Experimental evaluation of the motion-induced effects on turbulent fluctuations measurement on floating lidar systems
|2023-09-27 IN PRESS
|Thebault Nicolas1, Thiébaut Maxime1, Le Boulluec Marc2, Damblans Guillaume1, Maisondieu Christophe2, Benzo Cristina3, Guinot Florent1
|1 : France Énergies Marines, Technopôle Brest-Iroise, 525 Avenue Alexis de Rochon, 29280 Plouzané, France
2 : IFREMER, 1625 Route de Sainte-Anne, 29280 Plouzané, France
3 : Vaisala France SAS, 6A, rue René Razel, Tech Park, CS 70001, 91400 Saclay Cedex, France
|Wind Energ. Sci. Discuss. (Copernicus GmbH) In Press
|this preprint is currently under review for the journal WES.
This study investigates the impact of motion on the line-of-sight (LOS) turbulent velocity fluctuations derived from lidar profiler measurements. Onshore tests were conducted using a WindCube v2.1 lidar, referred to as the mobile lidar, mounted on a hexapod to simulate buoy motion, with a fixed lidar used as a reference. To assess the motion-induced effects on turbulent velocity fluctuations measured by floating lidar systems, the root-mean-square error (RMSE) of LOS velocity fluctuations obtained from the fixed and mobile lidars was calculated. A comprehensive wind dataset spanning 45 hours was analyzed, with a focus on regular motions involving single-axis rotations and combinations of rotations around multiple axes. The investigation of single-axis rotations revealed that the primary influencing factor on the results was the alignment between wind direction and the axis of rotation. The highest RMSE values occurred when winds propagated perpendicular to the rotation axis, resulting in pitch motion, whereas the lowest RMSE values were observed when wind propagated along the rotation axis, leading to roll motion. Furthermore, yaw motion was found to increase the RMSE compared to scenarios without yaw motion. Moreover, the addition of motion around extra axes of rotation was found to increase RMSE. High wind speed emerged as a significant driver of RMSE, with higher velocities leading to higher RMSE values. The study also indicated that the role of wind shear in influencing RMSE of LOS velocity fluctuations requires further investigation. Additionally, the study explored the impact of motion period, revealing that motion frequencies affect the LOS velocity spectra within the expected inertial sub-range. However, the impact on RMSE was found to be limited in comparison to the amplitude, wind direction, and wind speed.