# Solid Body rotating

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 April 9, 2011, 12:31 Solid Body rotating #1 New Member   Kristofer Estellen Join Date: Apr 2011 Posts: 6 Rep Power: 7 I am new to this forum, and I hope, that someone would help me with little problem. How can I specify rotational velocity using CEL on a hemisphere? Last edited by Svidd; April 9, 2011 at 16:27.

 April 10, 2011, 06:47 #2 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 12,638 Rep Power: 98 RotationAngle = omega * time omega is your rotational velocity, and set your hemisphere angle to RotationAngle.

 April 10, 2011, 08:29 #3 New Member   Kristofer Estellen Join Date: Apr 2011 Posts: 6 Rep Power: 7 I appreciate your responde, but can you tell me, how can I set hemisphere angle to my expression?

 April 10, 2011, 22:24 #4 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 12,638 Rep Power: 98 You have not yet said what you are trying to do. Are you using an immersed solid, rotating frame of reference or moving mesh approach? They are all different.

 April 11, 2011, 00:11 #5 New Member   Kristofer Estellen Join Date: Apr 2011 Posts: 6 Rep Power: 7 I tried to use rotating frame of reference, it seems to be the simplest way, but I still don't really understand how can I set one.

 April 11, 2011, 06:24 #6 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 12,638 Rep Power: 98 You still have not explained what you are trying to do. Can you post an image?

 April 11, 2011, 11:57 #7 New Member   Kristofer Estellen Join Date: Apr 2011 Posts: 6 Rep Power: 7 http://img861.imageshack.us/i/93422970.jpg/ As simple as that. I need to set this hemisphere rotating around Z axis, and then set an airflow around it, to determine what's going to happen with the flow depending on velosity of rotation

 April 11, 2011, 18:43 #8 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 12,638 Rep Power: 98 In that case no need for any of that. Just put a tangential velocity on the hemisphere surface. You will need to define a CEL expression to evaluation the tangential velocity as a function of XYZ location but that should be easy. This is then a simple analysis with no moving mesh, rotating frames of reference or anything tricky. Easy.

 April 12, 2011, 00:27 #9 New Member   Kristofer Estellen Join Date: Apr 2011 Posts: 6 Rep Power: 7 So I need to use wall boundary for hemisphere surface, and then give it tangential velocity? Therefore, I understand, how to set a tangential velocity ac a function of XYZ location, but I dont understand what to do with time dependence.

 April 12, 2011, 07:29 #10 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 12,638 Rep Power: 98 What time dependence? Is the angular velocity changing with time?

 April 12, 2011, 09:55 #11 New Member   Kristofer Estellen Join Date: Apr 2011 Posts: 6 Rep Power: 7 well, if I'll write this expressions: R=(x^2+y^2)^(1/2) f0=asin(x/R) X1=R*sin(f0+RotationAngle) Y1=R*cos(f0+RotationAngle) RotationAngle=Omega*Time That will do the right thing? and no, angular velocity is constant Last edited by Svidd; April 12, 2011 at 10:13.

 April 12, 2011, 18:37 #12 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 12,638 Rep Power: 98 I think you have missed the point. We are modelling in a Eularian frame so what the fluid sees at any point on the surface is just a constant tangential velocity. There is no time component.

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