Learning Forum

[Sellera]

Hello, I'am trying to model a ship roll natural deacay. 

But when I'am trying to calculate, it aborts saying there is 1 cell with negative volume. I've suppose that its probably because the remeshing can't follow at the time of one time-step, but I've already tried to reduce the time step a lot and the same error appears. Any idea on how to solve?

Edit: I just made my mesh a little coarsen and adjust the inflation and the calculation seems to improve going trought much more timesteps, but the negative volume cell problems persists and aborted again with 7746 negative volume cells. My time step size was 0.01 and the number of time steps 3000.(transient)

Follow the image of my setups and mesh.

[Federico]

Hello, 

in the remeshing settings window, click on Mesh Scale info and enter the reported sizings as parameters. You can also set the remeshing interval to 1.

[Sellera]

Hello thanks for your response.

What do you mean by entering the reported sizings as parameters?

I've tried to set the remeshing interval to one, but the problem persists.

[Federico]

If you click on Mesh Scale Info, you will get a new window which reports the actual scales of your mesh. Use the reported minimum as the Minimum Length scale, and reported maximum as the maximum. This should help with remeshing to keep a similar distribution as you have initially.

[Sellera]

 

 

I’ve done that too, but the problem still happening.

A little update: After I’ve removed the de inflation due the “instability” of oriented cells with the dinamic mesh but the problem with the dynamic mesh didn’t change.

 

 

[Federico]

Are your inflation layers moving along with the ship? I would suggest separating the boundary layer zone from the main fluid and assigning a passive rigid body motion to follow your ship.

To do this, create a Boundary cell register for the inflation layer:

Then separate the newly created cell register from the corresponding fluid zone:

Finally, in Dynamic mesh zone settings, set the inflation layer zone with rigid body motion with 6DOF set as passive. Select the same motion as for the Ship.

 

[Sellera]

Thaks for your response, actually I've removed the inflation. Due to inflation are organized cells they were having problems when the are "compressed" by the cell movement. 

Now, I've done a sphere of influence sizing and decreased the pressure coeficient the simulation finished with no prolems.

The only thing now is the time motion history(I need it to se if my experimental simulation is verified), I've selected to send it to my paste but I don't knows its extension.(Im my paste there are a .LOCK and a .Project_Cache) Do you know if there is any of these?

 

 

[Federico]

Glad to see that you were able to complete your simulation.

Not sure what you mean by "paste".

Make sure you enabled the Write Motion History from the SixDOF settings dialog box. If you have, you should be able to locate where it was stored as well on this page.

The extension of the file should be .6dof

[Sellera]

Hello, sorry for the late reponse. Thanks for your support, I've managed to obtain the 6DOF archive. Now I'm trying to make the daming to be equal with my experimental, but now I don't know what to try next. 

I will make a new post, since its a different subject but you have any idea on what could be could you give me some advice? Follow the difference between experimental(orange) and what I obtained in Ansys(blue).

Since the problem with the negative cells I'am working on elevation the coefficient of pressure from 0.09 initial since could be the reason of that diference but now I'm not seeing more improvemente making it higher.

Any idea of what can I do to improve my results?