Abstract
The calculation of the impact pressure on obstacles in granular flows is a fundamental issue of practical relevance, e.g. for snow avalanches impacting obstacles. Previous research shows that the load on the obstacle builds up, due to the formation of force chains originating from the obstacle and extending into the granular material. This leads to the formation of a mobilized domain, wherein the flow is influenced by the presence of the obstacle. To identify the link between the physical mobilized domain properties and the pressure exerted on obstacles, we simulate subcritical cohesionless and cohesive avalanches of soft particles past obstacles with circular, rectangular or triangular cross-section using the Discrete Element Method. Our results show that the impact pressure decreases non-linearly with increasing obstacle width, regardless of the obstacle’s cross-section. While the mobilized domain size is proportional to the obstacle width, the pressure decrease with increasing width originates from the jammed material inside the mobilized domain. We provide evidence that the compression inside the mobilized domain governs the pressure build-up for cohesionless subcritical granular flows. In the cohesive case, the stress transmission in the compressed mobilized domain is further enhanced, causing a pressure increase compared with the cohesionless case. Considering a kinetic and a gravitational contribution, we are able to calculate the impact pressure based on the properties of the mobilized domain. The equations used for the pressure calculation in this article may be useful in future predictive pressure calculations based on mobilized domain properties.Graphic
Highlights
The question of how bodies and granular materials moving relative to each other interact and create interaction forces is of fundamental interest in fluid dynamics and for the rheology of granular flows [1]
Thereafter, we show how cohesion affects the granular material in the mobilized domain (MD) and how this is linked to the change in impact pressure
We demonstrate that the non-linear decrease in the impact pressure on obstacles of increasing width is linked to the compression of the granular material consisting of soft particles
Summary
The question of how bodies and granular materials moving relative to each other interact and create interaction forces is of fundamental interest in fluid dynamics and for the rheology of granular flows [1]. Previous research shows that the force acting on the obstacle originates from force chains forming between jamming particles [11, 12]. The flow–obstacle interaction dynamics are governed by the coexisting formation and destruction of these force chains extending upstream of the obstacle into the flow. Cohesion is known to increase the persistence of the force chains and the contact network density [13, 14]. The strong force chains originating from the obstacle form a region which is referred to as the mobilized domain (MD) by some authors (e.g., [15–17]). The MD is the region in a granular flow encountering an obstacle, which experiences a significant increase in the contact forces between particles. The macroscopic force experienced by the obstacle is governed by the properties of the MD [16]
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