孤立波通過梯形潛堤之變形

DEFORMATION OF SOLITARY WAVES PASSING OVER A SUBMERGED BREAKWATER

李瓊瑜(Cyong-Yu Li)

指導教授 ： 林孟郁 ； 王安培

中原大學/工學院/土木工程研究所/碩士(2013年)

https://doi.org/10.6840/cycu201300954

摘要

本研究主要應用Lin and Huang (2009) 利用勢流-渦流分解法所發展之數值方法，進行孤立波通過梯形潛堤之二維流場模擬。此方法以邊界積分法處理自由液面與非旋性部分之計算，流場中的渦度場則由渦旋法(vortex method)進行求解。此方法之特色在於保留勢流架構下之優點，運用邊界積分法處理自由液面與非旋性流場，在處理旋性流場部分，則不同於傳統使用網格的數值方法，不需對整個計算域進行黏性流求解，因此在數值計算上具有速度之優勢。

為了瞭解波浪通過梯形潛堤後自由液面的變化現象，本研究著重於探討在不同波高水深比下，旋性流孤立波通過梯形潛堤後，渦度的生成與自由液面的變化，並與非旋性流之結果相互對比，以了解渦度的生成，對於自由液面所造成之影響。

經由數值模擬成果可知，在旋性流與非旋性流之假設條件下，孤立波通過梯形潛堤後，自由液面之變化有著相當大之差異。其原因在於孤立波通過梯形潛堤後，旋性流所生成之渦度，對於自由液面有抬升之效應;不同於非旋性流因自由液面產生向下震盪故導致提前產生碎波。由數值模擬結果亦可知渦度的生成強度與對於自由液面之干擾，隨著波高水深比增加而增強。若渦度消散至接近自由液面，仍具有一定強度時，則將對於自由液面產生劇烈的干擾，使得自由液面接近碎波現象。

關鍵字

潛沒堤 ； 孤立波 ； 變形

並列摘要

In this research, a numerical scheme that employs a potential-vorticity decomposition is used to simulate the two-dimensional flow of a solitary wave passing over a submerged breakwater. Free surface deformation and the induced irrotational flow field are solved using a boundary integral method, and the vertical flow field induced by vorticity is solved via a vortex method. The major advantage of this method is the efficiency of the boundary integral method for solving the free surface motion and irrotational flow field, and the essentially grid-free nature of the vortex method for the vorticity field, which is predominantly confined in compact regions.

In order to understand the deformation of solitary waves passing over a submerged breakwater, a series of simulations were performed with various wave heights to study the effect of vortex generation on the deformation of solitary waves.

According to the numerical results, the wave forms under the assumption of irrotational and rotational flow have considerable differences. The reason is that the generated vortex may uplift the free surface. The numerical results also show that the strength of vortex and the disturbance of free surface caused by vorticity become stronger when the incident wave is higher. If the shedding vortex moves close to the freesurface, severe disturbance will be produced and leads to wave breaking.

並列關鍵字

solitary wave ； deformation ； submerged breakwater

參考文獻

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