ECN publication
The influence of offshore floating foundations to the wind turbine generator. A study using aNySIMPHATAS
Hermans, K.W.; Peeringa, J.M.; Verbruggen, T.
Published by: Publication date:
ECN Wind Energy 5-1-2017
ECN report number: Document type:
ECN-E--16-032 ECN publication
Number of pages: Full text:
66 Download PDF  

In this report, three floating wind turbine foundation concepts are modelled; a Semi-submersible, Spar and tension leg platform type. The floating foundations are modelled with an NREL 5 MW reference turbine on top, and a monopile reference is included to act as a baseline model. An extensive set of 828 loadcases is simulated using the combined aero-elastic behaviour of PHATAS and hydrodynamic interaction from aNySIM. The floating structures are modelled as rigid bodies due to numerical solving limitations of the combined code. The environmental conditions simulated in the loadcases are applied equally to all floater types. Only the water depth differs for the models. The result is a large set of dynamic response data for the different floating foundations that can be compared directly. The Spar type foundation is shown to result in the largest loads on the turbine. However, sharp peaks in the load response are visible, likely caused by the dynamic stall model.

For the tension leg platform, a more detailed analysis is carried out for determining the tendon stiffness. This effort is finalized by proposing an integrated tendon design method for tension leg platforms.

Finally, an analysis is carried out for three mooring line configurations of the Semi-submersible floating foundation. Here a three line spread mooring configuration is compared with a three line hybrid configuration (applying chain and wire rope) and a six line configuration. The displacement and mooring line tension of all configurations remains within acceptable limits. The costs of the configurations have been estimated and a 25 % cost reduction can potentially be achieved when choosing the hybrid mooring line configuration over the other options.

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