Computational Particle Mechanics最新文献

In this study, the influence of fractures on the mechanical properties and cracking behavior of composite rock mass was investigated by preparing rock-like specimens of composite rock mass with different dip angles of fractures using customized molds. The failure process of the sample was recorded using a camera, and the rock failure process analysis technology was used for quantitative investigation of the mechanical mechanism of crack evolution during the loading process of the sample. Based on the experimental results, the crack propagation and coalescence modes of fractured composite rock mass were analyzed, and the distribution laws of contact force chain and maximum principal stress during initial crack initiation were studied from the microscopic perspective. The results show that with the increase in fracture dip angle, when the fracture is located in hard rock, the peak strength of the specimen decreases first, then increases and then decreases. When the fracture is located in both soft rock and hard rock, the peak strength of the specimen is mainly controlled by the fracture in soft rock. The initial crack mainly occurs at the tip of the soft rock fracture, and then converges with the cracks developed at the end of the hard rock fracture through the interface. The crack propagation type and coalescence mode are affected by the joint action of the fracture dip angle and position. In total, eight crack propagation types and six crack coalescence modes were observed during the failure process. The maximum principal stress concentration area is distributed around the fracture and is “butterfly” type. With the increase in fracture dip angle, the maximum principal stress concentration area gets gradually deflected perpendicular to the fracture direction, and does not pass through the interface of soft and hard rocks. The existence of the interface prevents the transmission of stress to a certain extent.

The mixing phenomenon of particles in a tilted tumbler is studied by the SIPHPM simulation. The particle motion in the tilted tumbler with three rotating velocities ω = 1π, 1.5π and 2π rad/s at tilt angles of α = 5°, 10°, 15°, 20°, 25°, 30°, 45° and 60° are simulated. We propose a construction principle of mixing indices depending on particle concentration. The mixing degree of these cases is evaluated by the new construction-principle-based mixing indices (NCPBMI). In addition, a modified formula is added to the construction principle, so that it can be used to evaluate the particle system with various particle sizes, and the difference between the two calculation methods of the total mixing index in the new mixing index construction principle is compared. In addition, the differences in the application range of various mixing indices are summarized. It is found that the influence of inclinations on the axial mixing of cubic particles in the inclined tumbler varies. At low inclinations, the particle system hardly mixes; at medium inclinations, the inclination plays a positive role in mixing; at high inclinations, the positive influence of inclination on mixing decreases. Also, the rotating speed is a negative factor for cubic particle mixing.

This study employs numerical simulations to scrutinize the influence of pre-existing fractures and in situ stress states on blast-induced crack propagation in fractured rocks. The geomechanical behavior of fractured rocks is simulated via a particle-based discrete element model with particles constructed and assembled by the Voronoi tessellation scheme based on the grain-size distribution of actual rock samples (specifically, Beishan granite), which captures solid vibrations under dynamic loading and realistically responds to crack growth and fracture displacement. The reliability of the model is also validated using Snell’s law and fracture mechanics. Based on the model, the effects of stress states and fracture configurations (such as single isolated fracture and two interacting fractures) on damage evolution are examined. It was observed that when the differential stress is aligned (or perpendicular) with the blasting wave, it amplifies (or reduces) the damaging effect of the blasting wave on the rock mass in most instances. The effect of the differential stress on the blasting wave is similar to that of an increase (or reduction) in the amplitude of the blasting wave. When the differential stress exceeds the tensile cracking stress, rock damage sharply escalates due to the generation of a plastic region, regardless of the angle between the blasting wave and differential stress. Meanwhile, a study of two interacting fractures reveals that differences in fracture geometry lead to different stress concentration and shadow zones in the specimen. This changes the location and extent of crack development and ultimately affects the strength of the rock. The findings from our simulations provide critical insights for understanding and characterizing excavation damage zones around underground excavations in fractured crystalline rock obtained by drilling and blasting methods and also provide safety predictions for constructed neighboring structures under dynamic loads.

This paper addresses the critical issue of leading edge erosion (LEE) on modern wind turbine blades (WTBs) caused by solid particle impacts. LEE can harm the structural integrity and aerodynamic performance of WTBs, leading to reduced efficiency and increased maintenance costs. This study employs a novel particle-based approach called hybrid peridynamics–discrete element method (PD–DEM) to model the impact of solid particles on WTB leading edges and target material failure accurately. It effectively captures the through-thickness force absorption and the propagation of stresses within the leading edge coating system composed of composite laminates. The amount of mass removed and the mean displacement of the target material points can be reliably calculated using the current method. Through a series of tests, the research demonstrates the method’s ability to predict impact force changes with varying particle size, velocity, impact angles and positions. Moreover, this study offers a significant improvement in erosion prediction capability and the development of design specifications. This work contributes to the advancement of WTB design and maintenance practices to mitigate LEE effectively.

The paper aims to study the mechanical characteristics of disintegrated carbonaceous mudstone in a triaxial stress state from a micro-perspective of particles. Based on the discrete element method (DEM), a spherical-polymer (SP) model that includes three different types of the particles (triangle-like, rectangle-like, and sphere) was proposed and combined the error diagram with R² to analyze the difference between the SP model and Ball–Ball (BB) model. Meanwhile, a sensitive analysis of micro-mechanical characteristics was carried out, which quantitatively described the sensitivity of different parameters according to stress–strain curves. The processes of deformation and failure for the disintegrated carbonaceous mudstone were finally analyzed based on the displacement diagram of the particle according to the energy theory. The results suggest that the SP model could better reflect the mechanical characteristics of disintegrated carbonaceous mudstone, for the SP models, the correlation coefficient (R²) range was larger than the BB model. From the sensitivity analysis of parameters, the decreasing rate of initial deformation modulus was 56–66% as the stiffness ratio was modified when fixing other factors. The peak strength correlated well with the tensile-shear strength ratio, stiffness ratio, and friction coefficient. The modification of abnormal-shaped particles’ volume fraction ratio could affect the peak shear strength significantly. For the disintegrated carbonaceous mudstone, the processes of deformation and failure were discussed by energy transference which particle elements go from a low-energy state to a high-energy state.

Deep-sea mining lifting pump differs from conventional solid–liquid two-phase flow pump, due to the complex and ever-changing operating environment. It is more likely to experience emergency shutdowns and particle reflux, leading to pump blockage and ultimately causing damage to the lifting system. Research on the influence of particle characteristic parameters on pump reflux performance can provide theoretical support for the design of high-performance deep-sea mining lifting pumps. The impact of particle size on the reflux performance of a mining lifting pump during shutdown was investigated in this study. The coupling method of CFD–DEM (computational fluid dynamics–discrete element method) was employed to simulate the reflux of spherical particles with different sizes (5 mm, 6 mm, 7 mm), and comparative analysis was conducted to the reflux performance of particles with varying sizes in the lifting pump. The results indicate that particles tend to accumulate at the junction between the impeller and guide vane when reflux occurs in the lifting pump. As the particle size increases, the distribution of particles in the first and second-stage pump becomes denser, resulting in less smooth reflux inside the pump and noticeable clogging. Moreover, particle accumulation gradually extends into the flow channel of the impeller and guide vane. The average velocity of particles gradually decreases with larger particle sizes; this leads to an increase in the time it takes for particles to pass through the pump and a gradual deterioration in the reflux performance of the lifting pump. Further analysis indicates that the ratio of collision number between particles to the total number of collisions increases continuously with the increase in particle size. Additionally, as the particle size increases, the proportion of collisions between the particles and the second guide vane significantly increases.

Sand erosion in pipelines during offshore oil and gas exploitation and transportation can lead to serious equipment failures, considerable economic losses, and environmental burdens. Accurate prediction of sand erosion in these pipelines, especially near elbow sections, is crucial to reduce pipeline failure. In this study, the CFD-DPM method verified by experiment data is used for numerical simulation. The effects of particle size, shape, and fluid viscosity on elbow erosion have been discussed. The results show that the maximum erosion rate decreases exponentially with the increase in fluid viscosity. It shows a decrease first and then increases with the increase in particle diameter, and an opposite trend with the increase in particle shape factor. More importantly, the correlation between the maximum erosion position of the elbow and the Stokes number has been derived. Our work is expected to provide theoretical guide for anti-erosion design strategy for submarine pipelines.

A modified apparent viscosity approach has been implemented for a weakly compressible SPH scheme for two-phase flows where a nonlinear phase must yield under erosive dynamics but also maintain a pseudosolid behaviour under the right conditions. The final purpose is to provide a means to model both dam-break dynamics and erosive interactions between different phases simultaneously while also keeping smooth pressure fields in spite of discontinuities introduced by viscosity variations of a nonlinear phase along with significant differences in mean density. Key contributions include purposeful avoidance of nonphysical elastic behaviour and the integration of a specific particle shifting technique that allows for proper replication of erosion and scouring. In this work, the method is validated by applying it to model a silted-up dam that collapses over a static water bed, effectively including all main elements of interest. Although the formulation is inherently three dimensional, validation is done by direct comparison with data from physical experiments of a dominant two-dimensional nature, assuming variable yield stress of medium-grain quartz sand according to the Drucker–Prager equation. Overall results show most of the expected interface dynamics, such as erosion and transportation of the nonlinear phase, sustained piling of the non-yielded volume of silt, and good correspondence of both granular and water surface position with experimental data. Finally, a series of modelling assumptions and implications for future developments are explicitly stated because of their direct impact on stability and versatility for multiphase, nonlinear flows in general.

Shear cutting introduces residual strains, notches and cracks, which negatively affects edge-formability. This is especially relevant for forming of high-strength sheets, where edge-cracking is a serious industrial problem. Numerical modelling of the shear cutting process can aid the understanding of the sheared edge damage and help preventing edge-cracking. However, modelling of the shear cutting process requires robust and accurate numerical tools that handle plasticity, large deformation and ductile failure. The use of conventional finite element methods (FEM) may give rise to distorted elements or loss of accuracy during re-meshing schemes, while mesh-free methods have tendencies of tensile instability or excessive computational cost. In this article, the authors propose the particle finite element method (PFEM) for modelling the shear cutting process of high-strength steel sheets, acquiring high accuracy results and overcoming the stated challenges associated with FEM. The article describe the implementation of a mixed axisymmetric formulation, with the novelty of adding a ductile damage- and failure model to account for material fracture in the shear-cutting process. The PFEM shear-cutting model was validated against experiments using varying process parameters to ensure the predictive capacity of the model. Likewise, a thorough sensitivity analysis of the numerical implementation was conducted. The results show that the PFEM model is able to predict the process forces and cut edge shapes over a wide range of cutting clearances, while efficiently handling the numerical challenges involved with large material deformation. It is thus concluded that the PFEM implementation is an accurate predictive tool for sheared edge damage assessment.

Numerical simulations were performed to study the particle shape effect on the particle-scale diffusion and mixing behavior in the mixer driven by the rotating paddles. Four shapes of particles, the sphere, the prolate spheroid, the oblate spheroid, and the cube, are simulated. Velocities, flow blockages, and diffusion of particles are analyzed. The mixing index is applied to quantitatively evaluate the mixing. Numerical results show that the circumferential velocity in the above-paddle region is much greater than in the paddle region. Compared to other shapes, the cubic particles have less movement in low velocity and more in high velocity. The cubic shape, rather than the ellipsoidal shape of different aspect ratios, plays a non-negligible role in flow blockage. For particle diffusion, the mean square displacement (MSD) varies linearly with time for the sphere, the prolate, and the oblate spheroids. The average diffusion coefficient is about 6.5 × 10^-5 m²/s. In contrast, the MSD of the cubes is greater than the other shapes, and a sub-diffusion phenomenon is observed. The mixing index increases with time and reaches approximately a steady value of 0.9 after 3.0 s. Because of the different particle–wall interactions, the mixing indices of the cube, the prolate, and the oblate spheroids in the mixer are less than those of the sphere. Finally, radial mixing and axial mixing are evaluated by the eight kinds of mixing functions. These mixing functions and their time-averaged values show that the cubic particle has significantly different features of mixing. Its radial mixing is stronger than other kinds of shapes. Also, the cube’ axial mixing upward is weaker whereas the mixing downward is the strongest.