Detection, localisation and identification of nonlinearities in structural dynamics

This paper discusses procedures for nonlinearity detection, localisation and identification in structures from time domain vibration measurements. The detection and the localisation techniques use pattern recognition tools and are based on a dissimilarity measure between the signals coming from a linear structure and the corresponding nonlinear one. The detection procedure distinguishes between linear structures and structures with a nonlinearity employing nearest neighbour techniques. The localisation procedure combines substructuring with a nonlinearity detection procedure. This technique is useful for cases of local nonlinearity, when its localisation can be of value for the consequent understanding and modelling of the structure. The identification procedure makes use of the Karhunen-Loeve transform, known also as Proper
Orthogonal Decomposition (POD). It is a powerful tool for solving inverse problems in nonlinear structural dynamics. The identification procedure works on the basis of the minimisation of a difference function between the experimental and the simulated proper orthogonal modes (POM). The proposed techniques are demonstrated on a beam test case with a local damping type nonlinearity.