Computational Particle Mechanics最新文献

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%.

Abstract

The Eulerian–Lagrangian approach is commonly employed in particulate flows, which can be classified into two subcategories: unresolved computational fluid dynamics-discrete element method (CFD–DEM) and resolved CFD–DEM. When the particle sizes are comparable to the cell sizes, the interphase coupling is not straightforward anymore and both the conventional unresolved CFD–DEM and resolved CFD–DEM are not applicable. In this paper, we propose a simple and novel coupling method for projecting and reconstructing the particle and interphase quantities, which is also called semi-resolved CFD–DEM. The particle quantities are uniformly distributed to the surrounding cells by expanding the fluid domain. The fluid phase quantities at the particle location are also reconstructed from the surrounding cells. Then, the relative velocity and the local void fraction for calculating the drag force are corrected. The expanding factor for the fluid domain is determined by comparing the drag force of the semi-resolved CFD–DEM with the resolved CFD–DEM results. It is found that the expanding factor increases linearly with the autocorrelation length. The developed method is validated by the simulation of a particle sedimentation and a sediment transport process, which proves that the present semi-resolved CFD–DEM fills the gap between the resolved and unresolved CFD–DEM. The difference between the implicit and explicit treatment of momentum exchange term is also discussed, and the explicit treatment shows better performance for large particles.

A Correction to this paper has been published: 10.1007/s40571-023-00602-0

To reveal the relationship between tool geometries and process parameters in Powder Bed Fusion (PBF), discrete element method is utilized for numerical simulation of PBF. The powder bed flatness and coefficient of variation are proposed to evaluate the quality of the powder bed. Results indicate that the powder bed voidage increases with the increase in the gap height, the decrease in the velocity and the increase in the blade fillet radius. When the blade inclination angle decreased from 45° to 30° and the average powder diameter is decreased from 50 to 30 μm, the porosity of the powder bed is decreased by 3.47% and 8.19%, respectively. The voidages in PBF with blade, roller and blade-roller are 55.78%, 49.08% and 47.57%. When the gap height is higher than 0.15 mm, the voidage in case of roller is obviously smaller than that in case of blade. The optimized combination of the parameters and tool can improve the powder bed flatness by 4.29% and reduce the voidage and coefficient of variation by 0.77% and 2.26%.

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.