[asubram8]

Hi All,
I have been trying to simulate the flow of waves over a spherical body as a project. For the numerical wave tank I have chosen a velocity inlet boundary condition for inlet, pressure outlet for the outlet and top. Bottom and far field are walls and I am using a symmetry plane. I have defined the inlet velocity and outlet pressure in terms of field functions of the waves. However I can see on the volume fraction scalar that there is a water build-up in the system.


Can anyone give me any ideas on what could be going wrong?
TIA
Akshith

[ashokac7]

Originally Posted by asubram8

Hi All,
I have been trying to simulate the flow of waves over a spherical body as a project. For the numerical wave tank I have chosen a velocity inlet boundary condition for inlet, pressure outlet for the outlet and top. Bottom and far field are walls and I am using a symmetry plane. I have defined the inlet velocity and outlet pressure in terms of field functions of the waves. However I can see on the volume fraction scalar that there is a water build-up in the system.


Can anyone give me any ideas on what could be going wrong?
TIA
Akshith

This is like inherited problem with VOF. To end up getting wrong volumes of phases. You may try to play with mesh or physical set up. But exact Eulerian multi-phase will give more accurate solution, which is as we know, on cost of more computational resource. But Eulerian multi-phase will provide data to compare your VOF results. So you can adjust the VOF results accordingly.

[asubram8]

Originally Posted by ashokac7

This is like inherited problem with VOF. To end up getting wrong volumes of phases. You may try to play with mesh or physical set up. But exact Eulerian multi-phase will give more accurate solution, which is as we know, on cost of more computational resource. But Eulerian multi-phase will provide data to compare your VOF results. So you can adjust the VOF results accordingly.

I am using a Eulerian Multiphase model. I can still see the increase in volume fraction of water. I personally feel this is a problem with the physics set-up as I did refine the mesh and make it coarse near the outlet so as to damp wave reflections into the system.
Any further comments?


TIA
Akshith

[HHK]

Originally Posted by asubram8

I have been trying to simulate the flow of waves over a spherical body as a project. For the numerical wave tank I have chosen a velocity inlet boundary condition for inlet, pressure outlet for the outlet and top. Bottom and far field are walls and I am using a symmetry plane. I have defined the inlet velocity and outlet pressure in terms of field functions of the waves. However I can see on the volume fraction scalar that there is a water build-up in the system.

Do you mind posting some pictures? I just want to see.

[asubram8]

Originally Posted by HHK

Do you mind posting some pictures? I just want to see.

Hi

Sorry for the delayed response.
This is how my volume fraction scene looks like before the run and after.volume_fraction_initialization.jpg

volume_fraction_after_run.jpg

[asubram8]

Do you have any suggestions as to what could be the problem? I have tried various meshing techniques and even used Ansys Workbench for meshing. The problem still seems to be there and it looks like something is wrong with the way I am defining my physics conditions.

[HHK]

Hi

I believe you are using VOF model.
My comments are (which come to my mind now),

1. Why the top and bottom boundaries are nearer to the sphere? Did you trying increasing them? (At least the depth).

2. If you are using first order (or fifth order wave), how many layers of cells did you keep to refine the wave height and wave length? I recommend to go for 40 layers cells per wave height and 80 layers of cells per wave length.

3. Is the sphere submerged at the starting point? I hope you set the water level in VOF Waves module correctly.

4. Are you using DFBI module to analyse the motions or the sphere is fixed? If you are using DFBI, are the initial values of rigid body properly set?

5. How did you choose you time-step? Is it 2nd order accurate? I recommend to choose 1/200th of your wave period.

Hope this helps.

[raquelcfd]

Hello,

Have you tried to change the boundary conditions?
I mean, It is usually to use the velocity inlet conditions in de inlet but also in the laterals of the tank and in the top side. Then use the wall condition in the botton and pressure outlet for the outlet.

[hamedha1371]

Originally Posted by asubram8

Hi All,
I have been trying to simulate the flow of waves over a spherical body as a project. For the numerical wave tank I have chosen a velocity inlet boundary condition for inlet, pressure outlet for the outlet and top. Bottom and far field are walls and I am using a symmetry plane. I have defined the inlet velocity and outlet pressure in terms of field functions of the waves. However I can see on the volume fraction scalar that there is a water build-up in the system.


Can anyone give me any ideas on what could be going wrong?
TIA
Akshith

Hello there. use wave damping at the outlet. set the damping length to be at least one wavelength. your tank should be long enough so that the sphere won't be in the damping area. try it and let me know if it works! good luck