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Coherent turbulent flow structure under plunging breaker on movable grain bed simulated by 3D DEM-MPS method

COASTAL ENGINEERING JOURNAL 2024年第4期66卷 675-702页

作者： Tazaki, Takumi Harada, Eiji Gotoh, Hitoshi Kyoto Univ Dept Civil & Earth Resources Engn Kyoto Japan

Breaking waves transport momentum, gas, and sediment vertically. Recent particle image velocimetry (PIV) measurements have elucidated the coherent vortex and turbulence structures under breaking waves. However, clarifying three-dimensional fluid motion under breaking waves with PIV remains challenging. Although particle methods have performed wave-breaking simulations, they have never been validated through velocity distributions for breaking waves above movable sediment beds. This study simulated the sediment transport process under plunging waves using a 3D Lagrangian fluid-particle mixture model. The investigation focuses on the first wave plunging for a fundamental investigation. Our simulation shows the instantaneous velocity distributions at different wave phases, which agree with the PIV measurement. A physically-based turbulence extraction method is introduced: a numerical filter based on the coherence between the water elevation and horizontal velocity. Visualized three-dimensional vortex and turbulence structures are consistent with previous studies. The transport equation of the kinetic turbulence energy investigates the turbulence budget near the bed surface and emphasizes the negative contribution of the fluid-particle interaction. Our findings show that a contribution of the pressure gradient to offshore sediment transport. The pressure gradient is difficult to correlate to the water surface gradient and is derived from the large vortex induced by the plunging wave.

关键词： Sediment transport surf zone coherent vortex moving particle semi-implicit discrete-element method

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Study on the mechanical properties of outwash deposits with random structure method

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Transportation Safety and Environment 2021年第3期3卷 316-330页

作者： Chaojun Jia Qiang Zhang Mingfeng Lei Jun Yu Rubin Wang Jingyan Liu School of Civil Engineering Central South UniversityChangsha410075China State Key Laboratory of Simulation and Regulation of Water Cycle in River Basin China Institute of Water ResourcesBeijing100048China China Institute of Water Resources and Hydropower Research Beijing100048China School of Transportation and Civil Engineering Nantong UniversityNantong226019China Research Institute of Geotechnical Engineering Hohai UniversityNanjing210098China College of Water Resources Science and Engineering Taiyuan University of TechnologyTaiyuan030024China

Outwash deposit is one of the major threats to the safety and stability of railway transit engineering in the Sichuan–Tibet *** this paper,different samples of outwash deposits were prepared based on the random structure method,and a series of large-scale direct shear tests were carried out under different normal *** influence of stone content and the spatial distribution of stone blocks on the physical and mechanical properties of outwash deposits were *** results show that with the increase of stone content,the shear stress-displacement curve changs from strain softening to strain *** shear zone is larger,and its shape is more tortuous due to the movement and rotation of stone *** internal frictional angle increases linearly while the cohesion diseases with the increase of stone *** main influence of the spatial distribution of stone blocks on the mechanical properties of outwash deposits is the peak *** shear zone is mainly determined by the distribution of the stone blocks near the shear zone.

关键词： outwash deposit mechanical property random mesostructure discrete-element method direct shear test

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Effect of aggregate structure on load-carrying capacity and deformation resistance of porous asphalt concrete based on discrete-element modelling

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INTERNATIONAL JOURNAL OF PAVEMENT ENGINEERING 2022年第11期23卷 4023-4033页

作者： Zhu, Junqing Ma, Tao Lin, Zihao Zhu, Haoran Southeast Univ Sch Transportat Nanjing Peoples R China JSTI Grp Co Ltd Nanjing Peoples R China

Porous asphalt concrete (PAC) constitutes large air voids and coarse aggregate, forming a unique aggregate structure. The open pore structure is advantageous in creating space for stormwater runoff to infiltrate into an underground basin and reduce tyre-road noise. However, this aggregate structure compromises the load-carrying capacity and deformation resistance of the mixture. Achieving balance between permeability and bearing capacity of PAC has been a major concern. This study evaluates effects of the aggregate structure on bearing capacity and the deformation resistance of PAC. Gradation-based framework was first applied to examine different gradations of PAC. discrete-element models of PAC with varying gradations were developed to evaluate its performance and characteristics of aggregate skeleton. A laboratory wheel track test was conducted to validate findings from the DEM analysis. It was found that gradation that meets the interlock check of the framework produced a mixture with optimal performance. More coarse aggregate provides additional strength but lacks sufficient smaller-sized particles to form a new skeleton when it breaks down. More fine aggregate diminishes the load-carrying capacity and deformation resistance of the mixture as no stable skeleton could be formed.

关键词： Porous asphalt concrete load-carrying capacity deformation resistance gradation-based framework packing theory discrete-element method

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Pore-scale modeling of flow in particle packs containing grain-coating and pore-filling hydrates: Verification of a Kozeny-Carman-based permeability reduction model

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JOURNAL OF NATURAL GAS SCIENCE AND ENGINEERING 2017年 45卷 537-551页

作者： Katagiri, Jun Konno, Yoshihiro Yoneda, Jun Tenma, Norio Natl Inst Adv Ind Sci & Technol Environm Management Res Inst Resources Separat Proc Res Grp 16-1 Onogawa Tsukuba Ibaraki 3058569 Japan Natl Inst Adv Ind Sci & Technol Res Inst Energy Frontier Methane Hydrate Prod Technol Grp Toyohira Ku 2-17-2-1 Tsukisamu Higashi Sapporo Hokkaido 0628517 Japan Natl Inst Adv Ind Sci & Technol Res Inst Energy Frontier Methane Hydrate Geomech Grp 16-1 Onogawa Tsukuba Ibaraki 3058569 Japan Natl Inst Adv Ind Sci & Technol Res Inst Energy Frontier 16-1 Onogawa Tsukuba Ibaraki 3058569 Japan

The permeability of the methane gas hydrate-bearing sand, which reflects the hydrate saturation and morphology of the sediments, significantly influences the rate of gas production. In this study, we formulated permeability reduction models for cubic packs of cylinders and spheres and random sphere packs with the grain-coating (GC) and pore-filling (PF) hydrates. Our models were based on the Kozeny Carman equation. Three assumptions were made: (1) electrical tortuosity could be used in place of hydraulic tortuosity, (2) the effect of hydrate saturation on the shape factor could be ignored, and (3) the presence of an overlapping surface area of the GC hydrate could also be ignored. To confirm the validity of these assumptions, we conducted a series of computational fluid dynamics simulations of particle packs with the GC and PF hydrates generated by the discrete element method. Assumptions (2) and (3) caused the simulated normalized permeability of the GC hydrate to diverge from the proposed models because the simulated hydraulic tortuosity and shape factor of the PF hydrate were different from their analytical counterparts. However, because these differences canceled out at low hydrate saturations, the simulated normalized permeability of the PF hydrate agreed well with the proposed model. This agreement disappeared as the hydrate saturation increased because the cancellation effect atrophied. We compared the prediction accuracy of the proposed models with that of existing models in our simulations and with published experimental results. The proposed models agreed well with the simulation results and the experimental data. We showed that the parameters of the proposed model had a physical meaning: the average size of small clusters of PF hydrates. Analyzing the values of this parameter, we found that the PF type was the dominant morphology in natural core samples used in previous experimental studies. (C) 2017 Elsevier B.V. All rights reserved.

关键词： Gas hydrate Hydrate morphology Permeability reduction Kozeny-Carman equation discrete-element method Computational fluid dynamics

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Simulation of material tests using meshfree Lagrangian particle methods

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PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART K-JOURNAL OF MULTI-BODY DYNAMICS 2008年第4期222卷 327-338页

作者： Gaugele, T. Fleissner, F. Eberhard, P. Univ Stuttgart Inst Engn & Computat Mech D-70569 Stuttgart Germany

This contribution presents an enhanced discrete-element model with special focus on modelling of cohesive ductile materials. The model is based on a basic three-dimensional discrete-element model consisting of spherical rigid particles, which is used to model non-cohesive granular material. This basic model is enhanced by including special interactions. These interactions allow for the description of cohesive ductile behaviour of the modelled material. It is shown that by including these interactions in the discrete-element model, the failure modes of highly ductile materials like aluminium can be qualitatively as well as quantitatively described. The validity of the model is shown by the comparison of different simulated material tests with the experimental counterpart.

关键词： discrete-element method particle model cohesive material breakable bonds

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ICY: An interface between COMSOL multiphysics and discrete element code YADE for the modelling of porous media

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COMPUTERS & GEOSCIENCES 2019年 123卷 38-46页

作者： Pirnia, Pouyan Duhaime, Francois Ethier, Yannic Dube, Jean-Sebastien Ecole Technol Super Lab Geotech & Geoenvironm Engn LG2 1100 Notre Dame Ouest Montreal PQ H3C 1K3 Canada

The thermal, mechanical and hydrodynamic behaviour of porous media in geoscience applications is usually modelled through the finite-element (FEM) or finite-difference methods. These continuum models tend to perform poorly when modelling phenomena that are essentially dependent on behaviour at the particle scale or phenomena that are not accurately described by partial differential equations (PDE), such as internal erosion and filtration. The discrete nature of granular materials can be modelled through the discrete-element method (DEM). However, in some instances, DEM models would benefit from an interface with continuum models to solve coupled PDEs or to model phenomena that occur at a different scale. This paper introduces ICY, an interface between COMSOL Multiphysics, a commercial finite-element engine, and YADE, an open-source discrete element code. The interface is centred on a JAVA class. It was verified using the simple example of a sphere falling in water according to Stokes' law. For this example, the drag force was calculated in COMSOL and body forces (gravity, buoyancy and drag) on the sphere were summed in YADE. The paper also presents an application example for the interface based on the modelling of internal erosion tests.

关键词： Porous media discrete-element method Finite-element method YADE COMSOL Internal erosion

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Algorithms for modelling 3D flexible pavements and simulation of vibration cutting by the DEM

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INTERNATIONAL JOURNAL OF PAVEMENT ENGINEERING 2019年第10期20卷 1127-1139页

作者： Guan, Yueqi Guan, Hanqing Hunan Inst Engn Dept Mech Engn Xiangtan Peoples R China Hunan Univ Coll Mech & Vehicle Engn Changsha Hunan Peoples R China

An algorithm for modelling 3D flexible pavements using the discrete element method (DEM) is put forward in this paper. Firstly, this algorithm can generate the various shapes, sizes and angularity of coarse aggregates and place them randomly within the model of flexible pavements, besides, the asphalt mastic and voids are generated. The micro parameters in DEM model are verified by the tests for mechanical properties. Then, the model of utilising vibration cutting for flexible pavements in road miller is established and corresponding formulas are inferred. Finally, two kinds of vibration cutting utilised in road miller are simulated and the results shown that utilising the vibration cutting along the horizontal direction is better than the elliptical vibration cutting, the amplitudes and frequency of vibration are optimised using DEM in PFC3D.

关键词： discrete-element method algorithm 3D modelling flexible pavements vibration cutting road miller

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Patterned Nonaffine Motion in Granular Media

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JOURNAL OF ENGINEERING MECHANICS 2013年第10期139卷 1479-1490页

作者： Peters, John F. Walizer, Laura E. US Army Engineer Res & Dev Ctr Geotech & Struct Lab Vicksburg MS 39180 USA

Vortex-like flow patterns are often observed in experiments on granular media for which uniform strain is expected based on the loading boundary conditions. These deformations become apparent when the motion associated with uniform strain is subtracted from the total particle motion. Besides presenting an interesting phenomenon that begs explanation, these vortex patterns suggest multiscale structure for nonaffine motion as suggested by modern continuum theories. Further, the authors note that the rotational velocity field added to a uniform strain field produces a planar slip field. Thus, these structures are associated with the slip-band fields that eventually form, which are generally associated with bifurcations in the solution path of the governing partial differential equations. The authors present a procedure to extract these motion fields from discrete-element simulations along with conjugate forces associated with these motions. A key finding from the simulations is that the motions that eventually lead to shear band formation develop throughout the loading history rather than arising as a distinct bifurcation. Further, the pattern of rotational fields, and hence the shear banding pattern, are controlled by the boundary conditions. A question, only partly resolved here, is the origin of forces driving the rotational fields.

关键词： discrete elements Localization Granular media Boundaries Affine motion Multiscale Nonlocal continuum Hierarchical discrete-element method Localization

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Parametric studies of the performance of particle dampers under harmonic excitation

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STRUCTURAL CONTROL & HEALTH MONITORING 2011年第1期18卷 79-98页

作者： Lu, Zheng Masri, Sami F. Lu, Xilin Univ So Calif Viterbi Sch Engn Los Angeles CA 90089 USA Tongji Univ State Key Lab Disaster Reduct Shanghai 200092 Peoples R China

The performance of particle dampers under dynamic loads is very complicated and highly nonlinear;consequently, no guidelines currently exist for determining the optimum strategies for maximizing their behavior. The underlying interaction mechanics involve energy dissipation and momentum exchange. This paper presents the concept of 'effective momentum exchange' to quantify its influence on the performance of particle dampers with low volumetric filling ratio. The paper also evaluates the effects of a large number of system parameters (such as number, size and particle material, mass ratio, excitation frequency and amplitude level, coefficient of restitution, damping ratio of the primary system, and the coefficient of friction), using high-fidelity simulations based on the discrete-element method. It is shown that applying more particles with a high value of the coefficient of restitution can result in a broader range of acceptable response levels. For a given mass ratio, the particle type and size have minor effects on the primary system performance. Increasing the mass ratio can improve the damper's effectiveness but only up to a certain level. Friction is usually detrimental in low volumetric filling ratio particle dampers. It is shown that by using a properly designed particle damper, a lightly damped primary system can achieve a considerable reduction in its response with a small weight penalty. Copyright (C) 2009 John Wiley & Sons, Ltd.

关键词： particle damper parametric study discrete-element method impact momentum

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Effects of morphological gene decay and mutation on the micro-macro mechanical behaviours of granular soils

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GEOTECHNIQUE 2022年第11期74卷 1076-1094页

作者： Xiong, Wei Wang, Jianfeng Wu, Mengmeng City Univ Hong Kong Dept Architecture & Civil Engn Hong Kong Peoples R China City Univ Hong Kong Shenzhen Res Inst Shenzhen Peoples R China

Particle morphology is multi-scale in nature. To investigate the effects of particle morphology at a specific length scale on the macro-micro mechanical behaviours of granular soils, morphological gene decay and mutation was incorporated into discrete-element method (DEM) simulations through spherical harmonic-based principal component analysis. All DEM samples were subjected to axial compression and constant confining stress. The macro-scale and grain-scale behaviours of the granular assembly were investigated. It was found that particle morphology shows significant effects on macro-scale behaviours including initial stiffness, peak stress ratio, volumetric contraction and dilation, and shear band formation, as well as grain-scale behaviours including coordination number, particle rotation and granular skeleton sustaining the major contact force chains. Among the different length scales, local roundness contributes the most to stress ratio, volumetric strain and particle coordination number, while general form contributes the most to shear strain, particle rotation and fabric structure. Another interesting finding was that the particle morphological effects are well reflected in the granular skeleton sustaining the major contact force chains, which is featured with a strong variation of the degree of particle shape irregularity among different kinds of gene-mutated samples.

关键词： discrete-element method discrete-element modelling fabric structure of soils morphological gene mutation numerical methods particle morphology particle-scale behaviour shear spherical harmonic analysis X-ray micro-computed tomography

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