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MECHIS

Framework calculations in 3-D

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Hi!
I'm currently doing a project where i'm constructing a framework for an engine mount connecting an airplane with an engine. The project involves both calculations by hand and with CAD(Creo), and i have no problem with the CAD part as i have done the simulations. 
The part with doing calculations by hand have caused some problems where i'm doing the calculations in 3-D, and its causing some problems.
The top and bottom diagonals are not to be considered in the calculation by hand. Therefore you have 6 symmetrical beams.
So far what I have done in the calculations is that i've created a equation system with help of directional cosines which seems to get me the wrong answers. So i'm looking for some help in creating the equations system for this problem. 

beams1-8.png

coordinatesxyz.png

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This looks like a very interesting and very real problem. If I have correctly understood your drawing, it appears that the system is symmetric about the y-z plane, so that should reduce the problem somewhat; is this correct?

I should mention that the end conditions on each member are extremely important. The simplest would be to assume essentially a ball connection at each joint (a 3D pin), but in reality, the joints are more likely to be welded. What did you assume in your FEA work, and what are you assuming in your hand calcs?

Are you able to post the work you have done? I'd like to see that rather than begin by re-inventing the wheel.

DrD

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