A method for nonlinear system classification in the time-frequency plane

This paper presents a new method for the classification of nonlinear systems based on the time-frequency analysis of the free oscillations. In particular, oscillators described by a nonlinear second-order differential equation are considered. The nonlinearity is due to a nonlinear function of the state variable, which produces free oscillations with a time-variant spectrum. The classification is based on two different estimates of the fundamental frequency of the free oscillations. The comparison between the two estimates allows a very efficient system classification. Both the proposed estimators and the way of combining the two estimates are new. Validation tests have shown the high performances of the proposed technique.