Research On Thruster Assisted Position Mooring

It is the urgent necessities of ocean resource exploitation causing the research of hightechology assembly are concerned more and more. Positioning technology is one of the keytechnologies in ocean exploitation. The dynamic positioning and position mooring are twomain positioning ways, but each of them has their advantages and disadvantages. Thrusterassisted position mooring technology raised in this paper can exploit the advantages and avoidthe disadvantages, and both of them can use the resource efficient and gain a good positioningresult. The research object of this paper is FPSO, the thruster assisted position mooringtechnology of turrent anchored FPSO is studied.First, the mathematics model of the FPSO and the ocean environment is established.Based on the establishing of the body-fixed frame and the north-east-down frame, thekinematic equations and the dynamics of three degree of freedom motion of FPSO areestablished. At the same time, the ocean environment mathematics model is given, whichincludes the disturbance mathematics model of the wind, wave and current to the FPSO.Then, the simulation model of FPSO mooring system is established basing on finiteelement analysis. With the study of the dynamic characteristic of mooring line, the dynamicsequation is given which is discretized into finite elements and the mooring sysyem whichcontains several lines is given. Then, two simulation examples of FPSO equipped with fourmooring lines are carried out in two different ocean environments, which verifies thepositioning ability of FPSO with mooring system.In the next step, the observer of FPSO is implemented to estimate the low-frequencyinformation. In order to improve the using of Kalman in the nonlinear systems, this paperstudies the improved algorithms including UKF and CKF, and two observers based on each ofthe algorithm are designed. The estimating precision of UKF and CKF is compared insimulation, which also proves that the CKF has higher presision.Last, the FPSO controler is designed using backstepping method to control the positionand heading. Based on the control Lyapunov functions recursive design technique, the FPSOmethematics model is treated as two cascaded systems, then the control Lyapunov functionsof each of them are found, finally the backstepping thruster assisted control law of mooredFPSO is given. In order to verify the controler, two simulating experiments of thruster assistedposition mooring system in medium and extreme ocean environment are taken out. The resultindicates that the thruster assisting can reduce the tension of mooring lines, at the same time the postion and heading of FPSO is controled.