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Plot Residuals in Postprocessing

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Old   March 31, 2016, 10:20
Default Plot Residuals in Postprocessing
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Hello,

I want to plot the residuals after the calculation is done. I am doing the calculation on a linux server without the graphical user interface where you can monitor the residuals. That's why i need to examine them afterwards. Has anyone an idea ? Thanks.
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Old   April 1, 2016, 23:52
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One way is to save the output to a text file.
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Old   April 2, 2016, 02:58
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Quote:
Originally Posted by Dog766 View Post
Hello,

I want to plot the residuals after the calculation is done. I am doing the calculation on a linux server without the graphical user interface where you can monitor the residuals. That's why i need to examine them afterwards. Has anyone an idea ? Thanks.
You can use gnuplot code..

http://www.gnuplot.info/
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Old   October 17, 2016, 11:51
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Quote:
Originally Posted by Dog766 View Post
Hello,

I want to plot the residuals after the calculation is done. I am doing the calculation on a linux server without the graphical user interface where you can monitor the residuals. That's why i need to examine them afterwards. Has anyone an idea ? Thanks.
Hi guys,

Dog766, did you managed to plot your residuals from old runs? I don't use Linux but Windows and I'm also looking for a way to plot old run residuals. My computer stopped and switched off during calculation due to external issues and I lost the graph on the Fluent window monitoring from iteration 0 (I have large number of iterations). I restarted the simulation from the last data file saved but I can only see the last iterations. My residuals converge very slowly and with the last data file saved I'm not able to see if the curve is constant or is still changing. I attach a photo.

I'm not able to open the data files in text mode (maybe too heavy files?).

Would you have any other suggestion?

Thanks in advance!
Attached Images
File Type: png For CFD online_V67_q1000_108952_residuals.png (165.6 KB, 120 views)
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Old   October 17, 2016, 12:37
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Hi, if you did not save your output to a textfile, there is no way to recover all the residuals, I think. Fluent by default stores the last 1000 iterations but that's it. You can change that value if you want but better save output to a file, so you have reference to what happend at any time. However, I think your case needs some revision, I think your model does not converge, maybe due to a poor quality mesh
Good luck!
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Old   October 18, 2016, 05:16
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Originally Posted by mome View Post
Hi, if you did not save your output to a textfile, there is no way to recover all the residuals, I think. Fluent by default stores the last 1000 iterations but that's it. You can change that value if you want but better save output to a file, so you have reference to what happend at any time. However, I think your case needs some revision, I think your model does not converge, maybe due to a poor quality mesh
Good luck!

Thanks mome

I'm not sure about your comment: "saving my output to a textfile"... do we have to specify that on Fluent? I save my output in a .dat file, I thought this was the only way. I see there are options to export solution data on different file formats but it's per cell or node and for like physical quantities, not residuals.

However, I finally solved my problem about plotting... I did specified in "monitors" -> "residuals" to store up to 100000 iterations but I hadn't updated the "iterations to plot" box... so silly! Now I can see all the residuals from iteration 0 in the graph but, is still any possibility to have the numeric data (eg, the maximum residual value for each equation so we can compare to the actual value and evaluate convergence)?

Concerning the convergence problems, I'm not sure that it's due to the quality of the mesh, I thought my mesh quality values were not so bad:

Analyse mesh ICEM
Min aspect ratio
0.137
Min equi-skew
0.45
Min quality
0.607
Min angle
40.8
Max mesh expansion factor
19.38
Min ortogonal quality
0.5487
Analyse mesh FLUENT
Min ortho quality
0.549
Max aspect ratio
13.47

Any other hints why my calculation might diverge?

Thanks in advance!
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Old   October 18, 2016, 07:25
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good that you got what you wanted! anyway, it's really handy if you get used to it:

i did not mean the data file, but a text file containing what fluent would return to the console.

on windows, I think you have to start a transcript for what you want to record. that would also be the way to go if you already started an interactive session and realise you want to log your text output to a file. you can do that by the TUI command
\file\start-transcript filename.out
and stop it by
\file\stop-transcript filename.out
this file will even contain all your actions in the GUI as scheme code for interactive sessions, but you can also just use it in your journal file to run in the background.

if you are using a linux system even better, you can just pipe your output to a file upon launch from command line, this is common to do if you run a job in the background, e.g.
"fluent -g 2ddp < 2dcase.jou > 2dcase.out 2>&1"
2dcase.jou defines what you want fluent to do, 2dcase.out contains what fluent returns. there is info about this in the manual, if you are not so familiar with it. it think that's all there is to it..

..about your convergence, that is a big topic you are opening and I don't think I can give you a general answer, sorry. the mesh metrics are not the only thing to consider, it depends how the actual flow is resolved etc. , could arise from boundary conditions and your numerical set-up. maybe read a little bit about it and try to imporve your solution by changing your schemes, solver settings and the mesh. I'm sure you'll get there.
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Old   April 6, 2022, 20:21
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Did you find a way to plot your fluent residuals ?







Quote:
Originally Posted by Dog766 View Post
Hello,

I want to plot the residuals after the calculation is done. I am doing the calculation on a linux server without the graphical user interface where you can monitor the residuals. That's why i need to examine them afterwards. Has anyone an idea ? Thanks.
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