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# Re: [femm] about Mixed boundary condition

- To: femm@yahoogroups.com
- Subject: Re: [femm] about Mixed boundary condition
- From: David Meeker <dmeeker@ieee.org>
- Date: Thu, 30 Jan 2003 23:29:43 -0500
- References: <1043409122.1030.21610.m12@yahoogroups.com> <3e33a8565adda@wp.pl>
- User-agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.1) Gecko/20020826 MultiZilla/v1.1.22

`Jan Zimon wrote:`

> `HI !`
> `Could anybody help me find some information about Mixed boundary condition in Axi-symmetrical problems (i'm beginner). Where can i find any informations about (*.pdf or webside)? Is it true condition
> A(r,z)= SIGMA[m=1..oo]((a_m/r^m)cos(mz+alpha_m)?
> Thank you for any help.`
> `Jan`
> ``

`I guess that what you are really asking for is a reference on the Axisymmetric case of the Asymptotic Boundary Condition. The form of the general solution for vector potential A isn't the same in the axisymmetric case as it is in the planar case, but everything comes out in the wash such that you enter in the same 1/(R*mu_o) value in the "c0 coefficient" box of the dialog, where R is the radius of a circular (or half circle, for axisymmetric) domain.`
`A reference for this would be:`
`S. Gratkowski, L. Pichon, and H. Gajan, "Asymptotic boundary conditions for open boundaries of axisymmetric magnetostatic finite-element models," IEEE Transactions on Magnetics, 38(2):469-472, March 2002.`
`They derive the boundary condition as dA/dR + 2 A/R = 0, where R is distance from the origin (i.e. working in spherical coordinates). If I remember correctly, there was sort of a subtle trick to converting it to the boundary condition form that is implemented in FEMM. The boundary condition that the program implements is (1/u)Grad(A).n + c0 A + c1 = 0. In the axisymmetric case, Grad(A) = A/R + dA/dR, so that to get the dA/dR + 2 A/R = 0 form, you have to pick c0=1/(u*R) and c1=0. Every time I run across that paper, I think "where did the 2 go?" and end up running through this same thought process again....`
`Dave.`

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

``

- References:
  - about Mixed boundary condition
    - From: "Jan Zimon" <zimonj@wp.pl>

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