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# updated v3.3a3

- To: FEMM Mailing List <femm@yahoogroups.com>
- Subject: updated v3.3a3
- From: David Meeker <dmeeker@ieee.org>
- Date: Wed, 12 Feb 2003 00:27:07 -0500
- User-agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.1) Gecko/20020826 MultiZilla/v1.1.22

`I've put an updated 3.3 development version on the FEMM website at:`

    http://femm.berlios.de/femm33bin.exe
    http://femm.berlios.de/femm33src.zip

`The most important change in this update is a set of new block integral used for calculating forces and torques. These new integrals are denoted: "Force via Weighted Stress Tensor" and "Torque via Weighted Stress Tensor". Instead of having to draw the "right" contour around the region of interest as with a the usual Stress Tensor line integral approach, the new integral allows one to just select the blocks upon which forces are desired and hit "integrate". This formuation converts the stress tensor line integral into a block integral in which the results of many possible different integration paths are averaged to give a result that is more accurate than any one line integral. Typically, more accurate force and torque results can be realized at lower mesh densities than with the stress tensor line integral.`
`A paper which describes the force integral approach can be downloaded at:
http://www.esat.kuleuven.ac.be/electa/publications/fulltexts/pub_942.pdf
However, the idea isn't really all that new. Also see:
S. McFee, J. P. Webb, and D. A. Lowther, A tunable volume integration formulation for force calculation in finite-element based computational magnetostatics, IEEE Transactions on Magnetics, 24(1):439-442, January 1988.`
`FEMM finds the weighting function by solving a Laplace equation for a potential (that we could call W) over the same set of elements as used for the magnetics analysis. The boundaries and non-air objects are fixed at a W=0, and all nodes in selected blocks at W=1. Level contours of W can then be interpreted as stress tensor integration paths. In the code, there are a number of different schemes implemented for weighting the individual elements; the one that is actually turned on in the self-installing executable version is a scheme in which each element is weighted by the mesh size specification for the region in which it lies. This tends to make regions with a finer mesh (and therefore more accuracy) contribute more to the weighted stress tensor integrations than regions with a coarse mesh. At any rate, it typically takes the program a second or two to solve for the weighting function (because it is actually solving a finite element problem to get the weighting function). A new check box has been added to the contour plot dialog that turns on the display of the level contours of the weighting function.`
`I've also implemented a "Depth" parameter for 2D-planar so that one isn't constantly multiplying by a scaling factor to get forces, inductances, etc, for planar problems. I think that I've propagated the Depth parameter to everywhere it needs to go in the postprocessor--tell me if you notice any place that I missed. For v3.2 and older 3.3a problems, this latest 3.3a3 version assumes a depth of 1 meter, since v3.2 and the older 3.3a versions calculated all planar results per meter of depth.`
`The manual has been updated--not all v3.3 stuff (e.g. "nonlinear time harmonic" formulation) was documented in the manual before.`
`There is also a new selection View|BH Curves in the postprocessor that lets you plot out the B-H curves that the program actually used. This is especially valuable for nonlinear time harmonic problems, where the program computes an "effective" B-H curve based on the DC curve, hysteresis lag parameter, lamination dimensions, etc.`
`Dave.`

    --
    David Meeker
    dmeeker@ieee.org
    http://femm.berlios.de/dmeeker

``

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