Floating LiDAR Technology

Floating LiDAR Technology: Oceanographic parameters influencing accuracy of wind vector reconstruction

Cool, G.A.

Bierbooms, W.A.A.M. (mentor)

Aerospace Engineering

Aerodynamics, Wind Energy & Propulsion

Wind Energy

2016-09-21

Wind assessment of new locations prior to the installation of wind turbines is an established process. However, this process is still very costly. The common way to measure offshore wind profiles is the usage of met masts, which get more expensive with increasing water depth and hub height. Recently, wind measurement LiDARs are installed on floating platforms to investigate the wind profile offshore. Floating LiDARs are a promising technology thanks to low cost and high flexibility. However, further understanding is required in order to make floating LiDAR technology fully acceptable. The movement of a floating LiDAR brings some uncertainty in reconstructing the wind vector and turbulence characteristics. These uncertainties hold back the full commercial acceptance of LiDAR technology in the offshore wind energy industry. In order to accept floating LiDARs as a valid technology, acceptance criteria need to be defined in terms of accuracy and confidence of the results. This thesis has developed a simulation tool to define and model the effect of uncertainties in floating Li- DAR technology, which influence the accuracy of the wind field characterisation. The model reconstructs wind vectors as seen by a specified LiDAR and is capable of analyzing the parameters influencing wind vector reconstruction. These parameters can be categorized in wave, wind and LiDAR conditions. Several wind profiles were used as input: a logarithmic wind profile for a first assessment, synthetic turbulent wind fields and Large Eddy simulations (LES) for a more realistic approach. Wave conditions based on the Airy wave and real-motion data are used to see the influence of wave height, wave period and wave number. It has been observed that floating LiDARs can reconstruct 10min velocities in a very accurate way, regardless of the experienced wave conditions which varied from normal to extreme conditions. For all considered wind tools, the error was less than 0.1 m/s for the averaged 10min wind speed, with a very small standard deviation, ¾. Reconstructing turbulence characteristics has been proven to be less accurate. The error is significant and cannot be ignored. With a reference turbulence intensity value of 8% at an altitude of 100m, the average bias can go up to 0.60% with a ¾-value of 0.52%for synthetic wind fields. In more extreme wave conditions, the average bias can go up to 1 % andmore. An error of more than 3%may occur at altitudes of 150m or higher for the turbulence intensity when using LES files in these extreme conditions. The use of motion correction is suggested to reduce this bias. This correction can happen with a mechanical system (motion stabilization platform) or a correction algorithm built into the software. Since the approach that was used in this research has proven to be successful, further research can be performed based on this study. Further investigation should be focused on understanding turbulence behaviour, measured by floating LiDARS. Also the usage of wind data coming from measurement campaigns should be valuable to proceed with in this research.

Windenergy

http://resolver.tudelft.nl/uuid:ab02439b-749b-400d-b113-adaf49e00134

Student theses

master thesis

(c) 2016 Cool, G.A.