COMPARISON BETWEEN THE TIME-DOMAIN FOURIER FILTER OUTPUT AND THE NON-LINEAR AUTO-REGRESSIVE METHODS FOR NON-LINEAR MODAL IDENTIFICATION

摘要

In this paper, a comparison is made between two methods for identifying the modal properties of a lightly damped single degree-of-freedom system with non-linear stiffness. Each uses the decaying free vibration response to yield quantitative estimates of the linear natural frequency, the damping ratio, and the non-linear stiffness parameters which cause the natural frequency to change with vibration amplitude. The first approach uses the Time-Domain Fourier Filter Output (TDFFO) method to obtain precise estimates of the natural frequency and amplitude variation during the decaying vibration, and the modal parameters are then obtained by iterative curve fitting. The second approach uses the Non-Linear Auto-Regressive (NLAR) method, which yields an identification by direct curve-fitting to the measured transient vibration signal. The methods are compared using both simulated and measured experimental data, and the effect of noise is also examined.