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Automatic extraction method of force chain information and its application in the flow photoelastic experiment of granular matter

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Particuology 2023年第12期83卷 142-155页

作者： Qingfa Chen Enlin Long Wenjing Niu Jun Liu Wenyu Fan Hangyu Li School of Civil Engineering and Architecture Key Laboratory of Disaster Prevention and Structural Safety of Ministry of EducationGuangxi UniversityNanning530004China School of Resources Environment and MaterialsGuangxi UniversityNanning530004China

The force chain is the core of the multi-scale analysis of granular *** extracting the force chain information among particles is of great significance to the study of particle mechanics and geological hazards caused by particle ***,in the photoelastic experiment,the precise identification of the branching points of force chains has not been effectively ***,this study proposes an automatic extraction method of force chain key ***,based on the Hough transform and the Euclidean distance,a particle geometric information identification model is established and geometric information such as particle circle center coordinates,radius,contact point location,and contact angle is ***,a particle contact force information identification model is established following the color gradient mean square *** model realizes the rapid calibration and extraction of a large number of particle media contact force ***,combined with the force chain composition criterion and its quasilinear feature,an automatic extraction method of force chain information is established,which solves the problem of the accurate identification of the force chain branch ***,in the photoelastic experiment of ore drawing from a single drawpoint,the automatic extraction method of force chain information is *** results show that the macroscopic distribution of force chains during ore drawing from a single drawpoint is left–right *** force chains are mostly located on the two sides of the model but in small numbers and they mainly develop ***,the ends are mostly in a combination of Y and inverted Y shapes,while the middle is mostly *** force chains are abundant and mostly distributed in the middle of the model,and develop in different *** proposed extraction method accurately extracts the force chain network from the photoelastic experiment images and dynami

关键词： granular matter Photoelastic experiment Digital image processing Force chain extraction method

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A pressure-sensitive rheological origin of high friction angles of granular matter observed in NASA–MGM project

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Chinese Physics B 2024年第6期33卷 559-567页

作者：程晓辉肖世泽杨森赵乃峰 Alex Sixie Cao Department of Civil Engineering Tsinghua UniversityBeijing 100084China College of Transportation Engineering Nanjing Tech UniversityNanjing 211816China Institute of Structural Engineering ETH ZurichZurich 8092Switzerland

An abnormally high peak friction angle of Ottawa sand was observed in(National Aeronautics and Space Administration) NASA–(Mechanics of granular Materials) MGM tests in microgravity conditions on the space shuttle. Previous investigations have been unsuccessful in providing a constitutive insight into this behavior of granular materials under extremely low effective stress conditions. Here, a recently proposed unified constitutive model for transient rheological behavior of sand and other granular materials is adopted for the analytical assessment of high peak friction angles. For the first time, this long-eluded behavior of sand is attributed to a hidden rheological transition mechanism, that is not only rate-sensitive, but also pressure-sensitive. The NASA–MGM microgravity conditions show that shear-tests of sand can be performed under abnormally low confining stress conditions. The pressure-sensitive behavior of granular shearing that is previously ignored is studied based on the μ(I) rheology and its variations. Comparisons between the model and the NASA microgravity tests demonstrate a high degree of agreement. The research is highly valid for pressure-sensitive and rate-dependent problems that occur during earthquakes, landslides, and space exploration.

关键词： granular matter microgravity pressure-sensitive NASA–MGM

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Behaviour of granular matter under gravity-induced stress gradient:A two-dimensional numerical investigation

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International Journal of Mining Science and Technology 2021年第3期31卷 439-450页

作者： Ruilin Li Guoqing Zhou Pin-Qiang Mo Matthew R.Hall Jun Chen Daqing Chen Shangyue Cai State Key Laboratory for Geomechanics and Deep Underground Engineering China University of Mining and TechnologyXuzhou 221116China GeoEnergy Research Centre Faculty of EngineeringUniversity of NottinghamNottingham NG72RDUK School of Mechanics and Civil Engineering China University of Mining and TechnologyXuzhou 221116China

Gravity is the most important load source in mining and geotechnical engineering,which causes both the stress level and stress gradient inside *** from the stress level,the influence of gravity-induced stress gradient on the behaviour of the material is still *** in-deep study on it will help to promote the understanding of material behaviour,especially for those cases related to unconventional gravity such as terrestrial ng physical modelling and extraterrestrial resource exploitation(g is the terrestrial gravitational acceleration).In this study,a high-order homogenization for granular materials is proposed at first,in which the stress gradient is drawn into the constitutive representation by adopting a representative volume element(RVE).The consolidation and shear strength behaviour of RVE are then investigated by performing numerical biaxial *** results show that all the compressibility,shear strength,shear stiffness,volumetric deformation,and critical state behaviour show a stress gradient dependence.A coupling between stress gradient,stress level,and material properties is also *** observations suggest that,besides the stress level,extra attention needs to be paid to material responses related to stress gradient during engineering practices.

关键词： Stress gradient Representative volume element granular matter Gravitational field Discrete element method

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Some open problems in granular matter mechanics

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Progress in Natural Science:Materials International 2009年第5期19卷 523-529页

作者： Qicheng Sun a, Guangqian Wanga, Kaiheng Hub a Department of Hydraulic Engineering, State Key Laboratory for Hydroscience and Engineering, Tsinghua University, Beijing 100084, China b Institute of Mountain Hazards and Environment, Chinese Academy of Sciences, Chengdu 610041, China [a]Department of Hydraulic Engineering State Key Laboratory for Hydroscience and Engineering Tsinghua University Beijing 100084 China [b]Institute of Mountain Hazards and Environment Chinese Academy of Sciences Chengdu 610041 China

granular matter is a large assemblage of solid particles, which is fundamentally different from any other type of matters, such as solid and liquid. Most models presented for granular matter are phenomenological and are only suitable for solving engineering problems. Many fundamental mechanical problems remain open. By analyzing characteristics of internal state structure, we propose that granular matter is intrinsically multiscale, i.e. microscale of particle size, mesoscale of force chain, and macroscale of the bulk of granular matter. The correlations among difference scales would be crucial. The mesoscale force chain network is determined by both particle properties and macroscopic boundary conditions. The evolution of the force the chain network contributes to macroscopic mechanical properties of granular matter. In addition, we discuss the drawbacks in simplifying contact forces in the current models, and the difficulties in analyzing the interaction of interstitial fluid in wet granular matter. As an appropriate application of granular matter, debris flow can be studied with granular matter mechanics; meanwhile, debris flow brings more challenges which certainly motivate future studies on granular matter.

关键词： granular matter Multiscale mechanics Force chain Contact mechanics Debris flow

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Buffer capacity of granular matter to impact of spherical projectile based on discrete element method

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Frontiers of Structural and Civil Engineering 2013年第1期7卷 50-54页

作者： Ying YAN Pengfei LI Shunying JI School of civil and Safety Engineering Dalian Jiaotong UniversityDalian 116028China State Key Laboratory of Structural Analysis for Industrial Equipment Dalian University of TechnologyDalian 116023China

granular matter possesses impact-absorbing property due to its energy dissipation *** investigate the impact-absorbing capacity of granular matter,the discrete element method(DEM)is adopted to simulate the impact of a spherical projectile on to a granular *** dynamic responses of the projectile are obtained for both thin and thick granular *** penetration depth of the projectile and the first impact peak are investigated with different bed thicknesses and impact *** a suitable bed thickness is crucial to the buffering effect of granular *** first impact peak is independent of bed thickness when the thickness is larger than the critical thickness.

关键词： granular matter impact peak buffer capacity discrete element method critical thickness

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Properties of surface waves in granular media under gravity

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Chinese Physics B 2014年第5期23卷 355-359页

作者：郑鹤鹏 Department of Mathematics and Physics Guilin Medical University

Acoustical waves propagating along the free surface of granular media under gravity are investigated in the framework of elasticity theory. The influence of stress on a surface wave is analyzed. The results have shown that two types of surface waves, namely sagittal and transverse modes exist depending on initial stress states, which may have some influence on the dispersion relations of surface waves, but the influence is not great. Considering that the present experimental accuracy is far from distinguishing this detail, the validity of elasticity theory on the surface waves propagating in granular media can still be maintained.

关键词： granular matter stress surface waves

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Effect of size polydispersity on the structural and vibrational characteristics of two-dimensional granular assemblies

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Chinese Physics B 2014年第7期23卷 589-595页

作者：张国华孙其诚石志萍冯旭顾强金峰 Department of Physics University of Science and Technology Beijing State Key Laboratory for Hydroscience and Engineering Tsinghua University

Two-dimensional disordered granular assemblies composed of 2048 polydispersed frictionless disks are simulated using the discrete element method. The height of the first peak of the pair correlation function, gl, the local and global bond orientational parameters ψ6^1 and ψ6^g, and the fluctuations of these parameters decrease with increasing polydispersity s, implying the transition from a polycrystalline state to an amorphous state in the system. As s increases, the peak position of the boson peak aJBp shifts towards a lower frequency and the intensity of the boson peak D（ωBP）/ωBp increases, indicating that the position and the strength of the boson peak are controlled by the polydispersity of the system. Moreover, the inverse of the boson peak intensity ωBP/D（ωBP）, the shear modulus G, and the basin curvature SIS all have a similar dependence on s, implying that the s dependence of the vibrational density of states at low frequencies likely originates from the s dependence of the basin curvature.

关键词： granular matter vibrational characteristics size polydispersity structural characteristics

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Effect of number density on velocity distributions in a driven quasi-two-dimensional granular gas

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Chinese Physics B 2010年第10期19卷 617-622页

作者： Sajjad Hussain Shah 李寅阊厚美瑛 Institute of Physics Chinese Academy of Sciences Physics Department Beijing Institute of Technology

The motion of mono-disperse spherical steel particles in a vibration driven quasi-two-dimensional （2D） square cell is studied. The cell is horizontally vibrated to eliminate the effect of gravity compaction. The velocity distributions at different particle number densities are studied and found to obey the form exp[-β（｜Vy｜/σy）α], in which Vy and （σy are velocity and its variance in the transverse direction, and α and β are fitting parameters. The value of α is found to decrease with the number density of particles increasing. To investigate the effect of the bottom plate, the molecular dynamics simulation without considering any bottom friction is performed. The accordance between the simulation result and the experimental result shows that the influence of bottom plate friction force on the high energy tail of the velocity distribution can be neglected.

关键词： granular matter velocity distribution

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Resistance law of a rod penetrating a multilayer granular raft

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Chinese Physics B 2023年第3期32卷 354-362页

作者：李宗霖田强胡海岩 MOE Key Laboratory of Dynamics and Control of Flight Vehicle School of Aerospace EngineeringBeijing Institute of TechnologyBeijing 100081China

This paper presents an experimental study on the resistance law of a rod vertically penetrating different kinds of multilayer granular rafts with a constant velocity so as to reveal the mechanical properties of the multilayer granular *** resistance was quasi-static under the chosen *** were conducted with different granular thicknesses,rod diameters and combinations of particles and *** study shows that the resistance–displacement relation of the rod has three smooth *** the first stage,the resistance rapidly *** the second stage,the resistance curve maintained an almost constant *** the third stage,the resistance smoothly changed with its slope continuously *** on the corresponding physical models for each stage,the study reveals the exponential dependence of the load-bearing capacity of the multilayer granular raft on its thickness,and clarifies the capillary effects on the resistance *** study extends the knowledge of the granular raft from monolayer to multilayer structure.

关键词： granular matter wet particles saturated particles capillary effects

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Stabilizing effect of plasma discharge on bubbling fluidized granular bed

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Chinese Physics B 2015年第7期24卷 288-292页

作者：胡茂彬党赛超马强夏维东 School of Engineering Science University of Science and Technology of China

Fluidized beds have been widely used for processing granular materials. In this paper, we study the effect of plasma on the fluidization behavior of a bubbling fluidized bed with an atmospheric pressure plasma discharger. Experiment results show that the bubbling fluidized bed is stabilized with the discharge of plasma. When the discharge current reaches a minimum stabilization current Cms, air bubbles in the bed will disappear and the surface fluctuation is completely suppressed.A simplified model is proposed to consider the effect of electric Coulomb force generated by the plasma. It is found that the Coulomb force will propel the particles to move towards the void area, so that the bubbling fluidized bed is stabilized with a high enough plasma discharge.

关键词： plasma fluidized bed granular matter stabilization effect

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