Abstract: The nonlinear behavior varying with the instantaneous response was analyzed through the joint time-frequency analysis method for a class of S.D.O.F nonlinear system. A masking operator on definite regions is defined and two theorems are presented. Based on these, the nonlinear system is modeled with a special time-varying linear one, called the generalized skeleton linear system(GSLS). The frequency skeleton curve and the damping skeleton curve are defined to describe the main feature of the non-linearity as well. Moreover, an identification method is proposed through the skeleton curves and the time-frequency filtering technique.

Key words: system identification, nonlinear dynamic system, non-stationary signal, time-frequency analysis, Hilbert transform