Solid Body rotating

Svidd · April 9, 2011, 12:31

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?

ghorrocks · April 10, 2011, 06:47

RotationAngle = omega * time

omega is your rotational velocity, and set your hemisphere angle to RotationAngle.

Svidd · April 10, 2011, 08:29

I appreciate your responde, but can you tell me, how can I set hemisphere angle to my expression?

ghorrocks · April 10, 2011, 22:24

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.

Svidd · April 11, 2011, 00:11

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.

ghorrocks · April 11, 2011, 06:24

You still have not explained what you are trying to do. Can you post an image?

Svidd · April 11, 2011, 11:57

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

ghorrocks · April 11, 2011, 18:43

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.

Svidd · April 12, 2011, 00:27

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.

ghorrocks · April 12, 2011, 07:29

What time dependence? Is the angular velocity changing with time?

Svidd · April 12, 2011, 09:55

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

ghorrocks · April 12, 2011, 18:37

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.

April 9, 2011, 12:31	Solid Body rotating	#1
Svidd New Member Kristofer Estellen Join Date: Apr 2011 Posts: 6 Rep Power: 15	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 12, 2011, 09:55		#11
Svidd New Member Kristofer Estellen Join Date: Apr 2011 Posts: 6 Rep Power: 15	well, if I'll write this expressions: R=(x^2+y^2)^(1/2) f0=asin(x/R) X1=Rsin(f0+RotationAngle) Y1=Rcos(f0+RotationAngle) RotationAngle=OmegaTime 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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April 10, 2011, 06:47		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	RotationAngle = omega * time omega is your rotational velocity, and set your hemisphere angle to RotationAngle.

April 10, 2011, 08:29		#3
Svidd New Member Kristofer Estellen Join Date: Apr 2011 Posts: 6 Rep Power: 15	I appreciate your responde, but can you tell me, how can I set hemisphere angle to my expression?

April 10, 2011, 22:24		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	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
Svidd New Member Kristofer Estellen Join Date: Apr 2011 Posts: 6 Rep Power: 15	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
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	You still have not explained what you are trying to do. Can you post an image?

April 11, 2011, 11:57		#7
Svidd New Member Kristofer Estellen Join Date: Apr 2011 Posts: 6 Rep Power: 15	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
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	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
Svidd New Member Kristofer Estellen Join Date: Apr 2011 Posts: 6 Rep Power: 15	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
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	What time dependence? Is the angular velocity changing with time?

April 12, 2011, 18:37		#12
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	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.