rotation and linear motion

Chroko · August 25, 2009, 09:36

Hi everybody,

I am a student and for my project thesis I need to model the motion of an air bearing segment in AnsysCFX (12). The segment is attached in one single point with a damper and a spring, So that it cane move in one direction back and forth and rotate around this point (like I tried to sketch in the picture). [IMG]file:///T:/Temp/lrt46331/moz-screenshot.jpg[/IMG]

I had (hardly) no (major) problems modelling the linear motion (with pressure, springforce, etc), but I can't find out how to implement the rotation.

Thank you for your help,

Chris

Chroko · August 25, 2009, 09:41

Hello again,

http://rapidshare.de/files/48203949/motion.bmp.html

I accidentally forgot to insert the picture link. Please excuse this.

Chris

ghorrocks · August 25, 2009, 19:27

I can't see your images.

But I think this is likely to be able to be done using the normal mesh motion stuff. You need to work out the equation of motion for the body based on the forces acting on it - looks like you have already done this for the linear stuff, you need to generalise for the rotation as well.

You may also be able to use the new submerged grid model in CFX12 with the 6DOF solver. That may also be a valid approach in this case.

Chroko · August 26, 2009, 10:40

Sorry again for the sketch. I tried another host:

hmasenger · August 26, 2009, 12:24

Quote:

Originally Posted by ghorrocks

I can't see your images.

But I think this is likely to be able to be done using the normal mesh motion stuff. You need to work out the equation of motion for the body based on the forces acting on it - looks like you have already done this for the linear stuff, you need to generalise for the rotation as well.

You may also be able to use the new submerged grid model in CFX12 with the 6DOF solver. That may also be a valid approach in this case.

hi glen
i wonder what should we do if we do not have any equation of the motion
and we just need to see how the structure is going to act with fluid flow ?

best regards.

ghorrocks · August 26, 2009, 18:34

? The equation of motion is simply based on F=ma, extended to include the degrees of freedom the body has and its various inertias (mass, moment of inertia etc). You cannot "see how the structure moves" without defining these things, that is defining an equation of motion.

Or are you referring to FSI modelling? In this case the FEA solver then works out the DOF and stiffnesses. In this case you don't work out the equation of motion, the FEA solver evaluates it for you - but it is still in there.

August 25, 2009, 09:36	rotation and linear motion	#1
Chroko New Member Chris Join Date: Aug 2009 Posts: 3 Rep Power: 16	Hi everybody, I am a student and for my project thesis I need to model the motion of an air bearing segment in AnsysCFX (12). The segment is attached in one single point with a damper and a spring, So that it cane move in one direction back and forth and rotate around this point (like I tried to sketch in the picture). [IMG]file:///T:/Temp/lrt46331/moz-screenshot.jpg[/IMG] I had (hardly) no (major) problems modelling the linear motion (with pressure, springforce, etc), but I can't find out how to implement the rotation. Thank you for your help, Chris

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August 25, 2009, 09:41		#2
Chroko New Member Chris Join Date: Aug 2009 Posts: 3 Rep Power: 16	Hello again, http://rapidshare.de/files/48203949/motion.bmp.html I accidentally forgot to insert the picture link. Please excuse this. Chris

August 25, 2009, 19:27		#3
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,690 Rep Power: 143	I can't see your images. But I think this is likely to be able to be done using the normal mesh motion stuff. You need to work out the equation of motion for the body based on the forces acting on it - looks like you have already done this for the linear stuff, you need to generalise for the rotation as well. You may also be able to use the new submerged grid model in CFX12 with the 6DOF solver. That may also be a valid approach in this case.

August 26, 2009, 10:40		#4
Chroko New Member Chris Join Date: Aug 2009 Posts: 3 Rep Power: 16	Sorry again for the sketch. I tried another host:

August 26, 2009, 18:34		#6
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,690 Rep Power: 143	? The equation of motion is simply based on F=ma, extended to include the degrees of freedom the body has and its various inertias (mass, moment of inertia etc). You cannot "see how the structure moves" without defining these things, that is defining an equation of motion. Or are you referring to FSI modelling? In this case the FEA solver then works out the DOF and stiffnesses. In this case you don't work out the equation of motion, the FEA solver evaluates it for you - but it is still in there.