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Fluent Parallel/Serial version..jump in residuals

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Old   December 8, 1999, 10:35
Default Fluent Parallel/Serial version..jump in residuals
  #1
Sandeep Abhyankar
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I have been encountering a rather strange problem while running Fluent 5.2.3 Parallel and Serial version. I have a case file which I am running using Fluent 5.2.3 Parallel version (using 2-CPU's ). The file runs fine and the residuals drop down smoothly. However when I save the case and data file and then continue to run these saved files further using a Serial 5.2.3 Fluent version, a sudden jump in the " continuity and the x,y,z vel residuals is seen in the residual plots...!!

I have seen this problem occur on win-nt, hp-unix and alpha-unix platforms. Any pointers as to why this might be happening ??

Thanks in advance.
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Old   December 9, 1999, 05:39
Default Re: Fluent Parallel/Serial version..jump in residuals
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Jonas Larsson
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I've seen similar things. I suspect that the numerics Fluent uses across partition boundaries is not exactly the same as in other regions. If you partition the case across many CPUs it is probably not possible to use the same "globally" implicit solver - the partition boundaries are probably treated in some explicit way. For very strongly swirling flows I have also sometimes had numercial problems across partition boundaries with "exploding" swirl velocites etc. Most often it converges to almost the same solution though.
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Old   December 10, 1999, 12:07
Default Re: Fluent Parallel/Serial version..jump in residuals
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Sandeep Abhyankar
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Thanks Jonas for your comments.

I had a talk with the tech support engineer at Fluent, and he told me that this has been reported as a bug in V5.2 and they have a fix for it in the next version.

Thanks anyways !
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Old   December 15, 1999, 03:57
Default Re: Fluent Parallel/Serial version..jump in residuals
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Jonas Larsson
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Heh, I have a feeling I've heard that one before ;-) 5.3 is out though, so you can test it yourself.
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Old   January 10, 2000, 10:57
Default Re: Fluent Parallel/Serial version..jump in residuals
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Sandeep Abhyankar
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Fluent tech support advised me that the bug regarding sudden jump in the residuals when you change from single to parallel processing has been fixed in Version 5.3 of Fluent.

However, I installed Version 5.3.18 recenlty, and I continue to see the same erroneous behavior.

Wonder if the bug was really fixed..!

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