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Abstract In this study, the optical flow method is used to measure the velocity distribution of a granular flow in a rectangular quasi-two-dimensional silo. Using the velocity gradient, a free-fall… Click to show full abstract
Abstract In this study, the optical flow method is used to measure the velocity distribution of a granular flow in a rectangular quasi-two-dimensional silo. Using the velocity gradient, a free-fall arch (FFA) is obtained and its geometric characteristics are calculated. A parabola-shaped FFA structure is discovered above the orifice in the steady flow state. The shape of the FFA affects the flow rate through the orifice. Furthermore, as jamming begins to occur, the geometry of the FFA disappears gradually from both sides and then from the middle; finally, the FFA disappears completely in the state of jamming. As the boundary between finite-stress and stress-free regions, the FFA facilitates further studies regarding the discontinuity of the stress area above the orifice.