Computational Particle Mechanics最新文献

Several rolling resistance models are documented in the literature and implemented in discrete element method (DEM) software. Specifically, constant directional torque (CDT) and elasto-slipping (ES) models are frequently used in similar simulation conditions but often lead to inconsistent outcomes. A limitation of CDT models is that they are known to be sensitive to numerical oscillations. In the present work, we attempt to define the range of validity of CDT models through the identification of a dimensionless oscillation number ((varPsi )) via an order of magnitude analysis. This oscillation number is demonstrated to effectively predict the division between two series of DEM simulations conducted using CDT and ES models.

This article comprehensively investigates the scouring mechanism of underwater cement paste (UWP) through parameter calibration, flume erosion testing, numerical simulations, and force chain analysis. Building upon the established ARR constitutive model, concurrent calibration involving flowability and rheological parameter experiments confirms that when fluidity ratio, yield stress, viscosity below 3.5, 7.5, 3.5%, the discrete element method (DEM) can effectively simulate fresh UWP performance. A comprehensive analysis of the slurry anti-erosion characteristics was then conducted using a one-sided flow erosion apparatus and 3D image reconstruction technology. Through physical and numerical comparative analysis, the feasibility of simulating anti-erosion performance within an error range of 4.42–10.93% for Ha and Hm values was finally confirmed using the DEM-CFD coupling method. After that, an in-depth analysis of particle force chains and displacement field was further carried out to elucidate the UWP anti-washout mechanism under dynamic water conditions. The results indicate that as the coordination number of cement particles decreases from 5.98 to 4.11 and relative displacement reaches 3.5 times their diameter, cohesive force chains within the suspension dissipate, resulting in the dispersion of the entire cement slurry. The UWP erosion process under dynamic water conditions unfold in two stages, with approximately 74.0% of the force chains rapidly fracturing within the initial 10% scouring time, while the remaining force chains break apart gradually through a slow tearing process.

The hammer mill is widely employed in various industrial sectors for crushing processes; however, its performance is often hindered by low grinding efficiency and high energy consumption. In this study, the discrete element method was used to investigate the crushing process of maize kernels within a hammer mill system. A comprehensive investigation was conducted to examine the influence of varying ruminant structures on particle circulation patterns. Quantitative assessment of crushing efficiency was performed through particle mass throughput and median particle size (D50), while screening efficiency was evaluated using damage degree index, collision frequency, and collision intensity under different ruminant structures. The findings reveal that the circulation motion of maize particles within the hammer mill significantly hinders both crushing and screening efficiency. Comparative analysis indicates that both conventional rumination troughs and the newly proposed rumination arch effectively disrupt the particle circulation motion. Quantitative analysis reveals that both the ruminant trough and the ruminant arch improve the crushing efficiency of the hammer mill. Specifically, the ruminant arch enhances crushing efficiency by 13.26% and the average particle size distribution by 5.78% compared to the ruminant trough. Moreover, both the ruminant trough and the ruminant arch contribute to improved screening efficiency in the hammer mill. When compared to the ruminant trough, the ruminant arch increases the damage degree to the particle circulation layer by 21.29%, the collision frequency by 24.62%, and the collision intensity by 18.97%. This study provides a novel approach for improving both the crushing and screening performance of hammer mills, offering insights for future optimization in industrial milling applications.

Concrete is widely utilized in the construction of critical structures such as nuclear plants, explosive material storage bunkers, and water-retaining facilities. These concrete constructions must be designed to withstand potential threats from terrorist attacks or accidental events, such as projectile impacts. When a slab undergoes severe impact loading, the concrete material experiences high loading rates and encounters a complex stress state, characterized by high confined compression stress near the point of projectile impact and tensile stresses near the slab’s free edges. This can result in potential spalling and scabbing on the front and rear faces of the slab. Addressing this issue, the discrete element method (DEM) proves particularly effective due to its capability to handle discontinuities with ease. To this end, a DEM model was implemented in the industrial computer program Europlexus, a finite element code for analyzing fluid–structure systems under transient dynamic loading. In the previous studies, the authors introduced a compaction model accounting for pore closure and free water presence in concrete, validated through simulations of penetration tests on thick concrete targets with passive confinement. This paper shifts focus to the DEM simulation of edge-on impact tests conducted on non-confined concrete tiles using ogive-nose projectiles. Unlike the aforementioned penetration tests, these original experiments involve moderate mean stress, highlighting the influence of tensile stresses on the fracturing process. The results validate the model’s ability to accurately represent fracturing and cratering processes in concrete, which are highly dependent on loading rates.

This paper presents a novel semi-implicit two-phase double-point Material Point Method (MPM) for modelling large deformation in geotechnical engineering problems. To overcome the computational limitations of explicit methods, we develop a semi-implicit approach that eliminates time step dependency in soil–water coupled problems. Unlike existing single-point methods that use one set of material points to represent soil–water mixtures, our approach employs two distinct sets of material points to model soil and water phases separately. To address MPM’s inherent stress oscillations, we introduce a stabilisation technique based on the modified F-bar method. Through validation against Terzaghi’s one-dimensional consolidation theory, one-dimensional large deformation consolidation, and large deformation slope stability studies, our method demonstrates superior performance. Further testing with the hyperelastic Nor-Sand constitutive model in landslide simulations reveals that the double-point approach produces significantly more reliable results than single-point methods, particularly for dilatant soils. Notably, while implementing two sets of material points, our method incurs less than 10% increase in computational cost while achieving markedly improved accuracy. These findings establish the double-point MPM as a robust and efficient approach for analysing large deformation geotechnical problems under fully saturated conditions.

Although resistive force during intruder penetration into granular layers plays a crucial role in various applications, its underlying mechanisms remain insufficiently understood. In this study, we investigate penetration resistive force using discrete element simulations, systematically varying the angle of repose, interparticle cohesion stress, intruder shape (tip angle and horizontal cross-sectional geometry), and the interface friction between the intruder and particles. The simulation results are then compared with estimations from the extended modified Archimedes’ law. As a result, the current model cannot fully capture the effects of these factors, except for intruder shape. Through the detailed strain field analysis of granular layer during intruder penetration, we identify that the discrepancy between the model and simulation results arises from differences in the failure modes of the granular layer. To address this, we modify the model parameters based on the failure modes. Furthermore, we introduce a formula that incorporates the effect of the interface friction, which is not accounted for in the current model. With these modifications, the model can quantitatively estimate penetration resistive forces in dry and cohesive granular layers across various simulation conditions. The analysis of variance indicates that the interface friction and angle of repose have a significant impact on prediction accuracy of the model, supporting the effectiveness of the modification. This study offers a comprehensive understanding of the key factors influencing penetration resistive forces and contributes to the development of more accurate predictive models.

A CFD-DEM coupling methodology was implemented to examine the influence of critical structural parameters of the curved seed-guiding tube, specifically the inner diameter (d), incident angle (α), curvature radius (ρ), and seed-dispensing angle (β), on key performance metrics including particle exit velocity (v_p), seed–seedbed collision force (F_c), and the coefficient of variation in seed spacing (CV_s). Statistical analysis revealed differential impacts of these structural features on performance metrics. The developed regression model successfully predicted optimal structural configurations: inner diameter of 22.67 mm, incident angle of 12.09°, curvature radius of 113.84 mm, and seed-dispensing angle of 35.91°. Empirical validation through physical bench testing demonstrated significant improvements, with the qualified rate increasing by 5.46% to reach 93.6–95.51%, while CV_s decreased by 7.21% to 13.59–18.53%. Optimal operational parameters were established at 4–5.5 km/h working speed with 5–6.5 m/s positive pressure airflow velocity.

During the mechanized harvesting process, fresh sweet potatoes are prone to damage, which affects their marketability; meanwhile, incomplete separation of potato tubers from the soil also reduces harvesting efficiency. This study employs the EDEM discrete element method to model and simulate the conveying and separation mechanism of the 4UZ-80 lightweight fresh sweet potato combine harvester, investigating the effects of key parameters on damage rate, skin breakage rate, and soil content. Simplified models of the mechanism, sweet potato particles, and soil particles were created using Inventor software, and the interactions among sweet potatoes, soil, and conveying chain rods during transport were simulated on the EDEM platform. The research focuses on the influences of conveying speed, conveying angle, and material generation speed on the forces acting on sweet potatoes and the efficiency of soil separation. Simulation results indicate that when the primary lifting chain operates at 0.45 m/s, with a conveying angle of 30° and generation speeds of 500 g/s for sweet potatoes and 2000 g/s for soil, the compressive force on the sweet potato particles is relatively low, while the soil proportion decreases from 77.92% at 0.2 m/s to 69.81% at 0.45 m/s, and further to 64.50% at 0.7 m/s. Moreover, increasing the conveying angle from 25 to 35° reduces the soil content from 75.49 to 64.38%, suggesting that a larger angle improves soil separation, although it increases the forces on sweet potatoes at the junction. Adjustments in material generation speed reveal that too low a speed leads to direct collisions on the sweet potatoes, whereas too high a speed exacerbates forces due to soil accumulation; both conditions significantly affect the separation outcome. Under the conditions of conveying speed of 0.45 m/s, conveying angle of 30°, and working speed of 0.25 m/s, the rate of sweet potato injury is about 0.84%, the rate of peeling is about 0.74%, and the soil content is 70.94%, which is consistent with the simulation results. These findings demonstrate that the EDEM discrete element method offers high predictive accuracy for optimizing the parameters of the conveying and separation mechanism, providing effective theoretical and technical support for reducing sweet potato damage and improving separation efficiency.

Deterministic Lateral Displacement (DLD) microsystems offer the ability to fractionate microparticles based on their size with high resolution. So far, this type of separation system has been used mainly for analytical purposes. However, when it comes to industrial applications for the fractionation of real particle suspensions, higher throughputs are of increasing interest. Since real particle suspensions are not only spherical, this work deals with the fractionation of non-spherical particles at higher volume flow rates. Resolved three-dimensional (3D) CFD-DEM simulations were used to investigate the separation behavior of spheroids at different particle aspect ratios, sizes and Reynolds numbers. The spheroidal particles were approximated using the multi-sphere approach. The results generally show that the separation size decreases with increasing Reynolds number. The behavior of the particles generally differs for prolate and oblate as well as for more compact and less compact spheroids depending on the Reynolds number: Prolate spheroids show a tendency to align themselves longitudinally in the gap in the direction of flow and tumble around the post, whereby this behavior becomes stronger with increasing aspect ratio and Reynolds number. Compact spheroids follow the streamlines better and turn their axis of symmetry parallel to the post. This is why their separation size corresponds roughly to their smallest axis and particles with a larger aspect ratio are in contrast more prone to deflection. While oblate spheroids tumble around the posts at low Reynolds numbers, inertial conditions result in a behavior that can be described by inclined log-rolling. Therefore, it is no longer the smallest but rather the largest axis that is crucial for fractionation. The separation of spheroidal particles is, therefore, not exclusively influenced by the size of the smallest axis of the particles, but by a combination of several shape-specific and inertia-dependent effects.

In the fluid injection stimulation process of unconventional reservoirs, proppants are frequently used to maintain the opening of fractures for economic resource recovery. Understanding proppant transport in rock fractures is important to constrain fracture geometry and inform fluid injection design. In this study, we establish a coupled CFD-DEM model to simulate the transport process of proppants in fractures. A systematic parametric study is performed to investigate the influence of injection parameters (proppant density and fluid viscosity) and fracture morphology (fracture tortuosity and fracture width). The flow field distribution and mechanical characteristics of particles (proppants) are analyzed, and the velocity change and spatio-temporal accumulation evolution of particles are examined, revealing proppant transport and laying mechanism. Our results show that proppants accumulate horizontally, forming layers over time when the proppant density and fluid viscosity are low in smooth fractures. On the contrary, proppants often accumulate vertically over time when the proppant density and fluid viscosity are high. When the sand-carrying fluid flows through tortuous fracture, fluid erosion occurs at tortuous corners, forming a sand bank depression. It is also noted that the fluid velocity increases at tortuous corners, implying that more particles could be transported in fractures with higher tortuosity.