# Definition of omega

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 April 6, 2009, 14:33 Definition of omega #1 Member   Join Date: Apr 2009 Posts: 94 Rep Power: 10 Sponsored Links Dear All, I am modeling a moving, rotating solid inside a fluid volume. The solid has to rotate around an axis which passes through its center of mass. I am using dynamic mesh. Motion of the solid is done with profile: time, x, y, z, omega_z. I don't use theta_x, theta_y, theta_z because they are always zero and don't change throughout the motion. My question is: Does FLUENT know that vector omega_z should pass through the center of mass of my solid? I read 10.6.4 "Solid-Body Kinematics" \Fluent6.2Manual\html\ug\node398.htm but was unable to understand the definitions of omega. Appreciate the help.

 April 7, 2009, 00:38 #2 Super Moderator     Maxime Perelli Join Date: Mar 2009 Location: Switzerland Posts: 3,232 Rep Power: 34 omega-z = d(theta-z)/dt If theta-z = 0 in your case, then you don't have any rotation about z-axis.

 April 7, 2009, 11:03 #3 Member   Join Date: Apr 2009 Posts: 94 Rep Power: 10 mAx, thank you very much for your answer. You are talking about rotation of the center of mass. Is this the definition of omega?: Definition: in solid-body kinematics profile, "omega" is the angular velocity vector of the center of mass. It has components omega_x, omega_y, omega_z. Your answer seems to match the FLUENT manual, especially Figure 10.6.16. Unfortunately, what I am trying to achieve is a rotation of my solid with respect to an axis that passes through the center of mass. Imagine a football moving through fluid volume, the football rotates as it moves (a spinning ball). Then the center of gravity moves and the axis of rotation moves with it. From your answer it seems that a spinning ball cannot be modeled with a profile and dynamic mesh. Am I going wrong here?

 April 7, 2009, 11:41 #4 Super Moderator     Maxime Perelli Join Date: Mar 2009 Location: Switzerland Posts: 3,232 Rep Power: 34 6-dof can help you http://eps.fluent.com/5903/500000762/20060904/6DOF.pdf

 April 7, 2009, 15:06 #5 Member   Join Date: Apr 2009 Posts: 94 Rep Power: 10 mAx, thanks for the link. It got me thinking.

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