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How to manually set max iterations on Design3D

JosephSmith

Hi Everyone,

My question is how to manually set the max iteration to run each simulation in the database for Design3D. context: I am attempting to start a multipoint optimization of a centrifugal impeller with water as the fluid. I am using the Spalart-Allmaras turbulence model with the following boundary conditions in the turbo solver:



The Barotropic Cavitation model within Fine turbo is enabled. I only changed the saturation pressure based on the operating temperature, and Amin value to 80 based on a rough calculation of the speed of sound in the two phase medium.



The initial simulation converged to global residuals of -3.8 with the above selections. However, all the samples failed to converge in design3d. It was not a mesh failure, only convergence errors. Opening up the job_eranus files for each computation showed that sometimes the simulation would stop at just 200 iterations. Other times it would stop at 3000. I've summarised them below



I suspect the convergence would improve if I manually set the max iterations to 5000, like my initial simulation. I would like to know how to do this in fine design 3d as I only saw the option to set the convergence level. Alternatively, I would appreciate any other angles to resolve the error.

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  • 0

    The bad news: when the simulation stops at 218 iterations is because it diverged. You can see the residual for the continuity equation goes from -1 to +2, with the maximum going to +40. 

    The file job_euranus stores the content of the *.std file produced by Fine Turbo. You can also open a monitor and look at the residuals of the simulation to get a better idea of what's happening. By looking at the files, it seems that the max residual is in block 5, which should correspond to the leading edge of the impeller (not betting any money on this).

    The good news: there are a few tricks to make the optimization faster. My favorite option is to restart all simulations in the DoE from an already converged solution and "reset the convergence". Supposing that the geometry changes a little (a few degrees for the blade angles, something along these lines), the flow field won't be too dissimilar, therefore it represents a great initial solution for the other designs.

    This means that the convergence level is not going down too much (maybe to -2), so better add a few iterations more to be sure to have a converged solution.

    My favorite approach:

    - run a geometry and get a converged solution

    - create a _restart_ computation from the previous one: this is the computation that I'm going to use for the optimization

    - in Fine Turbo, the convergence level is -10, the max number of iterations is to be chosen appropriately. The solver will run until reaching the max number of iterations, since the residuals won't go to -10.

    - in Fine Design3D, go to Simulation settings, turn on expert mode, set the convergence level higher than -3. Fine Design3D will consider that all simulations with the job_euranus showing a last line with a residual higher than the number you have there.

  • 0 in reply to domen

    Hi Domen,

    Thanks for the advice and sharing your approach. I would like to clarify a few things regarding it:

    1. for the ''create a _restart_computation from previous one'' - does this mean creating a new fine turbo project and using the run file from the first converged solution as the initial solution (in fine turbo, going to the Initial Solution> from file> selecting the run file of the first converged simulation)?. If that is the case, you then change the convergence to  -10 for this second simulation so the number of iterations becomes the stopping indicator for the simulation

    2. For the design3D case, do you actually mean lower? like -4 etc. Besides more result fidelity, is there a reason to lower it in this scenario? 

  • 0 in reply to JosephSmith

    1. yes, perfect!

    2. No, I'd set it higher (+3). I let Fine Turbo converge (or not), and not Fine Design3D assess the convergence. 

  • 0 in reply to domen

    Alright thanks, will try it out and let you know the outcome

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