Computational Particle Mechanics最新文献

Recent advancements in the Material Point Method (MPM) have significantly improved the simulation of fluid–structure interaction (FSI) problems. However, regardless of the significant advantages of FSI simulation that the MPM can offer, further improvements in flow visualization are essential for analyzing a complicated fluid field. This article presents an innovative approach that integrates Lagrangian Coherent Structures (LCS) with both weakly compressible MPM (WCMPM) and incompressible MPM (iMPM) to improve the identification and analysis of flow structures in complicated FSI problems. The MPM excels in tracking material motion and accurately computing deformation gradients, which is a crucial step for the extraction of the LCS. This combination renders the MPM an ideal complement to the LCS technique, facilitating a detailed examination of complex vortex patterns within flow fields. Unlike traditional particle methods such as Smoothed Particle Hydrodynamics, the MPM boasts a distinct advantage in accuracy for calculating the deformation gradients, which can mitigate errors associated with particle shifting techniques as the deformation gradients are calculated based on the velocities on the background grid. The utility of the LCS visualization within the MPM framework is demonstrated through various numerical experiments, which include the analysis of a water–snow interaction problem, a viscous wake generated by an inclined ellipse, models of fish-like swimming, and liquid sloshing with baffles under different conditions. These studies highlight the ability of the method to offer detailed insights into flow dynamics, confirming the superior capability of the MPM in capturing the complex characteristics of LCSs in viscous incompressible flow fields.

Quantitative evaluations of blasting damage evolutions of concrete structures are the premise of improving the design codes of concrete blasting engineering. However, traditional numerical methods have some limitations in dealing with the large deformation and discontinuity problems during concrete blasting. In view of this, the improved SPH momentum equation considering blasting load is derived. The “birth and death coefficient” χ is defined, and the traditional SPH smoothing kernel function is then improved, thus realizing the simulations of dynamic blasting damage evolutions under the SPH framework. The methods of determining the concrete meso-structures as well as distinguishing different materials are proposed, which can realize the generations of SPH particles such as aggregates, interfacial transition zones and pores. Firstly, four typical numerical examples are simulated: (1) blasting damage evolution model with one blast hole and one 45° prefabricated fissure; (2) blasting damage evolution model with one blast hole and three parallel prefabricated fissures; (3) blasting damage evolution model with one blast hole, one vertical prefabricated fissure and one horizontal prefabricated fissure; and (4) blasting damage evolution model with two blast holes, two empty holes and two prefabricated fissures. The numerical results are compared with previous experimental results to verify the correctness of the improved method. Then, the concrete mesoscopic blasting damage models are established, and the blast damage evolution processes under different concrete mesoscopic structure properties as well as different dynamic blasting parameters are simulated, and results show that: (1) The blasting cracks are limited around the blast hole when the aggregate content is larger, while when the aggregate content is smaller, the blasting cracks expand to the model boundary by propagating around the aggregates. The increase in the pore content leads to a different crack propagation mode: combinations of crack propagating around the aggregates and connecting the pores. (2) The increase of peak stress wave value and blast stress loading rate leads to the increase in the damage degree around the blast hole, but decrease in the damage degree of the whole model. (3) The damage counts increase rapidly in the initial stage of blasting, but maintain a low level in the later stage when the aggregate content is larger, while it is the opposite when the aggregate content is smaller. The increase in the pore content leads to the decrease in the model damage degree. (4) The dynamic blasting parameters donate less effects on concrete damage counts, and the blasting damage counts decrease with the increase in the peak stress wave value and the loading rate.

Under the joint action of anchoring force and high in situ stress, the broken rock mass (BRM) in deep metal mines is actually under three-dimensional (3D) compressive stress, and its triaxial compression mechanical behavior is the key factor to control the stability of the surrounding rock. Therefore, it is necessary to perform research on the macro-mechanical behavior and micro-structural evolution of BRM under such similar stress state. In this work, based on 2D images, we propose a high-efficiency and low-cost method to reconstruct the 3D topographic features of the BRM. The particle flow code is used to study the effects of confining pressures and particle sizes on the mechanical properties, porosity, coordination number, acoustic emission characteristics, and fragmentation characteristics of the BRM. The results show that as the confining pressure increases, the compressive capacity and volume shrinkage of the BRM increase. The compressive capacity of the BRM reduces, and the secondary fragmentation become more violent with the increasing of particle sizes. At lower confining pressure, the rotation and translation of the BRM are main reasons for the change in the porosity. At higher confining pressure, the secondary fragmentation of the BRM as well as the migration of the small volume of rock are responsible to the change in the porosity. Secondary fragmentation of the BRM is mainly induced by tensile failure. The ratio between shear and tensile cracks in number decreases with increasing particle size of BRM. The results can provide some guides for the support design of the BRM in deep metal mines.

The accuracy of simulation parameters for spinach sowing process was enhanced by establishing the seed simulation model based on the intrinsic parameters of spinach seeds using the Hertz–Mindlin model. Calibration of simulation parameters between spinach seeds and contact materials (ABS resins and stainless steel) was performed using free-fall collision method, inclined plane sliding method, and inclined plane rolling method. The results indicated: coefficients of restitution, static friction coefficients, and rolling friction coefficients between spinach and ABS resins were 0.310, 0.467 and 0.045, respectively. Coefficients of restitution, static friction coefficients and rolling friction coefficients between spinach and stainless steel were 0.346, 0.505 and 0.047, respectively. Considering inter-seed contact parameters, a study was conducted using the relative error between measured repose angle and simulated repose angle as the indicator. This involved steepest ascent experiment and three-factor five-level rotational combined design experiment with the optimisation goal of minimising relative error. Through optimal analysis of test data, the following results were obtained: coefficients of restitution, static friction coefficients, and rolling friction coefficients between spinach seeds were found to be 0.47, 0.37 and 0.04, respectively. Calibration results were validated through sowing verification experiments, demonstrating that the qualified rate, multiple rate and missing rate of both simulation and actual tests were less than 5.8%, verifying the reliability of the calibration results. The research findings can serve as a theoretical reference for the design and simulation optimisation of spinach sowing devices.

Filamentous microorganisms enable the production of a wide range of industrially relevant substances, such as enzymes or active pharmaceutical ingredients, from renewable side products and waste materials. The microorganisms' growth is characterized by the formation of complex, porous networks (mycelium) of tubular, multi-branched cells (hyphae). The mycelium is increasingly used in textiles, packaging, food and construction materials, in addition to the production of chemical substances. Overall, the mycelium's mechanical behavior is essential to many applications. In submerged cultures, spherical hyphal networks (pellets) are formed. The pellets are subjected to mechanical stress during cultivation, which can lead to structural changes affecting product titer and process conditions. To numerically investigate the mechanical behavior of pellets under normal stresses, the discrete element method (DEM) was used for the first time to simulate pellet compression. Initially, pellet structures were generated using a biological growth model and represented by a flexible fiber model. Force–displacement curves were recorded during compression to investigate the influencing factors. The effects of pellet size, fiber segment length, biological growth and DEM model parameters were studied. A strong influence of the growth parameters on the radial hyphal fraction and thus on the compression force was shown. Furthermore, the mechanical properties of the fiber joints significantly determined the pellet mechanics in the considered compression range. Overall, the simulation approach provides a novel tool for the digital investigation of stress on different mycelia, which may be used in the future to enhance mycelial structures through genetic and process engineering methods.

The utilisation of particle flow code to establish discrete element models represents an effective approach for addressing the issue of discontinuous media. This methodology has been employed by numerous scholars to analyse the mechanical properties and damage laws of geotechnical materials. However, the complex nature of the particle action mechanism within the discrete element model necessitates a considerably longer time frame for the completion of an elaborate simulation experiment than that required for a laboratory test. This presents a significant challenge for researchers seeking to investigate the mechanical properties of a large number of geotechnical materials through the discrete element method. In order to accelerate the prediction of mechanical properties for various specific discrete element models, a mathematical model of the geotechnical micro-parameters and the geotechnical strength macro-parameters has been developed using an orthogonal design considering interactions and a back propagation neural network based on Bayesian regularisation. The geotechnical strength macro-parameters, such as compressive strength and tensile strength, can be derived directly from the geotechnical micro-parameters of the discrete element models through this mathematical model. The results show that the trained network model demonstrates an aptitude for predicting the uniaxial compressive strength, tensile strength, cohesion, and friction angle of geotechnical materials. The mean square error is 11.611 for the training set and 14.207 for the test set. In the test set, the median deviation rates of the predicted values of the four strength macro-parameters from the target values are 3.90%, 4.82%, 4.30%, and 7.30%.

Mactra veneriformis represents the dominant species in China’s mudflat aquaculture. The discrete element model of M. veneriformis and its contact parameters serve as an important basis for the optimization design and simulation study of aquaculture and processing equipment. The contact parameters of the discrete element model of M. veneriformis were measured and calibrated by a combination of experimental testing and simulation calibration. The study measured the range of collision recovery, static, and rolling friction coefficients between M. veneriformis and stainless steel. The Plackett–Burman multifactorial significance screening test was then conducted for the split-cylinder method, the rotate-cylinder method, and the single-cylinder method particle characterization test methods. The ANOVA results were utilized to calibrate the contact parameters. The collision recovery coefficient of 0.29 between M. veneriformis–M. veneriformis and 0.28 between M. veneriformis–stainless steel. The coefficient of static friction of 0.41 was determined between M. veneriformis–M. veneriformis, a coefficient of static friction of 0.62 between M. veneriformis–stainless steel, and a coefficient of rolling friction of 0.23 between M. veneriformis–M. veneriformis and a coefficient of rolling friction of 0.16 between M. veneriformis–stainless steel. After calibration, simulation tests were conducted using the side plate lifting method to verify the contact parameters of the discrete elements of M. veneriformis. The results showed that the simulation angle of repose of the calibrated M. veneriformis had an error of 4% concerning the true angle, thus verifying the contact parameters of the M. veneriformis. The findings of this study can serve as a valuable reference for future research on the optimal design and simulation of the sowing, harvesting, and processing equipment of M. veneriformis. The research methodology employed can provide novel insights for research on discrete elemental parameter calibration of agricultural materials, which has not been extensively studied.

We utilized the discrete element method to simulate the packing of a powder layer by blade spread. Our study revealed the following findings: (1) We uncovered a hereditary relationship that exists between the pouring heap and the packing layer, which plays a significant role in the non-uniform distribution of powder in the packing layer in terms of sizes and shapes. (2) We systematically analysed the influence of sliding speed on powder packing and recommended a threshold sliding rate of 0.15 m/s for achieving a high packing quality. (3) Contrary to the conventional belief that non-spherical powders tend to reduce packing density, our study discovered that the inclusion of a small portion of non-spherical powders can create pathways for efficient gap-filling, resulting in denser packings. (4) By adjusting inter-powder interactions, we observed a transition from discrete powder packing to cluster deposition. (5) We proposed and demonstrated the efficacy of a two-step spreading technique followed by multiple shaking cycles in achieving maximum random packing density. Overall, our work provides a comprehensive understanding of mechanisms involved in the powder spreading process through blade sliding, which may lead to enhanced powder packing density and uniformity and ultimately improved outcomes in additive manufacturing.

The improvement of soil behaviour by the bacterial precipitation of calcium carbonate has been extensively studied in geotechnical engineering. However, the evolution of bio-cementation bonds under shear conditions is only partially understood. This research presents a micromechanical approach to gain a deeper insight into the interaction between bio-cemented particles. A series of glass bead samples were treated with Microbial Induced Calcite Precipitation (MICP) and then subjected to direct shear tests. A calibrated model based on the Discrete Element Method was used to reproduce the macro-mechanical paths observed in the experiments, allowing the detailed analysis and description of the bond evolution at the microscopic scale in the treated samples. In general, it was found that a higher rate of bond breakage occurred before the peak shear strength was reached, and this was followed by a relatively constant rate of bond breakage associated with a macroscopic softening trend. Tensile stress was identified as the primary fracture mechanism. Finally, it was determined that the bond breakage mechanism is influenced by several factors, such as bond distribution, particle array, and the mechanical parameters of the bond.