重建台灣九棚海嘯石之古海嘯事件及孤立波與水下圓板交互作用之模擬

Reconstructing the Paleotsunami Event at Jiupeng, Taiwan, from Tsunami Boulders and Simulation of Interaction Between Solitary Wave and Submerged Circular Plate

柯利鴻(Li-hung Ko)

指導教授 ： 吳祚任 ； 劉立方

國立中央大學/地球科學學院/水文與海洋科學研究所/碩士(2014年)

摘要

台灣東南方之九棚灣發現三顆海嘯石（Matta et al., 2013），為5000年內古海嘯事件之證據。本文利用海嘯石之位置與地形，以波浪動力學為基礎重建該海嘯事件，並探討其他可能遭受影響之地區。首先，我們利用潛在海嘯源逆向追蹤法（Tsunami Reverse Tracing Method, TRTM）找出可能對研究區域造成影響之海嘯源。TRTM是以線性波理論及頻散關係（dispersion relationship）為基礎所發展，藉由此法，能迅速排除不可能之情境，節省大量之分析時間。其後將可能之海嘯源進行情境分析，並以三維流固耦合模式SPLASH3D進行模擬，以求得海嘯湧潮高度、速度與海嘯石推移距離之關係，並推估可能之情境海嘯波高。根據TRTM之結果，僅來自琉球、馬尼拉和亞普海溝所產生之海嘯有可能傳播至九棚灣，模擬之情境海嘯規模範圍為Mw 8.1 ~ 9.3。
在海嘯減災部分，本文以三維數值模擬SPLASH3D，探討孤立波通過平板型潛堤之消能行為，首先與美國康乃爾大學Prof. Philip L.-F. Liu所提供之解析解及實驗數據比對（Lo and Liu, 2014），數值解、解析解及實驗數據有相當程度之一致性。完成模式驗證後，我們對孤立波與水下圓板型潛堤之交互作用進行三維之數值模擬，並輔以解析解（Lo and Liu, personal communication）進行校驗，比對結果大致良好，但當模擬案例之非線性強度增強時，數值解與解析解開始產生明顯之偏差，孤立波在通過圓板時，波形變得陡峭、近乎破碎，探討不同浸沒深度之案例對於流場之影響時，發現圓板主要扮演壓力屏蔽之角色，且在浸沒深度越小時影響越明顯，屏蔽壓力之效果，使得流場中形成許多局部流場，且在圓板邊緣產生明顯之環狀渦流現象；此外，浸沒深度越小，對於能量消散與透射波波高之影響有越明顯之趨勢。

關鍵字

海嘯石 ； 海嘯 ； 海嘯源逆向追蹤法 ； 流固耦合 ； 孤立波 ； 潛堤

並列摘要

Three tsunami boulders were found at the Jiupeng coast in the Southeastern Taiwan (Matta et al., 2013), and can be the evidence of a paleotsunami event happened within 5000 years. In this study, we intended to reconstruct this tsunami event and learn the potential large tsunami that might attack the southern Taiwan. The first step is to find the possible tsunami sources by means of tsunami reverse tracing method (TRTM). TRTM is developed based on the linear wave theory and dispersion relationship. By TRTM, we can also rule out the impossible ones. As the probable tsunami sources are located, the second step is to setup the tsunami scenarios, and to eliminate the cases with results contradicted with the relationship between bore height, or velocity, and displacement of tsunami boulder, which can be derived from 3D fluid-solid two-way coupling model. The result of reverse tracing method shows that only the tsunamis from Ryukyu, Manila, and Yap Trenches are able to reach the coast of Jiupeng.
In terms of the tsunami hazard mitigation, a coastal structure may be able to protect the shore from being attacked by a tsunami. In this thesis, we intend to study the energy dissipation from a circular plate in a solitary long wave by means of three-dimensional numerical simulations, SPLASH3D. For the model validation, we performed 2D simulations with a solitary wave interacting with a flat plat and compared our results with the analytical solutions and experimental data proposed by Prof. Philip L.-F. Liu at Cornell University, USA (Lo and Liu, 2014). We found that the numerical solutions were very close to the analytical solutions and experiment data. After that, we utilized our model to the 3D simulation of interaction between solitary wave and submerged circular plate. The simulations were also compared with the analytical solutions (Lo and Liu, personal communication). When the nonlinearity increased, deviation between simulation and analytical result became more obvious. A steep and nearly breaking wave was observed above the circular plate. Cases with different submergence were compared, and the circular plate play a role of pressure shield, especially in cases with smaller submergence, which caused a pressure gradient induced local flow field and a strong vortex rings were also presented around the edge of the plate. Besides, smaller submergence had greater effect on energy dissipation and wave height of transmission wave.

並列關鍵字

Tsunami Boulder ； Tsunami ； Tsunami Reverse Tracing Method ； Fluid-solid Coupling ； Solitary wave ； Submerged Breakwater

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