Offshore platforms, which work in hostile marine environment, are prone to be damaged. Hence, it is of essential importance to assess the structural integrity and safety of offshore structures. An offshore jacket platform, which works in Bohai Bay of China, has exhibited excessive vibration under mild environment. Field measurements were performed and vibration signals at different locations were recorded. Empirical mode decomposition (EMD) was applied to acquire the intrinsic mode functions (IMF). Then Hilbert-Huang transform (HHT) was used to compute the time-frequency distribution of the recorded signals. The vibration frequencies were found to be varying during the recording period. Results show that the EMD-HHT based approach provides a useful tool for structural performance evaluation.
Structural condition and performance are essentially important for the safety of offshore platforms, due to the harsh environment where the offshore platforms are working in. Structural assessment of offshore platforms could be conducted based on API RP 2SIM (API, 2009). SIM starts with data collection, which in turn becomes the inputs to the evaluation structural integrity, leading to an overall inspection and maintenance strategy. Therefore it is very important to find the potential damages for the structural integrity assessment. Generally, visual inspection and other localized method are traditional ways to monitoring the potential damages. However, there is a clear need to develop new approaches for monitoring the structural condition and performance of offshore platforms. One reason is the increasing depth of water in offshore oil exploitation which makes it hard to perform the visual inspection of structural damages. The other reason is the unreliability and the high cost of visual inspection and currently the most commonly used method. Moreover, more and more offshore platforms are approaching their design life around the world. These problems lead to the development of simpler monitoring techniques for performance monitoring of the structural safety.
