FPSO Mooring Assistant Dynamic Positioning System Modeling And Input Saturation Control

With the increasingly fierce competition of marine environmental resources,floating production storage and offloading vessel(FPSO)has been widely used in the exploitation of deep-sea oil,because of the advantages of strong wind and wave resistance and large oil storage and offloading capacity.In the face of the harsh marine environment frequently encountered by deep-sea development,the safety of FPSO is increasingly valued by scholars.In this paper,the model of FPSO mooring system is established,and in order to make it resist the interference of marine environment,a sliding mode controller considering the input saturation is designed to realize the auxiliary dynamic positioning function of mooring.The main research contents of this paper are as follows:The kinematics and dynamics mathematical model of FPSO hull,mooring system model with pontoon and marine environment model are established.Firstly,the kinematic model and dynamic model of FPSO hull are established by taking the North East coordinate system and the hull coordinate system as the reference coordinate system;secondly,the cable of the internal turret FPSO mooring system is analyzed,and the mooring system model with pontoon is established based on the catenary method;finally,the marine environment model is established,and the mathematical model of hull motion and the dynamic model are established by simulation analysis The correctness of the mooring system model is the basis of the subsequent dynamic positioning control system design.Aiming at the established FPSO mooring system model,the mooring system simulation software termsim provided by Marin pool in the Netherlands is used to check the single point mooring state model of internal turret FPSO.In the termsim simulation environment,the hull model and mooring system model of FPSO are established respectively,and the parameters of wind,wave and current ocean environment are set up to obtain the mooring position distribution of FPSO in the ocean environment.Through the simulation,the position and attitude of the ship and the force of the mooring system change with time are analyzed,and the validity of the positioning of the FPSO,the safety of the mooring system and the effect of the wind vane under the condition of single point anchoring are verified.Aiming at the established mathematical model of FPSO motion,a sliding mode controller for dynamic positioning of mooring based on structural reliability is designed.Firstly,by introducing the structural reliability factor of the mooring system cable,the design matrix combines the mooring positioning system with the dynamic positioning system;secondly,the sliding mode control algorithm is used to design the auxiliary dynamic positioning controller of the mooring system and the Lyapunov theorem is used to prove the stability of the system.Finally,through the simulation experiment,the controller is compared with the traditional sliding mode controller without considering the structural reliability and the backstepping controller with considering the structural reliability,to verify the effectiveness,safety and energy saving of the proposed sliding mode controller based on the structural reliability.Considering the problem of input saturation of the dynamic positioning system propeller in the actual situation,the sliding mode controller of anchor assisted dynamic positioning based on the structure reliability is further improved.Firstly,a smooth bounded function with hyperbolic tangent function is introduced to smooth the output control force.Then,a saturation compensation auxiliary system is designed to compensate the input saturation of the system,and the stability of the system is proved by Lyapunov theorem.Finally,the simulation results show that the two controllers can realize the dynamic positioning control under the condition of considering input saturation and ensuring the safety of the mooring system.