Mooring system design for floating wind turbines
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Recently, there has been a lot of research on floating wind turbines. These structures have to be moored for a station keeping, which is relatively straightforward for deep waters. In transitional water depths (35-70 m) however, it is not obvious how to find a good, cost-efficient mooring system.In this thesis a catenary mooring system for a typical floating wind turbine is designed with different options for the cables: chains, metal and synthetic rope, mixed type and clump weights. The analyses are executed with a Matlab model developed by the author. This helps to explore and improve the design and therefore lower the cost.Mooring system stiffness is calculated for catenary lines, and the environmental excitations are modelled as turbulent wind and random waves. The results are verified with DNV software, using a model for a floating wind turbine that already exists. The results are same, and a mooring system with clump weights is proposed to a floating wind turbine. This is because clump weights ensure horizontal loads to the anchors. Therefore the possibility for shorter lines and lower costs, compared to other options.The reader will find the developed model in appendix helpful in optimizing mooring systems with different line segments, and clump weights. Input is wave and wind loading, output is station keeping performance.The primary reference used for this thesis is "Developments in Offshore Engineering: Wave Phenomena and Offshore Topics" (Herbich, 1999). This book provides a method to calculate tension-displacement characteristics for a mooring line of different segments and clump weights. The reader is encouraged to consult the references for through discussion of the various topics connected to optimizing a mooring system for a floating wind turbine.This subject requires more discussion than can be afforded herein. For further work, the stability of the floating wind turbine needs to be studied.