以滾筒實驗及理論研究間歇性崩塌與土石流應用

Abstract

本論文針對渠道以固定速率增加斜率的產生的流動，會有間歇性的運動行為進行探討， 利用理論以及實驗研究間歇性崩塌的成因。理論部分，本研究以質量守恆、動量守恆方程式搭配動能方程式，加上滾筒的邊界條件來作為本研究的控制方程式，並且在求解過程使用深度積分適度簡化來模擬非穩態狀況下的流場變化。實驗則是利用固定低轉速的滾筒實驗來重現間歇性崩塌，並透過粒子影像分析方法，紀錄崩塌事件發生時的表面流速，用以與理論比較。 實驗結果顯示，間歇性崩塌的開始和結束分別會有最高以及最低的斜率控制，當流場表面斜率超過最高斜率就會開始流動，直至流場表面達到最低斜率。在理論方面，本研究提出簡化的侵蝕與堆積模式，利用流動曾底部的剪率大小區分流動狀況並加以預測，將模式預估結果與實驗相比較，順利預測了間歇性崩塌的現象以及崩塌發生時的表面流速.最後藉由尺度分析定義了一個無因次化參數並將數值模型應用到現地模擬土石流。

This thesis examines the intermittent motion of a flow generated by a drum with a constant rate of increasing slope, and investigates the causes of intermittent collapse both theoretically and experimentally. The equations of conservation of mass, momentum, and kinetic energy, which together with the boundary conditions of the drums serve as the controlling equations for the simulation of the unsteady flow field in this study. By using depth integration, we are able to simulate flow field variation under unsteady conditions. To reproduce the intermittent avalanches, we used a drum with a constant low rotational speed, then measured the surface flow velocity during the avalanches event using PTV for comparison with theory. Experimental results indicate that intermittent avalanches begin and terminate based on the slope of the flow surface, where the flow begins when the slope reaches the highest slope and ends when the flow field surface reaches the lowest slope. Through theory, we propose a simplified erosion and deposition model based on estimating the shear rate at the base of the flow layer to differentiate the flow conditions. We compared the results of the model prediction with those obtained from the experiment. We were able to predict the phenomenon of intermittent avalanches and the surface velocity at the time of avalanches. Finally, we perform a scale analysis and define a dimensionless number called, which controls the behavior of landslides, then we apply the numerical model to the in situ simulation of landslides.