顆粒形狀在簡單滑道與複雜滑道流動行為的影響研究

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Title:	顆粒形狀在簡單滑道與複雜滑道流動行為的影響研究
Authors:	林驛軒;Lin, Yi-Xuan
Contributors:	機械工程學系
Keywords:	滑道顆粒流;形狀效應;離散元素法;流速分佈;顆粒流能量分佈;應力分佈;摩擦啟動因子;granular chute flow;particle shape affect;discrete element method;velocity profiles;energy distribution;stress distribution;contact mobilized friction
Date:	2023-01-03
Issue Date:	2023-05-09 18:14:36 (UTC+8)
Publisher:	國立中央大學
Abstract:	本研究使用離散元素法 (Discrete Element Method, DEM) 探討不同長寬比顆粒體 (長寬比1.0、長寬比1.5、長寬比2.0、長寬比2.5及長寬比3.0) 在簡單滑道與複雜滑道的流動行為，並分析顆粒流的流速、能量分佈、應力與摩擦啟動因子，以了解顆粒形狀對顆粒流傳輸性質與內部性質的影響，研究結果顯示在簡單滑道中非球形顆粒體因為互鎖效應較強，顆粒間傾向聚集流動，導致沿深度方向的速度梯度較小，在複雜滑道條件下，顆粒流流速隨長寬比的增加而減少。顆粒流耗能機制主要有兩種，摩擦耗能與碰撞耗能，不論在簡單滑道或是複雜滑道，不同形狀顆粒流皆以摩擦為主要耗能機制，且摩擦耗能占比隨長寬比的增加而增加，碰撞耗能占比則隨長寬比的增加而減少。在滑道沒有障礙物的條件下，不論簡單滑道或複雜滑道，顆粒流的應力沿流動方向呈現長寬比越大應力值越低的現象，主要是因為互鎖效應隨長寬比增加而增加，顆粒間傾向聚集流動，顆粒間劇烈碰撞減少，導致應力值下降。球形顆粒流摩擦啟動因子分佈較為平均，主要以滾動摩擦為主，因此流速較快，非球形顆粒流則因為摩擦啟動因子多分佈於0.8~1.0之間，因此流速較慢，且不同長寬比顆粒流流速差距較小。由研究結果得知在互鎖效應強弱的影響下，球形顆粒體(長寬比1.0)與非球形顆粒體(長寬比1.5、長寬比2.0、長寬比2.5及長寬比3.0)的流動行為差異較大，但非球形顆粒體間的流動行為差異較小。;The aim of this study is to investigate the effect of particle shape on transport properties and internal stresses as well as energy dissipation of granular flows down a simple chute and a complex chute by using Discrete Element Method (DEM) modeling. The aspect ratio of particles was varied between 1.0 and 3.0 with an increment of 0.5. Results reveal that non-spherical particles tend to gather and flow due to interlocking effect between particles, resulting in a small velocity gradient along the flowing depth. Especially in the complex chute, the particle flow velocity decreases with the increase of the aspect ratio. In the simple chute or the complex chute, friction is the main mechanism of energy dissipation for granular flows. The proportion of frictional energy dissipation increases with aspect ratio, while that of collision energy dissipation decreases with the increase of aspect ratio. In the granular flows down the simple chute or the complex chute, the granular stress decreases with the increase of the aspect ratio, mainly because the interlocking effect increases with aspect ratio. The interlocking effect causes the particles to reduce their velocities, and the intensive collisions between particles decrease, leading to a decrease in the stress value. The spherical granular flows exhibit more uniform probability distributions in the mobilized friction, indicating that the contacts between particles mainly lie in rolling friction regime. However, the contact mobilized friction in the non-spherical granular flows is mostly distributed between 0.8 and 1.0, approaching sliding friction regime. The flow behaviors between spherical and non-spherical granular flows are significantly different due to the interlocking effect, but those between non-spherical granular flows with the aspect ratio larger than 1.5 are small.
Appears in Collections:	[Graduate Institute of Mechanical Engineering] Electronic Thesis & Dissertation

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