| To assess the performance of damping augmentation strategies, accurate and reliable damping identification techniques are needed for both linear and nonlinear damping mechanisms. In this work, the transient response of a single degree of freedom system having either viscous, solid, Coulomb or quadratic damping is considered. Two analyses for identifying damping from transient test data are evaluated: an analysis based on a periodic Fourier series decomposition and a Hilbert transform based technique. Analytical studies for a spectrally isolated mode are used to determine the effects of block length, noise, and error in identified modal frequency on the accuracy of these techniques. The effect of a mode that is spectrally close to the primary mode of interest is also assessed. The primary mode has either Coulomb or quadratic damping, and the spectrally close mode is either undamped or has a specified viscous damping level. A comprehensive evaluation of the effects of close mode amplitude, frequency, and damping level is performed. The case of an extremely dominant, lightly damped close mode is also considered. A classifier is developed to identify the dominant damping mechanism in a signal of ‘unknown’ composition via one of three approaches. The first is based on minimizing the LMS error between the predicted and identified envelope signals, while the other two utilize the concepts of equivalent viscous, equivalent Coulomb, and equivalent quadratic damping. |
