Rigid body

Birkov · February 1, 2010, 04:19

Hi to all,
I tried solve rigid body (beta) and I have few questions if anybody can help me.
First I tried just put cube in to the water to find out how to work with rigid body. I can't find any tutorials to solve rigid body so I combined few similar tutorials. It seems to be working but soon or later I get negative element error. I tried change time step or make finer mesh but I got same error. Is any known relevance between mesh and time step for rigid body solution?

Model is make as cube[20x20x20[m]] in cube[2x2x2[m]].
For domain cube I used 5 faces as wall and top face as open BC.
Initial condition: HydroP by expre., VaterVF by expre., speed in all directions is 0.
Rigid cube is drowned (1/2).

I will be happy for every suggestions and advice.

Thank you very much.

B.

ghorrocks · February 1, 2010, 17:03

The negative element volume means a mesh element has turned itself inside out. This means you need to either improve your mesh smoothing approach or do a remeshing step.

Alternately you could use the immersed body solver and you will have no mesh problems, but you will loose boundary layer fidelity. But for bodies which have a large motion the immersed body solver is a good choice as the grid motion is very difficult to get working.

smn · February 2, 2010, 01:17

Quote:

Originally Posted by Birkov

Hi to all,
I tried solve rigid body (beta) and I have few questions if anybody can help me.
First I tried just put cube in to the water to find out how to work with rigid body. I can't find any tutorials to solve rigid body so I combined few similar tutorials. It seems to be working but soon or later I get negative element error. I tried change time step or make finer mesh but I got same error. Is any known relevance between mesh and time step for rigid body solution?

Model is make as cube[20x20x20[m]] in cube[2x2x2[m]].
For domain cube I used 5 faces as wall and top face as open BC.
Initial condition: HydroP by expre., VaterVF by expre., speed in all directions is 0.
Rigid cube is drowned (1/2).

I will be happy for every suggestions and advice.

Thank you very much.

B.

hi:
have you tried v11 or v12?

Birkov · February 2, 2010, 01:24

Thank you very much.

I will try improve my mesh(I already working on it) and try solve rigid body by immersed body solver for now.

I tried v12.

B.

belgacem · May 25, 2012, 06:26

Hi ghorrocks
I am also studying immersed boundary method and and try to simulate a block falling in the water. I am using "immersed solid" then rigid body 6DOF and I let it fall freely but it can't stoped in the bottom where the velocity must be zero. I give a density to the block and i let it fall freely under gravity. Noted that the rigid body is defined as an immersed solid. i have specified a stationary coordinate frame that has its origin at the center of mass of the physical rigid body. Another fixed coordinate frame was specified related to the water at rest.
What can I do to stopped the rigid body in the bottom where the potentiel energy must be zero?

thank you!

February 1, 2010, 04:19	Rigid body	#1
Birkov New Member Join Date: Jul 2009 Location: Prague Posts: 28 Rep Power: 0	Hi to all, I tried solve rigid body (beta) and I have few questions if anybody can help me. First I tried just put cube in to the water to find out how to work with rigid body. I can't find any tutorials to solve rigid body so I combined few similar tutorials. It seems to be working but soon or later I get negative element error. I tried change time step or make finer mesh but I got same error. Is any known relevance between mesh and time step for rigid body solution? Model is make as cube[20x20x20[m]] in cube[2x2x2[m]]. For domain cube I used 5 faces as wall and top face as open BC. Initial condition: HydroP by expre., VaterVF by expre., speed in all directions is 0. Rigid cube is drowned (1/2). I will be happy for every suggestions and advice. Thank you very much. B.

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February 1, 2010, 17:03		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	The negative element volume means a mesh element has turned itself inside out. This means you need to either improve your mesh smoothing approach or do a remeshing step. Alternately you could use the immersed body solver and you will have no mesh problems, but you will loose boundary layer fidelity. But for bodies which have a large motion the immersed body solver is a good choice as the grid motion is very difficult to get working.

February 2, 2010, 01:24		#4
Birkov New Member Join Date: Jul 2009 Location: Prague Posts: 28 Rep Power: 0	Thank you very much. I will try improve my mesh(I already working on it) and try solve rigid body by immersed body solver for now. I tried v12. B.

May 25, 2012, 06:26		#5
belgacem New Member belgacem Join Date: Jan 2012 Posts: 22 Rep Power: 14	Hi ghorrocks I am also studying immersed boundary method and and try to simulate a block falling in the water. I am using "immersed solid" then rigid body 6DOF and I let it fall freely but it can't stoped in the bottom where the velocity must be zero. I give a density to the block and i let it fall freely under gravity. Noted that the rigid body is defined as an immersed solid. i have specified a stationary coordinate frame that has its origin at the center of mass of the physical rigid body. Another fixed coordinate frame was specified related to the water at rest. What can I do to stopped the rigid body in the bottom where the potentiel energy must be zero? thank you!