Abstract
Abstract
Highlights
Despite most natural and man-made granular materials being composed of grains of varying size, shape and frictional properties, the majority of continuum flow modelling has largely been restricted to perfectly monodisperse aggregates
Coupling the flow rheology to the local constituent concentrations is important because the mobility of a granular flow is strongly affected by the local frictional properties of the grains
Striking examples of segregation induced feedback on the bulk flow are found during levee formation (Iverson & Vallance 2001; Johnson et al 2012; Kokelaar et al 2014) and fingering instabilities (Pouliquen, Delour & Savage 1997; Pouliquen & Vallance 1999; Woodhouse et al 2012; Baker, Johnson & Gray 2016b), which commonly occur during the run-out of pyroclastic density currents, debris flows and snow avalanches
Summary
Despite most natural and man-made granular materials being composed of grains of varying size, shape and frictional properties, the majority of continuum flow modelling has largely been restricted to perfectly monodisperse aggregates. Particle simulations, using the discrete element method (DEM), provide important rheological information as evolving velocities, stresses and constituent concentrations can be directly computed given only minimal approximations Such results can be used to motivate models for the bulk flow (GDR MiDi 2004; Jop, Forterre & Pouliquen 2006; Singh et al 2015) and to form connections between flow and segregation processes (Hill & Fan 2008; Staron & Phillips 2015). The combination of kinetic sieving and squeeze expulsion produces a net upward motion of large particles as the smaller grains percolate downwards These concepts formed the basis of the theory of Gray & Thornton (2005) who focused on this form of gravity-driven segregation in granular free-surface flows. The new experimental segregation law of Trewhela, Ancey & Gray (2021) is tested against the steady-state DEM solutions of Tripathi & Khakhar (2011) in § 6.3 and used in § 7 for the rotating drum simulations, which are able to spontaneously generate petal-like patterns that have previously been seen in the experiments of Hill et al (1999), Ottino & Khakhar (2000) and Mounty (2007)
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