Karamba - Springs and shells

Hello everybody,

I just started playing around with springs in karamba, i want to use them to define joints between shell elements. Is this possible in theory or are there any limitations?

I figured I started with a very simple case study, a beam strip with a spring/hinge in the center, but I am confused that the translational stiffness of the spring (in this case global z direction, but basically every direction) does not seem to have any influence on the deformation? I would expect a gap between the 2 segments once I reduce the spring stiffness. To reproduce this, see the attached file and modify the translational spring stiffness, basically nothing happens...

The rotational spring seems to work, at least the kink in the deformation is visible once I decrease the corresponding stiffness of the spring and if it is decreased too much a mechanism appears and the solver finds a rigid-body movement.

Any help is appreciated,

Cheers

Daniel

Attachments:

150312_karamba_spring_shell.gh, 42 KB

Replies to This Discussion

Permalink Reply by Karamba3D on March 12, 2015 at 2:10pm

Hello Daniel,

AnalyzeTHI and AnalyzeTHII are both based on the assumption of small displacements. That is the reason why no in-plane forces develop in your shell-strip. You can see this when enabling the display of reaction forces in the ModelView-component.

With large deformation analysis the expected gaps shows up (see attachment). The disadvantage of the implementation of large displacement analysis in Karamba 1.1.0 is however that it does not give you cross section forces.

Best,

Clemens

Attachments:

150312_karamba_spring_shell_CP.gh, 35 KB

Permalink Reply by Daniel Sonntag on March 13, 2015 at 2:35am

Hi Clemens,

thanks for the quick response. Actually it helped even though I was thinking of the vertical gap due to out-of plane shear forces. But the test case is actually useless for that, as the shear force is 0 in this case, so no differential displacement to expect, my bad. I modified my example and it seems to work just fine, thanks.

Btw. is it possible to have those springs as zero-length elements in that case?

Cheers

Daniel

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