Problems moving a ball - mesh crashes

ghorrocks · February 16, 2016, 04:10

I think I can see the problem. You have the side walls of the multibody mesh bit set to mesh motion option stationary. It should be set to undefined.

lbergmann · February 16, 2016, 04:36

I just tried running with "undefined" It changed nothing. The ball moves back and fourth a little before it crashes just the same way as before.

lbergmann · February 16, 2016, 04:46

Also, why does it move back and fourth not just in one direction? I just tried raising the inlet velocity, but only change was the amount of iterations before crashing. I am monitoring the mesh displacement while solving

ghorrocks · February 16, 2016, 05:00

If the ball moves back and forth (it was not clear what it was doing versus time in the images) that is a sign of numerical instability. Try smaller time steps. I am not too familiar with the rigid body solver, but look for options which improve rigid body convergence and accuracy.

lbergmann · February 16, 2016, 08:01

Thanks for all your help. I am trying to fiddle with the solver controls now. I have a time step of 1e-7, hope I don't have to go lower than that.

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February 16, 2016, 04:10		#21
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	I think I can see the problem. You have the side walls of the multibody mesh bit set to mesh motion option stationary. It should be set to undefined.

February 16, 2016, 04:36		#22
lbergmann New Member Line Bergmann Join Date: Sep 2013 Posts: 20 Rep Power: 12	I just tried running with "undefined" It changed nothing. The ball moves back and fourth a little before it crashes just the same way as before.

February 16, 2016, 04:46		#23
lbergmann New Member Line Bergmann Join Date: Sep 2013 Posts: 20 Rep Power: 12	Also, why does it move back and fourth not just in one direction? I just tried raising the inlet velocity, but only change was the amount of iterations before crashing. I am monitoring the mesh displacement while solving

February 16, 2016, 05:00		#24
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	If the ball moves back and forth (it was not clear what it was doing versus time in the images) that is a sign of numerical instability. Try smaller time steps. I am not too familiar with the rigid body solver, but look for options which improve rigid body convergence and accuracy.

February 16, 2016, 08:01		#25
lbergmann New Member Line Bergmann Join Date: Sep 2013 Posts: 20 Rep Power: 12	Thanks for all your help. I am trying to fiddle with the solver controls now. I have a time step of 1e-7, hope I don't have to go lower than that.