Abstract
Cylindrical floating production storage and offloading (FPSO) units represent a new core asset in offshore oil exploration and development, where their stability and safety under complex sea conditions are critical. The design of their large waterline surface and the fluid resonance effect in the moonpool result in highly complex heave characteristics that are difficult to predict accurately. This paper implements and refines an iterative viscous-damping correction framework to enhance the motion response analysis of a moonpool-equipped cylindrical FPSO. Initially, the platform’s motion is captured using ANSYS AQWA and then utilized as a forced-motion input for ANSYS Fluent to simulate the viscous flow field. The equivalent viscous damping coefficients are extracted from the dynamic equilibrium of the drag response and fed back into the potential flow solver. This process is iterated until the heave response achieves convergence, explicitly accounting for the nonlinear dependency of damping on motion amplitude. For regular waves with headings of 0° and 90°, the converged heave damping coefficients were 1.533 × 107 and 2.226 × 107 N·s/m, respectively, corresponding to a dimensionless damping coefficient Cd ≈ 0.67 in both cases. In the time domain under the design sea state, the predicted heave amplitude decreased by approximately 50% compared with the uncorrected potential-flow result. Results indicate that the viscous damping correction method significantly reduces the platform’s response amplitude operator (RAO), drag, and heave response under, effectively mitigating excessive responses caused by the moonpool effect. This study provides a more reliable framework for the structural design and mooring configuration of cylindrical FPSOs.