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 Mojtaba February 14, 2009 01:56

Torque Calculation at Arbitrary Point

Hi everybody I've simulated motion of a rigid body (solid structure) in fluid stream. I've performed this in two-way FSI manner (CFX and Workbench together). I've encountered a problem in post processing in CFX-POST. How can I calculate the torque on arbitrary point? In other word I want to calculate torque on a certain point attached to a certain node which moves? Do I have to do anything in CFX-PRE before run my simulation? For example define a local coordinate system? I didn't succeed in define a local coordinate system which its origin attached to the certain node. Thank a lot.

 Glenn Horrocks February 15, 2009 18:56

Re: Torque Calculation at Arbitrary Point

Hi,

I did not quite understand your question.

I assume you are trying to find the torque of a surface about a specified axis. To do this you get the torque about the x,y and/or z axis, and the forces in x, y and z directions and use some simple mechanics to transpose the torque to the desired axis.

Is this what you mean?

Glenn Horrocks

 Felix February 16, 2009 13:02

Re: Torque Calculation at Arbitrary Point

You can also define a new system of coordinates in CFX-Post (you have an icon for this) and then evaluate your torque relative to this new set of axis. It can be done quite easily using Tools > Function calculator.

Felix

 Mojtaba February 17, 2009 00:56

Re: Torque Calculation at Arbitrary Point

Dear Horrocks, Thank for your attention, I would have explained my problem better, I want to calculate torque of a surface about a Z axis, but the center of torque calculation is varying, for example I want to calculate torque of a surface about a Z axis on the center of surface while the surface and its center are moving. So I think I have to define a point attached to a certain node. How can I do this? Do I have to try in CFX-post or CFX-pre? I did successfully this for calculate pressure history for a point on a surface while that point moves. (A surface which falls in water) Apologize for my English sincerely

 Mojtaba February 17, 2009 01:04

Re: Torque Calculation at Arbitrary Point

Dear Felix, Thank for your attention, I want to calculate torque of a surface about a Z axis, but the center of torque calculation is varying, for example I want to calculate torque of a surface about a Z axis on the center of surface while the surface and its center are moving. So I think I have to define a point attached to a certain node. I did successfully this for calculate pressure history for a point on a surface while that point moves. (A surface which falls in water). Can I do this for define a point attached to a node for origin of new coordinate system? I will try and announce you.. Best wishes

 Glenn Horrocks February 17, 2009 18:06

Re: Torque Calculation at Arbitrary Point

Hi,

I assume you are trying to get this torque as the run progresses rather than as post-processing. In post-processing it is easy as Felix has suggested.

To do it as the run progresses so you can output the result to a monitor point, get the torque about the X/Y/Z axis using the torque_x/y/z CEL expressions and the force on the surface using force_x/y/z CEL expressions. Then using simple mechanics you can transfer the torque axis to any axis you like. I trust you can do the mechanics required here - if you can't then forget about CFD and go back to school.

Glenn Horrocks

 Mojtaba February 21, 2009 00:35

Re: Torque Calculation at Arbitrary Point

thank Glenn

 Mojtaba March 1, 2009 01:21

Re: Torque Calculation at Arbitrary Point