Granular Matter最新文献

Jet grouting is a geotechnical consolidation technique commonly used to improve soil mechanicals. Despite its successful applications, understanding micro-level interactions between the jet and soil is incomplete. This paper utilizes the Smoothed Particle Hydrodynamics (SPH) and Arbitrary Lagrangian-Eulerian (ALE) methods to simulate fluid-soil interactions in both non-submerged and submerged environments. Analysis covers the flow fields and soil erosion. Findings show erosion velocity remains steady in non-submerged conditions, with the jet compacting and flushing soil. In submerged conditions, the simulated jet flow field under soil constraint is similar to that in the free submerged conditions. However, influenced by soil deformation, damage, and the backflow of the slurry, the jet flow field under soil constraint displays distinct features. For instance, velocity distributions in certain cross-sections cannot be accurately described by normal distribution, and axial velocity distribution curves exhibit different partitions compared to free submerged jet theory. Comparative simulations vary jet pressures, grout water-cement ratios, and soil compactness to analyze the erosion process. It is found that jet pressure significantly affects the depth of the erosion pit. The limit erosion distance in ALE simulations were compared with theoretical values derived from an established theory, and a model experiment was also conducted to analyze the jet-grouted diameter at different left speeds and rotational speeds of rod. The results show that ALE method can offer high accuracy in predicting the jet-grouted diameter and proves to be a feasible approach for fluid-soil interaction simulations in jet grouting.

We investigate the influence of particle stiffness on the grasping performance of granular grippers, a class of soft robotic effectors that utilize granular jamming for object manipulation. Through experimental analyses and X-ray imaging, we show that grippers with soft particles exhibit improved wrapping of the object after jamming, in contrast to grippers with rigid particles. This results in significantly increased holding force through the interlocking. The addition of a small proportion of rigid particles into a predominantly soft particle mixture maintains the improved wrapping but also significantly increases the maximum holding force. These results suggest a tunable approach to optimizing the design of granular grippers for improved performance in soft robotics applications.

Graphic abstract

Plastic consumption is on the rise, particularly in Europe, where million tonnes are produced each year, with only 10% recovered. Optimizing the recycling processes in all its phases is vital. Understanding particle movement in some components of the plastic recycling plants can be addressed by the Discrete Element Method (DEM). The characterization of DEM materials is often performed through the study of the angle of repose (AoR). This study aims to advance DEM simulation of shredded polymeric waste, proposing a scaling and calibration procedure of the relevant simulation parameters. A total of six distinct types of polymeric particles, with different shape and size, have been characterized in this study, measuring their density, their shape estimators, their size distribution and their angle of repose. The AoR has been measured through a hollow cylinder lifting test. First, sensitivity analyses have been performed to establish a suitable range for the numerical parameters and to reduce the dimensionality of the problem. Then, the scaling and calibration procedure is described and tested on the six batches. The proposed procedure allows to predict very well the AoR, with an error below 1%, and the other geometrical variables of a heap, although it deteriorates in fully predicting its shape when the sphericity of the particles decreases.

Graphical Abstract

The powder consolidation and equipment damage caused by frequent pressurization of the lock hopper silo seriously affect stable powder discharge and transportation. This paper investigated the powder compression and gas permeation characteristics during the silo pressurization by experiment and simulation. The spherical glass powder and irregularly shaped coal powder were selected as the granular materials. The modified drag model agrees well with the experiments for spatial pressure cumulative distribution and full-process pressure drop. The coal powder has a higher average compression ratio than the glass powder. The local porosity of the powder layer experiences two stages of rapid decrease and slow stabilization. The powder compression arises from particle rearrangement and bed pore structure reconstruction under airflow disturbance. The nonlinear growth of pressure accumulation curves at different spatial points in the early stage of silo pressurization forms a fusiform envelope surface. As the average pressure-increasing rate increases, the peak gas pressure gradient of the powder layer increases approximately linearly. The penetration time difference of glass powder between powder layers I and V is less than 1 s, while that of coal powder is close to 4 s. There was a significant time hysteresis effect for gas penetration in the coal powder silo.

Graphic abstract

The mechanics of granular materials at the macroscopic scale inherently depends on the particle interactions occurring at the microscopic scale. In recent decades, growing investigations have explored the mechanics of granular materials subjected to thermal cycles, as they involve complex responses that bear significance for science, engineering, and technology. However, the fundamental understanding of the mechanics of granular materials subjected to thermal cycles remains hindered by the absence of empirical evidence into the microscopic particle interactions that govern the macroscopic response of such materials. For the first time, this study presents direct experimental evidence obtained via synchrotron X-ray microtomography to reveal the behavior of the particles that constitute granular materials during thermal cycling. This work experimentally confirms the existing theory by which thermally induced particle interactions drive a macroscopic volumetric expansion and contraction of granular materials upon heating and cooling, respectively, and the development of irreversible volumetric deformations upon the completion of thermal cycles. The results uncover the evolution of particle non-uniform translations, rotations, and contact variations during thermal cycling, which all inherently depend on particle shape.

This study investigates the influence of particle shape on the void space morphology and topology in granular materials. Numerical samples with spherical and ellipsoidal particle shapes were generated using the discrete element method. A segmentation algorithm was used to extract the pore space characteristics. The results reveal that particle shape significantly affects both constriction and pore sizes, with distinctive features according to flatness index or elongation ratio, the former being more significant than the latter. The obtained results were validated by conducting numerical filtration tests, which illustrated a direct correlation between the constriction properties derived from the pore space extraction and the blockage rate of fine particles in the filtration tests. The study revealed the importance of considering particle shape in filter design, emphasising its significant impact on pore space characteristics and filtration performance.

Graphic abstract