Structure Damage Identification By Wavelet Analysis

Structures such as planes, aircrafts, bridges and offshore structures may damage due to various loading applied and various accidents in their lives. The accumulated damage may give rise to the failure of structures and lead to the loss of property and life. To guarantee the safety of structures and to minimize the maintenance cost, it is desired to find an effective and efficient method to identify the occurrence, location and extent of damage.In this paper, a relatively new tool, wavelet analysis combined with vibration based structure analysis is used to detect damage. The question of how to use wavelet analysis to extract damage signature and how to minimize the noise are considered.First, the continuous wavelet transform (CWT) by Mexican hat and haar were applied on displacement mode shapes and curvature mode shape respectively, specific examples show that the contour plot of the CWT's coefficients can give the position of crack in beam and the magnitude of the Lipschitz exponent can be used as a useful indicator of the damage extent.Second, the WT based method is used to estimate structure modal parameters from the acceleration responses of a cracked beam. The influence of the transform scale and mother wavelet is studied. The result shows that the estimation is accurate and can be used to identify the existent of any damage.Third, damage identification of time varying structure is studied, the theoretical analysis show that the logarithmic decay envelop of the CWT's coefficients at corresponding scale is a good indicator of the structure varying and damage, since their difference can be distinguished by using neural network, this method is valuable.