Research On Mooring Dynamic Positioning Control Method Of Arctic FPSO

In recent years,the oil and gas resources in open seas have been decreasing year by year due to the increasingly frequent exploitation of offshore oil and gas resources.There are rich resources and mineral reserves in arctic,and the glaciers and snow are gradually melting along with global warming,which provides favorable conditions for the exploitation and acquisition of resources.Floating Production Storage and Offloading(FPSO)is the most important platform in offshore oil and gas resource exploitation activities.Currently,FPSO has been applied in arctic regions.Based on the research background of oil and gas exploitation in arctic environment,this paper studies the mooring dynamic positioning control method of FPSO,the specific research contents are as follows:(1)The FPSO kinematic model,mooring system model and arctic environments model are established.Firstly,according to the kinematics and dynamics principles,the FPSO kinematics and dynamics model are established to lay the foundation for the subsequent observer and controller design.Secondly,considering the arctic environment problems,a wind,waves and currents environment model and ice loads model are established.Then,the catenary method is used to analyze the mooring lines,and the detachable buoy mooring line model is established.Finally,under a given constant disturbances,Simulations of the FPSO and mooring models verifies the validity and correctness.(2)Considering the influence of disturbance in process of the FPSO state estimates,an Acceleration Feedforward(AFF)state observer is designed under ice loads.Firstly,using the measured value of the FPSO acceleration,an AFF term with a measurement delay is designed and combined with a nominal state observer to form an AFF state observer;then,in order to prove the consistent final boundedness of the observer’s error,the Lyapunov stability discriminant method is introduced for stability analysis;finally,in different marine environments,the accuracy of the designed AFF observer is verified by simulation.(3)Considering the safe positioning of arctic FPSO under extreme external disturbances such as sea ice,an acceleration feedforward-nonlinear model predictive controller(NMPC)is designed to realize the positioning control of FPSO.Firstly,the AFF control law is designed by using velocity and acceleration terms obtained from the AFF observer;secondly,the FPSO motion model is feedback linearized by using the method of differential homeomorphism,and NMPC is designed to form an composite control with AFF,which achieves disturbance suppression and precise positioning;finally,simulation experiments are carried out in the icefree marine environment and the arctic marine environment,respectively,the effectiveness of the designed AFF-NMPC and the safety of arctic operations is verified.(4)Considering the safety of mooring lines and the energy-saving performance of FPSO in arctic environments,a structural reliability index that characterizes the reliability of mooring lines is added to the original FPSO model,and an AFF-NMPC based on the structural reliability is designed.Firstly,the structural reliability index and the motion of the FPSO are correlated by transformation,and the motion model of the FPSO based on the reliability design of the cable structure is established;then,feedback linearization is performed for the transformed model,and an AFF-NMPC with a reliability-based mooring system is designed;finally,the FPSO motion simulation of the AFF-NMPC is compared with the reliability-based AFF-NMPC to verify the safety and energy saving of the designed controller.