波浪通過海岸植生消能之數值模擬

Numerical study of wave propagation through the coastal vegetation

楊子逸(Tze-Yi Yang)

指導教授 ： 詹益齊

國立臺灣大學/工學院/土木工程學研究所/碩士(2019年)

https://doi.org/10.6342/NTU201900614

摘要

海岸植生與海岸環境間的關係涉及許多自然因素，本研究透過改變不同植生條件，例如植物莖幹直徑、垂直於地面之高度與生長密度，利用XBeach進行模擬計算。
已往前人之研究，實驗植生的條件變化性較小。實驗中多為單一植物之直徑、高度或密度，改變波浪邊界條件，並量測植物對波高之衰減量。最後藉由波浪運動條件等參數，求得阻力係數與該參數之迴歸關係式。此關係式乃受到實驗條件之限制，適用條件因此而侷限，換言之，改變實驗條件或參數後，阻力係數之關係式就已無法適用。
本研究欲解決此問題，係透過XBeach數值軟體，進行數值實驗擬合阻力係數，觀察阻力係數與不同植生條件或波浪條件之相關性，探討植物阻力之影響因子。並以此影響因子求得適當且具有物理意義之阻力係數關係式，改善以往阻力係數關係式僅適用於某些特定條件之缺點。模擬結果顯示，阻力係數與植物相對於水深之高度、雷諾數具有高度相關性，透過上述之兩個影響因子，求得阻力係數與影響因子之關係式。在不同地域環境，植生條件改變時，方能利用此關係式快速求得阻力係數。

關鍵字

海岸植生 ； XBeach ； 植物阻力 ； 阻力係數 ； 波浪消散

並列摘要

The relationship between coastal vegetation and coastal environment involves many natural factors. This study explores the influence factors of vegetation drag force by changing different planting conditions, such as plant diameter, height and density with XBeach model for simulation.
In previous studies, vegetation conditions of experiment were less variable. Most of the vegetation conditions in the experiment are with fixed diameter, height or density, and with unfixed wave boundary conditions and the measured attenuation of wave height. Finally, parameters such as wave motion conditions, were added to obtain the relationship between the drag coefficient and the parameter. This relationship is limited by the experimental conditions, and thus the applicability is limited. In other words, after changing the experimental conditions or parameters, the relationship of the drag coefficient is no longer applicable.
In order to solve this problem, XBeach numerical model is used to fit the drag coefficient by numerical experiment. The influence of drag coefficient and different vegetation conditions are investigated. These influence factors are then used to obtain an appropriate drag coefficient of regression relation with physically meaning. The obtained drag coefficient of regression relation is believed to overcome the shortcoming in the previous work, which the regression relation can be applied to only certain conditions. The simulation results show that the drag coefficient is affected by the relative height of vegetation and the Reynolds number. Through the above two influence factors, the relationship between the drag coefficients is obtained. When the geographical environments and vegetation conditions change, the drag coefficient can be quickly obtained by using this relationship.

並列關鍵字

Coastal vegetation ； XBeach ； Vegetation damping ； Drag coefficient ； Wave dissipation

參考文獻

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