# Find Center of Pressure?

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December 22, 2012, 09:45
#21
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Join Date: Nov 2010
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Carrying on with the brute force and ignorance approach...

Using the method shown further up the thread I set up to create results on 11 CoR's 100mm apart on a straight line on the XZ plane, this covered the 1m where I guessed the CoP was somewhere within.

Plotting out the results as shown below where the line crosses the X axis torque is 0, therefore that's the CoP in the X direction.
Attached Images
 MY.JPG (48.9 KB, 14 views)

 December 22, 2012, 17:27 #22 New Member   Join Date: Nov 2012 Location: Scotland, UK Posts: 19 Rep Power: 4 I'm 99% sure the moments are due to the vortexes shed by the wheel, which oscillate and why I don't get 100% convergence. Eliminating the wheel moments / atleast in x and z axes (which seems reasonable) and having y as non-zero, I can get two equations in the form of x and z, and use simple simultaneous equations to solve, however it's dependant on the CofR I pick. That said your latest method makes the most sense of all methods I've tried, because centre of pressure will be where the moments are zero, so plotting My/Mx/Mz from several CofR's should give you the location. Genius! Always looking for something more complex than it should be Edit - had a think, but that's till dependant on the CofR because that will give you the position of zero torque at 0 height, which means CP would occur at more than one position, and you'd need to do a lot of iterative solutions before finding it? Last edited by GPan1; December 23, 2012 at 13:25.

 December 26, 2012, 20:46 #23 Member   Join Date: Nov 2010 Posts: 50 Rep Power: 6 Yeah, you are right my last effort will give the zero torque point at the elevation stated. more thought required

 January 2, 2013, 04:11 #24 Member   Join Date: Nov 2010 Posts: 50 Rep Power: 6 So now I believe that finding the CoP using the data on forces.dat on its own is not possible. Regardless of the number of files produced for different CoR's. I think the most that can be proven is that there will be a line upon which the CoP lies. I'm pretty certain the method that needs to be followed is as julien.decharentenay describes in post 2 of this thread.

 February 12, 2013, 10:45 #25 Senior Member   stephane sanchi Join Date: Mar 2009 Posts: 300 Rep Power: 9 Hi, following the link below you will find a paper called "Forces and moments in CFD analysis" and written by Zdeněk Říha. http://ebookbrowse.com/riha-forces-a...pdf-d253480950 Comments about this paper are welcome. Regards, Stephane. FJSJ likes this.

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