Laboratory measurements of an equilibrium-range constant for wind waves at extremely high wind speeds

When improving wave models, it is important to determine the equilibrium-range constant for the wind-wave spectrum and find the dominant velocity parameter that well represents the equilibrium-range constant both at normal and extremely high wind speeds. Eight dominant velocity parameters were evaluated using laboratory experiments in two wind-wave tanks. One tank, installed at Kyoto University, is used for generating mechanically-generated large wind-waves. This tank has a maximum 10-m wind speed (U-10) of 67 m/s and is equipped with a programmable irregular wave generator for the loop-type wave-generation method, which was originally developed in our previous study. The other tank, installed at Kyusyu University, is used for generating pure large wind-waves, and has a total length of 54 m. The results show that at extremely high wind speeds the equilibrium-range constants for mechanically-generated large wind-waves agree with those of pure small wind-waves. In addition, comparison of the correlation coefficients of the eight dominant velocity parameters with the equilibrium-range constant reveals that three dominant velocity parameters of (u*C-2(p))(1/3), ((U10Cp)-C-2)(1/3), and U-LS/2 (u*: friction velocity; C-p: phase velocity; U-LS/2: wind velocity at half the height of wavelength over the ocean) well correlate with the equilibrium-range constant at both normal and extremely high wind speeds.