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Discontinuities in the probe signal

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Old   April 2, 2014, 10:33
Default Discontinuities in the probe signal
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Hello OpenFOAMers,

I run a simulation but it seemed to me that there was not enough samples so I run more time steps from the last saved time. However I have got a different signal, and confirmed by a the same simulation run form 0 to the new end time.
I did not do reconstructPar because it was simply to run the same case in the same number of processors.
However I have other cases where I did the reconstructPar and then the decomposePar -force and a shift is present.

Does anyone know what this might be ?

Thanks in advance

I have attached some examples with the data from the probes.
(Forgive me if I did not put the images in the usual way.)

no_reconstruction_fewsamples.jpg

no_reconstruction_more_samples.jpg

reconstruction_shift_0.jpg

reconstruction_shift_1.jpg

reconstruction_shift_2.jpg
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Old   April 4, 2014, 16:04
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Hi guilha,

There are several possibilities that come to mind, so to list just a few:
  1. Old OpenFOAM version, which has a bug that possibly has already been fixed, associated to restarting a case from a previous step. I very vaguely remember a few bug reports on this topic.
  2. "deltaT" in use is not compatible with the actual physical phenomenons that are associated with your case. An example I can think of: a simulation trying to recreate a Kármán vortex street - for the same boundary conditions, geometry shape+location and turbulence mode - can develop very difference vortexes, depending on the mesh resolution and the deltaT setting.
  3. There was a recent thread on a topic of steady-state vs transient simulations, which has got some nice tips on the topic of fvSchemes... ah, here we go: http://www.cfd-online.com/Forums/ope...t-solvers.html
Beyond this, I suggest that you create a small test case with which this issue can reproduced and share that small test case, so that we (anyone on the forum) can try to reproduce the same issue with the same OpenFOAM version you're using and with newer OpenFOAM versions as well, to ascertain where the problem might be.

Best regards,
Bruno
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