Damage Identification in Offshore Structures Using Wavelet Transform of Space Domain Signal

Large structures such as bridges, towers, offshore platforms are designed to be used over a long-time period. However, due to the unpredictable and out-of-control events, structural damages occur prematurely. Poor performance or failure of these structures will lead to irreparable impacts. To avoid these losses, engineers always look for methods to detect damages in structures in early stages of occurrence and to reveal their remaining life at the lowest cost. Thus developing a method for detecting system defects is a vital step. One of the main issues in damage detection methods is to seek some damage indexes that are sensitive to structural damage. In this research, a method is developed based on wavelet transform of structural responses and a good index for damage detection in offshore platforms is proposed. Structural data obtained from modal and time-history analysis of a fixed offshore platform under wave and ocean current loads are used as input data for wavelet analysis. The results of these two analysis after wavelet transform have been compared together, and feasibility of using the displacement of the structure subject to environmental loads as an index to detect damage of the structure using wavelet analysis has been investigated. The results showed that time- history responses are more sensitive to stiffness reduction and has better performance in damage detection than modal response of the first mode of platform