Examining The Use Of Idealized Granular Material In Validated Dem Simulations
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Author | : Anjana Thoroppady Kittu |
Publisher | : |
Total Pages | : 280 |
Release | : 2018 |
Genre | : Discrete element method |
ISBN | : |
Discrete element method (DEM) modeling, is becoming widely used for understanding the micro-mechanical behavior of granular materials at the particle level. This dissertation presents important considerations regarding the experimental boundary conditions and idealized granular materials used in DEM validations. A common issue in DEM validation studies for direct shear and direct simple shear is selecting top and bottom cap boundary conditions that allow for shear transmission while also being efficiently modeled in the DEM simulations. While the traditional grid boundary types used in the laboratory can be replicated in the numerical models, researchers have also used fixed-particle boundaries, sawtooth boundaries, and high friction boundaries with no projections. To examine any effects from these boundaries at the macro-scale, direct shear tests on physical specimens of dense and loose sand, and dense and loose steel ball bearings were conducted. The influence of friction on the boundary was further examined at the particle scale using two simple DEM simulations replicating the physical steel ball bearing specimens with a high and a low friction coefficient on the top and bottom boundaries. The DEM stress-displacement responses are compared to the laboratory results for tests using the boundary plates with no projections and then the particle-scale results of the validated simulations are analyzed. In addition to boundary effects, the idealized materials used in validation studies were also examined. Commonly used steel ball bearings or glass ballotini restrict the direct comparison of DEM simulations to spherical particles, thus limiting understanding of real materials with more complex shapes. This study shows that additive manufacturing (AM) can be used to create analogue soils with a variety of shapes which can be used for DEM validations. The AM particles were characterized to ensure their suitability for laboratory testing and to determine the material properties to input into future DEM models. The second part of the dissertation describes the determination of material properties and surface characteristics of two AM materials. Because a Hertzian contact law is typically used in DEM models, a comparison of the materials' response under uniaxial compression and the theoretical response for Hertzian behavior was carried out.
Author | : Michelle Lee Bernhardt |
Publisher | : |
Total Pages | : |
Release | : 2014 |
Genre | : |
ISBN | : |
Simple shear testing is used to study a number of practical geotechnical problems including: soil conditions directly below a loaded surface, adjacent to a driven pile shaft, soils deposited on a slightly inclined slope, and most notably the response of soils subjected to earthquake-type loading. While each of these problems still have important questions to be answered, earthquakes and earthquake triggered geohazards are the most complex and also pose the highest risk. An important aspect of assessing the risk associated with earthquakes is the need to accurately predict soil behavior. True field loading conditions involve multidirectional shearing and the rotation of principal planes and are much more complex than the triaxial laboratory testing methods and models often used to describe them. Simple shear testing allows for the in situ conditions to be replicated; however, several limitations of the device make data interpretation difficult. The inability to apply complementary shear stresses and the inability to measure the horizontal normal stresses results in non-uniform stresses across the boundaries, as well as an undefined stress state during shearing. This, in turn, requires assumptions to be made about the failure conditions before any state parameters can be determined. Even when only monotonic testing is conducted, there are still many important questions to be answered about the actual severity of the non-uniform stresses on the boundaries, as well as the internal stresses and the microscopic response of granular soils. Discrete element method (DEM) modeling has the advantage of being able to examine particle-to-particle interactions. Once validated with the measured laboratory data, these models provide a vast quantity of information about the fundamental mechanisms underlying the observed complexity of the response of the soil mass as a whole. The goal of this research is to gain insight into the particle-to-particle interactions driving the overall response of granular samples subjected to multi-directional cyclic simple shear conditions. The main objectives of this proposed project are to (1) characterize the macroscopic response of metal ballotini representing idealized sand under simple shear loading conditions and (2) model the physical element tests using DEM simulations to gain insight into the microscopic response of the gran℗Ưular material. Findings from this study showed that the DEM simulations could be successfully validated by laboratory data and that the overall trends observed agreed reasonably well with the experimental data from this study, as well as previous studies by other researchers. Analyses showed that density not only influences shear strength of a sample, it also affects the angle of shearing resistance, the magnitude of principal stress rotation, the angle of non-co axiality, and the orientation of the principal fabrics for strains below those needed to reach critical state. Vertical effective stress was instead shown to have very little influence on these parameters. The initial fabric appears to play the largest role in the behavior of samples tested at different vertical stresses. The simulations also showed the non-coaxial behavior of the granular samples in terms of principal stress and strain rate orientations, as well as particle displacements. A number of other sensitivity studies were conducted to examine the influence of the model simplifications on the observed response. Several of these simplifications were shown to affect the shear strength obtained and should be included in future analyses. The electronic version of this dissertation is accessible from http://hdl.handle.net/1969.1/151646
Author | : Liang Cui |
Publisher | : LAP Lambert Academic Publishing |
Total Pages | : 392 |
Release | : 2010-10 |
Genre | : |
ISBN | : 9783843362351 |
Discrete element methods (DEM) are promising numerical methods for analysing the complexities of granular material response as they can consider the particle scale interactions in these materials. In this book a virtual test environment was developed for granular materials using DEM. Two fundamental geotechnical laboratory tests, the direct shear test and the triaxial test, were implemented in this virtual test environment. This test environment was validated by comparing simulation results with physical experiment results. Further DEM simulations were then performed to analyse the sensitivity of the macro-scale specimen response to some selected parameters (e.g. particle friction, size distribution). Using the results of the DEM simulations, comprehensive analyses of the particle scale parameters were performed to explore the relationship between the observed macro-scale specimen response and the particle scale interactions, including the internal stresses, the contact forces, the fabric, and the particle displacements.
Author | : Shunying Ji |
Publisher | : Springer Nature |
Total Pages | : 399 |
Release | : 2020-03-18 |
Genre | : Technology & Engineering |
ISBN | : 9811533040 |
This book systematically introduces readers to computational granular mechanics and its relative engineering applications. Part I describes the fundamentals, such as the generation of irregular particle shapes, contact models, macro-micro theory, DEM-FEM coupling, and solid-fluid coupling of granular materials. It also discusses the theory behind various numerical methods developed in recent years. Further, it provides the GPU-based parallel algorithm to guide the programming of DEM and examines commercial and open-source codes and software for the analysis of granular materials. Part II focuses on engineering applications, including the latest advances in sea-ice engineering, railway ballast dynamics, and lunar landers. It also presents a rational method of parameter calibration and thorough analyses of DEM simulations, which illustrate the capabilities of DEM. The computational mechanics method for granular materials can be applied widely in various engineering fields, such as rock and soil mechanics, ocean engineering and chemical process engineering.
Author | : Farhang Radjaï |
Publisher | : Wiley-ISTE |
Total Pages | : 0 |
Release | : 2011-05-03 |
Genre | : Mathematics |
ISBN | : 9781848212602 |
This book brings together in a single volume various methods and skills for particle-scale or discrete-element numerical simulation of granular media. It covers a broad range of topics from basic concepts and methods towards more advanced aspects and technical details applicable to the current research on granular materials. Discrete-element simulations of granular materials are based on four basic models (molecular dynamics, contact dynamics, quasi-static and event driven) dealing with frictional contact interactions and integration schemes for the equations of dynamics. These models are presented in the first chapters of the book, followed by various methods for sample preparation and monitoring of boundary conditions, as well as dimensionless control parameters. Granular materials encountered in real life involve a variety of compositions (particle shapes and size distributions) and interactions (cohesive, hydrodynamic, thermal) that have been extensively covered by several chapters. The book ends with two applications in the field of geo-materials.
Author | : Pasquale Giovine |
Publisher | : Springer Nature |
Total Pages | : 288 |
Release | : 2020-11-09 |
Genre | : Mathematics |
ISBN | : 3030492672 |
This contributed volume provides an up-to-date overview of the mechanics of granular materials, ranging from sparse media to soils. With chapters exploring state-of-the-art theoretical, experimental, and applied trends in the study of granular matter in various states, readers will be motivated to learn about the current challenges and potential avenues of exploration in this active area of research. Including a variety of perspectives, this volume will be a valuable reference for audiences in a number of fields. Specific topics covered include: X-ray tomography techniques for analyzing sand Evaluation of effective stress in unsaturated soils Hyper-plasticity Wave propagation in granular systems Partly saturated porous media Multi-scale approaches to the dynamics of sparse media Views on Microstructures in Granular Materials is an ideal resource for PhD students and researchers in applied mathematics, solid-state physics, civil engineering, and mechanical engineering.
Author | : Catherine O'Sullivan |
Publisher | : CRC Press |
Total Pages | : 574 |
Release | : 2011-04-06 |
Genre | : Technology & Engineering |
ISBN | : 1482266490 |
The first single work on DEM providing the information to get started with this powerful numerical modelling approach. Provides the basic details of the numerical method and the approaches used to interpret the results of DEM simulations. It will be of use to professionals, researchers and higher level students, with a theoretical overview of DEM as well as practical guidance.Selected Contents: 1.Introduction 2.Use of DEM in Geomechanics 3.Calculation of Contact Forces 4.Particle Motion 5.Particle Types 6.Boundary Conditions 7.Initial Geometry and Specimen Generation 8.Time Integration and Discrete Element Modelling 9.DEM Interpretation: A Continuum Perspective 10.Postprocessing: Graphical Interpretation of DEM Simulations 11.Basic Statisti
Author | : Kenichi Soga |
Publisher | : CRC Press |
Total Pages | : 1668 |
Release | : 2014-08-26 |
Genre | : Technology & Engineering |
ISBN | : 1315737329 |
Geomechanics from Micro to Macro contains 268 papers presented at the International Symposium on Geomechanics from Micro and Macro (IS-Cambridge, UK, 1-3 September 2014). The symposium created a forum for the dissemination of new advances in the micro-macro relations of geomaterial behaviour and its modelling. The papers on experimental investigati
Author | : Bernard Cambou |
Publisher | : Springer |
Total Pages | : 403 |
Release | : 2014-05-04 |
Genre | : Technology & Engineering |
ISBN | : 370912526X |
This book presents a complete and comprehensive analysis of the behaviour of granular materials including the description of experimental results, the different ways to define the global behaviour from local phenomena at the particle scale, the various modellings which can be used for a D.E.M. analysis to solve practical problems and finally the analysis of strain localisation. The concepts developed in this book are applicable to many kinds of granular materials considered in civil, mechanical or chemical engineering.
Author | : Thorsten Pöschel |
Publisher | : Springer Science & Business Media |
Total Pages | : 454 |
Release | : 2001-02-27 |
Genre | : Science |
ISBN | : 3540414584 |
"Granular Gases" are diluted many-particle systems in which the mean free path of the particles is much larger than the typical particle size, and where particle collisions occur dissipatively. The dissipation of kinetic energy can lead to effects such as the formation of clusters, anomalous diffusion and characteristic shock waves to name but a few. The book is organized as follows: Part I comprises the rigorous theoretical results for the dilute limit. The detailed properties of binary collisions are described in Part II. Part III contains experimental investigations of granular gases. Large-scale behaviour as found in astrophysical systems is discussed in Part IV. Part V, finally, deals with possible generalizations for dense granular systems.