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# Re: [femm] Force on a conductor?

- To: femm@yahoogroups.com
- Subject: Re: [femm] Force on a conductor?
- From: David Meeker <dmeeker@ieee.org>
- Date: Tue, 21 May 2002 00:02:15 -0400
- References: <abo21l+l3fs@eGroups.com>
- User-agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.0rc2) Gecko/20020510

emacoustics wrote:

> `Hey folks,
> Once more I have come to pick your brains! If anyone remembers, I am
> doing a project at Uni that involves simulating a loudspeaker voice
> coil. What I would ideally like to do is to be able to plot a graph
> of the force on the coil (or a point on the coil, for example the
> leading edge) vs current in the coil. Is there a way of obtaining
> the force at a point?
> `

Well, the force density a point in the coil is J X B (where the X represents the cross-product). Therefore, the easiest thing to do is to plot the radial component of B, using the usual "X-Y plot" functionality. In the same dialog box where you select what type of plot you want to make, there is also a check box that you can select so that the data gets written to disk instead of plotted to the screen. You can write the data to disk; slurp it into mathcad, matlab, mathematica, or (insert your favorite program here); multiply all the B values on the line by the J carried by the coil; and plot this modified result.
If you want to get more complicated, you can compute J X B inside a Lua script and then write that to disk.

> `
> Also, can FEMM output and input numerically? For example running two
> simulations, outputting numerical results to sum the two together (ie
> superposition) and then inputting them back into FEMM as a data
> file? If so, how do I do it?
> `

You can do things like this through the use of Lua scripting. It's described some in the manual, and there are some examples on the website at femm.berlios.de/examples.htm However, you may have to get creative to do exactly what you are after.
Dave.
--
David Meeker

- References:
  - Force on a conductor?
    - From: "emacoustics" <michael.wheeler@ic.ac.uk>

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