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# [FEMM] Merry Christmas to David !!!

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- Subject: [FEMM] Merry Christmas to David !!!
- From: "Bruce G. Kang" <xiandaiwuxue@yahoo.com>
- Date: Mon, 22 Dec 2003 10:26:31 -0800 (PST)
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    David:

    Thank you!

    Merry Christmas and a Happy New Year!!!

    Bruce

    --- David Meeker <dmeeker@foster-miller.com> wrote:
    > Bruce G. Kang wrote:
    >
    > >Dear David:
    > >
    > >I need your help again. Please see attachment in
    > >figures about the question:
    > >
    > >1. for ferrite, we want to know the leakage field
    > at
    > >one side region about 3~5 times the ferrite
    > dimension.
    > >basically it is a 3D problem. You suggested to use
    > BEM
    > >methods to solve it. But I found BEM is difficult
    > to
    > >pick up.
    > >
    > >
    > Your request was for a recommendation for a
    > commercial program that
    > would be good for examining the distant leakage
    > field.  Although this is
    > certainly possible to calculate this sort of thing
    > with finite elements,
    > boundary element techniques are well-suited to this
    > particular problem
    > since no outer boundary of the solution region need
    > be defined.  One
    > example of such a commercial code would be IES
    > Amperes, which is a good
    > and fairly intuitive program.  As far as freeware,
    > there is Radia
    >
    (http://www.esrf.fr/machine/groups/insertion_devices/Codes/Radia/Radia.html),
    >
    > which is actually a volume integral code (rather
    > than a boundary
    > integral code) but has the the same nice properties
    > with respect to
    > evaluating the field at distant locations. However,
    > you have to have
    > Mathematica installed to be able to run Radia.
    >
    > >2. Is this a good idea? To change the vector
    > problem
    > >into a potential problem as in "Answer.bmp"? Due to
    > >mu_r is much larger than 1, we can claim each side
    > >have different potentials. The rest will be a
    > >finite-difference problem to get all the potential
    > >distribution of the region. B will be the gradient
    > of
    > >potential.
    > >
    > >Please comment and suggest.
    > >
    > >Best Wishes,
    > >
    > >Bruce
    > >
    > >
    > My original suggestion still stands--at a big enough
    > distance,
    > everything looks like a dipole (or perhaps a
    > collection of a small
    > number of dipoles).  You could use a 2D finite
    > element solution to back
    > out a dipole moment for your device as seen from a
    > distance, and then
    > shove that dipole moment into the equation for the
    > field of a dipole in
    > 3D space.
    >
    > If one wanted to get more complicated, one could
    > build up a 3D solution
    > for the leakage field from the contributions of the
    > magnetization in
    > each element of the 2D mesh containing iron (where
    > you'd use the 2D
    > solution to determine the magnetization), plus
    > contributions from the
    > coils.  In this approach, the contribution from each
    > element would be
    > represented as a point dipole located at the center
    > of the element, and
    > the resulting field contribution would be that of a
    > point dipole in 3D
    > space.  The Biot-Savart law would be used to account
    > for the
    > contributions of the coil.
    >
    > Dave.
    >
    > --
    > David Meeker
    > Senior Engineer
    > Foster-Miller, Inc.
    > 350 Second Avenue
    > Waltham, MA 02451-1196
    > 781-684-4070
    > 781-890-3489 (fax)
    > dmeeker@foster-miller.com
    > http://femm.foster-miller.com
    >
    > _______________________________________________
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- References:
  - Re: [FEMM] Help again
    - From: David Meeker <dmeeker@foster-miller.com>

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