Granular Matter最新文献

Thermal backfill is an integrated part of underground electrical cable infrastructures systems, ground heat source pumps and radioactive waste repositories, as it minimizes resistance to heat transfer away from these systems. The heat transfer capacity and current carrying capability of underground electrical cables are significantly affected by thermal conductivity of backfill material and the surrounding soil media. Therefore, this research paper compares the thermal conductivity and shrinkage results of compacted (low to high densities) fly ash- and sand-bentonite mixtures with bentonite contents of 30%, 50%, 60%, 80% and 100%. The thermal conductivity of mixtures increased from 1.05 Wm⁻¹K⁻¹ to 1.20 Wm⁻¹K⁻¹ with the addition of fly ash content from 20 to 70% by weight in bentonite. The thermal conductivity bentonite-sand mixture was also found to be increased from 1.21 Wm⁻¹K⁻¹ to 1.83 Wm⁻¹K⁻¹ with increasing sand content. Additional to this, the bentonite-sand and bentonite-fly ash-based backfill materials surrounding heat-sensitive structures experience shrinkage and desiccation cracking due to thermal drying. Therefore, the desiccation volumetric shrinkage tests of bentonite-sand and bentonite-fly ash mixtures were conducted and found that the presence of sand or fly ash reduces shrinkage strain. Based on the experimental results, this study suggests a sustainable utilization of fly ash up to 50%-70% as an effective thermal backfill material in electrical cable infrastructure systems. Thus, the application of fly ash as a construction material reduces environmental impact and cost, aligning with the goals of sustainable development.

In this paper, real-time measurements of three-dimensional wind speed, electric field and dust concentration during the floating-dust event were carried out in Lanzhou. The scaling relationship of different physical quantities in spectral space and the effect of turbulent events on dust and heat transport are studied by spectral method and octant analysis method. Our results show that the logarithmic value of power spectrum of dust concentration, relative humidity (RH), streamwise and vertical wind speed (u and w) between 0.06 Hz and 0.435 Hz meets the linear relationship with the logarithmic value of frequency (f), and decreases with the logarithmic value of f. For different stages, in the frequency range from 0.06 Hz to 0.218 Hz, the slope of the u first increases and then decreases. The slope of dust concentration and RH did not change significantly in the development stage, but decreased in the decay stage. The slope of the temperature (T) first decreases and then increases. In the frequency range from 0.218 Hz to 0.435 Hz, the slope of u and RH first increase and then decrease. The slope of the dust concentration does not change significantly during the development stage and decreases in the decay stage. The slope of w first increases and then decreases. In the second stage, the contribution of ejection and sweep events to the turbulent motion increases. For dust and heat transport, the O₅ and O₈ have a larger number contribution. Although the number and intensity contribution ratio of all octants increased or decreased in the second and third stages, in terms of the intensity of a single event, the contribution of all octants to the dust and heat transport increased.

The liquid bridge rupture has attracted much attention in various fields such as powder technology, micro gripping, and wet agglomeration. In present study, an artificial neural network (ANN) model was developed to predict the liquid bridge rupture between two plates, focusing on the rupture distance and the transfer ratio. The initial weights and biases of the ANN model were optimized by the grey wolf optimization algorithm (GWO). The GWO-ANN model prediction is compared with the BP-ANN model prediction. Based on the testing dataset, the mean square error (MSE) and correlation coefficient (R²) of the rupture distance for the optimized GWO-ANN model were calculated as 4.65 × 10^− 4 and 0.9586, and that of the transfer ratio was 2.15 × 10^− 4 and 0.975, respectively. The effectiveness of the constructed GWO-ANN model for the liquid bridge rupture prediction was verified by experimental investigations. The effect of input parameters including contact angles, stretching speed, liquid volume and liquid viscosity on the rupture was discussed in detail.

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