Modifying number of elements for Eigenmode calculation?

Hi,

Is it possible to reduce the number of elements for eigenmode calculation? I'm only interested in where the whole structure would buckle (global eigenmode?), where a node would be deformed out of the double curved shape, not the elements them self. (See figure)

Correct me if I'm wrong, my guess is that it has to do with the mesh of elements. In my model i have 202 elements, however when assembled it has collected 522 elements and an increase of nodes. I guess the number of elements increases in regard to the FEM-analysis, but i wish to reinstate the the unmeshed geometry for eigenmode calculation.

This will be used for a optimization problem.

Best,

Johan

Attachments:

global buckling.jpg, 574 KB

Replies to This Discussion

Permalink Reply by Karamba3D on August 12, 2014 at 12:02pm

Hi Johan,

without knowing how the structure is supported it is hard to tell whether the eigen-mode in the above picture is plausible.

Did you try to eliminate duplicate lines and nodes with the 'Remove Duplicate Lines'- and 'Remove duplicate Points'-component?

Best,

Clemens

Permalink Reply by Johan Reissmuller on August 13, 2014 at 2:45am

Hi!

Eliminating duplicate points and lines is not an issue. When assembling the model, the input is a set of 202 beams. The number of elements increases in the "assemble model"-component. I guess there is a good reason for it. However could it apart of my eigenvalue problem?

I noticed that Eigenmode #66 and those who follows, is what I'm looking for. These modes keep the straightness of beams and only the structure buckles. Modes 0-65 seems to be some kind of local modes due to the compressive elements. However local buckling is considered in Eurocode design of cross sections of elements, but in another software.

Since the other software also computes eigenvalue, and beams are not re-meshed, the first eigen-modes is always the ones from: 66,67,...,n. (at least the first the first modes in the order)

I can't help to think the number 66 (the 67th value) has to do with nodes on which load is applied, The doubble curved geometry (excl. column's bottom nodes) also has 67 nodes.

Please see attachement,

//Johan

Attachments: