Numerical Research Of Wave Evolution Near Reefs In The South China Sea

Coral reef is one of representative landforms in the South China Sea.The water depth on reef flats is often very shallow,but the outside water depth will drop sharply to 100 meters or more.When waves travel from deep sea to reef,the huge water depth difference will cause wave breaking and reflection,the waves at reefs will show strong nonlinearity.In order to provide reasonable wave parameters for offshore reef engineering,accurate prediction of wave enviroment under reef topography becomes extremely important.WAVEWATCH-III model(hereinafter referred to as WW3)has been used by many scholars to simulate wave field because of its high accuracy in large-scale sea area.However,when considering the calculation efficiency,its grid size is often larger compared to reefs size.Therefore,the WW3 model introduces the multi-grid to refine the grid near islands and reefs and improve the accuracy of calculation.For this reason,the multi-grid based on WW3 model is used to calculate the wave field in the South China Sea.Firstly,the typhoon field constructed by WRF model is used as the input field to calculate the typhoon waves generated by typhoon "Kalmaegi(1415)","Kujira(1508)" and "Sarika(1621)" using WW3 multi-grid model.Compared with the measured data,the results show that the height and direction of typhoon wave simulated by WW3 are highly correlated with the measured data.Meanwhile,the wind wave and swell of typhoon "Kalmaegi" are calculated by spectral energy separation method,and the cause of double-peaked wave spectrum formation at the measuring point is analyzed.Subsequently,the wind-generated waves in the South China Sea from 2014 to 2018 are calculated by using WW3 multi-grid model.The simulation results show good agrement with measured datas.It is found that the annual average wave heights are between 0.5m and 1m,wave periods are mainly 1s~3s,and wave directions are between ENE and NNE.Finally,the seasonal distribution characteristics of the annual mean wave height in the South China Sea are studied.It is found that the distribution of the mean wave height in the South China Sea is closely related to the seasonal monsoon climate.The mean wave height in the South China Sea is the highest in the whole year in winter,and the minimum in spring.In the Xisha sea area of concern,the annual average wave height is 0.5m~1m,which is less affected by seasonal variation.In this paper,the calculation results of wave field in the South China Sea island and reef environment can provide reference for subsequent engineering construction.