Kangaroo

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Kangaroo is a Live Physics engine for interactive simulation, optimization and form-finding directly within Grasshopper.

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To high spring stiffness causes model to "explode"

by Carlor

May 4, 2011

Hey,

 

I'm trying to observe and compare kangaroo to ANSYS (FE method) in a small example in my work.

I'm well known to the compatible unit systems (m - N - Pa) (mm - N - Mpa) etc.

I presume spring stiffness can be chosen as A*E/L if I want to model a beam. (L = total length, A = cross section, E = 200GPa steel)

However the model will "explode" during the simulation if I change the stiffness higher than 6000 +/-.

Is this a kangaroo problem or is the structure too stiff above that number, and thus a design issue? But since the default setting is 1000 I presume the units are allready defined in some sort? I haven't found anything in the manual or in previous posts. So sorry I'm repeating solved problems.

 

kind regards

 

Load Previous Replies
  • up

    Carlor

    Hey, thanks for the info the model works now.

     

    I'm just defining one imaginary 2D truss and comparing the displcaments.

    This on the simple model, but also an actuated version to check if the kinematics are also approximated in a proper way. 

    I'll send the data in a PM if you want to take a look at it.

     

    greetz Carlo

    3

    May 4, 2011

    • up

      Ángel Linares

      Nice! I've been using kangaroo this year in the bar position and pattern design stage for a big stadium project at my school. I've used SAP2000 for the final calculations.

      The results and process was really nice because kangaroo give us kick feedback about how the structure could work; with this data in our hand modifications and redesign was really straight forward. 

      For final steps because the nature of the project (we design 2 big supports attached to the structure and floor with steel wires) we needed to use multi-step calculus. 

      My experience in this workflow is that Kangaroo in impressively good and quick for first design stages but when things comes harder, you always will need a good FEA app. 

      You can see that I implemented a simple interface to check compression-traction bar state.

      Best.

      2

      Aug 9, 2012

      • up

        Bernardo Cossio

        Hi Carlo,

        Thanks for posting this topic about units of the stiffness has been very helpful. Just one question the L in your formula es the complete length of the truss? or the individual elements / divisions?

        Thank you for your help,

        Bernardo

        2

        Aug 20, 2013