Restarting simulation if convergence isn't reached

Hi All,

I am curious whether it is possible to implement the ability to continue running a simulation that reaches the end time before convergence. For example you are running a steady CFD case and you set the end time to 10000 and the solution reaches that time without hitting the convergence criteria, currently, you have to delete the run and increase the end time and re-run the full simulation. From some experience using OpenFOAM I know this is easily performed with OpenFOAM, so it would seem to me that it shouldn’t be too hard to setup in Simscale. Thanks for your time.

-Ian

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@steezorigineez Ian,

very much agreed! To use an existing solution field as the “starting point” for a new simulation run is something we’re working on. However it’s too early to provide a release date on it but I’ll keep you posted on the development of this feature. In the meantime a brief hint (maybe you’re already using this): For most flow simulation analysis types, under “Simulation Control” you can set the option that the simulation shall be initialized with a potential flow solution (see screenshot below).

It’s obviously not a replacement for a real restart feature but can help sometimes to speed up convergence.

Best,

David

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Hi @dheiny,

I also wanted to ask this question but I see that it already exists. So is this feature already available? This is not only needed when you run out of time but also if set to little time steps to reach solution. Unfortunately potentialFoam is not a solution here.

Best regards,
Andrzej

Hi Andrzej (@akosior ),

I have the feeling I do say this too often lately to you :slight_smile: - but: not yet. It’s in the works but no release date yet.

As another hint in the meantime, if you’re dealing with steady-state simulations: The Numerics tree item let’s you set convergence criteria / residual tolerances for all solution fields:

That way you can bump up the number of iterations but set a criterion at which it should terminate the simulation / consider it converged. This approach could help at least in some cases.

Best,

David

Hi Any news about restarting from an already ran CFD? Thanks

Sometimes you will see a ‘Continue’ icon:

EDIT: The fix has already been made so that the ‘Continue’ icon is always there, see below and thank-you @rszoeke :clap:

Capture

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Hi @plott,
as @DaleKramer showed, the functionality to continue a steady state run if its not yet converged, is already available (actually since the beginning of the year). You can get some more information around it form this feature release post: https://www.simscale.com/blog/2019/01/product-update-run-continuation/

Best,
Richard

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@rszoeke Can you confirm that you can only use it once per sim run?

Also, can you confirm that it uses the same numerics and simulation control parameters that the sim run started with, except end time and max run time of course (even if those values have been changed in the current parameters)?

Thank you Dale. This is not 100% what I was after.

Hi @DaleKramer,
actually the number of continuations is not limited. The only restriction though, is that the last time step is actiually saved. What could have happened in your case is that you for example run a first step for 3000 iterations with a write interval of 1000. If you then continue for another 500 the same settings were used for the continuation (which answers your 2nd question) including the write control, that means you have a last time step of 3500, but no additional data point had been saved and thus the results are out of sync and the program won’t let you continue a 2nd time.

Luckily, by a strange case of coincidence, we have just fixed this problem at the beginning of this week and will release a fix either today or tomorrow. From then on, regardless of the write control, we will ALWAYS save the last time step for a successful simulation and you will always be able to continue a successful steady-state analysis.

Best,
Richard

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Thank-you, a long standing mystery solved for me :slight_smile:

I want to talk to you from now on :wink:

Sure @DaleKramer, I 'll send you my private phone number. :wink:

In the meantime we actually released the fix. Now always the last time step will be saved and the continuation is also always possible. Enjoy!

Best,
Richard

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While I have your ear :wink:

It would be really nice if you could show on that image I posted, accumulated minutes and core hours for the 1st run plus all continuation runs INSTEAD of just the last continuation run… :pray: