Engineering Mechanics Institute

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Automated modal identification for thin shell finite element eigen-buckling solutions
Junle Cai, Zhanjie Li, Cristopher Moen, Mihai Nedelcu, Benjamin Schafer

Building: Michael DeGroote Centre for Learning and Discovery
Room: 1305
Date: 2014-08-08 11:15 AM – 11:35 AM
Last modified: 2014-06-22

Abstract


This presentation introduces a freely available tool for performing automated thin-shell finite element (FE) eigen-buckling modal identification. Commercial finite element software is commonly used to study thin-walled members because it can easily handle complex geometries, perforations, and arbitrary loading and boundary conditions.  Each buckling analysis produces many mode shapes that are mixtures of fundamental modes, for example, local buckling, distortional buckling, and global buckling. These fundamental modes are important for use in strength prediction and design code development, however their relative participation can be difficult to quantify in an FE analysis. A modeler may have to sift through hundreds of modes, and even then, the modal identification and participation is subjective.

 

A custom-built Matlab program is presented that performs automated FE eigen-buckling modal identification. Recent research advances have led to software that performs automated eigen-buckling modal identification and participation with the constrained finite strip method (cFSM)1 and the generalized beam theory (GBT)2. Our program wraps around this existing code to perform modal decomposition on an FE-generated buckled mode shape. The FE mode shape is input as 3D coordinates from a text file that can be generated by any commercial finite element program. Cross-sectional mode shapes provided by cFSM or GBT are employed to approximate each buckling mode and to determine the modal participation of the fundamental modes3. The novelty of the presented method lies in using only the cross-section deformation modes instead of member base shapes. Using the special orthogonality properties of the cross-section deformation modes, the GBT amplitude functions of the fundamental modes are extracted from the FEM displacement field, with great speed and stability.