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Emergency! Problem in multiphase Simulation

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Old   December 14, 2012, 11:24
Exclamation Emergency! Problem in multiphase Simulation
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Mohammad Fereshtehpour
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Dear friends
Hi
I couldn't model flow in pipe correctly and as you can see in the pictures attached, depth of flow increases as time passes. It is impossible in reality. I really test a lot of ways to overcome this problem but I didn't succeed. Now I'm in pressure because of my results and lack of time.

Thanks in Advance
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Old   December 15, 2012, 07:16
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Try a hex mesh
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Old   December 15, 2012, 09:28
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Quote:
Originally Posted by akidess View Post
Try a hex mesh
Dear Anton, thanks for your reply
I use salome for meshing. As you can see in the picture attached here I have to mesh both pipe and connected box. I've tried a lot of way to use hexa mesh but I didn't succeed due to this combination of pipe and box.

Do you know exactly why this event happen?
What should I do to overcome the problem in meshing?
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Old   December 15, 2012, 13:42
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Greetings to all!

@MOHAMMAD67, I'm sorry to say that I'm only able to give some hints:
  1. Always check your mesh before trying to use the solver! First use:
    Code:
    checkMesh
    And out of suspicion, you should also check with the full diagnostics, just in case:
    Code:
    checkMesh -allGeometry -allTopology
  2. Did you first try doing a simpler version of your case? For example, a simple long box, just to first confirm that you were configuring the solver properly?
  3. A good mesh can be a serious pain to generate, specially if you have little time. If it was some weeks earlier, I would suggest that you try SwiftBlock and/or SwiftSnap instead of Salome.
Good luck!
Bruno

Last edited by wyldckat; December 16, 2012 at 06:21. Reason: typo...
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Old   December 16, 2012, 05:01
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Are you really sure it is unphysical? Is it steady state? If so, you can integrate (in paraview) mass flow across intersections to see if you really loose mass. The water depth level alone cannot tell, as mass flow through a pipe intersection is: area(depth) * U(x,y,z)

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Old   December 16, 2012, 12:20
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Quote:
Originally Posted by kalle View Post
Are you really sure it is unphysical? Is it steady state? If so, you can integrate (in paraview) mass flow across intersections to see if you really loose mass. The water depth level alone cannot tell, as mass flow through a pipe intersection is: area(depth) * U(x,y,z)

K
i agree, it can be told it is unphysical just by the height of water, it may be a slug, and it is totally physical phenomena
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Old   December 16, 2012, 13:30
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Quote:
Originally Posted by kalle View Post
Are you really sure it is unphysical? Is it steady state? If so, you can integrate (in paraview) mass flow across intersections to see if you really loose mass. The water depth level alone cannot tell, as mass flow through a pipe intersection is: area(depth) * U(x,y,z)

K
Dear friend
I also model it experimentally and I haven't see such a these phenomenon. This event change for each flowrate. for example in a particular case with constatnt mesh, for Q=25 l/s pipe will be pressurized!!! but for an upper Q just increase in water depth happened.
Could it be related to boundary conditions? I use an air inlet in the upstream end of the pipe and atmosphere for upper wall of the box.
However, I think here mesh is very important and I'm really interested in hex mesh for upstream pipe. Is there an easy way to do this nothing that I haven't work with snappy hex mesh yet.?
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Old   December 16, 2012, 14:17
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is it a steady solution?

yes, it is possible to use snappyHexMesh for generate hex mesh for this geometry
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Old   December 16, 2012, 14:29
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Quote:
Originally Posted by nimasam View Post
is it a steady solution?

yes, it is possible to use snappyHexMesh for generate hex mesh for this geometry
Dear Sam
Salaam

Water depth in the upstream pipe reaches steady state but generally it's a transient problem.

I've searched about snappyhexmesh today. But I couldn't understand how I can create geometry with .stl format. Does it need another software?
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Old   December 16, 2012, 15:38
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as your geometry is not so complicated, i guess you can make stl file even with paraview (maybe seems strange)
also i think you can do it even with out stl, file, i think you need to dig more snappyHexMesh in OpenFOAM
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Old   December 21, 2012, 14:27
Default Problem of meshing solved but depth increasing is still seen
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Dear Friend
Fortunately, My problem related to use hexahedral mesh has been solved with the help of my friend Saint Michael in Salome forum.
If you are interested, you can see this page:

http://www.salome-platform.org/forum/forum_10/61041109



But my problem is still seen!!
I don't know what to do? please help

Best Wishes
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Old   December 21, 2012, 16:16
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some general recommendations:
1- in fvSolution, turn on momentom prediction
2- increase alpha correction
3- increase non-orthogonality correction
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