SIMULATION OF UNDERWATER MOORING DYNAMICS USING A SIMPLIFIED NUMERICAL METHOD: A CASE STUDY OF FLOATING PRODUCTION STORAGE AND OFFLOADING SYSTEM

ABSTRACT Floating, Production, Storage, and Offloading (FPSO) vessels play a pivotal role in offshore oil and gas production, demanding a nuanced understanding of their mooring systems' dynamic behavior in complex marine environments. Marine cable systems face persistent challenges arising from dynamic environmental factors. This research delves into the details of mooring dynamics, considering environmental factors such as waves, currents, and wind. The study adopts a comprehensive approach, addressing the challenges posed by the three-dimensional nature of marine systems. The research emphasizes the significance of accurately modeling hydrodynamic drag, which can contribute up to 80% of the overall damping in the mooring system. The complexity arises from the lack of definitive solutions for the dynamic equations governing cable motion, exacerbated by quadratic hydrodynamic drag. To address this, the study employs numerical methods, focusing on the lumped mass method for its clarity, simplicity, and efficiency. Key numerical simulations were conducted using ANSYS AQWA, validated against a simplified numerical method. The hydrodynamic responses of the FPSO and its mooring system were analyzed, encompassing cable forces, mooring sum forces, and the effects of FPSO offset. Results indicate that the system experiences dynamic loading, with tension forces in the mooring cable ranging from 188,873.27 N to 397,107.78 N. The mooring sum forces exhibit fluctuations, reaching a minimum of -78,858.34 N and a maximum of - 31,710.57 N in the global X direction. In the heave direction, forces range from -389,218.63 N to -186,192.23 N. The proposed recommendations for future research focus on refining hydrodynamic drag models, incorporating advanced nonlinear dynamics, and addressing timedependent behaviors in mooring systems. Advanced meshing techniques, sensitivity analysis, and the integration of real-time environmental data are proposed for improved simulation accuracy. Collaboration with industry experts, application of machine learning, and investigation of dynamic responses under extreme conditions are highlighted to enhance the practical relevance and application of research outcomes. In conclusion, this research contributes to the comprehensive understanding of mooring system dynamics, providing valuable insights for the design, operation, and safety of FPSOs in challenging marine environments. The proposed recommendations chart a course for future research, aiming to advance the field and address practical complexities encountered in offshore engineering.