Dynamic Positioning Control Research For Pipe Lay Vessel

Dynamic positioning(DP) control method of pipelay vessel is the key technology ofdesigning a ship dynamic positioning control system for laying deep sea oil and gas pipe.Combined with related engineering requirements, this dissertation carries on theoreticalresearch about modeling of J-lay dynamic positioning vessel and output feedback controlmethod of dynamic positioning pipe lay vessel. The main contents of dissertation are asfollows:Kinematic and dynamic equations of DP vessel with sea environment model which isconsidered as the main disturbance are derived. A catenary theory based nonlinear equationmethod is proposed to calculate the pipe forces that acting on J-lay vessel: ship position,heading, motion velocity, rate of turn and the pipelay speed are all taken into consideration. Asimulation system comprised by the above three parts of models is given, and simulation testresults are shown based on the above model.The elementary problem of designing a DP pipelay vessel output feedback controller issystem states estimation. For solving this issue, a robust strong tracking extended Kalmanfilter(RST-EKF) is proposed. An exponent fading factor is added in EKF to form a ST-EKFfor making filter converge rapidly by enlarging the current position and heading weightsunder model parameter uncertainties. Simultaneously, a piecewise stable matrix functiondepending on different innovation situations is involved to enhance robustness when facinginnovation gross error caused by wild values from position reference system and gyrocompass,so one can avoid the unreasonable zooming out of gross error by the fading factor andguarantee the filter robustness. Simulation shows that the designed algorithm can improvestate estimation convergence speed and be robust to gross error from innovation in case ofmodel parameter uncertainties. However, EKF is unable to guarantee the global stability ofsystem. To overcome this weakness, an adaptive sliding mode passive nonlinear observer isproposed with the model structure uncertainties problem. A kind of switching adaptive updatelaw is derived to estimate the upper bound of sliding mode surface, so the estimation vibrationcaused by large gain and system unstability results from small gain situations are bothavoided, uniform global boundedness of estimation errors is proved. Simulation process isbased on DP pipelay vessel model with nonlinear hydrodynamic matrix, it shows that theobserver can give satisfied estimations and be robust to model structure uncertainties causedby unknown nonlinear hydrodynamic matrix. For the optimal following control problem of DP pipelay vessel, an adaptivebackstepping inverse optimal state feedback tracking controller is proposed: first, an optimalpath following controller is designed for linearized parts of the system, time varying algebraicRiccati equation of the linear optimal path following controller combined with backsteppingprocedure are adopted to carry on system transformation, adaptive law is designed forestimating ocean slow varing disturbance, then the adaptive backstepping tracking control lawwhich can make system stable is given. Finally, index function is specified based on thetracking control law with inverse optimal process. In simulation case, optimal controlmethods with two groups of parameters and a traditional PID algorithm are compared to showthe validity of proposed algorithm. Based on the results mentioned above, for the purpose ofgiving a more suitable controller for vessel moving----stoping pipelay situations, abackstepping inverse optimal state feedback path following controller with speed assignmentis proposed, which can adjust desired speed conveniently. Inverse optimal backstepping pathfollowing control law is designed for making vessel body converge to desired path, then theindex function based on control law is specified, finally gradient update law is given to makethe speed error converge to zero. Simulation shows that the proposed algorithm can controlpath and speed simultaneously and give satisfied optimal control effects on vesselmoving----stoping procedure.For the problem of position differences between DP vessel path and and seabed pipe path,the distance between pipe-seabed touch down point and vessel body is assumed to be fixed,then pipelay path is mapped to vessel path by coordinates transformation. A feedbacklinearization tracking controller is used for testifying the coordinates transformation,simulation results show that the above method can make the vessel and pipe both trackdesired path. In addition, for the purpose of giving a more suitable controller to vesselacceleration----constatn speed----decceleration pipelay process, a feedback linearizationstate feedback path following controller with acceleration assignment is proposed, which canadjust desired acceleration conveniently. Control term of DP pipelay vessel second ordersystem is differentiaed to get a new three order augmented system, then feedback linearizationpath following control law is given for this augmented system to force the system outputfollow desired path asymptotically, and gradient update law is designed to make accelerationconverge to zero. Finally a constant speed control strategy is given by adjusting the desired acceleration. Simulation case illustrates the effects on path following and acceleration control,it can make the vessel achieve desired motion states during moving process.