The Moon, rich in resources, is vital for space exploration. Space manufacturing requires in situ resource utilization due to high shipping expenses. Among these resources, lunar regolith is abundant but poorly suited for additive manufacturing due to its low flowability. This study investigates the effect of incorporating spherical stainless steel (SS316L) particles into the angular regolith simulant LHS-1 (lunar highland simulant) to improve granular flow behavior. By systematically varying the SS316L volume fraction and particle size distribution, we show that adding 50 vol
The structural parameters of a dry-mix mixer can significantly affect both the mixing uniformity and the mixing energy consumption of dry-mix mortar. In this study, a multi-objective optimization of a twin-shaft paddle mixer for dry-mix mortar was performed based on the discrete element method, with the aim of systematically elucidating the coupled relationships between key structural parameters and performance indicators. The effects of paddle number, paddle angle, paddle phase angle, and paddle arrangement on mixing uniformity, quantified by the coefficient of variation (CV), and on energy efficiency, evaluated by specific power, were analyzed. The results show that increasing the paddle number enhances diffusive mixing and reduces CV, but it markedly increases energy consumption. A paddle angle of 45° provides a more favorable balance between axial and circumferential transport, and a larger phase angle promotes particle mobility and improves the final mixing homogeneity. The paddle arrangement exhibits a pronounced influence on specific power, whereas its impact on CV is relatively minor. Multi-objective optimization further yielded an optimal structural configuration comprising eight paddles, a paddle angle of 49.6°, and a paddle phase angle of 90°. Compared with the baseline design, the optimal configuration reduced CV by 10.4
The screening efficiency of the indented cylinder separator is significantly influenced by the axial-radial segregation of rice particles. Industrial-grade indented cylinder separators typically feature high length-to-diameter ratios (L/D > 0.25), yet the underlying segregation mechanisms under such conditions remain incompletely understood. Therefore, this study employs the Discrete Element Method (DEM) to investigate the causes of rice particle separation phenomena inside long indented cylinder separator under industrially relevant conditions featuring a high L/D ratio (L/D = 1) and fixed end walls. The results indicate that the radial segregation mechanism is dominated by percolation, while axial segregation mechanism arises from non-uniform axial porosity distribution and is influenced by the motion state of the end walls. Moreover, the radial mixing index decreases much faster, reaching a minimum at approximately 50 s, while the axial mixing index stabilizes only after about 200 s, demonstrating that radial segregation temporally precedes axial segregation, however, its later evolution is influenced by axial segregation, resulting in a reduction of the overall radial segregation level within the cylinder separator. These findings provide fundamental insights into segregation dynamics in non-spherical, size-polydisperse granular systems and inform industrial particle separation processes.
The loading performance of star wheel loading mechanism directly determines the overall efficiency of the tunneling system. To improve this performance, this study selects two variables—wheel spacing and coal particle size, and proposes a total loading energy consumption calculation method based on an “integration-summation” step-by-step strategy. It introduces two loading energy consumption evaluation indicators: effective ratio and effective energy consumption per unit payload, and proposes a blockage rate to characterize the degree of loss in coal throughput. Furthermore, by combining effective loading mass with coal returning mass, a loading performance evaluation system is reconstructed. By integrating theoretical analysis, discrete element simulation, and a full-factorial experimental design, this study investigates the compatibility between wheel spacing and coal particle size, as well as the patterns by which they influence loading performance. The results indicate that for coal in Groups A, B, and C, overall loading performance is optimal at wheel spacing of 1600 mm, 1900 mm, and 2200 mm, respectively. As the wheel spacing increases, the effective loading mass and effective ratio first increase and then decrease, while the coal returning mass and effective energy consumption per unit payload first decrease and then increase; the total loading mass gradually increases and stabilizes, while the blockage rate gradually decreases and then levels off. Larger particle sizes help improve loading efficiency but simultaneously increase loading energy consumption; coal within different particle size ranges each correspond to an optimal wheel spacing, which is positively correlated with particle size. This study provides a theoretical basis and methodological support for the parameter selection and optimized design of star wheel loading mechanism.
Foam agents are widely used in Earth Pressure Balance (EPB) shield tunneling to reduce the excavated soil’s permeability and prevent uncontrollable slurry blowout. However, field observations show their limited effectiveness in modifying the permeability of soil with insufficient fines and the underlying mechanisms remain insufficiently understood. In this study, a coupled Computational Fluid Dynamics-Discrete Element Method (CFD-DEM) approach is employed to examine how soil gradation influences the modification of foam for the permeability of soil. Additionally, image processing and pore structure characterization methods are employed to investigate the variation of pore throat sizes during seepage. Finally, a novel indicator and its determination method are proposed to assess whether foam agents can improve soil’s permeability. Results show that the temporal variation of permeability in foam-conditioned soil is governed not only by initial open pore size but by fine particle content, pore geometry, and hydraulic pressure. The temporal evolution of the permeability coefficient varies with different d₁₀ values, while it remains almost independent with various d₆₀ values. A higher concentration of fine particles in foam-conditioned soil leads to more significant changes in both the number and spatial distribution of soil pore throats with radii smaller than the minimum foam particle diameter. Moreover, the proposed critical soil throat ratio (CSTR) effectively evaluates the modification effectiveness of permeability through foam agents. These findings offer practically feasible criteria for selecting suitable soil conditioners for EPB tunneling through sandy soil.
The presence of clay and silt significantly influences the maximum dry density (ρdmax) and minimum dry density (ρdmin) of sand-silt-clay mixtures. This paper investigates the effects of test method, clay type, fines content (FC), and clay-silt ratio (CS) on ρdmax and ρdmin. The results show that the variation trends of ρdmin measured by the funnel method and the cylinder method are similar. The ρdmin measured by the cylinder method is generally lower than that measured by the funnel method under the same clay type, FC, and CS. The ρdmax and ρdmin of mixed soil with bentonite are higher than those of mixed soil with kaolin under the same FC and CS. When kaolin is used, both the ρdmax and ρdmin decrease with increasing CS under the same FC. When bentonite is used, the ρdmax decreases and ρdmin increases with increasing CS under the same FC. For both clay types, the ρdmax decreases and ρdmin increases with decreasing FC under the same CS. The observed differences in ρdmax and ρdmin are attributed to the distinct particle sizes and morphologies of bentonite and kaolin. From an engineering perspective, the cylinder method is recommended for determining ρdmin of sand-silt-clay mixtures. Using the funnel method can overestimate relative density, which may in some cases lead to unconservative liquefaction assessments for transportation and marine infrastructure. The results also indicate that existing testing standards should be revised to account for clay type and clay-silt ratio, particularly for bentonite-bearing soils where ρdmax differs significantly from kaolin-bearing soils under identical fines content.
This study investigated the macro–micro shear characteristics of binary mixtures with varying fines contents fc via coupled DEM-FDM simulations. The results revealed a distinct non-monotonic dependency of shear strength on fc. Specifically, the peak friction and maximum dilation angles reached their maxima at a threshold fc of 30
Elastic hysteresis and shape irregularity are important sources of rolling resistance at the particle scale and significantly affect the packing stability of granular materials. However, the mechanisms through which these two factors influence particle rolling resistance, and their relative contributions, have not been systematically investigated. To address this issue, a phenomenological rolling resistance model was developed based on the asymmetric contact pressure distribution associated with elastic hysteresis. The proposed formula introduces a power-law index β as a key parameter, providing a quantitative measure of the energy dissipation capacity associated with elastic hysteresis. Furthermore, two modeling approaches were developed to describe irregular particle geometries, using Fourier series and regular polygons, respectively. Finite element simulations verified the equivalence of these two approaches in predicting the rolling response and revealed a logarithmic relationship between the rolling resistance moment and the circularity coefficient. For model validation, a high-precision experimental platform equipped with a laser sensor was established to accurately identify the rolling resistance from the displacement–time histories of cylindrical specimens. Comparison with experimental measurements shows that the trends predicted by the proposed models agree reasonably well with the measured rolling resistance. The calculated results further indicate that the total rolling resistance arising from geometric effects is approximately 9.3 and 2.7 times that induced by elastic hysteresis for the polyurethane and rubber specimens, respectively.
In coal mine anchor hole drilling, cuttings discharge efficiency directly impacts energy consumption and construction stability. This study, based on the specialized drill structure and positive circulation hydraulic cuttings discharge process, employs CFD-DEM coupling to simulate drilling in limestone, coarse sandstone, and coal seams. It investigates the effects of rotational speed (n), drilling rate (v), and flushing pressure (p) on multiphase flow field characteristics, particle migration behavior, and discharge efficiency, achieving bidirectional dynamic simulation of flushing fluid and cuttings transport. Results reveal a complex circulating flow at the bit outlet, comprising a main jet, backflow, and local stagnation zones. Within the hole, the flow follows an ‘upward in the center, downward at the periphery’ pattern, while cuttings particles ascend spirally but are prone to deposition at the bottom due to reflux. To quantify performance, Cuttings Removal Efficiency (CRE) is introduced, with orthogonal experiments, range analysis, variance analysis, and multiple regression yielding predictive models per rock type. Flushing pressure dominates in hard rocks, while rotational speed is more sensitive in soft coals. Models achieve R² > 0.81 and average error < 10
To understand the phenomenon of vibration-induced frictional weakening of granular materials, experimental studies were conducted using a resonant column apparatus. Superimposed vibrations with controlled amplitude and frequency were applied on sheared dry glass bead specimens vibration. Experiments demonstrate that vibration reduces deviatoric stress, which slowly recovers to its initial state once vibration is terminated while monotonic shearing continues. The influential factors considered in the investigation of glass beads of three particle diameters (0.3 mm, 0.6 mm, and 0.8 mm) are vibration frequency, amplitude, confining pressure, and particle diameter. Experimental evidence shows a more notable drop in deviatoric stress with increasing amplitude and frequency of the vibration, particle diameter and decreasing confining pressure. Using dimensional analysis, we derive a general mathematical expression for the dimensionless vibration number that includes the effect of these factors. With the adoption of the proposed vibration number, a physical scaling is revealed, which correlates the degree of shear weakening, quantified by the reduction in the coefficient of friction and the intensity of vibration, with the vibration of sheared dry glass bead specimens, characterised by the vibration number.
This study investigates nonlinear sand-ripple formation in granular media using a hybrid analytical–computational framework. Three nonlinear partial differential equation models are examined, incorporating key physical mechanisms such as surface diffusion, dispersion, and nonlinear steepening. Exact travelling–wave and solitary–wave solutions are derived via an ansatz–based analytical method, providing clear insight into ripple stability and morphology. The analytical solutions are subsequently utilized as training data for an artificial neural network approximation (ANNA), allowing a mesh-free characterization of the solution space. These two ANNA therefore both do well to a level of order 10^-4 in mean squared error (MSE), while even the fully generalized form has at best modest loss of accuracy, as expected from additional higher-order non-linear residual interactions. The new hybrid approach presents an inherently powerful and interpretable medium through which to conduct nonlinear wave propagation and pattern formation analyses of granular systems.
A layer of monodisperse circular steel disks in a nearly square horizontal cell forms, for small shear amplitudes, hexagonal close-packed regions that grow and merge until a single ordered domain fills the container. Increasing the shear amplitude leads to another reproducible regime in which a few large, locally ordered domains grow, shrink, and rotate with shear cycling, but do not evolve into a single ordered domain that fills the container. We use orientational order to describe the phenomena of order and disorder that we have observed. These results are robust within certain ranges of applied pressure and shear frequency. This work avoids two major limitations of sheared three-dimensional experiments: gravitational gradients and the difficulty of determining the interior three-dimensional structure.
The Cone penetration test (CPT) is a cornerstone of geotechnical site investigation and a critical tool for assessing soil compaction in agricultural soils, yet the fundamental mechanisms governing the contrasting behavior of dry and saturated soils during penetration remain incompletely understood. This study employs CFD–DEM framework to investigate CPT in granular soils under both conditions. The superior capability of model performance was verified via the Ergun equation test and upward seepage experiments in mono-disperse particle columns Simulations reveal that the mean cone resistance in dry soil is consistently higher than in its saturated soil, a phenomenon attributed to the pore fluid carrying part of the external load and reducing the effective stress transmitted through the particle skeleton. Micromechanical analysis demonstrates that the presence of pore water fundamentally alters the deformation mechanism: in dry soil, deformation is characterized by a wider disturbed zone and larger particle displacements, whereas in saturated soil, viscous damping and pore pressure buildup confine deformation to a more localized region around the cone tip. Furthermore, the evolution of contact fabric shows that dry sand progressively homogenizes towards an isotropic state, while saturated sand exhibits a partial recovery of directional alignment due to fluid-induced stress redistribution. Microhydraulic analysis highlights drag force as the key hydrodynamic mechanism. These insights advance understanding of coupled hydro-mechanical processes during CPT, providing a numerical tool for interpreting field data in variably saturated soils.
By means of extensive two-dimensional Direct Numerical Simulations utilizing a coupled Lattice Boltzmann Method – Discrete Element Method approach, we analyzed the settling dynamics of a single disk-shaped particle in a Newtonian fluid, confined by lateral walls or periodic conditions. By varying the systems parameters we obtained particle’s Reynolds number ranging from Re≃ 10^-4 to 10^4 . This broad range of Re enables a comprehensive analysis of the settling dynamics in 2D across the viscous, visco-inertial and inertial settling regimes. With no-slip wall conditions, our simulations align well with literature data up to moderate Re . Beyond this threshold, increasing grid resolution and lower compressibility become essential. With periodic boundaries, the pressure beneath the particle scales with its buoyant weight divided by the periodic distance and does not depend on the settling dynamics. For all system parameters, the pressure drop across the particle follows the same scaling, with a pre-factor that depends to the Reynolds number. A sigmoidal function provides a good fit of this pre-factor, with two asymptotic values: 1 in the viscous regime and 2.5 in the inertial regime. Between this two regimes a transition occurs, corresponding to the visco-inertial regime. We also discuss the confinement effects, due to periodic conditions, on the settling dynamics. Interestingly, a confinement length scale is identified and is shown to scale with the inverse square of the Reynolds number in the viscous regime, while remaining constant at high Re .
Unlike a fluid, the pressure at the base of a granular silo does not increase indefinitely with filling height. Instead, frictional interactions between the grains and the confining walls cause the pressure to saturate, a phenomenon known as the Janssen effect. Here, we investigate whether a similar stress-screening mechanism can arise when the confining boundary is not rigid but consists of a soft, self-assembled interface. The system studied is an underwater granular column of hydrophobic Magic Sand. When poured into water, the grains spontaneously form a thin confining layer, referred to as a granular skin, that encloses a dry core of grains and trapped air. By measuring the stress at the base of submerged sand columns of varying height, we observe a clear Janssen-like pressure saturation. Comparison with a conventional dry granular column shows that the granular skin supports a significant fraction of the applied load, leading to an enhanced stress screening. Synchrotron X-ray tomography reveals that this load-bearing capacity originates from the pinning of air–water interfaces to the hydrophobic grain surfaces, which stabilizes the confining skin. These results demonstrate that the pinned liquid-interfaces can act as effective load-bearing boundaries and play a central role in the mechanical stability of submerged granular structures.
Accurate calibration of microscopic contact parameters is essential for ensuring that discrete element method (DEM) simulations reproduce the macroscopic mechanical responses of soils. Conventional calibration approaches based on repeated trial and error simulations are computationally expensive and inefficient. To address this problem, a Bayesian Optimized Dynamic Back Propagation neural network (BO-DyBP) framework is proposed for the rapid calibration of microscopic parameters in soil DEM models. A macro-micro dataset containing 8000 parameter sets was constructed from biaxial DEM simulations under four confining pressures of 50, 100, 150, and 200 kPa. The BO-DyBP model was trained to establish the mapping from microscopic contact parameters to pressure dependent macroscopic deviatoric stress responses. On an independent test set, the model achieved R2 values of 0.984, 0.985, 0.983, and 0.999 under the four confining pressures, with corresponding mean absolute percentage errors (MAPE) of 3.70
For the purpose of investigating the effect of particle roundness on the mechanical properties of coarse-grained materials, four specimen models with varying particle roundness were constructed through numerical simulation, ensuring that other particle shape parameters remained constant. Triaxial shear simulation tests were conducted under different confining pressure conditions, and the deterioration of material properties due to particle abrasion was further analyzed based on the simulation results. The findings indicate that in the natural piling state, sharp particles enhance the structural stability of the material, resulting in a larger angle of repose. Specimens with sharper particle morphologies generally exhibit higher strength and greater resistance to deformation. However, excessively sharp particles can reduce material strength. Under high-stress conditions, the influence of particle roundness on the mechanical properties of the material diminishes. Particle abrasion significantly weakens material strength, with increased abrasion depth leading to a gradual decline in strength. Higher confining pressure exacerbates the detrimental effect of particle abrasion on material performance.
Stringing particles are granular materials formed by connecting discrete particles with rope, and there is a lack of load-bearing behaviors and mechanisms of such granular materials. In this paper, the load-bearing mechanism of the stringing particles system is investigated by using the Discrete Element Method (DEM), and a discrete elemental model of the stringing particles is developed in YADE; the direct shear test of the stringing particles shows that contact of rope effectively enhances the load-bearing capacity of the granular system. The direct shear experimental model was established through the simulation platform, and the simulation results of each group of specimens coincided with the experiments, and the established model of stringing particles was reliable in predicting the load-bearing capacity of the particle system, and at the same time, the analysis of the chain of contact forces within the particles, the anisotropy, the ratio of effective rope-particle contact forces and the average contact force of effective rope-particle contact forces showed that the contact state of the particles in the specimens was changed by rope-particle contact forces and the degree of change was related to the rope-particle contact force.
Frictional coefficient is one of the dominant factors for sand grains to control the mechanical behaviors of the granular soils. In this study, a friction weakening model is adopted to describe the negative impact of contact force on inter-particle frictional coefficient. A series of DEM simulations are conducted to investigate the influence of friction-weakening on granular soil behaviors with different void ratios. From macro-mechanical perspective, friction-weakening enhances the contraction for loose samples and attenuates dilation for dense samples. The effect of friction-weakening is more significant for samples under a higher confining pressure. From micro-mechanical perspective, samples with friction-weakening have a higher value of sliding contacts ratio and coordination number compared with samples with constant friction. During the shearing process, friction-weakening will reduce the fabric anisotropy of granular soils. At critical state, the difference of fabric anisotropy between samples with different friction model is mainly reflected in fabric anisotropy indicator in terms of tangential contact forces.
