顆粒體是指一群獨立且不會相互發生化學變化的固體粒子。而顆粒流為描述一群顆粒體分散於水或空氣之兩相流的運動。本實驗使用輸送帶設備運載顆粒體，將其上之顆粒體運轉至穩定均勻流的條件觀察慢顆粒流，並運用用Voronoï影像法以期得到全區域之流場。研究目的為除了可以瞭解微觀上粒子的型態，並希望能與巨觀上顆粒整體之行為做一關連。 本研究主要探討如何從數位攝影機取得連續圖檔，並舉一組資料為例子，分別說明如何得到單張之顆粒位置、多張顆粒位置之比對、進而得到速度剖面圖與擾動速度關係圖，並說明程式執行中如何刪去錯誤比對以及最佳化的過程，得到具統計意義之物理量。最後，再說明如何利用Voronoï鄰邊關係得到dd值；其與速度擾動量相關，並從中發現孔洞擴散平衡模式，此與Rouse輸砂理論裏的懸浮載平衡公式有異曲同工之妙。 Focusing on the details of particle motions and patterns, the present experimental study examines the behaviour of slow granular flows. Steady uniform free surface shear flows of dry grains are generated in a tilting flume equipped with a conveyor belt. Granular positions close to the transparent flume sidewall are extracted from digital images. The Voronoï diagram is then used both to track particles over successive frames and to characterise the patterns formed by neighbouring grains. Specifically, quantitative estimates for the strength of velocity fluctuations and for the density of lattice defects are obtained. Overall, both the macro- and microscopic kinematics of the frictional flow are found to be controlled by the speed of the conveyer belt. On a microscopic scale, lattice defects and velocity fluctuations are found to be positively correlated with each other. Profiles of defect density over the flow depth suggest that three competing effects are at play: 1) static disruptions of crystalline arrangement close to the bottom due to the conveyer belt geometry; 2) gravitational pull of the granular assembly towards a state of close packing; 3) diffusive downwards infiltration of voids originating from the agitated free surface. After subtraction of effect 1), the measured profiles strikingly mirror the curves of the Rouse theory of suspended sediment transport.
