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# 3 phase cable/animation & thanks

- To: femm@yahoogroups.com
- Subject: 3 phase cable/animation & thanks
- From: lkloesel@mail.qnet.com
- Date: Thu, 25 Oct 2001 21:16:26 -0000
- In-reply-to: <d6.d881100.290822d4@aol.com>
- User-agent: eGroups-EW/0.82

    OK. Thanks, I sped up the calculations using:

    function cos_alt(x)
    return floor(cos(x)*1.e4)/1.e4
    end

    which basically rounds to 4 places. I have placed one of the
    animations in the folder 3_phase_cable called "mumetalall.gif". This
    demostrates a 1/4" plate of mu metal, 3 meters wide over a 3 phase
    cable carrying 500 amps.

    Once again thanks

    --- In femm@y..., dcm3c@a... wrote:
    > In a message dated 10/23/01 4:17:33 PM Eastern Daylight Time,
    > lkloesel@m... writes:
    >
    > > Dear All,
    > >
    > > I was trying to simulate the rotating fields around a 3 phase
    cable
    > > (see FEMM folder 3_phase_cable). In order to change the
    currents, I
    > > used modifycircprop() lua command. As you can see, in the
    > > pre-processor script, I changed the currents by adding 10 degrees
    > > to each program loop. The post-processor file will take a
    snap-shot
    > > of
    > > the field, to which I will eventually assemble with a
    gif-animator to
    > > reveal a very nice animation of the fields.
    > > My problem is this: FEMM hangs in the fkern portion, the
    biconjugate
    > > gradient solver just sits there. I had to add 0.5 (or 0.1) to the
    > > currents in order to get fkern to unhang. I believe there may be
    a
    > > bug here which warrents review. I changed the precision, but
    that
    > > didn't work. I looked for a simple lua method of rounding the
    > > numbers
    > > after they were created from the sin() and cos() functions, but
    found
    > > none readily available.
    >
    > It is theoretically possible for the BiCG iteration to break down
    (i.e. not
    > converge), although this "rarely happens in practice." This appears
    to be
    > one of those "rarely happens in practice" situations... The
    iteration
    > converges nicely when I force it to start from a random initial
    guess, but it
    > hangs when I start it from an initial guess of all zeros. I'll try
    to muck
    > around with the solver to see if I can get it to be a bit more
    robust to this
    > situation.
    >
    > In the mean time, things also appear to converge OK when I round the
    sin()
    > and cos() functions to single precision. To get it do this, you can
    define
    > the following functions at the beginning of your script:
    >
    > function cos_alt(x)
    > return floor(cos(x)*1.e8)/1.e8
    > end
    >
    > function sin_alt(x)
    > return floor(sin(x)*1.e8)/1.e8
    > end
    >
    > Then, make calls to cos_alt() and sin_alt() rather than cos() and
    sin(). The
    > script seems to run ok with this modification.
    >
    > Anyhow, thanks a lot for pointing this out--I really appreciate it.
    >
    > Dave Meeker
    > --
    > http://members.aol.com/_ht_a/dcm3c

- References:
  - Re: [femm] 3 phase cable
    - From: dcm3c@aol.com

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