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dc.contributor.advisorBachynski, Erin
dc.contributor.advisorLarsen, Kjell
dc.contributor.advisorS. Andersen, Håkon
dc.contributor.authorDanielsen, Oda Emilie Nilseng
dc.date.accessioned2019-09-11T08:50:56Z
dc.date.created2017-06-08
dc.date.issued2017
dc.identifierntnudaim:17092
dc.identifier.urihttp://hdl.handle.net/11250/2615028
dc.description.abstractThis thesis considers the possibilities of cost reduction of the mooring system for a floating semi-submersible wind turbine by inclusion of fibre rope instead of, or together with, chain mooring lines. Polyester fibre rope is cheaper, has lower weight and better fatigue life performance compared to chain, but has significantly lower abrasion resistance. The mooring system considered is made for the semi-submersible substructure OOStar Wind Floater, designed by Dr. Techn. Olav Olsen, with a 6MW wind turbine and for operation at 100 meters water depth. The work comprehended initial modelling of the substructure and tower as rigid bodies, implementation of the finite element wind turbinemodel, given by Statoil ASA, and establishment of an initial catenary mooring system, made of chain. Next, different configurations of taut leg mooring systems with polyester fibre rope were considered and compared with the initial system. The performance of the chain system and the fibre rope system were analysed through constant wind tests, free decay tests, ultimate strength analysis and fatigue life analysis. Finally, basic cost estimations of both systems were completed. The chain mooring system consisted of three 730 m long lines of 147 mm studless chain links. The pretension of the system was 50 tonnes. The first system analysed with fibre rope was a pure fibre rope mooring system, but the simulations showed slack in the mooring lines, as well as extensive pitch motions. Hence, the system was not approved. One clump weight were included on each mooring line to avoid slack loads. To increase the abrasion resistance, chain segments were included in the ends of the fibre ropes. Different configurations of systems with chain, polyester fibre rope and clump weights were analysed. The final fibre rope system consisted of polyester fibre rope mooring lines with end segments of chain (80 m in total) and clump weights of 140 tonnes. The total mooring line length was 600 m and the pretension was 384 tonnes. Polyester fibre rope with minimum break load of 1600 tonnes was used, while the minimum break load for the chain links which were included was 2160 tonnes. The simulations of the fibre rope system showed a satisfactory behaviour and an improved performance with respect to pitch motions relative to the chain system. The analyses of the 50-year storm condition proved to be most critical for both systems and the largest responses were found during this condition. In particular, the extreme condition analyses showed a prominent coupling between surge and pitch in both systems, but the two systems responded differently to this coupling. This was an interesting and unexpected finding that should be investigated further. The two systems had relatively similar behaviour in the other performance aspects that were analysed. The cost estimations of the components were simplified, but assumed to be correct relative to the other components. The fibre rope mooring system was dominated by the certification cost when only considering one turbine. But for a wind park with several wind turbines, this one-time cost has less relative importance. For a wind park of 50 wind turbines, the chain system had a total cost of 136 mEUR, while the fibre rope mooring system cost for 50 wind turbines was 48.7 mEUR. This implies a cost reduction of 87mEUR, i.e. 64%. The thesis work has shown that the mooring system with fibre rope, clump weights and chain segments has a satisfactory behaviour and significantly lower cost. Therefore, further design and analyses of this type of system is recommended. vien
dc.languageeng
dc.publisherNTNU
dc.subjectMarin teknikk, Marin hydrodynamikken
dc.titleAnalysis of Innovative Mooring Systems for Floating Semi-Submersible Offshore Wind Turbinesen
dc.typeMaster thesisen
dc.source.pagenumber140
dc.contributor.departmentNorges teknisk-naturvitenskapelige universitet, Fakultet for ingeniørvitenskap,Institutt for marin teknikknb_NO
dc.date.embargoenddate10000-01-01


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