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# Re: Why femm sometimes never finised the calculation ?

- To: femm@yahoogroups.com
- Subject: Re: Why femm sometimes never finised the calculation ?
- From: "matthewc_98" <matthewc_98@yahoo.com>
- Date: Thu, 06 Dec 2001 22:03:06 -0000
- In-reply-to: <3C0FBD1E.8F1E2315@foster-miller.com>
- User-agent: eGroups-EW/0.82

    Dave,

    Thank you very much for your advice. You're a real expert
    on this topic, because you help me to fix the problem that
    noised me for two weeks. My problem was caused by
    nonlinear material of initial permeability. After smooth out the
    curve, there is no problem to execute the software.

    Thank you in advance,

    Matthew
    --- In femm@y..., David Meeker <dmeeker@f...> wrote:
    > matthewc_98 wrote:
    >
    > > Hi All,
    > >
    > > I have used femm ver. 3.1 for one month. I would like to
    > > thank Dave, because this is a great sofware. There is one question
    > > needed to have your advice. I used femm to simulate the solenoids.
    > > In some types of solenoids, it works very well, but in other types
    > > of solenoids, it never ending the calculation.Even I used
    different
    > > mesh densities; it still didn't work. Can you help me to answer
    this
    > > question? Thank you so much.
    > >
    > > Best Regards,
    > >
    > > Matthew
    >
    > Hmm--it's hard to say what's going on without seeing an example.
    >
    > Sometimes bad things can happen if you have very small angles
    between lines
    > in your mesh (or a line tangent to a circle, for example)--
    triangle, the
    > meshing program, can break down in that case, or make a mesh that
    causes
    > things to hang. If this is the case, try redrawing the problem
    region in a
    > way that avoids the sharp angles.
    >
    > It is also might be possible to make a nonlinear material that has
    > convergence problems--this might happen in some materials with a
    really
    > pronounced "initial permeability" region. The solver can then end
    up
    > bouncing around that section of the curve, never finishing the
    Newton
    > Iteration part of the solution. You can try substituting linear
    materials to
    > see if this is the problem. If so, you might have to "smooth out"
    the
    > initial permeability region to get things to converge.
    >
    > Dave.

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