Computational Particle Mechanics最新文献

The discrete element method (DEM) is suitable to investigate problems where large deformations occur especially in granular material. The fitting of reliable DEM parameters is crucial and a challenge which is caused by the high number of DEM parameters and the computational effort. Despite its drawbacks, a trial and error approach is often used for the DEM parameter calibration. The knowledge of the DEM parameter influence on the model response is necessary to improve the calibration and to check whether the experiment is suitable to calibrate specific parameters or not. It is possible to reduce the dimensionality of the optimisation problem by omitting parameters whose influence on the model response is negligibly small. One approach is to perform a global sensitivity analysis based on Sobol’ indices. A frequently used calibration experiment in literature is the pile experiment. The deviation between the experiment and the simulation is evaluated with the angle of repose. In the present paper, an algorithm to determine the angle of repose considering the three-dimensional shape of the heap is discussed. The global sensitivity analysis is performed for two different experimental heap set-ups. To decrease the computational effort of the sensitivity analysis, the model response is approximated with metamodels whose predictability is evaluated using the root mean squared error (RMSE) based on a separate sampling point set.

Railway operation in desert areas faces unique challenges due to wind-blown sand penetration on the safety of the line. In-depth research on the impact of wind-blown sand penetration on the shear performance of the railway ballast is crucial for understanding potential problems in sandy railways and formulating effective maintenance strategies. This paper conducts a series of direct shear tests under various sand contents and load conditions using an independently developed automatic control loading direct shear test apparatus suitable for railway ballast. By accurately considering the interaction between sand and ballast particles, some direct shear numerical models of different sand-containing ballast boxes based on refined particle simulation are established based on the discrete element method (DEM) and particle scaling method, exploring the variation in shear strength, shear deformation, contact relationships, and rotational characteristics of railway sand-containing ballast from macroscopic and microscopic perspectives. The results show that with the increase in shear strain, the shear stress of the ballast with various sand contents increases first and then tends to stabilize, and the phenomenon of dilation occurs in all cases. When the normal load is constant, the shear strength and cohesion of the ballast show a trend of first decreasing and then increasing with the increase in sand content. The wind-blown sand penetration inhibits the rotational deformation during shearing, enhancing particle aggregation. With the increase in sand content, the contact coordination number, powerful force chain number, and total force chain number all increase continuously. However, the average contact force shows a trend of gradually decreasing and then increasing. This study provides theoretical support and experimental backing for the operation and maintenance of the ballast bed in sandy railways.

In this paper, an accurate meshless method for solving time-fractional wave equation (TFWE) based on KDF-SPH approximation is proposed. In this method, finite difference method is used to discretize the time-fractional derivative defined in the Caputo sense. The spatial discretization is achieved using KDF-SPH meshless method. At the same time, the kernel approximation and particle approximation expressions are given. In order to prove the effectiveness and order of numerical convergence of the proposed method, a number of 1D and 2D initial boundary value problems are numerically simulated in regular and irregular domains, and the meshless method is compared with the existing methods. Numerical results show the effectiveness and accuracy of the proposed method, and the second-order accuracy is achieved in space in the regular calculation area.

A better understanding of the relevance between mixing and heat transfer of granular material is necessary for the design of mixers in various industries. In this work, the effect of impeller speed and filling rate on the mixing and heat transfer of granular material in a ribbon reactor was studied based on DEM simulations. Quantitative criteria which are characterized by the critical mixing time and critical heating time were proposed based on the simulation results. It was found that the area near the vessel wall is heated first, and then the top surface area and the region near the impeller shaft are heated sequentially due to the recirculation effect. Increasing the impeller speed and decreasing the filling rate can improve the mixing and heat transfer performance. The effects of impeller speed and filling rate on mixing and heat transfer weaken as they increase. Results obtained in this work indicate that increasing the mixing performance can enhance the heat transfer of granular material in the ribbon reactor.