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Stress distribution and surface instability of an inclined granular layer

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Chinese Physics B 2013年第4期22卷 205-212页

作者：郑鹤鹏蒋亦民彭政 School of Physics and Electronics Central South University School of Basic Medical Sciences Guilin Medical University

Static granular materials may avalanche suddenly under continuous quasi-static drives. This phenomenon, which is important in many engineering applications, can be explained by analyzing the stability of the elastic solutions. We show this for a granular layer driven by its inclination angle in gravity, where the elastic problem can be solved generally and analytically. It is found that a loss of stability may occur only at the free surface of the layer. This result is considered to be relevant for understanding surface avalanches and the flows observed experimentally.

关键词： granular matter nonlinear elasticity stress surface instability

Intruder trajectory tracking in a three-dimensional vibration-driven granular system:Unveiling the mechanism of the Brazil nut effect

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Chinese Physics B 2023年第10期32卷 106-111页

作者：李拓程可彭政杨晖厚美瑛 School of Optical-Electrical and Computer Engineering University of Shanghai for Science and TechnologyShanghai 200093China Soft matter Laboratory Institute of PhysicsChinese Academy of SciencesBeijing 100190China School of Physics Central South UniversityChangsha 410012China College of Medical Instrumentation Shanghai University of Medicine&Health SciencesShanghai 201318China

We employ a Hall-effect magnetic sensor array to accurately track the trajectory of a single magnetic sphere,referred to as the“intruder,”within a three-dimensional vibro-fluidized granular bed to unravel the underlying physical mechanism governing the motion of the *** the acceleration range of 3.5 g≥Γ≥1.5 g,we find that,regardless of the intruder's initial position,it consistently reaches the same equilibrium depth when the vibration acceleration(Γ)and frequency(ω)are ***Γ≤2.5 g,the equilibrium position lies on the surface of the granular bed,while forΓ>2.5 g,it shifts below the ***,intruders with different densities exhibit varying equilibrium depths,with higher density resulting in a deeper equilibrium *** understand the mechanism behind the intruder's upward or downward motion,we measure its rising or sinking velocities under different vibration *** findings demonstrate that the rising velocity of the intruder,under varying vibration accelerations(Γ)and frequencies(ω),can be collapsed using the ratioΓ/ω,while the sinking velocity remains unaffected by the vibration *** confirms that the upward motion of the larger sphere,associated with the Brazil nut effect,primarily arises from the void-filling mechanism of the bed ***,our experiments reveal that the presence of convection within the bed particles has minimal impact on the motion of the intruder.

关键词： granular matter segregation Brazil nut effect vibro-fluidization

Density Waves in One-Dimensional granular Flows Driven by Non-Uniform Force Field

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Communications in Theoretical Physics 2013年第11期60卷 610-614页

作者：苏涛冯耀东赵宏武黄德财孙刚 Key Laboratory of Soft matter Physics and Beijing National Laboratory for Condensed matter Physics Institute of Physics Chinese Academy of Sciences Department of Applied Physics Nanjing University of Science and Technology

We introduce a non-uniform gravity-like force field to control the granular flow state in a quasi-one- dimensional system, and study the system by the molecular dynamics simulation. We find that the granular flow under non-uniform force field can be well described by a density wave with fixed time period if a fixed partiele number condition is used. The base frequency of the density wave does not depend on the position of the flow, while both the average density and oseillation amplitude of the flow vary continuously with the position. The formation of the density wave results from the aggregation of the granules in the decelerated region and the feed-back mechanism in the fixed particle number condition.

关键词： granular matter random force molecular dynamics simulation

Visualization of force networks in 2D dense granular materials

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Frontiers of Structural and Civil Engineering 2010年第1期4卷 109-115页

作者： Jianguo LIU Qicheng SUN Feng JIN State Key Laboratory of Hydroscience and Engineering Department of Hydraulic EngineeringTsinghua UniversityBeijing 100084China

Dense granular matter is a conglomeration of discrete solid and closely packed *** subjected to external loadings,the stress is largely transmitted by heavily stressed chains of particles forming a sparse network of larger contact *** understand the structure and evolution of force chains,a photoelastic technique was improved for determining stresses and strains in the assemblies of photoelastic granular disks in this paper.A two-dimensional vertical slab was *** contains 7200 polydispersed photoelastic disks and is subjected to a localized probe penetrating at the top of the slab to mimic the cone penetration *** interparticle contact force distribution was found a peak around the mean value,a roughly exponential tail for greater force and a dip toward zero for smaller *** force chain network around the probe tip was depicted,and the contact angle distribution of particles in force chains was found to be well aligned in the directions of major principal stress.

关键词： granular matter force chain multiscale modeling

Mesoscopic properties of dense granular materials:An overview

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Frontiers of Structural and Civil Engineering 2013年第1期7卷 1-12页

作者： Qicheng SUN Feng JIN Guohua ZHANG State Key Laboratory of Hydroscience and Engineering Tsinghua UniversityBeijing 100084China Physics Department University of Science and Technology of BeijingBeijing 100083China

A granular material is a conglomeration of discrete solid *** is intrinsically athermal because its dynamics always occur far from *** highly excited gaseous states,it can safely be assumed that only binary interactions occur and a number of kinetic theories have been successfully ***,for granular flows and solidlike states,the theory is still poorly understood because of the internally correlated structures,such as particle clusters and force *** current theory is that the mesoscale characteristics define the key differences between granular materials and homogeneous solid *** interest in granular materials has arisen among physicists,and significant progress has been made,especially in understanding the jamming phase diagram and the characteristics of the jammed *** this paper,the underlying physics of the mesoscale structure is discussed in detail.A multiscale framework is then proposed for dense granular materials.

关键词： granular matter macroscopic structure jamming phase transition

Force fluctuations in sheared granular disks

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Frontiers of Structural and Civil Engineering 2013年第1期7卷 46-49页

作者： Mingbo YUAN Qicheng SUN Feng JIN Shandong College of Electronic Technology Jinan 250014China State Key Laboratory of Hydroscience and Engineering Tsinghua UniversityBeijing 100084China

The internal structure established within granular materials,often observed as force chains,is dominant in controlling bulk mechanical *** designed a two-dimensional Hele-Shaw cell to contain photoelastic disks,and two servos were used on the top and right boundaries *** experimentally monitored the fluctuations in force on the top plate while slowing the shearing of the well-confined disks and keeping the right boundary at a contactconfined force of 0.2 *** particle rearrangements were found to correspond to bulk force drops and were observed in a localized zone with a length of approximately 5 particle *** results help reveal the structure and mechanics of granular materials,and further investigations are ongoing.

关键词： granular matter force chain stick and slip

Correlation mechanism between force chains and friction mechanism during powder compaction

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Chinese Physics B 2022年第2期31卷 423-433页

作者： Ning Zhang Shuai Zhang Jian-Jun Tan Wei Zhang School of Mechanical&Automotive Engineering Fujian University of TechnologyFuzhou 350118China

The relation between friction mechanism and force chains characteristics has not yet been fully studied in the powder metallurgy research *** this work,a uniaxial compression discrete element model is established based on the compaction process of ferrous ***,the correlation mechanism between force chains and the friction mechanism during powder compaction is *** simulation results reveal a strong correlation between the variation of the friction coefficient and the evolution of force *** the powder compaction,the friction coefficient would eventually tend to be stable,a feature which is also closely related to the slip ratio between *** side wall friction and the friction between particles would have an important effect on the direction of force chain growth in about one-third of the area near the side *** research results provide theoretical guidance for improving the densification process of the powder according to the force chain and friction.

关键词： powder compaction force chains granular matter discrete element method

STUDIES ON STRUCTURAL AND MECHANICAL PROPERTIES UNDER ISOSTATIC COMPRESSION WITH LARGE-SCALE DISCRETE ELEMENT SIMULATIONS

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Acta Mechanica Solida Sinica 2014年第2期27卷 129-136页

作者： Jianguo Liu Qicheng Sun Feng Jin Qingkai Liu State Key Laboratory of Hydroscience and Engineering Tsinghua University High Performance Computing Center Institute of Applied Physics and Computational Mathematics

granular systems undergo a jamming transition at point J simply by increasing the packing fraction. A large-scale parallel discrete element code （THDEM： TsingHua Discrete Element Method） was used to obtain a satisfying statistical description of the structural and me- chanical properties near point J. The isostatic compressions of 100,000 polydispersed frictionless particles were simulated on high performance computers to clearly observe the sophisticated con- figurations of force chains. The first peak of the pair correlation function, coordination number, spatial distribution of the packing fraction, and stress were calculated to analyze their variations with increasing packing fraction. The critical packing fraction at point J is determined to be 0.62. The incremental stress and coordination number from point J scale well with the power law, and coincide with previous theoretical predications. The distribution of the packing frac- tion is a normal distribution around the average value. The standard deviation decreases with increasing packing fraction, indicating the system is more uniform with a denser packing.

关键词： granular matter jamming transition force chains parallel computing

Experimental study and analysis on the rising motion of grains in a vertically-vibrated pipe

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Chinese Physics B 2015年第3期24卷 224-229页

作者：刘煜赵俊红 Electric Power Research Institute Henan Electric Power Company Luoyang College Civil Aviation Flight University of China

Previous experimental investigations have shown that when a narrow pipe is inserted into a granular bed and is vibrated vertically but the granular bed is kept still, the grains in the bed can enter the pipe and rise against gravity along the pipe and finally stabilized at a certain height. The growth velocity and final stable height of the grain column inside the pipe can be controlled by varying the vibration conditions. In this paper, we discuss those experimental findings. We establish a mathematic relation between the grain column height（h） and time（t）, and by using the relation we discuss the change of the growth velocity（ dh/ dt） and acceleration（ d^2h/ dt^2） with t and h, respectively. We also analyze the mechanism of the rising motion of the grains during vibration. Furthermore, we derive a theoretical expression for describing the final stable height（h st）, which shows that the main factors influencing the height are vibration strength（Γ）, bulk density of grains,inner diameter of the pipe, and vibration frequency, and that h st increases nonlinearly in the presence of air and linearly in a vacuum environment with increasing Γ.

关键词： granular matter vertical vibration theoretical analysis