Elements of a Nonlinear System Identification Methodology of Broad Applicability with Application to Bolted Joints

Abstract

This chapter presents a recently proposed nonlinear system identification methodology that has the promise of broad applicability based on a global–local approach. In the proposed nonlinear system identification methodology, measured time series are decomposed in terms of approximately monochromatic dominant intrinsic mode functions, which are either depicted in frequency-energy plots (the global aspect of nonlinear system identification), or are used to construct local models in terms of sets of intrinsic modal oscillators (the local aspect of nonlinear system identification). The proposed nonlinear system identification methodology is applied to the analysis and modeling of the nonlinear damping effects induced by a frictional interface on the dynamics of a beam with a bolted joint connection. In particular, we show that by studying the temporal decays of the logarithms of the moduli of the complex amplitudes of the forcing functions of the intrinsic modal oscillators, we can deduce the nonlinear damping effects in the dynamics. The nonlinear system identification methodology can be employed to study nonlinear damping effects in structural assemblies with more complex mechanical joints, and nonlinear stiffness effects in structural components with local or distributed nonlinearities of a different source. Moreover, it is possible to study the effects of nonproportional (linear or nonlinear) damping distribution on the modal responses, and conceive methods for modeling such effects and for examining how these effects perturb the result of classical modal analysis.