颱風來襲時，所夾帶的風暴潮會造成沿海地區的水位上漲，海水倒灌於河道之中，加上河川上游流下的洪水，可能溢淹過河口附近的跨河構造物(橋梁、攔河堰、輸水管線等)。這些構造物便會受到風暴潮引起的巨浪及洪水的衝擊而損壞，但一般的工程師並不會計算跨河構造物所受的波浪和水流衝擊力。本計畫預備採用水槽實驗和三維的大渦流模式(LES)與流體體積分率法(VOF)計算風暴潮流入河道之中，跨河構造物上、下游的流況及所受的水流衝擊力，模式模擬結果將與水槽實驗量測得之自由水面及表面壓力比較，以驗證CFD數值模式的正確性。然後再利用CFD模式進行一系列的模擬，檢視潛沒深度、阻滯比、福祿數、波高和波長等流場參數對矩形橋面板、圓柱形水管的阻力、升力係數及渦流逸散之影響。本計畫之研究成果將有助於跨河構造物的設計與維護，以避免此類結構物的損壞。 ;Cross-river structures (bridges, weirs, and pipelines) in the estuarine areas could be flooded and attacked by the torrential flows and wave during storm surges. Due to the difficulty to predict the dynamic process of turbulent flows and surge-induced wave around the cross-river structures, the engineers usually neglect the hydrodynamic loading on these structures. However, the failure of cross-river structures usually occurs in the event of extreme floods and storm surges which deviate tremendously from the steady assumption. In this research project, we plan to integrate a three-dimensional Large Eddy Simulation (LES) model and Volume of Fluid (VOF) method to investigate the flow fields around the cross-river structures. The simulation results will be compared and verified by laboratory experiments. Then the validated numerical model will be employed to study the effects of submergence, blockage ratio, wave length and height on the hydrodynamic force of the bridge deck and circular pipelines underneath the water surface. The results can be used to improve the design and maintenance of cross-river structures.
