Nonlinear FEM Analysis of Dropped Risers in Offshore Platform Operations

Offshore platform is an important infrastructure for exploitation of marine resources, and the operation safety is a key issue in the offshore platform industry. Dropped risers and other dropped objects would threat the platform structure and personal safety. In order to analyze the risk of damage caused by the dropped risers, a practical engineering analysis is presented using the engineering simulation platform ANSYS/LS-DYNA, a useful and powerful tool with an explicit dynamic solver. The impact angle of the dropped object may have different impact consequences on the offshore platform deck in respects of dimension and strength. By using ANSYS/LS-DYNA, the dropped riser's impacts on the platform deck under different angles circumstances are simulated and analyzed. Based on the simulation results, the nonlinear fitting approaches of polynomial fitting and BP neural networks were used to analyze the nonlinear mapping between impact angles and collision results. The results of the fitting were analyzed and verified by LS-DYNA and the fitting accuracy of the two methods was further discussed. This method can be used in conventional risk analysis studies for evaluating the risk for offshore platform and subsea pipelines from dropped objects.