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Question about alpha.water in interFoam

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Old   March 13, 2019, 10:36
Default Question about alpha.water in interFoam
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HMQ
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Hi!
I'm very new about OpenFoam. I followed the damBreak tutorial and wanted to change it to jet flow in 3D. I meshed and set the boundary condition with Pointwise, when I checkMesh, it said mesh OK, then I setFields, it looked correctly in paraview. But when I started to compute, the max alpha.water was rapidly becoming much more than larger 1 rapidly, and I cant find the problem.
Here's the error code:



PIMPLE: iteration 1

smoothSolver: Solving for alpha.water, Initial residual = 0. 00144282, Final residual = 5.6773e+102, NO Iterations 1000

Phase-1 volume fraction = 8.32042e+103 Min(alpha .water) = -1.27119e-09 Max(alpha .water) = 4.70168e+110

MULES: Correcting alpha. water

#0 Foam: :error: rintStack (Foam: :Ostream&) at ??:?
#1 Foam: :sigFpe: :sigHandler (int) at ??:?
#2 ? in "/lib/x86_ 64- Linux-gnu/libc.so.6"
#3 Foam: : tmp<Foam : :GeometricField<double, Foam: : fvsPatchField, Foam: : surfaceMesh> > Foam: :mag<Foam: :Vector<double>, Foam: : fvsPatchField, Foam: : surfaceMesh> (Foam: :GeometricField<Foam: :Vector<double>, Foam: : fvsPatchField, Foam: : surfaceMesh>const&) at ??:?
#4 Foam: : interfaceProperties: :calculateK() at ??:?
#5 ? at ??:?
#6 _libc_start_main in "/lib/x86_ 64-linux-gnu/libc. so.6"
#7 ? at ??:?
[1] 98269 floating point exception (core dumped) interFoam |
98270 done tee log


Thanks for your help!
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Old   March 15, 2019, 03:06
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Geir Karlsen
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Your simulation appears to be blowing up. This could be caused by any number of reasons, but from your description I would guess that you have increased the velocity without reducing the time step accordingly (high Courant number). This could cause stability issues. You might need to provide some more information if this does not help you. Please see:

How to give enough info to get help
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Old   March 17, 2019, 22:27
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HMQ
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Thank you for your guidance!
I used Pointwise to mesh and set BC, than exported it into OF. I set the initial conditions accordingly like the tut damBreak and setFields, and I didn't change other factor like fvschemes or others, but it just can't work out. Before I use blockMesh to make the same mesh the same as this and it ran correctly with the value of max/min alpha.water was 1/0. I didn't know if I ignored some important step when I export the mesh?
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Old   July 11, 2019, 05:05
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Chiara Viola
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Hi! Did you solve your problem? I'm running interFoam and I want to simulate a propagation of waves against a dike but I had a similar problem with high value of max (alpha.water) , say 20, and the min value is around -0.06. I had also the floating point exception error and I really don't know how to solve it.

Also, can you explain me please if you understood the meaning of a high value of alpha?I thought that the max value has to be around 1 since it means a cell full of water in the VoF method..
The wave theories I tried are StokesI and StokesII and both gave me errors after 3 seconds of simulation, instead the solitary wave gave me a first overtopping but then the solver was blocked at running the same time step for other hours... Do you have any suggestion?


Best regards,

Chiara
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Old   July 12, 2019, 07:04
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Yang
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Quote:
Originally Posted by HMQ View Post
Thank you for your guidance!
I used Pointwise to mesh and set BC, than exported it into OF. I set the initial conditions accordingly like the tut damBreak and setFields, and I didn't change other factor like fvschemes or others, but it just can't work out. Before I use blockMesh to make the same mesh the same as this and it ran correctly with the value of max/min alpha.water was 1/0. I didn't know if I ignored some important step when I export the mesh?
Hi, HMQ
I used the mesh generated from Pointwise to calculate a two-phase flow problem before. Divergence happened but I dont why. Using the blockMesh tool with the same case is ok. So I guess maybe sth is not right in the mesh exported from pointwise and I dont use it anymore...
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Old   March 21, 2020, 14:46
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Gui Miotto
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I had this issue too. The problem was also caused by the mesh.
Eventhough
Code:
checkMesh -allGeometry -allTopology
was all OK, the mesh was somehow broken. I generated it again changing some minor details and the exploding alpha vanished.
I still don't know what was wrong with the first mesh.
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