Computational Particle Mechanics最新文献

Steel silos with corrugated walls exhibit friction phenomena between the bulk material and the silo wall quite different from those produced in smooth walls. A silo model was designed, and discrete element method (DEM) simulations were performed to analyze an influence of the depth and wavelengths of corrugations on mass flow rate, wall pressures, location of the shear band and effective wall friction coefficient. The dimensions of the geometry adopted correspond to one of the vertical sections of the silo model with corrugated steel walls instrumented by the authors. This silo model consisted of a square cross section (0.45 x 0.45 (m^2)) and 0.75 m in height, a flat bottom with a centric, square outlet (0.06 x 0.06 (m^2)), corrugated lateral steel walls, and smooth, transparent methacrylate front and back walls. The bulk material was pinewood pellets, whose mechanical and numerical properties had been previously obtained by the authors. The numerical results show an influence of the depth of corrugation and the wavelength on the velocity of the granular particles and the friction forces against the wall. The initial position of the shear band was found to be placed between 1 and 3.5 times the average size of the particles from the vertical line connecting two consecutive corrugation peaks closest to the silo outlet. The effective wall friction coefficient for corrugated walls depends on the wavelength and the depth of the corrugations, varying in the range of 0.42 to 0.9, in opposition to the single theoretical value of 0.78 proposed by Eurocode EN 1991-4, for a sinusoidal profile, regardless of the geometrical parameters.

In engineering disciplines such as tunnel construction, underground projects, oil and gas storage, and slope engineering, rocks frequently experience the effects of cyclic loading. Although existing contact models in commercial software can simulate rock materials, they demonstrate significant limitations in accurately capturing the mechanical behavior of materials under cyclic loading and unloading. In this research, a cyclic loading–unloading contact model, incorporating damage considerations, was developed specifically for rock materials. This developed discrete element method enhances the efficiency of model generation by improving internal algorithms and offers high editability. The numerical results were compared with experimental data and showed strong agreement across three different types of rock. The developed method and contact models effectively capture the plastic failure process of rock material under cyclic loading, with the resulting stress–strain curves displaying characteristic hysteresis loops. In comparison with traditional discrete element software using parallel bonding models, this program produces more accurate results, making it more suitable for simulating the cyclic loading–unloading behavior of rocks.

This study investigates the efficacy of two connected vertical flat plates, utilized as controlling devices, to suppress the fluid forces by averting the vortex shedding around a square cylinder. Such fluid flow controlling strategy has been very less adopted in past. It consists of two identical controlling plates fitted to the top and bottom sides of a square cylinder within the framework of a passive flow control gadget. The height of control plates (l) progressively varied from 0.1 to 3.75 times the cylinder’s size with a fixed width of 0.2 times cylinder’s size. Through this strategy, complete control of flow is achieved much earlier at smaller heights of plates as compared to the conventional passive control strategies. With the growing height of the plates, a trio of flow patterns appeared in the wake of cylinder: unsteady flow within l = 0.1–1.4, transient flow within l = 1.5–2.6 and steady flow for l ≥ 2.7. The streamlines exhibit various shape structures in the wake depending on the heights of the control plates. Such flow structures are referred to as an oval shaped structure for l = 0.1–1.1, an extended sized vortex for l = 1.2–1.7, a D-type structure for l = 1.8–2.2 and an ellipse like structure for l = 2.4–3.75. The control plates are found efficient in controlling the vortex shedding, the Strouhal number and amplitude of fluctuating drag as well as altering the base pressure at all the heights while the amplitude of lift, the rms value of drag and the lift tend to reduce as plates’ height reached the value 2.2.

Granular grippers are a promising approach to the flexible handling in soft robotics. As a result of the used granular materials, these grippers can grasp a wide spectrum of objects with many different shapes, especially compared to conventional mechanical or suction cup grippers. However, accurately predicting the graspability of differently shaped objects remains a challenge. Additionally, a comprehensive understanding of the various influences within the grasping mechanism is still lacking. Therefore, a specific granular-based gripper combining the principles of jamming and vacuum grippers was previously experimentally investigated for different object shapes, while varying various design parameters. In this study, the previous work is expanded through numerically modelling this specific gripper. For this purpose, the first sequence of the grasping process (moulding process) is modelled using the discrete element method, while the bonded particle method is used to model the membrane behaviour. The simulation shows good agreement with the experimental moulding results of differently shaped objects through optical comparisons. Furthermore, the parameters characterising the moulding are compared with a previously introduced object characteristic parameter, enabling the identification and characterisation of influences within the grasping mechanism.

The ceramic–steel double-layered target subjected to high velocity impact which includes complex multiphase and multiphysics phenomena is a challenging problem to address. In this paper, the meshless smoothed particle hydrodynamics (SPH) method is employed to simulate a variety of numerical cases pertinent to the high velocity impact of ceramic–metal composite structures. Firstly, the simulation of the high velocity impact of an aluminum spherical projectile on aluminum and copper plates was conducted to validate the correctness of the SPH computational model. After the verification of the developed in-house SPH solver, the numerical model was subsequently applied to investigate the dynamic behavior and mechanism of a double-layer ceramic–metal target plate subjected to high velocity impact. Moreover, the damage patterns and damage area of this double-layered plate were studied under the variation of the physical parameters. The numerical results obtained from the GPU-accelerated SPH solver are in good agreement with previous experimental data, indicating that the in-house SPH solver can predict the physical process of the damage patterns of the ceramic–steel double-layer targets under high velocity impact well; the ceramic specimen improves the momentum absorption and the impact resistance of the double-layered target plate effectively.

Hydraulic fracturing can effectively improve the cuttability of hard rock and provide a novel approach for the non-explosive mechanized mining within hard rock. Considering the hydraulic-mechanical coupling, a hydraulic fracturing numerical model was developed based on the industrial-scale discrete element method in this study. The effects of Young's modulus, shear modulus, water pressure, cohesion, density and porosity on the number of cracks and the peak cutting force during hydraulic fracturing were examined. The results demonstrate that crack evolution exhibits three distinct stages under different influencing factors, including a rapid growth stage, a steady growth stage, and a slow growth stage. Four main controlling factors significantly impact the effectiveness of hydraulic fracturing: Young's modulus, shear modulus, water pressure, and cohesion. Additionally, the functional relationship between the number of cracks, peak cutting force, and the main controlling factors was established, and the weights of the four main controlling factors in the crack evolution process were determined. Consequently, an integrated characterization method for the peak cutting force after hydraulic fracturing was developed. The verification results demonstrate that the mean absolute percentage error calculated by the proposed integrated characterization method for peak cutting force ranges from 1.91 to 2.05%, indicating that the proposed method exhibits a high level of calculation accuracy. Finally, a calculation method for cutting indexes was proposed, and then a classification table for hard rock's cuttability was established. This study provides a theoretical basis for mechanized mining assisted by hydraulic fracturing techniques for hard rock cutting.

In this paper, we proposed a novel grain-based model based on particle flow code to realistically reproduce the heterogeneous structure of crystalline granite. Then, it is applied to the cyclic loading and unloading simulation. Based on the quantitative analysis of the three-dimensional multilevel force chain network, the evolution of force chain characteristics of crystalline granites with different minimum radii of the grains R_G during cyclic loading and unloading is investigated. Our results demonstrate that specimens with varying R_G exhibit stress–strain curves that form a “hysteresis loop” due to nonideal elasticity deformation. As R_G increases, the proportion of intragranular contacts with higher micro-strength and micro-modulus rises, enabling it to bear more loads and exhibit greater deformation resistance. The microscale slip between particles is also reduced when an intragranular contact fractures. Consequently, both the upper stress threshold and the elastic modulus of the sample increase as R_G increases, while the variation range of strain values decreases. During loading, most cracks primarily propagate in an orientation range orthogonal to the loading direction. As R_G increases, the average value and sum value of whole general force chains increase. The main orientation of high-strength force chains (HF) aligns with the loading direction. With an increase in R_G, the numbers of HF in whole structures and intragranular structures rise, while the number of HF in intergranular structures decreases. As R_G increases, the number of basic elements and contacts within the mineral structure that can jointly bear the load increases, and the formed force chain network can bear a higher level of load. Due to the difference of micro-strength, the bearing capacity of the intragranular structure is greater than that of the intergranular structure.

In accordance with the fractal characteristics of fractures, the flow path of fluid in fractures is regarded as a rough capillary bundle in this paper. Combined with the influence of effective stress on seepage in rock fracture, the fractal model of permeability and the normalized permeability model in rough rock fracture considering effective stress are established. The effects of effective stress and relative roughness on fracture permeability and the relationship between normalized permeability and Young’s modulus, Poisson’s ratio were investigated. The findings reveal that the normalized permeability in the rough fracture is inversely related to both relative roughness, Poisson’s ratio and effective stress while exhibiting a direct proportionality to Young’s modulus. In addition, the model presented in this paper is subjected to a comparative analysis alongside existing models and experimental data, which shows that the model in this paper can effectively describe the seepage properties of fluid within rough fractures subjected to stress conditions.

Discrete element modeling (DEM) is an important technique for particle dynamics simulation. The field of metal additive manufacturing often utilizes DEM to simulate the rheological behaviors of powder. Standard contact and short-range interactions are sufficient in most cases but insufficient to describe the particle dynamics with the influence of an electric field. Modeling such a system requires additional physics to describe the particle–field interactions. The relevant physics has been experimentally understood but is not yet available in DEM. Here, we develop a charge exchange and an electric force module. The electric force module governs particle response to the electric field, while the charge exchange module enables particles to acquire proper charge during contact with charged geometries. We validate the modules against analytical calculations and high-speed videos of electrostatic powder deposition experiments. Notably, the model struggles to capture the initial particle levitation. We later deploy a modified electric field, as supported by static electric field simulation, to better approximate the electric field penetration into the powder layer. This modification improves the model’s capability of simulating realistic particle levitation. The results highlight the challenges of modeling particle behaviors in the electric field while demonstrating the feasibility of obtaining quantitative results, which are difficult to measure experimentally.

This paper studies the effects of acid–base/KH550 composite-modified basalt fibers (BFs) on the fracture characteristics of basalt fiber-reinforced asphalt mixtures (BFRAM) via the discrete element method (DEM), providing an experimental basis for further optimization. The semicircular bending (SCB) test was conducted on BFRAM, along with DEM simulation. This study revealed that (1) compared with those of blank group A, the fracture energies of BFA, BFA-H, BFA-N, BFA-NK and BFA-HK increased by 17.2%, 33.6%, 37.4%, 39.0%, 55.0% and 56.6%, respectively, and the flexibility indices increased by 18.8%, 55.8%, 58.3%, 45.3%, 63.9% and 73.3%, respectively. Fiber modifications, especially acid etching/KH550 composite modifications, are beneficial for improving the crack resistance and toughness of BFRAM. (2) The indoor SCB load–displacement curves of the BFRAMs are located mainly in the DEM simulation area where the fiber interface coefficient (FIC) is 0.6–0.9, which proves that the surface modification of the BF is conducive to improving the adhesion of fibers and asphalt. (3) The maximum contribution rate of the fiber units to resisting the external load in the DEM sample is 6.7% (FIC = 0.9), which is 2.09 times that of the DEM sample with FIC = 0.6. In the postpeak stage, the contribution rate of fiber units in the DEM samples remained at a high level of 3.5–6.7% (FIC = 0.9).