# Jumping boat?

 Register Blogs Members List Search Today's Posts Mark Forums Read

 July 26, 2012, 04:44 Jumping boat? #1 New Member   Angus Bishop Join Date: Apr 2012 Posts: 17 Rep Power: 6 Sorry , this should be my last question I have a hollow cylindrical hull shape for a boat , I'm running a rigid body simulation to show stuff , I have timesteps of 0.025 seconds but after the 7-8th one the boat jumps out of the water by around 1m for the previous timesteps it would move only 1cm or less. Have i done something fundamentally wrong? Or does CFX not handle flow inside and outside hollow tubes very well? Thanks in advance for replies

 July 26, 2012, 06:04 #2 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 12,638 Rep Power: 98 I've heard of jumping beans but not jumping boats And no need for apologies, the forum is here to ask questions and you are welcome to do so. It sounds like you have a numeric instability in your simulation. You need to stablise the rigid body motions. I have little experience in rigid body stuff so cannot help you with exactly how to do this.

 July 26, 2012, 06:47 #3 New Member   Angus Bishop Join Date: Apr 2012 Posts: 17 Rep Power: 6 That sounded fancy Thanks Now just hope someone knows how to sort that out. Running simulations at this stage are taking about an hour so trial and error is out of the question.

 July 26, 2012, 07:44 #4 New Member   Angus Bishop Join Date: Apr 2012 Posts: 17 Rep Power: 6 Also how would i go about takingg just the value of an expression without dimensions at then putting dimensions on it? I have a formula that pumps out values in seconds at the moment and i was it to be in meters per second.

 July 26, 2012, 18:53 #5 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 12,638 Rep Power: 98 Have a look at the numerical controls for rigid bodies. There will be stability controls there, that is what you need to play with. CEL uses units for your own protection - you cannot just convert a time measurement to a velocity. Of course you can just say vel = 1 [m]/time_var and then you have m/s but most of the time this is not somethign you want to do.

 Thread Tools Display Modes Linear Mode

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post jesus garcia Main CFD Forum 2 July 8, 2015 16:50 matteoL ANSYS Meshing & Geometry 4 May 7, 2012 10:23 Birkov CFX 5 August 26, 2010 06:50 hasim FLOW-3D 12 March 29, 2010 09:34 wieke FLUENT 2 May 19, 2005 02:11

All times are GMT -4. The time now is 18:37.