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Point of Attack of force on surface

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Old   October 4, 2006, 04:14
Default Point of Attack of force on surface
  #1
Andy
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Hello,

I am working on a blunt body and need to decompose the lift force into its two components at the two axles. I know how to get the forces in all three directions (force_x()@..., etc.) and also the torques about the global space directions (function calculator). In order to split the lift I am using a simple mechanical model. However therefore I need the distances that is the points of attack of the forces, too. For example I need the point of attack of the drag (=force_x...) on my blunt body but could not find a way to get. I could not find anything in the manual, either.

Does anybody know how to solve this problem? Thanks!
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Old   October 4, 2006, 10:26
Default Re: Point of Attack of force on surface
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Robin
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Hi Andy,

If you have the forces and torques, it is relatively straightforward to do a moment balance (on the back of an envelope or in CEL to find the point about which there are no moments.

Regards, Robin
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Old   October 4, 2006, 13:24
Default Re: Point of Attack of force on surface
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Andy
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Hey Robin,

principally, that is right. However, I do not have all the forces and moments. The only thing I have is the equivalent system with respect to the point of origin, I guess (2 force and a torque). This point is within my symmetry plane and I have a uniform free flow parallel to the x-axis, so two moment balances (yaw and roll) do not work at all, I only got a pitching moment.

The supports on the front and rear axles, however, require 2 forces and a moment each, so I have 6 unknowns and only 3 equations (those from the xz-plane)...

I just thought that CFX is calculating the forces on the surfaces by integrating pressure and shear over the surface. So there should be an easy way for displaying the point of attack of the resulting force, I had hoped.

But thanks anyways
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Old   October 4, 2006, 14:38
Default Re: Point of Attack of force on surface
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Andy
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Hey Robin,

of course you are absolutely right, also in my case. I have thought much to complicated or kinda "real-world-like". Of course, my only support is my virtual balance, just like in the wind tunnel... And then it is embarrissing easy

thanks and regards Andy
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