 # Custom section of multiple tube profiles

Hey,

I’m trying to understand how to define a section of 2 parallel tubes running next to each other?

In my system model, they are displayed as a single curve which makes things easy but in reality it will be double tubes so I’m trying to bring my simulation as close as possible to the real setup. I can see there’s a deconstruct / construct section component, however my engineering knowledge is limited to calculate those values myself. Isn’t there a way to input a custom cross section geometry and let Kiwi calculate all the forces for the structure?

Hey, there is no possibility in Kiwi to compute the crosssectional values from e.g. a drawing of the cross section. You need to get the crosssectional values - either by another plugin or program or by computing on your own. In the case of two tubes, it would be quite simple to compute the values with R being the outer radius and r the inner one.
A=(R²-r²)* pi * 2
Iy=2* pi/4*(R^4-r^4)
Iz=2* pi/4*(R^4-r^4)+(A* R) if connected
It=4*(((R+r)/2)²* pi)²/((R+r)/2* 2* pi* 2)
The German wikipedia page provides also some examples for other cross sections: Flächenträgheitsmoment – Wikipedia

Wow, that’s great input!

What about Wy, Wz, Ay, Az? Do you know by any chance formulas to those too?

Wy=Iy/R*2
Wz=Iz/R
Ay and Az are not that clear.

But you do not need those values for the analysis. It’s only for the stress evaluation.

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Thanks Anna, this is really helpful!