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smoothSolver diverges - solution in using PBiCG solver? |
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December 15, 2009, 14:49 |
smoothSolver diverges - solution in using PBiCG solver?
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#1 |
Senior Member
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Hi all!
I have 2 points to discuss: 1st one: I wrote a heat transfer solver based on pimpleFoam, adding heat transfer equation. I use high Courant numbers (up to 5) to speed up calculations. Flow simulation runs without problems (GAMG solver for pressure, smoothSolvers for U and turbulent parameters). By analogy I used smoothSolver also for TEqn in my solver: Code:
T { solver smoothSolver; smoother GaussSeidel; tolerance 1e-05; relTol 0; nSweeps 1; } Then I just switched TEqn solver to PBiCG with DILU preconditioner Code:
T { solver PBiCG; preconditioner DILU; tolerance 1e-05; relTol 0; } So what is the reason for such behavior? 2nd point: Why am I using pimpleFoam? I solve more complicated task with solidification and turbulent flow. For some cases I search for steady state. One approache is to use steady state solvers, another - to apply transient or cvazi-transient solvers to reach steady state when solution will become stable. I tried to use simpleFoam just to test such posibility for my task. It reached solution which transient solvers achieve and do not change later, but instanteniously solution deverged! Residuals got a big jump and solution crashed... Am wondering why it happend? Stable solution for that simmetric geometry which I used was assimetric, because there are 3 jets and in 2D they cannot be stable because two zones of low pressure do not have a connection. Is assymethry of solution the case for steady state solver to deverge? So now I an forced to use PISO or PIMPLE technics to solve my problem... But it is time-consuming! So, waiting for your opinion! Have a good day!
__________________
Best regards, Dr. Alexander VAKHRUSHEV Christian Doppler Laboratory for "Metallurgical Applications of Magnetohydrodynamics" Simulation and Modelling of Metallurgical Processes Department of Metallurgy University of Leoben http://smmp.unileoben.ac.at |
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August 20, 2013, 16:22 |
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#2 |
New Member
Jackie Chou
Join Date: Mar 2013
Posts: 12
Rep Power: 13 |
Hello, Dr. Alexander VAKHRUSHEV,
I have met the same situation as you had. Have you got an idea about it? Jackie |
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August 21, 2013, 11:17 |
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#3 |
Senior Member
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Hi Jackie!
My post was from 2009, since that OpenFOAM improved a lot in numerics. So I do not observe that now in my simulations... Sometimes under-relaxation really helps to avoid simulation from explosion. Cheers, Alexander
__________________
Best regards, Dr. Alexander VAKHRUSHEV Christian Doppler Laboratory for "Metallurgical Applications of Magnetohydrodynamics" Simulation and Modelling of Metallurgical Processes Department of Metallurgy University of Leoben http://smmp.unileoben.ac.at |
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September 11, 2013, 12:44 |
Multigride
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#4 |
Member
Join Date: Oct 2012
Posts: 47
Rep Power: 13 |
Hi Dr.Alexander
Can you tell me what the difference is GAMG algorithms algorithms AMG? THANKS |
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