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-   -   how to check convergence?? (https://www.cfd-online.com/Forums/openfoam/82206-how-check-convergence.html)

 gandesk November 19, 2010 11:23

how to check convergence??

Hello all,

I am new to openFoam and started learning it with the available tutorials. I am able to run the case but I am not sure how to check if the residuals are converging. Where do I check them?? and where do I specify the the convergence criteria??

Any help woud be appreciated!!

Thanks a ton!!
Sandeep

 FG_HSRM November 19, 2010 12:10

Hello Sandeep!

Take a look at system/fvSolution and check the screen output.
Alternatively you can save the screen output in a log file.
Regards
fritz

 gandesk November 19, 2010 12:15

Hi fritz,

I am sorry I did not understand what u meant to check the screen output. fvSolutions file has just solvers and PISO dictionaries in it.

 FG_HSRM November 19, 2010 13:58

How are you running your case?
Normaly, you see something like below on your screen and in the log-file, too.
Quote:
 Time = 0.495 Courant Number mean: 0.116925 max: 0.852134 DILUPBiCG: Solving for Ux, Initial residual = 1.99665e-07, Final residual = 1.99665e-07, No Iterations 0 DILUPBiCG: Solving for Uy, Initial residual = 4.36311e-07, Final residual = 4.36311e-07, No Iterations 0 DICPCG: Solving for p, Initial residual = 1.0746e-06, Final residual = 3.53797e-07, No Iterations 1 time step continuity errors : sum local = 5.37651e-09, global = -2.9125e-19, cumulative = 8.07944e-18 DICPCG: Solving for p, Initial residual = 6.81574e-07, Final residual = 6.81574e-07, No Iterations 0 time step continuity errors : sum local = 8.06059e-09, global = 9.28097e-19, cumulative = 9.00754e-18 ExecutionTime = 0.16 s ClockTime = 0 s Time = 0.5 Courant Number mean: 0.116925 max: 0.852134 DILUPBiCG: Solving for Ux, Initial residual = 1.89493e-07, Final residual = 1.89493e-07, No Iterations 0 DILUPBiCG: Solving for Uy, Initial residual = 4.14522e-07, Final residual = 4.14522e-07, No Iterations 0 DICPCG: Solving for p, Initial residual = 1.06665e-06, Final residual = 3.39604e-07, No Iterations 1 time step continuity errors : sum local = 5.25344e-09, global = -9.50761e-19, cumulative = 8.05678e-18 DICPCG: Solving for p, Initial residual = 5.36118e-07, Final residual = 5.36118e-07, No Iterations 0 time step continuity errors : sum local = 6.86432e-09, global = 4.62063e-19, cumulative = 8.51884e-18 ExecutionTime = 0.16 s ClockTime = 0 s

 robingilbert November 19, 2010 19:50

http://www.cfd-online.com/Forums/ope...residuals.html

try that link. it shows how to plot residuals.
or u can see the screen output while running the simulation. it shows the initial and final residual at each time step. generally as far as i know if the initial residuals are going down, it means solution is converging. Somebody please correct me if i am wrong.

 mrshb4 November 21, 2010 10:20

yes!

you are correct!! but I think thats not enough!! you should monitor some characteristics of your case in some points.( you can try sampleDict for this).

To plot residuals you can try pyFoam. It works properly.

 elvis November 22, 2010 03:41

 GregorS December 21, 2010 09:07

Hello!

You can also use the foamLog script.

http://www.openfoam.com/docs/user/mo...hp#dx35-201001

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