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-   -   VOF waves breaking in my simulation (http://www.cfd-online.com/Forums/star-ccm/82989-vof-waves-breaking-my-simulation.html)

mbn1454 December 10, 2010 12:23

VOF waves breaking in my simulation
 
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....:confused:
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.

naimishharpal December 11, 2010 18:15

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.

mbn1454 December 11, 2010 23:45

5 Attachment(s)
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

naimishharpal December 11, 2010 23:59

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.

mbn1454 December 12, 2010 05:27

5 Attachment(s)
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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