| Offshore platform is one of the most essential buildings in offshore oil industry. Affected by the environment, vibration and other factors, the structure problems such as fracture defect, corrosion, wear, fatigue damages may occur, which affect the platform safety seriously. This problems may lead to platform collapses or slips, and cause huge casualties, economic losses and environmental pollution and so on.The acoustic emission(AE) technology has been applied to the structure damage monitoring of offshore platform successfully in terms of early damage detection, alarming and location in foreign researches. It is available to gain time to repair and avoid economic losses, moreover, has important research significance and application value. The optimal placement of sensors, AE signal acquisition, AE source location and structural safety evaluation in offshore platform were investigated by using the acoustic emission detection experimental system which belonged to China University of Petroleum(East China) offshore oil equipment laboratory, which provide guidance for sensor placement and acquisition parameters determines in AE source location for offshore platform.(1) Study on optimal placement of sensorsThe placement of sensors was optimized by damage risk analysis for each node in the offshore platform, which was calculated with finite element analysis and historical data, and monitoring area defining by AE signal attenuation rules and the distances between each node which were determined by the shortest path algorithm in the graph theory. Exhaustive method was used to propose the placement of sensors.(2) AE experiment on damaged offshore platformTaking the undamaged and damaged offshore platform jacket model under the vibratory loading as the laboratory experiments researching object, the structure behavior was identified from the recorded AE signal features which were extracted by the EMD, HHT and wavelet package method. Field experiment was conducted on the in-service offshore work over platform of CNOE. The normal signal analysis and wavelet analysis of the pencil lead breaking source were performed, which provides basis for the AE application in engineering structures.(3) AE source location analysis based on the graph theorySensors were placed according to the aforementioned method. The AE source in the structure was located in various zones by matching the distance between the nodes and the sensors and the arrival time for the AE signals based on the graph theory. The accurate location was performed by the normal ?T location in the determined zones. Combined with the two AE location methods, the source location accuracy can be guaranteed, the efficiency was increased, the applicable area was enlarged.(4) AE source location for irregular structural based on graphIn irregular structural, the AE source location was determined by calculating the shortest AE signal propagating path obtained by discreting the local structural and controlling the discretized precision.(5) Structural safety evaluation based on AE characteristicsThe structural damage evaluation based on AE method was presented by considering the frequency and amplitude characteristics in the detected AE signals. The location algorithm for damage location in offshore platform which is based on graph theory was developed on MATLAB software. |
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