本研究以數值模式模擬三維海嘯之上溯。研究案例為2010年10月25日Mentawai海嘯。經現場調查，該海嘯於Sibigau島呈現特殊之衝擊現象。該島嶼內陸大多數之植生被摧毀，然而沿海之植生卻僅受極有限之破壞。由於此處沿海地形後方有一陡峭之斜坡，本研究推估此地形對於湧潮破壞行為將產生影響。此假說若成立，代表未來於海嘯攻擊下，山邊離岸之建築物亦可能遭受海嘯之破壞。為研究此一現象，本文以數值方法進行模擬與分析。模擬案例包括與實驗數據之驗證，及三維Sibigau海嘯溢淹模擬。 於實驗驗證部分，本研究與新加坡南洋理工大學黃振華教授之實驗結果進行比對。該實驗以孤立波模擬海嘯波入射與上溯，並探討孤立波上溯後，湧潮施於細圓柱之水平力和轉動彎矩。數值模擬求解三維紊流大渦模式（LES），並以Morison公式推估海嘯力。比對結果發現數值模式於海嘯湧潮之水位與流速預測方面有良好之結果，而海嘯力之推估亦有合理之準確度。 本研究並探討三種不同峭壁角度之流場行為。研究發現，三種角度之峭壁造成湧潮之反彈，並進而對峭壁前之結構物及底床造成第二次衝擊。此現象說明Sibigau島出現之現象即有可能為峭壁反彈波所造成。為確認此現象，本研究進一步進行實際尺度之溢淹模擬。Sibigau島之溢淹模擬分兩個部分，其一為以COMCOT海嘯數值模式進行Mentawai海嘯之模擬，模擬分三層巢狀網格進行。其中第三層網格置於Sibigau島，解析度為120 m。第二部分以三維LES-VOF模式進行，並將COMCOT第三層計算結果作為LES-VOF之入流邊界條件。模擬結果發現，海嘯波入射後以海嘯湧潮上溯，並於撞擊至山壁後反彈，反彈波之位置符合Sibigau島內陸樹林被摧毀之區域。In this study, we use a 3D numerical model to simulate the processes of tsunami run-up. The study case is the Mentawai tsunami happened in October 25, 2010. The field survey showed an interesting phenomenon that most of the vegetation inland was destroyed, while, in contrary, only limited damage observed at the coastal area. Because a steep cliff is located right behind this area, we assume that this special topography might be one of the reasons. If this hypothesis sustains, the hillsides buildings might also under the tsunami threat. To study this case, the numerical method is adopted. Validation with experimental data and Sibigau tsunami simulation are included. As for the model validation, the simulation results are compared with the experimental data obtained from Professor Zhenhua Huang in Singapore Nanyang Technological University. In the experiment, a solitary wave is used to represent the tsunami incident wave. The force and bending moment from the run-up bore acting on a small circular cylinder are recorded. Our numerical model solves 3D Large-Eddy Simulation（LES）model, and estimate the tsunami force by Morison formula. The result shows that the numerical model is able to predict the bore height and velocity field accurately, and reasonable accuracy on the force prediction. We also study the flow characteristics of three cliff angles. The result shows that the rebounded bore is presented in all of the cases. This rebounded bore causes the second impact on the structures at the toe of the cliff. It might explain phenomenon observed on Sibigau Island. To confirm this hypothesis, this study precedes the overflow simulation in the real scale. The complete tsunami simulation on Sibigau Island is divided into two parts. The first part is the 2D simulation of the Mentawai tsunami by COMCOT model. Three layers of nested grids are adopted. The third layer focuses on Sibigau Island with a resolution of 120m. The second part is the 3D simulation by LES-VOF model. The third-later COMCOT result is adopted as the inflow boundary condition. The result shows that the tsunami waves transforms into tsunami bores, and then rebound after reaching the hill. The position of the rebounded wave consists with the field observation.
