Re-Meshing
 

Hi,

I have a buoyant object in water and air that is moving on waves (translational & rotational) created by a moving wall. I'm using a rigid body solution but I keep getting errors. I think my setup is correct so I'm wondering if you have to do remeshing with this type of rigid body?

It is a bit easier to guess what the problem is when you include the error message.

While you are at it, include your CCL and an image of what you are modelling.

This is the image of what I'm modelling http://i.imgur.com/3kn8Iuv.png. I think it could possibly be a problem with my ccl alright.

Here are the ccls I'm using : volume fraction for water--> step(1-y / 2.5 [m]). volume fraction for air--> 1.0 - water vf. Motion of the moving wall--> if( x >= 0[m], wxdisp*x/(5[m]+wxdisp), 0[m])

where: "wxdisp"-->if( (t-tOn) >=0[s], -0.5[m]*sin(min(t-tOn,0.5[s])*(pi/2.[s rad^-1])), 0[m]).
"tOn"--> 0.075 [s]

The solution runs and begins plotting the data but after a few minutes (accumulated timestep = 12, where the timestep is 0.025 [s] running for 3 [s]) I get a "size mismatch" error where the solver "expected 191 values, but found 54". The solver still runs for awhile but records no data on the graph and eventually ends with an "error return code 1" and then "the solver failed with a non-zero exit code of : 2"

I have tried using a simple wall movement ccl--> if(x>=2[m], -1[m], 0[m]) but the solution doesn't run and ends with an "error return code 1" and then "the solver failed with a non-zero exit code of : 2"

Please post the full and actual CCL from your simulation, not just editted highlights.

Also post your output file which shows the error message.

Looks like you are doing the tutorial from CFX.

The size mismatch is unrelated to the solver crashing. I used to get this alot when monitoring solutions running across a network. Seems the solver manager gets confused on the graphing. Closing Solver Manager and reopening will fix this (at least until it occurs again).

I have run that tutorial before. Using the settings "as-is" will not allow it to run indefinately. It does indeed diverge. Before you ask me, no, I did not try to "fix" it to run on out. I was only interested in the setup and method, which the tutorial does fine with.

Sorry for the late reply Glenn I couldn't get onto a computer with Ansys. These are all of my expressions http://i.imgur.com/QgVZesK.png

Firstly I get a size mismatch error and then I get : An error has occurred in cfx5solve: |
| |
| The ANSYS CFX solver exited with return code 1. |
+--------------------------------------------------------------------+

End of solution stage.

+--------------------------------------------------------------------+
| The following transient and backup files written by the ANSYS CFX |
| solver have been saved in the directory U:/My |
| Documents/FYP/upsol1_pending_tasks/dp0_CFX 1_Solution_1-1/Fluid |
| Flow CFX_012: |
| |
| 9.trn, 6.trn, 3.trn, 24.trn, 21.trn, 18.trn, 15.trn, 12.trn, 0.trn |
+--------------------------------------------------------------------+


+--------------------------------------------------------------------+
| The results from this run of the ANSYS CFX Solver have been |
| written to U:/My Documents/FYP/upsol1_pending_tasks/dp0_CFX |
| 1_Solution_1-1/Fluid Flow CFX_012.res |
+--------------------------------------------------------------------+


This run of the ANSYS CFX Solver has finished.​

Yes its basically a simplified version of the "Buoy" tutorial (without the subdomain & interface) however I've looked at this several times and i still can't get my solution to run so maybe it's my wall movement expression?

I am not asking for just the expressions. I need the full CCL of your simulation to see what you have done. I suspect you do not know what the CCL is.....

In that case please post the full output file of a simulation as an attachment, or linked to somewhere.

I think these are my results here, you should be able to see them. https://www.dropbox.com/s/ct1ozyce8l..._007_cgns.cgns

It is pretty obvious what has happened there. You mesh has got squashed to oblivion on the bottom of the hull.

You still have not posted your CCL or an output file. I am going to give up asking soon.

Sorry I did't realise what to send, here is the output file https://www.dropbox.com/s/gj46yj30opjwbnx/output.txt

At last. And as usual, it has shown some major issues - that is why we ask for it.

You are using a mixture model multiphase model, but have turned free surface model off. Why did you do this? If this thing is meant to be floating on the water surface you will need to turn the mixture model off and turn free surface model on.

There is a CFX example of a buoy floating on the water surface. It does not come with CFX but ANSYS support will have it. You should ask support for it because it will show you exactly how to set this sort of simulation up.

I've changed the option to free surface and emailed ANSYS support for an example but I'm waiting for a reply. The problem with the solver crashing seems to be that the Hull doesn't remain floating on the water and falls down dragging the enclosure with it as the failed results show http://i.imgur.com/a7kmfuu.png

My reference density for buoyancy is set as the same same as the air (1.185 kg m^-3).

Do you know why this could be happening? Here is my output file https://www.dropbox.com/s/z7z3prllkedpuo8/output2.txt

You are not using the correct multiphase model so a free surface will not form. The hull floats on the fluid interface so you have to establish a proper fluid interface before it will float.

Can you post an image of the initial condition of volume fraction, and what it looks like after a few time steps.