Motion response of FPSO system under bimodal spectrum waves

The South sea of China is affected by tropical cyclones and typhoons in the western Pacific Ocean, which are prone to double-peak or even multi-peak waves in the form of mixed waves, which are potentially hazardous to the operational safety of marine floating structures. Therefore, based on the potential flow theory and considering the influence of different loading states, a comparative study was conducted on the motion response of FPSO and shuttle tanker side-by-side system under double-peak spectral wave and single-peak spectral wave states. The motion responses of the two hulls in the double-peak spectral wave states of mainly wind waves, wind waves and surge are equal, and mainly surge and the single-peak spectral wind waves state are calculated respectively. The calculation results show that (1) the amplitude of the motion of the two hulls in vertical, horizontal and longitudinal directions increases with the increase of the ratio of the low-frequency energy to the total energy; (2) it is the largest when the surge is dominant, the second largest when the wind waves and surge are equal, and the smallest when the wind waves are dominant; (3) the motion amplitude of both hulls in the double-peak spectral waves is greater than that of the single-peak spectral wind waves under the premise that the total energy is the same, and (4) the motion amplitude of both hulls in the double-peak spectral waves is greater than that of the single-peak spectral wind waves. The study shows that the influence of double-peak spectral waves should be considered in the mooring design and safety planning of FPSO operation system.