Identification of multi-degree of freedom non-linear simulated and experimental systems

In this paper, the potential classification of a real dynamic system (e.g. aircraft) with a large number of modes into a number of different categories of modes (i.e. linear / non-linear, coupled / uncoupled in damping and/or non-linearity) that may be identified individually, or in small groups, is presented. The use of a multi-exciter identification approach using a mixture of classical curve fitting for modes that behave linearly with proportional damping, and appropriated excitation applied in bursts for modes behaving nonlinearly or exhibiting damping coupling, is presented. The approach is illustrated on a non-linear 9 degree-of-freedom simulated system and experimentally on a non-linear single-bay panel structure. This burst approach, based on an extension of the Resonant Decay Method, is essentially a derivative of the Restoring Force Surface method and involves a regression analysis based in modal space.