APPLIED MECHANICS LABORATORY

We report experiments performed on granular flows over an inclined and spring-supported base. We observe the energy proles of steady granular flow and compare our findings with simulations. The figure shows our experimental setup. It consists of two 40 mm wide acrylic channels aligned longitudinally. We use steel balls of 4 mm diameter as the flowing granular material. The same balls are stuck to the base in order to make the latter bumpy. The first channel is a 2 m long `guideway' which is fixed to an iron frame and guides the flowing steel balls into the second 1 m long `spring-supported' channel whose base is supported by springs at either end. Both channels rest upon an iron frame that can be tilted to change the inclination. During experiments, the spring-supported channel oscillates primarily in its first mode of vibration. When the flow has fully developed, the pitching motion of the base, corresponding to the second mode of vibration, is observed to be small and is thus ignored. We employ particle tracking and image processing techniques to obtain quantitative data from the flow. We track the positions of steel balls and, so, compute their velocities. To capture these images, we use three high-speed cameras (Phantom V9.1 with a Zoom-NIKKON 50 mm f/1.8D lens) with a resolution of 480 X 480 pixels. We use a halogen display lamp that focuses on the targeted window from the front. To track the steel balls it is necessary to ensure that a ball does not travel more than one ball diameter distance between two consecutive frames. This corresponds to about 25 ms, which sets the shutter speed at 3910 fps. To observe flow development, we employ cameras at ve different locations, covering 3 meters of the length of the flow as shown in the figure. Each experiment is repeated four times, and the averaged data is reported. The images are processed in MATLAB for further analysis.