Loads and Dynamic Response Characteristic on FPSO Under Internal Solitary Waves

According to the established prediction model of internal solitary wave loads on FPSO in the previous work, the lumped mass model and the movement equations of finite displacement in time domain, the dynamic response model of interaction between internal solitary waves and FPSO with mooring lines were established. Through calculations and analysis, time histories of dynamic loads of FPSO exerted by internal solitary waves, FPSO's motion and dynamic tension of mooring line were obtained. The effects of the horizontal pretension of mooring line, the amplitude of internal solitary wave and layer fluid depth on dynamic response behavior of FPSO were mastered. It was shown that the internal solitary waves had significant influence on FPSO, such as the large magnitude horizontal drift and a sudden tension increment. With internal solitary wave of -170 m amplitude in the ocean with upper and lower layer fluid depth ratio being 60:550, the dynamic loads reached 991.132 kN (horizontal force), 18067.3 kN (vertical force) and -5042.92 kN<middle dot>m (pitching moment). Maximum of FPSO's horizontal drift was 117.56 m. Tension increment of upstream mooring line approached 401.48 kN and that of backflow mooring line was -140 kN. Moreover, the loads remained nearly constant with different pretension but increased obviously with the changing amplitude and layer fluid depth ratio. Tension increments of mooring lines also changed little with the pretension but increased rapidly when amplitude and layer fluid depth ratio increased. However, FPSO's motion increased quickly with not only the horizontal pretension but also the amplitude of internal solitary wave and layer fluid depth ratio.