Separating swell from mixed waves around island through wave action balance modeling

Wind seas and swells typically co-occur around islands, resulting in a wave spectrum with a frequency characterized by double or multiple peaks. Separating the wave energies of wind seas and swells is crucial for accurately estimating the wave loads exerted on offshore structures around islands. This study presents a novel method for accurately separating wind sea and swell, considering the effects of wind fields and topographic features around the island on the wave spectrum. The fetch around the island was determined by the wave conditions and wind sea growth curve with respect to wind velocity, and the local wind field was then vanished and the wave action balance model executed again to obtain the swell component. The remaining energy in the wave spectrum was regarded as wind sea. The proposed method was validated using the observed wave conditions during Typhoon Sarika in the Atoll area of the South China Sea. The method successfully separated the wind sea and swell, and both exhibit wave spectra, which differ from the separation frequency obtained by traditional methods. Furthermore, both the one-dimensional and directional spectra demonstrated excellent performance.