| Currently,with the increasing demand for oil and gas,exploration activities are moving to deep sea.Position mooring(PM)system has proved to provide a cost-effective alternative to permanent platforms for offshore oil production.PM system combines the advantage of mooring system with the advantage of dynamic position system.The reason is that the mooring system provides effectively passive control at the intermediate water depths,and the thrusters can perform active control to assist the mooring system when necessary in severe environmental conditions.This thesis study the control method of internal turret position mooring FPSO in different sea conditions.Firstly,the kinematics and dynamics of the moored FPSO hull mathematical model is established.The environmental mathematical model is also established.The catenary method is applied to analyze the mooring line forces,and mathematical model of the single mooring line is set up based on the catenary equation.Then mathematical model for the whole turret mooring system is established.Secondly,adaptive WF filtering observers and nonlinear PID contorller are designed in calm sea.A structural reliability index is defined to evaluate the breaking strength of each mooring line and an optimal set-point was calculating based on structural reliability index.Then adaptive WF filtering observers and PID controller which based on local optimal position are designed in moderate sea condition.An observer without WF filtering and a state feedback controller using the backstepping technique are designed in extreme sea condition.Finally,a hybrid control system including supervisory control system is constructed based on scale-independent hysteresis switching logic to operate in varying operational conditions from calm to extreme seas.The simulations show that the hybrid control system can ensure the mooring line safety in different sea condition,and switching among controllers does not affect the stability and performance of the whole system. |
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