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# Re: [femm] The contour creation for force calculation

- To: femm@yahoogroups.com
- Subject: Re: [femm] The contour creation for force calculation
- From: matthew chung <matthewc_98@yahoo.com>
- Date: Mon, 17 Dec 2001 09:15:35 -0800 (PST)
- In-reply-to: <F257LjHGozRC9W3XyNk00005114@hotmail.com>

    Kehaty,

    Yes, you're right. Side force is the critical
    facotr for force testing. Fortunately, our force
    tester
    can pull the core steel bar (plunger) in the
    Z direction. I also found that if there is a side
    force during the test, the result will be totally
    different. So I always try hard to avoid the side
    force. Thank you so much for your suggestion.

    I think Dave's suggestion is highly recommended for
    people who want to get the accurate result of the
    force
    simulation. After changing the density of mesh, I got
    the more smooth force curve compared to the previous
    one. But it took me about 6 hours to finish the
    program
    under Win 2000, and PIII 700, 512 Mbytes memory
    environmen.

    It's my pleasure to join this group, because most
    people is willing to contribute their ideas.

    Merry X'mas,

    Matthew
    --- Israel Kehaty <tsiporak@hotmail.com> wrote:

    <HR>
    <html>

    <div style='background-color:'>
    <DIV>
    <P><BR><BR></P>Concerning the 15% error between FEMM
    and the solenoid tester, it may be due to the side
    force on the solenoid punger. Every plunger will have
    a side force due to the fact that the punger is not
    ideally centric to the solenoid house therefore your
    tester may test the friction force on the plunger due
    to the side force.</DIV>
    <DIV>&nbsp;</DIV>
    <DIV></DIV>
    <DIV></DIV>&gt;From: David Meeker<DCM3C@EARTHLINK.NET>

    <DIV></DIV>&gt;Reply-To: femm@yahoogroups.com
    <DIV></DIV>&gt;To: femm@yahoogroups.com
    <DIV></DIV>&gt;Subject: Re: [femm] The contour
    creation for force calculation
    <DIV></DIV>&gt;Date: Thu, 13 Dec 2001 21:49:23 -0500
    <DIV></DIV>&gt;
    <DIV></DIV>&gt;
    <DIV></DIV>&gt;
    <DIV></DIV>&gt;matthewc_98 wrote:
    <DIV></DIV>&gt;
    <DIV></DIV>&gt; &gt; Hi All,
    <DIV></DIV>&gt; &gt;
    <DIV></DIV>&gt; &gt; I use FEMM to simulate the
    solenoid and so far, it works pretty well.
    <DIV></DIV>&gt; &gt; But there is a question I cannot
    understand and hope you can help me
    <DIV></DIV>&gt; &gt; to explain it. The question is as
    following:
    <DIV></DIV>&gt; &gt;
    <DIV></DIV>&gt; &gt; Currently, when I would like to
    calculate the pull force of the
    <DIV></DIV>&gt; &gt; solenoid, I always creat the
    contour path as close as possible to the
    <DIV></DIV>&gt; &gt; surface of core steel bar (the
    contour is away from the steel bar
    <DIV></DIV>&gt; &gt; which means the path is within
    air). But while I read the User's
    <DIV></DIV>&gt; &gt; Manual, I found that Dave
    suggested user to creat the contour at
    <DIV></DIV>&gt; &gt; least two elements from any
    interfaces and boundaries.
    <DIV></DIV>&gt; &gt; Could you tell me that what the
    definition of the element (distance ?
    <DIV></DIV>&gt; &gt; inch ???)?
    <DIV></DIV>&gt;
    <DIV></DIV>&gt;If you push the toolbar button with the
    yellow triangles in the
    <DIV></DIV>&gt;postprocessor, the elements will appear
    on the screen as yellow
    <DIV></DIV>&gt;triangles. The elements don't have a
    fixed size--you can make them as
    <DIV></DIV>&gt;small or you want, depending on the
    mesh size that you define for each
    <DIV></DIV>&gt;block label. Anyhow, you don't want to
    draw your contour through
    <DIV></DIV>&gt;triangles that touch the boundaries. In
    theory, the contour that you
    <DIV></DIV>&gt;pick doesn't really matter, as long as
    it passes through air and
    <DIV></DIV>&gt;encircles the object that you are
    interested in--there's no reason to
    <DIV></DIV>&gt;try to draw your integration path close
    to the object. However, if you
    <DIV></DIV>&gt;draw close to the surface of objects,
    you tend to pollute the force
    <DIV></DIV>&gt;results with relatively inaccurate
    field results that can occur around
    <DIV></DIV>&gt;sharp corners. Also, the part of H that
    is tangential to an interface
    <DIV></DIV>&gt;tends to be less accurate than a bit
    farther out, owing to some aspects
    <DIV></DIV>&gt;of the smoothing scheme that femm uses.

    <DIV></DIV>&gt;
    <DIV></DIV>&gt; &gt;
    <DIV></DIV>&gt; &gt; So far, I used the force data of
    FEMM to campare force data that from
    <DIV></DIV>&gt; &gt; our force tester in the lab, and
    found that the error is within 15%.
    <DIV></DIV>&gt; &gt; (Assume the force data of force
    tester is ideally correct).
    <DIV></DIV>&gt; &gt; Is there any way to narrow the
    error of force simulation of FEMM?
    <DIV></DIV>&gt;
    <DIV></DIV>&gt;A good way to go is to try the
    simulation with progressively finer
    <DIV></DIV>&gt;meshes, increasing the mesh density
    until the result from the force
    <DIV></DIV>&gt;integral converges to whatever
    tolerance you want.
    <DIV></DIV>&gt;
    <DIV></DIV>&gt;In general, mileage may vary in
    comparing to experimental tests--even if
    <DIV></DIV>&gt;the program is giving exactly the
    correct answer to the numerical
    <DIV></DIV>&gt;problem that it is solving, there can
    always be significant differences
    <DIV></DIV>&gt;between the experimental setup and the
    as-modeled problem, due to
    <DIV></DIV>&gt;mechanical tolerances, differences in
    material properties, measurement
    <DIV></DIV>&gt;errors, and so on.
    <DIV></DIV>&gt;
    <DIV></DIV>&gt; &gt;
    <DIV></DIV>&gt; &gt; Anyway, I really appreciate and
    satisfy FEMM.
    <DIV></DIV>&gt; &gt; Thank you so much, Dave.
    <DIV></DIV>&gt; &gt;
    <DIV></DIV>&gt; &gt; Best Regards,
    <DIV></DIV>&gt; &gt;
    <DIV></DIV>&gt; &gt; Matthew
    <DIV></DIV>&gt; &gt;
    <DIV></DIV>&gt; &gt;
    <DIV></DIV>&gt;I hope that the program proves to be
    useful to you.
    <DIV></DIV>&gt;
    <DIV></DIV>&gt;Dave.
    <DIV></DIV>&gt;
    <DIV></DIV>&gt;
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- References:
  - Re: [femm] The contour creation for force calculation
    - From: "Israel Kehaty" <tsiporak@hotmail.com>

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