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# Re: Circuits in FEMM

- To: femm@yahoogroups.com
- Subject: Re: Circuits in FEMM
- From: frank.e.lenning@boeing.com
- Date: Fri, 07 Sep 2001 17:49:16 -0000
- In-reply-to: <f8.f1694d1.28c9a635@aol.com>
- User-agent: eGroups-EW/0.82

    --- In femm@y..., dcm3c@a... wrote:
    > In a message dated 9/5/01 12:52:32 PM Eastern Daylight Time,
    > frank.e.lenning@b... writes:
    >
    >
    > >
    > > Thanks Dave. What is the equation that FEMM solves for the time
    > > harmonic case and where does it do it in the FEMM source code?
    > >
    > >
    > >
    > I've put a brief note in the "files" section on the extra equation
    that the
    > program solves associated with each current constraint:
    > <A
    HREF="http://groups.yahoo.com/group/femm/files/currentconstraint.pdf";>
    http://groups.yahoo.com/group/femm/files/currentconstraint.pdf</A>
    >
    > The source code associated with it lives (for the 2d planar case) in
    the
    > prob2big.cpp and (for the axisymmetric case) prob4big.cpp files of
    fkn. The
    > code that enforces it is sort of strewn around, because the extra
    equation
    > really gets built implictly. Only the upper diagonal of the matrix
    is
    > stored, because of the symmetry of the problem, so the extra
    equation gets
    > built by adding extra forcing terms associated with the unknown
    gradient to
    > the elements that live in the regions associated with the circuit.
    Look for
    > the comments that show where the circuit parts live (e.g. lines
    > 78-89,294-302, 335-340 in prob2big, similar implementation in
    prob4big) . In
    > the source code, the voltage gradients are included in the vector of
    unknowns
    > right after the nodal values of potential. The voltage gradients
    also get
    > written to disk in the .ans file.
    >
    > Dave.

    Way cool Dave. Thanks. What I was really trying to do was understand
    better how FEMM solved this problem to tell if I could get another
    code, Quickfield, to do the same problem (I've been using FEMM but
    some others in my workgroup already own Quickfield). By your fine
    writeup, I believe the answer is no since Quickfield doesn't exactly
    have the same circuits capability and without setting up and solving
    the equations with the unknown potentials, you have nothing better to
    do but to guess at them and iterate...ugly. Your open source is great.
    I had already found the place in prob2big and your note will help me
    understand what I'm seeing better. BTW, your support of this group is
    nothing short of amazing. Microsoft could take some product support
    lessons from you.

    On a related subject, I'm interested in a 3D FEM as well. Is there a
    public domain 3D mesher out there like triangle (or can triangle do
    it)?? I assume one could use the same solver engine as FEMM but the
    mesher and visualizations would need to change.

- References:
  - Re: [femm] Re: Circuits in FEMM
    - From: dcm3c@aol.com

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