Simulating Lenz's Law

[Blainiac]

Hello everyone.  I understand FEMM is for viewing static magnetic simulations, and not really for dynamic simulations.  I know you can 'make' it dynamic by running LUA scripts and stuff, but you can't really simulate Lenz's Law that I know of.

If I'm having a change in magnetic flux through a rod with a coil of wire wrapped around it, there will be a current induced in the coil, which also induces a secondary magnetic field that opposes that change.  How does that opposing field act on the first field in this case?  Can I simulate what happens to the field inside the bars in the picture?

Thank you.

[Blainiac]

I guess I really should ask, how does the opposing field work against the magnets that are moving if the changes are occurring inside the bars?

[mscoffman]

I think if you look up Lentz Law in Wikipedia you will see that Lentz
Law really is just the generator principle. What you are looking for
I think should be called "Eddy Current", or "Eddy Current Braking".
It is not purely magnetic. To simulate it in one go would require an
electrodynamics simulator rather then just a magnetic one.

A changing direction/intensity of a magnetic field across a bulk conductor
material (a) induces a current in the conductor (b) which doesn't bother to
travel in the bulk conductor very far before the current +/- loops back on
itself. That loop is just like a coil which then produces an magnetic field
mirror image of the exciting field of it's own. (c) Therefore there is an
attraction between the originator of the first magnetic field and the bulk
conductor. The problem is the bulk conductor has a path resistance and
that causes some energy to be lost to heating.

The same principle is used in the rotor of an AC induction motor, so the
operation is not all negative. There may be a way to use an AC motor
design simulator package to get the information close to what you want.

:S:MarkSCoffman

[Low-Q]

Hello everyone.  I understand FEMM is for viewing static magnetic simulations, and not really for dynamic simulations.  I know you can 'make' it dynamic by running LUA scripts and stuff, but you can't really simulate Lenz's Law that I know of.

If I'm having a change in magnetic flux through a rod with a coil of wire wrapped around it, there will be a current induced in the coil, which also induces a secondary magnetic field that opposes that change.  How does that opposing field act on the first field in this case?  Can I simulate what happens to the field inside the bars in the picture?

Thank you.

In this case the magnetic field would follow the other path - through the bar on the top, and less through the coil.

Vidar

[Blainiac]

Thank you very much guys.  I'm starting to pull more away from purely mechanical setups, and for some reason couldn't think about how it would apply inside of cores.