# free surface

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 June 1, 2006, 04:23 free surface #1 Zhoulin Guest   Posts: n/a Anyone knows how to make the VOF surface appear? I am doing VOF simulation for flow over ships, in unsteady state.using time step of 0.05, 1000 times steps. After that,I tried adapting the surface to gradient of volume fraction, but could not see free surface of water. I have already patch the water and air by volume fraction before iterating. Anyone got any idea? Thanks.

 June 1, 2006, 05:42 Re: free surface #2 Charles Guest   Posts: n/a Make an iso-surface of water volume fraction=0.5

 June 1, 2006, 06:05 Re: free surface #3 Gernot Guest   Posts: n/a To create the surface : surface / iso-surface : surface of constant : phases Iso - Values : 0.5 ( for example )

 June 5, 2006, 02:10 Re: free surface #4 zl Guest   Posts: n/a does anyone know whether adapting is needed , in order to see the free surface?

 June 5, 2006, 02:52 Re: free surface #5 Charles Guest   Posts: n/a No. To see the free surface you only need to plot an iso-surface of volume fraction = 0.5. It is possible to adapt the mesh to the volume fraction to better capture the surface, but if you are going to be doing that the best way is to use the geo-reconstruct scheme, and to let that do the adaption.

 June 5, 2006, 09:33 Re: free surface #6 zl Guest   Posts: n/a i got one big problem: My residual does not go down. I am using unsteady , implicit, time step 0.05. No matter how i adjust (to low levels) my under relaxation factors, i cant get the residuals to go down. I am using almost 700000 hex cells.

 June 5, 2006, 09:47 Re: free surface #7 Charles Guest   Posts: n/a Unless you are particularly interested in the transient, you could give steady implicit a try. This is not a great problem for monitoring convergence on residuals, you definitely need to monitor your forces as well. Get used to the idea that convergence is going to take a looooong time. I think this is at least partly related to the fact that disturbances and inaccuracies can only propagate out at wave speed, not the speed of sound.

 June 5, 2006, 21:25 Re: free surface #8 zl Guest   Posts: n/a i follow the advice creating iso surface 0.5 of water volume fraction but only see very subtle free surface. I am using unsteady implicit. I have seen people successful with that method. anyone can advised on exactly what might be wrong that i cant see the free surface?

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