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# Re: Plots of Je

- To: femm@yahoogroups.com
- Subject: Re: Plots of Je
- From: "David Meeker" <dmeeker@ieee.org>
- Date: Fri, 11 Jul 2003 20:52:31 -0000
- In-reply-to: <000a01c34682$b43a0560$6c405142@robertmacy>
- User-agent: eGroups-EW/0.82

    The time-harmonic problem that FEMM is solving is:

    curl((1/mu)curl(A)) = -j*omega*sigma*A + Jsrc

    where mu is permeabilityin H/m, omega is frequency in rad/sec, sigma
    is conductivity, and A is vector potential in T*m

    Jsrc is source current density in MA/m^2--that is, there current that
    would be in the winding either at zero frequency or if conductivity is
    equal to zero.

    When you plot "Jeddy", you are plotting just the -j*omega*sigma*A
    term--that is, the induced currents that tend to buck the source currents.

    When you plot "Jeddy+Jsrc", you are plotting the complete RHS, or all
    contributions to current.

    In the case where the total current in a region is specified via a
    "circuit" property, the program is automatically picking the Jsrc term
    so that the integral of "Jeddy+Jsrc" adds up the the specified value.

    To get a prescribed to total current in a conductive region for
    frequency not equal to zero, you have to prescribe the total current
    via a "circuit" property.

    Dave.
    --
    http://femm.berlios.de/dmeeker

    --- In femm@yahoogroups.com, "Robert Macy" <macy@c...> wrote:
    > Here is more on my problems plotting Je....
    >
    > *IF* the conductor has zero conductivity (as in a wire bundle), then the
    > plots of Je and Js+J_eddy all make sense whether the current is
    defined by
    > Js in the materials section or whether it is defined as a total
    current in
    > the circuit section.
    >
    > *IF* the conductor has nonzero conductivity (as in a solid wire)
    *and* the
    > current is defined by total current in the circuit section, the
    answers all
    > make sense with the plot of Js+J_eddy being appropriate. However, Je by
    > itself goes way wonky inside the conductor. Outside the conductor where
    > there is no source current flowing the plots are still correct.
    Conclusion:
    > Only use Js+J_eddy.
    >
    > *IF* the conductor has nonzero conductivity (as in a solid wire)
    *and* the
    > current is attempted to be defined as Jsource in the materials
    section, then
    > the analysis really shifts the value of the source current and the
    results
    > are useless. Can't remember about the plots, but the errors make them
    > worthless. Conclusion: Always use circuits to define current in a
    solid
    > wire.
    >
    >
    >
    > Did I misuse the femm program without knowing it? Is a Jsource for
    > conductive wires just incorrect?
    >
    > - Robert -
    >
    >
    >
    > ----- Original Message -----
    > From: robert Macy
    > To: femm@yahoogroups.com
    > Sent: Tuesday, July 08, 2003 8:17 PM
    > Subject: [femm] Plots of Je
    >
    >
    > I'm having difficulty interpreting the significance of
    > plotting eddy currents.
    >
    > I'm plotting eddy currents both in the magnetic material
    > and in the conductor's area.
    >
    > In the magnetic material where there is no circuit current
    > if I plot Je or Js+J_eddy, the plots are identical and look
    > as expected.
    >
    > In the conductor area if I plot Js+J_eddy, the plots look
    > as expected. But when I plot Je by itself, I get
    > outlandish values.
    >
    > If I plot from the magnetic area into the conductor area
    > using only Je, I get identical values to earlier plots
    > until the line gets to the conductor, suddenly everything
    > goes wonky - making no sense.
    >
    > Right now the safe thing to do is to simply only use
    > Js+J_eddy for all locations, plot to file, then manually
    > remove Js in Excel to see what Je looks like.
    >
    > Am I doing something wrong here?
    >
    > There is no mention of eddy currents in the manual.
    >
    > - Robert -

- References:
  - Re: [femm] Plots of Je
    - From: "Robert Macy" <macy@california.com>

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