A New Approach to Model Updating in Symmetric Structures

Finite element model updating and system identification in symmetric structures is hampered by the inability of the eigenvalues to distinguish between symmetric parameter perturbations. A typical approach is to employ eigenvectors, or even antiresonances, as updating variables. These tend to be less accurate than the eigenvalue measurements however. In this paper, a method for updating symmetric parameters is presented based on quantitative information from the eigenvalues and qualitative information from the eigenvectors. It exploits the effect of eigenvalue curve veering, manifested through modal couplings. The curve veering is measured experimentally by variation of a control parameter. A computationally efficient updating scheme is applied, requiring only a single eigensolution at each iteration. Using experimental data the method is shown to be capable of producing a unique solution to a doubly symmetric updating problem. The ideas presented are expected to prove valuable in localisation problems, stability studies and damage detection.