侵入物於不同縱橫比圓柱顆粒振動床內運動現象之研究

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Title:	侵入物於不同縱橫比圓柱顆粒振動床內運動現象之研究
Authors:	王立元;Wang, Li-Yuan
Contributors:	機械工程學系
Keywords:	顆粒流;振動床;侵入物;圓柱顆粒;巴西豆效應;Granular;Vibrated bed;Intruder;Cylindrical particle;Brazil nut effect
Date:	2025-01-15
Issue Date:	2025-04-09 18:28:03 (UTC+8)
Publisher:	國立中央大學
Abstract:	本研究使用類二維矩形容器為床體，以同體積但不同縱橫比(Aspect Ratio)的圓柱顆粒為背景顆粒，在改變振動頻率與無因次振動加速度下，透過實驗的方式來探討侵入物於振動顆粒床中的上升行為。圓柱顆粒分別以0.67、1.3、2.25、3.66與5.33的縱橫比來進行顆粒分離運動的實驗，藉由高速攝影機來進行影像拍攝，並以粒子影像測速技術((Particle Image Velocimetry, PIV)與MATLAB做影像處理與分析，由此探討侵入物的上升時間、各階段上升速度、背景顆粒堆積密度、背景粒子溫度與侵入物上升阻力等物理特性，以了解侵入物於不同縱橫比圓柱顆粒中分離行為與流動變化。實驗結果顯示，振動頻率的增加會使侵入物上升時間增加，而圓柱顆粒的縱橫比越高，侵入物的上升時間也會越長。這是因為當圓柱顆粒的縱橫比大於1，動態堆積密度會隨著縱橫比增加而逐漸下降，動態堆積密度的降低會有更高的孔隙率，使侵入物可更容易與圓柱背景顆粒產生分離，因此高縱橫比會有較短的上升時間。而不同振動頻率在低振動加速度時，侵入物的上升速度隨高度升高而降低，這是受顆粒堆積密度隨時間而增加的影響，使背景顆粒在後期較難流動到侵入物下方而減少背景顆粒對侵入物的推升，造成侵入物上升速度減慢。以背景粒子溫度來看各階段流動狀態可發現，在隨振動時間增加的不同階段中，接近顆粒床底部的背景粒子溫度會因堆積效應而逐漸趨近於零。因此由實驗結果可知，圓柱顆粒於垂直振動床的運動，容易因形狀形成的堆積效應而影響顆粒床的流動性質。 ;This study employs a quasi-two-dimensional rectangular container as the bed, using cylindrical particles with the same volume but different aspect ratios (AR) as the background particles. Through experiments, the rising behavior of an intruder in a vibrated granular bed is investigated under varying vibration frequencies and dimensionless vibration accelerations. The experiments on granular segregation involve cylindrical particles with aspect ratios of 0.67, 1.3, 2.25, 3.66, and 5.33. High-speed cameras captured the particle motion, and Particle Image Velocimetry (PIV) with MATLAB was employed for image processing and analysis. The analysis focuses on the intruder′s rising time, rising velocity at different stage, granular temperature of the background particles, bulk density of the background particles and the rising resistance of the intruder, aiming to understand the segregation behavior and flow dynamics of the intruder among cylindrical particles with different aspect ratios. Experimental results show that increasing frequency leads to longer rising times for the intruder, and the rising time increases with the AR of cylindrical particles. This is because, for AR > 1, the bulk density of the particles decreases, resulting in higher porosity, which facilitates separation between the intruder and the background particles. Thus, higher aspect ratios result in shorter rising times. At low vibration accelerations, the intruder′s rising velocity decreases with increasing height due to the increasing bulk density, which reduces the flow of background particles beneath the intruder in the later stages. Analyzing the background particle temperature near the bed′s bottom approaches zero over time due to packing effects. These findings demonstrate that the motion of cylindrical particles in a vertical vibrated bed is significantly influenced by shape-induced packing effects, which affect the flow properties of the granular bed.
Appears in Collections:	[Graduate Institute of Mechanical Engineering] Electronic Thesis & Dissertation

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