| 摘要: | 本研究採用離散元素法模擬三種不同顆粒振動床(I 型、II 型與 III 型)在不同振動條件下，顆粒體在顆粒振動床內部的流動行為與內部性質，首先探討振動床 I 型物理實驗與 DEM 模擬的比較，證明本研究所提 DEM 模型的合理性，接著採用驗證合理的 DEM模型探討振動條件對顆粒體在振動床 II 型內能量消散的影響，最後探討顆粒層數與無因次振動加速度對顆粒體在振動床 III 型內流動型態的影響，並進一步探討顆粒體的內部性質，並根據無因次振動加速度及層數兩個參數，依粒子溫度區分顆粒體的流動型態。
研究結果顯示：(1) 在振動床 I 型的模擬中，比較模擬結果與物理實驗結果，兩者對應的物理量相當吻合。(2) 振動床 I 型左右兩側下方因顆粒體迴流運動產生較多的碰撞，故產生較大的正向與切向應力。隨著高度的上升，粒子體積佔有率與配位數隨之下降，且左右兩側因膨脹效應，導致邊壁區域呈現較小的粒子體積佔有率。(3) 在振動床 II 型模擬中，隨著振動幅度與振動頻率的增加，總機械能、應變能、碰撞耗能、摩擦耗能與振動床對顆粒體的作功量皆隨之上升，且在顆粒振動床中碰撞耗能皆大於摩擦耗能。(4) 在振動床 III 型模擬中，在顆粒層數 2 層的 Γ=10、20、30 時，皆為顆粒體氣態行為(Gas like)；在顆粒層數 5 與 9 層的 Γ=10 時，皆為波動態；在顆粒層數 5 層的 Γ=20 時，呈現顆粒體彈跳床行為；在顆粒層數 5 層的 Γ=30 時，則呈現顆粒體浮力對流行為；在顆粒層數 9 層的 Γ=20 時，處於波動態與萊頓弗羅斯特現象之間；在顆粒層數 9 層的 Γ=30時，則呈現萊頓弗羅斯特現象。;This study uses the discrete element method (DEM) to simulate the flow behavior and internal properties of granular materials in three types of vibrated beds (Type I, Type II, and Type III) under different vibration conditions. First, the study provides the comparison between physical experiments and DEM simulations for vibrated bed Type I , proving the validity of the DEM model proposed in this study. Then, using the validated DEM model, the study investigates the effect of vibration conditions on energy dissipation of granular materials within the vibrated bed Type II. Finally, the study examines the influence of the number of granular layers and dimensionless vibration acceleration on the flow patterns of granular materials in the vibrated bed Type III, and further explores their internal properties. According to granular temperature , the study categorizes the flow patterns of granular materials in the vibrated beds.
The major findings are summarized below: (1) In the DEM simulations for vibrated bed Type I, the simulation results match well with the experiment results in terms of physical properties; (2) In the DEM simulations for vibrated bed Type I, more collisions occur at the lower left and right sides, inducing larger normal and shear stresses. The solid volume fraction and coordination number decrease with height, and those in the sidewall region appear smaller due to the dilation effect on the left and right sides; (3) In the DEM simulations for vibrated bed Type II, as the vibration amplitude and frequency increase, the total mechanical energy, strain energy, collision energy, friction energy, and the work done by the vibrated bed on the granular materials all increase, with collision energy always exceeding friction energy within the granular vibrated bed; (4) In the DEM simulations for vibrated bed Type III, for 2 layers of ABS beads subjected to Γ=10, 20 and 30, the granular assemblies behavior like gas. For 5 and 9 layers of ABS beads subjected to Γ=10, the granular assemblies exhibit undulation behavior. At 5 layers with Γ=20, a bouncing bed behavior is observed, and at 5 layers with Γ=30, buoyancy convection occurs. At 9 layers with Γ=20, the granular assemblies behavior between undulation and Leidenfrost phenomena, and at 9 layers with Γ=30, the Leidenfrost phenomenon appears. |
