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small numerical fluctuations in the solution

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Old   June 7, 2013, 11:23
Default small numerical fluctuations in the solution
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Vishal Nandigana
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Dear Foamers,

I was trying to characterize the dynamics of my system. I was solving the system using implicit (Backward Euler) method with very small time step. I found that the solution reaches a steady state at a finite time (say T). However, I observed small numerical fluctuations with error (of about 0.4% about the mean before it reached a steady state). I would like to know if it is possible to control this numerical error. I had tried reducing the time step and also played with the solver tolerance value, but could not reduce this small numerical fluctuation. Please let me know your suggestions.

Attached is the plot of the solution.

Thanks
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File Type: jpg current_vs_time_sigma_pt2mC_m2_smaller_time_step.jpg (16.1 KB, 22 views)
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Old   June 13, 2013, 18:00
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Hello Vishal,

Your fluctuations doesn't look so large. I don't know your case so I am not sure but this maybe because of something numerical. My advice for you is taking the average of your output after your system reaches steady state.

Hope this helps,

Kilroy
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Old   June 18, 2013, 00:37
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Quote:
Originally Posted by kilroy View Post
Hello Vishal,

Your fluctuations doesn't look so large. I don't know your case so I am not sure but this maybe because of something numerical. My advice for you is taking the average of your output after your system reaches steady state.

Hope this helps,

Kilroy
Thanks, Kilroy. Yes, I figured out that they were indeed numerical fluctuations about the tolerance level specified by me.

I would like to know if you have experience with SnappyHexMesh tool in OpenFOAM. I have couple of queries on this. Please let me know.

Thanks

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Vishal
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Old   June 18, 2013, 01:46
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Nima Samkhaniani
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dear Vishal
Open new thread for SnappyHexMesh tool, then OpenFOAM users will help you there
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Old   June 18, 2013, 03:01
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Quote:
Originally Posted by nimasam View Post
dear Vishal
Open new thread for SnappyHexMesh tool, then OpenFOAM users will help you there
Dear Nima,

Thanks for your reply. I have posted the question as a new thread. Below is the link for the same.

http://www.cfd-online.com/Forums/ope...tml#post434559

Please let me know if you can provide some help.

Thanks

Regards
Vishal
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