台灣四面環海，位處於環太平洋地震帶上，地震頻繁發生；觀察周遭海底地形，台灣東北以及西南海域，因地形較平緩遼闊，適合海嘯傳遞、淺化等過程，為易受海嘯災害之高潛勢區。回顧2011年日本東北地震所引發巨大規模的海嘯，海嘯長波無視沿岸巨大海堤越波後，繼續往內陸溯升漫淹，造成人民的死傷以及建築財產的受損，發人深省！ 而因應此類長波的災害，前人提出潛沒式堤防的概念，但其堤防皆建築於平底床上，參考真實海底地形，本實驗嘗試將堤防建置於斜坡上，探討斜坡上的潛沒式堤防消減長波溯升的效用。本次試驗於成功大學水工試驗所精密流力造波水槽進行，以坡度1/20來建置實驗斜坡，並以孤立波來模擬海嘯長波，實驗的主題為利用潛堤減少長波之波能;將低於水面的堤防建築於斜坡上，一方面反射部分波能，另一方面促使長波發生碎波，碎波時混入大量空氣產生紊流渦旋進一步衰減波能。試驗中利用溯升高度作為依據判斷堤防的效用。經試驗最佳效益能夠衰減約70％（hs=0 cm、Xb= 0 cm、ε= 0.11），而雙堤的試驗最佳效益為90％（hs=0 cm、Xb= 0、112 cm、ε= 0.11），說明斜坡上潛沒式堤防在衰減長波上有其功用，能夠達到減少長波溯升，減少海嘯漫淹區域。 除了量測孤立波溯升的衰減外，實驗亦以氣泡影相測速儀（BIV, Bubble Image Velocimetry）量測碎波區之流體速度。BIV系統架設於碎波帶，藉由可視化並量化流場的速度，討論潛堤在消減孤立波後，碎波延斜坡溯升時的速度變化，由速度的變化來計算潛堤消減的波能。 關鍵字：孤立波、溯升、潛堤、BIV

SUMMARY
Taiwan is an island located in the Ring of Fire such that earthquakes occurred frequently. Observing the surrounding seabed topography, northeast and southwest coastal area of Taiwan is relatively gentle and extensively flat, which is suitable for the shoaling and amplification processes of tsunamis, which means that Taiwan is a high potential area of tsunami catastrophe. Recalling the 2004 India Ocean tsunami and the 2011 Tohoku earthquake tsunami, tsunami were caused by mega scale earthquakes that brought tremendous catastrophe in the disaster regions. It is thus of great importance to develop innovative approach to achieve the reduction and mitigation of tsunami hazards.
We propose a concept of using multiple submerged breakwaters to mitigate tsunami-like long wave by means of solitary waves. However, previous investigations of submerged breakwaters under long waves considered that the target obstacles built on a flat bottom. In this study, we installed submerged breakwaters on a mild slope instead to discuss the possible mitigation of run-up heights. Experiments were performed in a glass-walled wave tank located at the Tainan Hydraulics Laboratory, National Cheng Kung University. The slope is 1/20 and solitary waves is used to simulate extremely long wave such as tsunami due to its hydraulics similarity. The subject of this study is to use submerged breakwaters to mitigate long wave energy, enhance the breaking processes due to shoaling and, in part, to reflect the incoming wave due to the presence of obstacle. When waves are breaking, lots of air bubbles were entrained into the testing fluid and the fluid becomes turbulent. By this process, submerged breakwaters once again reduce long wave energy. In this study, we used Max. run-up heights to judge different scenario’s utility.
When waves are breaking, lots of air bubbles were entrained into the testing fluid making the fluid to be turbulent, in this way, submerged breakwaters will further reduce the wave energy of incoming waves. Here, we use maximum run-up heights to judge the capabilities of different configuration of breakwaters. The optimal single breakwater scenario in our teat can mitigate about 70% run-up height (hs= 0 cm, Xb= 0 cm, ε=0.11), and best dual breakwater scenario is 90% (hs= 0 cm, Xb= 0&112 cm, ε= 0.11).Therefore, submerged breakwaters are indeed possible to reduce long-wave energy.
In addition, we use a state-of-the-art measuring technique Bubble Image Velocimetry, which features non-intrusive and image-based measurement. The measured wave kinematics in the highly aerated region due to solitary-wave shoaling, breaking and uprush can be quantitated. The measured results in terms of velocities will be used to complete the conjunction with run-up height reduction.
Key words: solitary wave, run-up, breakwater, BIV

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