
[Sponsors] 
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 = 1.660614399e06, Final residual = 1.382107362e16, No Iterations 2 DILUPBiCG: Solving for Uy, Initial residual = 2.725991237e05, Final residual = 1.71994151e15, No Iterations 2 DILUPBiCG: Solving for h, Initial residual = 4.640570901e07, Final residual = 2.664924362e17, No Iterations 2 FDICPCG: Solving for p, Initial residual = 1.311912104e06, Final residual = 3.564637383e15, No Iterations 6 FDICPCG: Solving for p, Initial residual = 7.244953397e14, Final residual = 2.568884643e15, No Iterations 1 diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0 time step continuity errors : sum local = 2.343009192e16, global = 1.367661713e17, cumulative = 2.07229617e08 rho max/min : 2.417134107 2.398184636 FDICPCG: Solving for p, Initial residual = 2.735098395e09, Final residual = 5.153284331e15, No Iterations 4 FDICPCG: Solving for p, Initial residual = 5.535348519e14, Final residual = 2.142343159e15, No Iterations 1 diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0 time step continuity errors : sum local = 2.334873446e16, global = 1.47642379e17, cumulative = 2.072296172e08 rho max/min : 2.417134107 2.398184636 FDICPCG: Solving for p, Initial residual = 1.335350283e11, Final residual = 6.963764942e16, No Iterations 3 FDICPCG: Solving for p, Initial residual = 4.134830709e14, Final residual = 1.474027945e15, No Iterations 1 diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0 time step continuity errors : sum local = 2.301559708e16, global = 1.40876864e17, cumulative = 2.072296173e08 rho max/min : 2.417134107 2.398184636 PIMPLE: iteration 10 DILUPBiCG: Solving for Ux, Initial residual = 1.82942849e06, Final residual = 5.541810383e17, No Iterations 2 DILUPBiCG: Solving for Uy, Initial residual = 2.959945528e05, Final residual = 2.277521743e15, No Iterations 2 DILUPBiCG: Solving for h, Initial residual = 6.035283727e07, Final residual = 9.136129994e17, No Iterations 2 FDICPCG: Solving for p, Initial residual = 1.595530764e06, Final residual = 3.504793444e15, No Iterations 6 FDICPCG: Solving for p, Initial residual = 7.14289137e14, Final residual = 2.634399827e15, No Iterations 1 diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0 time step continuity errors : sum local = 2.339840533e16, global = 1.340257095e17, cumulative = 2.072296174e08 rho max/min : 2.417134107 2.398184636 FDICPCG: Solving for p, Initial residual = 2.868202145e09, Final residual = 5.345704264e15, No Iterations 4 FDICPCG: Solving for p, Initial residual = 5.420100184e14, Final residual = 1.936677383e15, No Iterations 1 diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0 time step continuity errors : sum local = 2.324211337e16, global = 1.342398081e17, cumulative = 2.072296176e08 rho max/min : 2.417134107 2.398184636 FDICPCG: Solving for p, Initial residual = 1.966838831e11, Final residual = 6.116982397e16, No Iterations 3 FDICPCG: Solving for p, Initial residual = 4.085579847e14, Final residual = 1.43049529e15, No Iterations 1 diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0 time step continuity errors : sum local = 2.304000431e16, global = 1.357813178e17, cumulative = 2.072296177e08 rho max/min : 2.417134107 2.398184636 PIMPLE: not converged within 10 iterations Code:
solvers { p { solver PCG; preconditioner FDIC; tolerance 1e14; 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 1e012; relTol 0;*/ } pFinal { $p; relTol 0; } "rho.*" { $p; tolerance 1e12; relTol 0; } "(UehRkepsilonomega)" { solver PBiCG; preconditioner DILU; tolerance 1e12; relTol 0; maxIter 25000; } "(UhRkepsilonomega)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 1e16; residualControl { "(pUkomega)" { 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. Postdoctoral Fellow Research Center for Computational Mechanics (CIMEC)  CONICET/FICHUNL T.E.: 543424511594 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:
Bruno
__________________


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 hardcore 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... Hardcore 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
__________________


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. Postdoctoral Fellow Research Center for Computational Mechanics (CIMEC)  CONICET/FICHUNL T.E.: 543424511594 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. 

Thread Tools  
Display Modes  


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
pisoFoam with kepsilon turb blows up  Some questions  Heroic  OpenFOAM Running, Solving & CFD  26  December 17, 2012 04:34 
AMI speed performance  danny123  OpenFOAM  19  October 24, 2012 07:44 
Floating point exception error  Alan  OpenFOAM Running, Solving & CFD  10  April 6, 2012 14:02 
Problem with FloatingObject  Leech  OpenFOAM Running, Solving & CFD  10  March 29, 2012 15:24 
High Courant Number @ icoFoam  Artex85  OpenFOAM Running, Solving & CFD  9  January 3, 2012 09:06 