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April 6, 2009, 14:33 
Definition of omega

#1 
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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 "SolidBody 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 
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Maxime Perelli
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omegaz = d(thetaz)/dt
If thetaz = 0 in your case, then you don't have any rotation about zaxis. 

April 7, 2009, 11:03 

#3 
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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 solidbody 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 
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Maxime Perelli
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6dof can help you
http://eps.fluent.com/5903/500000762/20060904/6DOF.pdf 

April 7, 2009, 15:06 

#5 
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mAx,
thanks for the link. It got me thinking. 

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