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-   -   rotation and linear motion (http://www.cfd-online.com/Forums/cfx/67740-rotation-linear-motion.html)

Chroko August 25, 2009 09:36

rotation and linear motion
 
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.htmlhttp://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:http://img38.imageshack.us/img38/5227/motion.th.jpg

hmasenger August 26, 2009 12:24

Quote:

Originally Posted by ghorrocks (Post 227479)
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.:confused:

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.


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