At the moment I am testing PrePoMax 2.1.0 for the buckling analysis of a wind turbine tower, the tower is a shell with multiple different sections (different wall thicknesses
I start with a “Buckle” Analysis and it seems to me that PrePoMax can only handle 2 different sections, If I use only 2 Sections I get about the expected result (buckling factor = 3.4), If I try more than 2 different sections I get (buckling factor = 1).
“Update: During writing of the post I tried the same analysis with quadelement and second order and it works ! in the first try I used only linear tri elements. Still strange error though”
Hello, I am encountering similar problems. When I try to solve the model using S4/S4R elements it works correctly for a cylinder of constant thickness, but when I include several thicknesses it does not give adequate results. Can this be attributed to the computational capacity of my PC (8Gb RAM), or what is the reason?
I am modelling the cylinder with shell elements, so I where using S4/S4R. I tried different meshes finer and coarser, but similar results. Yes, I have specially noticed this in LBAs, but it is true that I tried in other computer (with less RAM) and it has similar problems for LA, that’s why I asking about computational capacity.
I solved a similar problem (looks like the same) some time ago based on a well documented result of a FEM contest.
Mesh was dense + S8R. See picture.
In my experience from diferent problems solved along the time, S4R is not reliable for Buckling analisys.
Pay special attention to boundary conditions on the base. You have to constrain rotations on a curved surface. That’s not trivial to achieve.
Thanks for the comment. I have been working a lot with shell buckling (it is true that it is in ABAQUS), and I have obtained very good results using S4R. In fact, the second part of the paper you have shared is the reference solution and they proposed the use of S4R. So, my question here is, are the problems with S4R limitation of Calculix?
Ok, thank you. So, now I understand why this problem occurs when considering different thicknesses. So, how do you solve this by considering S8R since in this case it is not possible to avoid the generation of such knots because of the variable thickness?
Sometimes it makes sense to try with corresponding solid elements in the case of such issues with expanded shells in CalculiX. PrePoMax has a tool for that - Thicken Shell Mesh.
You are very close.
Try to increase the accuracy in the Buckling step window. That should improve your mode shape.
Regarding your buckling factor (slightly low) , read the paper carefully because you are making a mistake that is described in it.