Computational Particle Mechanics最新文献

A three-dimensional grain-based model based on the discrete element method is proposed for reconstructing the filling and grouping of minerals in granite, then a batch of numerical disc specimens with different grain sizes R_G are subjected to the Brazilian splitting test. In addition, the force chain networks in the numerical samples are subjected to multi-level classification and quantitative analysis, and the grain size effect on the tensile mechanical behavior of granite is discussed from the perspective of force chain networks. The results show that the mechanical properties and micro-cracking behavior of fine- and coarse-grained samples obtained experimentally and from simulation are consistent, including the load–displacement curve, the peak load, the failure displacement, and the proportion of intergranular/transgranular cracks. Therefore, the reliability of the model is verified. As R_G increases, the number of intragranular contacts increases, while the number of intergranular contacts decreases. The bearing capacity and deformation resistance of the samples increase. As R_G increases, both the number and sum of force chains for intragranular structures increase gradually, while these two parameters for intergranular structures decrease; meanwhile, the average values for intragranular and intergranular structures increase with increasing R_G. As R_G continues to increase, the number of contacts within mineral grains capable of withstanding external loads increases, forming a robust force chain network to bear external loads. It becomes challenging for a low-level load to break the contacts within the mineral, leading to an increase in the sample’s load-bearing capacity.

This paper explores the numerical solution of the Fisher–Kolmogorov–Petrovsky–Piskunov (FKPP) equation through two meshless methods: a space–time cloud method and an explicit method employing generalized finite difference formulas (GFDM). The efficacy of the space–time cloud method in addressing this equation is demonstrated, and a comparative analysis with the results obtained from the explicit method using GFDM is conducted. The findings suggest that the space–time finite difference method delivers precise and stable solutions for the Fisher–KPP equation.

Many landslides occur on the slopes due to heavy rainfalls that are considered a major triggering reason. It is a novel study on simulating flood flow over a slope inside a partial layer of different porous structures. This work will serve in constructing the flood defense, coastal area defense, and preventing massive landslides. The mesh-free nature of the incompressible smoothed particle hydrodynamics (ISPH) method helps in handling the large deformation of nonlinear free surface flow over different porous structures. The ISPH simulation and the artificial neural network (ANN) model are used to anticipate wavefront tracking of dam breach flow over different porous materials. The precise alignment of the ANN model prediction values with the goal values shows that the current ANN model can accurately estimate wavefront tracking. The linear and nonlinear factors of non-Darcy porous media are applied in the momentum equation. The dam break over a porous structure in the horizontal plane is tested compared to the experimental data by the current scheme of the ISPH method. This test gives confidence in the adopted ISPH method. The simulations revealed that the porosity parameter plays a significant role in shrinking the wavefront of dam break over slopes. Once the fluid flow reaches a porous structure at approximately (t = 0.25) sec, the maximum velocity of the fluid decreases from (555) m/s to (30) m/s by (t = 4.0) sec. Physically, the reduction in porosity parameter enhances the porous resistance which slows down the free surface flow in the porous structures.

In this study, the shear behavior of the concrete-soft rock interface was simulated using PFC3D software and the results were compared with physical tests. While the interface between concrete and rocks has different geometries, concrete also penetrates the voids of the rock. The concrete and gypsum had tensile strengths of 1.2 MPa and 0.51 MPa, respectively. Samples with dimensions of 15 cm × 15 cm × 5 cm containing plaster and concrete layers were made. Concrete is located in the middle part of the sample, and its two sides are surrounded by plaster so that the concrete can penetrate the plaster. Nine different geometries for the concrete–rock interface were chosen i.e., the asymmetric zigzag interface, non-asymmetric zigzag interface, and planar interface. Nine different geometries for the concrete–rock interface were obtained by changing the concrete teeth height, concrete teeth base, and teeth angles. At the fixed interface, concrete penetrated into plaster in one, two, and three channels from each side. Twenty-seven different models are prepared. Samples using special templates, have been replaced in the UCS device and were tested under punch shear loading. Simultaneously by conducting experiments, numerical simulation was done. In such a way that the model and PFC software are calibrated and then numerical modeling of common shear behavior of concrete and rock takes place. The results showed that the fracture pattern of the rock-concrete interface was affected by concrete teeth geometry. In the samples without concrete teeth, a tensile fracture occurs at the interface; but with increasing roughness angle, in addition to tensile fracture, tensile cracks are formed at the tip of the roughness in the sample. By increasing the angle from 0 to 30, the number of tensile cracks in the sample increases. By increasing the concrete injection channels in the rock, the final fracture pattern does not change but crack initiation stress, shear stiffness, and final stress were increased. There is a good match between the experimental and numerical results.

Treating ballast and subgrade soil as an integrated unit for sampling and loading has proven to be an effective method for investigating the interaction between ballast and subgrade soil. Given that direct testing of specimens containing large ballast is constrained by the capabilities of standard laboratory equipment, adopting a model material of smaller size is recommended. Parallel gradation method is widely used for this purpose. This study performed an evaluation of parallel gradation method based on the response of ballast penetration into subgrade soil. Discrete element models were developed to simulate the penetration of crushed ballast, featuring three different parallel gradations, into subgrade soil. On this basis, dynamic triaxial simulations were conducted on these models. By comparing the macroscopic and mesoscopic mechanical characteristics at different scaling ratio, the applicability of the parallel gradation method for assessing ballast penetration into subgrade soil was evaluated. At the macroscopic scale, the scaling ratio of crushed ballast significantly influences the axial, volumetric, and lateral deformations observed during penetration into subgrade soil. Specifically, a smaller average grain size of ballast correlates with reduced deformations in these specimens. The penetration of crushed ballast into subgrade soil significantly increases the porosity of subgrade soil, particularly at the interface between ballast and subgrade. This increase in porosity is more pronounced with larger average grain sizes of ballast. At the mesoscopic scale, larger average grain sizes of ballast lead to more localized high contact forces and more significant stress concentrations. The parallel gradation method substantially affects the mechanical properties of ballast penetration into subgrade soil, at both macroscopic and mesoscopic scales. Therefore, a cautious approach is necessary when relying on this method for precise assessments.

Rockslide is a hot topic and universal phenomenon in the mountainous regions prone to geological hazards, which may pose substantial threats to property. The discrete element method (DEM) has been widely used to simulate the movement process of rockslide and avalanche. However, the rockslide involving jointed rock mass needs more adequate study to evaluate the safety implications effectively. In this paper, a series of DEM tests are conducted to study the movement and fragmentation of blocks with varying structure. The results show that at sliding angle of 45°, horizontal velocity reduces more slowly than vertical velocity because the particles move in a forward direction after impacting the bottom wall. The existence of a baffle structure limits sliding particle movement effectively and enhances the arch effect through the distribution of contact force chains. The number of joints, slope angle and sliding distance have considerable impact on bond breaking percentages and the displacement of the rock mass center. All bond break percentages are close to 90%, and number of joints and slope angle have little impact on the displacement of the rock mass center. This study can guide landslide disaster prevention.

Ejector deep hole drilling achieves high-quality boreholes in production processes. High feed rates are applied to ensure a high productivity level, requiring reliable chip removal from the cutting zone for a stable process. Therefore, a constant metalworking fluid flow under high volume flow rates or high pressure is required. Experimental results show a vortex formation at the outer cutting edge. This vortex can lead to delayed chip removal from the cutting zone, and ultimately, it can lead to chip clogging and result in drill breakage due to increased torque. This paper investigates modified drill head designs using the smoothed particle hydrodynamics method. The investigated modifications include various designs of the chip mouth covering. Besides graphical analysis based on flow visualizations, flow meters are placed at the tool’s head to evaluate the impact of the modifications on the flow rate and possible increased resistance and relocation of the fluid flow from the outer cutting edge to other parts of the tool. The simulation results for the reference design show the experimentally observed vortex formation, validating the simulation model. By adding the tool’s rotation in the SPH simulation, which is not included in the experiments for observation reasons, the vortex formation is positively influenced. In addition, some designs show promising results to further mitigate the vortex formation while maintaining a sufficient fluid flow around the cutting edges.

Virtual crime scene investigation using numerical models has the potential to assist in the forensic investigation of firearm-related fatalities, where ethical concerns and expensive resources limit the scope of physical experiments to comprehend the post-impact biomechanics comprehensively. The human cranial numerical model developed in this study incorporates three main components (skin, skull, and brain) with dynamic biomaterial properties. The virtual model provides valuable insights into the post-impact biomechanics of cranial ballistic injuries, particularly in high-speed events beyond conventional investigative capabilities, including the velocity of ejected blood backspatter, cavitation collapsing, and pressure waves. The validation of the numerical model, both quantitatively and qualitatively, demonstrates its ability to replicate similar bone fractures, entrance wound shapes, and backward skin ballooning observed in physical experiments of the human cranial geometry. The model also yields similar temporary cavity sizes, wound sizes, and blood backspatter time against the physical cranial model, aiding in bloodstain pattern analysis. Additionally, the numerical model enables exploration of ballistic factors that vary in each crime scene environment and influence cranial injuries, such as projectile type, velocity, impact location, and impact angle. These established injury patterns contribute to crime scene reconstruction by providing essential information on projectile trajectory, discharge distance, and firearm type, assisting in the resolution of court cases. In conclusion, the developed human cranial geometry in this study offers a reliable tool for investigating firearm-related cranial injuries, serving as a statistical reference in forensic science. Virtual crime scene investigationsusing these modelshave the potential to enhance the accuracy and efficiency of forensic analyses.

When metals and alloys are exposed to ultrasonic vibrations (UV), a softening behavior occurs, caused by the phenomenon of acousto-plasticity. To obtain accurate results in a deformation analysis, this phenomenon must be included in the formulation of the constitutive material model. In this work, an acoustic-plastic model is proposed to capture the effects of ultrasonic vibrations during machining. The desired effect is to modify the chip morphology to reduce the magnitude of the cutting forces and thus reduce the energy consumption of the process. The study focuses on the modeling of ultrasonic vibration-assisted micromachining (VAMM). The particle finite element method is used and extended to perform a thermo-mechanical analysis capable of capturing the responses of conventional micromachining (CMM) and VAMM operations of 32 HRC stainless steel. The cutting speed and UV parameters, including amplitude and frequency, are integrated into the Johnson–Cook constitutive model to account for the effects of acoustic softening on the machining characteristics. The results show that the influence of UV on microcutting leads to thinner chips and lower cutting force. In the VAMM operations, an average reduction in cutting forces of 20% is achieved at five different cutting speeds. In addition, the contact length between the tool and chip decreases at different cutting speeds from 29% to a maximum of 44%. Furthermore, the thermal analysis results show that there is a negligible temperature change during the CMM and VAMM simulations, indicating that the study of the machining process can focus exclusively on its mechanical aspects when performed at the microscale. The predicted average chip thickness and effective shear angle of the workpiece material are in strong agreement with the experimental results, emphasizing the importance of considering acoustic softening in VAMM studies.

To determine the desirable bonding parameters of the soybean-bonded particle model for accidentally simulating the working process of a pneumatic soybean seed-metering device. Taking the compressive destructive force (F_c,p) derived from the uniaxial compression test of soybean seeds as the evaluation index for the compression simulation tests. The Plackett–Burman and the steepest ascent tests were executed to identify the centroids of the influential factors that substantially affect the bonding force of the soybean-bonded particle model. The optimal values of the significance influencing variables were determined based on the Box–Behnken response surface test. The results indicated that the effect of bonded disk radius (R_B,p) between fraction particles on the F_c,p was extremely significant, and the effects of the restitution coefficient (e_p-steel) and static friction coefficient (μ_p-steel) of soybean-steel, normal stiffness per unit area (k_n,p) and critical normal stress (σ_max,p) were found to be statistically significant. The preferred values identified by Box–Behnken response surface test were 0.520 for e_p-steel, 0.274 for μ_p-steel, 4.082 × 10⁷ N/m³ for k_n,p, 3.517 × 10⁵ Pa for σ_max,p, and 0.982 mm for R_B,p, respectively. The compressive destructive force of soybean seeds was 211.32 N at this point, which was 0.2% less than the measured value of 211.74 N. The results of comparing the grain morphologies during the actual and simulated compressions indicated that the compression states had a superior consistency. It was determined that the DEM simulation input parameters for the soybean-bonded particle model calibrated were proven to be effective and dependable. The investigation presented in this paper can be utilized to effectively analyze the working process of the pneumatic soybean seed-metering devices through coupled simulation. It can also serve as a reference for other researchers to construct a particle model for DEM simulation using the BPM approach.