Discrete Element Simulation on Sand-Bed Collision Considering Surface Moisture Content

Hongchao Dun,Jie Zhang,Peng Yue,Ning Huang

doi:10.3390/pr10010052

Abstract

The process of aeolian sand transport is an important mechanism leading to the formation and evolution of local landforms in coastal areas and desert lakes. For a long time, the role of surface moisture in incipient motion of sand grains by wind stress has been extensively studied but, in fact, sand-bed collision is the main mechanism in steady aeolian sand flow. At present, the lack of understanding of surface moisture content on sand-bed collision limits the application of aeolian sand transport models in wet coastal areas. In this paper, we adopt numerical simulations to discuss and analyze the effect of cohesive forces formed by surface moisture content on the sand-bed collision process based on discrete element method. High density contact forces appear with the surface moisture increasing, and form a closed structure around the edge of crater to resist the avulsion in horizontal direction. Under high moisture condition, even though the ejected sand grains saltate away from the surface, the tension forces will prevent from leaving. The ejected number trend with incident velocity shows some nonlinear characteristics due to the unequally distributed force chains and liquid bridges in the unsaturated sand bed surface.

Highlights

Academic Editor: Joanna WiacekCoastal aeolian sand transport is a first-order control on growth of local dunes and ripples, shaping the landforms and resulting in the generation and evolution of desertification [1,2,3,4]
High density contact forces appear with the surface moisture increasing, and form a closed structure around the edge of crater, which inevitably has a better performance to resist the avulsion in the horizontal direction
Even though the ejected sand grains saltate away from the surface and generate a considerable distance from the adjacent particles, the tension forces will pull them from leaving until the liquid bridges are stretched to break

Summary

Introduction

Academic Editor: Joanna WiacekCoastal aeolian sand transport is a first-order control on growth of local dunes and ripples, shaping the landforms and resulting in the generation and evolution of desertification [1,2,3,4]. The role of surface moisture in the incipient motion of sand grains by the wind has been extensively studied, and numerous empirical and physical models have been proposed to quantify this effect [8,9,10,11,12,13,14,15,16]. The sand-bed collision formed by saltation is the main mechanism in steady aeolian sand flow, in which sand grains move forward by nearly ballistic trajectories under the forces of gravity and wind drag, collide with the loose sand surface and eject new sand particles [17,18] (Figure 1). The almost complete lack of knowledge about the effect on sand-bed collision precludes the deep understanding of aeolian physics and improving numerical simulation accuracy

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