Computational Particle Mechanics最新文献

Tunnel excavation in weak surrounding rock areas is prone to landslide accidents, and the use of high-pressure rotary piles to pre-strengthen the soil in the local area can enhance the strength and bearing capacity of the surrounding rock. Discrete lattice spring model is established with the three-dimensional morphology modeling system of the rotary pile reinforcement. It is used to quantitatively characterize the reinforcement effects of high-pressure rotary piles, to analyze the influence of the reinforcement ratio and reinforcement function. The results show that compared with the deformation of unreinforced stratum, the high-pressure rotary pile can better control the ground surface settlement. The larger the reinforcement ratio is, the better the reinforcement effect of the rotary spray pile is, especially with the increase in reinforcement ratio, the contact between individual piles bites to form a row of piles, which can significantly improve the ability of the formation to resist deformation. Under the same reinforcement situation, the square root type reinforcement function has the best reinforcement effect, the line function has the middle reinforcement effect, and the quadratic type reinforcement function has the worst effect.

This research investigates how inserting notched gypsum filling between granite specimens affects their breakage under uniaxial compressive testing. Various thicknesses of gypsum filling slabs were placed between granite specimens, incorporating different dimensions and notch configurations. The investigated parameters include elastic modulus, Poisson’s ratio, uniaxial compressive strength, and Brazilian tensile strength of 5 GPa, 0.18, 7.4, and 1 MPa, respectively. Compression testing, at an axial load rate of 0.05 mm/min, was conducted on a total of 9 different models. Numerical simulations were performed on models with notched gypsum filling, varying thicknesses, and notch angles using Particle Flow Code in 2D. The results demonstrated that breakage behavior was primarily influenced by filling thickness and notch angle. The uniaxial compressive strengths in samples were found to be affected by fracture patterns and the breakage mechanism of the filling. The study revealed that the behavior of discontinuities is influenced by the number of induced tensile cracks, which increase with thicker filling. Acoustic emission (AE) hits during loading’s initial phase, a rapid increase in AE hits before the applied stress reached its peak, and significant AE hits accompanying each stress drop were observed. The breakage patterns and strengths were found to be similar in both experimental and numerical approaches.

With the increasing number of projects in cold regions and the widespread use of artificial freezing methods, conducting research on the dynamic properties of frozen soil has become a considerable issue that cannot be avoided in permafrost engineering. Currently, the numerical simulation research on the dynamic mechanical behavior of frozen soil is less concerned with the changes in stress, strain, and particle damage inside the material. The necessary conditions for conducting this study are compatible with the core idea of smooth particle hydrodynamics (SPH). In this study, the Eulerian SPH method was modified to address numerical oscillations and errors in solid mechanics, particularly impact dynamics problems. A numerical scheme for simulating the split Hopkinson pressure bar test was developed within the modified Eulerian SPH framework and implemented using self-programming. The frozen soil dynamic mechanical behavior was simulated under three strain rates. The accuracy and superiority of the SPH method were verified through calculations and experiments. The simulation captures the stress and strain responses within the sample at different moments during the impact process, indicating that the frozen soil strain rate-strengthening effect resulted from microcrack expansion and inertial effects.

Rock bridges are important structures for maintaining rock mass stability, but their shapes are not well known. The researchers propose a method for determining the shape of rock bridges based on experiments, discrete element methods and machine learning, which is applicable to complex joints with arbitrary spatial distribution. Numerical models are constructed using the discrete element method, and parameter matching is performed based on experimental results. The particles were clustered using the k-means algorithm with the maximum principal stress (σ₁) as an indicator and the selection of initial values was optimized. The density-based spatial clustering of applications with noise (DBSCAN) algorithm was used to delete the noise from the particles. Finally, the boundary lines of the particles were extracted by self-programming, and the shape of the rock bridges was determined. Twenty-four sets of simulations were used to analyze the effect of rock bridges on the specimens. The results show that the failure mode of the specimen changes from shear to tensile damage as the cohesive force of the rock bridges increases. The peak strength and peak strain of the specimens increased with the increase of cohesion in the rock bridge. Rock bridges are the fastest growing areas of stress in the specimen.

Abstract

Railway ballast modeling can be performed by different approaches, through continuous or discrete models, which have their comparative advantages and disadvantages, such as excessive volumes of material for testing and calibration steps. This paper aims to adapt and propose the use of the Hybrid Lattice-Discrete Element Method for modeling railway ballast aggregates. The advantages of using this technique for this purpose are: (i) one-step calibration of the rock material from laboratory test results; (ii) simulation of fractures in rock materials; (iii) visualization of micromechanical phenomena, such as particle slippage and fracture modes; (iv) realistic representation of various geometries compared to the conventional use of the Discrete Element Method. First, parameter calibration was performed from laboratory test results on granite rock obtained from the literature. Then, particle generation, Voronoi discretization and packing algorithms were used to build models of railway ballast samples. These models were used to simulate mechanical tests, namely single particle compression, confined uniaxial compression, monotonic triaxial compression and cyclic triaxial compression. There was consistency between the results and the empirical observations reported in the literature. In addition, variations in particle size distribution were observed during the simulations, as well as the causes of failure in each specimen, either by shear or particle breakage, in addition to the fracture modes of the ballast aggregates. By analyzing these elements together, knowledge is obtained about the phenomena occurring inside the railway ballast under different loading conditions, in addition to the results of strength, failure and deformation. Finally, it is concluded that the proposed method is effective for modeling railway ballast, besides being versatile, allowing to simulate the material for different loading configurations and boundary conditions.

Since most of the current researches on the crushed-rock interlayer for highway embankment in permafrost region are based on thermal properties, there are few studies on their mechanical deformation characteristics. In order to study the deformation and failure process of crushed-rock interlayer under the long-term settlement deformation of permafrost foundation and to fully consider the discrete characteristics of the crushed-rock interlayer, the finite element model and discrete element model were coupled in this study to accomplish the numerical calculation of long-term settlement deformation of crushed-rock interlayer highway embankment as well as permafrost foundation. The results show that as for the granite blocks adopted in the Gonghe–Yushu expressway, the blocks in the interlayer would be rarely broken, and the deformation of crushed-rock interlayer is mainly caused by the relative movement and rearrangement of the blocks. Based on the calculation results, it is suggested to adopt the uncompacted randomly piled crushed-rock interlayer, which is composed of crushed blocks with more sharp corners. When the size of block varies from 20 to 40 cm, the block size has no obvious effect on the deformation of crushed-rock interlayer, and therefore, the block size could be determined only by the cooling effect of crushed-rock interlayer. At the meantime, the structure layer above the crushed-rock interlayer should also be rigid enough to ensure a smaller uneven settlement value for the superstructure.

A new kinetic particle modeling framework was developed to investigate electrostatic transport of lunar regolith dust particles with applications to the concept of electrostatic sieving. The new approach is based on kinetic particle dynamics and includes major modules of sampling the particle size distribution, solving electric fields, and tracking motion of charged dust grains. A case study for a concept of electrostatic sieving was chosen to validate the new model. The simulation achieved similar performance of particle size classification as reported in the literature. The new model is computationally efficient (takes a few minutes on a PC-type laptop computer) so that researchers can use it as a design and analysis tool to explore large parameter space for system optimization.

A novel implicit material point method (MPM) using a cell-based integration scheme is proposed to solve large deformation static problems. An incremental weak form based on the updated Lagrangian approach is formulated for the implicit MPM. The volume integrals of the incremental weak form are evaluated at the integration points of grid cells instead of material points, which eliminates the cell-crossing error and reduces the integration error in MPM computations. Grid cells are equally sub-divided into grid cell sub-domains. The centers and the particle volumes of the grid cell sub-domains are, respectively, taken as the integration points and corresponding weights for the numerical integration of the incremental weak form. Particle information is transferred through grid nodes to the integration points of grid cells by using grid shape functions. A volume-weighted nodal averaging scheme is used for transferring the deformation gradient from material particles to grid nodes to correctly consider the particle volumes associated with the deformation gradient. Numerical results show that the present implicit MPM can effectively and efficiently solve large deformation static problems.

Abstract

Using ionized fluids in a magnetic field has numerous applications in engineering and industry. Therefore, heat transport in ionized fluids with thermal memory effects should be predicted using numerical simulations. To achieve this objective, the generalized heat transport in ionized fluid (following a cross-rheological constitutive relation) is modeled, and the governing system is solved numerically using the Galerkin finite element method (GFEM). After the successful implementation of GFEM, the solutions are made grid-independent and convergent. Furthermore, the results are validated with existing literature. Our numerical results show that the memory effects are favorable factors in enhancing heat transport. The Joule heating and heat generation are the characteristics that adversely affect thermal performance. Therefore, heat-absorbing and non-Ohmic dissipative fluids are recommended for optimized heat transport. Similarly, using ionized fluid in the presence of a magnetic field is recommended, as Hall and ion slip currents significantly reduce the Ohmic dissipation in the fluid during heat transport. Hall and ion slip currents induced by the movement of ionized fluid subjected to a variable magnetic field tend to cancel out the retarding effects of Lorentz force, due to which the friction force between fluid particles and the solid surface is reduced. Thus, it is concluded that if stress at the surface caused by fluid movement is required to minimize, then ionized fluid is recommended as a working fluid for transporting heat. Thermal memory effects in mono-nanofluid are stronger than those in fluids with di- and tri-nanoparticles. Moreover, the heat transfer of fluid dispersed with tri-nanoparticles is the best working fluid for thermal efficiency in transporting heat.

This study is based on indoor experiments using PFC2D to conduct numerical tests on the uniaxial compression of layered rock masses with multiple sets of parallel rough joints at a loading rate of 0.1 m/s. The layered rock mass is composed of hard matrix and weak interlayer, with uniaxial compressive strengths of 45.43 MPa and 16.08 MPa and elastic moduli of 4.47 GPa and 3.20 GPa, respectively. This study numerically investigated the influences of bedding inclination α (0°–90°), joint roughness coefficient JRC (0–19.55) and anchor bolts on crack propagation, fracturing responses, crack initiation stress, mechanical properties, ultimate failure modes, and brittleness index for the rough layered rock mass. The results show that, with an increasing bedding inclination, the peak strength of the layered samples exhibits a “U”-shaped variation trend, first decreasing and then increasing. For the bedding inclination = 30°–75°, the peak strength increases with an increasing JRC. The failure modes of the sample are mainly influenced by the bedding inclination. For the bedding inclination = 0°–30° and 90°, the samples mainly experience tensile splitting failure. For the bedding inclination = 45°–75°, the samples undergo shear slip failure along the weak interlayer. The crack initiation stress of the layered samples first decreases and then increases with an increasing bedding inclination and increases with an increasing JRC. The peak strength and failure mode of the samples are both functions of the bedding inclination and JRC. Based on the different failure modes, a nonlinear strength failure criterion for the layered rock masses with multiple sets of parallel rough joints is established. Comparison with the experimental results shows that this criterion can better reflect the mechanical properties of layered rock masses. Anchor bolts can effectively increase the peak strength, reduce the brittleness characteristics, and restrict the shear slip deformation for the samples. The peak strength increases by 18.03–26.21% with an increasing initial anchoring force (0–20 MPa). When the anchoring force is 10 MPa, the peak strength of the anchored samples decreases first and then increases regarding the bedding inclination. Compared with the unanchored samples, the peak strength increases by 9.44–42.13% and the brittleness index decreases by 18.58–72.44%. The peak strength of the anchored samples increases with JRC. Compared with unanchored samples, the peak strength increases by 14.72–26.21%, while the brittleness index decreases by 69.05–73.19%.