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# [femm] Re: Strange looking nonlinear curve

- To: femm@egroups.com
- Subject: [femm] Re: Strange looking nonlinear curve
- From: "David Meeker" <dmeeker@foster-miller.com>
- Date: Wed, 29 Sep 1999 10:21:33 -0400
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- In-reply-to: <19990928224404.29827.qmail@hotmail.com>
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    On 28 Sep 99, at 15:44, James Peng wrote:

    > The following BH curve looks weir in Femm. I checked with excel and
    > everything looks fine. Even the solution seems ok. Does anyone have similar
    > experience with FEMM? What should I do to get it fixed?
    >
    > 0.000000	0.000000
    > 0.699870	39.788736
    > 0.700011	79.577472
    [...]

    You have a really abrupt transition in your B-H curve, basically
    going from an incremetal relative permeability of about 14,000 to 1
    in a single step. Femm trys to fit this data with a cubic spline, and
    the resulting fit isn't very good for this particular case.

    The cure is to add more points in the neighborhood of the transition-
    -for this case, a lot of points probably on the range of H from 30 to
    60 A/m, so that, locally, the transition looks like a smooth curve.

    Dave

    --
    David Meeker, Ph.D.
    Senior Engineer
    Foster-Miller, Inc.
    350 Second Avenue
    Waltham, MA 02451-1196
    781-684-4070
    781-890-3489 (fax)
    dmeeker@foster-miller.com
    personal webpage: http://members.aol.com/dcm3c

- References:
  - [femm] Strange looking nonlinear curve
    - From: "James Peng" <james_p_peng@hotmail.com>

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