Structural Damage Localization by Outlier Analysis of Signal processed Mode Shapes: Analytical and Experimental Validation
Abstract Contrary to global modal parameters such as eigenfrequencies, mode shapes inherently provide structural information on a local level. Therefore, this particular modal parameter and its derivatives are utilized extensively for damage identification. Typically, more or less advanced mathematical methods are employed to identify damage induced discontinuities in the spatial mode shape signals, hereby, potentially, facilitating damage detection and/or localization. However, by being based on distinguishing damage induced discontinuities from other signal irregularities, an intrinsic deficiency in these methods is the high sensitivity towards measurement noise. In the present paper, a damage localization method which, compared to the conventional mode shape based methods, has greatly enhanced robustness towards measurement noise is proposed. The method is based on signal processing of a spatial mode shape by means of continuous wavelet transformation (CWT) and subsequent application of a generalized discrete Teager Kaiser energy operator (GDTKEO) to identify damage induced mode shape discontinuities. In order to evaluate whether the identified discontinuities are in fact damage induced, outlier analysis is conducted by applying the Mahalanobis metric to major principal scores of the sensor located bands of the signal processed mode shape. The method is tested analytically and benchmarked with other mode shape based damage localization approaches on the basis of a free vibrating beam and validated experimentally in the context of a residential sized wind turbine blade subjected to an impulse load.