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Diverging solution on HPC cluster

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Old   April 17, 2021, 15:58
Exclamation Diverging solution on HPC cluster
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Priyanka Gautam
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Hi,

I am running Reef3D on an HPC cluster, but unfortunately ever since I had updated Reef3D to the latest version, the solutions are diverging (values exceeding the critical velocity).

Interestingly, the same control files are running normally on a 4-core PC.

Any suggestion in this regard will be greatly appreciated!

Thanks in advance.
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Old   April 17, 2021, 18:57
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Thanks for the feedback. What type of simulation are you running?
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Old   April 19, 2021, 07:35
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Hello, sir. Thank you for the prompt response.

I am simulating open channel flow around a cylinder in a rectangular domain.

The umax parameter is exponentially increasing with each time step, crossing a value of 500 m/s.
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Old   April 19, 2021, 08:19
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Hi Priyanka,
could you please share your input files so that we can take a closer look?
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Old   April 19, 2021, 08:32
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Hi Arun

I am attaching the control files.
Attached Files
File Type: txt control.txt (135 Bytes, 4 views)
File Type: txt ctrl.txt (269 Bytes, 4 views)
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Old   April 19, 2021, 08:37
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When you are running the case on the laptop, do you use the same mesh width?
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Old   April 19, 2021, 09:04
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While running on the laptop, I have kept the same mesh width.

PS: All the functions (except the M10 parameter), are kept the same in both control.txt and ctrl.txt files.
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Old   April 19, 2021, 15:37
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I am not sure why it works locally and fails on the cluster, but the solution is most probably to avoid using N 40 6. This crashes cases for me locally as well with open channel flow.
Use N 40 3 and the problem should be solved.
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Old   April 19, 2021, 18:04
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Yes, Arun is correct, N 40 6 can be less stable than N 40 3. But his should be independent of the processor count. We are currently looking in to the matter.

Another idea: maybe you did not make clean the previous build on your HPC cluster before you compiled the newest version? Maybe you have a go, make clean and then compile again?
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Old   April 22, 2021, 06:09
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A small update. With the latest version of the model, N 40 6 seems to work fine (but I would still advice caution while using it).
I do notice though that the cylinder you have in the domain has about the same diameter as the grid size. I would advice using a stretched grid to include more cells around the structure.

And finally something that might just solve the cluster problem, add M 20 2 to control.txt
(Since I cant really reproduce the error, I am limited to looking all possible options, one by one)

Did you see a change after making a fresh compilation of the latest version?
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Old   April 22, 2021, 08:08
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We have tested your files with 24 cores. Everything works, so I think it is a compilation problem. As I wrote before:
maybe you did not make clean the previous build on your HPC cluster before you compiled the newest version? Maybe you have a go, make clean and then compile again?
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