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Author: Keng-Wit Lim
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
This dissertation is concerned with the development of a new discrete element method (DEM) based on Non-Uniform Rational Basis Splines (NURBS). With NURBS, the new DEM is able to capture sphericity and angularity, the two particle morphological measures used in characterizing real grain geometries. By taking advantage of the parametric nature of NURBS, the Lipschitzian dividing rectangle (DIRECT) global optimization procedure is employed as a solution procedure to the closest-point projection problem, which enables the contact treatment of non-convex particles. A contact dynamics (CD) approach to the NURBS-based discrete method is also formulated. By combining particle shape flexibility, properties of implicit time-integration, and non-penetrating constraints, we target applications in which the classical DEM either performs poorly or simply fails, i.e., in granular systems composed of rigid or highly stiff angular particles and subjected to quasistatic or dynamic flow conditions. The CD implementation is made simple by adopting a variational framework, which enables the resulting discrete problem to be readily solved using off-the-shelf mathematical programming solvers. The capabilities of the NURBS-based DEM are demonstrated through 2D numerical examples that highlight the effects of particle morphology on the macroscopic response of granular assemblies under quasistatic and dynamic flow conditions, and a 3D characterization of material response in the shear band of a real triaxial specimen.
Author: Keng-Wit Lim
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
This dissertation is concerned with the development of a new discrete element method (DEM) based on Non-Uniform Rational Basis Splines (NURBS). With NURBS, the new DEM is able to capture sphericity and angularity, the two particle morphological measures used in characterizing real grain geometries. By taking advantage of the parametric nature of NURBS, the Lipschitzian dividing rectangle (DIRECT) global optimization procedure is employed as a solution procedure to the closest-point projection problem, which enables the contact treatment of non-convex particles. A contact dynamics (CD) approach to the NURBS-based discrete method is also formulated. By combining particle shape flexibility, properties of implicit time-integration, and non-penetrating constraints, we target applications in which the classical DEM either performs poorly or simply fails, i.e., in granular systems composed of rigid or highly stiff angular particles and subjected to quasistatic or dynamic flow conditions. The CD implementation is made simple by adopting a variational framework, which enables the resulting discrete problem to be readily solved using off-the-shelf mathematical programming solvers. The capabilities of the NURBS-based DEM are demonstrated through 2D numerical examples that highlight the effects of particle morphology on the macroscopic response of granular assemblies under quasistatic and dynamic flow conditions, and a 3D characterization of material response in the shear band of a real triaxial specimen.
Author: Farhang Radjaï
Publisher: Wiley-ISTE
ISBN: 9781848212602
Category : Mathematics
Languages : en
Pages : 0
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Book Description
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: Siqiang Wang
Publisher: Springer Nature
ISBN: 9819999278
Category : Technology & Engineering
Languages : en
Pages : 240
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Book Description
This book focuses on discrete element methods for arbitrarily shaped granular materials, including super-quadric models, spherical harmonic functions and level set methods, and numerical analysis of the flow characteristics of non-spherical granular materials. This book is used as a reference book for scientific researchers engaged in dynamic analysis of granular materials and optimal design of equipment structures in the fields of engineering mechanics, applied physics, mechanical engineering, and chemical engineering, as well as for graduate students or senior undergraduates of related majors in institutions of higher education.
Author: Bruno Chareyre
Publisher: Elsevier
ISBN: 0081010788
Category : Technology & Engineering
Languages : en
Pages : 150
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Book Description
Handbook of Discrete Element Method for Dense Granular Solids provides scientists and engineers with the solutions to the basic problems of DEM modeling of granular solids, both conceptual and practical. In order to help new users, this book follows the main steps, from conceptual model to numerical simulation of dense granular materials. This includes contact models, numerical schemes, simulation setup, and post-processing. The authors present many examples, including the complete code which assists the reader in reproducing the simulations with open-source code—Yade-DEM—that was developed by the author and his colleagues at the University of Grenoble. Presents the basics, along with effective usage of DEM code Details state-of-the-art, practical implementation for research and numerical methods Provides examples with scripts, linking the book to online content and freely available software (yade-dem.org)
Author: Maytee Chantharayukhonthorn
Publisher:
ISBN:
Category :
Languages : en
Pages : 98
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Book Description
Capturing the propagation of microscale physics to macroscale phenomena is intractable for many large systems. Scale propagation is a major issue in granular media, wherein two extremes are often taken. In one, granular materials are modeled as a continuum, which greatly reduces the number of degrees of freedom that describe the system and can thus be simulated relatively quickly. However continuum models are not always precise and have difficulty capturing certain effects such as particle size dependence. In discrete element methods (DEM), every grain and the interactions between them are simulated. DEM is accurate but solve time scales poorly with large grain numbers. Here, we present a hybrid simulation scheme, which seeks a best-of-both-worlds solution by bridging these two approaches. A mass of granular media is partitioned into three domains: a continuum domain represented using the material point method (MPM), discrete grains using DEM, and a transition zone of both MPM and DEM that are coupled via kinematic constraints. An "oracle" determines which areas of the domain are MPM and which are DEM, and converts between the two. In the canonical example of silo flow, flow with a sufficiently small orifice jams, resolving length scale dependent effects. Collapse of granular columns modeled with the hybrid method compare quantitatively well with pure discrete simulation and experiments in literature. A significant speedup is seen with the hybrid method over a similar domain of pure discrete grains.
Author: Kenichi Soga
Publisher: CRC Press
ISBN: 1315737329
Category : Technology & Engineering
Languages : en
Pages : 1668
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Book Description
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: Alexander Popp
Publisher: Springer
ISBN: 3319901559
Category : Science
Languages : en
Pages : 235
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Book Description
The book conveys modern techniques and the latest state-of-the-art with regard to the most fundamental aspects of computational contact mechanics. However, since contact can readily be interpreted as a special type of interface problem, it seems advisable not to isolate contact mechanics, but rather to address it in the context of a broader class of problems denoted as computational interface mechanics. The book gives a clear understanding of the underlying physics of interfaces, and a comprehensive insight into the current state-of-the-art and selected cutting-edge research directions in the computational treatment of interface effects. It focuses on the modeling of friction, wear, lubrication, cohesive interfaces, grain boundaries, phase boundaries, fracture, thermo-mechanics and particulate contact (e.g. granular media). Also the most important computational aspects are addressed, including discretization techniques for finite deformations, solution algorithms for single- and multi-processor computing environments, multi-scale approaches, discrete element models and multi-physics problems including contact and interface constraints. Among the computational techniques covered in this book are finite element (FEM) and boundary element (BEM) methods, atomistic models, molecular dynamics (MD), discrete element methods (DEM), coupling approaches for multi-scale simulations, and tools for an efficient automated FEM code generation.
Author: Qiong Zhang (Mechanical engineer)
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
Granular materials are ubiquitous in industrial and geophysical scenarios. At a high computational expense, the discrete element method (DEM) simulates granular materials with a high accuracy by tracking individual particles. At the other extreme, empirical formulas based on dimensional analysis and continuum models are convenient to be applied to large scale problems, but calibrations may be needed. In this thesis, DEM simulations are carried out as virtual experiments to study the particle-scale physics and then guide the formulation of empirical relations or continuum models for two applications. Dynamic similarity, commonly applied in fluid systems, has recently been extended to locomotion problems in granular media. Our previous research was limited to locomotors in cohesionless, flat beds of grains under the assumption of a simple frictional fluid rheology. However, many natural circumstances involve beds that are sloped or composed of cohesive grains. Expanded scaling relations are derived and DEM simulations are performed as validation, with inclined beds and cohesive grains using rotating "wheels" of various shape families, varying size and loading conditions. The data show a good agreement between scaled tests, suggesting the usage of these scalings as a potential design tool for off-road vehicles and extra-planetary rovers, and as an analysis tool for bio-locomotion in soils. In the bedload sediment transport process, the variability in the relation between sediment flux and driving factors is not well understood. At a given Shields number, the observed dimensionless transport rate can vary over a wide range in controlled systems. A two-way coupled fluid-grain numerical scheme has been validated against physical experiments of spherical sediment particles. It is used to explore the parameter space controlling sediment transport in simple systems. Examination of fluid-grain interactions shows fluid torque is non-negligible near the threshold. And the simulations guide the formulation of continuum models for the bedload transport and the creep flow. Furthermore, a numerical scheme has been developed to simulate the transport of natural shaped sediment particles. Conglomerated spheres, approximating the real shapes from CT scanning, are constructed in DEM and coupled with the fluid solver. Agreement with the corresponding flume experiments is observed.
Author: Shashank Agarwal (Scientist in mechanical engineering)
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
Granular intrusions such as ballistic impacts, vehicular and animal locomotion in natural terrains, and stirring of materials in industrial processes are common. Granular media often exhibits coupled solid-like and fluid-like multiphase characteristics in such systems that are commonly not shown by simple solids (like metals) and fluids (like water). This makes modeling granular media challenging. While the field of granular physics extensively uses grain-scale Discrete Elements Modeling (DEM) to model such characteristics of granular systems, they are computationally expensive. On the other hand, capabilities to model such systems in real-time are critical in numerous applications such as path planning and efficient maneuvering of vehicles in sandy terrains on earth and extra-terrestrial environments. Due to their shape-and media-specific forms, existing reduced-order intrusion modeling methods have limited capabilities.
Author: Stefan Luding
Publisher: Elsevier
ISBN: 0081012071
Category : Technology & Engineering
Languages : en
Pages : 150
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Book Description
Calibration and Validation of Granular Continuum Models from Particle Data: Bridging the Micro-Macro Gap reviews recent advances in the field and describes how to obtain continuum fields from particle level data. After a review of several methods, it focuses on one method, coarse-graining, and demonstrates the power of this method via various examples of granular continuum models, e.g., for shallow and segregating flows. Presents the coarse-graining method to overcome accurate result challenges by applying a local smoothing kernel with a well-defined smoothing length that automatically generates fields satisfying the continuum equations Presents a very flexible solution that can be extended to complex situations, such as two-phase flows and situations with complex external boundaries Shows readers how to apply such methods to calibrate and validate some of the most common granular flow models
