The Frøya database and maritime boundary layer wind description

Abstract

High-quality maritime wind-turbulence data obtained at exposed sites on the western coast of Norway during gale and stormy conditions are described. With a resolution of 1 Hz, and a height range of 10–100 m, the database is most suitable for describing the wind structure of the maritime boundary layer (MBL) with relevance for offshore compliant floating structures. The established description covers both static and dynamic wind, the latter with particular attention given to the low-frequency range 0.002–0.03 Hz (0.5–10 min). The relevance for and extrapolation to very strong wind speed design conditions has been emphasized. The static description of wind is found to be consistent with the Charnock relation reflecting the interaction between wind and waves. A most important conclusion is reached for the one-point wind speed spectrum. The low-frequency range (<0.01 Hz) is significantly more energetic than indicated by land-based studies. Concerning correlations, it is noteworthy that coherence for lateral separation is significantly lower than indicated by some other studies. Coherence for vertical separation is on the low side but in reasonable agreement with these studies. The data does not support a low-frequency asymptote for coherence different from 1.