Higher-Order Motion Response of Freely Floating FPSO System at Different Water Depths

The rapid expansion of the offshore industry has significantly grown into deep and ultra-deepwater fields in the last few decades. This study assesses the performance and viability of floating production storage and offshore (FPSO) platforms in such challenging environments. Using advanced numerical tools like Ansys Aqwa, comprehensive first- and second-order motion response analyses were conducted for an unmoored FPSO system at depths of 300[Formula: see text]m, 1[Formula: see text]300[Formula: see text]m, and 2[Formula: see text]100[Formula: see text]m. The study included hydrodynamic diffraction analyses to determine the response amplitude operators (RAO) for the first-order responses. It assessed the steady drift forces and quadratic transfer functions (QTF) as second-order responses. A key focus of this study is to provide a detailed comparison of higher-order force impact across varying water depths of offshore fields, an area rarely explored in the existing literature. Experiments were conducted in a state-of-the-art wave basin ([Formula: see text][Formula: see text]m) at IIT Madras, using a 1:90 scale model to validate and verify the numerical process. The results show significant differences in the roll and pitch motions across different sea conditions and depths, underscoring the importance of accounting for higher-order forces in FPSO design. This study provides valuable insights into the conceptual design and mooring line requirements of FPSO platforms, improving their stability and hydrodynamic performance in deep and ultra-deepwater environments and providing suggestions for future improvements.