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# RE: [femm] want high-accuracy measurement of force between 2 magnets

- To: <femm@yahoogroups.com>
- Subject: RE: [femm] want high-accuracy measurement of force between 2 magnets
- From: "James Rabchuk" <ja-rabchuk@wiu.edu>
- Date: Thu, 6 Mar 2003 14:14:21 -0600
- Importance: Normal
- In-reply-to: <b488dt+36ob@eGroups.com>
- Reply-to: <JA-Rabchuk@wiu.edu>

    A number of possibilities:

    First of all, have you downloaded the beta version 3.3a of FEMM? It has a
    weighted stress tensor that takes an average of a number of integration
    paths around the object of interest. Much improved accuracy and consistency.
    But ....

    you do need to increase the mesh density around the moving object.

    Third, make your problem space large enough, and use the mixed boundary
    conditions to mimic an infinite domain.

    Fourth, try using the coenergy method. The force is the positive derivative
    with respect to the space coordinate.

    Maybe you've tried these things already, but these are the thoughts that
    come to mind right off the bat.

    Jim
    -----Original Message-----
    From: mikeshonle [mailto:mike@psychonic.net]
    Sent: Thursday, March 06, 2003 1:44 PM
    To: femm@yahoogroups.com
    Subject: [femm] want high-accuracy measurement of force between 2
    magnets

    Hi, I'm trying to measure the force vs. distance between two magnets
    over the range of 3 to 3.5 inches. I have a script running, etc.,
    but the final result is not monotonic and varies considerably and is
    sometimes even negative.
    What all can I do to increase the accuracy? Is a finer mesh more
    important than the solver accuracy? What is a good minimum mesh
    spacing and accuracy limit? What is the practical limit of accuracy?
    Thanks,
    -Mike

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- References:
  - want high-accuracy measurement of force between 2 magnets
    - From: "mikeshonle" <mike@psychonic.net>

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