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There has been growing interest in applying the DEM (discrete element method) to study the charging and burden distribution in a BF (blast furnace). In practice, the real particles in a BF are non-spherical. However, spherical particles have mostly been used in previous DEM investigations. Furthermore, various particle models have been developed to describe non-spherical particles. However, the effects of using different particle models on particle behavior in a BF are still unclear. Therefore, a comparative study of how the particle shape model impacts the burden charging in a BF was conducted. Specifically, the DEM using a multi-sphere model, polyhedral model, and super-ellipsoid model was first established. Then, experiments and DEM simulations of the charging and burden distribution of non-spherical quartz sand particles in a lab-scale bell-less top BF were performed. The results indicated that the number of sub-spheres, the principle of creating the particle for multi-spheres, the number of planes for polyhedrons, and the shape indices for super-ellipsoids could all affect the accuracy and efficiency. Moreover, applying the super-ellipsoid model and multi-sphere model could achieve reasonable accuracy and efficiency, with the highest simulation accuracy for the polyhedral model but at the cost of a rather heavy computational burden.

Modular charging is an advanced technique designed to meet the requirements of auto-loading artillery, whereby granular propellants are stored within modular cartridges that are loaded into the gun chamber. This study employed an extended coupled computational fluid dynamics-discrete element method (CFD-DEM) approach to investigate the gas-particle flow within modular charges. After model validation, we analyzed the distribution characteristics, velocity, coordination number, and orientation of cylindrical pellets in a simulator chamber. Four different loading positions for modular cartridges were examined to assess their impact on particle distribution. Numerical simulations revealed a combination of gentle, horizontal, and steep slopes in the particle distribution. The maximum particle velocity experienced a rapid increase during the initial phase, followed by a zigzag decline after reaching its peak. High-coordination number particles tended to accumulate primarily in the middle layer of steep accumulation. Additionally, the particles exhibited an inverted V-shape orientation range from 0° to 180°, suggesting their tendency to assume upright positions. This established model significantly enhanced our understanding of particle distribution following module cartridge rupture and provided valuable guidance for optimizing the design of large-caliber artillery charges.

A multi-sphere (MS) model combined with rolling friction was considered for modelling elongated particles of irregular shape. The performance of the model was investigated by numerical simulations of the rice grain flow. A set of 5000 poly-dispersed milled rice grains were selected for the investigation purposes. They were characterised by a constant aspect ratio 3.5, while their maximum size was ranging from 6.4 to 7.3 mm. Filling and discharge flow as well as piling were simulated numerically with and without rolling resistance of particles. Simulation results were validated on the basis of experimental results. Good agreement of numerical and experimental results in terms of the discharge time and repose angle of the pile was reached simultaneously, when rolling resistance was introduced.

This paper describes variations in shear behavior among specimens with the same packing fraction but different coordination number (different packing patterns). The multi-sphere models to express grain shapes of Toyoura sand were employed in discrete-element method (DEM) simulation. Specimens with different packing patterns were produced by two methods: changing interparticle friction angle (FC method) and applying cyclic simple shear (CC method). A series of simple shear DEM simulation was carried out using the FC and CC specimens. The shear response in small strain range (secant shear modulus) of FC was larger than CC specimens, while difference in peak shear stress (bulk shear friction) between FC and CC specimens were insignificant. Strong correlation was found in the relation between secant shear modulus and coordination number of the system, as well as between the bulk shear friction and packing fraction. The initial coordination number rapidly decreases with increasing shear strain, and thereafter it reaches an isostatic value. On the other hand, the packing density required large shear strain for reaching the critical state. It was found that the initial difference in coordination number between FC and CC specimens disappeared before reaching their bulk shear frictions. Therefore, the bulk shear friction strongly correlates with the packing density.

The paper reports the modelling of randomly shaped particles. An emphasis is placed on the illustration of random properties of particles, using simulations with a controlled probability distribution for the depth of the surface profile. The randomly-shaped quasi-spherical particles were described by applying a multi-sphere approximation and a statistical evaluation technique, and the surface of the particles was approximated using randomly located overlapping subspheres. The concept of statistically similar particles, i.e., particles characterised by having a similar probability distribution for the depth of the surface profile, was employed for these purposes, and an original method involving the application of a stochastic optimisation was developed. The optimization method was demonstrated by generating statistically similar particles. The contact behaviour was investigated by simulating a random particle impact against a wall, using the discrete element method. It was observed that statistically similar particles did not show statistically similar contact characteristics. The results of this study suggested that the refinement of the multi-sphere model (achieved by increasing the number of subspheres) was non-unique, not only in a deterministic context but also in statistical context, and that this subject requires further investigation.

Compound extremes, whose socioeconomic and ecological impacts are severer than that caused by each event occurring in isolation, have evolved into a hot topic in Earth Science in the past decade. In the context of climate change, many compound extremes have exhibited increasing frequency and intensity, and shown novel fashions of combinations, posing more pressing demands and tougher challenges to scientific research and disaster prevention and response. This article, via a perspective of multi-sphere interactions within the Earth System, systematically reviews the status quo, new scientific understanding, and deficiencies regarding the definition, mechanism, change, attribution, and projection of compound extremes. This study also sorts out existing challenges and outlines a potential roadmap in advancing the study on compound extremes with respect to data requirement, mechanistic diagnosis, numerical modeling, attribution and projection, risk assessment, and adaptive response. Further directions of compound extremes studies and key research topics that warrant multi-disciplinary and multisectoral coordinated efforts are also proposed. Given that climate change has reshaped the type of extremes, a transformation from the traditional single-event perspective to a compound-event perspective is needed for scientific research, disaster prevention and mitigation, and climate change adaptation, calling for bottom-up innovation in research objects, ideas, and methods. This article will add value to promoting the research on compound extremes and interdisciplinary cooperations.

Realistic yet efficient representation of particle shape is a major challenge for the Discrete Element Method. This paper uses angle-of-repose and direct-shear test simulations to describe the influence of several shape representation methods, and their parameters, on the bulk response of granular assemblies. Three rolling resistance models, with varying coefficient of rolling friction, are considered for spherical particles. For non-spherical particles, superquadrics with varying blockiness and multi-spheres with varying bumpiness are used to model cuboids and cylinders of several aspect ratios. We present extensive quantitative results showing how the various ways used to represent shape affect the bulk response, allowing comparisons between different approaches. Simulations of angle-of-repose tests show that all three rolling friction models can model the avalanching characteristics of cube/cuboid and cylindrical particles. Simulations of direct-shear tests suggest that both the shear strength and the dilative response of the considered non-spherical particles (but not their porosity) can only be predicted by the elasto-plastic rolling resistance model. The quantitative nature of the results allows identifying values of the shape-description parameters that can be used to obtain similar results when using alternative shape representation methods.

When a high-speed rotating projectile faces high impact loads, the sensitive parts of the control system can get damaged, resulting in operational failure. It is crucial to develop a unique buffer structure that offers impact resistance and has a small contact area. An annularly distributed multi-sphere point contact structure was designed and fabricated on a magnesium alloy substrate based on the Hertz contact theory. The accuracy of the finite element numerical model, constructed using Abaqus/Explicit, was verified through hydraulic impact tests. The impact mechanical properties of the structure were studied by analyzing the influence of the number, diameter, and cavity radius of hemispheres using an experimentally verified finite element model. The axial and radial deformations of the structure were compared and analyzed. The research findings indicate that the deformation and impact resistance of the structure can be greatly influenced by increasing the number of hemispheres, enlarging the hemisphere diameter, and incorporating internal cavities. Specifically, with 6 hemispheres, each with a diameter of Φ 6 mm and a cavity radius of R1.5 mm, the axial and radial deformations are only 1.03 mm and 3.02 mm, respectively. The contact area of a single hemisphere is 7.16 mm2. The study offers new perspectives on choosing buffer structures in high-impact environments.

Adequacy of approximation of ellipsoidal particles composed of a set of sub-spheres for numerical Discrete Element Method (DEM) simulations is examined. The algorithm of adaptive hierarchical multi-sphere (MS) model is suggested for composing elliptical particles. Numerical simulation of the piling problem is used as a test problem for evaluating the adequacy of MS model approximation in comparison to the model of smooth ellipses for multiparticle system. The accuracy of MS approximation with the increasing number of sub-spheres is examined in detail by comparison of macroscopic and microscopic parameters of granular dynamics. It was determined that the data on macroscopic parameters yielded by the MS model tend to converge to those of the smooth ellipsoid with the increasing number of the constituent sub-spheres, and the MS model approximates the smooth perfect ellipsoid with a reasonable number of sub-spheres within the limits of the appropriate tolerance. It can be concluded that a multi-sphere model remains a realistic and relatively simple particle model applicable to DEM simulations of the behaviour of the real smooth and rough elliptically shaped particles.

In this study, a numerical model of a partial wellbore is developed by coupling computational fluid dynamics (CFD) with the discrete element method (DEM) in order to simulate the operation of a double-circulation system (DCS) in coalbed methane (CBM) well drilling, which is a novel technique used for cuttings transport. The values of the flow field are computed by a fluid solver and the motions of the particle phase are calculated by the DEM, for which an additional multi-sphere particle model is integrated. After verification of the model, the analysis centers on the working mechanism, the DCS parameters, and optimization of the angle θ of the injection nozzles, which is the most critical parameter affecting the efficiency of the DCS. Simulations reveal the working details of the DCS and prove its applicability to cuttings transport, especially in the curved and horizontal parts of the well. The effects of viscosity and particle size are investigated, and a low-viscosity drilling fluid is recommended. The optimal range for θ is obtained as 30° to 50°. This work provides a reference for the engineering application of DCSs, and by feedback from drilling sites the reliability of the results can be verified.