Hi everyone...
I have been trying to simulate ship movement in Head Waves in Star CCM+ v8.06 using overset mesh. In order to capture the wave height correctly, around 40 cells have to be provided and when I initialize, overset mesh shows error..!!
So I removed volumetric refinement and then tried, It initialized..!!
What I understand is that if the refinement goes less than maximum cell size in the overset mesh (Global Value) it is not getting initialized...
But I can not avoid the volumetric refinement since it is essential for wave simulation.
Anyone experienced same issue..?
Someone can tell me how to resolve this issue..?
Hi Dear Hariharan.
It is very important that height of the refinement should be refined as well as other directions and have some space for the free-surface. It is recommended to not use Over-set mesh, DFBI models could help you. Check the motion specs in the tools node.
hi, I use gambit for CFD problems. For such situations first I use a medium size mesh then after a initial convergence I use the (Adapt) commands which refine the based on y plus or gradians and so on
Thank you AShkan for your answer. You mesh in Gambit and import into Star CCM+..?
Hi Kallath
You need to take care that in the interpolation zone, you have at least a ratio of 1/4 cells to interpolate over. That is, you need to make sure that each cell in the overset or background region has at most 4 cells from the background or overset region. I would recommend something like 1:2.
The problem is most likely in your refinement zones, and it is not an intrinsic Star-CCM+ problem. You need to have the same refinement in both regions.
You will get some headaches until you get the refinements right, but after that it's pretty much straightforward. Be aware that the ship moves, so the size of your fine refinement zones should reflect this. See also that where you have symmetry (assuming you run head seas), this is not part of the overset boundaries.
Hi Cosmin
Thank you for such a detailed answer.
I want to explain my issue a little more to you.
I have attached two .jpg images Case 1 and Case 2. Kindly check them.
When initialize them, Case 1 is okay and Case 2 shows the error "Found Acceptors in Region "Overset" with zero donors . This might be due to too fine or too coarse mesh."
But when we do a head wave simulation, we require a mesh like Case 2 . Correct..?
Thank you
Yes, you do require a fine mesh.
Most likely, the refinement of the free surface in the background does not match the refinement in the overset. Or, you refine equally fine the overset, and don't do anything with the corresponding background mesh towards the corners of your overset.
Again, check that you have about 2 cells in one. This means that e.g. you have x and y sizes equal, and z size half of "the other". If you have x, y and z "half of the other", you already have 8 cells inside one, and it will never work.
Make section planes in both regions, at the same coordinates, in all directions, and check carefully your cell size.
Hi Cosmin,
I think I got it now.Let me try it out.
Thank you very much.
Hi Dear Hariharan.
It is very important that height of the refinement should be refined as well as other directions and have some space for the free-surface. It is recommended to not use Over-set mesh, DFBI models could help you. Check the motion specs in the tools node.
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