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Old   April 9, 2011, 12:31
Unhappy Solid Body rotating
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Kristofer Estellen
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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.
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Old   April 10, 2011, 06:47
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Glenn Horrocks
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RotationAngle = omega * time

omega is your rotational velocity, and set your hemisphere angle to RotationAngle.
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Old   April 10, 2011, 08:29
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I appreciate your responde, but can you tell me, how can I set hemisphere angle to my expression?
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Old   April 10, 2011, 22:24
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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.
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Old   April 11, 2011, 00:11
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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.
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Old   April 11, 2011, 06:24
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You still have not explained what you are trying to do. Can you post an image?
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Old   April 11, 2011, 11:57
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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
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Old   April 11, 2011, 18:43
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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.
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Old   April 12, 2011, 00:27
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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.
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Old   April 12, 2011, 07:29
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What time dependence? Is the angular velocity changing with time?
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Old   April 12, 2011, 09:55
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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.
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Old   April 12, 2011, 18:37
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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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