Discrete Element Modeling of Railway Ballast for Studying Railroad Tamping Operation

2020 ◽  
Author(s):  
Nilesh Dama ◽  
Mehdi Ahmadian
Keyword(s):  
Simulation Model ◽  
Element Model ◽  
Discrete Element ◽  
Performance Comparison ◽  
Particle Flow Code ◽  
Computer Simulation Model ◽  
Discrete Element Modeling ◽  
Railway Ballast ◽  
Insertion Force ◽  
Elliptical Motion

Abstract The dynamic behavior of ballast particles during track tamping is studied by developing a computer simulation model using the Discrete Element Model (DEM) method. The simulation model is developed in a commercially available DEM software called PFC3D (Particle Flow Code 3D). The study primarily evaluates a complete tamping cycle as defined by insertion, squeeze, hold, and withdrawal. Using a Taguchi approach, the effect of Tine motion’s frequency and amplitude, insertion velocity, and squeeze velocity are evaluated on tamping effectiveness. The compactness of the ballast particles, as defined by the average number of contacts per particle (referred to “Coordination Number”) is used as a measure of the effectiveness of tamping. Setting up the DEM model and important elements such as selection and calibration of particle shapes, ballast mechanical properties, contact model, and parameters governing the contact force models are described in detail. The tamping process is evaluated using a half-track layout with a highly modular code that enables a high degree of adjustability to allow control of all parameters for improved simulation flexibility. A parametric study is performed to find the best values of tine motion parameters for improving tamping efficiency. A performance comparison is made between linear and elliptical tamping. The results indicate that smaller squeeze and release velocities of the tines yield better compaction. Of course, reducing the velocities would result in increased tamping time. Additionally, the results indicate that the linear motion of the tines potentially result in better compaction than elliptical motion, although the latter may require less insertion force (power) and cause less ballast damage.

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.

A Wear Simulation of the Fixed Soft Abrasive Film Based on Discrete Element Method

2014 ◽  
Vol 1017 ◽  
pp. 452-457
Author(s):  
Zhao Zhong Zhou ◽  
Kai Ping Feng ◽  
Ju Long Yuan
Keyword(s):  
Element Model ◽  
Discrete Element ◽  
Particle Flow ◽  
Particle Flow Code ◽  
Discrete Element Model ◽  
Optic Fiber ◽  
Wear Property ◽  
Factors Affecting ◽  
Main Factors ◽  
Simulation Results

A new polishing method by using fixed soft abrasive film is proposed to polish the end-face of the optic fiber connector. In order to study the wear property of the fixed soft abrasive film, the Particle Flow Code program was employed to simulate the interaction of surface topography. The discrete element model of the optic fiber connector and the fixed soft abrasive film were established. Through the interaction of the surface of two models, the process of contact and friction between the fixed soft abrasive film and the end-face of the optic fiber connector could be simulated. Simulation results showed that the main factors affecting the wear of the fixed soft abrasive film were pressure and speed, which mainly affected the normal stress and the tangential stress respectively. And the wear of the surface was mainly related to pressure and speed. The greater the speed and pressure were, the more serious wear of the fixed soft abrasive film was.

Discrete Element Modeling of Soil Displacement Resulting from Hoe Openers

2019 ◽  
Vol 62 (2) ◽  
pp. 253-262
Author(s):  
Steven Murray ◽  
Ying Chen
Keyword(s):  
Performance Indicator ◽  
Discrete Element ◽  
Travel Speed ◽  
Particle Flow Code ◽  
Discrete Element Modeling ◽  
Side Band ◽  
Element Modeling ◽  
Soil Displacement ◽  
Modeling Software ◽  
Single Shoot

Abstract. Soil displacement is the most important performance indicator for seed openers, as it affects the uniformity of seeding depth. In this study, a hoe opener was modeled using Particle Flow Code in 3 Dimensions (PFC3D), a discrete element modeling software program. The objective was to simulate soil displacement in terms of soil throws. To validate the model, an air drill with hoe openers was tested in a field with clay soil at a working depth of 38 mm and travel speed of 8 km h-1. Soil throw resulting from the hoe opener was measured. To calibrate the model, a virtual soil shear test was created within PFC3D, and the output soil shear torque was compared to the torque measured in the same field. The result showed that the calibrated effective modulus, a critical micro-parameter of model particles, was 5.692 × 107 Pa. With this calibrated value, the simulated soil throws agreed well with the measured throws, with a relative error of 15%. The model was used to compare different hoe opener designs: single-shoot spread, double-shoot side-band, double-shoot paired-row, and triple-shoot openers. Among all these openers, the side-band opener resulted in the least lateral soil throw, and the paired-row opener resulted in the lowest vertical soil throw but the highest lateral throw. The developed model was effective for examining the effects of opener geometry on soil displacement. Keywords: DEM, Hoe, Opener, PFC3D, Soil displacement.

Modeling of Granular Flow and Combined Heat Transfer in Hoppers by the Discrete Element Method (DEM)

2005 ◽  
Vol 128 (3) ◽  
pp. 439-444 ◽  
Author(s):  
Harald Kruggel-Emden ◽  
Siegmar Wirtz ◽  
Erdem Simsek ◽  
Viktor Scherer
Keyword(s):  
Discrete Element Method ◽  
Heat Transport ◽  
Granular Flow ◽  
Granular Media ◽  
Element Model ◽  
Discrete Element ◽  
Waste Utilization ◽  
Discrete Element Modeling ◽  
Particle Assemblies ◽  
Element Method

The discrete element method can be used for modeling moving granular media in which heat and mass transport takes place. In this paper the concept of discrete element modeling with special emphasis on applicable force laws is introduced and the necessary equations for heat transport within particle assemblies are derived. Possible flow regimes in moving granular media are discussed. The developed discrete element model is applied to a new staged reforming process for biomass and waste utilization which employs a solid heat carrier. Results are presented for the flow regime and heat transport in substantial vessels of the process.

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.

Discrete Element Simulation (DEM) for Coupled Description of Material and Energy Flow Within Moving Granular Media

2005 ◽  
Author(s):  
Harald Kruggel-Emden ◽  
Siegmar Wirtz ◽  
Erdem Simsek ◽  
Viktor Scherer
Keyword(s):  
Heat Transport ◽  
Energy Flow ◽  
Granular Media ◽  
Element Model ◽  
Discrete Element ◽  
Waste Utilization ◽  
Discrete Element Modeling ◽  
Discrete Element Simulation ◽  
Element Simulation ◽  
Particle Assemblies

The discrete element method (DEM) can be used for modeling moving granular media in which heat and mass transport takes place. In this paper the concept of discrete element modeling with special emphasize on applicable force laws is introduced and the necessary equations for heat transport within particle assemblies are derived. Possible flow regimes in moving granular media are discussed. The developed discrete element model is applied to a new staged reforming process for biomass and waste utilization which employs a solid heat carrier. Results are presented for the flow regime and heat transport in substantial vessels of the process.

scholarly journals External signal preservation in halokinetic stratigraphy: A discrete element modeling approach

Geology ◽  
2021 ◽  
Author(s):  
Zoë A. Cumberpatch ◽  
Emma Finch ◽  
Ian A. Kane
Keyword(s):  
Element Model ◽  
Discrete Element ◽  
Discrete Element Model ◽  
External Signal ◽  
Discrete Element Modeling ◽  
The North ◽  
The North Sea ◽  
Lateral Extent ◽  
Tectonic Forces ◽  
Dynamic Interplay

Subsurface salt movement in the absence of external tectonic forces can affect contemporaneous sediment deposition, mask allocyclic signals, and deform older strata. We used a discrete element model (DEM) to better understand salt-related modification of a sedimentary sequence with an increasing sedimentation rate. This permitted quantification of thinning rates and analysis of the lateral extent of synkinematic layers. Results show realistic evolution of salt-related faults, defining two salt-withdrawal basins, beyond which strata are undeformed. Thinning of stratigraphy is four times greater between the salt flank and crest than between the undeformed zone and flank, confirming an intense zone of halokinetic modulation adjacent to the diapir. Early, slowly aggrading layers are isolated within the salt-withdrawal basin and strongly influenced by salt growth, whereas later, quickly aggrading layers are more laterally extensive, matching inferences made from subsurface and outcrop data. Halokinetic modulation reduces up the stratigraphic section, mirroring observations around the Pierce diapirs, in the North Sea, offshore UK. Our DEM provides quantitative insights into the dynamic interplay between halokinetic and allocyclic controls on salt-stratigraphic relationships.

A Discrete Element Approach to Model Breakable Railway Ballast

2012 ◽  
Vol 7 (4) ◽  
Author(s):  
Christian Ergenzinger ◽  
Robert Seifried ◽  
Peter Eberhard
Keyword(s):  
Experimental Data ◽  
Element Model ◽  
Discrete Element ◽  
Quantitative Agreement ◽  
Discrete Element Model ◽  
Compression Tests ◽  
Railway Ballast ◽  
Element Approach ◽  
Strong Rock ◽  
Granular Solid

A discrete element approach to assess degradation processes in ballast beds is presented. Firstly, a discrete element model describing strength and failure of strong rock is introduced. For this purpose a granular solid is created by bonding of adjacent particles. A method to define angular ballast stones made from the granular solid is proposed. The strength of these stones is evaluated by compression between parallel platens. Comparing these results to published experimental data yields very good qualitative and reasonable quantitative agreement. Finally, the failure of aggregates of breakable stones is investigated by simulation of oedometric compression tests and indentation of a sleeper into a ballast bed.

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