Computational Particle Mechanics最新文献

This paper presents a constrained particle dynamics (CPD) framework with explicit and implicit algorithms for simulating differential–algebraic equations of motion for systems of particles under constraints. Addressing limitations in existing techniques such as position-based dynamics (PBD), commonly used in computer graphics but prone to inaccuracies, the CPD approach utilizes Hamilton’s variational principle and Lagrange multipliers to ensure accurate constraint enforcement. The explicit CPD (xCPD) algorithm employs a central difference scheme, enhancing efficiency by advancing the system under external forces and applying a correction term for constraints. The implicit CPD (iCPD) algorithm uses the Trapezoidal rule, solving a saddle point problem that integrates dynamic and constraint equations, offering robustness for larger time steps. The effectiveness of the CPD algorithms is demonstrated through mathematical analysis and numerical comparisons of benchmark problems. Results indicate that CPD algorithms achieve higher accuracy and superior energy conservation properties compared to PBD, exhibiting second-order convergence rates; whereas, PBD shows only first-order convergence.

Cavitation erosion is a pervasive issue in hydraulic machinery and ocean engineering, characterized by the collapse of bubbles, micro-jetting, and impact erosion, all exhibiting strong transient, microscale, and fluid–solid coupling features. Understanding these phenomena is essential for elucidating the mechanisms behind erosion and for developing strategies to prevent wear damage. Recognizing the limitations of conventional numerical methods, this study employs the smoothed particle hydrodynamics (SPH) method to develop a fluid–solid coupling model that simulates cavitation erosion at the bubble scale. The Lagrangian and mesh-free nature of SPH make it well-suited for tracking the transient processes of asymmetric bubble collapse, jet formation, and the subsequent impact on elastic–plastic materials. A comprehensive fluid–solid coupling SPH model is constructed, encompassing bubbles, surrounding liquids, and elastic–plastic materials. This model includes a compressible multiphase SPH approach for simulating the interaction between highly compressible bubbles and liquids. To address gas phase over-compression during bubble collapse, a modified particle regeneration technique (PRT) is introduced, allowing for automatic adjustment of particle resolution in the gas domain as it expands or compresses. For the solid simulation, an elasto-plastic constitutive model and a failure model are integrated into the SPH framework to describe material deformation and failure due to microjet impacts. These enhancements enable the simulation of the entire cavitation erosion process within a unified, mesh-free context. The SPH model is validated through simulating bubble collapse and jetting induced by shock waves. It is then applied to investigate the dynamics of cavitation erosion near both rigid and elastic–plastic materials, providing quantitative analysis of the erosion process. The outcomes of this research contribute significantly to our understanding of cavitation erosion mechanisms and offer a robust computational tool for predicting and mitigating erosion damage in related engineering applications.

Currently, most experts only focus on the surface failure characteristics of material structures. Moreover, previous damage constitutive models were unable to simulate the nonlinear deformation characteristics of cement crushed stone during the initial compaction stage. To study the microdamage of cement crushed stone after freeze–thaw cycles and uniaxial compression, further exploration was conducted on the changes in displacement, number of microcracks, relationship between acoustic emission events and microcrack development after freeze–thaw cement gravel loading, as well as the number of force chains before and after loading. Based on the theory of damage mechanics, this article establishes a damage constitutive model that can simulate the entire deformation process of cement crushed stone under uniaxial compression conditions using a particle flow program. Based on the numerical model created by the discrete element method, this article reproduces the entire process of internal fracture of cement crushed stone from a microscopic perspective, which has certain advantages in studying the complex mechanical behavior of cement crushed stone. After freeze–thaw treatment, irreversible damage occurs inside the cement-stabilized crushed stone. The more freeze–thaw cycles, the lower the compressive strength of cement-stabilized crushed stone.

In this paper, we focus on three issues related to applications of material point methods (MPMs) to objects with complex geometries. They are material point generation, compatibility of material points with a mesh, and sensitivity to mesh orientation. An efficient method of generating material points from a stereolithography (STL) file is introduced. This material point generation method is independent of the mesh used in MPM calculations. The compatibility between the material points and the mesh is then studied. We also show that the original MPM and the dual domain material point (DDMP) method are sensitive to mesh orientation. These issues are related to the calculation of the internal force and are concerns of the MPMs. They become more prominent when MPMs are applied to complex geometries. Our numerical results show that the recently developed local stress difference (LSD) algorithm (Perez et al. in J Comp Phys 498:112681, 2024) can be used to effectively address them.

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%.