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PO090: Power performance measurements with nacelle mounted lidars for floating offshore wind turbines
Moritz Gräfe, Research Assistant, Universität Stuttgart
Floating offshore wind turbines (FOWT) have the potential to exploit wind resources in deep waters, where fixed bottom offshore turbines are not applicable. Several demonstrators and first commercial projects have shown the potential of floating offshore wind energy. It is expected that the installed capacity of floating offshore wind turbines in Europe will increase significantly in the coming decade . Compared to onshore or fixed bottom wind turbines new technical challenges occur due to the motions of floating platforms. Inflow conditions of floating wind turbines differ significantly from fixed wind turbines due to the dynamics of the floating platforms which imposes additional fluctuations in the inflow wind field. One way of measuring inflow conditions is utilizing nacelle based, forward-looking lidars measuring the incoming wind field characteristics. Power Curve assessment with nacelle-based lidar systems is a promising alternative to traditional methods and has already been investigated in the literature (see e.g. ). However, until now there is little experience on the use of nacelle-based lidar systems on floating wind turbines. In this contribution we introduce two approaches to investigate the use of nacelle based lidar systems on FOWT. The analysis is focused on wind field characteristics most relevant for performance analysis, namely rotor effective wind speed, shear and turbulence intensity. A numerical approach, coupling the publicly available lidar simulation framework ViConDAR (Virtual Constrained turbulence and liDAR measurements)  with an aeroelastic floating offshore wind turbine simulation is employed to evaluate the influence of floater dynamics on lidar wind measurements. Different motion cases are examined individually and combined to evaluate the influence of rotational and translational degrees of freedom. With the results we can quantify the influence of floater dynamics on lidar estimated wind field characteristics. In a second approach we use the data from a forward looking lidar mounted on the nacelle of a 2MW offshore floating wind turbine and analyse reconstructed wind field characteristics. We compare the lidar wind measurements and corresponding power curves to those obtained from a nacelle mounted sonic anemometer. From this analysis we draw conclusions on the applicability of nacelle based lidar systems for power curve assessment and performance monitoring. Thus, we contribute to the better understanding of lidar measurements on floating wind turbines in power performance assessment applications.  WindEurope. Wind energy and economic recovery in Europe. Pages 1-104, 2020  Rozenn Wagner, TF Pedersen and Michael Courtney. Power curve measurement with nacelle mounted lidar. Wind Energy, (June 2013): 1-20, 2013.  Pettas V, García F, Kretschmer M, Rinker J, Clifton A and Cheng P A numerical framework for constraining synthetic wind fields with lidar measurements for improved load simulations 2020 Proceedings of AIAA Scitech 2020 Forum (Aerospace Research Central (ARC))