Discrete element modeling of solid formation during electrophoretic deposition

Electrophoretic deposition (EPD) of colloidal ZrO₂ ceramic powder was examined with respect to the internal colloidal forces and the external electrical field. The influence of electrolytic dissociation of water close to the deposition electrode (cathode) on the electrostatic interaction between the particles and the local electric field is discussed. The discrete element method (DEM) was used to get an insight into the kinetics determining particle packing and density gradient microstructures. The simulation indicates that high particle concentrations combined with low electric field strength result in coagulated flocs and a low packing density in the deposit layer. Tentative phase diagrams for various colloidal forces and electrical field strengths were established.     

Discrete element investigations of wire-reinforced geomaterial in a three-dimensional modeling

The aim of the study is to build discrete numerical models of a wire-reinforcement for geomaterials to perform multi-scale investigations. Non Smooth Contact Dynamics is used to carry out large or small strain mechanical tests on a granular sample. Different numerical experiments distinguish the main reinforcement micro-mechanisms and their consequences for macroscopic behavior.     

Discrete element modeling of granular hopper flow of irregular-shaped deformable particles

Many natural and engineered granular materials have relatively deformable particles. Besides particle size and shape, particle deformability is another salient factor that significantly impacts the material’s flow behavior. In this work, the flow of irregular-shaped deformable particles in a wedge-shaped hopper is investigated using discrete element simulations. A bonded-sphere model is developed to simultaneously capture irregular particle shapes and particle-wise deformations (e.g., compression, deflection, and distortion). Quantitative analysis of the effects of irregular shapes and particle deformations shows that the increase in particle stiffness tends to increase initial packing porosity and decrease the flow rate in the hopper. Rigid particles tend to have clogging issues, whereas deformable particles have less chance to, indicating particle deformation reduces the critical bridging width in the hopper flow. Detailed analysis of stress fields is also conducted to provide insights into the mechanism of particle flow and clogging. Stresses and discharge rates calculated from numerical simulations are compared and show good agreement with Walker’s theory and the extended Beverloo formula. Simulations with various particle shape combinations are also performed and show that the initial packing porosity decreases with an increasing percentage of fibers while the discharge rate has a complex dependency on particle shapes.     

The role of particle collisions

The effect of collisions between monodisperse particles on their entrainment by a flow is investigated by treating the system of suspended particles as a continuum.     

Discrete element modeling and experimental investigation of hot pressing of intermetallic NiAl powder

This paper presents the numerical and experimental analysis of hot pressing of NiAl powder with an emphasis on the best possible representation of its main stages: initial powder compaction and pressure-assisted sintering. The numerical study has been performed within the discrete element framework. In the paper, an original viscoelastic model of hot pressing has been used. In order to ensure that the applied values of material parameters in numerical simulations are appropriate, the reference literature has been reviewed. It produced the relations and equations to estimate the values of all required sintering material parameters of the considered viscoelastic model. Numerical simulations have employed the geometrical model of the initial dense specimen generated by a special algorithm which uses the real grain distribution of powder. The numerical model has been calibrated and validated through simulations of the real process of hot pressing of intermetallic NiAl material. The kinetics of compaction, sintering and cooling stage indicated by the evolution of density, shrinkage and densification rate have been studied. The comparison of numerical and experimental results has shown a good performance of the developed numerical model.     

Numerical study of dynamic behavior of concrete by meso-scale particle element modeling

Based on the Particle Element Method, a meso-scale dynamic model is developed for numerical study of the dynamic failure behavior of three-phase concrete i.e., aggregate, mortar, and interface, under different strain rates. First, a pre-processing approach based on the background grid search method proposed in our previous work is applied to generate the three-phase concrete specimen in meso-scale; second, the meso-mechanical parameters of three phases of concrete are determined by inverse method; and third, using the meso-scale dynamic model, the complete force-deformation relationship and the corresponding dynamic increase factors (DIF) at different strain rates are obtained for dynamic splitting tensile and uniaxial compression tests of concrete. The results match satisfactorily with the preceding experiments in related literatures. Different fracture patterns, consumed energy curves and force chain distributions are discussed under different strain rates, explaining the mechanism of strain rate effects in concrete. The numerical simulations show that the higher the strain rates, the more reticular meso-cracks occur, the kinetic and frictional energies become more important, and the force chains in the specimen exhibit more bifurcation, implying that the fracture process at high strain rates requires more energy demand to reach failure.     

瓢型摆振槽颗粒偏析效果的离散元模拟

为了强化瓢型摆振槽在摆振时物料颗粒的偏析效果,以三维离散元法为手段,选用塑料球和钢球的二元干颗粒,依次对光槽时单独摆振、光槽时组合摆振、添加凸起槽时组合摆振3种情况颗粒偏析过程进行离散元模拟研究,并以颗粒体积分数为评判标准,且结合模拟偏析云图,进行颗粒偏析效果评价。结果表明:组合摆振强于单独摆振的偏析效果;添加凸起槽强于光槽分层效果;相较于光槽时单独摆振,添加凸起槽时组合摆振时颗粒的偏析程度可提高10%~15%。     

Discrete element modeling of first shear strain gradient effects on mechanical behaviors in granular materials

Granular Matter - We introduce an improved version of a computational algorithm that “clones”/generates an arbitrary number of new digital grains from a sample of real digitalized...     

Discrete element study of bubble behaviors in Type D particle fluidization with and without interparticle cohesive forces

Granular Matter - The arrangement of calculation samples with a high initial solid fraction and lower computation times are the primary concern of discrete element simulations. When generating...     

A numerical method for non-linear flow about a submerged hydrofoil

Summary A numerical method is presented for computing two-dimensional potential flow about a wing with a cusped trailing edge immersed beneath the free surface of a running stream of infinite depth. The full non-linear boundary conditions are retained at the free surface of the fluid, and the conditions on the hydrofoil are also stated exactly. The problem is solved numerically using integral-equation techniques combined with Newton's method. Surface profiles and the pressure distribution on the body are shown for different body geometries.     

Discrete element modelling of railway ballast

The discrete element method has been used to simulate the behaviour of railway ballast under different test conditions. Single particle crushing tests have been simulated using agglomerates of bonded balls, and the distribution of strengths correctly follows the Weibull distribution, and the size effect on average strength is also consistent with that measured in the laboratory. Realistic fast fracture can be obtained if non-viscous damping is reduced. Oedometer tests on aggregates of crushable ballast particles have also been simulated and compared with the results from laboratory tests. Finally, box tests which simulate traffic loading have been simulated using both spherical balls and 8-ball clumps. It is found that the 8-ball clumps give much more realistic behaviour due to particle interlocking.     

Calculation of particle collisions in concomitant dispersed flows

Relationships are obtained for the relative fraction of the number of particle collisions in concomitant dispersed flows by means of a probability model, and they are verified experimentally.     

A displacement-based geometrically non-linear constant stress element

A triangular geometrically non-linear constant stress element is presented, applicable to thin-shell problems involving finite rotations. The element has the same degrees of freedom as the linear element following from the superposition of the constant strain triangle and the constant moment triangle. In the derivation of the non-linear strain-displacement relations, special attention is given to the correct representation of the rigid body motions of a patch of elements. Based on a second-order out-of-plane displacement field, an initial deflection is introduced. This improves the effectiveness of the element, since curved shell geometries can be described more accurately. Several demonstrative examples are included.     

Mathematical modeling of particle growth

Continuity equations for particle distributions by size and residence times are considered in processes associated with particle growth. The relation between these equations and the particle-balance equation in phase space is shown.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 32, No. 2, pp. 346–349, February, 1977.     

Discrete element method simulation analysis of the generation mechanism of cooperative behavior of disks falling in a low-density particle bed

Pacheco-Vázquez and Ruiz-Suárez reported an interesting cooperative behavior for disks falling in a particle bed. This behavior involved the formation of upward and downward convex configurations during the falling of five steel disks into a bed of polystyrene particles. We used discrete element method simulations to investigate the generation mechanism for this cooperative behavior. Particles with a diameter of 5.0 mm and a density of 14.0 kg/m³ were placed randomly in a container with a width of 900 mm or 2700 mm and a height of 2700 mm. Model spheres with the same mass and diameter as the steel disks with a diameter of 25.4 mm and a thickness of 5.0 mm were then dropped into the particle bed, and we investigated the cooperative behavior of the model spheres. Similar cooperative behaviors were observed for the containers with widths of 900 mm and 2700 mm, indicating that the container side walls do not affect the occurrence of this behavior when the width is larger than 900 mm. The falling velocity of each disk was strongly dependent on the packing fractions over the disk and the flow velocity of the bed particles around the disks. Based on these results, the generation mechanism of the upward and downward convex configurations is discussed.