Computational Particle Mechanics最新文献

Dense granular flows down inclined channels are ubiquitous, with applications from industrial processes like grain handling to geophysical events like rock avalanches. Despite their widespread occurrence, understanding their behavior remains a challenge due to the complexity of grain interactions. This study investigates the impact of channel boundaries on flow dynamics through numerical simulations of four distinct configurations: smooth, structured (bumpy) walls and combined geometries. Surprisingly, we found that the substrate’s texture has minimal influence on flow velocity and density. Conversely, roughness introduced by bumpy sidewalls significantly hinders the flow, suggesting a crucial role in governing overall behavior. These findings contribute to a deeper understanding of granular flows and their dependence on channel geometry.

Deep foundation pits, pipe gallery troughs, culverts, and other infrastructure often require backfilling operations. Soil-based controlled low-strength material (soil-based CLSM), with its advantages of self-compaction, self-leveling, and self-hardening, has garnered significant attention in recent years and shows potential as a replacement for traditional rolling compaction backfill materials. Based on the backfill project of the pipe gallery at the Xihong Bridge in Ningbo, this study investigates the unconfined compressive strength, permeability coefficient, compression characteristics, and flow behavior of soil-based CLSM with varying curing agent ratios, assessing its engineering feasibility through field testing. The results demonstrate that soil-based CLSM, particularly with polycarboxylate superplasticizer agent, exhibits substantially improved strength, permeability, construction workability, and other service performance. Additionally, a detailed simulation of the entire pipe gallery foundation pit construction process—including pipe gallery construction, trench backfilling, support removal, and road construction—was performed using the Hardening soil with small strain stiffness model of the soil. The deformation characteristics were analyzed under different backfill conditions to assess the suitability of soil-based CLSM for trench backfilling. The analysis also considered soil deformation under varying curing ages and upper load conditions. The optimized backfilling solution for soil-based CLSM was obtained and validated with field test data. The findings suggest that using soil-based CLSM for foundation trench backfilling can effectively mitigate settlement issues.

The effects of confining pressure and particle breakage on the mechanical behavior of tailings were investigated using the discrete-element method to simulate conventional triaxial tests. The particle breakage was simulated using the octahedral shear stress breakage criterion and 14 Apollonian fragments replacement method. The macroscopic behavior of tailings revealed that the peak shear stress ratio is sensitive to confining pressure and the critical shear stress ratio is less sensitive to particle breakage. Confining pressure and particle breakage affect shear expansion, leading to changes in shear damage patterns. The quantitative study shows that particle breakage is the main factor influencing the nonlinear variation of the tailing strength. However, the influence proportion of particle breakage is gradually decreasing with the increase in the confining pressure. Microscopic analysis reveals a positive correlation between the overall anisotropy and the shear stress ratio, with the anisotropy of the normal contact force distribution contributing the most. The variation of the overall anisotropy is caused by the variation of the contact state, in which the sliding contact state is the main influencing factor.

In the simulation analysis of the bimetallic coin embossing, challenges such as mesh distortion, managing contact between different materials, and the computational demands of intricate relief patterns arise. To address these issues, this paper proposes a dual-grid material point method (MPM), which avoids mesh distortion and decreasing time steps that often occur in finite element methods (FEMs). The method utilizes surface patches for the rigid mold and material points for the blank surface, employing a point-surface contact algorithm to resolve virtual contact. For the contact between the core and the outer ring of the blank, two sets of background grids describe their movements separately until real contact occurs. CUDA parallel acceleration technology is applied to the MPM to manage large-scale computations. The advantages of MPM over FEM are shown through a comparison of calculation results and efficiency using a single-color commemorative coin embossing example. Additionally, embossing results for six different gaps between the core and outer ring of bimetallic coins are compared to optimize the embossing gap, achieving a maximum speedup of 39 times on a single CUDA machine.

The mixing homogeneity of granular materials plays an important role in the manufacturing and construction of various products. The geometry of particles considerably affects the mixing performance of the granular materials during mixing processes. This investigation explores the mixing mechanism of non-spherical particles in an industrial-scale double U-shaped ribbon mixer using the discrete element method. The grid size is selected to be approximately 4.2 times the average equivalent volume diameter of the particles for the calculation of the Lacey index, which is used to evaluate the mixing homogeneity of non-spherical particles. Subsequently, the effects of the particle aspect ratio, volume, and sliding friction coefficient on the mixing performance of non-spherical particles in the ribbon mixer are investigated numerically. The numerical results indicate that the particle volume and sliding friction coefficient significantly affect the mixing efficiency of non-spherical particles, whereas the aspect ratio of the oblate or prolate particles has a relatively small effect. Furthermore, it is found that the relative velocities between the contact points in the vertical direction at the beginning and end of contact can be used to explain the effects of the parameters mentioned above on the mixing efficiency of the non-spherical particles, and larger relative velocities at the contact points are beneficial for the mixing performance of non-spherical particles.

Blowout preventers (BOPs) are critical for ensuring operational safety in oil and gas development. Seal failure can lead to catastrophic accidents, such as uncontrolled blowouts. In engineering applications, the injection of bridging particles has been proposed as a temporary solution to plug leak points, providing a crucial time window for emergency response. However, the existing plugging mechanism remains poorly understood, limiting the advancement of plugging techniques. To address this issue, a numerical model for BOP hole-type seal failure was developed in this study using computational fluid dynamics (CFD) and discrete element method (DEM) simulations. Fluid–structure coupling analysis was conducted to clarify the particle bridging and plugging process. The influence of key parameters—including wellhead pressure, particle shape, particle size, pumping displacement, and particle concentration—on the plugging effect was comprehensively investigated. The results indicate that under 10 MPa and 40 MPa conditions, rectangular or cylindrical particles are preferred to enhance the plugging success rate and stability. At 10 MPa, the pumping displacement should be less than 1.5 m³/min, and the particle concentration should exceed 8%. At 40 MPa, the pumping displacement should exceed 2.0 m³/min, and the particle concentration should be greater than 6%. For higher pressures (70 MPa), particles larger than the leak point size are recommended, with a pumping displacement exceeding 2.0 m³/min and a particle concentration greater than 8%. This study provides practical recommendations for pumping displacement and particle selection under blowout conditions, significantly improving the success rate and efficiency of plugging operations. It also serves as a valuable reference for the development of plugging processes and technologies for BOP seal failure.

The proportional strain loading test is a prevalent method for investigation diffuse instability. The majority of current research concentrates on narrowly graded materials, with relatively less focus on binary mixtures under proportional strain loading. Therefore, a series of numerical tests have been conducted using the discrete element method to study the influence of fine content and strain increment ratio on the binary mixtures. The test results show that the fine content of binary mixtures is intimately connected to the critical strain increment ratio which precipitate a transition from stability to instability. Binary mixtures characterized by a low stress ratio at the onset of instability also demonstrate a heightened sensitivity to shifts in strain increment ratio. The macroscopic responses, such as the stress ratio at the onset of instability, shear strength, and pore water pressure, exhibit different trends of variation with the fine content compared to microscopic responses, including coordination number, friction mobilization index, and the proportion of sliding contacts. Furthermore, the anisotropy coefficient is introduced to dissect the sources of anisotropy at onset of instability, revealing that strong contact fabric anisotropy can mirror the evolution of the stress ratio. The stress ratio at onset of instability is predominantly influenced by anisotropy in contact normal and normal contact force.

The coupling effect between mixing uniformity and heat transfer of particles in the double barrel with differential velocity (DBDV) was studied. The particle motion model, heat transfer model and their coupled processes were established. The velocity and temperature fields of particles and fluids and the coupling relationship were analyzed. The results indicate that the particle flow direction in the mixing zone is opposite to the fluid flow direction. The velocity and temperature of the fluid are low where particles exist. The velocity and temperature of the fluid closer to the outlet are higher in the mixing zone. The dispersion coefficient decreases with increasing temperature at low and high linear velocities. The dispersion coefficient generally increases with the increase of temperature at medium linear velocity. It is advisable to choose the medium linear velocity to obtain particles with high uniformity and high temperature. This provides theoretical guidance for the development of DBDV.

Understanding the behavior of rock failure under the influence of grain size and temperature is a critical topic in rock mechanics due to its complexity and significance. The impact of these factors, particularly on crack initiation and propagation processes, is a complex and multifaceted issue that has been the focus of engineering rock studies. These effects are especially noticeable when temperature changes drastically, such as deep mining projects or construction in high-temperature regions. Based upon the distinct element method (DEM), this study used the particle flow code (PFC) to numerically simulate the rock fracture process under three-point loading on semi-circular bending (SCB) specimens. A total of 96 fracture toughness tests were simulated on samples with grain sizes of 0.5, 0.75, 1, and 1.5 mm at temperatures ranging from 25 to 700 °C and under mode I, mode II, and mixed-mode fracture loading conditions. The numerical models were validated against uniaxial compressive strength and Brazilian tensile strength test results. This study uniquely examines how temperature and grain size affect crack propagation velocity across different loading conditions. The findings showed that, as temperature increases, microcracks lead to thermal expansion in the samples, and the crack propagation velocity also increases. Additionally, there is an inverse relationship between grain size and crack propagation velocity. Notably, the results showed that the effects of grain size and temperature on crack propagation velocity vary across different fracture modes.