Uphill solitary waves in granular flows

TL;DR

This paper reports the discovery of uphill solitary wave-like fluctuations in granular surface flow, observed experimentally and explained through traffic models and Saint-Venant equations, revealing novel dynamics in granular heaps.

Contribution

It introduces the observation of uphill solitary waves in granular flows and provides a theoretical explanation using traffic models and Saint-Venant equations.

Findings

Uphill soliton-like fluctuations observed experimentally.

Flow dynamics explained via traffic models.

Soliton behavior modeled with Saint-Venant equations.

Abstract

We have experimentally observed a new phenomenon in the surface flow of a granular material. A heap is constructed by injecting sand between two vertical glass plates separated by a distance much larger than the average grain size, with an open boundary. As the heap reaches the open boundary, "soliton-like" fluctuations appear on the flowing layer, and move "up the hill" (i.e., against the direction of the flow). We explain the phenomenon in the context of stop-and-go traffic models, and show that soliton-like behavior is allowed within a Saint-Venant description for the granular flow.