Granular Matter最新文献

Understanding the migration trajectory characteristics of top coal in longwall top coal caving (LTCC) is crucial for studying the flow properties of granular top coal, drawing laws, and optimizing the coal drawing process. To monitor the migration trajectory of top coal during the drawing process, an experimental platform was developed for monitoring the top coal migration trajectory in LTCC. Using this platform, physical simulation experiments of LTCC were conducted. A multi-step experimental procedure was designed, including “model construction, marker point installation, simulated coal drawing, data collection, and trajectory inversion.” The migration trajectories of top coal at different layers during the coal drawing process were obtained, and the drawing body of top coal was inferred. Additionally, a bi-directional top coal drawing body equation was theoretically derived, establishing a quantitative relationship between the gangue content (cumulative and instantaneous) and top coal recovery. Based on this, field process optimization was carried out, adjusting the “four-level” method to a double-opening group coal drawing method. The instantaneous gangue content threshold at the coal drawing openings was set to 35%. The measured top coal recovery at the working face reached 90.12%, an increase of approximately 14.87% points compared to the previous recovery. The cumulative gangue content was controlled at around 9.25%, and the coordination efficiency of coal caving reached 68.2%, which is close to the theoretically derived results. This indicates that the theory can provide certain theoretical guidance for determining relevant process parameters in coal drawing operations.

Graphical Abstract

Top - Coal Migration Trajectory and Optimization of Coal Caving Technology

Liquefaction behaviors of sand deposits with impervious stratum are quite different from that of homogeneous geological conditions. However, the micro- liquefaction behaviors of the interlayered deposits have been infrequently documented. This study introduces a novel experimental methodology aimed at examining the influence of silt interlayer on the liquefaction mechanisms of sand deposits from both macro and micro perspectives. In the experiments, the Excess Pore Water Pressure (EPWP) was analyzed in conjunction with recorded micro liquefaction images. The migration mechanism of fine sand particles beneath the silt interlayer was revealed. The existence of low permeability interlayer leads to prolonged retention of EPWP beneath the silt interlayer. Substantially, the water film on the base of the interlayer is demonstrated to be the mixture of pore water and silt particles flowing with high velocity under seismic motions, thereby resulting in significant strain localization. An agminated zone of loose fine sand particles is usually generated beneath the silt interlayer after the dissipation of EPWP.

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The motion of wireless capsule endoscopes (WCE) in the gastrointestinal tract is complex and variable. Measuring its motion patterns accurately is crucial for optimizing diagnostic, therapeutic procedures and improving diagnostic accuracy. To gain a deeper understanding of the motion patterns of WCE in the gastrointestinal tract, particularly its behavior in different regions. A simulation measurement system based on magnetic localization technology is proposed in a laboratory environment. We designed a cylindrical-conical-cylindrical structure simulation device. The free fall motion of soft hydrogel granules is designed to mimic fluid motion in the gastrointestinal tract. A hard-targeted pellet with a permanent magnet simulated the WCE. It measured parameters such as trajectory, vertical velocity, vertical acceleration, and attitude angle of the targeted pellet during its drop at different initial positions in a silo during unloading in a soft granules environment were measured. The experimental results reveal the motion characteristics of a hard pellet in a silo during unloading in a soft granules environment, in the specific wide channel region, as well as in the transition region from the wide channel to the narrow channel. These findings are valuable for understanding the complexity of flow behaviours in different regions of the soft granules environment. And, these findings provide data references for understanding the dynamic behavior of WCE in the gastrointestinal tract, thereby aiding in optimizing WCE design and enhancing its clinical efficacy.

Analyzing geotechnical problems associated with granular material like cohesionless soil typically necessitate constitution of a physical model exhibiting a homogenous soil structure. Such well-conditioned model aids in reliable and reasonable interpretation of soil’s in-situ behavior under controlled conditions. However, such well-conditioned model needs to be reconstituted multiple times with a high degree of consistency. To this motive, the present study aims at the development and performance assessment of a novel mechatronic assisted air pluviation system (MAPS). The modular design of MAPS and the user commanded mechatronics integrated within its operational ecosystem were smartly used to facilitate a uniform and controlled reconstitution of specimen from a cohesionless soil. The reconstitution performance of MAPS was assessed by conducting several air pluviation trails with a poorly graded fine sand (D₅₀ = 0.22 mm), and further examining the effect of pluviation control parameter such as height of fall, sieve porosity, number of diffuser sieve, and diffuser ratio on characteristics of reconstituted sand. A wide range of relative density, ranging from 12 to 90% was achieved for reconstituted specimen upon utilizing the developed MAPS. Further, the mean coefficient of variation in relative density in horizontal and vertical direction of specimen was found to be well within acceptable limit of 5% and 7% respectively.

In this study, we investigate the stability and solid fraction of columns comprised of highly non-convex particles. These particles are constructed by extruding arms onto the faces of Platonic solids, a configuration we term Platonic polypods. We explore the emergence and disappearance of solid-like behavior in the absence of adhesive forces between the particles, referred to as geometric cohesion. This investigation is conducted by varying the number of arms of the particles and the thickness of these arms. To accomplish this, columns are assembled by depositing particles within a cylindrical container, followed by the removal of the container to evaluate the stability of the resulting structures. Experiments were carried out using three distinct materials to assess the influence of the friction coefficient between the grains. Our findings reveal that certain granular systems exhibit geometric cohesion, depending on their geometrical and contact properties. Furthermore, we analyze the initial solid fraction of the columns, demonstrating that these arrangements can achieve stability even at highly loose states, which contrasts with traditional granular materials.

Graphical Abstract

The particles were Platonic polypods with varying arm thickness and different numbers ofarms. Depending on their shape and friction characteristics, these systems can exhibit either frictional or cohesivebehavior.

This study investigates the impact of particle plasticity on the mechanical behaviour of a model granular system under plane stress conditions simulated with the Discrete Element Method. A contact model transitioning from nonlinear elasticity to linear plastic deformation is integrated to analyse its effects on a 576-ball-bearing assembly subjected to varying loads. Simulations were conducted using Yade, comparing them with experimental results and traditional elastic models. The findings show that incorporating plastic deformation improves the accuracy of simulated force distributions and the material’s frictional response, particularly under high external loads. These results underscore the need for plasticity-inclusive models in realistic granular simulations, providing valuable insights for practical applications in industries handling high-stress granular systems.

In this article, lentils are used as a case study to characterise the particulate behaviour of soft granular materials. Experiments were carried out on a single lentil particle or a pair of lentils. The single particle or a pair of particles in contact were compressed vertically to crushing or to a fixed vertical load. Then, in inter-particle tests, pairs of particles were slid over each other at a constant vertical load, and the tangential stiffness and coefficient of friction were estimated. The pairs of lentil particles in contact were also subjected to repeated normal and tangential loading. The presence or absence of the cover of lentil particles (shell) was found to affect their behaviour significantly under these loading conditions. The lentil particles have a very compliant shell and stiff core in normal loading; the stiffness of the shell is constant, and the core follows Hertz contact law. The lentil particles show less variability in their crushing strength, with high Weibull modulus (~ 10), in comparison to other natural granular materials like sand. With repeated cycles of vertical loading, the contact between a lentil pairs of particles becomes more stiff and less damp. In tangential loading, the coefficient of friction between lentil particles decreases with normal force while the contact stiffness increases. Further, in cyclic tangential loading, the coefficient of friction decreases and the contact stiffness increases with cycles. A simple contact model is also proposed to use in discrete element simulations.

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The heterogeneity of a dense sand specimen in triaxial compression has been revealed in many different studies using tools such as x-ray computed tomography. It has been shown that a significant variation of the soil variables already exists at the initial state and that, if shear banding occurs, all variables localise inside the specimen. To resolve the discrepancy between such observations and the assumption of a homogeneous specimen, which is commonly made in the interpretation of triaxial tests, one could either extract the local soil behaviour rather than the global one or use the initial distribution of the variables as the initial state of a boundary value problem. For both purposes, the size of a representative elementary volume (REV) is determined regarding the void ratio, two contact fabric descriptors, the volumetric and deviatoric strain. The size of the REV is either determined for individual loading states or by considering the evolution of deforming elements throughout the triaxial test. At the final loading state, a REV size of 3.6 (d_{50}) is identified, which is also the size where the statistical distribution of the variables becomes independent of the element size. The same size is determined for the deforming elements and is therefore used to extract the soil behaviour from the evolving shear band. The local soil behaviour is found to be much simpler than the global one, which suggests that the complexity of the global behaviour mainly results from homogenising the highly different zones inside the specimen.

Graphical Abstract

Extraction of the soil behaviour inside the evolving shear band with the help of deforming representativeelementary volumes. The volumetric behaviour is represented by the evolution of the void ratio and the evolution ofthe contact fabric anisotropy is closely connected to the stress-strain behaviour. The soil behaviour on the REVscale might form the basis for an alternative approach for the development and calibration of constitutive modelsconsidering the heterogeneity of a soil specimen.

This investigation delves into the scaling laws governing pressure and key mean variables throughout the first and second jamming transitions previously observed in asymmetric bidisperse granular packings. Motivated by a theoretical model integrating crucial parameters—size ratio, (delta), concentration of small particles, (X_{mathrm{S}}), packing fraction, (phi), mean contact number, (langle Z rangle), mean overlap, (langle alpha ^{c}_{n} rangle), and mean branch vector length (langle ell ^{c}_{n} rangle)—we employ molecular dynamics simulations to validate the model. Our findings reveal a non-linear relationship between pressure and (phi) stemming from the dynamic interaction of mean variables with (phi) during compression. Regardless of (X_{mathrm{S}}) for δ = 0.73, the scaling exponent (c_{Z}) characterizing (langle Z rangle) with (phi) consistently approximates 0.5, holding true for δ = 0.73 and high (X_{mathrm{S}}) values. Intriguingly, for δ = 0.15 and low (X_{mathrm{S}}), where the two jamming transitions are observed, (c_{Z}) exhibits distinct values. At the first transition, where large particles jam, (c_{Z}) slightly exceeds 0.5, while it diminishes to approximately 0.3 at the second transition following the jamming of small particles. Additionally, the exponents associated with the scaling of (langle alpha ^{c}_{n} rangle) and (langle ell ^{c}_{n} rangle) with (phi) consistently converge around (c_{alpha } = c_{ell } sim 0.92) varying with changes in (X_{mathrm{S}}) and (delta). Moreover, the pressure model aligns seamlessly with simulation trends, exhibiting a consistent exponent around (c_{p} sim 1.1)–1.3 throughout the first and second jamming transitions. These results offer valuable insights into the compression behavior of highly asymmetric bidisperse packings, emphasizing the substantial influence of (delta) and (X_{mathrm{S}}) on the system’s macroscopic properties.

The air entrainment caused by the transportation, loading and unloading of industrial bulk materials is the main cause of dust diffusion. Local exhaust is the most effective means to control the diffusion of industrial pollutants. In order to study the flow field disturbance and control effect of the exhaust hood on the entrained air. First, a numerical model was established for the exhaust hood to control the air entrainment caused by the particle flow falling and hitting the wall. Secondly, the numerical model was verified using experimental data. Finally, the control of entrained air by the exhaust hood was analysed using a coupled CFD-DEM method, with the exhaust air velocity, the exhaust hood size and the exhaust hood position as variables. The results showed that the best effect on entrained air control was achieved when the exhaust air velocity was 7.5 m/s, the exhaust hood diameter was 125 mm, and the position of the exhaust hood was flush with the secondary wall impact point of the particles flow. The relative velocity recovery coefficient is pioneered to analyze the degree of influence of the three variables on the flow field of entrained air. It was found that the exhaust hood size has the greatest influence on the entrainment air velocity distribution, followed by the exhaust wind speed, and the least impact is the position of the exhaust hood.

Graphical Abstract