why PIMPLE doesn't converge at each time step but no diverging?

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 February 28, 2013, 12:02 why PIMPLE doesn't converge at each time step but no diverging? #1 Senior Member     Ehsan Join Date: Oct 2012 Location: Iran Posts: 2,205 Rep Power: 17 I have set Pimple nCorrectors to 10 but despite of this high value pimple doesn't converge at each time step.my problem is transient. what does that message about not converging mean?then why diverging doesnt occurs immediately after not converging at a time step? Code: ```PIMPLE: iteration 9 DILUPBiCG: Solving for Ux, Initial residual = 1.660614399e-06, Final residual = 1.382107362e-16, No Iterations 2 DILUPBiCG: Solving for Uy, Initial residual = 2.725991237e-05, Final residual = 1.71994151e-15, No Iterations 2 DILUPBiCG: Solving for h, Initial residual = 4.640570901e-07, Final residual = 2.664924362e-17, No Iterations 2 FDICPCG: Solving for p, Initial residual = 1.311912104e-06, Final residual = 3.564637383e-15, No Iterations 6 FDICPCG: Solving for p, Initial residual = 7.244953397e-14, Final residual = 2.568884643e-15, No Iterations 1 diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0 time step continuity errors : sum local = 2.343009192e-16, global = 1.367661713e-17, cumulative = 2.07229617e-08 rho max/min : 2.417134107 2.398184636 FDICPCG: Solving for p, Initial residual = 2.735098395e-09, Final residual = 5.153284331e-15, No Iterations 4 FDICPCG: Solving for p, Initial residual = 5.535348519e-14, Final residual = 2.142343159e-15, No Iterations 1 diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0 time step continuity errors : sum local = 2.334873446e-16, global = 1.47642379e-17, cumulative = 2.072296172e-08 rho max/min : 2.417134107 2.398184636 FDICPCG: Solving for p, Initial residual = 1.335350283e-11, Final residual = 6.963764942e-16, No Iterations 3 FDICPCG: Solving for p, Initial residual = 4.134830709e-14, Final residual = 1.474027945e-15, No Iterations 1 diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0 time step continuity errors : sum local = 2.301559708e-16, global = 1.40876864e-17, cumulative = 2.072296173e-08 rho max/min : 2.417134107 2.398184636 PIMPLE: iteration 10 DILUPBiCG: Solving for Ux, Initial residual = 1.82942849e-06, Final residual = 5.541810383e-17, No Iterations 2 DILUPBiCG: Solving for Uy, Initial residual = 2.959945528e-05, Final residual = 2.277521743e-15, No Iterations 2 DILUPBiCG: Solving for h, Initial residual = 6.035283727e-07, Final residual = 9.136129994e-17, No Iterations 2 FDICPCG: Solving for p, Initial residual = 1.595530764e-06, Final residual = 3.504793444e-15, No Iterations 6 FDICPCG: Solving for p, Initial residual = 7.14289137e-14, Final residual = 2.634399827e-15, No Iterations 1 diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0 time step continuity errors : sum local = 2.339840533e-16, global = 1.340257095e-17, cumulative = 2.072296174e-08 rho max/min : 2.417134107 2.398184636 FDICPCG: Solving for p, Initial residual = 2.868202145e-09, Final residual = 5.345704264e-15, No Iterations 4 FDICPCG: Solving for p, Initial residual = 5.420100184e-14, Final residual = 1.936677383e-15, No Iterations 1 diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0 time step continuity errors : sum local = 2.324211337e-16, global = 1.342398081e-17, cumulative = 2.072296176e-08 rho max/min : 2.417134107 2.398184636 FDICPCG: Solving for p, Initial residual = 1.966838831e-11, Final residual = 6.116982397e-16, No Iterations 3 FDICPCG: Solving for p, Initial residual = 4.085579847e-14, Final residual = 1.43049529e-15, No Iterations 1 diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0 time step continuity errors : sum local = 2.304000431e-16, global = 1.357813178e-17, cumulative = 2.072296177e-08 rho max/min : 2.417134107 2.398184636 PIMPLE: not converged within 10 iterations``` my fvSolution is: Code: ```solvers { p { solver PCG; preconditioner FDIC; tolerance 1e-14; relTol 0; nsweeps 1000; maxIter 25000; /*solver GAMG; smoother DICGaussSeidel; cacheAgglomeration true; nCellsInCoarsestLevel 200; nPreSweeps 0; nPostSweeps 2; nFinestSweeps 2; agglomerator faceAreaPair; mergeLevels 2; tolerance 1e-012; relTol 0;*/ } pFinal { \$p; relTol 0; } "rho.*" { \$p; tolerance 1e-12; relTol 0; } "(U|e|h|R|k|epsilon|omega)" { solver PBiCG; preconditioner DILU; tolerance 1e-12; relTol 0; maxIter 25000; } "(U|h|R|k|epsilon|omega)Final" { \$U; relTol 0; } } PIMPLE { momentumPredictor yes; nOuterCorrectors 10; nCorrectors 5; nNonOrthogonalCorrectors 1; rhoMin rhoMin [ 1 -3 0 0 0 ] .6; rhoMax rhoMax [ 1 -3 0 0 0 ] 8.5; //convergence 1e-16; residualControl { "(p|U|k|omega)" { relTol 0; tolerance 0.0000000001; } } } /*relaxationFactors { fields { p 0.9; } equations { U .99; k .99; omega .99; h .99; e .99; }*/```

 March 1, 2013, 16:49 #2 Senior Member     Santiago Marquez Damian Join Date: Aug 2009 Location: Santa Fe, Santa Fe, Argentina Posts: 418 Rep Power: 15 What value of residuals are expected for convergence? Regards. __________________ Santiago MÁRQUEZ DAMIÁN, Ph.D. Post-doctoral Fellow Research Center for Computational Mechanics (CIMEC) - CONICET/FICH-UNL T.E.: 54-342-4511594 Ext. 1005 Güemes 3450 - (3000) Santa Fe Santa Fe - Argentina http://www.cimec.org.ar

 March 2, 2013, 01:35 #3 Senior Member     Ehsan Join Date: Oct 2012 Location: Iran Posts: 2,205 Rep Power: 17 what do you mean?should not all values converge? The PIMPLE says that it doesn't converge as its shown but values are converged(final residuals are low) then what does that mean that PIMPLE doesn't converge?

 March 2, 2013, 08:17 #4 Super Moderator   Bruno Santos Join Date: Mar 2009 Location: Lisbon, Portugal Posts: 8,488 Blog Entries: 34 Rep Power: 86 Greetings to all! @Ehsan: I don't have a test case for confirming this myself, but I believe the issue is as follows: You're specifying that "p", "U", "k" and "omega" have to abide to the tolerance of... ... "1e-10 == 0.0000000001": Code: ```residualControl { "(p|U|k|omega)" { relTol 0; tolerance 0.0000000001; } }``` If you look at the output you've provided, on the last iteration you have: Code: ```DILUPBiCG: Solving for Ux, Initial residual = 1.82942849e-06, Final residual = 5.541810383e-17, No Iterations 2 DILUPBiCG: Solving for Uy, Initial residual = 2.959945528e-05, Final residual = 2.277521743e-15, No Iterations 2``` It's the initial residual that counts for control and both "Ux" and "Uy" are well above 1e-10. I think this is why Santiago made that quick question. Best regards, Bruno __________________ OpenFOAM: Frequently Asked Questions | Useful links for building and using Forum: How to ask for help | Posting code and output with [CODE] My to-do list and when I'll be able to come to the forum: http://wyldckat.github.io And please: Read this before sending private messages to me

 March 2, 2013, 09:08 #5 Senior Member     Ehsan Join Date: Oct 2012 Location: Iran Posts: 2,205 Rep Power: 17 thank you dear Bruno. Please verify im correct or not:variables set in residualControl check for initial residuals that be lower than set value. But tolerances of variables that set in other dictionaries are related to final residuals.is it ok? Then 1)how can i be certain that solution at each time step is converged? 2)What is better for tolerances in separate dictionaries for p,U,k,omega,... 3)which value for tolerances in residualControl is appropriate for sureness of convergency at each time step? 4)whats the usage and beneficient of residualControl totally?

 March 2, 2013, 09:38 #6 Super Moderator   Bruno Santos Join Date: Mar 2009 Location: Lisbon, Portugal Posts: 8,488 Blog Entries: 34 Rep Power: 86 Hi Ehsan, Questions 1 to 3 - read this excellent post on the topic of convergence: Convergence Question 4: AFAIK, it's an automated feature that hard-core CFD users rarely use . It will stop when the defined value is reached, but it cannot decide whether it's the right time to stop or not... Hard-core CFD users look at the residual plots and decide from there when it's converged or what needs adjusting. I think the decision process is described in the post above. Good luck! Best regards, Bruno immortality likes this. __________________ OpenFOAM: Frequently Asked Questions | Useful links for building and using Forum: How to ask for help | Posting code and output with [CODE] My to-do list and when I'll be able to come to the forum: http://wyldckat.github.io And please: Read this before sending private messages to me

 March 2, 2013, 10:43 #7 Senior Member     Santiago Marquez Damian Join Date: Aug 2009 Location: Santa Fe, Santa Fe, Argentina Posts: 418 Rep Power: 15 Hi, my question was about what value you set in the residualControl option. Regards. __________________ Santiago MÁRQUEZ DAMIÁN, Ph.D. Post-doctoral Fellow Research Center for Computational Mechanics (CIMEC) - CONICET/FICH-UNL T.E.: 54-342-4511594 Ext. 1005 Güemes 3450 - (3000) Santa Fe Santa Fe - Argentina http://www.cimec.org.ar

 May 19, 2013, 14:16 #8 Senior Member     Ehsan Join Date: Oct 2012 Location: Iran Posts: 2,205 Rep Power: 17 Hi dear Santiago sorry for delay in reply. in fact i have seen your message now accidently. thanks.I never use residualControl anymore. I think its for steady_state problems rather than transients. is my conclusion true? thanks for your before reply again. __________________ Injustice Anywhere is a Threat for Justice Everywhere.Martin Luther King. To Be or Not To Be,Thats the Question! The Only Stupid Question Is the One that Goes Unasked.

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