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.

在这项研究中，使用光流方法测量矩形准二维筒仓中颗粒流的速度分布。使用速度梯度，获得自由落体弓（FFA）并计算其几何特征。在稳态流动的孔口上方发现了抛物线形的FFA结构。FFA的形状会影响通过孔的流量。此外，随着干扰开始发生，FFA的几何形状从两侧逐渐消失，然后从中间逐渐消失。最终，FFA在干扰状态下完全消失。作为有限应力区域和无应力区域之间的边界，FFA有助于进一步研究孔口上方应力区域的不连续性。