Granular Matter最新文献

In mass finishing processes, the large number of granular media leads to low efficiency in discrete element method (DEM) simulations. Currently, common approaches such as GPU-accelerated computing, adjustment of simulation parameters, and coarse-grained methods exhibit respective advantages and limitations in terms of simulation cost and accuracy. Similarity theory has been employed to establish equivalent models for mass finishing processes. However, its primary objective lies in reducing experimental costs and simplifying process operations, rather than addressing the issue of simulation efficiency. To solve this problem, a construction method of gravity-size distortion equivalent model was proposed. Two specific distortion schemes were determined: enlarging the diameter of granular media and reducing the sizes of container and workpiece. The validity of the equivalent model was verified by DEM simulations and experimental tests, and the improvement degree in simulation efficiency was further analyzed. The results show that the equivalent model has favorable consistency with the real model under various vibration parameters. The scheme of enlarging granular media has higher prediction accuracy in velocity (96.66%) compared to the scheme of reducing the container and workpiece sizes (92.42%), whereas the latter yielded superior accuracy in predicting normal force. The average prediction accuracies of two distortion schemes are 83.62% and 90.13%, respectively. Furthermore, the gravity-size distortion equivalent model significantly enhances the computational efficiency of DEM simulations. The fundamental reason is that the equivalent model significantly reduces the number of granular media. When the number of granular media is identical, the two distortion schemes resulted in simulation efficiency improvements of 60.27% and 78.15%, respectively, with the scheme of reducing container and workpiece sizes demonstrating superior performance. This research provides a methodology for efficient DEM simulation and low-cost experimental research in mass finishing, thereby promoting process development. Additionally, it can also be extended to other discrete element fields.

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This paper presents a laboratory study that aims to validate whether the thermal creep motions of granular assembly can be an intrinsic material behavior. In the laboratory tests, 2-dimensional packed specimens of polycarbonate disks were subjected to controlled uniform and gradient heating cycles under given stress conditions using a stress-and-temperature-controlled biaxial shear device that is incorporated with photoelastic recording and hence allows the calculation of granular fabric anisotropy. By eliminating most extrinsic factors, it is shown that significant irreversible thermal volumetric and shear creep strains can be intrinsically induced by uniform heating cycles without temperature gradients, greatly governed by the anisotropy conditions of stress and granular fabric. Irreversible changes of granular mesostructures are observed under uniform temperature cycling with changes of force chains and granular fabrics. It is shown that this intrinsic thermal creep mechanism under uniform temperature conditions may dominate the thermo-mechanical granular behavior even when there are large temperature gradients in the granular assembly. However, it is noted that the temperature gradient may serve as a complementary mechanism of the intrinsic granular thermal creep behavior.

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The entrainment effects of granular flows are widespread and significantly impact their dynamics. This study uses the discrete element method to create a chute model simulating the granular flow entrainment process. It examines how entrainment affects erosive force, flow behavior, and energy, considering various flow volumes, soil cohesion strengths, and distances from the entrainment zone to the source area. Results show that the basal normal and shear forces are minimally influenced by particle cohesion in the entrainment zone but are significantly affected by flow volume and distance from the source. The primary factors influencing shear and normal forces are, in order: distance from the source, volume, and cohesion strength. For entrainment volume, the order is: volume, distance, and cohesion strength. Energy monitoring reveals that entrainment significantly impacts the kinetic energy and velocity of granular flows, with a bimodal evolution as the distance increases. Entrainment increases collisional energy dissipation, reducing the overall kinetic energy of granular flows. The result enhances the understanding of the mechanisms of granular flow entrainment.

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The transfer and transportation of bulk materials is common in industrial production, which can realize automation and efficient production. However, this process has become a major source of dust pollution in the production environment, which seriously threatens the health of workers and hidden safety production hazards. The dust source of the bulk material transferring and conveying process has a certain velocity, and the dust pollution formed belongs to the problem of moving dust source. Based on this, this paper establishes a dust fugitive model of mobile dust source through wind tunnel laboratory. The effects of moving velocity, air velocity and particle size on dust dispersion are analyzed by experimental and numerical methods, and the dust initiation rate is introduced to evaluate the dust initiation intensity. The results show that the difference between the air velocity and the set air velocity near the dust source increases with the increase of the set air velocity, and the deviation rate of the velocity is in the range of 8% to 13%. The mass loss of the moving dust source increases with the increase of the air velocity, and the peak value of the dust initiation rate increases as well; When the moving velocity of the dust source increases from 0.15 m/s to 0.3 m/s, the mass loss decreases from 13.89 g to 9.87 g. The dust initiation rate decreases with the increase of the moving velocity of the dust source, and when the moving velocity is 0.15 m/s there is a maximum dust initiation rate of 5.79 × 10^− 4s. These results provide quantitative insights into the dynamics of moving-source dust dispersion, supporting the design of targeted control strategies in industrial settings.

The widespread distribution of aeolian sand makes understanding its shear strength characteristics under different saturation levels crucial for engineering construction. This study, based on a numerical simulation method and validated through comparison with laboratory direct shear tests, clarifies the influence of different saturation levels on the shear strength of aeolian sand particles. It also investigates the interaction mechanisms between particles in aeolian sand, considering the effects of liquid bridges. Research reveals that the shear strength of aeolian sand exhibits an “inverted S-shaped” pattern with increasing saturation level: at low saturation, the strength is dominated by the internal friction angle between particles; at medium saturation, liquid bridge forces prevail, and shear strength increases with the rise in cohesion; at high saturation, the liquid bridge effect diminishes, leading to a decrease in shear strength. The liquid bridge effect significantly influences the shear band width and force chain strength by enhancing inter-particle cohesion and stress transmission. The numerical simulation results align with the experimental findings, validating the model’s effectiveness. This study offers new insights into the mechanical behavior of aeolian sands under different saturation conditions and provides theoretical guidance for practical engineering applications involving aeolian sands.

Screening Efficiency (SE) and Screen Surface Load (SSL) are important factors for the vibrating screening process design. In this work, inherent mechanism for the collaborative optimization of SE and SSL in our previous study is further explored numerically. Firstly, the particle-screen collision motion and the particle swarm screening motion are studied to reveal the SE&SSL related particle behavior. Then, the particle swarm behavior characteristics in both high SSL and low SSL modes are comparatively studied. In addition to enhanced local screened particles mass uniformity, the low SSL mode is about 47% lower in particle mass and 55% faster in flow velocity. Finally, the correlation between particle swarm behavior and process parameters, leading to high SE and low SSL, has been summarized. With small vibration amplitude 4.3 mm, low frequency 13 Hz and small vibration direction 50°, the vibration intensity (:{K}_{v}) is maintained at the lowest level 2.24, which indicates small particle-screen impact force and short throwing cycle. A large inclination angle 4.7° helps release the gravitational potential energy of particles, together with the small vibration direction, resulting in a rapid flow velocity, which suggests low particles mass. While small impact force and low particles mass are beneficial to the SSL reduction, rapid flow velocity with short throwing cycle, enabling sufficient particle-screen contacts, tends to maintain the high SE. This paper provides a deeper insight into the mechanism of high-performance vibrating screening.

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Soil penetration, a typical process of driving a penetrator into soil at a constant speed, is common in geotechnical engineering. In addition to this pure penetration movement, natural organisms also employ rotational motions in their burrowing strategies, which are believed to reduce penetration resistance and are beneficial for the design of self-burrowing robots. In this study, the three-dimensional discrete element method (DEM) was employed to investigate the effect of confining pressure on the reduction of rotation-induced penetration resistance. It is observed that the rotation-induced reduction in penetration resistance weakens progressively with increasing confining pressure. This study investigates the underlying mechanisms of rotational and confining pressure effects from a microscopic perspective by combining complex network analysis. The introduction of rotation not only markedly reduces the number of particles in contact with the penetrator but also reorients particle displacement toward the horizontal direction, providing greater space for the penetrator to advance. However, increasing confining pressure suppresses dilatancy, resulting in larger vertical components of particle displacement and a greater alignment of tangential contact forces beneath the cone along the vertical direction. The denser and more stable particle structure manifests in higher average degree and clustering coefficient. Moreover, a distinct linear relationship is identified between the weighted average degree and the stable value of penetration resistance, bridging microscopic network features with macroscopic response.

We examined the influence of siliciclastic coating on the tribological behavior of sand particles. A new coating method was developed for this purpose, which is based on the principle of precipitation, allowing for a fairly uniform distribution of the microparticles to be developed, achieving a higher consistency of the test results in the normal and tangential directions to particle contacts. The investigation included both monotonic and cyclic tests as well as the application of preloading in some of the experiments. Particular emphasis was placed in the data analysis including contact Young’s modulus, coefficient of friction, contact stiffness in the normal (K_N) and tangential (K_T) directions and the stiffness ratio (K_N/K_T), as well as the analysis of elastic and plastic fractions of displacement, work done and the energy dissipation at the contacts of the particles. While the siliciclastic coating had a major influence on the contact stiffness and friction, the mechanisms of friction would be rather controlled by both the interlocking and inference of the microparticles as well as asperity interlocking of the sand grains, as revealed from post-shearing image observations. Overall, the contact behavior and the role of microparticle coating may be considered a key in understanding the meso- and macroscopic mechanics of granular systems and the mechanisms of energy dissipation.

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Static fatigue refers to the failure of materials under sustained stress levels lower than their short-term strength, which significantly affects the long-term stability of structures built on or within calcareous sand. This study investigates the progressive static fatigue behavior of calcareous sand, a material widely encountered in geotechnical engineering. Despite its widespread distribution, the underlying mechanisms governing the time-dependent mechanical degradation of calcareous sand remain insufficiently explored, necessitating further research. In this work, we employed an advanced non-destructive monitoring method, acoustic emission (AE) technology, to track real-time internal microstructural evolution, enabling a more detailed investigation of progressive failure mechanisms at a microscopic scale. Specifically, AE parameters such as hit rate and frequency characteristics are analyzed to provide quantitative insights into the initiation and propagation of micro-cracks. By utilizing AE monitoring, this research systematically evaluates the time-dependent mechanical degradation of calcareous sand under sustained loading, identifying key AE signatures associated with different phases of the static fatigue process. The findings offer valuable insights into the micro-mechanical behavior of calcareous sand during sustained loading, contributing to a better understanding of its long-term deformation and failure characteristics in engineering applications.

In the field of geotechnical engineering, the evaluation of passive earth pressure on retaining walls is crucial. Due to the heterogeneity of soil, soluble minerals tend to aggregate. The localized dissolution of soluble minerals reduces soil strength, which in turn may cause an overestimation of the passive earth pressure on retaining walls. In this study, the Discrete Element Method (DEM) was employed to illustrate the impacts of localized dissolution on passive earth pressure through pressure dissolution. The influences of the size and location of dissolvable zones on passive earth pressure under translation mode were analyzed. The results demonstrated that an increase in the size of the dissolvable zones correlates with a gradual decrease in the passive earth pressure. When the wall displacement is minimal, the passive earth pressure decreases as the dissolvable zone approaches closer to the moving retaining wall and the bottom of the backfill. However, with greater wall displacement, the effect of the dissolvable zone’s location on passive earth pressure becomes less pronounced. The presence of dissolvable zones in critical areas, coinciding with the plane of shear failure surface in the absence of dissolution, leads to a significant reduction in the shear strength of the backfill. Furthermore, variations in the size and location of the localized dissolvable zone impact the distribution of force chain and formation of shear bands.

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