Computational Particle Mechanics最新文献

The dynamics of material particle chains exhibit the interesting property of sub-dynamics interaction. This paper discusses identical synchronization as a potential interaction of these sub-dynamics within the externally excited dynamics of an orthogonal lattice of chained material particles. The coupling elements between the particles possess viscous, linear and/or nonlinear elastic characteristics. One or more particles in the chain are subjected to periodic excitation. The extent of the synchronization effect varies based on the properties of the coupling elements, as well as the position and frequency of the excitations. A multi-parameter analysis was conducted through numerical simulations in the phase space of the output variables of the coupled particles, accompanied by diagrams illustrating synchronization errors. The analysis of signal propagation and delays was derived from the synchronization capabilities of adjacent particles under different external excitation positions and for different lengths of the chains. The time delay of signals was estimated from the synchronization error diagrams by measuring the duration required for transient changes prior to achieving identical and phase synchronization. The time taken for signal travel and delay is influenced by other system parameters. As the values of coupling parameters increase, the time for signal travel also increases. Also, shorter chains achieve faster synchronization, which is crucial for detecting signal transmission speed and delay in lattice of orthogonal chains of material points.

The sand carrying flow in the wellbore is commonly present in reservoirs that are prone to sand production. Even with sand control devices installed, some sand particles produced from the formation will still be carried to the surface by the fluid. The concentration and particle size distribution of sand in the formation are of great significance for the flow law of sand carrying in the wellbore. In this study, computational fluid dynamics and discrete element method coupled simulation method was established to systematically study the relationship between wellbore sand concentration and formation sand production concentration with different well inclination angles, fluid viscosity, particle size distribution of formation sand, and velocity. Firstly, a study was conducted on the influence of different sensitive parameters such as formation sand particle size distribution, fluid velocity, viscosity, wellbore inclination angle, and sand production concentration on wellbore sand carrying capacity. The influencing factors of wellbore cross section sand concentration were obtained. Then, based on the coordination of two subsystems, the formation fluid supply—sand production system and wellbore sand carrying system, and the relationship between the sand concentration in the heterogeneous suspended layer and the formation sand production concentration, a new method for predicting the critical sand production concentration of reservoirs based on the stationary bed theory is proposed from the perspective of the integration of reservoir—wellbore and sand production—sand carrying.

In this study, we developed a tsunami simulator using a multi-resolution particle method to address complex phenomena such as wave pressure on onshore structures and the stability of wave-dissipating blocks. The multi-resolution method used is the overlapping particle technique (OPT) for multi-resolution simulation of particle methods. In addition, the simulator was enhanced by the introduction of the energy-tracking impulse method, which allows rigid body contact and friction calculations. The OPT-based simulator has been validated in wave and onshore structure impingement simulation and stability analysis of wave-dissipating blocks.

Ecological permeable concrete (EPC), as a building material with high permeability and environmental friendliness, has its permeability significantly influenced by its pore structure. To explore the meso-structural characteristics of EPC and its permeability behavior, this study proposes an improved quartet structure generation set (I-QSGS) method to construct a meso-porous medium model that aligns with the characteristics of EPC. This model was then compared with real computed tomography (CT) scan data for validation. Additionally, the Lattice Boltzmann method (LBM) was used to simulate the permeability process of EPC, investigating its anisotropic permeability and the impact of pore structure parameters on permeability. Finally, the Grey Relational Analysis (GRA) was used to analyze the degree of influence of pore structure parameters on permeability. The results demonstrate that the pore structure of the three-dimensional porous medium model shows high similarity with the real pore structure in terms of average roundness distribution (Euclidean distance ξ = 0.162, classified as "Very Similar"). The permeability process of EPC exhibited rapid permeability in the initial phase, slowing down in the middle phase, and stabilizing in the later phase. EPC shows significant anisotropy in permeability, with the permeability in the Z-direction being significantly better than in the X and Y directions. As the pore size decreases, permeability sharply decreases, exhibiting a nonlinear negative correlation between permeability and pore size. Further analysis of the pore-specific surface area and permeability reveals the controlling effect of pore structure complexity on the fluid permeation process. A significant linear relationship was observed between porosity and permeability, with increases in porosity effectively enhancing the material’s permeability, and this enhancement shows a noticeable increment effect. The influence of pore structure parameters on the permeability of EPC is ranked as follows: porosity(n) > pore size (d) > pore-specific surface area (S), with grey relational degrees of 0.7570, 0.7423, and 0.5224, respectively. This indicates that porosity is the key factor determining the permeability of EPC. This study provides a theoretical basis for the design and optimization of EPC and offers data support for its practical application in engineering.

In this paper, a new type of composite pile called mud absorption (MA) pile was proposed, which is composed of a precast core pile and the paste slurry. Based on the field static load test and three-dimensional coupled discrete element method-finite difference method (DEM-FDM) simulation, the compressive bearing characteristics and load transfer mechanism of the MA pile were investigated. The results indicate the MA pile is the friction pile with higher bearing capacity. The vertical load on the pile top is jointly borne by the core pile and the paste slurry and transferred to the surrounding soil, forming a composite structure with a stiffness gradual that transitions from strong to medium to weak. By monitoring the displacements of the core pile, paste slurry, and the surrounding soil, it has been demonstrated that the core pile and paste slurry work synergistically. This synergy effectively enlarges the pile radius and enhances the bearing capacity of the pile foundation. The effects of paste slurry properties and the ratio of core pile side length to pile diameter on the bearing capacity were finally investigated, providing assistances for the design and application of MA piles.

Rockfill dam materials undergo large wetting deformation under the action of water, which leads to uneven settlement of the dam body in the later stage. In this work, on the basis of the discrete element method particle flow code, a triaxial wetting numerical simulation test is carried out to explore the macroscopic mechanical properties of rockfill under wetting and reveal its microscopic deformation and failure mechanism from the macro-mesoscale perspective. The results show the following: (1) The single- and double-line method: according to the test results, there is no significant difference between the single- and double-line methods in terms of the macroscopic stress–strain–volume change and wetting axis-volume change. The particle breakage rate and particle number of the single-line method are greater than those of the double-line method. The corresponding force chain distribution, particle fracture zone position, particle fracture distribution, and displacement field distribution of the single-line method are also more obvious than those of the double-line method, and the wetting path of the single-line method is more in line with the actual situation of the project. (2) Macroscopic law: In numerical tests, wetting deformation increases with increasing stress. The deformation trends observed in the single-line method and the double-line method exhibit similarities. The particle breakage rate associated with the single-line method is 1.48% higher than that of the double-line method, and the increase in particle number is 10% greater compared to the double-line method. Preloading wetting effectively reduces the total deformation of rockfill, and the path of wetting influences the overall deformation to some extent. (3) Microscopic observation: The strong chain density between the particles following wetting exceeds that of the dry particles. A relationship exists between the distribution of particle breakage and the distribution of particle fractures during the wetting process, which shows the occurrence of stress concentration, with the number of cracks in the single-line method significantly exceeding those in the double-line method. The expansion area of the displacement field after wetting is markedly larger than that of the dry sample, and the displacement of particles at both ends of the sample in the single-line method is more pronounced compared to the double-line method. (4) Improving model: the relationship between wetting axial strain and stress level aligns well with an exponential function. The degree of fitting for the linear equation parameters d and f, along with the confining pressure in relation to wetting volumetric strain and wetting stress level, is low. The exponential function relationship is fitted by improving the parameters d and f and the confining pressure, resulting in a higher fitting degree for the improved model curve compared to the original model.

Thermal cracking mechanism is an important topic for better understanding the strength and deformation behavior of rock in high-temperature-associated engineering. To investigate the crack propagation and stress evolution in marble under thermal–mechanical condition, a thermal–mechanical coupling model is developed in a grain-based model (GBM) using distinct element method (DEM). The developed GBM is first verified by comparing results derived from Fourier’s law of heat conduction. The micro-parameters in GBM are then carefully calibrated to match a large amount of macroscopic properties obtained from laboratory test. At last, the calibrated model is utilized to simulate the cracking behavior of a marble model under both thermal and mechanical loadings. The results show that as temperature in the treatment increases, the change in the number of thermally induced cracks exhibits a consistent trend with the variation of strength parameter in the model. In the thermal loading process, grain boundary tensile cracks are dominant among the generated cracks, accounting for more than 85%. The intra-grain tensile cracks gradually increase as the treatment temperature increases. In the mechanical loading process, the failure is tensile-shear mixed mode in thermally damaged model, and shear ratio in the failure mode gradually decreases as the treatment temperature increases. The thermally damaged model exhibits a lower vertical stress and a slower crack propagation rate during the initial loading stage when compared to the results of unheated model. Both the number of micro-cracks and the vertical stress slowly increase during the initial loading stage as the treatment temperature increases. However, as the peak stress is approached, the growth of both micro-crack quantity and vertical stress progressively diminishes. The results in this study improve our understanding of thermal damage mechanism in marble.

The Xiyu conglomerate is widely distributed in the north and south of Tianshan Mountain in Xinjiang and has softening characteristics in contact with water. Based on the uniaxial compression test of calcareous cemented Xiyu conglomerate, this paper establishes a particle flow fine-scale model to study the macroscopic mechanical response of rock samples in uniaxial compression test under water immersion and explores the distribution characteristics and evolution law of contact force, cracks and other fine-scale structural parameters of rock samples in the process of the test. The results show that the stress–strain curves of calcareous cemented Xiyu conglomerate samples under water immersion are basically the same, including compression, elasticity, yielding and destruction stages; with the increase in water immersion time, the uniaxial compressive strength and elasticity modulus show a deterioration trend in general, of which the deterioration effect is especially obvious when immersed in water for 7 d. The uniaxial compressive strength and modulus of elasticity show an overall deterioration trend when immersed in water for 7 d, which is the most obvious. The specimens obtained by PFC numerical simulation can represent the macroscopic mechanical properties of calcareous cemented Xiyu conglomerate, and the water immersion effect leads to the gradual deterioration and reduction of the bond strength between particles within the specimen, the non-uniformity is enhanced, and the overall bearing capacity is gradually reduced, and the damage mode is gradually changed from the tensile damage to the tension-shear mixing damage; With the gradual increase of the immersion time, the sudden change points of the number of three types of cracks, namely, total cracks, tensile cracks and shear cracks, within the rock samples corresponded to the damage characteristic points of the macroscopic stress-strain curves, with the tensile cracks always dominating, and the proportion of shear cracks gradually increasing. With the increase in axial load, the number of contact force gradually changes from spherical to spindle-shaped distribution before loading, and its direction is 90° to the loading direction; the number of contact force decreases after the peak, and macroscopically, it is manifested as the sharp decrease in rock bearing capacity and final destruction. The conclusions of the study can provide a reference for the analysis and control of engineering deformation and stability related to the Xiyu conglomerate.

We establish a theoretical framework of the particle relaxation method for uniform particle generation of smoothed particle hydrodynamics. We achieve this by reformulating the particle relaxation as an optimization problem. The objective function is an integral difference between discrete particle-based and smoothed-analytical volume fractions, which globally measures zero-order inconsistency in the interior domain. The analysis demonstrates that the particle relaxation method in the domain interior is essentially equivalent to employing a gradient descent approach to solve this optimization problem, and we can extend such an equivalence to the bounded domain by introducing a proper boundary term. Additionally, each periodic particle distribution has a spatially uniform particle volume, denoted as characteristic volume. The relaxed particle distribution has the largest characteristic volume, and the kernel cut-off radius determines this volume. These insights explain the equivalence between uniform particle distributions and optimized zero-order consistency and enable us to control the relaxed particle distribution by selecting the target kernel cut-off radius for a given kernel function.

The removal of straw from the seed bed to the inter-row prior to sowing maize is a critical agricultural practice. However, this process is inherently uncertain due to the variability in straw displacement. To investigate this interaction, this study developed a flexible straw model utilizing a discrete element approach, employing hollow cylinders to linearly connect the particles. Experiments were conducted to ascertain the mechanical properties of the flexible straw, with a focus on its biological and mechanical parameters. Subsequently, a full-coverage soil bin model of wheat straw was established to simulate the straw removal process, enabling the analysis of the interaction between the removal device and the straw during operation. The results indicate that varying operating speeds significantly enhance the influence of the straw removal device on the straw, thereby improving the straw removal rate. The maximum relative error of the traction force required for both simulation and experimental testing was found to be 21.27%. Additionally, a combined device was employed to simulate the straw removal process, with straw disturbance analyzed in both paired and single-direction scenarios. Finally, by comparing simulation results with bench test outcomes, the established model demonstrated a high degree of accuracy in simulating the straw displacement process. This research provides a valuable reference for the development of discrete element models for other crops and for enhancing the efficiency of straw removal devices.