# Too many iterations causing long simulation time :(

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 February 26, 2018, 18:55 Too many iterations causing long simulation time :( #1 Member   Shafik Walakaka Join Date: Oct 2017 Posts: 38 Rep Power: 5 Hi everyone, I am trying to simulate a two-phase stratified flow in a pipe. However, my simulations are taking extremely long. It states that it takes 1001 iterations to obtain pressure , does anyone know what could be the cause of this issue? PIMPLE: iteration 1 smoothSolver: Solving for alpha.water, Initial residual = 0.000529543, Final residual = 2.66809e-11, No Iterations 2 Phase-1 volume fraction = 0.517887 Min(alpha.water) = 0 Max(alpha.water) = 1.06837 MULES: Correcting alpha.water MULES: Correcting alpha.water Phase-1 volume fraction = 0.517887 Min(alpha.water) = -8.72144e-07 Max(alpha.water) = 1.06794 DICPCG: Solving for p_rgh, Initial residual = 1, Final residual = 0.880426, No Iterations 1001 time step continuity errors : sum local = 0.00204219, global = -2.39327e-05, cumulative = -4.39327e-05 DICPCG: Solving for p_rgh, Initial residual = 0.270516, Final residual = 0.753417, No Iterations 1001 time step continuity errors : sum local = 0.00579181, global = -2.39253e-05, cumulative = -6.7858e-05 DICPCG: Solving for p_rgh, Initial residual = 0.510678, Final residual = 0.1488, No Iterations 1001 time step continuity errors : sum local = 0.00170815, global = -1.19552e-05, cumulative = -7.98132e-05 ExecutionTime = 12.26 s ClockTime = 12 s Regards Shafik

 February 27, 2018, 03:03 #2 Senior Member     Uwe Pilz Join Date: Feb 2017 Location: Leipzig, Germany Posts: 588 Rep Power: 10 You get such effects if something wrong with your boundary or initial conditions. Or you set up your case in a non physical way. __________________ Uwe Pilz -- Die der Hauptbewegung überlagerte Schwankungsbewegung ist in ihren Einzelheiten so hoffnungslos kompliziert, daß ihre theoretische Berechnung aussichtslos erscheint. (Hermann Schlichting, 1950)

February 27, 2018, 15:52
#3
Member

Shafik Walakaka
Join Date: Oct 2017
Posts: 38
Rep Power: 5
Quote:
 Originally Posted by piu58 You get such effects if something wrong with your boundary or initial conditions. Or you set up your case in a non physical way.

Could you kindly elaborate what you mean by wrong boundary/initial conditions or non physical?
Because I am getting accurate results when modelling single phase flow (Unless it is possible to obtain good results with my error). Which is why I am confused, what do you mean by wrong boundary/initial conditions or non physical way?

Kind regards
Shafik

 February 28, 2018, 02:14 #4 Senior Member     Uwe Pilz Join Date: Feb 2017 Location: Leipzig, Germany Posts: 588 Rep Power: 10 Good morning, if yopu take additional effects in to account, the behaviour of the solver may change. Somtimes, it ist more or less a different solver. I see two ways that anybody may help you. Either you reduce the effect you see to the simples thinkable case and report is as an error. Or you describe what is your real problem and which connection to the physical worls it has. May be there are other ways to solve it. __________________ Uwe Pilz -- Die der Hauptbewegung überlagerte Schwankungsbewegung ist in ihren Einzelheiten so hoffnungslos kompliziert, daß ihre theoretische Berechnung aussichtslos erscheint. (Hermann Schlichting, 1950)

February 28, 2018, 06:41
#5
Member

Shafik Walakaka
Join Date: Oct 2017
Posts: 38
Rep Power: 5
Quote:
 Originally Posted by piu58 Good morning, if yopu take additional effects in to account, the behaviour of the solver may change. Somtimes, it ist more or less a different solver. I see two ways that anybody may help you. Either you reduce the effect you see to the simples thinkable case and report is as an error. Or you describe what is your real problem and which connection to the physical worls it has. May be there are other ways to solve it.
Good morning!

Thank you for your kind reply. I am currently using the interFoam solver which uses the Pimple algorithm. I notice that when I change the deltaT, the number of iterations required for pressure correction to converge reduces!

Is there an explanation for this?

Regards
Shafik

 Tags iterations, openfoam