Computational Particle Mechanics最新文献

The deep-buried rock is subjected to true triaxial stress states and is affected by repeated disturbance loads. The discrete element method was employed to investigate the mechanical behavior and fracture mechanism of marble under true triaxial cyclic loading and unloading. The particle-based marble model with the calibrated microparameters was established based on true triaxial compression. The true triaxial cyclic loading and unloading simulations with different stress states were conducted. The increase in intermediate principal stress results in significant deformation anisotropy. The brittle–ductile transformation characteristics are presented with the increase in minimum principal stress. The crack damage stress initially increases and subsequently decreases with the increase of equivalent plastic strain under different stress states. The plastic strain increments ratios exhibit prominent nonlinear variation during the progressive failure. The rock strength presents the asymmetric distribution by the effect of intermediate principal stress, and the minimum principal stress has an enhancing effect on strength. With the increase in intermediate principal stress or the decrease in minimum principal stress, that is, the effect of high differential stress, the failure plane changes from inclined to parallel to the direction of maximum principal stress. The microcrack numbers present the S-shaped increasing trend during the progressive failure. The increasing number of microcracks parallel to the direction of intermediate principal stress and the anisotropy of microcrack tendency are subjected to high differential stress.

The collapse of bubbles in hydraulic machinery has emerged as a prominent area of research. To grasp the interplay between bubbles, a model of double-bubbles is built. The bubble morphology, total pressure (P), and the center of mass displacement (L_com) are taken as research objects, and the influence temperature (T), and bubble radius (R), bubble distance (L) on bubble collapse is summarized. Results show that the distance between the bubbles is smaller, the total collapse time is longer. However, L_com increases when the distance is increased or decreased to some extent. Moreover, in the case of the double-bubbles model with r₁ = 10 Å, as the bubbles (r₂ = 7.5, 10, 12.5 Å) collapse, the released pressure gradually increases, then decrease, and the release pressure of the double-bubbles model (r₁ = 10 Å, r₂ = 12.5 Å) is 1.08 times that of the model (r₁ = 10 Å, r₂ = 15 Å). Based on the differential pressure parameters (∆P₁ and ∆P₂), the significance order of temperature (T), bubble distance (L), and bubble radius (r) is L ≈ r > T. The aim of the paper is to provide technical guidance and a theoretical basis for industrial applications of techniques by enhancing the theory of cavitation.

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.