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# FEA 2D to 3D extrapolation

## FEA 2D to 3D extrapolation

(OP)
I've ran some 2D FEA simulations on some cylindrical permanent magnets and measured their magnitudes for increasing radii. After a certain distance away from the magnet the magnitudes are constant at a given radius regardless of rotation, and governed by the equation y=a/r^-b. 'b' is an integer equal or greater than 2, depending on the pole count (b=#poles/2+1).

However, by the time these equations become valid the magnet in question could be better approximated as a point source rather than an infinitely long cylinder as simulated. Perhaps an analogous situation is the point charge/line charge/sheet charge series of equations, where electric field strength is a function of r^2, r^1, and r^0 (i.e. constant) respectively. That analogy leads me to believe that I can better approximate reality by increasing the exponent 'b' by 1 (and adjusting 'a' as necessary).

So if the original equation is y=100/r^2, the new equation might be y'=200/r^3.

Does this seem like a valid approach?
Replies continue below

### RE: FEA 2D to 3D extrapolation

Yes. But it ignores the 3 dimensional lobe pattern of the field, and so it is a rough guide at best in th near field. In the far field then if it is a point source the answer is the pen and paper solution.

Cheers

Greg Locock

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