Computational Particle Mechanics最新文献

An ASTM B213 standard Hall Flowmeter Funnel experiment was conducted for Ti 6–4 powder particles and simulated utilizing a discrete element method approach implemented in the LIGGGHTS package. Particle interactions were described with a modified simplified Johnson–Kendall–Roberts theory that includes adhesion as a function of the particle surface free energy. Experimental data for the powder particle size distribution were used as input for the simulations. Adjustable parameters, such as cohesion energy density, coefficient of restitution and dynamic friction, were tuned to match the general shape of the experimentally obtained particle pile. Geometrical properties of the simulated powder pile, including its diameter, height and inside/outside slope angles, were computed and compared with the experimental results where available. Local particle size distributions for different areas within the pile (top vs. bottom) were obtained, indicating the dominance of larger particles at the top of the pile, akin to the Brazil nut effect.

Migration of particles in porous media is confined by the structure of the porous media, which results in the clogging of particles in porous media and the alteration of the topology of porous media. Particle clogging is primarily determined by the size of particles and topology of porous media. The recent micro-scale research on the migration of mono-size particles in the saturated porous media showed that the particle clogging occurred when the Stokes number of particles in the porous medium was larger than 1, and the local volume fraction and diameter of particles were higher. In this study, the fluid dynamics of poly-dispersed particles were studied on migration and clogging of particles in a porous medium. The effect of the larger particles in poly-dispersed particles was investigated and discovered to be the primary element determining the fluid dynamics and clogging of poly-disperse particles in porous media. The particle clusters with larger particles surrounded by smaller particles and velocity difference between each size of particles in poly-disperse distribution can increase the local volume fraction of particles and result in the particle clogging.

The generation and propagation of cracks are influenced by dynamic loading stresses induced by different fracturing methods. In order to investigate the influence of dynamic loading stress rate on the crack propagation and crack distribution characteristics, theoretical analysis and numerical simulation were used to study the crack propagation mechanism and distribution state of the rock, and zoning standards for different loading stresses were proposed. The form of fracture around the borehole is determined by the peak value of dynamic loading stress and the dynamic strength of the rock, while the number of rock fractures is influenced by the propagation rate of dynamic loading stress and the dynamic path of unloading wave propagation. Under high-stress and rapid dynamic loading, the rock around the borehole undergoes dynamic compression failure. For moderate dynamic loading, the rock mass experiences initial fracture due to tensile stress, leading to the generation of multiple radial cracks through the combined action of shock and unloading waves. Under quasi-static loading, the rock mass undergoes tensile failure under tensile stress and is effectively unloaded. Based on the peak value of dynamic loading and loading time, different fracture modes are divided into crushing fracture zone, multiple fracture zone, and single fracture zone. The relationship between the characteristics of rock fragments and loading stress was determined, and the fractal method was used to describe the distribution characteristics of cracks. The effects of loading rate and rock fragmentation were finally discussed, providing guidance for the selection and utilization of different fracturing methods.

Abrasive waterjet (AWJ) is a technology that removes a target material with an abrasive accelerated by ultra-high-pressure water. Recently, its application for rock excavations in civil and geotechnical engineering has increased. AWJ excavation performance is affected by the abrasive velocity formed by momentum transfer during mixing and acceleration. The abrasive velocity varies owing to changes in the abrasive flow rate, focusing tube diameter, and focusing tube length. In this study, the momentum transfer efficiency (MTE) according to the abrasive flow rate and focusing tube geometry was investigated by a numerical analysis to better understand the multiphase flow inside the AWJ system. The MTE was defined based on the theoretical relationship between the abrasive velocity ratio and focusing tube factor, and evaluated through the empirical relationship between the water stiffness and focusing tube length. The optimal abrasive flow rate for generating efficient MTE was approximately 15 g/s, which enabled economical and effective acceleration of abrasive particles. Accordingly, a prediction model based on the derived MTE was developed for the final abrasive velocity generated at the tip of the focusing tube. Using the prediction model, it is possible to evaluate the comprehensive relationship between various AWJ parameters. Based on the prediction model, the abrasive–water flow ratio to generate the optimal abrasive velocity was 0.83. The developed prediction model provides guidelines for selecting the optimal focusing tube geometry and applying an economical abrasive flow rate when designing an AWJ system.

This study focuses on the build-up of residual stresses of cohesive-frictional materials under moving surface loads, and corresponding micromechanisms are studied in particle scales using discrete element methods. The numerical procedure is validated with macroscopic residual stresses obtained by experimental tests and finite element methods. It is found that residual stresses are dominated by normal contact and normal bond forces, and strong force chains make a leading contribution to build-ups of residual stresses. A further study indicates that the increase of averaged interparticle forces is a critical factor to growths of residual stresses, which is generally accompanied with decreased proportions of contacts carrying small forces. Simultaneously, the averaged magnitude of interparticle forces belonging to single orientations generally grows with developments of residual stresses, and for resultant forces it distributes almost isotropically. Nevertheless, because of gradual developments of residual stresses, macroscopic stress fields should be anisotropic, which is subsequently validated to be dominated by the fabric anisotropy.

In this work, the incompressible smoothed particle hydrodynamics (ISPH) method is utilized to simulate thermosolutal convection in a novel annulus barred by NEPCMs. The novel annulus is formed between a horizontal curved rectangle connected to a vertical rectangle containing a vertical ellipse. It is the first attempt to investigate the heat and mass transmission of NEPCM in such a unique annulus. NEPCM’s sophisticated designs of closed domains during heat/mass transfer can be applied in energy savings, electrical device cooling, and solar cell cooling. The ISPH method solved the fractional time derivative of governing partial differential equations. The artificial neural network (ANN) is integrated with the ISPH results to predict the average Nusselt (overline{{text{Nu}} }) and Sherwood numbers (overline{{text{Sh}} }). The scales of physical parameters are Hartmann number (Ha = 0–80), buoyancy ratio parameter (N = − 10–20), Dufour/Soret numbers (Du = 0–0.4 & Sr = 0–0.8), Rayleigh number (Ra=10³–10⁵), fractional time derivative (α = 0.85–1), nanoparticle parameter (φ = 0–0.15), and fusion temperature (θ_f = 0.05–0.95). The main findings showed the importance of buoyancy ratio and Rayleigh number in enhancing the buoyancy-driven convection which accelerates the velocity field and strengths the isotherms and isoconcentration. The velocity field decreases according to an enhancement in Hartmann number and nanoparticle parameter. The exact agreement of the ANN model prediction values with the goal values demonstrates that the created ANN model can predict the (overline{{text{Nu}} }) and (overline{{text{Sh}} }) values properly. The complicity of a closed domain by carving the horizontal rectangle and inserting the ellipse inside a vertical rectangle can be utilized into cooling equipment, solar cells, and heat exchangers.

The particle–wall collision behavior plays a crucial role in determining particle motion during the simulation of multiphase flow processes. The coefficient of restitution (COR) is generally used to characterize the particle–wall collisional behavior. Correct consideration of COR is essential for obtaining accurate results in numerical simulations. In the present work, the COR during the normal impact of a rigid prolate ellipsoidal particle on the target wall is investigated using the finite element method. The loss in kinetic energy of the particles after impact is used to analyze the COR. The simulations are conducted with a particle of sphericity 1, 0.9, 0.8, 0.7, and 0.5 impacted at different orientation angles (angle between particle major axis to the horizontal plane) in the range 0°–90°. The effect of particle sphericity, particle orientation before impact, impact velocity, and target surface material on COR is determined. Further, an understanding is established on the deviation in COR for the impact of non-spherical particles as compared to the COR for the impact of spherical particles. The insights gained from this study are valuable for accurately predicting the motion of non-spherical particles in multiphase processes using the discrete element method.

Some numerical simulations of drained and undrained triaxial tests on granular materials with different initial densities are carried out with the three-dimensional discrete element method. An in-depth particle-scale analysis is performed quantitatively to illustrate the physical mechanism of the shear mechanical behaviors, with a special attention paid to the characteristics of quasi-steady state and critical state. The simulation results show that the initial density and shear drainage condition both have significant effects on the evolution of stress–strain, coordination number, fabric anisotropy factor, force chains and clusters. The chained grains ratio and the mean length of force chains in the specimens are constantly adjusted to bear and transfer the changing external loads. The transitions between small clusters and large clusters are also continually taking place in varying degrees, correlating to volumetric contraction or dilation. For the loose undrained triaxial specimen presenting quasi-steady state during shearing, the coordination number decreases obviously to nearly 4 and then increases again; the chained grains ratio decreases after a slight increase in the initial loading stage, and then begin to increase again after a period of lower value of around 0.285; the volume ratio of small, submedium and medium clusters all first decreases and then increase gradually, meanwhile volume ratio of large clusters increases sharply to as much as 0.28 and then decreases gradually. The macroscopic critical state of granular materials is a comprehensively external manifestation when the microscopic coordination number and mesoscopic force chains and clusters all evolute to a dynamic equilibrium. At the critical state, the deviator stress, void ratio, coordination number, fabric anisotropy factor, and the volume ratio of small clusters and large clusters all manifest a respectively unique linear relationship with the mean effective stress.

This study proposed a novel fluidized bed (NRFB) accompanied by grid trays, air distributor, and other internals, which can realize the continuous production of gas–solid non-catalytic reactions. In the reactor, the reverse flow of the gas–solid phase enabled the solid particles to contact efficiently with the gas and to produce solid particles. The discrete phase model was used to simulate the characteristics of the gas–solid two-phase flow and distribution in NRFB with different types of air distributors and different amounts of grid trays. The improved equal-area torus method and the uniformity index were used to quantitatively investigate the particle’s time-average radial concentration in NRFB. The results show that the air distributor can effectively ensure the uniform distribution of gas in the discharge area in NRFB. “Core-annulus” structures occur in the dense phase section in the NRFB without grid tray. The radial distribution uniformity of particle concentration can be improved by about 17% with 9 grid trays installed in NRFB, and more particles would stay in the dense phase section, which is more suitable for reaction, which can effectively improve the reaction efficiency. The guidance for the construction of experimental equipment and fluidization operation can be provided by the results, which are of great significance for the continuous production of “gas–solid non-catalytic reactions” in fine chemical industries.