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# Re: [femm] discontinuities in stress tensor mask in thin air

- To: femm@yahoogroups.com
- Subject: Re: [femm] discontinuities in stress tensor mask in thin air
- From: David Meeker <dmeeker@ieee.org>
- Date: Sun, 09 Mar 2003 22:22:25 -0500
- In-reply-to: <F1029s4ddqN19bBLmUj00000cfd@hotmail.com>
- References: <F1029s4ddqN19bBLmUj00000cfd@hotmail.com>
- User-agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.3b; MultiZilla v1.1.34 (d)) Gecko/20030210

`James Rabchuk wrote:`

> `As I understand from Dave's description of the technique, the mesh density serves as a type of permeability in the solution of the differential (Laplaces?) equation which sets the level contours, the gradient of which becomes the weighting function for the volume integral carried out in the air over the divergence of the stress tensor. The abrupt change in permeability between regions of different mesh density leads to abrupt changes in the "mask". Regions of higher density will have a greater percentage of the level contours.`
> `But how about your force values? Were they more realistic, smoother, etc.?`
> `Jim`

`The way that things are currently set up, the program solves a Laplace equation to get the "mask." It uses the inverse of the mesh size specification sort of like a "permeability," so that more highly meshed regions tend to contribute more to the force calculation than less highly meshed regions. The lines can change directions at boundaries between mesh densities--this is analogous to the change in direction of flux lines at the interfaces between materials of different permeabilities. I don't think that this should particularly cause any problems with the integration.`
`mikeshonle wrote:`

>     I'm using version 3.3a3. And what's a good practical upper
>     limit on the number of mesh nodes?

`
The "practical" upper limit depends on how much memory you have. If the problem is so big that you start running off of virtual memory, things can bog down a lot--that's really the upper limit.`
`Dave.`

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

``

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- References:
  - Re: [femm] discontinuities in stress tensor mask in thin air
    - From: "James Rabchuk" <jarabchuk@hotmail.com>

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