rigid Body levitation

FrankW · March 19, 2024, 04:05

Hi,

I try to make a small sphere (density slightly higher than water) levitate in water. The sphere is being streamed from below. In a transient simulation, I get absurdly high accelerations of the ball at the beginning and the smaller I make the time steps, the higher the acceleration becomes. Is there a way to dampen this?

best regards
Frank

ghorrocks · March 19, 2024, 16:46

High accelerations on start up are not a problem as long as they settle down quickly to a sensible value. This start up transient should sort itself out quickly and end up only being a insignificant blip at the start of the results. So I would let your simulation continue and see if it progresses well.

FrankW · March 20, 2024, 03:25

I then managed it. The simulation is running. Unfortunately, I had to use the "General Coupling Control" to get it stable. But when I use it, the automatic timestepping doesn't work.

March 19, 2024, 04:05	rigid Body levitation	#1
FrankW Member Frank Weise Join Date: Mar 2009 Location: Germany Posts: 55 Rep Power: 17	Hi, I try to make a small sphere (density slightly higher than water) levitate in water. The sphere is being streamed from below. In a transient simulation, I get absurdly high accelerations of the ball at the beginning and the smaller I make the time steps, the higher the acceleration becomes. Is there a way to dampen this? best regards Frank

March 19, 2024, 16:46		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	High accelerations on start up are not a problem as long as they settle down quickly to a sensible value. This start up transient should sort itself out quickly and end up only being a insignificant blip at the start of the results. So I would let your simulation continue and see if it progresses well. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Whole domain movement rigid body with overset	pj_design	OpenFOAM Running, Solving & CFD	1	March 23, 2024 08:52
Specifying Mesh Deformation & Rigid Body Motion on a Cell Zone Using UDF	zx9cp	Fluent UDF and Scheme Programming	3	July 11, 2023 05:14
Rigid body in creeping flow - COMSOL	MultiPhy	CFD Freelancers	1	June 8, 2017 01:38
rigid body motions- no external force	armin najarian	Main CFD Forum	1	July 6, 2016 03:19
Rigid body motion on transient fluent mrf	ghost82	EnSight	4	September 6, 2014 11:24

March 20, 2024, 03:25		#3
FrankW Member Frank Weise Join Date: Mar 2009 Location: Germany Posts: 55 Rep Power: 17	I then managed it. The simulation is running. Unfortunately, I had to use the "General Coupling Control" to get it stable. But when I use it, the automatic timestepping doesn't work.