Zero length element as spring

Hi, everybody! I have recently started to use Grasshopper and Karamba. I'm very interested in gridshells made from flat square net (formfinding, analysis). I would like to do something similar to http://www.youtube.com/watch?v=5iqkMJbaOnU&feature=player_embedded.

I was looking to example file http://www.karamba3d.com/form-finding-i/. If I understand right Karamba by default make stiff connections between beam elements. But in real connections between lath are allowing rotations (like at scissor), so this simulation is not correct. How to model connection like that? In manual it is mentioned to use spring beam with zero length. I was trying to model that, but without success...always some error (red color). Can somebody help me... do you have some example where you used springs...

Also anything connected with gridshells (.gh files, scripts,...) are welcome.

Wish you all a lot of amazing projects with Karamba!

Damir

Tags: gridshell, length, scissor, spring, zelo

Replies to This Discussion

Permalink Reply by Robert Vier on July 23, 2012 at 9:05am

Hey Damir,

in general you have to be carefull when dealing with large deflections. a linear FE-solver like karamba is made to give exact results (which of course just is an approximation of the real world by a mathematical model) for 'small' deformations, where small means something at the scale from 1/50 to 1/1000 of the length of an element.

doing form-finding with the large deformations module is better, of course, but still just a good approximation.

this component also sets the internal forces to zero from one step to the next, this is the reason why all the internal forces are zero in the end.

but this definition does the job with zero-length springs as joints for a scissor-system with prescribed support displacements and large deformations:

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