Study On The Evolution Law Of Waves With Double-Peaked Spectra Under The Condition Of Islands And Reefs Nearby

Various types of floating platforms near islands and reefs are important equipment for the development and utilization of marine resources in the South China Sea.Accurate prediction of the ocean environment near islands and reefs nearby can provide important guarantees for the safe operation of the platform.Waves with double-peak spectra occurring in the South China Sea frequently as a special spectrum wave,which cannot be ignored in safe operation of the project near islands and reefs for the double-peaked characteristic that energy peaks exist in both the low-frequency and high-frequency regions.In this paper,three methods including measured buoy data,numerical model calculation and physical model experiment are used to study the evolution law of waves with double-peaked spectra in the environment near the islands and reefs.Firstly,the actual measurement data of buoys located near a reef in the South China Sea is analyzed.The average occurrence probability of waves with the double-peaked spectra in the target sea area per month is obtained,and the seasonal law of the double-peaked spectra wave is discussed.It is found that terrain and monsoon are significant for the generation of waves with double-peaked spectra.Then the six-parameter fitting method is used to fit the typical sea waves with double-peaked spectra in the measured data,and the result can be used as the input spectral pattern for the experiment.Secondly,double-layer nested Simulating Waves Nearshore model(SWAN)is used to perform a numerical wave report on the No.201415 typhoon named Kalmaegi and the extreme wind speed in 100 years is calculated to obtain the law of distribution and evolution of waves with double-peaked spectrum.Finally,the three-dimensional model experiment for wave evolution near islands and reefs,based on the measured topography,is conducted in the experimental pool at the State Key Laboratory of Coastal and Offshore Engineering of Dalian University of Technology to further explore the evolution law of waves with double-peaked spectra under the condition of islands and reefs nearby.It was found that the annual average probability of double-peaked spectrum waves in the target island and reef area is more than 30%,which occurs more frequently during the transition of the monsoon.Typhoons and terrain are important factors in the formation of waves with double-peaked spectra,and the terrain of the target island and reef lagoon will cause the double-peaked spectrum waves.The diffraction of long-period waves in the external field and the superposition of limited wind moments in the internal field under complex terrain conditions near islands and reefs are the main reasons for the generation of the wave with double-peaked spectra near the target island and reef.The change trend of the wave significant height of waves with double-peaked spectra is consistent under the same terrain profile.The evolution law of double-peaked spectrum waves near islands and reefs revealed in this paper can provide important support for the construction site selection and safe operation near islands and reefs.