Problem with setting up small scale units in Karamba3D

Hello Karamba3D experts!
I am trying to simulate a very small scale model, but I am facing a couple of problems. In order to test the units for plausibility I used an example file to test out the new unit setup. But I only get weird results and the beam bends upwards. The model weight changes, as soon as I change the internal length unit to ‘mm’, which is good. But some other parameters for example ‘N’ seem to stay ‘kN’. Am I missing something here?

How can I setup Karamba units the right way?
I need to setup Karamba for simulating stresses in a small scale 150 mm length, plastic model.

Here is my definition:
small_scale_test (28.5 KB)

And here my .ini-file:

karamba_user.ini (13.4 KB)

Thank you so much for your help!

Best regards,
Sebastian Schanz

Hello @sebastianschanz,

the problem lies in the definition of the box cross section (see here: (32.0 KB)

When switching to millimeters as the new unit for the cross section geometry the default values are converted from the old to the new units. By default the ‘Fillet Radius’ is 6mm. When left unchanged then in combination with a height and width of 5mm, this leads to a negative moment of inertia when evaluated according to EN10210.

Manipulating the ini-settings via the ‘Settings’-component like in the example above is problematic: The changes apply only after the component executes - so sometimes one needs to reevaluate a definition before the changes take effect. The other downside is, that it has an impact on all definitions currently opened in Grasshopper.
The more clearer alternative is to change the ‘karamba.ini’-file. The disadvantage there is, that the help-text of components regarding physical units does not update when the karamba.ini-file is changed.

– Clemens