Fault Tolerant Control of Thruster-Assisted Position Mooring System
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- Institutt for marin teknikk 
This thesis fo cu ses on the fau lt-to lerant control al gor ithm o f the thr u ster-assiste d posi tio nmoor ing system ( TAPM). TAPM is an energy-efficient and reliable stationkeeping method fordeep water structures. System failures significantly endanger the marine control systems,and ultimately reduce the reliability and safety during operation and production.First of all, mooring line breakage is difficult to detect without failure alarms. The statisticdata shows that 50% of the floating production, storage and offloading (FPSO) in the NorthSea cannot monitor line tension in real time, and 78% of them do not have line failure alarmsin 2005. Therefore, line break detection is a crucial issue for the TAPM systems, especiallythose built decades ago.Additionally, the global positioning system (GPS) signals may experience drifts duringsome extreme conditions, such as solar events and sudden ionospheric disturbances (SID).A typical position reference (posref) drift failure mode in a dynamic positioning (DP) systemis that all GPS measurements starts to drift due to SID.Furthermore, the tensioned-based localization accuracy is not sufficient when the anchors are unknown. Additionally, class society news shows that one anchor lost per 100 shipsa year. To remove breaking anchor and chain is an expensive task.Finally, the position of the upper moored vessel not only influences the mooring forcearrangement, but also the riser angles at the top and bottom ends. Previous works appliesfinite element method (FEM) model and winch control to determine the vessel s equilibriumpoint. However, FEM model does not have analytical solution, and winch control is notapplied during practical operation. Therefore, new setpoint chasing algorithm of TAPM isrequired to ascertain the safety of the operation and production. First of all, a TAPM toolbox was developed in Simulink. MSS TAPM is a expansion pack ofMSS GNC and MSS Hydro toolbox. MSS TAPM is a Simulink lib for modelling TAPM system,especially the turret-based mooring system. In this lib, there are a group of different modules and examples, including two mooring line modules, a turret module, a TAPM module,an animation generation function, etc. Additionally, two papers were refined based on theworks from the specialization project which are submitted to and accepted by the 10th IFACii iConference on Manoeuvring and Control of Marine Craft (MCMC2015) after refinement. Another two papers will be submitted after further refinements and more strict verification.