From: David Meeker <dmeeker@xxxxxxxxxxxxxxxxx>
Reply-To: femm@xxxxxxxxxxx
To: femm@xxxxxxxxxxx
Subject: Re: [femm] Force calculation on an axisymmetric model
Date: Fri, 29 Sep 2000 16:24:31 -0400
Paulo José Gameiro Pereirinha wrote:
> Hello!
>
> I'm in Portugal and trying to compute the atraction magnetic force on an
> plunger electromagnet with axisymmetric geometrie. I'm using the Femm
3.0.
> To compute the force exerced on the iron can I just define a contour in
the
> air around the iron (which means that one side of the contour will be on
> the line of coordinate z=0) and integrate the Maxwell Stress Tensor?
(i.e.
> is this command valid for axisymmetric models?). If I do so, I obtain
> -2.783e-3 N, but the experimental result is about 1.35 N. I'm sending
the
> model in attachement.
>
> Thanks in advance.
Well, I looked at your data file, and I think that the problem is the
material
property definition for your Steel material. The relative permeability in
the
radial direction is defined as 1384, but the relative permeability in the
axial
direction is defined as 1. I'd guess that you would want to define the
permeability to be 1384 in both directions.
Anyhow, stress tensor is valid in axisymmetric problems as well. When I
run
the problem with the above change in permeability in the z-direction and
integrate force along the box you have defined around your iron part
through
the air, I get a force of 0.5685 N. As a sanity check, I ran the same
geometry
on the IES Amperes 3-D boundary element solver, which I happen to have
laying
around the office. The force result from Amperes was 0.5456 N. The
implication is that the femm force result seems reasonable. I can't say
what
the discrepancy is that causes the difference with the experimental result
of
1.35 N.
Dave.
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