| 摘要(英) |
The purpose of the study is to investigate the convection behaviour of spherical and non-spherical particles in quasi-2D vibrating beds by using discrete element method (DEM). The study includes two parts: one is the effect of particle shape on convection behavior (Part I), and the other is the micro exploration of convection mechanism (Part II). In Part I, four kinds of donut-shaped particles used in the study are respectively composed of 8, 9, 10 and 11 sub-spheres by adopting multi-sphere method, and these donut-shaped particles have the same mass and moment of inertia despite different outlines. The numerical results reveal that the transport properties increase with the increase of sub-sphere number, especially in rotational behaviour. This is attributed to the fact that the surface roughness increases with the decreasing sub-sphere number, leading to stronger inter-locking behaviour between particles. In Part II, the convection behavior of a spherical granular assembly is explored from the micro-scale point of view, and a vibrating cycle, including ascending and descending processes, is divided into 12 phases. The DEM results corroborate that the shear bands occur at the regions near the sidewalls during the descending process, whereas take place at the bottom base during the ascending process. It is the shear bands that drive the granular assembly circulate in the vibrating bed. The central part of the vibrating granular bed shows higher coordination number but smaller contact force than the sidewalls and bottom base. In addition, the mobilized friction factor at the sidewalls and bottom base are larger than that in the central part. The fabric analysis also reveals that the contact orientation approaches the vertical direction during the ascending process, but the horizontal direction during the descending process. The micro-scale analysis further points out that, during an entire cycle, the particles collide the most drastically between the balanced position and the wave crest in upward motion. |
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