How to apply shear load and moment on thin-walled cylinder FEM

[Sleight]

How do I apply a shear load, V, and bending moment, M on a thin-walled cylindrical shell FEM to capture the correct bending stresses and shear stresses according to beam theory? According to beam theory, the bending stress is a function of sine, fb = M*Sin(theta)/(Pi*r^2*t) and the shear stress is a function of cosine, fv = V*Cos(theta)/(Pi*r*t) where theta is the angle above the neutral axis.

Thanks!

 

[Onda]

Johnhors, I understand your point, but, to avoid the problem you mention, the tube could be meshed with a regular pattern of CQUAD4 elements, without mid-side node and with all grid point aligned.
In this case You could apply the shear load with a RBE3 with a weight function of the location.

 

[rb1957]

yeah, i can see your point john ... it's more to do with the weighting function than the stiffness of the structure (isn't it).

of couse, you could mesh with CQUAD4s ... but where'e the fun in that

 

[johnhors]

Yep, a regular mesh of 4 node quads may work fine with a RBE3. The point is not to assume a RBE3 has any intelligence, without linear elements or uniform mesh it won't give you a uniform or realistic load distribution.

 

[GregLocock]

This is sort of getting away from any area of expertise I have, but one way I've applied complex loadings to a structure without upsetting it is to use an intermediate layer of 'soft' elements and apply the loads to them. These then distribute the load smoothly into the structure of interest.

This is somewhat equivalent to an impedance matching problem.



Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[Sleight]

I did a comparison of methods to apply loading (axial, shear, and moment) on a cylinder example for RBE2, RBE3, and the statically equivalent loading methods.

The statically equivalent loading method was the best overall in comparsion with beam theory results. The results show that the RBE3 method for applying the loads is very good for applying axial forces and moments, but does poorly for applied shear forces. For shear forces, the results show that the RBE3 elements produce a rigid-body like(sliding) motion with a corresponding high Ny force at the top of the cylinder. The results also show that RBE2 method for applying loads is good for shear forces, but introduces high Ny forces at the load application point for applied axial forces and moments.