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Erdem April 24, 2009 09:45

Saving ppm images in "adaptive time stepping"

I am simulating an incompressible flow in a complex geometry and I am using adaptive time stepping for iterations. My question is; if it is possible to save ppm images at certain time (current_time)?

Or else the ppm images will be saved at inequal intervals (delta T between the images will not be the same) and it will be impossible to make a movie out of these image.

Does anybody have an idea or suggestion?

Ralf Schmidt April 24, 2009 12:29

I don't think, that this is possible.
Fluent ONLY calculates the solution on the time steps you provide.

So time steps in between are NOT available.

You might interpolate in between the time steps by yourself: Taking the results of two time steps (e.g. temperature profile on a surface), interpolate the results to your desired time step) e.g. with matlab) and plot the data with any plotting software (matlab, or maybe even Fluent could read that profile).
But I think, this could be very difficult... And might work only for a 2D problem...

Another option: if the time steps are not equal... just change the duration of the images appear in the movie.
like: time step is 1 second -> image duration is 1 second,
time step is 2 seconds -> image duration is 2 seconds (or use that image twice for each 1 second)
For that, you have to find the least common denominator of the time step size....


Erdem April 29, 2009 05:00

Thank you very much for the answer Ralph. Have a nice day.

Erdem April 30, 2009 09:00

One more question:

- Can we force Fluent to iterate at certain time steps (so that we can take ppm images at certain times) ?

Ralf Schmidt April 30, 2009 09:36

sure... with non adaptive time stepping...

you might write a journal, that sets different time steps (e.g. first 80 time steps with 0.1 seconds, than 60 time steps with 0.5 seconds and finally 60 time steps with 1 second, 10 iteration each time step).





Erdem May 7, 2009 06:08

Thanks again Ralf;

with a colleague we have managed to do what we need. Let me explain:

we are running the adaptive iteration up to a time value that we define as "End Time" and when the iteration stops, by using text commands we open a new window, display the contours (or anything else), take hardcopy of the window and we close it. Then we continui iterating with a new value of end time and so on.

my colleague wrote a VBA code to write a journal file with all the text commands and now we are able to take images (in tiff format directly) at the intervals we define.

your last post was really inspiring for us. Thank you very much again

Best Regards

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