Definition of a way to improve the alignment performance of a weathervaning offshore wind platform with the wind direction in sites with high crossed sea currents influence

Floating Wind (FW) power is slowly but surely becoming a reality in Europe. In order to reduce costs and make FW a cost effective industry, companies are devel- oping new technologies merging different concepts and ideas previously used in the Oil and Gas (OG) sector. Among them, is the use of weathervaning platforms to eliminate the need of an active yaw system at the nacelle to align the turbine with the wind direction. This thesis aims to study the impact that sea currents have on the alignment perfor- mance of weathervaning platforms in installation sites with great crossed currents influence and under slow wind scenarios. To do so, a floater designed by the disrup- tive spanish company X1 Wind, featuring a 15 MW turbine designed by NREL, will be taken as reference. At the same time, this thesis work will also propose, compare and study different ways and mechanisms to improve its alignment. The results obtained showed a slight degree of misalignment of the floater with the wind direction for scenarios with strong currents, over 0.8 m/s, and wind speeds in between the cut-in and rated speed of the turbine, with an angle offset between them around the 90 °. With the intention of proposing different helping mechanism, both an analytical and a virtual model, using Ashes, a low order modelling software developed by Simis, were created to predict the dynamic behaviour of the floater and to test a set of generated concepts based on a previous patent research and a literature study. Thanks to both models, it could be concluded that the use of a passive system based on rigid sails, such as the ones used in Wind Assisted Propulsion Systems (WAPS) would not be enough in these kind of scenarios and so an active system was devel- oped. Said system featured a mechanism that allowed the nacelle to rotate within a small range of motion close to -5°and 5°, which showed a reasonable alignment performance