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Negative pressure

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Old   April 10, 2014, 03:30
Default Negative pressure
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Josef Camilleri
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Hi all,

I am trying to simulate a wedge falling onto a calm water surface using Star CCM+. I am using the overset mesh model and DFBI rotation and translation. I have a background region with two volumetric controls (an overlap and one for the water surface) and an overset region with one volumetric control a refined block around the wedge. The mesh (Wedge2A_Mesh) can be seen in the first image attached. The pressure plots (Wedge2A_Pressure P1 - P6 Plot) can be seen in the second image.

The problem is that when I change the height of the refined block around wedge (Wedge5A_Mesh), I start getting negative pressures after the 6 pressure probes (seen as orange spheres in the image) become immersed (Wedge5A_Pressure P1 - P6 Plot). I created a pressure and velocity scalar scene to see where these negative pressures are coming from. I noticed that the air part of domain becomes negative (around -2000Pa) when the wedge becomes immersed (Wedge5_Pressure Scalar). Can anyone give a physical explanation to this?

What I wanted to know is if any of you know what might be causing this negative pressure. I have tried a number of different options but none of them worked so far:
1. Green-Gauss gradient to check if the problem is coming from the mesh
2. Increased the height of the background domain to avoid influence from bottom wall
3. Inviscid and laminar models
4. Reference density = 0
5. Different heights below and above the wedge

Any ideas?
Attached Images
File Type: jpg Wedge2A_Mesh.jpg (21.3 KB, 21 views)
File Type: jpg Wedge2A_Pressure P1 - P6 Plot.jpg (42.9 KB, 17 views)
File Type: jpg Wedge5A_Mesh.jpg (36.9 KB, 17 views)
File Type: jpg Wedge5A_Pressure P1 - P6 Plot.jpg (45.3 KB, 20 views)
File Type: jpg Wedge5_Pressure Scalar.jpg (25.4 KB, 15 views)
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Old   April 10, 2014, 05:27
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the negtive pressure in air do not influent your result. you can set your pressure reference point in the air zone. then you can get the proper pressure in the air zone.
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negative pressure, overset mesh, pressure, water impact, wedge

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