風力作用下顆粒連續躍移機制之研究

Abstract

在風力作用下，地表土壤顆粒產生懸移、躍移及地表蠕移等運動，並以躍移為主要形式，進而導致地貌的侵蝕現象。其中連續躍移運動中強大的降落衝擊力是造成地表風蝕的主要原因，亦是造成懸移運動及地表蠕移運動的首要來源。本研究將以單顆粒連續躍移運動做為研究主題，以風洞試驗為基礎，結合高速攝影技術，在不同風速下量測連續躍移顆粒之運動軌跡、運動速度及碰撞角度等躍移特徵，並探討其物理現象及統計之特性，建立二維連續躍移數學模式。 顆粒連續躍移模式分為兩部分：單步躍移模式、躍移顆粒與底床間的碰撞機制。由驗證結果顯示，本模式在給定剪力速度及相關顆粒條件下，模擬顆粒連續躍移的軌跡及躍移歷程中諸項物理特性的沿程變化可獲得相當不錯成果。且發現近床顆粒運動不僅具有受力學特性主導的定率特性，亦同時具有受隨機碰撞效應影響的隨機性質。最後經由可靠度分析建立平均躍長與躍高的信賴區間與試驗結果比較，驗證本模式的合理性。

Under wind shear, the particle motion of soil on the surface including the particle suspension, saltation and surface creeping, in which saltation is the key factor, results in the landform erosion. The powerful dropping thrust of particles is the main factor for the cause of the aeolian sand motion and the landform erosion. The wind tunnel experiment is conducted to visualize and analyze the particle saltant motion. To measure the motion orbit, motion speed, and the collision angle of the particle continuous saltant process under different wind velocity the high speed photographic technique is applied. Based on the observed data, the physical phenomenon and the statistical characteristics for the particle motion are explored. In the sequence 2-D mathematical model of particle continuous saltation is established. The particle continuous saltation model established in this study includes two parts: the single-step saltant model and the collision model. The simulation results reveal that the trajectory and saltant characteristics can be interpreted under the given conditions of the ejection velocity and the size of particle. Moreover, from the analysis and find that the inter-particle collision behavior not only follows the Newton’s laws but also is controlled by random processes. Finally, the confidence level for the average saltant length and height is compared with the experimental data, showing that the proposed model is able to simulate the particle continuous saltation reasonably.