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# Re: [FEMM] Capacitance benchmarks

- To: FEMM mailing list <femm@list.foster-miller.net>
- Subject: Re: [FEMM] Capacitance benchmarks
- From: David Meeker <dmeeker@foster-miller.com>
- Date: Mon, 01 Dec 2003 09:50:08 -0500
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`Mark Smith wrote:`

> `Hi all`

>     I've been putting Bela through some extensive tests (FEMM 4.0 beta) to
>     confirm some results I'm getting with my 3D BEM electrostatic solver and I'm
>     pleased to say I get good agreement. What I'm looking for is example
>     geometries where there are known analytic solutions for the capacitance,
>     other than the standard concentric sphere, coaxial conductor etc. Can anyone
>     suggest a good source of reference?
>     I've done extensive searches with google & I'm just finding lots of the well
>     known ones.

>     TIA
>     Mark

> ``

`The problem is that it's hard to obtain analytical solutions for more complicated geometries. For more complicated geometries, the only recourse could be to look at solutions from other codes for comparison. Some finite element vendors have published example problems on the web, e.g http://www.quickfield.com/advanced/big_mesh.htm or http://www.fieldp.com/library/estat50.pdf`

>     p.s. David thanks for the acknowledgement in the BELA user's manual. Bela is
>     equal to Quickfield IMHO.

>     p.p.s It would be nice to have a little more control (refinement) over the
>     mesh. I think the speed at which the mesh size grows is too fast ? is this
>     not controllable in triangle ?

> ``

`Well, I haven't yet incorporated any notion of automatic mesh refinement (i.e. multiple solution steps in which the mesh is refined on the basis of a posteriori error estimates, say like Ansoft's Maxwell 2D), but I might at some point. Triangle already has the capability to refine meshes based on some sort of error criteria, so it might not be all that hard to implement. I view this as more important to a 3D code--although you can overwhelm just about any 2D problem with elements due to the current price of computer speed and memory, the same is not yet the case with 3D problems (and probably won't be for some time).`
`In the latest 4.0 development release, I've also added a new "Min Angle" parameter in the "Problem Definition" dialog. This parameter controls the minimum angle that Triangle will allow in a mesh. It also has the effect of making transitions between finely meshed regions and more coarsely meshed regions sharper or more gradual, depending on what you specify as the parameter. The default is 30 degrees, which tends to yield a high-quality mesh with a fairly gradual transition between mesh densities. If you specify a smaller value, transitions will be quicker, and smaller meshes will result.`
`Dave.`
`--
David Meeker
Senior Engineer
Foster-Miller, Inc.
350 Second Avenue
Waltham, MA 02451-1196
781-684-4070
781-890-3489 (fax)
dmeeker@foster-miller.com http://femm.foster-miller.com`
``

- References:
  - [FEMM] Capacitance benchmarks
    - From: Mark Smith <mark.smith@linx.co.uk>

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