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VOF waves breaking in my simulation

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Old   December 10, 2010, 12:23
Default VOF waves breaking in my simulation
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Mehrdad
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I am trying to generate first order VOF waves with amplitude of 0.405m and wave period of 2.5 s.
After few iterations waves start to break. Is it because of incorrect BC or large time step or....
I am using t=0.003 s and boundary conditions are velocity inlet at left hand side and pressure outlet at right hand side and symmetry plane on two sides of simulation.
Any help in the regard would be highly appreciated.
Thanks.
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Old   December 11, 2010, 18:15
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Naimish Harpal (MS Aerospace Engr)
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Hi,
It seems that the BCs are not defined correctly. Make sure you define Inlet BC including Front and Side walls of the domain. Also, for velocity inlet and pressure outlet regions, define velocity & pressure as 'Velocity of FirstOrderVofWave' and 'Hydrostatic Pressure of FirstOrderVofWave'. Furthermore, specify the Volume Fraction as 'Composite' and define them with corresponding Volume Fraction of Heavy OR Light Fluid of FirstOrderVofWave.

I don't know your problem, but time-step of 0.003 s looks very small. Try 0.01s since your wave-length is 2.5s.

Let me know if you have further questions.
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Old   December 11, 2010, 23:45
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Mehrdad
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Thank you so much for your reply.
I used pressure outlet on right hand side and velcoity inlet in left hand side and on top and bottom and sides of simulation domain. (kind of similar to DFBI tutorial in starccm manual).I also defines velocity and pressures correctly (as the tutorial)
I used T=0.01s and H=0.405m. Still it seems that waves deform abnormally as you see in these pictures. Can you please help me figure this out ? (looks at the figures I posted under this post)
Thank you so much
Attached Images
File Type: jpg Scene_3image00600.jpg (23.6 KB, 66 views)
File Type: jpg Scene_3image01200.jpg (23.6 KB, 56 views)
File Type: jpg Scene_3image01800.jpg (23.6 KB, 50 views)
File Type: jpg Scene_3image03000.jpg (23.5 KB, 48 views)
File Type: jpg Scene_3image03600.jpg (23.5 KB, 50 views)
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Old   December 11, 2010, 23:59
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Naimish Harpal (MS Aerospace Engr)
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I see what's the problem. Most probably, you don't have mesh resolution on free surface (after breaking point).
(infact this is the method used to avoid wave interaction near the side walls of domain by defining coarse mesh)
Anyways, use fine mesh using control volume box method near entire free-surface. I am hoping that it will resolve the problem if your physics model setup is correct.

Thanks.
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Old   December 12, 2010, 05:27
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Mehrdad
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I have refined the mesh on free surface (mesh size on free surface is about 2.4cm)
still the wave changes its shape although I am using inviscid model not sure why it becomes steeper as it progress.
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File Type: jpg Scene_5image01200.jpg (22.1 KB, 26 views)
File Type: jpg Scene_5image03600.jpg (22.1 KB, 28 views)
File Type: jpg Scene_5image05400.jpg (22.1 KB, 31 views)
File Type: jpg Scene_5image07100.jpg (22.3 KB, 34 views)
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