AQWA-Based Motion Response Analysis of a Suezmax FPSO

Abstract

To investigate the motion response characteristics of a long-term moored floating production, storage and offloading unit (FPSO) under wave action, a Suezmax FPSO was selected as the research object. Based on three-dimensional linear potential-flow theory and wave radiation/diffraction theory, numerical simulations of the motion responses under wave loading were conducted using AQWA. The six-degree-of-freedom response amplitude operators (RAOs), first-order wave excitation forces, and time-domain motion response characteristics of the platform under different wave directions were systematically analysed. The effects of wave frequency and wave direction on the seakeeping performance of the FPSO were also discussed.The results show that the six-degree-of-freedom motion responses of the FPSO exhibit significant directional dependence. The RAO peaks are mainly concentrated in the low-frequency range, and the motion responses are significantly amplified when the wave frequency approaches the natural frequency of the platform. Moreover, the RAO peaks are not determined solely by the maximum value of any single type of excitation force, but result from the combined effects of the Froude–Krylov force, diffraction force, and other hydrodynamic forces. The time-domain analysis further verifies the frequency-domain results, indicating that the pitch and roll responses increase most significantly under severe sea conditions.