Numerical Simulation Of Typical Typhoon Waves And Cold Waves In Zheiiang Adjacent Seas With Refined Grids

The study of ocean waves is one of the important research contents of ocean dynamics.Until now,the wave numerical model has gradually evolved from the first generation model to the third generation model.The SWAN model has become one of the most important tools for numerical simulation of offshore waves with its high stability and high accuracy.Besides,it has also become one of the ocean-forecasting models with wide applications.In this paper,we firstly use software to construct a detailed unstructured mesh grid in Zhejiang offshore areas through the satellite shoreline data,combined with the measured water depth data of nearshore in Zhejiang Province and etopl data;all the data are unified to the average sea level.Then,we use numerical experiments to explore the impact of the startup time of the SWAN model and the startup method on the simulation results.The developed SWAN model is then used to simulate the Typhoon Megi in 2016 and the cold wave in January 2016 with the nest technology.The simulation result shows that the detailed unstructured mesh grid and the SWAN model can reasonably reproduce the extreme values and variations of typhoon waves and cold waves,especially the peak values,which can meet the requirements of practical application.Then,we use the SWAN model to simulate multiple typhoons including"Chanhong"(2015),"Ampil"(2018),"Maria"(2018)and "Yagi"(2018):1)The SWAN model is used to study the influence of the bottom friction coefficient,the wave breaking parameter,the wave nonlinear interaction mode and the wind energy input mode on the simulation results,and the dominant parameters are selected to simulate the 1509 "CHAN-HOM" typhoon.According to the simulation results,the spatial wave height distribution is drawn.And the error statistics belong to the reasonable range and the spatial wave height distribution can basically agree with reality.2)Different combinations of parameter schemes(Komen+Jonswap?Westhuysen+Collins?Komen+Collins)and different wind drag coefficient schemes(Anderson(1993),L&P(1981),Oey(2006),and Wu(1982))are selected to simulate the 1810 Typhoon "Ampil",the 1808 Typhoon "Maria" and the 1814 Typhoon "Yagi".Overall,the Oey scheme has the best simulation effect;when the wind speed is small,the simulation effect of the Wu scheme is optimal;when the wind speed is large,the simulation effect of the Oey scheme is significantly better than the other schemes.At last,the SWAN model was used to simulate the two typical cold waves affecting Zhejiang Province(the cold wave in January 2016 and the cold wave in March 2015).It can be seen from the simulation results that the simulation results are in good agreement with the observations,indicating that the SWAN model can simulate the cold waves caused by the cold front in Zhejiang offshore areas.Based on this,the wave height distribution during the cold front events of the whole study area is obtained.The spatial wave height distribution is basically in line with reality.From the results of multiple sensitive numerical experiments,the preliminary conclusions of cold waves affecting the offshore areas of Zhejiang Province is obtained as:?The cold wind direction can significantly affect the distribution of offshore waves in Zhejiang;?In the selected area,it can be roughly divided into four parts,and the responses of these parts to wind direction changes are not the same;? For Zhejiang Province,especially the adjacent areas of Ningbo,Zhou Shan and Wenzhou,the response to the wind direction is very intense,which indicates that the nearby ports and fishing boats need to strengthen the cold wave protection work in winter.