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# Re: continuous looping in fkern

- To: femm@yahoogroups.com
- Subject: Re: continuous looping in fkern
- From: "David Meeker" <dcm3c@earthlink.net>
- Date: Tue, 12 Nov 2002 20:48:41 -0000
- In-reply-to: <aqq84u+a0oi@eGroups.com>
- User-agent: eGroups-EW/0.82

    --- In femm@y..., "shazanaz2000" <smartmicro@h...> wrote:
    > hi,
    >
    > I'm doing some small fea analysis. my pc is a celeron500 with 64mb
    > memory. My problem is not more than 100mm x 100mm planar. mesh size
    > varies from 0.1mm in some blocks to 5mm in air. total node count is
    > around 18k to 30k (depending on mesh sizes).
    >
    > The problem I face is:
    > sometimes..., fkern loops for an inordinately long time without
    > upgrading the newton iteration counter while continuously looping
    > in "matrix construction" and "conjugate solver". If I stop fkern and
    > adjust my file (I move any one or two node points or change the mesh
    > size -slightly- at any one place) the next time fkern completes. this
    > I've noticed in not one problem but in many. Am I doing something
    > wrong? is my computer slow? I've even seen the NI count decreasing!!
    > Is that supposed to happen?

    There can sometimes be convergence problems in nonlinear problems if
    you are using a material with a strong "initial permeability" region.
    The most expedient way of fixing things is to zap out the first few
    points of your B-H curve, eliminating the initial permeability region.
    I'm looking at ways of trying to get the solver to recognize and
    remedy this when it happens automatically. At the very least, I'll put
    a user-specifiably relaxation factor for the Newton iteration in the
    next significant revision of the program so that materials with a
    significant initial permeability can be forced to converge.

    Dave.

- References:
  - continuous looping in fkern
    - From: "shazanaz2000" <smartmicro@hotmail.com>

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