Challenges in the design of tension moored floating wind turbines

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Wright, Christopher S.
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University College Cork
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In order to harness the extensive offshore wind resource, both in Ireland and in many parts of the world with deep offshore seas, the deployment of wind turbines on floating structures is required. Tension moored floating wind turbines are one type of platform with potential to be used for such deployments. These highly constrained platforms offer many benefits but also unique challenges compared against other platform stability types. This thesis investigated the use of such platforms through a combination of numerical simulations and experimental wave basin tank testing. Design improvements in an existing platform, HEXWIND, are identified, leading to the design of a novel platform, TWind. As tension moored platforms are highly constrained in heave, pitch and roll motions, a significant coupling and design complexity is introduced between the wind turbines flexible tower and the pitch/roll motions. The effect of this tower flexibility is parametrised in this work. As tension moored platforms rely on the tendon pretension for stability, operations such as installation and maintenance towing without tendons are statically unstable. Additional float for tow stability are designed and analysed in this work. These floats are designed to become wave energy converters once the platform is installed on site. The structural dynamic and hydrodynamic interaction effects of including these WEC are analysed in detail. Novel survival modes for the WEC floats are proposed. Design considerations related to potential tendon anchor misplacement are also analysed. A platform parameter study has led to a greater understanding of the design effects of modifying the floating concept dimensions. The addition of active WEC on the TMFWT is seen to significantly increase the platform forces and dynamics, with the tower root bending moment doubling compared to the standalone TMFWT. With 100's of GW's of proposed floating offshore wind capacity to be developed this century, the results from this thesis help improve the state of the art in tension moored floating wind design, installation and survivability.
TLP , Simulation , Experiment , Floating wind , Concept design , Wave basin , Tension moored floating wind , Wind turbine
Wright, C. S. 2022. Challenges in the design of tension moored floating wind turbines. PhD Thesis, University College Cork.