Moving mesh adaptation

Birkov · April 28, 2010, 11:50

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, 09:27

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, 09:36

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, 09:42

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, 04:49

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, 07:28

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

April 28, 2010, 11:50	Moving mesh adaptation	#1
Birkov New Member Join Date: Jul 2009 Location: Prague Posts: 28 Rep Power: 0	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

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April 29, 2010, 09:27		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,854 Rep Power: 144	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.

April 29, 2010, 09:36		#3
Birkov New Member Join Date: Jul 2009 Location: Prague Posts: 28 Rep Power: 0	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.

April 29, 2010, 09:42		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,854 Rep Power: 144	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.

April 30, 2010, 04:49		#5
Birkov New Member Join Date: Jul 2009 Location: Prague Posts: 28 Rep Power: 0	I found this. Maybe it helps for someone with similar problem. http://www.edr.no/blogg/ansys_blogge...cfx_re_meshing

April 30, 2010, 07:28		#6
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,854 Rep Power: 144	Nice one! That looks like a very nice tutorial of how to set up a dynamic remeshing simulation. Good work.