Shells of revolution

Hi Clemens,

I was calculating deformations of a simple shell of revolution based on membrane theory as my homework, but I was not able to get the same results from Karamba. Can't figure out what is the problem. Normally what is the poisson's ratio considered by Karamba?

Thanks in advance,

Mariam

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Permalink Reply by Karamba3D on February 9, 2015 at 10:58pm

Hi Mariam,

the poisson's ratio nue can be calculated from E and G:

G = E/(2*(1+nue))

In your case nue = 0.2.

The difference in the solution according to membrane theory and that calculated by Karamba could be caused by the support conditions. In membrane theory moments are neglected and the shell is assumed to be supported in such a way that no moments arise. Try to support the edge in tangential (in case of a half sphere vertical) direction only. In order to avoid a kinematic structure add a point support in the middle with horizontal displacements and rotation about the vertical axis blocked.

A second factor which might causes a difference is the fact that Karamba's shell elements take bending into consideration. For shells with bending analytical solutions exist (see e.g. 'Theory of Plates and Shells' by Timoshenko and Krieger).

A third factor could be the discretization of the shell. Try to apply meshes of different size and check whether the results vary.

Best,

Clemens

Permalink Reply by mariam khademi on February 10, 2015 at 1:56am