Finite element analysis (FEA) based system identification of a metal-composite spar using Eigensystems Realization Algorithm (ERA)

Abstract

A process of characterizing an unknown system based on the inputs and outputs is called System Identification (SI). Characteristics of a structural system include its stiffness, mass and damping matrices, eigenvalues and eigenvectors and strain energies etc. Eigensystem Realization Algorithm (ERA) is a very useful system identification technique which employs theory and concept of simple linear algebra and Hankel matrix. The aim of this paper is to implement the Eigensystem Realization Algorithm (ERA) on metal-composite spar under impulse loading. Full finite element model of a metal-composite spar in cantilever position is used for the modal and transient response analysis in MSC. Nastran. Modal analysis is used to get the frequencies and mode shapes while transient response analysis is done under impulse loading to get the displacement response at three nodes by exciting each of the three nodes one by one. These nine displacement response vectors are then fed into the ERA code in Matlab to get the displacement responses, mass and stiffness matrices and eigenvalues of the beam by black box identification technique. These structural identification parameters are then compared with the FEM and good correlation is found. The proposed system identification method perform very well and indicate its great potential within the domain of damage detection and Test-FEM correlation.