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Wedge water impact DFBI Overset mesh

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Old   March 30, 2014, 15:56
Default Wedge water impact DFBI Overset mesh
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Josef Camilleri
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Hi all,

I am trying to simulate a wedge dropping on a calm water surface using Star CCM+. Overset mesh is used; background region and overset region. In the background region I have two control volumes: one overlapping region with the same cell size as that of the overset region and a water surface control volume. In the overset region I have one control volume surrounding the wedge with a refine mesh. I am using the trimmer model in the background region and trimmer and surface remesher in the overset region. Simulation is transient using the implicit unsteady model. Wedge motion is achieved using the DFBI model with translation in the vertical direction only. Pressure is measured at six different positions along the bottom of the wedge surface

The problem is, when I use a coarse mesh (cell size near wedge = 1.25cm) and a time step of 0.001s the pressure plots seem to be correct however the CFL number is around 5 and the normalized residuals are very high (around 10^7). When I decrease the time step to get lower CFL values, the pressure plots show a lot of noise and the last two pressure probes (located at a 'far' distance from the wedge apex) give negative values. Also, the residuals are still on the order of 10^7.
I get the same results when I refine the mesh and lower the time step.

Any ideas?

Thanks,

Josef
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Old   March 31, 2014, 12:58
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5 is pretty high, I tend to keep the CFL on the free surface to be about 0.5
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