scholarly journals Vertical grain size sorting in bedload transport on steep slopes with a coupled fluid-discrete element model

2018 ◽  
Vol 40 ◽  
pp. 04013
Author(s):  
Philippe Frey ◽  
Rémi Chassagne ◽  
Raphaël Maurin ◽  
Julien Chauchat
Keyword(s):  
Grain Size ◽  
Fine Particles ◽  
Element Model ◽  
Discrete Element ◽  
Bedload Transport ◽  
Initial Time ◽  
Discrete Element Model ◽  
Size Sorting ◽  
Bedload Sediment ◽  
Particle Bed

In order to study vertical grain size sorting in bedload sediment transport, numerical experiments of two-size particle mixtures were carried out, using a validated coupled fluid-discrete element model developed at Irstea. A 3D 10% steep domain, consisting at initial time of a given number of layers of 4 mm particles deposited on top of a coarser 6 mm particle bed, was sheared by a turbulent and supercritical fluid flow (Shields numbers of 0.1 and 0.3). The elevation of the centre of mass of the infiltrated fine particles is observed to follow the same logarithmic decrease with time, whatever the initial number of fine layers. This decrease is steeper for a higher Shields number. The main result is that this typical behaviour is related at first order to the particle shear rate depth profile.

Study on a large-scale discrete element model for fine particles in a fluidized bed

2012 ◽  
Vol 23 (5) ◽  
pp. 673-681 ◽  
Author(s):  
Mikio Sakai ◽  
Hiroyuki Takahashi ◽  
Christopher C. Pain ◽  
John-Paul Latham ◽  
Jiansheng Xiang
Keyword(s):  
Fluidized Bed ◽  
Large Scale ◽  
Fine Particles ◽  
Element Model ◽  
Discrete Element ◽  
Discrete Element Model

scholarly journals Investigation of vertical size segregation in bedload sediment transport with a coupled fluid-discrete element model

2017 ◽  
Vol 140 ◽  
pp. 09025
Author(s):  
Philippe Frey ◽  
Raphaël Maurin ◽  
Lamia Morchid-Alaoui ◽  
Shashank Gupta ◽  
Julien Chauchat
Keyword(s):  
Sediment Transport ◽  
Element Model ◽  
Discrete Element ◽  
Discrete Element Model ◽  
Size Segregation ◽  
Bedload Sediment ◽  
Vertical Size

scholarly journals Impact of Ballast Fouling on the Mechanical Properties of Railway Ballast: Insights from Discrete Element Analysis

Processes ◽  
2021 ◽  
Vol 9 (8) ◽  
pp. 1331
Author(s):  
Luyu Wang ◽  
Mohamed Meguid ◽  
Hani S. Mitri
Keyword(s):  
Shear Strength ◽  
Mechanical Response ◽  
Fine Particles ◽  
Element Model ◽  
Discrete Element ◽  
Shear Loading ◽  
Discrete Element Model ◽  
Railway Ballast ◽  
Fouled Ballast ◽  
Interparticle Friction

Ballast fouling is a major factor that contributes to the reduction of shear strength of railway ballast, which can further affect the stability of railway supporting structure. The major sources of ballast fouling include infiltration of foreign fines into the ballast material and ballast degradation induced by train movement on the supported tracks. In this paper, a discrete element model is developed and used to simulate the shear stress–strain response of fouled ballast assembly subjected to direct shear loading. A simplified computational approach is then proposed to model the induced ballast fouling and capture the mechanical response of the ballast at various levels of contamination. The approach is based on the assumption that fine particles comprising the fouling material will not only change the interparticle friction angle, but also the contact stiffness between the ballast particles. Therefore, both the interparticle friction coefficient and effective modulus are adjusted based on a fouled ballast model that is validated using experimental results. The effect of ballast degradation is also investigated by gradually changing the particle size distribution of the ballast assembly in the discrete element model to account for the increased range of particle sizes. Using the developed model, the effect of ballast degradation on the shear strength is then evaluated. Conclusions are made to highlight the suitability of these approximate approaches in efficiently modeling ballast assemblies under shear loading conditions.

scholarly journals A minimal coupled fluid-discrete element model for bedload transport

2015 ◽  
Vol 27 (11) ◽  
pp. 113302 ◽  
Author(s):  
R. Maurin ◽  
J. Chauchat ◽  
B. Chareyre ◽  
P. Frey
Keyword(s):  
Element Model ◽  
Discrete Element ◽  
Bedload Transport ◽  
Discrete Element Model

Discrete simulations of an armoured sediment bed during bedload transport

2020 ◽  
Author(s):  
Rémi Chassagne ◽  
Raphaël Maurin ◽  
Julien Chauchat ◽  
Philippe Frey
Keyword(s):  
Numerical Experiments ◽  
Element Model ◽  
Discrete Element ◽  
Bedload Transport ◽  
Transport Rate ◽  
Discrete Element Model ◽  
Small Particles ◽  
Flowing Fluid ◽  
Wide Range ◽  
Large Particles

<p><span><span>Bedload transport (transport of particles by a flowing fluid along the bed by rolling, sliding and/or saltating) has major consequences for public safety, water resources and environmental sustainabilty. In mountains, steep slopes drive an intense transport of a wide range of grain sizes implying size sorting or segregation largely responsible for our limited ability to predict sediment flux and river morphology. Size segregation can lead to very complex and varied morphologies of bed surface and subsurface, including armouring, and can drastically modify the fluvial morphology equilibrium. In this work, the transport rate of an armoured bed, made of large particles on top of a small particles bed, is studied. </span></span></p><p align="justify"> </p><p><span><span>In order to gain understanding of this process, bedload transport numerical experiments of two-size particle mixtures were carried out, using a coupled Eulerian-Lagrangian fluid-discrete element model validated with experiments (Maurin et al. 2015, 2016). It is composed of a 3D discrete element model (based on the open source code Yade), describing each individual particle, coupled with a one dimensional Reynolds Average Navier Stokes model (Chauchat 2017). A 3D 10% steep domain (angle of 5.71°) is considered. Three different configurations are compared: 2 layers or 4 layers of 6mm particles deposited on top of a bed composed of 3mm particles, and a monodisperse case with only 6mm large particles. The bed is then submitted to a turbulent, hydraulically rough and supercritical water flow until steady transport rate. Shields numbers ranging from 0.1 to 0.5 are considered.</span></span></p><p> </p><p><span><span>The numerical experiments show that in all three configurations, the transport law, relating the dimensionless transport rate to the shields number, is a power law. In addition, it is observed that for the same Shields number, the transport rate is higher in the bidisperse cases than in the monodisperse case. This result can be explained by the rheological properties of bidisperse granular media. Finally, we show that the particles at the interface between large and small particles should be in motion in order to have an increase of particle mobility.</span></span></p><p align="justify"><br><br></p><p><span><span>Chauchat J. 2017. A comprehensive two-phase flow model for unidirectional sheet-flows. </span></span><span><span><em>Journal of Hydraulic Research</em></span></span><span><span>: 10.1080/00221686.2017.1289260.</span></span></p><p><span><span>Maurin R, Chauchat J, Chareyre B, Frey P. 2015. A minimal coupled fluid-discrete element model for bedload transport. </span></span><span><span><em>Physics of Fluids</em></span></span> <span><span><strong>27</strong></span></span><span><span>(11): 113302.</span></span></p><p><span><span>Maurin R, Chauchat J, Frey P. 2016. Dense granular flow rheology in turbulent bedload transport. </span></span><span><span><em>Journal of Fluid Mechanics</em></span></span> <span><span><strong>804</strong></span></span><span><span>: 490-512.</span></span></p>

scholarly journals Discrete element model for general polyhedra

2021 ◽  
Author(s):  
Alfredo Gay Neto ◽  
Peter Wriggers
Keyword(s):  
Frictional Contact ◽  
Virtual Work ◽  
Particle Surface ◽  
Element Model ◽  
Discrete Element ◽  
Discrete Element Model ◽  
Principle Of Virtual Work ◽  
Dynamics Model ◽  
Railway Ballast ◽  
Multibody Dynamics Model

AbstractWe present a version of the Discrete Element Method considering the particles as rigid polyhedra. The Principle of Virtual Work is employed as basis for a multibody dynamics model. Each particle surface is split into sub-regions, which are tracked for contact with other sub-regions of neighboring particles. Contact interactions are modeled pointwise, considering vertex-face, edge-edge, vertex-edge and vertex-vertex interactions. General polyhedra with triangular faces are considered as particles, permitting multiple pointwise interactions which are automatically detected along the model evolution. We propose a combined interface law composed of a penalty and a barrier approach, to fulfill the contact constraints. Numerical examples demonstrate that the model can handle normal and frictional contact effects in a robust manner. These include simulations of convex and non-convex particles, showing the potential of applicability to materials with complex shaped particles such as sand and railway ballast.

Study on Machining Mechanism of Glass Using Discrete Element Method

2014 ◽  
Vol 577 ◽  
pp. 108-111 ◽  
Author(s):  
Ying Qiu ◽  
Mei Lin Gu ◽  
Feng Guang Zhang ◽  
Zhi Wei
Keyword(s):  
Discrete Element Method ◽  
Element Model ◽  
Discrete Element ◽  
Rake Angle ◽  
Milling Process ◽  
Micro Milling ◽  
Discrete Element Model ◽  
Machined Surface ◽  
Damage Depth ◽  
Element Method

The discrete element method (DEM) is applied to glass micromachining in this study. By three standard tests the discrete element model is established to match the main mechanical properties of glass. Then, indentating, cutting, micro milling process are simulated. Results show that the vertical damage depth is prevented from reaching the final machined surface in cutting process. Tool rake angle is the most remarkable factor influencing on the chip deformation and cutting force. The final machined surface is determined by the minimum cutting thickness per edge. Different cutting thickness, cutter shape and spindle speed largely effect on the mechanism of glass.

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