Prediction Method of Fatigue Intensity in Whole Life Period of the Semi-Submersible Platform Based on 3D Potential Flow Theory

In the fatigue assessment of marine structures, the peak distribution of alternating stress is simply regarded as a narrow-band distribution by the frequency domain spectrum analysis method, which does not conform to the characteristics of broadband sea state, and the fatigue results are often conservative. Although the full-time domain method has high calculation accuracy, the whole process is too time-consuming and difficult to be applied in practical engineering. Utilizing the 3D potential flow theory, we computed the hydrodynamic load. In conjunction with the wave spread diagram of the operating area, the nine characteristic wave loads, and the structural response and fatigue stress amplitude of the platform subjected to fatigue wave loads, we determined the fatigue damage value and fatigue life based on simplified fatigue theory and fatigue stress amplitude. The evaluation results show that the key nodes of the platform structure meet the fatigue strength design requirements. Compared with other fatigue analysis methods, this method requires less work. In the initial stage of structural design, there are great changes in the structure type, functional type and operating area of the platform, and the fatigue design can be carried out by short-term statistical forecasting or long-term statistical forecasting. Therefore, the proposed prediction method for fatigue intensity of semi-submersible platforms offers a valuable reference for similarity analysis.