FEM-definition for the shell element of Karamba

I'm wondering what type of FEM element Karamba uses to approximate shell behaviour.

I can tell, that it is triangular but what about the element DOFs; are they similar to the STRI3-element of Abaqus? (Click link, i.e. 3 corner nodes, each with 3 translations and 3 rotations)

Cheers

Replies to This Discussion

Permalink Reply by Karamba3D on June 8, 2015 at 11:40pm

Hi Daniel,

the shell element formulation used in Karamba is based on the TRIC element (see e.g. The TRIC shell element: theoretical and numerical investigation. / Argyris, J H ; Papadrakakis, M ; Apostolopoulou, C ; Koutsourelakis, S ; Koutsourelakis, Phadeon-Stelios. In: Computer Methods in Applied Mechanics and Engineering, Vol. 182, No. 1-2, 04.02.2000, p. 217-245.).

These are the main characteristics:

Contrary to the TRIC element the shell element in Karamba is based on the Kirchhoff theory.
There are six DOFs per node.
A constant strain state is assumed for each layer.
No in-plane rotational stiffness is added. This is the reason why one has to specify a rotational support perpendicular to a flat patch of Karamba shell elements.

Best,

Clemens

Permalink Reply by Daniel Kolling Andersen on June 9, 2015 at 4:16am

Thanks Clemens!

I'm assuming that transverse shear deformation isn't accounted for then.

Permalink Reply by Romain Mesnil on August 11, 2015 at 3:04am

Hi Clemens,

I also have a question related to shell elements in Karamba. The shell forces components does not retrieve shear forces (at least in the 1.0.5 version). I understand that Kirchhoff's theory does not account for contribution of shear to the total elastic energy, but it should be possible to get a shear force from equilibrium (much like with Euler-Bernoulli beams). The equation is something like this, using Einstein notation:

Mab,a+Qa=0 (1)

However, I don't know if the elements used in Karamba can deal with this? It would be very helpful to have information on shear forces in some cases...

Best,

Romain

Permalink Reply by Karamba3D on August 11, 2015 at 12:00pm

Hi Romain,

it is indeed possible to get the shear forces on the basis of equilibrium equations as you propose above.

I will try to include them in the next release.

Best,

Clemens

Permalink Reply by Romain Mesnil on August 12, 2015 at 5:33am

Thank you for your answer! I look forward to the next release then =-)

Best,

Romain