Karamba3D super thin shell cross-section

Grasshopper Karamba3D
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1

Hello Karamba3D team,

I am modeling in Rhino7, Grasshopper, and Karamba3D. My model looks great, however, I am analyzing a shell element (similar to a hollow column) with loads applied to the top and I want to see the displacement due to varying thicknesses (small). I understand the default thickness Karamba uses is 1 [cm] and I see a component in modifying the maximum cross-section “height,” or the thickness parameter, but is there a way to control how small I can go? I want to go smaller, to as thin as 0.1 [mm], however, the model/analysis seems to cause issues at thicknesses smaller than 0.5 [cm] such that the deformed shape is not what it should be regardless of the thinness of the material.

Do you know how I can go about fixing this issue with very small mesh shell cross-sectional thickness?

2

Hello Alycia,
it could be that your model tarts to buckle below a certain wall thickness.
Could you send a small gh-definition where the problem occurs?
– Clemens

3

Attached is a small file of the issue. The desired model is in units of [mm] so the variables (inputs) are conversions from the default Karamba3D metric units. I believe the problem occurs when the thickness is around 0.02 [cm], and I would like to see it as low as 0.01 [mm]. It might result from buckling as you suggested and showing up (in shell view) as it is due to FEA, but I would like to double-check to see if there is a possible error in my code that can be corrected. Thank you so much!
karamba columns_thickness issue.gh (49.6 KB)

4

Hi @Alycia,
I tested the model in RH8 with Karamba3D 3.1.40531 and cannot reproduce the problem. With a material thickness of 0.0005mm I get a maximum displacement of 65cm (see
karamba columns_thickness issue_cp.gh (59.3 KB)).
The model buckles though when doing ThII analysis.
What version of Karamba3D do you use?
– Clemens

5

Hi Clemens,
Thank you for looking at the file. I am using Karamba3D 2.2.0.180-230616 for RH7 (educational license). When I open up your file, it looks the same as what I am seeing on my end and I see the same displacement of 65cm that you got, so perhaps the results I was getting were okay despite the resulting shell view looking strange (for its deformed shape). I forgot there are multiple analyses Karamba can run so I will look into ThII analysis as well.