Applying Gravity Load to Shell - New Karamba User

Grasshopper Karamba3D
1

Hello,

I am new to Karamba and FEM in general, so I am in the process of getting my bearings.

My goal is study how the included geometry sags as a function of decreasing modulus, thus my only load condition is gravity, with fixed supports at the tabs.

When I attempt to simulate this using Karamba, I am noticing this unexpected sagging towards the centroid of the part:

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ezgif.com-gif-maker (1).gif1104×534 68.6 KB

I brought the model into SimScale and ran the simulation with similar conditions and yielded this result, which is what I would expect:

com-gif-maker
ezgif.com-gif-maker.gif1012×462 63 KB

Does anyone know where I am going wrong in my Karamba setup? Thank you for your help.

Gravity_Load_Troubleshoot.gh (27.9 KB)

2

Hi @jptroise,
You need to analyze the geometry as a surface with a defined cross section rather than a solid. Please also take care of the units of the model. The deformation shows similar results to the image from SimScale.

Gravity_Load_Troubleshoot_MT.gh (53.6 KB)

best,
Matthew

3

Thanks @matttam

I appreciate your response. If I understand correctly, Karamba cannot operate on an arbitrary 3D geometry - I must decompose this 3D geometry into elements that Karamba can comprehend.

What is my recourse if the input geometry is not as simple as what I have shared - perhaps with variable cross section? I see that there is the Shell Var option. Shall this be my only alternative?

James

4

Yes, that is correct. You can use the shell variation cross section to define the thickness of all the mesh faces.
Matthew