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Birkov April 28, 2010 10:50

Moving mesh adaptation
 
Hi to all,

I have question about moving mesh. I tried to solve 6 DOF case with rigid body beta feature (sphere put in to the water)

If I set denstity to sphere about 200 kg/m^3 sphere is floating and it solved fine, but if I changed density to about 500 and above sphere starts to dive and mesh deformation is very big and sovler stops due to negative elements.

I made very basic mesh
Before defomation
http://img121.imageshack.us/img121/602/normalmesh.jpg
and after deformation
http://img88.imageshack.us/img88/5803/deformedmesh.jpg

My question is if I can control mesh deformation during moving or how to set remeshing after few steps.

Thank you very much for your time.

Birkov

ghorrocks April 29, 2010 08:27

Any moving mesh simulation with a motion of any size runs the risk of folding the mesh. It is very difficult to avoid. If you insist on using the moving mesh approach then you might be able to use a tricky smoothing weighting factor such that elements near walls (or near the sphere) do not get smoothed and ones further away get progressively smoothed. I think there is an example of how to do this in the doco somewhere. This does not always work anyway.

You need to consider a remeshing step. Ask your CFX support person for information about remeshing with a 6DOF solver.

If you can model your stuff using the immersed solid approach then all the mesh folding issues disappear. This is a much easier and more robust approach, but does mean that the mesh resolution around the body is not as good.

Birkov April 29, 2010 08:36

In the future I would like to solve hulls with 6DOF but if I'm not able to set "just" sphere I'll try to find other way.
I'm trying immersed body now so I'll see what will happen.

I'll write to CFX support for help with 6DOF.

Thank you very much.

ghorrocks April 29, 2010 08:42

I have seen a very nice 6DOF simulation of a bomb being dropped from an aircraft wing (I presume dropping medicines or food, nothing nasty I presume). Make sure you check it out, the support people should have it.

Birkov April 30, 2010 03:49

I found this. Maybe it helps for someone with similar problem.

http://www.edr.no/blogg/ansys_blogge...cfx_re_meshing

ghorrocks April 30, 2010 06:28

Nice one! That looks like a very nice tutorial of how to set up a dynamic remeshing simulation. Good work.


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