Replies to comments on wes-2021-75

Rieska Mawarni Putri

doi:10.5194/wes-2021-75-ac1

Abstract

<strong class="journal-contentHeaderColor">Abstract.</strong> The one-point and two-point power spectral densities of the wind velocity fluctuations are studied using the observations from an offshore mast at Vindeby Offshore Wind Farm, for a wide range of thermal stratifications of the atmosphere. A comparison with estimates from the FINO1 platform (North Sea) is made to identify shared spectral characteristics of turbulence between different offshore sites. The sonic anemometer measurement data atÂ 6, 18, and 45âmâa.m.s.l.Â (above mean sea level) are considered. These heights are lower than at the FINO1 platform, where the measurements were collected at heights between 40Â and 80âm. Although the sonic anemometers are affected by transducer-flow distortion, the spectra of the along-wind velocity component are consistent with those from FINO1 when surface-layer scaling is used, for near-neutral and moderately diabatic conditions. The co-coherence of the along-wind component, estimated for vertical separations under near-neutral conditions, matches remarkably well with the results from the dataset at the FINO1 platform. These findings mark an important step toward more comprehensive coherence models for wind load calculation. The turbulence characteristics estimated from the present dataset are valuable for better understanding the structure of turbulence in the marine atmospheric boundary layer and are relevant for load estimations of offshore wind turbines. Yet, the datasets recorded at Vindeby and FINO1 cover only the lower part of the rotor of state-of-the-art offshore wind turbines. Further improvements in the characterisation of atmospheric turbulence for wind turbine design will require measurements at heights above 100âmâa.m.s.l.

Highlights

In the early 1990s, the first generations of offshore wind farms were commissioned to test the viability of extracting wind power in the marine atmospheric boundary layer (MABL)
The wave-induced stress may increase the friction velocity at 6 m amsl, and a lower-than-expected φw. 270 For an unstable atmosphere (ζ < 0), the values of φw estimated at 18 m remain under eq (5), which were not observed on FINO1 (Cheynet et al, 2018)
This study explores the turbulence spectral characteristics from wind records of a year duration on an offshore mast called South 480 Mast West (SMW) near the first offshore wind farm Vindeby

Summary

Introduction

In the early 1990s, the first generations of offshore wind farms were commissioned to test the viability of extracting wind power in the marine atmospheric boundary layer (MABL). Was the Vindeby project the first offshore wind farm, but it provided precious information on meteorological conditions in the MABL using offshore and onshore meteorological masts. The data collected has been used to study the characteristics of the mean wind speed profile under various atmospheric conditions (Barthelmie et al, 1994; Barthelmie, 1999). Since the 2010s, several studies have indicated that diabatic wind conditions may significantly affect the fatigue life of offshore wind turbines (OWTs) components (Sathe et al, 2013; Hansen et al, 2014; Holtslag et al, 2016; Doubrawa et al, 2019; Nybø et al, 2020; Putri et al, 2020). To model properly the wind load for wind turbine designs, a better understanding of the spectral structure of turbulence in the MABL is necessary, which addresses partly the first of the three great challenges in the field of 35 wind energy (Veers et al, 2019)

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