Item: Experiments and numerical simulation of ping-pong ball avalanches
Title: Experiments and numerical simulation of ping-pong ball avalanches
Proceedings: Proceedings of the 1998 International Snow Science Workshop, Sunriver, Oregon
Authors: Ito Y., Nishimura K., Nohguchi y., J. McElwaine, S. Keller, and Izumi K.
Abstract: Snow avalanche experiments at a ski jump have been carried out since 1995. Instead of snow, we used up to 550,000 ping-pong balls to simulate three-dimensional granular flows along the inclined plane. A laser radar system revealed the distribution of the flow thickness; a head with about 0.8m long and 0.5m high was clearly recognized for 200,000 ping-pong balls flow and the oval lateral cross-section with 13m long and 0.1-0.2m high was found for 20,000 balls flow. After the head, particle concentration became low and the specific structure like "eyes· appeared in the flow. Video camera positioned above gave us not only the distance of a single ball but also its velocities. Obtained results revealed that the vertical and outward (horizontal) activities are rather high around the head. A new device, that is composed of 4 pipes with open ends pointing up, down, left and right and connected to 4 pressure difference sensors through a 20m long tube was also developed to investigate the three dimensional air flow structures. The movement of balls and the surround~g air obtained suggest a strong interaction each other. Computer simulation with the OEM (Discrete Element 'Method) shows reasonable results for small avalanches. However, the air drag will be a crucial factor for the larger flows in which specific structures like head and eddies are observed in the experiments.
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Keywords: snow avalanche, ping-pong ball, ski jump, particle and air interaction
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