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Old   November 4, 2004, 11:56
Default Different Under Relaxation Factors
  #1
Ertan
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Hello everybody,

My question is, did anyone of you faced with different flow solutions if you keep everything same but only change Under Relaxation Factors?

thank you for contribution...
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Old   November 5, 2004, 04:47
Default Re: Different Under Relaxation Factors
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Michael
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In my opinion the solution of the problem shouldn't change. If you under-relax you should achieve the same results, however it will need more iterations.
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Old   November 5, 2004, 05:08
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SAM
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refine ur mesh . is ur mesh fine enough

did u make mesh dependence study

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Old   November 8, 2004, 15:13
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Ertan
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My mesh is 0.03inches tetrahedral. How can I make mesh dependence study?
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Old   November 9, 2004, 03:52
Default Re: Different Under Relaxation Factors
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SAM
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number ur number of noded

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Old   November 10, 2004, 13:21
Default Re: Different Under Relaxation Factors
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gts
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if you use a (very) small under relaxation factor you will have no changes in the solution and you can obtain the steady state. You shoul also try to take lower residuals
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Old   November 10, 2004, 19:38
Default Re: Different Under Relaxation Factors
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ap
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If you use too small under-relaxation factors you risk to obtain false convergence.

This means that in unsteady calculations, you have a sort of lag between the real flow conditions at a time and the predicted flow condition.

In steady calculations, false convergence means you don't reach the solution.

Under relaxation factors have to be reduced with care, keeping in mind that you just have to reduce them in order to obtain a stable solution.

Hi

ap
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Old   November 11, 2004, 05:07
Default Re: Different Under Relaxation Factors
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gts
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Of course the steady state obtained using a small ur could be a "wrong steady state"
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