Granular Matter最新文献

This study investigates the evolution of downsized barchan dunes in a water tunnel experiment, emphasizing the influence of inflow velocity on their crescent-shaped attractor. Based on image processing methods, the kinematic and morphological features of barchan dune evolution are determined. The results reveal that the varying inflow velocity will affect the crescent-shaped attractor. Furthermore, a cubic relationship is established between flow velocity and the aspect ratio of barchan dunes. Additionally, there is a morphological threshold in the evolution of the crescent-shaped attractor to evaluate its stability. This study highlights the sensitivity of the crescent-shaped attractor to inflow velocity and confirms its steady evolutionary pattern, and it provides a new perspective on the formation of the barchan dune swarms in the field of wind-blown sand dynamics.

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The distribution of rock fragmentation after blasting is an important indicator for assessing the effectiveness of mine blasting. The quantitative characterization of blasting fragmentation is a challenging problem for the evaluation of blasting effects. The use of U-Net network technology to segment blasting images provides a new means for obtaining quantitative statistics from blasting fragmentation. Although the U-Net network is generally capable of segmenting images, there are issues in improving the accuracy and efficiency for ores. To solve these problems, this paper proposes a new network structure - ResOreNet. ResOreNet first integrates the Feature-Fusion module into the U-Net network to become a FU-Net network that enhances the model’s identification of target locations and morphological details, thereby improving the accuracy of ore image segmentation. More specifically, it incorporates the residual network into the FU-Net network, which effectively solves the phenomenon of blurring the boundary of the mineral rock image segmentation caused by the overfitting of the model, and the introduction of the residual network effectively mitigates the problem of the gradient vanishing of the loss function during the backpropagation, and also further improves the computational efficiency of the model, and provide a new technical means for obtaining evaluation indicators of blasting effects in mines.

A rheological model for loose granular media is developed to capture both solid-like and fluid-like responses during shearing. The proposed model is built by following the mathematical structure of an extended Kelvin–Voigt model, where an elastic spring and plastic slider act in parallel to a viscous damper. This arrangement requires the partition of the total stress into rate-independent and rate-dependent stress components. To model the solid-like behavior, a simple frictional plasticity model is adopted without modifications, thus contributing to the rate-independent stress. Instead, the fluid-like or rate-dependent stress is further decomposed into deviatoric and volumetric parts, by proposing a new formulation based on a combination of the (mu (I)) relation, originally developed under pressure-controlled shear, with a pressure-shear rate relation derived under volume-controlled shear. The proposed formulation allows the model to capture both the increase in the friction coefficient and the enhanced dilation at high shear rates. High-fidelity simulation data, obtained from discrete element method and multiscale modelling, are used to evaluate the performance of the proposed constitutive model. The model provides accurate results under both drained and undrained simple shear paths across a wide range of shear rates. Furthermore, it successfully reproduces at much lower computational cost the flowslide mobility computed through multiscale simulations, which is primarily regulated by the shear rate dependence of the material properties during the dynamic runout stage.

Mixing performance and heat transfer was investigated in dry granular flows in cylindrical geometry where heat is transferred from cylindrical walls to granular bed. The discrete element method (DEM) was used to simulate these flows and to investigate the effect of different parameters on mixing and heat transfer that include impeller speed, blade rake angle, number of blades and polydispersity. The effect of impeller rotation on heat transfer was also investigated. Mixing quantification was done by using the latest subdomain mixing index (SMI). Results of DEM simulations for these parameters were concluded for mono and poly-dispersed flows. Velocity and heat transfer profiles were drawn. Better mixing was observed in the case of four blades. Higher impeller speed also showed better mixing and heat transfer. In this study, the effect of polydispersity—an often-overlooked factor—is studied. In all cases it was observed that polydispersity had a negative effect on both mixing and heat transfer due to enhanced segregation and reduced thermal conduction. It is also the first-of-its-kind analysis of coupled impeller-geometry effects on particulate mixing and thermal transport in granular media.

Graphical Abstract

Vibratory finishing is widely used in aerospace, weapon industry, high-grade computer numerical control machine tools, rail transportation equipment, and other high-end equipment manufacturing industries. Processing parameters are critical to processing efficiency and processing effect. Island-less bowl vibratory finishing equipment is commonly used to process medium and large disk parts. Compared with traditional bowl vibratory finishing equipment, the lack of an island structure in the shape of the container and the low motor mounting position can lead to changes in the container motion and the flow field of the particulate medium. In this work, a bowl vibratory finishing mathematical model and numerical model were established, the velocity of the granular media at different locations in the container and the magnitude of the force was analyzed, the change rule of the container amplitude size, granular media motion characteristics and force behavior under different processing parameters was elucidated, the container amplitude test experiments and the force test experiments were carried out. The results show that during bowl vibratory finishing, the container performs periodic three-dimensional elliptical motion in space. The lack of island structure in island-less bowl vibratory finishing results in lower motion speed and frequency of the granular media in areas far away from the container wall. The granular media makes a spiral motion around the container’s central axis consisting of circular and tumbling motions in an extended period and performs irregular velocity-changing annular spiral motion in a short period. The phase difference will change the motion direction of the granular media. The mass of the upper eccentric block affects the intensity of the circular motion of the granular media, and the mass of the lower eccentric block affects the intensity of the tumbling motion of the granular media. Selecting a phase difference of 90°, increasing the motor rotational speed and the eccentric block’s mass can increase the granular media’s velocity and force. This study provides a reference for improving processing efficiency and changing granular media flow field motion.

Graphical Abstract

Particle characteristics (particle shape and size), along with relative density, significantly influence the frictional characteristics and liquefaction behavior of granular materials, particularly sand. While many studies have examined the individual effects of particle shape, gradation, and relative density on the frictional characteristics and liquefaction behavior of sand, they have often overlooked the combined effects of these soil parameters. In this study, the individual effect of these three soil parameters on the strength characteristics (angle of internal friction) and liquefaction resistance has been quantified by analyzing the data available in the literature. A novel dimensionless parameter, the ‘packing index ((alpha )),’ was developed to account for the bulk characteristics (relative density - RD) and grain properties (gradation, represented by the coefficient of uniformity ((C_u)), and particle shape represented by the shape descriptor regularity ((rho ))) of the granular soils. Through statistical analysis, a power law-based equation was proposed and validated to relate the cyclic resistance ratio (CRR) and angle of internal friction ((phi )) with the packing index. Finally, an approach to assess the liquefaction resistance was detailed considering the intrinsic soil parameters, aiming to bridge the gap between field observations and laboratory analysis to facilitate a comprehensive understanding of soil behavior under cyclic loading.

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Hydraulic structures such as embankments and dams are essential for water storages, flood control, and transportation, but are vulnerable to suffusion under complex loading conditions. This study investigates the effect of suffusion on the cyclic shear behavior of gap-graded soils using the coupled computational fluid dynamics and discrete element method (CFD-DEM). A series of seepage infiltration and drained cyclic shear tests are conducted on specimens with varying mean stresses and initial stress anisotropy to systematically evaluate the mechanical consequences of suffusion. The findings reveal that the higher mean stress and initial stress anisotropy significantly exacerbate fines loss and deformation, particularly along principal seepage directions during suffusion. Furthermore, the eroded specimens exhibit substantial stiffness degradation and microstructural changes, including the deteriorated interparticle contacts and more pronounced fabric anisotropy. Notably, fines loss intensifies the load-bearing reliance on coarse particles during cyclic loading. These results provide new micromechanical insights into suffusion-induced degradation, offering valuable implications for developing advanced constitutive model of gap-graded soils accounting for suffusion-induced fines loss and cyclic loading conditions.

Entangled matter provides intriguing perspectives in terms of deformation mechanisms, mechanical properties, assembly and disassembly. However, collective entanglement mechanisms are complex, occur over multiple length scales, and they are not fully understood to this day. In this report, we propose a simple pick-up test to measure entanglement in staple-like particles with various leg lengths, crown-leg angles, and backbone thickness. We also present a new “throw-bounce-tangle” model based on a 3D geometrical entanglement criterion between two staples, and a Monte Carlo approach to predict the probabilities of entanglement in a bundle of staples. This relatively simple model is computationally efficient, and it predicts an average density of entanglement which is consistent with the entanglement strength measured experimentally. Entanglement is very sensitive to the thickness of the backbone of the staples, even in regimes where that thickness is a small fraction (< 0.04) of the other dimensions. We finally demonstrate an interesting use for this model to optimize staple-like particles for maximum entanglement. New designs of tunable “entangled granular metamaterials” can produce attractive combinations of strength, extensibility, and toughness that may soon outperform lightweight engineering materials such as solid foams and lattices.

The flow characteristics of granular materials under gravity represent the primary scientific challenge involved in caving mining. Conducting in-depth research in this area contributes to improving ore recovery results. This study introduces an innovative discrete particle dynamics model that combines the advantages of soft-sphere and hard-sphere algorithms to significantly improve the simulation of granular flow in caving mining. The proposed soft-hard sphere coupling model achieves remarkable computational efficiency while accurately capturing the influence of particle shape on flow behavior. By developing a specialized collision resolution algorithm and implementing advanced contact detection methods, the model successfully simulates the isolated draw process for particles of various shapes, including circular, polygonal and elliptical particles. The reliability of the model is thoroughly validated through comparison with physical experiments and theoretical models. Furthermore, the study demonstrates how the rolling resistance coefficient can effectively characterize particle shape effects in circular particle simulations, providing a practical approach to balance computational efficiency and accuracy. These developments offer valuable insights for optimizing ore recovery in caving mining operations.

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Geogrid is one of the most widely used geoinclusions in railway engineering to improve the bearing capacity of ballasted tracks. However, its effectiveness in mitigating ballast degradation, recognized as the most critical engineering challenge, remains limited, particularly in the context of the increasing demand for faster and heavier haul transportation nowadays. Rubber granules (RG), manufactured from waste rubber tires, possess high energy-absorbing properties that dampen vibration, reducing the stresses on ballast particles and helping to prevent ballast degradation. In order to explore the practical methods to delay the degradation of ballast and improve the performance of track bed, in this study, a series of large-scale direct shear tests were conducted on ballast aggregates with different geogrid-inclusion conditions and various RG content to investigate the shear behavior and performance of ballast under different configurations. The results show that while the RG effectively reduces the breakage of ballast particles, it negatively impacts the development of shear strength in aggregates, with or without geogrid reinforcement. As RG content increases, ballast aggregate exhibits lower peak shear strength, smaller maximum volumetric dilation, and greater volumetric contraction during shearing. For geogrid-reinforced ballast, incorporating 5% rubber granules (by volume) results in a reduction of aggregate shear strength by approximately 12%, while simultaneously mitigating ballast breakage by more than 30%. By balancing the enhancement of ballast durability with the maintenance of adequate shear strength, a 5% RG content by volume is recommended as a suitable proportion for practical applications. Based on experimental observations, a set of empirical equations has been proposed to estimate the shear strength and volumetric deformation of geogrid-reinforced ballast in the presence of RG. The findings from this study provide valuable insights for improving the design and performance of ballasted railway tracks, particularly in addressing ballast degradation and ensuring track resilience under modern loading demands.

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