本研究主要針對臺灣綠島北側海域進行三維分層流與地形交互作用之水動力研究，透過開放原始碼數值模式OpenFOAM建置簡化真實海域地形(二元高斯分佈)模擬環境，並蒐集該區域相關背景資料。採用高解析度的大渦模擬(Large Eddy Simulation, LES)紊流模式且配合非靜水壓假設(Non-hydrostatic assumption)之方式進行模擬評估。在模擬分析流程一開始利用大型分層水槽渦旋實驗[Stiperski et al., 2017]的實驗結果作為模式模擬校正條件，從流態與波形尺度比較評估模式之正確性，再使用現地觀測之都卜勒流速剖面儀(Acoustic Doppler Current Profiler, ADCP)和鹽溫深儀(Conductivity Temperature Depth, CTD)所量測到的資料作為初始條件，與聲納回波儀(Echo Sounder, EK)所測得之不穩定波波形做比較。研究模擬結果可知，模式在均勻流速邊界下改變流速大小，可以重現出實驗論文之流場狀態，與相似之長度尺度。而在現地尺度縮尺模擬，分層剪力流(Stratified shear flow)與地形作用下，流場中之流體不穩定性(Shear instability)會逐漸發展，連帶造成流體垂直向的非線性過程與高頻小型渦流成分產生，並主導水動力運動行為。模擬之紊流耗散率在時間上變化的週期、振幅，與現地觀測的EK回波訊號之結果相似，其空間分布亦與2019年的EK回波訊號之二維觀測結果類似。而控制海岸水動力環境不穩定波之關鍵無因次參數，除了定義不穩定性發生與否的梯度理查爾森數Ri，亦與分層流中山尖之地形尖銳度Sc有關，Sc會影響不穩定波的水平尺度與樣貌，即與不穩定波週期保持反比關係。

This research focuses on the 3-D hydrodynamic study of the interaction between the stratified flow and submerged topography on the northern side of Green Island. The numerical model OpenFOAM is used to carry out a simplified simulation for the real seamount and collect relevant data in this area. LES model with non-hydrostatic assumption are used for this research. First, the experimental results of the large stratified water flume [Stiperski et al., 2017] were used for the model calibraion, and then the in-situ data measured by ADCPs and CTD are used as the initial conditions to simulate the flow pattern and the instability waves and compare with the measurement from echo sounder. The simulation results show that the model can reproduce the flow field and the similar length scale of instability waves observed in the field. Under the interaction between the stratified flow and the seamount, the fluid instability in the flow field gradually develops, and dominates the hydrodynamic motion. The wavelength and amplitude of the simulated turbulent dissipation rate are similar to the results of the echo sounder signals in 2016 observations, and the spatial distribution of the salinity field is also similar to observations in 2019. The key dimensionless parameters that control instability waves in coastal hydrodynamic environment, in addition to Ri, which affects the occurrence of instability waves, are related to the nondimensional parameters Sc, which is inversely proportional to the period of the instability waves.

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