發展移動固體法並用於山崩海嘯過程與海嘯石運動之研究;Developing a Moving Solid Algorithm to Study the Generation of Landslide Tsunamis and the Movement of Tsunami Boulders

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Title:	發展移動固體法並用於山崩海嘯過程與海嘯石運動之研究;Developing a Moving Solid Algorithm to Study the Generation of Landslide Tsunamis and the Movement of Tsunami Boulders
Authors:	胡順凱;Hu, Shun-Kai
Contributors:	水文與海洋科學研究所
Keywords:	移動固體法;剛性流體法;流固耦合;流體體積法;山崩海嘯;2017年格陵蘭山崩海嘯;九鵬;海嘯石;Moving Solid Algorithm;RFM;Fluid-Structure Interaction;VOF;Landslide Tsunami;2017 Greenland Tsunami;Jiu Peng;Tsunami Boulders
Date:	2018-08-22
Issue Date:	2018-08-31 11:36:14 (UTC+8)
Publisher:	國立中央大學
Abstract:	2017年6月，格陵蘭島西岸之卡拉特峽灣（Karrat Fjord）發生山崩海嘯事件，估計體積約4500萬立方公尺之山崩滑落，引發之海嘯侵襲南方之Nuugaatsiaq漁村，造成結構物破壞以及數人死亡。相較於海底地震引發之海嘯，山崩海嘯具有較強烈之垂直擾動，且往往伴隨劇烈之碎波，必須以三維數值方法獲得更精確之模擬。　　台灣為較易受海嘯攻擊之海島，亦有十數筆歷史海嘯以及古海嘯紀錄（Wu, 2013），然而海嘯石為研究古海嘯之重要地質線索，由海嘯石最終所停留之位置，有機會一窺當時海嘯來臨時之波高與流速，並釐清動力來源，如海嘯或颱風巨浪。此外，台灣屏東九鵬已發現三顆海嘯石（Matta et al., 2013），透過分析其動力機制，有機會還原古海嘯之情境。　　然而，山崩海嘯與海嘯石之運動皆關係到雙相流流體力學與固體力學之耦合，為此，本研究開發嶄新之剛性流體法（Rigid-Fluid Method, RFM），求解三維不可壓縮流之Navier-Stokes方程式，以流體體積法（VOF）搭配PLIC法描述自由液面，並應用離散元素法（DEM），透過收集網格中之壓力及剪力，計算固體之移動及旋轉。本文使用RFM法，對半圓球山崩海嘯實驗、格陵蘭山崩海嘯以及九鵬海嘯石，進行一系列之模擬以及分析，獲得非常準確之驗證，以及符合文獻描述之模擬結果。　　本研究結果顯示，半圓球山崩之側向流速將逐漸增大，且塊體浸沒深度達2.5倍半圓球直徑後，已難影響上層之流場。將模擬之尺度放大後，模擬結果之參數皆符合福祿數相似時之倍數關係。格陵蘭山崩模擬之溯上高度可達90公尺，符合Nature News報導之數據。在1:5坡度條件下，海嘯石搬運之條件為至少1.5倍直徑波高之湧潮，以及至少 √2gh 之流速。;In June, 2017, a landslide-tsunami event took place at Karrat fjord, locating at the west coast of Greenland. The volume of the landslide is approximately 45 million cubic meter. As the result, the tsunami brought destructions and several casualties to a fishing village at Nuugaatsiaq. In order to investigate further physical properties of this event, we must not ignore the high nonlinearity of breaking waves induced by great vertical vibration. Therefore, a 3D numerical analysis is taken to obtain accurately reproduce the scenario. 　　Rigid-Fluid Method (RFM), which solves the Navier-Stokes equation for three-dimensional incompressible flow, is developed to calculate the movement and rotation of a moving solid. With the data of the pressure and shear stress in each grid collected by Discrete Element Method (DEM), the moving solid is granted to be involved in the simulation; while the free surface is reconstructed by Piecewise Linear Interface Calculation (PLIC). 　　A series of simulations and analyses of the Greenland Tsunami, the Jiu Peng tsunami boulders, and a hemisphere landslide tsunami experiment have been performed. The numerical results, which concur with the literature records, indicate the correctness of this method even a moving solid is included.
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