A major challenge for material point method (MPM) is to model multi-body and multi-material interactions. Prevailing contact schemes developed for MPM suffer from numerical instabilities, especially ...for the coexistence of multiple material boundary conditions. This study proposes a generalized contact scheme based on a hybrid scheme of MPM and discrete element method (DEM) to tackle such issues. The new scheme contains two novel features of particle–particle and particle–structure contact schemes guided by a DEM contact model to handle multi-material interactions. It leverages the advantages of both MPM and DEM, offering a unified way to flexibly handle either the boundary–particle or particle–particle multi-material interactions. Several typical physical processes are simulated to showcase the versatility of the proposed approach, including interface rotation and sliding, penetration, and granular material impact. It demonstrates that the generalized contact scheme can flexibly capture the mechanical responses of multi-body and multi-material systems in MPM.
To investigate the landing performance of airbag cushion systems on the discrete lunar soil, this study proposes a novel modeling approach that couples multi-physics fields, including the flexible ...multibody systems (FMBS), the granular systems, and the gas effects. In this model, the GPU parallelism technique is utilized to address challenges arising from the large number of particles and complex contact detection involving large deformation and overall motions, and an efficient contact implementation between finite elements and particles is introduced. Additionally, contact modeling between airbags is realized using master–slave techniques. Then, a modified conventional serial staggered procedure is employed to couple flexible multibody dynamics (FMBD) and discrete element method (DEM) modules. Finally, a series of numerical examples is presented to validate the proposed dynamic model. The validated model successfully simulates the interaction between landing airbags and lunar soil. Subsequent parametric analysis contributes to the design optimization of the landing system. Moreover, discussions regarding computational efficiency illustrate that the proposed CPU–GPU-based FMBD-DEM is advantageous in engineering scenarios involving flexible components and large-scale granular systems.
•A novel coupling model is proposed to simulate the airbags-lunar soil interaction.•Multiple physics fields are integrated in the proposed model.•Efficient GPU-based contact detection between airbags and particles is conducted.•Parameter analysis for the landing airbags is conducted.•Compared with CPU-based approach, a speedup of 119.3 can be obtained in this model.
The rheology of dense granular flows is investigated through discrete element method (DEM) simulation of a vane shear cell. From the simulation, profiles of shear stress, shear rate, and velocity are ...obtained, which demonstrates that the flow features in the vane shear cell are equivalent to those in the classic annular Couette cell. A novel correlation for the apparent viscosity is formulated and leads to a new expression for μKT in the kinetic theory analysis. The μKT formulation is able to qualitatively capture the μ-I relation in the shear cell. A correlation length is added in the energy dissipation term to account for the effects of the particle motion correlation. A simplified correlation length model is derived based on DEM results and is compared with the literature. The modified granular kinetic energy equation is able to correctly predict the granular temperature profiles in the shear cell.
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•Flow patterns in the vane shear cell is analogous to the classic annular Couette cell.•A novel constitutive law for granular flows is proposed from DEM simulations.•The new constitutive law qualitatively recovers the μ-I relation.•Modified kinetic theory is able to predict granular temperature evolution.
Cyclic behavior of granular soils under multidirectional shaking is significantly different from that under unidirectional loading. In this study, a series of undrained simple shear simulations were ...conducted using a discrete-element method (DEM) under unidirectional and multidirectional loading conditions. Although the excess pore water pressure within a sample cannot reach the initial confining pressure, large shear strains of a similar amplitude still develop in samples under multidirectional loading. The simulation results further illustrate that granular soils have vastly different liquefaction resistance under different loading conditions. Evolution of soil fabric is also quantitatively studied in terms of inter-particle contacts and particle-void distribution. The same “stable state” of soil fabric will be reached under different multidirectional loading paths, which corresponds to that of a post-failure hardening state under unidirectional loading. The DEM study provides a new perspective in terms of microstructure evolution of granular soils under a variety of loading conditions.
A discrete element method (DEM) model was developed for a co-rotating twin-screw mixer (TSM) consisting of conveying and kneading elements. This model was used to simulate the mixing of a cohesive ...binary system of particles (P1 and P2). The particles were calibrated using angle of repose and dynamic yield strength simulations. Properties of P1 were kept constant throughout the study while properties of P2 were varied. The TSM model was used to study the influence of particle size, density, and flowability of P2 on process outputs such as powder holdup, mean residence time (MRT), and degree of mixing along the length of the TSM. All the three particle properties were varied at three-factor levels with flowability ranging from good flow (GF), poor flow (PF), and very very poor flow (VVPF) based on Carr’s classification. The model provides fundamental insights into the differences in mixing in the conveying sections of the mixer for materials with different flowability. Due to the co-rotating nature of the screws, the majority of the material in the conveying sections was carried on one side of the TSM for GF and PF particles, while both the screws carried VVPF particles. The total steady-state holdup and the mean residence time (MRT) of particles inside the TSM were heavily influenced by particle flowability compared to the other two tested particle parameters. The holdup in the conveying compartments ranged from 11%–15% of the total holdup, while the kneading compartment comprised 40% of the total holdup in the mixer. The simulations found that VVPF particles mixed the fastest and that the GF particles had the highest tendency to demix. The model was also used to suggest and test other screw design configurations to improve mixing. A screw design with kneading elements closer to the mixer outlet resulted in better mixing of GF particles. A screw design consisting only of conveying elements achieved the same degree of mixing as the original screw design for VVPF particles.
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•A model for a co-rotating twin-screw mixer was developed using DEM.•Holdup and mean residence time was influenced by the particle flowability.•Particles were transported mainly on one of the conveying screws.•The model was also used to suggest changes to screw design configurations.
•The impacts of confining pressure and gas on coal-rock combination are analyzed.•The meso-damage response and process of the coal-rock combination is studied by DEM.•The failure mechanism of ...combination under confining pressure effect is determined.
The research on mechanics properties and destroy behavior of coal-rock combination is extremely crucial for deep coal mining. However, there are few studies on the gas-containing coal-rock combination under the confining pressure effect, resulting in insufficient comprehension of the failure mechanism of the combination with different confining pressure. In this paper, a discrete element method (DEM) model of combination with stress-gas coupling is established. The related mechanics properties of single coal samples and combination samples under stress-gas coupling are compared and studied, such as axial stress, crack generation and failure mode. The results demonstrate that the coal mass in the coal-rock combination is continuously damaged and compacted during the loading process with different confining pressure. The interfacial effect caused by the circumferential expansion or irregular deformation of coal mass, and the improvement of compression intensity of the compacting coal mass jointly induce damage of the rock mass. The combination with confining pressure 4, 7 and 10 MPa exhibit the macroscopic failure characteristics of coal mass dominant, coal and rock mass together, and rock mass dominant, respectively. Meanwhile, the confining pressure effect also greatly determines the formation of the final failure pattern of combination samples after macroscopic failure.
It is important to understand the flow behaviour inside wedge-shaped hoppers and accurately predict the discharge rate for the processing and handling of granular materials, regardless of whether the ...wedge hopper is symmetric or asymmetric. In this paper, the discrete element method (DEM) was used to reveal the flow behaviour of pellet feed in an asymmetric wedge-shaped hopper from the discharge rate, flow pattern, velocity distribution, normal contact force between particles and free-fall arch. The results showed that, with the hopper angle decreasing, the area of the active region of the particles increased, the stagnation zone decreased, and the free-fall arch became unstable. When the unilateral hopper angle was less than 45°, the discharge rate of the wedge-shaped hopper increased, and the average discharge rate reached the maximum value of 1.070 kg s−1 when the left and right hopper angles were equal to 15°. In addition, using the discharging mass proportion coefficient to represent the size of the region in which the unilateral hopper angle affected the flow of particles in the hopper, the hopper angle term in the Brown and Sellers model was corrected. The predictive errors of the corrected discharge rate model were less than 7.6% and 3.3% in the simulated and actual discharging tests respectively, which was better than that of the Brown and Sellers model. The results of the study could provide a theoretical basis for the intelligent upgrading of feed accurate handling equipment, and provide a reference basis for the design of asymmetric wedge-shaped hopper.
•Simplified modeling of pellet feeds applied.•Discharge characteristics of an asymmetric wedge-shaped hopper revealed.•Discharge rate prediction model for an asymmetric wedge-shaped hopper developed.
Vertical stirred milling is a major technique for grinding fine and ultra-fine particles. In this study, attritor designs of varying pin number and projected area were examined over a range of ...impeller rotational speeds using the Discrete Element Method (DEM). Analysis determined that additional pins improved the potential for effective grinding due to an increase of average collision energy. However, this was accompanied by a greater power draw. When projected area was maintained, there were fewer differences between designs, meaning that the specific configuration of the pins may not be as important. A template of the mill can be found at https://github.com/darhyme147/ligggghts_stirred_mill_template.
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•We vary attritor pin number with constant size and constant total projected area.•Adding more pins of constant size strongly increases mean pair stress energy.•Changing configuration of the same pin area has a much weaker effect.•Pin spacing needs to be included when calculating the mill shear volume.
The microscale modeling of spray-dried granules for porcelain tile manufacturing with different moisture contents under uniaxial compaction is investigated in this paper. The Discrete Element Method ...(DEM) and the Bonded Particle Model (BPM) were applied for the investigation. To describe the mechanical behavior of granules during compression, an elastic-plastic bonded model was implemented, in which the moisture content is linked to the properties of the bonds. A good agreement was reached between experiments and simulations for the second and third stages of compaction. Herein, we obtained a mathematical model that links moisture, bond behavior during rupture, and porosity after compression. Different experimental studies have validated the model with high-achieving correspondence between the experiments and simulations. Thus, the proposed simulation methodology proved effective in predicting the porosity of the particles' bulk after uniaxial compaction.
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•High influence of moisture during compaction of spray- dried porcelain granules.•Development of an elastic-plastic bonded model for DEM-BPM numerical investigations.•Moisture linked to properties of bonds.•Good agreement between experiments and simulations.•Porosity prediction of moist spray-dried granules after compaction.
•The progressive face failure of a shield tunnel in sand is analyzed.•The coupled FDM-DEM is adopted.•The effect of particle shape on the failure process is investigated.•Results of soil movement, ...surface movement and supporting force are presented.•The force chains and distribution of microscopic contacts of particles are analyzed.
The face failure of tunnels has been extensively studied. However, the effect of particle shape on the failure process still remains unclear. In this paper, the progressive face failure of a shield tunnel in sand is analyzed with coupled discrete element method (DEM) and the finite difference method (FDM) in three-dimension. Soils at the tunnel face, where large deformation occurs and continuum mechanics description does not apply, are modeled with DEM. And the FDM is used for the rest areas where deformation and displacement are relatively small. In order to obtain appropriate parameters for soils as reference, a series of triaxial tests on both loose and dense soils are conducted. The face failure is generated by moving the tunnel forward and backward, which, respectively, simulates the collapse failure corresponding to the tunneling speed higher than soil excavating speed and the blow-out failure corresponding to the converse case. In particular, the effect of particle shape on the failure process is investigated in detail by adopting tetrahedral particles, elongated particles and spherical particles with rolling resistance coefficient of 0.0, 0.1, 0.2 and 0.4. The soil movement, ground surface movement, supporting force of the tunnel face, and the distribution of microscopic contacts are analyzed during the progressive failure of the tunnel face, which demonstrate a significant effect of particle shape.
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