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February 9, 2018, 12:27 
Unable to plot residuals (Interfoam) [Solved]

#1 
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Shafik Walakaka
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Hi everyone,
I am currently working on a twophase laminar flow through a pipe. To check my mesh, I ran a simulation with only air through the pipe (alpha = 0) using the interFoam solver and the results matches the hagenpoiseuille equation. However, I am currently trying to plot the residuals using help from the forum in the following link: plot residuals The residual plot was successful in the past when I was using the simpleFoam solver. However, using the interFoam solver, I am getting an error message stating the following
Does anyone have any idea of what I am doing wrong? p/s: I also notice that in my log file, they are only solving for the p_rgh term and no ux,uy or uz term Kind regards Shaq Last edited by walakaka; February 28, 2018 at 14:04. Reason: solved 

February 10, 2018, 12:54 

#2 
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Tobias Holzmann
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Hi,
you donīt solve for p, thus you have to grep for p_rgh if you want to get the residuals for p_rgh. In most cases there is no need to solve the momentum prediction. In your fvSolutions you momentumPredictor is false. Thats why you donīt see Ux, Uy and Uz residuals.
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February 10, 2018, 17:59 

#3  
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Shafik Walakaka
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Quote:
Thanks for getting back to me. I had a look in the fvSolution folder and it is true that my momentumPredictor is set to "no". Could you kindly explain the following please:
Kind regards Shaq 

February 10, 2018, 19:33 

#4 
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Hi,
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February 18, 2018, 19:49 

#5  
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Shafik Walakaka
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Quote:
I have another question: When not activating the momentum predictor, the solver only solves the residual for p_rgh. However, every time iteration has 3 p_rgh residuals, Which one should I take from each iteration? Also, if one does not activate the momentum predicture, what are the recommended tolerance for pressure residuals? Will it have to be below 1e7 or will a residual of magnitude below 1e5 be reasonable? Regards Shafik Last edited by walakaka; February 26, 2018 at 18:42. 

February 26, 2018, 18:42 

#6  
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Shafik Walakaka
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Quote:


February 26, 2018, 18:59 
Example!

#7 
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Shafik Walakaka
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For example, the logs below, Which residual do I grep for? The first, second or final one? Or do I grep for each of them in succession (even though they are the resultant value from 1 particular iteration)
PIMPLE: iteration 1 smoothSolver: Solving for alpha.water, Initial residual = 0.000529543, Final residual = 2.66809e11, No Iterations 2 Phase1 volume fraction = 0.517887 Min(alpha.water) = 0 Max(alpha.water) = 1.06837 MULES: Correcting alpha.water MULES: Correcting alpha.water Phase1 volume fraction = 0.517887 Min(alpha.water) = 8.72144e07 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 = 2.39327e05, cumulative = 4.39327e05 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 = 2.39253e05, cumulative = 6.7858e05 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 = 1.19552e05, cumulative = 7.98132e05 ExecutionTime = 12.26 s ClockTime = 12 s Regards Shaq 

March 7, 2018, 16:27 
Pimplefoam residual

#8  
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Shafik Walakaka
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Quote:
I have used your advice and greped for p_rgh successfully, is there a command to only grep the final residual in every outer loop iteration? Because at the moment, my residual plot is plotting every single iteration (inner loop and outer loop) as shown in the attached file. Yaxis: residuals Xaxis: Iterations Kind regards Shafik 

February 6, 2022, 07:59 
velocity component residuals are missing (multiphaseEulerFoam)

#9  
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saeed sangchooly
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Quote:
I'm working with multiphaseEulerFoam solver with 3 phases I did set momentumPredictor to yes and I've also tried setting nUcorrectors to 0; but still I can't see the velocity component residuals. why is that? how can I fix this? Last edited by saeed sangchooly; February 6, 2022 at 09:54. 

February 6, 2022, 16:57 

#10 
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Tobias Holzmann
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Can you provide use the solver log file?
If you have the momentumPredictor activated, you have to see it. Maybe its related to the solver and the residual control function object (don't know how you are extracting your data) should give the velocity field. Otherwise, its a feature we would / could be implement in newer versions.
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February 7, 2022, 06:45 

#11  
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saeed sangchooly
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Quote:
this is what I get in log file: (RAS bubble column tutorial in multiphaseEulerFoam): Code:
PIMPLE: Iteration 1 MULES: Solving for alpha.air MULES: Solving for alpha.water air fraction, min, max = 0.293331 2.33203e178 1 water fraction, min, max = 0.706669 0 1 Phasesum volume fraction, min, max = 1 1 1 MULES: Solving for alpha.air MULES: Solving for alpha.water air fraction, min, max = 0.293331 6.74315e178 1 water fraction, min, max = 0.706669 0 1 Phasesum volume fraction, min, max = 1 1 1 Constructing momentum equations smoothSolver: Solving for e.air, Initial residual = 0.000387688, Final residual = 1.57809e08, No Iterations 1 smoothSolver: Solving for e.water, Initial residual = 1.45421e06, Final residual = 4.86519e11, No Iterations 1 air min/max T 300  350 water min/max T 300.159  350 GAMG: Solving for p_rgh, Initial residual = 3.32827e06, Final residual = 8.8626e09, No Iterations 5 it seems that momentunPredictor can not be actually activated in multiphaseEulerFoam. because the solver gave no error that for example UFinal is undefined in fvSolution like other solvers. thank you so much for your answer btw. 

February 7, 2022, 07:35 

#12 
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Tobias Holzmann
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You mix up a few things here. However, you are right, the momentumprediction is not implemented: https://develop.openfoam.com/Develop...erFoam/UEqns.H
So probably, there is a reason why its not implemented or why we cannot use a prediction step prior to the pressureequation. I am not familiar with multiphase flows. However, UFinal, if you don't set the "*.Final" Relaxation, it is commonly 1. It should be a <lookupOrDefault> value. So I never had issues that "*.Final" is not defined in terms of relaxation factors. Furthermore, in the UEqns.H file, you can see that the relaxation of the matrix is commented. Hence, not used at all. Note. In the Foundation version, there you have the relaxation included: https://github.com/OpenFOAM/OpenFOAM...oam/pU/UEqns.H
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February 9, 2022, 05:38 

#13  
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saeed sangchooly
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Quote:
is there any chance that other versions don't have this bug? 

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