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Dhondtguido / CalculiX

This repository contains the source files of CalculiX, a three-dimensional Finite Element Program (www.calculix.de).
GNU General Public License v2.0
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First buckling mode skipped when applied load is much bigger than buckling load #74

Open FEA-eng opened 6 months ago

FEA-eng commented 6 months ago

Consider a rectangular bar 100x100x3000 mm, made of steel (E=210000 MPa, v=0.28), fixed at one end and with a compressive force applied at the other end. When the load is smaller than the buckling load or close to it (1 N or Euler critical load of 470437.10 N applied), the results of a linear buckling analysis are correct. But when the applied load is significantly larger than the buckling load (e.g. 980665 N), the buckling factor might be predicted incorrectly (4.37 in this case which should be the second eigenvalue). The issue seems to be mesh- and solver-dependent. Spooles may even provide different results for each run when more than 2 processors are used.

I shared the input file here.

victorkemp commented 6 months ago

Sounds like the existing bug which causes buckling factors less than approximately one to be missed. I made a pull request to fix it here which is just uncommenting some code that used to be enabled many versions ago.

https://github.com/Dhondtguido/CalculiX/pull/44

CCX compiled with multithreaded Spooles is known to be wrong for buckling or frequency or maybe both.