Granular Matter最新文献

Compaction characteristics and maximum dry density control constitute critical considerations for over coarse-grained soil filler. In this study, DEM simulations of surface vibration tests were conducted and parametric analyses were carried out to investigate the effect of maximum particle size and gradation on compaction characteristics and maximum dry density behavior of over coarse-grained soil. The results show that the maximum dry density was positively correlated with the maximum particle size. Pores could be sufficiently filled when the content of small particles reached 25%, and soil skeleton was loosened when the content of small particles exceeded 35%. Giant and medium particles at a low content increased the maximum dry density by replacing small particles and void between them, and forming the soil skeleton when the content exceeded 40%. The increase in maximum dry density caused by small particles filling the pores and the decrease caused by the loosening of soil skeleton result in a peak value of maximum dry density when the content of small particles is between 25 and 35%. The effects of particles in soil can be concluded into four effects: framework effect, filling effect, substitution effect, and loosening effect. This study provides a scientific basis for predicting models and compaction methods of over coarse-grained soil.

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We explored experimentally the static and dynamic behavior of magnetic repelling particles confined in a two-dimensional cell using two particle geometries, namely, disks and rectangular bars. Despite the contactless interaction, typical static features of granular materials are observed for both particle shapes when the material rearranges under the action of gravity: pile formation with an angle of repose, and pressure saturation (Janssen-like effect), which can be explained by considering the magnetically-induced torques that generate friction between particles and confining walls. When the material is forced to be rearranged by compression, particle shape effects become notorious: while disks rearrange increasing the hexagonal ordering, bars augment their orientational ordering forming larger non-contact force chains mediated by the magnetic field; however, in both cases, the resistance to compression rises continuously, in contrast with the fluctuating compression dynamics (stick–slip motion or periodic oscillations) that characterizes granular systems with inter-particle contacts. Our results indicate that continuum approaches of granular materials can be used to characterize the system, despite the contactless interaction and specific shape of the constitutive particles.

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Angle of repose, Janssen effect and other features of conventional granular matter are also observed in a system of contactless repelling particles.

Discrete element method and theoretical analyses were performed to investigate the evolution characteristics of dynamic normal stress on a silo wall with hyperbolic hopper. Results show that the hyperbolic hopper promotes the development of stagnant zone, which avoids the concentration of large dynamic normal stress on a silo wall effectively. Compared with the conical hopper, the hyperbolic hopper reduces the peak normal stress by 14.42%, and increases the range of large normal stress from 0.2 to 0.5 m. The large stagnant zone causes a flow zone with large velocity gradient to develop, which drives the granular materials to flow out from the hyperbolic hopper in an orderly manner, thereby weakening the oscillation strength of the granular materials against silo wall. The hyperbolic hopper weakens the inertial force generated by the instantaneous arch during its formation and breaking, resulting in reducing the dynamic normal stress on silo wall with a hyperbolic hopper.

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The influence of the raised-bottom on the dissipation behavior of three-dimensional (3D) oscillating closed granular system is studied by discrete element simulation in this work. Firstly, the damping effect and motion phase states of granular balls in a flat-bottom closed container are investigated in the interested range of excitation parameters, which reveals two different high damping granular dissipation behaviors. Then, the damping characteristics of the same quantity of granular balls in flat, concave and raised bottom containers are compared, which indicates that the granular system with a 2 mm raised-bottom exhibits relatively better damping effect. Moreover, the difference between flat-bottom and 2 mm raised-bottom granular system in the dissipation behavior of optimal damping granules is further analyzed. Finally, the essence of enhanced damping effect of the 3D granular system by the 2 mm raised-bottom is revealed, i.e., the fact that the change of injection mode of vibration energy into granular system caused by the raised-bottom makes it easier for ideal dense granular cluster to appear in the oscillating granular bed.

In order to accurately and efficiently predict the landslide hazard and post-failure behavior of soil-rock mixtures (SRM), this study adopts the smoothed particle hydrodynamics (SPH) method. Rocks with arbitrary shapes are generated by employing the Monte Carlo random sampling principle. Subsequently, a lattice-based particle generator is proposed to interpret the geometrical model of SRM slopes and to construct the SPH numerical model. Furthermore, this study examines the effects of varying rock contents, sizes and shapes on the failure characteristics of SRM slopes. The findings reveal that the shear zone exhibits non-circular form during SRM slopes failure, presenting four distinct plastic expansion modes: Bypass, diversion, penetration, and inclusion. For identical rock content, an increase in large-sized rocks enhances the interlocking effect, thereby improving SRM slope stability. Conversely, the roundness of rocks significantly affects their failure behavior within SRM slopes, with higher roundness contributing to easier instability. The results demonstrate that the SPH method provides an innovative approach for investigating the failure behavior of heterogeneous materials, such as geotechnical bodies. Moreover, this method exhibits substantial potential for broader applications across various geotechnical engineering domains.

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A method to measure rolling friction coefficients for spheres rolling down an inclined two-cylinder track is described. The estimated coefficients of rolling friction are correlated with the equivalent radius of the deformation in the contact region, which can be calculated from Hertz’s contact model using available values of Young’s modulus and Poisson’s coefficient. The values of the coefficients of rolling friction determined in prior literature and those obtained here for steel spheres moving on a steel two-cylinder track show a variation in the sphere radius consistent with that expected from the contact model. The transition from pure rolling to rolling plus sliding regimes is also studied.

The mechanisms of granular flow-structure interactions and impact dynamics serve as a foundation for bridge engineering design. However, the design of bridge piers to counter granular flow continues to be influenced by the particle size distribution and the Froude characteristics’ impact on pier performance. A three-dimensional numerical model is established in this study, using the Discrete Element Method (DEM), and its reliability is confirmed through flume tests. The interaction mechanisms and dynamic impact characteristics of granular flow, coupling with particle size and Froude number (Fr), and pier’s shapes, were explored. The flow characteristics of granular flow have been revealed, as well as the interplay mechanism between granular flow and pier, the energy evolution mechanism, and escalation. The impact force distribution of granular flow on pier was clarified. A comparative analysis was conducted on the peak impact force resistance coefficient (C_d) for pier of assorted cross-sectional shapes. We have further developed a unified particle size-bridge pier-special design diagram, quantifying the influence of particle size and Fr on the hydrodynamic α. The analysis indicates that the existing models calibrated by limited experiments may overestimate the peak impact force on round and round-end bridge piers, while underestimating it for square bridge piers.

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When granular gases in microgravity are continuously excited mechanically, spatial inhomogeneities of the particle distribution can emerge. At a sufficiently large overall packing fraction, a significant share of particles tend to concentrate in strongly overpopulated regions, so-called clusters, far from the excitation sources. This dynamical clustering is caused by a complex balance between energy influx and dissipation. The mean number density of particles, the geometry of the container, and the excitation strength influence cluster formation. A quantification of clustering thresholds is not trivial. We generate ‘synthetic’ data sets by Discrete Element Method simulations of frictional spheres in a cuboid container and apply established criteria to classify the local packing fraction profiles. Machine learning approaches that predict dynamic clustering from known system parameters on the basis of classical test criteria areoposed and tested. It avoids the necessity of complex numerical simulations.

Because of its unique structure, graded porous materials are widely utilized in filtration, separation, energy and catalysis. However, there are many defects in the traditional manufacturing methods, and the manufacturing process is much complicated. It is of great significance to realize the orderly separation and arrangement of different size particles quickly and conveniently, so as to realize the construction of graded porous materials. In this paper, the discrete element method (DEM) was employed to simulate the vibration process of fine particles with continuous size distribution, and the influences of vibration amplitude (A) and frequency (f) on the segregation behavior and related properties of packing structure were systematically investigated. The dynamics and mechanism of vibration segregation were analyzed through packing morphology, particle trajectory and velocity information. Finally, the graded pore structure could be obtained by appropriate vibration. The results show that for the 316L stainless steel powder used in this paper, the graded particle structure is prone to be gained within a range of large vibration intensities (e.g., A = 13.5 μm and f = 600 Hz). Simultaneously, the overall porosity (ε) is also higher (ε = 0.44). The difference in size between large and small particles causes the difference in motion behavior during movement, which makes it easier for small particles to drill into the pores formed by large particles, and directly leads to particle segregation. In the typical graded porous structure (e.g., A = 13.5 μm and f = 600 Hz), the pore volume distribution of the bottom particles is narrow, and its volume is only 0–0.2 × 10^–13 m³. Along the + Z direction, the size distribution width of the pores increases, the peak position moves to the right, and the average pore volume becomes larger. The exploration results of this paper will provide a novel idea and theoretical basis for the construction of graded porous materials.

Measuring a temperature rise in tapered bearings is very important. This paper proposes a model for calculating the rise in temperature of bearings that considers the presence of contaminants in the lubrication. This study develops a discrete lubrication model for the Hertzian contact zone of a bearing using the Lattice Boltzmann method (LBM). The model analyzes the effect of particles on grease film flow and pressure. The temperature rise of the bearing was then calculated. Meanwhile, the study solved the bearing temperature rise in the lubricating grease using the finite difference method (FDM). The results of the LBM calculations were compared with those of the FDM calculations. Finally, an experimental study is conducted to investigate the temperature increase of the raceway in the presence of particulate matter in sealed grease lubrication. The results of the study show that the presence of particulate matter has little effect on the temperature rise of the bearings. The study results show that burnout is caused by a lack of grease rather than particles.

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