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Re: [femm] The contour creation for force calculation
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@xxxxxxxxxxx> wrote:
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<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> </DIV>
<DIV></DIV>
<DIV></DIV>>From: David Meeker<DCM3C@xxxxxxxxxxxxx>
<DIV></DIV>>Reply-To: femm@xxxxxxxxxxxxxxx
<DIV></DIV>>To: femm@xxxxxxxxxxxxxxx
<DIV></DIV>>Subject: Re: [femm] The contour
creation for force calculation
<DIV></DIV>>Date: Thu, 13 Dec 2001 21:49:23 -0500
<DIV></DIV>>
<DIV></DIV>>
<DIV></DIV>>
<DIV></DIV>>matthewc_98 wrote:
<DIV></DIV>>
<DIV></DIV>> > Hi All,
<DIV></DIV>> >
<DIV></DIV>> > I use FEMM to simulate the
solenoid and so far, it works pretty well.
<DIV></DIV>> > But there is a question I cannot
understand and hope you can help me
<DIV></DIV>> > to explain it. The question is as
following:
<DIV></DIV>> >
<DIV></DIV>> > Currently, when I would like to
calculate the pull force of the
<DIV></DIV>> > solenoid, I always creat the
contour path as close as possible to the
<DIV></DIV>> > surface of core steel bar (the
contour is away from the steel bar
<DIV></DIV>> > which means the path is within
air). But while I read the User's
<DIV></DIV>> > Manual, I found that Dave
suggested user to creat the contour at
<DIV></DIV>> > least two elements from any
interfaces and boundaries.
<DIV></DIV>> > Could you tell me that what the
definition of the element (distance ?
<DIV></DIV>> > inch ???)?
<DIV></DIV>>
<DIV></DIV>>If you push the toolbar button with the
yellow triangles in the
<DIV></DIV>>postprocessor, the elements will appear
on the screen as yellow
<DIV></DIV>>triangles. The elements don't have a
fixed size--you can make them as
<DIV></DIV>>small or you want, depending on the
mesh size that you define for each
<DIV></DIV>>block label. Anyhow, you don't want to
draw your contour through
<DIV></DIV>>triangles that touch the boundaries. In
theory, the contour that you
<DIV></DIV>>pick doesn't really matter, as long as
it passes through air and
<DIV></DIV>>encircles the object that you are
interested in--there's no reason to
<DIV></DIV>>try to draw your integration path close
to the object. However, if you
<DIV></DIV>>draw close to the surface of objects,
you tend to pollute the force
<DIV></DIV>>results with relatively inaccurate
field results that can occur around
<DIV></DIV>>sharp corners. Also, the part of H that
is tangential to an interface
<DIV></DIV>>tends to be less accurate than a bit
farther out, owing to some aspects
<DIV></DIV>>of the smoothing scheme that femm uses.
<DIV></DIV>>
<DIV></DIV>> >
<DIV></DIV>> > So far, I used the force data of
FEMM to campare force data that from
<DIV></DIV>> > our force tester in the lab, and
found that the error is within 15%.
<DIV></DIV>> > (Assume the force data of force
tester is ideally correct).
<DIV></DIV>> > Is there any way to narrow the
error of force simulation of FEMM?
<DIV></DIV>>
<DIV></DIV>>A good way to go is to try the
simulation with progressively finer
<DIV></DIV>>meshes, increasing the mesh density
until the result from the force
<DIV></DIV>>integral converges to whatever
tolerance you want.
<DIV></DIV>>
<DIV></DIV>>In general, mileage may vary in
comparing to experimental tests--even if
<DIV></DIV>>the program is giving exactly the
correct answer to the numerical
<DIV></DIV>>problem that it is solving, there can
always be significant differences
<DIV></DIV>>between the experimental setup and the
as-modeled problem, due to
<DIV></DIV>>mechanical tolerances, differences in
material properties, measurement
<DIV></DIV>>errors, and so on.
<DIV></DIV>>
<DIV></DIV>> >
<DIV></DIV>> > Anyway, I really appreciate and
satisfy FEMM.
<DIV></DIV>> > Thank you so much, Dave.
<DIV></DIV>> >
<DIV></DIV>> > Best Regards,
<DIV></DIV>> >
<DIV></DIV>> > Matthew
<DIV></DIV>> >
<DIV></DIV>> >
<DIV></DIV>>I hope that the program proves to be
useful to you.
<DIV></DIV>>
<DIV></DIV>>Dave.
<DIV></DIV>>
<DIV></DIV>>
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