| As one of the most important port areas in eastern China,a number of world-class port terminals have been built along the coast.However,in areas such as the Zhoushan Islands and the Taizhou Islands,which are representative of complex offshore islands,there are numerous nearshore islands and complex waterways.In the construction of such multi-island complex sea areas,if the wave and current characteristics under extreme conditions can be revealed,it can not only provide theoretical support for the safety construction of marine engineering in this sea area,but also predict the development trend of estuaries and coasts.This article uses MIKE21 numerical software as a research tool to establish a large-scale hydrodynamic and wave model that includes the Zhoushan Archipelago and Taizhou Islands in the central-northern part of Zhejiang Province.Based on the reliability of the model,the influence of multi-island characteristics on tidal current and wave is analyzed.It further studies the hydrodynamic situation,sediment erosion and deposition changes,and wave characteristics of the Taizhou Bay area before and after engineering construction in a certain fishing port dock in Linhai City,which has significant island characteristics.The study also investigates the effects of the same and various extreme wind speeds in different directions on the wave and current fields.The results show that:(1)The marine features of multiple islands are mainly the diverting and aggregating effects at both ends of the islands and narrow channels,which divide the flow path into two.Near the river mouth,the main effects are changes in water level and flow velocity,with erosion observed in areas with high flow velocity and sedimentation in areas with slower flow.The changes are mainly due to alterations in the original coastline,with only a 2 km change observed after the construction of the harbor,and a clockwise vortex appearing within the harbor.(2)Under extreme wind speeds,the currents are mainly affected by the deep sea depth,and changes in offshore flow velocity are driven by wind pushing the current.The flow direction changes very little.In the nearshore area,the islands are scattered,and the direction of the wind field is changed by the topographical gradient and changes in water depth,with wind speed playing a dominant role in affecting the currents.When subjected to the same extreme wind speed,the wind from the N～NNE direction has a greater impact.(3)Under the 50-year and 100-year recurrence interval,different extreme water levels result in rogue waves and storm waves in the offshore area of the Dongji Island group.Nearshore,the "I-shaped" island shape influences the size of the windward area,with a larger lee area under strong winds from the ESE～SE direction than from the N～NNE direction.When considering the same bottom friction,the energy loss of waves in the offshore areas outside the broken zone is mainly affected by the distance from the shore,with wave height decreasing along the path.(4)After being blocked and refracted by the islands,the wave height and wave energy of the offshore waves are weakened.The changes in wave height outside the port are mainly caused by the superposition of incident waves and reflected waves when the waves reach the forefront of the pier.Under extreme high water levels that occur once every 50 years,the wave height in the offshore area outside the harbor increases by around 80%compared to the design high water level occurring once every 50 years,while inside the harbor,the increase is only between 12.5% to 20%. |
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