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## Damping Factor!

Hi
I build a model that a piece of iron is on top of a polymer stage, then a permanent magnet is underneath. Then I wanna see how the bridge bends due to the magnetic force.Then I apply transient analysis, it is supposed that the bridge will vibrate forever since I didn't set any damping factor yet. But it stopped at the end. After this, I tried static analysis, comsol said "No convergence, even when using the minimum damping factor(but I didn't set any damping). Returned solution has not converged."
Here is the question, Does Comsol will apply damping factor automatically when the solution is not converged?

Thanks a lot if anyone can help!

3 Replies Last Post 30.09.2009, 03:46 GMT-4

Hi

there are a couple of possible "damping factors" in any FEM calculation, the "numerical" ones to be sure your calculations converge, and in your case you might have motion induced "Eddy current" damping, if you have the correct physics active: bacause in any conductor that is moving in a static magnetic field (or the opposite, or both) will see a current generated in the conductor, that due to it's finite electric resistance will dissipate power. This current generates an opposed magnetic field (to the external) and they will interact.

Check the documentation, on the solvers for numerical damping, or have a look at the other discussion by a "Search" on

numerical damping

By the waym, how long did it take to "stop" or what is about the 1/e factor ?

good luck
Ivar

Hi Ivar,
Thank you very mush for your help!
Actually, my simulation is not converged since I can only do transient analysis but not static. I am using magnetostatic (emqa) in which I didn't set any conductor parameter (no electrical conductivity setting in this module).
Basically, I am using magnetostaic module to get the total force on the iron (attracted by a magnet underneath) using boundary integral of surface tensor. Then I apply this force on iron in solid, stress-strain module (structure-mechanic) to have the bending shape. But I can't do the static analysis since comsol stopped and said it was not converged. So I have to do the transient.. Do you think I am using the right modules, any suggestion?
I also check the solvers for numerical damping, the" manual tuning of damping parameter" is not activated.
When I do the transient analysis, the shaky iron stopped in 5ms and I didn't find any 1/e factor..

Thank you again for your help!

Hi

Sorry I do not have enought time currently to study in more detail your issue (my replies here on the Forum are done on my free night time, my job is to answer my collegues problems and to build and execute high techn R&D projects, and I'm just another fan and time-totime user of Comsol).

But, I would suggest to you to look into the Model Gallery, i.e. Magnetic break or Magnetic Drug Targeting models, I beleive you will find here some answers, it looks like you are missing the "force link" between your static magnetic calculations (this is also how I would approach a field estimation from a magnet) and the structural deformation section.

You could also study how COMSOL has linked the fluid-structure interactions for some of their cases. Obviously COMSOL has considered the magnetic to structure case too obvious and has not proposed any ready-set physics model.

Finally, you could also check how you treat your solver manager, you should first solve only for the magnetostatics, store the solution and then solve for the structural case, you can automatise this by storing the solver settings in the last tab to the right in the Solver manager window (V3.5a though)

there is one or two other discussions going on, and I belive they are linked to of lack of good understanding how you link the physics in COMSOL, this means that really you have to understand (this took me about 2 years to feel comfortabel in a few physics, I'm still no specialist for many, but also I'm only a part time user of the tool, as I have sevaral other tasks on my daily agenda :)

Good luck
Ivar

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