Automated analysis of angle of repose of a conical bead pile using Python

A conical bead pile subject to slow driving is used as a model critical system to experimentally investigate the distributions of avalanche sizes and time between events. The pile is composed of roughly 20 000 steel beads, 3 mm in diameter; we drive the pile by adding one bead at a time to the apex of the pile. To better understand the dynamics of individual avalanches, a side view camera captures an image of the pile after every bead drop; images are compiled after an entire run for analysis of the changing repose angle of the pile. Prior work by Bennett Anderson allowed automatic measurement of the global angle of repose, or an average angle for the overall slope of the pile. Here we have improved that analysis, creating a new analysis algorithm in Python to address previous problems with consistently defining the top and bottom edges of the pile. In addition to measuring the left and right global angles of the pile, the analysis now determines multiple angles along the pile slope to better characterize how areas near the apex differ from the base. In testing, results from the new Python program support previous observations that the repose angle of the pile decreases as avalanches occur and increases when cohesion is added to the system. The program allows investigation of the different effects on the base and apex slopes during avalanches as well as the movement of beads down the pile in surface-only avalanches where no mass leaves the pile.