山崩誘發之海嘯之數值研究;Numerical Study of Landslide-induced Tsunami

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题名:	山崩誘發之海嘯之數值研究;Numerical Study of Landslide-induced Tsunami
作者:	武荷芳;PHUONG, VU HA
贡献者:	水文與海洋科學研究所
关键词:	海嘯;海底山崩;淺水波方程式;頻散效應;Navier-Stokes方程式;Tsunami;Submarine landslide;Shallow water equations;Dispersive effect;Navier-Stokes equations
日期:	2017-07-31
上传时间:	2017-10-27 13:07:21 (UTC+8)
出版者:	國立中央大學
摘要:	近幾十年來，由山崩引起之海嘯造成諸多災害。在本研究中，使用COMCOT和SPLASH3D研究山崩海嘯 (landslide tsunami)，其中COMCOT為2D淺水波方程 (Shallow water equations, SWE) 模式，SPLASH3D為3D納維-斯托克斯方程 (Navier-Stokes equations) 模式。山崩海嘯之特徵為易於表現出頻散行為。為克服此問題，本研究採用淺水波方程中之頻散改良演算法 (dispersive-improved algorithm) ，並與理論與實驗結果進行比對。在理論比對方面，頻散改良演算法之結果與布氏方程 (Boussinesq equations) 之結果比對部分，純粹之淺水波方程式在初始波峰和波谷後之振盪波 (Oscillatory waves) 無法完全符合布氏方程式之結果。相對地，頻散改良演算法可以顯示弱頻散之波紋。此結果對於山崩模擬有助益，因為此法相較於傳統之布氏計算有高效率之優點。在COMCOT裡，使用三種山崩模組，分別為Module 1：Transient seafloor motion、Module 2：Customized profiles of water surface displacement、Module 3：Landslide Model Law of Motion。本研究詳細比對上述三種之模擬結果，並發現模擬結果有可接受之差異。因此，此三種山崩模組可應用在研究越南之潛在山崩海嘯情境。Meridianal斷層系統靠近越南中南沿海地區 (Southern Central Vietnam coast)，該斷層引發之海嘯能在數分鐘內襲擊該沿海地區。而此研究結果有助於山崩海嘯之災害防治。此外，本研究亦也使用於SPLASH3D模式求解三維不可壓縮流，並採用移動固體法 (Moving Solid Algorithm)，以迭代指定速度和壓力來模擬由固體運動引起之流場變化。但在現實中，3D模式難於應用在實際狀況，因為模擬海嘯為大尺度模擬。然而在現階段仍然使用3D模式之結果來詳細解釋波之物理特性。關鍵詞：海嘯，海底山崩，淺水波方程式，頻散效應，Navier-Stokes方程式。 ;A landslide-induced tsunami has increasingly recognized and studied due to major natural disasters caused by this phenomenon in the last decades. In this thesis, both of 2D Shallow water equations model (COMCOT) and 3D Navier-Stokes equations model (SPLASH) were used for studying landslide tsunami. Landslide-induced tsunamis are characterized by shorter wavelengths that tend to display dispersive behavior. The dispersive-improved algorithm in Shallow water equations (SWE) is an option to simulate the landslide tsunami. Series of validations were conducted by comparing to the laboratory experiments. The results of the dispersive-improved in SWE by using Wave Maker are able to match with the results of Boussinesq equations model. It can be seen that the oscillatory waves train behind the initial peak and trough are not fully captured in the simulations obtained with the SWE. On the contrary, the dispersive-improved algorithm in SWE can display weakly dispersive ripples. These may still be useful for modeling landslides due to the high computational efficiency and satisfactory results for a wide class of problems. Multiple landslide modules for landslide induced tsunami are adopted in COMCOT as Transient seafloor motion (Module 1), Customized profiles of water surface displacement (Module 2) and Landslide Model Law of Motion (Module 3). All of landslide modules are able to simulate landslide tsunami with reasonable results which are shown in the comparison between modules. A slight difference can be accepted because of the difference in the mechanisms to generate tsunami waves. Thereby the multiple landslide modules are applied for a scenario potential landslide tsunami in Vietnam. Because the meridianal fault system along Southern Central Vietnam coast is very close to the coast, generated tsunami can hit the coast within minutes. These preliminary results have a contribution to preparatory steps to prevent and respond to natural disasters caused by landslide tsunamis and minimize the damage as well as losses of the coastal communities in Vietnam. Besides, SPLASH3D model which solves 3D incompressible flow with Navier-Stokes equations was also applied. Moving Solid Algorithm is adopted by iterating specified velocity and pressure to simulate the change of the fluid field caused by the movement of the solid. In fact, it is difficult to apply the 3D model to real cases due to a huge scale of tsunami simulation. However, we still use the results from the 3D model to explain in details the physical properties of waves in the current stage. Key words: Tsunami, Submarine landslide, Shallow water equations, dispersive effect, Navier-Stokes equations.
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