Computational Particle Mechanics最新文献

In the fluid injection stimulation process of unconventional reservoirs, proppants are frequently used to maintain the opening of fractures for economic resource recovery. Understanding proppant transport in rock fractures is important to constrain fracture geometry and inform fluid injection design. In this study, we establish a coupled CFD-DEM model to simulate the transport process of proppants in fractures. A systematic parametric study is performed to investigate the influence of injection parameters (proppant density and fluid viscosity) and fracture morphology (fracture tortuosity and fracture width). The flow field distribution and mechanical characteristics of particles (proppants) are analyzed, and the velocity change and spatio-temporal accumulation evolution of particles are examined, revealing proppant transport and laying mechanism. Our results show that proppants accumulate horizontally, forming layers over time when the proppant density and fluid viscosity are low in smooth fractures. On the contrary, proppants often accumulate vertically over time when the proppant density and fluid viscosity are high. When the sand-carrying fluid flows through tortuous fracture, fluid erosion occurs at tortuous corners, forming a sand bank depression. It is also noted that the fluid velocity increases at tortuous corners, implying that more particles could be transported in fractures with higher tortuosity.

Underwater concrete is vulnerable to the coupling erosion of water pressure and chlorides, threatening the durability of underwater concrete structures. To predict this process more realistically, a chemical-hydraulic-mechanical peridynamic-finite element method (PD–FEM) model of the chloride erosion of reinforced concrete under hydraulic pressure was developed to investigate the entire process of reinforced concrete damage caused by chloride erosion under water pressure. A multi-phase concrete model with irregular aggregates was employed to simulate the effects of aggregates and the interfacial transition zone (ITZ) on water penetration, chloride diffusion, and steel corrosion. The proposed PD–FEM model focuses both on the unsaturated transport process of water and chloride and the corrosion failure of unsaturated reinforced concrete under water pressure. The proposed PD–FEM model in simulating the mechanical effects and seepage-diffusion coupling was verified by two numerical experiments, and the entire process of corrosion expansion failure of underwater reinforced concrete is simulated by this model. The numerical results show that the proposed chemical-hydraulic-mechanical coupling PD–FEM model can simulate the penetration of water and chloride in unsaturated concrete and failure process of concrete caused by chloride corrosion under water pressure, as well as the effects of aggregates and the ITZ on water penetration, chloride diffusion, and steel corrosion. Furthermore, parameter sensitivity analysis indicated that water pressure accelerated the transport of water and chloride in concrete and softened the concrete, accelerating the durability failure of underwater concrete.

Soil in slope engineering is a granular material, so it is more advantageous to study the movement of particles during slope instability by discrete element method. A three-dimensional discrete element numerical model for gravelly soil slopes was established, and a new energy-based criterion was introduced to define slope failure in this paper. The slope stability was assessed according to the principle of strength reduction method, and the slope safety factor was determined based on the energy criterion. The results show that there was a significant inflection point in the evolution of kinetic energy, elastic strain energy, and dissipation energy with strength reduction factor, and the corresponding strength reduction factor is the slope safety factor. The slope safety factor determined based on the energy criterion was 1.4, which is consistent with that obtained by the change in particle displacement and theoretical equation, verifying the correctness of the slope safety factor determined by the energy criterion in this paper. The research work in this paper provides a novel approach for the stability analysis of slopes.

Calendering is a critical step in the manufacturing process of lithium-ion batteries, but simulating this process presents challenges due to the binder, which bonds discrete particles to the continuous metal foil. In this study, we propose a numerical model to simulate the calendering process effectively. The model treats the metal foil as a continuum using the finite element method (FEM) and represents the active particles as discrete entities using the discrete element method (DEM). To account for the binder’s effect on the metal foil, a set of ghost particles is embedded within a narrow zone of the continuum, enabling volume coupling. A damage variable is introduced at the level of individual particles to assess the effects of the calendering process. Additionally, we present a comprehensive approach for calibrating material parameters through physical experiments. The model’s effectiveness is demonstrated through two examples, highlighting its ability to analyze key manufacturing parameters such as roller compression and curvature. This study provides a valuable tool for simulating the calendering process, capturing the essential role of the binder, and guiding the optimization of electrode manufacturing.

Offshore wind power plays a crucial role in the global development of clean energy. However, the concrete piles of offshore wind turbines face the problem of frost heave cracking in cold sea areas. In this study, the meso-scale frost heave cracking mechanisms of concrete is investigated. Traditional smoothed particle hydrodynamics (SPH) method is improved. A fracture marker is introduced to simulate the progressive failure processes of particles, and a method for generating the meso-structures of concrete is proposed. By embedding the temperature equation and combining with the equivalent thermal expansion method, the frost heave cracking process of concrete is simulated. Simulation schemes with different aggregate percentages, aggregate sizes, pore percentages, and prefabricated fissure angles are set up to study the influence of various factors on the frost heave cracking of concrete. The results show that different factors have a significant impact on the frost heave cracking of concrete. The improved SPH method can effectively simulate the frost heave cracking process of concrete. Compared with traditional numerical methods, it has more obvious advantages in dealing with particle failure and complex meso-structures. This study reveals the laws of concrete frost heave cracking under different meso-structure factors, providing a solid theoretical basis for the anti-frost heave design of concrete piles in offshore wind farms.

The material point method (MPM) is a particle method, suitable for large-deformation analysis. Bodies are represented by particles, the so-called material points. These carry all information such as mass, velocity, position and deformation state, to name just a few. With this in hand, the Lagrangian representation of the body is combined with a computational background grid in an Eulerian sense in order to solve the differential equations of interest. Since the grid does not keep track of history data it is reset at the beginning of each time step using the same geometry throughout the simulation. As a result, mesh distortion is diminished, enabling large deformations throughout the simulation. While using (C^0)-continuous shape functions, stress oscillations are likely to occur. One way of solving this issue is the application of higher-order shape functions. In this contribution, focus is on (C^0)-continuous shape functions in combination with the grid-shift technique in order to reduce stress oscillations. Here, the initial placement of the grid nodes is altered, i.e., the grid is translated in space at the beginning of each time step. This method is realized by randomly shifting the origin of the grid, resulting in no computational overhead and a straightforward implementation. Comparisons of four numerical examples are analyzed using the standard fixed grid approach and the grid-shift technique with respect to oscillations in the stress field, alternative application of boundary conditions and energy conservation.

In this study, the erosion behavior of elbows in natural gas–hydrogen pipelines was investigated using CFD-DEM under dense phase (DP), pseudo-dense phase (PDP), and vapor phase (VP) conditions. Three pipeline models were analyzed: model 1 with 0% hydrogen, model 2 with 2%, and model 3 with 4%. The simulations explored the effects of Reynolds numbers (2,000,000–5,000,000), particle diameters (100–300 μm), and particle mass flow rates (100–300 kg/h) on the erosion rate. The results showed that across all models, the erosion rate increased with Reynolds number, particle mass flow rate, and particle diameter. At Reynolds number 2,000,000, the erosion rate in DP was about 60% lower than in VP for model 1, 64% lower for model 2, and 60% lower for model 3. As hydrogen mole fraction increased, the erosion rate slightly decreased: in DP at Reynolds 2,000,000, the erosion for model 3 was 5% lower than model 2 and 2.5% lower than model 1. Across all particle diameters, the maximum erosion rate in DP was 63% lower than in VP and 20% lower than in PDP. At 100 μm, the DP erosion rate for model 1 was 67% and 31% lower than VP and PDP; for model 2, 70% and 19% lower; and for model 3, 65% and 16% lower. The Reynolds number had a stronger effect on erosion than particle mass flow rate or diameter. High hydrogen content slightly reduces erosion but requires higher pressure.

In order to explore the influence of particle shape on the reflux performance in mining lifting pump, the CFD-DEM coupling method was used to numerically simulate the solid–liquid two-phase flow in the mining lifting pump, and the effects of spherical particles, square particles and cylindrical particles on the reflux characteristics in the pump were compared and analyzed. The research results show that when the reflux occurs in the pump, the high-speed particles are mainly distributed at the inlet of the first-stage and second-stage impellers and the outlet of the first-stage guide vane. The accumulation phenomenon mainly occurs on the pressure surface of the guide vane blade and the junction between the impeller and the guide vane. When particles of different shapes reflux in the pump, the distribution area of the spherical particles in the first-stage and second-stage impellers is the smallest, followed by the cylindrical particles, and the largest is the square particles. The accumulation phenomenon of the spherical, cylindrical, and square particles in the pump gradually extends toward the impeller passage in turn. In addition, the average velocity of the particles decreases in the order of spherical, cylindrical, and square particles, and the total number of collisions of the particles increases in the order of spherical, cylindrical, and square particles. The time required for the spherical particles to reflux through the pump is the shortest, and the time required for the non-spherical particles to pass through the pump is similar, with the square particles having the lowest passage rate of 43.98%. These factors cause the reflux performance of the spherical, cylindrical, and square particles to decrease in order.

Using discrete element modeling, the unique characteristics of a bed of grains contained in a translating rectangular box with or without acceleration on a straight horizontal path have been studied. The inclined free surface shape has apparent similarities to its hydrodynamic equivalent at constant acceleration; nevertheless, due to the particle nature of the medium, there are some distinct differences. One of the notable differences is the nonlinear free surface of the granular bed. The effective slope of the accelerating granular bed is much higher compared to that of the liquid pool for the same dynamic condition. In the accelerating granular bed, the free surface profile is not affected by the particle density, but the particle size and inter-particular friction weakly influence it. Meanwhile, acceleration has an impact on the local gradient of the free surface. Nonetheless, the simulation results clearly imply that although typically, bed behavior is similar to solid body motion, locally, the discrete nature of the medium influences the distribution and motion of the particles. Contrary to the hydrodynamics case, a translation without acceleration also results in a slope in the free surface of the granular bed.

A virtual rutting experimental model was established based on the discrete element method (DEM) to investigate the influence of microscopic initial defects on the mechanical properties of asphalt materials. The data from the model, which determines the mesoscopic parameters by parameter inversion, were compared with the data from the actual rutting test. To ensure the accuracy of the model data, the discrete fracture network (DFN) was used to characterize the microscopic initial defects of the material. It indicated that the virtual rutting experiment results were consistent with the actual experimental results. The effect of incipient defects on asphalt mixtures could be well characterized by a virtual rutting test model. Microscopic defects had a significant effect on the mechanical properties of materials. The overall structural strength of the material decreased significantly. When the length of the micro-crack was greater than 4 mm and the width (dist) was between 0.15 mm and 0.45 mm, the reduction in material strength was most significant. During construction, the length and width of cracks were controlled by effective means, which was beneficial for improving the crack resistance of materials.