Re: [femm] Meaning of flux lines?

[David Meeker <dmeeker@xxxxxxxxxxxxxxxxx>]

peter.ceelen@xxxxxxxxxx wrote:

> The meaning and interpretation of the flux lines displayed in
> femmview is not clear to me. Do these lines represent some
> equipotential (if I follow a line does some value remain constant)?
> How is the number of lines related to some numeric value (in other
> words what is the difference in value between any two given lines at
> a particular number of lines)? Thanks in advance for your help.

The lines are paths along which the flux flows, like streamlines in a fluid
flow.

In planar problems, the flux lines are equipotentials of magnetic vector
potential (denoted A), and the difference in A between two flux lines equals
the amount of flux that flows in the section between the two lines. Since
femm plots the flux lines at even intervals of A from its minimum to maximum
value, you can interpret the distance between flux lines as an indication of
flux density.

For axisymetric problems, the situation is similar, though there are subtle
differences. For axisymmetric problems, level contours of 2*Pi*r*A (denoted
"Flux" in the axisymmetric point properties output) are plotted, where r is
the radius from the centerline. Plotting this quantity still gives lines
that are tangential to the flow of flux (i.e. the lines are still flux
streamlines), and the difference in Flux between two points is still the
amount of flux flowing through the section between the two points. In
axisymmetric problems, however, the interpretation of distance between flux
lines as an indication of flux density doesn't apply, because a given amount
of flux translates to different flux densities at different radii. To
graphically display flux density in axisymmetric problems, you can always
turn on the density plot that displays different flux levels as different
colors on the screen.

Dave.
--
http://members.aol.com/dcm3c

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