com
- Subject: Re: [femm] Re: Incorrect force direction
- From: Dave Squires <djsquires@plix.com>
- Date: Wed, 03 Jan 2001 22:15:35 -0800
- References: <5b.fefc9e5.27823eac@aol.com> <000901c07451$cd9c00e0$52e78ec6@ibmbn145hv> <3A534275.E66BF094@foster-miller.com> <000901c075ce$f329f5a0$a2e78ec6@ibmbn145hv> <003b01c07678$9f0609a0$d18ecfa9@Pstretzsj>

    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: FE magnetics commercial ware
    - From: "C.Prem Kumar" <prem@rnd.bhel.co.in>
  - Re: [femm] Re: Incorrect force direction
    - From: "Steven Stretz" <stretzsj@execpc.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>

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