Abstract
This article provides some statistical features of the sea surface roughness given as a function of the spectral wave steepness and the significant wave height suggested by Taylor and Yelland (J Phys Oceanogr 31:572–590, 2001), which is best to use for mixed wind sea and swell, and for swell-dominated situations (Drennan et al., J Phys Oceanogr 35:835–848, 2005). Results are obtained using the Myrhaug and Fouques (2008) bivariate statistics of the spectral wave steepness and the significant wave height representing wind sea, swell, and combined wind sea and swell. Associated results are also given for the sea surface drag coefficient and the turbulent energy density, as well as a procedure of estimating the sea surface roughness from 1-, 10- and 100-year contour lines. Finally, a simple example of application is given, demonstrating the effect of the sea surface roughness on slowly varying surge motion of marine structures exposed to wind gust.
Highlights
The sea surface roughness depends on the mechanisms of air–sea interaction and its estimation is difficult; no consistent theory exists covering the range from small waves to big waves including wind waves, combined wind waves and swell, as well as swell
Norway tion of the spectral wave steepness and the significant wave height proposed by Taylor and Yelland (2001) [see Eq (1)] was the best to use for mixed wind sea and swell, and for swell-dominant situations (see Drennan et al (2005) for more details)
Some recent works related to load assessment studies for offshore wind power systems have advocated the use of the Hsu (1974) relationship for z0 where the sea surface roughness depends on the wave conditions, taking the Charnock parameter equal to the wave steepness s, i.e. β s H /λ, where H is the wave height and λ is the wave length
Summary
The sea surface roughness depends on the mechanisms of air–sea interaction and its estimation is difficult; no consistent theory exists covering the range from small waves to big waves including wind waves, combined wind waves and swell, as well as swell. The main purpose and the novelty of the present article is to demonstrate how the Myrhaug and Fouques (2008) bivariate statistics of the spectral wave steepness and the significant wave height representing wind sea, swell, and combined wind sea and swell can be used to obtain statistical properties of the sea surface roughness for sea states given by Taylor and Yelland (2001), which are best to use for mixed wind sea and swell and for swell-dominated situations This is relevant to the assessment of local wind conditions at sea, e.g. related to wind load studies on marine structures.
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