Numerical Simulation On The Response Of Single Point Moored FPSO Under The Extreme Wave Group

With the ongoing process of China's maritime power strategy,we are constantly exploring Marine resources,and more and more offshore operating platforms are being put into use.But ocean waves are difficult to predict and the sea surface changes rapidly,making the safety of offshore platforms a top priority.In recent years,the number of extreme damage incident waves,caused heavy casualties and serious economic losses,so in order to study under the extreme wave action,the motion response of offshore structures in this paper,based on the classical AQWA,explore in different sea conditions,single point mooring FPSO system train in adopting the "new wave" model and "bound" new wave model,And the motion response law of extreme wave groups determined by the recognition method of Rare wave groups.In this paper,three extreme wave group theories are introduced firstly,and the numerical simulation is carried out.The advantages and disadvantages of the three extreme wave group theories as well as the influence of spectrum width and period on wave group morphology are compared and analyzed.Then the dynamic response of FPSO is analyzed based on the three extreme wave group theories.The model adopted was a 150,000-ton FPSO single point mooring system with 3×3 groups of mooring cables.The sea conditions were sea conditions of Level 6,Level 8 and Level 9 in the South China Sea,and the spectrum types were P-M spectrum and JONSWAP spectrum.In this paper,the response law of extreme wave groups to FPSO motion is studied from the following three aspects:(1)The theoretical similarities and differences of the three extreme wave groups,as well as the influence of the period and spectral width on the wave morphology of the extreme wave group generated by the theoretical model are analyzed.It is found that the longer the period is,the greater the time interval between the extreme wave height and the adjacent wave peaks will be.Spectral width parameters have no significant effect on wave morphology,but the narrower the wave spectrum,the denser the large waves near the extreme crest,and the higher the adjacent crest.(2)The time-domain model was used to analyze the influence of wave direction on the motion response of FPSO under the action of 500 groups of 3-hour random waves and the coaction of wind,wave and current,as well as the statistical distribution law of each response,which provided reference and comparative data for the subsequent simulation environmental conditions.The research found that under the condition of wind,wave and current collinearity,The incident Angle had no significant effect on the distribution of the extreme value of motion response of FPSO,so the 180° wave heading condition was used for analysis and comparison in the subsequent analysis.(3)Respectively,based on the theory of three different kinds of extreme wave group generated extreme wave group of time series,and simulates the FPSO in these extreme wave motion responses of a train,statistical analyses under the condition of different sea state theory of motion response of the cumulative distribution function,and compared with the data under random wave,the engineering design are given more appropriate use of extreme wave group theory.It is found that the extreme value distribution of the "constrained" new wave theory can cover the analysis results in the time domain,and it is safe and reliable to use this theory in engineering analysis and design.Using the rare wave group theory,it is found that the motion response caused by wave groups with wave numbers of 3 and 5 is greater than that caused by a single extreme wave.