CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > FLUENT

Rigid body rotation NOT through the CG?

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

Reply
 
LinkBack Thread Tools Display Modes
Old   July 18, 2007, 16:45
Default Rigid body rotation NOT through the CG?
  #1
Joe
Guest
 
Posts: n/a
I would like to rotate a rigid body through an axis that does NOT pass through its centre of gravity e.g. a long rod rotating about one of its own ends like a clock pendulum.

My understanding is that the DEFINE_CG_MOTION, as its name implies, can ONLY be used to specify translational and angular velocities for the body's centre of gravity. Could someone confirm this for me please?

If this is the case then presumably I HAVE to use the DEFINE_GRID_MOTION macro???

Rotating a body around its CG is trivial e.g.

#include "udf.h"

DEFINE_CG_MOTION(james,dt,vel,omega,time,dtime)

{

/* reset velocities */

NV_S(vel, =, 0.0);

NV_S(omega, =, 0.0);

if (!Data_Valid_P()) return;

omega[2] = 0.523599 * cos(392.699 * time) * 392.699;

}

But again this doesnt help my situation as the rotation only occurs about the CG which is not what I need.

Thanks for any clarification!
  Reply With Quote

Old   July 18, 2007, 17:05
Default Re: Rigid body rotation NOT through the CG?
  #2
Joe
Guest
 
Posts: n/a
Just to add another thought ... My understanding is that the DEFINE_GRID_MOTION macro is mainly for use with deforming bodies i.e. non-rigid bodies as the nodes in the zone undergoing motion are moving relative to each other.

This is the problem: Neither the DEFINE_CG_MOTION nor DEFINE_GRID_MOTION macros seem directly applicable to my case?

  Reply With Quote

Old   July 19, 2007, 12:09
Default Re: Rigid body rotation NOT through the CG?
  #3
Joe
Guest
 
Posts: n/a
Problem solved ... I just managed to confuse myself.
  Reply With Quote

Old   July 20, 2007, 08:35
Default Re: Rigid body rotation NOT through the CG?
  #4
amir
Guest
 
Posts: n/a
Dear Joe i have a problem about dynamuc mesh. can you tell me how can i model a vessel by dynamic mesh.? whit king regards Amir
  Reply With Quote

Old   July 20, 2007, 16:21
Default Re: Rigid body rotation NOT through the CG?
  #5
Joe
Guest
 
Posts: n/a
Do the dynamic mesh tutorial 12 and implement the DEFINE_CG_MOTION and DEFINE_GRID_MOTION examples in the UDF manual. That will get you started.
  Reply With Quote

Old   April 12, 2010, 14:13
Default User defined functions
  #6
New Member
 
Juan Carlos
Join Date: Feb 2010
Posts: 9
Rep Power: 7
Juan Carlos is on a distinguished road
Dear Joe
In my case I trying to simulate a flapper valve and I'd like to rotate a valve, like a rigid body, through an axis that doesn't pass through its centre of gravity.
Here the flow moves the valve by exerting forces on it. To reproduce the body motion of the valve due to hinge moment I must use Compute_Force_And_Moment function to determinate the moment, but I don’t know how it does.
Do you have any suggestions that can help me?
Juan Carlos is offline   Reply With Quote

Old   May 28, 2010, 11:03
Default
  #7
New Member
 
euzinho
Join Date: May 2010
Posts: 15
Rep Power: 7
euzinho is on a distinguished road
Hi Joe,
I am having the same problem, I donīt know how to rotate a butterfly valve,
and my code is a lot like your
can you explain me how did you resolve the problem?

thanks so much
Quote:
Originally Posted by Joe
;143594
I would like to rotate a rigid body through an axis that does NOT pass through its centre of gravity e.g. a long rod rotating about one of its own ends like a clock pendulum.

My understanding is that the DEFINE_CG_MOTION, as its name implies, can ONLY be used to specify translational and angular velocities for the body's centre of gravity. Could someone confirm this for me please?

If this is the case then presumably I HAVE to use the DEFINE_GRID_MOTION macro???

Rotating a body around its CG is trivial e.g.

#include "udf.h"

DEFINE_CG_MOTION(james,dt,vel,omega,time,dtime)

{

/* reset velocities */

NV_S(vel, =, 0.0);

NV_S(omega, =, 0.0);

if (!Data_Valid_P()) return;

omega[2] = 0.523599 * cos(392.699 * time) * 392.699;

}

But again this doesnt help my situation as the rotation only occurs about the CG which is not what I need.

Thanks for any clarification!
euzinho is offline   Reply With Quote

Reply

Thread Tools
Display Modes

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 Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Rigid body Birkov CFX 4 May 25, 2012 06:26
Turbulent solver rigid body mechanics philippose OpenFOAM Running, Solving & CFD 53 July 16, 2011 13:35
6-dof rigid body solver AUN CFX 2 July 11, 2011 22:59
Rigid Body with 3-DOF rotation aeropeng OpenFOAM 3 June 28, 2011 04:43
Rotation of a 3d rigid body through its free end M-Ray FLUENT 0 May 20, 2008 09:56


All times are GMT -4. The time now is 01:14.