高速顆粒流衝擊阻礙物下流場行為與應力變化之研究

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題名:	高速顆粒流衝擊阻礙物下流場行為與應力變化之研究
作者:	劉鈺文;Liu, Yu-Wen
貢獻者:	機械工程學系
關鍵詞:	顆粒流;阻礙物;震波;衝擊力;爬坡高度;Granular flow;Barrier;Shock wave;Impact force;Run-up height
日期:	2024-08-08
上傳時間:	2024-10-09 17:25:03 (UTC+8)
出版者:	國立中央大學
摘要:	隨著全球氣候變遷及人類活動日益增加，自然災害的頻率與強度亦隨之上升，其中山崩、土石流、雪崩及地震引發的坡地災害尤為顯著。這些災害不僅對人類社會安全構成威脅，也對生態系統與地形的長期變遷造成深遠影響。因此，本研究透過實驗的形式，來觀察顆粒崩塌的流動行為。本研究旨在探討高速顆粒流衝擊阻礙物時的流場行為與應力變化。透過封閉式傾斜滑槽做為實驗設備，以實驗的方式研究了不同顆粒材質(玻璃砂和石英砂)以及不同阻礙物材質(PVC、EPE和LDPE)，在不同傾斜角度下對顆粒流動行為和衝擊力的影響。為了觀察顆粒在流場的速度變化，使用粒子影像測速(Particle image velocimetry,PIV)計算流場速度，而應力變化則是使用壓力感測器進行量測。在實驗中，調整了滑槽傾斜角度，並記錄了每組實驗中的流場行為和應力分布。實驗結果表明，顆粒材質對顆粒流的動態行為有顯著影響，主要表現為垂直噴射模式與堆積模式。隨著傾斜角度的增加，流場的最大速度與衝擊速度均提高，但會隨著流動長度遞減，其中衝擊速度普遍低於最大速度。對於玻璃砂而言，震波速度在小傾斜角下隨流動長度減少而降低；在大傾斜角下，震波速度則呈現先急遽減少後平緩的趨勢。對於石英砂，在較低傾斜角下，震波速度保持在固定範圍內，這是由於其安息角大於傾斜角造成的特殊流動現象。在衝擊力方面，衝擊力隨著傾斜角度增加而增加，且改變阻礙物材質能有效降低衝擊力，並觀察到衝擊力分布非線性變化，可分為五種不同類型。此外，使用理論模型去預測最大爬坡高度與最大總衝擊力，並以實驗數據對比，發現在密度比為1時，能有效預測最大爬坡高度，而在顆粒為玻璃砂時，理論預測最大總衝擊力誤差一般在±10%內。最後，為了量化差異，計算了沉積角，並且發現沉積角隨著傾斜角度增加而增加，所對應的福祿數也相應增加。 ;As global climate change intensifies and human activities increase, the frequency and severity of natural disasters have risen accordingly, with landslides, debris flows, avalanches, and earthquake-induced slope failures being particularly significant. These events pose direct threats to human safety and have profound effects on ecosystems and long-term geomorphological transformations. Consequently, this study focuses on observing the flow behavior of granular collapses through experimental methods. This research aims to explore the behavior of high-speed granular flows impacting obstacles. Experiments were conducted using a closed inclined chute to investigate the effects of different granular materials (glass sand and quartz sand) and various barrier materials (PVC, EPE, and LDPE) at different inclination angles on the flow behavior and impact forces of the granular streams. Particle Image Velocimetry (PIV) was utilized to measure the velocity changes in the flow field, and load cell were employed to assess stress variations. Throughout the experiments, the inclination of the chute was adjusted, and detailed records of the flow behavior and stress distribution for each set of experiments were maintained. The experimental results indicate that the material properties of the granules significantly influence the dynamics of the granular flow, primarily manifesting as vertical jetting or accumulation modes. As the inclination angle increases, both the maximum flow velocity and the impact velocity also increase, yet they decrease along with the flow length, with the impact velocity generally being lower than the maximum velocity. For glass sand, the shock wave velocity decreases with the flow length at smaller inclination angles; at larger inclination angles, the shock wave velocity initially decreases sharply and then stabilizes. For quartz sand, at lower inclination angles, the shock wave velocity remains within a fixed range due to its angle of repose being greater than the inclination angle, resulting in unique flow behavior. Regarding the impact forces, they increase with the inclination angle, and altering the material of the obstacle can effectively reduce these forces, with the distribution of impact forces showing nonlinear variations, categorized into five distinct types. Additionally, theoretical models were employed to predict the maximum run-up height and the overall impact force, with comparisons to experimental data revealing that when the density ratio is 1, the predictions accurately reflect the maximum run-up height. For glass sand, the predicted maximum total impact force generally has an error margin within ±10%. Finally, to quantify the differences, the deposition angle was calculated and found to increase with the inclination angle, with the corresponding Froude number also increasing accordingly.
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