IDENTIFICATION OF NONLINEAR-INTERACTIONS IN STRUCTURES

Recent experiences in phenomenological identification of nonlinear int eractions in structures are presented. Free oscillations of quadratica lly and cubically coupled pairs of oscillators are analytically studie d to illustrate nonlinear interactions between structural modes involv ed in two-to-one and one-to-one frequency relationships. In light of t his analytical study, results obtained from application of the Eigensy stem Realization Algorithm (ERA) toward identification of a beam-mass structure with a two-to-one frequency relationship and quadratic coupl ing are presented and discussed. The internal resonance in the structu re causes the identified damping coefficients to be oscillatory and to assume negative values. The present effort should be of relevance to the identification of structural systems in which factors, such as sym metry, modal density, frequency relationships, and flexibility contrib ute to the likelihood that nonlinear interactions may occur.