Experimental Research On Damage Detection And Early Warning For Structural System Of Offshore Platforms

At present, the service year of a fairly large number of platforms are much long in offshore oil development of our country, and exist certain degree of damage, this aged platforms will bring risks to our safety in production. Acoustic emission(AE) technology can monitor micro-cracks and trace the changing of the little cracks. Buiding up early warning system for offoreshore platform based on AE technology can ensure working safety on offore platform which can monitor offoreshore platform in all weather and find the hurts of the platform, so the early wrining system has immense research value. The dissertation focuses on building up early warning system for offshore platform which is a part of the"863"High Technology Research and Development Program of China (2006AA09Z355)of"Research on Life Extension Technology for Aged Offshore Platforms".Offshore platform model and steel rods are used to carry out experimental study on structure damage detection based on AE technology. The damage of steel rods are simulated by fabricating defects, and use Carbon Fibre Reinforced Plastics (CFRP) to repair parts of steel rods. Using original rods and reinforced rods to carry out fatigue fracture tests, and collect acoustic emission (AE) signals timely during tests, using wavelet analysis, bispectrum analysis and many other signal processing methods to analyzed AE signals. Through the contrastive analysis results of the two types of rods, CFRP can repair the damage of steel rods effectively, and the influence of AE signals characteristics from using CFRP to reinforce rods is revealed in time domain, frequency domain and time-frequency domain, all this become the theory support for offshore platform damage repairing.The offshore platform model tests are designed, the damage of some rods on offshore platform structural system may happen, and the simulation and experimental methods of the damage is determined. using sine signal of different frequency (15Hz, 20Hz, 25Hz) to load damage and undamaged platform model respectively, collect AE signals of model timely and take many signal processing methods to analyze the AE signals. The results indicate that in time domain and frequency domain AE signals of different level of the damage of offshore platform model have different characteristics and using AE technology to carry out detecting of complex structural system is valid and reasonable. Through the contrastive analysis of every kind of signal processing methods, wavelet packet energy spectrum analysis and bispectrum analysis is more suitable to AE signals than the others. Finally, Early Warning system for Offshore Platform is started to research based on the above experimental research, communication technique detecting technique and other modern high techniques, Multi-index model of security early warning indexs is established by Rise time, Root-Mean-Square voltage (RMS), and Energy Ratio Variation Deviation (ERVD), the value of every security early warning index is determined by experimental results,the assment of security early warining system indicates that the reliability of the system is high.