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transient ship hull with free surface: Unwanted wave pattern

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Old   October 16, 2019, 19:12
Unhappy transient ship hull with free surface: Unwanted wave pattern
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Erick Giraldo Perez
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Hi all

I am simulating a static monohull in transient state at 5 m/s in order to study wave pattern formation and the hull drag. By now, i'm dismissing trim angle and sinkage because I want to dominate simpler cases first.

In the link I attach below, there is a video showing the animation. It can be seen a wave formation coming from the inlet, which is absolutely undesirable since my objective is to simulate the hull in calm water conditions. In the VOF setup I made sure "Open channel flow" was activated instead of "open channel wave bc" so I do not know what is the cause of this wave formation.

In boundary conditions I have the next setup

-Inlet: pressure inlet, 5 m/s, surface level: 0 m, bottom level: -200 m (there is not the possibility of the waves forming due to shallow water effects). Located at 3.5 hull lengths (LoA)
-Outlet: Pressure outlet, equal conditions for surface and bottom. Located at 7 hull lengths (LoA)
-Symmetry: ship is cut in half lenghtwise by a plane
- Wall (boat hull): stationary wall, no slip, standard roughness, 90 contact angles
- Imaginary walls of the tunnel (symmetry), far field condition. located at (away from the boat) 1.6 LoA portside and 1 LoA top and bottom.

I already patched it (see image attached) and checked the materials were properly assigned to every mesh zone. I am using a k-omega SST turbulence model.

The only clue I have found is that when I plotted the static pressure contour at the inlet and outlet, it can be observed a slightly difference in pressure at the bottom and they should be equal, unless the wake of the hull is changing the pressure (but it should change all the pressure countour, not only the bottom).

I also attach an image of the mesh. It is a conformal mesh so a matching static configuration was chosen for the interface between the hexa en tetra meshes. It can be observed a refinement was made near the free surface and an inflation near the hull in order to account for the boundary layer effects. The result was a mesh of 2'245.675 mixed cells, 685.000 of them hexahedral and the other tetrahedrical.

Kindly help me with this, it should not be happening since all the boundary conditions should be ok .

link to the animation:

PD: I did not find the way to attach the video so i attached the link. In case you do not want to open the link on suspicious of i want to infect your pcs with a virus or the like (which i'm certainly not), I can attach you images of the free surface.

Thank you all beforehand!
Attached Images
File Type: png volumeFraction.PNG (17.8 KB, 21 views)
File Type: jpg pressure-InletOutletFreesurface.jpg (53.2 KB, 29 views)
File Type: jpg mesh.jpg (140.9 KB, 22 views)
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conformal mesh, free surface, ship hull, transient 3d, wave generation

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