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Introduction
Published in Srinivasan Chandrasekaran, Offshore Semi-Submersible Platform Engineering, 2020
The sea state can be described using a suitable scale based on sea conditions, wave height, and wind speed. One such empirical measure used for expressing the sea state is the Beaufort scale, developed by Irish Royal Navy Officer Francis Beaufort in the 19th century. As per the World Meteorological Organization, the scale is standardized into thirteen classes, from zero to twelve. Because the description of the sea surface is more useful than the wind speed and wave heights alone, the World Meteorological Organization and MetService started defining the sea state using the Douglas sea scale, developed in 1920 by Captain H.P. Douglas. It describes the roughness of the sea from smooth to very high. However, offshore structures are also rehabilitated using a perforated cover around the main members to reduce the response from the wave impact (Chandrasekaran and Merin, 2016; Chandrasekaran and Madhavi, 2014a–e; 2015a–d; 2016; Chandrasekaran et al., 2013b; 2014e; Chandrasekaran and Abhishek, 2010).
Meteorology and modelling
Published in Abhishek Tiwary, Jeremy Colls, Air Pollution, 2017
Wind speed is measured in m s–1 or knots (one knot is one nautical mile per hour; one nautical mile is 6080 feet, or 1.15 statute miles). Although the use of SI units is encouraged in all scientific work, some professions have stuck with earlier systems. Thus mariners, pilots and meteorologists are all comfortable with knots. Mariners also use the Beaufort scale, which relates wind speed to its effects on the sea.
Ocean Waves and Wind Forces
Published in Srinivasan Chandrasekaran, Faisal Khan, Rouzbeh Abbassi, Wave Energy Devices, 2022
Srinivasan Chandrasekaran, Faisal Khan, Rouzbeh Abbassi
where Hs is the significant wave height, Tz is the zero-crossing period, and ω is the frequency. The spectral plot shows that the wave energy is concentrated on a narrow band. The typical wave energy PM spectra under different sea states are shown in Fig. 1.6. The sea state can be described using a suitable scale based on sea conditions, wave height, and wind speed. One such empirical measure for expressing the sea state is the Beaufort scale, developed by Irish Royal Navy officer Francis Beaufort in the nineteenth century. As per the World Meteorological Organization, the scale is standardized into thirteen classes, from zero to twelve. Since the description of the sea surface is more useful than the wind speed and wave heights alone, the World Meteorological Organization and MetService started defining the sea state using the Douglas sea state, developed in 1920 by Captain H. P. Douglas, which describes the roughness of the sea from smooth to very high (Chandrasekaran and Merin, 2016; Chandrasekaran and Madhavi, 2014a; 2014b; 2014c; 2014d; 2015a; 2015b; 2015c; 2015d; 2016; Chandarsekaran and Vishruth, 2013; Chandrasekaran et al., 2013; 2014a; 2014b; 2014c; Chandrasekaran and Abhishek, 2010).
Quality of the ERA5 and CFSR winds and their contribution to wave modelling performance in a semi-closed sea
Published in Journal of Operational Oceanography, 2023
Emre Çalışır, Mehmet Burak Soran, Adem Akpınar
Table 3 gives error statistics of the CFSR and ERA5 wind speeds at the different speed ranges against Gloria measurements in 2006. For defining the speed ranges, the Beaufort scale, an empirical measure for describing wind intensity based on observed sea conditions, is used. The scale starts with 0 (Calm) and goes to a force of 12 (Hurricane). The results in Table 3 indicate that in the low wind speeds (1.6–3.4 m/s) both the models overestimate the wind speeds but in other wind speed ranges the wind speeds are underestimated in both ERA5 and CFSR. Although the correlation coefficient is higher at higher speeds and there is higher correlation between ERA5 winds and measurements, overall, the correlation between measurements and hindcasts is low. In terms of the RMSE, model errors increase in both data sets at higher speed ranges. In all speed ranges except Beaufort number 7 the CFSR winds have higher errors compared with the ERA5 winds. As the si parameter, ERA5 performs, respectively, 14%, 6%, and 4% better than the CFSR in the lowest first third speed ranges. However, in the highest speed ranges, the CFSR executes 3% better than the ERA5. This clearly shows that the ERA5 winds perform better in the lowest speed ranges, while CFSR gives lower error in the highest speed range, whereas in the cases of fresh and strong breeze winds, a similar performance is observed in both data sources.