Problems with Karamba and Millimeters?

Hi Guys,

We used Karamba (free version) with a model in millimeters today in a class and it crashed all our computers. When we changed the unit to meters and reduced the size of our model, it worked again.

Is that a known issue? Also is there a way to scale up the rendered members of the model?

Many thanks for a great plugin!

Arthur

Replies to This Discussion

Permalink Reply by Karamba3D on July 4, 2012 at 12:04am

Hi Arthur,

did Karamba simply crash or did it return an error message?

Karamba assumes all geometric input to be in meter. Scaling a structures geometry by a factor of thousand and leaving the cross sections at their original size may lead to numerical difficulties: The members bending and axial stiffness then have different orders of magnitude which makes the stiffness matrix ill-conditioned and makes the matrix solver assume the system was singular. So if you adapt the cross section size the static response should be OK.

A reason for a crash could be, that there is no upper limit for the mesh faces that are created when rendering the cross sections, stresses and so on: In case of eccessive deflections the beams get very long and the number of mesh faces for rendering the structure increases and thus the time for rendering.

Best,

Clemens

Permalink Reply by Arthur Mamou-Mani on July 8, 2012 at 9:24am

Hi Clemens,

Thank you very much for your reply. It crashed Grasshopper without displaying an error message. It crashed when the "Model View" component was connected to either the "Assemble Model" or the "Analyze" component. The same operation worked well when working with meters (Just posted a video). Should I change the upper limit of the mesh faces in the "Model View" before connecting? How can I adapt the cross section size?

Many thanks,

Arthur

Permalink Reply by Karamba3D on July 8, 2012 at 10:03am

Hi Arthur,

you can adapt the mesh-size for rendering cross sections with the 'Length/Subdivision' and the 'Faces/Cross section' sliders in the ModelView-component.

In case of very large deformations you should first switch off all mesh-output, check the maximum displacement at the Analysis component, set an appropriate 'Length/Subdivision'-value (double-click on the slider knob if the numeric range is not sufficient), then switch on mesh output again.

Best,

Clemens

Permalink Reply by Karamba3D on September 17, 2012 at 12:23am

Hi Arthur,

Karamba 1.0.1 solves the above problem by limiting the maximum number of sections per beam.

Best,

Clemens

RSS