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Using gnuplot to plot probe data

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Old   June 13, 2019, 02:36
Default Using gnuplot to plot probe data
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Fab
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Hello everyone.


I started using gnuplot because it is a convenient tool to plot data. Basically, you just have to type a line or two in a terminal to have your data plotted.
Yet I don't understand the syntax, I found a way to plot my residuals using an openfoam command which extracts the data in my log file and puts it in a single column text file. This way I can tell gnuplot to plot it correctly using simple commands.
This is what I do :


foamLog -n "name of my log file"
gnuplot
plot './Uz_0'


It works well for single column data files created by foamLog. Now my problem is that I want to do the same with probes. Often, my probe files are two columns files, time/iteration versus quantity of interest. But for the velocity, the file is much more complicated with "(" and ")" and four columns.


Is there a simple way to tell gnuplot how to plot a two column file ? Is there an openFoam utility that can convert the velocity probe file into something more manageable like several one column files, as foamLog does for the logfile ?


Thank you all for any input.
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Old   June 14, 2019, 03:34
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Tom Fahner
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Hi,

Not an OpenFOAM utility, but sed would work for this:

Code:
sed 's/[()]/ /g' postProcessing/probes/0/U > postProcessing/probes/0/U_noBrackets
Or if you just want to keep the file, you can do replacement inside the file itself as:

Code:
sed -i 's/[()]/ /g' postProcessing/probes/0/U
And than plot on the U_noBrackets or new U file.

Regards,
Tom
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Old   June 17, 2019, 02:29
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Thank you for your answer tomf, it was helpful.


For those who will read this, here is the gnuplot syntax to plot a file with multiple columns : https://stackoverflow.com/questions/...-all-on-y-axis


Another thing : I realised that gnuplot can actually handle parenthesis. You don't need to remove them before trying to plot. Looks like it just ignores them, which is practical.

Last edited by Rotidpor; June 18, 2019 at 04:02.
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