The second-order output spectrum-based method for fault localization in ring type structures

In this paper, the application of properties of the second-order output spectrum (SOOS) for nonlinear fault localization in ring type structures is studied. A more general ring type multiple-degree-of-freedom model, which regards nonlinear faults (bolt loosening or fatigue crack) and inherent material or boundary nonlinearities as nonlinear restoring forces, is utilized to describe the nonlinear behavior of ring type structures. Through harmonic excitation analysis and a novel local tuning approach, properties of the SOOS of nonlinear ring type structures are analyzed and clearly demonstrated with examples. Based on these properties, a novel SOOS-based method with a local damage index is proposed for nonlinear fault localization. The effectiveness and feasibility of this novel method are validated with multiple bolt loosening fault localization on a satellite-like structure in experiments and are further illustrated through comparisons with several existing methods.