Granular Matter最新文献

The hydro-mechanical coupling interaction of the sandstone is an essential scientific issue in geological and geotechnical fields, which always holds the key to understanding the meso-mechanism underlying the water-induced geohazards such as water inrush and piping erosion. In this study, a new fluid–solid coupled numerical method is developed by combining the finite difference method (FDM) with the discrete element method (DEM). The proposed FDM-DEM coupling method not only solves the seepage field through FDM discretization but also dynamically updates the permeability by explicitly capturing fracture initiation and propagation within sandstone. A representative case of hydro-mechanical coupling interaction of the sandstone was used to validate the accuracy of the proposed method. The effects of confining pressure and seepage pressure on the mechanical properties and permeability evolution of sandstone were evaluated by normalizing the test conditions. Moreover, the evolution laws of the fluid velocity field, particle displacement field, and fractures within the sandstone under the hydro-mechanical were discussed. The distribution characteristics of normal and tangential contact forces within the sandstone were studied. All the numerical results were in good agreement with the experimental or analytical results reported in literatures. The results of the study can provide a new insight into the meso-mechanics of complicated fluid–solid interaction in sandstone.

The paper presents the behaviour of samples made of self-manufactured polydimethylsiloxane (PDMS) grains in a photo-elastic confined uniaxial compression test. PDMS particles were produced using the water-based method, resulting in grain shapes that are close to spherical, with diameters ranging from 2.0 to 16.0 mm. The samples tested were of the same size; however, they consisted of grains of different fractions, diameter spans, and aspect ratios relative to the dimensions of the test box. They were subjected to a load-unload cycle according to several scenarios, first to determine the load that induces a measurable photo-elastic effect. To study the potential relationship between the uniaxial strain calculated based on the change in a sample’s height and the corresponding optical parameters, a parallel analysis was conducted using the average image brightness. It led to the proposal of standardised strain and brightness parameters, which reduced the influence of loading scenarios and camera settings on the test results, allowing for the study of the other factors. On this basis, a unique relationship has been found between normalised uniaxial strain and normalised relative average image brightness, encompassing both loading and unloading regimes. In contrast, two calibration curves are required to calculate stress from brightness. The most interesting finding is that, despite the different force network structures observed in the uniaxial compression test, they do not appear to affect the behaviour of the granular samples on a macro-scale.

Graphical abstract

The shape of particles is an inherent property that significantly influences the breakage strength of calcareous granular material, but the quantitative relationship between these factors remains unclear. In this study, the shape indicators of calcareous sand particles were calculated using three-dimensional scanning results. Subsequently, uniaxial compression tests were conducted to obtain the breakage strength of calcareous sand, and the influence of shape variations on breakage strength was determined. The results indicate that as the aspect ratio of particles decreases or sphericity increases, the average breakage strength (( sigma _{{text{m}}} )), characteristic breakage strength (( sigma _{{text{0}}} )), and theoretical average breakage strength ((bar{sigma})) of calcareous sand all decrease progressively. Furthermore, the required breakage energy also declines, following a nearly linear trend. Both breakage strength and energy of calcareous sand exhibit a Weibull distribution, with the Weibull modulus (m) for breakage strength ranging between 1 and 2, and for breakage energy ranging between 4.48 and 6.49. These findings provide valuable insights for theoretical research, engineering practice, and numerical simulations.

We present a simple, strongly nonlinear and short inverse tapered granular alignment (radii small to big) that can transform an impulse into a progressively wider and slower moving solitary wave. The system curiously also serves as an impact dispersion system for an impulse initiated at the smallest grain.

Solitary wave expansion in the Inverse Tapered Chain

The abrupt interruption due to the closure of the valve during the gravity-driven drainage of a liquid and granular medium results in the backflow of materials, which is widely encountered during pneumatic conveying. This phenomenon bears a strong resemblance to the classical water hammer effect, which is reported for the first time by the present authors in “Backward flow and jet formation of liquid and granular medium in a gravity drainage system following a sudden valve closure”, Powder Technology, Volume 438 (2024). Under specific conditions, one may encounter jet formation at the free surface. The current article produces a computational investigation on the effect of the rate of contraction on the backflow of materials and jet formation. Detailed parametric research is executed to characterize and compare the phenomenon for both the flowing medium,—liquid, and granular matter with the variation of rate of contraction. The Rayleigh Plateau instability led interesting phenomenon of jet rupture is also articulated in this article during the collapse of the long liquid jet at a lower level of rate of contraction (r (as described in Eq. 18) < 1). The current article addresses the effect weber number (We) on the jet rupture and energy dissipation due to jet rupture during the collapse of it. The present article also introduces the formation of a hollow granular jet at a lower level of r (r = 0.27) due to the introduction of a long reducer between the drainage tube and the extension line and drastic reduction of bulk density of the jet. The investigation is further extended to understand and differentiate the evolution and collapse of hollow and solid jet. The comparison of the energy dissipation during the formation and collapse of both the jets is studied too.

Graphical Abstract

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.

Graphical abstract

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.

Graphical Abstract

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.

Graphical Abstract

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.