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Large-scale landslide dams can induce significant hazards to human lives by blocking the river flows and causing inundation upstream. They may trigger severe outburst flooding that may devastate downstream areas once failed. Thus, the advancement in understanding the formation of landslide dams is highly necessary. This paper presents 3D numerical investigations of the formation of landslide dams in open fluid channels via the discrete element method (DEM) coupled with computational fluid dynamics (CFD). By employing this model, the influence of flow velocity on granular depositional morphology has been clarified. As the grains settle downwards in the fluid channel, positive excess water pressures are generated at the bottom region, reducing the total forces acting on the granular mass. In the meantime, the particle sedimentations into the fluid channel with high impacting velocities can generate fluid streams to flow backwards and forwards. The coupled hydraulic effects of excess water pressure and fluid flow would entrain the solid grains to move long distances along the channel. For simulations using different flow velocities, the larger the flow velocity is, the further distance the grains can be transported to. In this process, the solid grains move as a series of surges, with decreasing deposit lengths for the successive surges. The granular flux into the fluid channel has very little influence on the depositional pattern of particles, while it affects the particle–fluid interactions significantly. The results obtained from the DEM-CFD coupled simulations can reasonably explain the mechanisms of granular transportation and deposition in the formation of landslide dams in narrow rivers.

The air-suction precision seed-metering device is prone to the instability of the seed adsorption state, which arises from blockage of the suction hole and leads to uneven seeding. This paper analyzed and determined key structural parameters of the seed-metering plate, then established an adsorption mechanics model of the seed during the migration process and designed the key structure of the air-suction seed-metering device with the aim of improving the uniformity of high-speed direct seeding of vegetables. Furthermore, we used the DEM-CFD coupling method to analyze the influence of the law of seeds on the change of the flow field with different hole types. Results showed that the turbulent kinetic energy (202.65 m2∙s−2) and the coupling force to the seeds (0.029 N) of the B-type hole are the largest, which is the best fluid domain structure for the suction hole of the seed-metering plate. Moreover, we used Adams to analyze the meshing process between the knock-out wheel and the seed-metering plate, affirming the rationality of the knock-out wheel design. Finally, in order to improve the working efficiency of the seed-metering device, we performed one-factor and response surface experiments of seeding performance using the air-suction seed-metering device designed with the optimized structure as the experimental object. Analysis of the influence of weights across each factor on the experimental performance evaluation indicators revealed an optimal combination of seeding performance parameters in the air-suction seed-metering device, namely a seed-throwing angle of 13°, a working speed of 14.5 km/h, and negative pressure of 3.1 kPa. Results from verification experiments revealed the corresponding experimental indicators, namely qualified, multiple, and missing indexes of 95.9, 1.2%, and 2.9%, respectively.

Rock collapse with large volumes can attain high speeds during their freefall motion. The impact of such a falling mass on the ground surface can initiate a powerful air blast with far-field destructive impact. To investigate the formation, disaster-causing mechanism and dynamic characteristics of rock collapse-induced air blasts, an existing coupled discrete-element method (DEM)–computational fluid dynamics (CFD) approach is employed on a rock collapse-generated air blast in Zengziyan, China (ZRC). The generated air blast shows a maximum velocity of over 50 m/s and subsequently dissipated rapidly. The high consistency between the simulated air blast dynamics and the video verified the DEM–CFD coupled method in the air blast modeling. Combined with the ZRC-induced air blast analysis, a simplified generalized model was designed to observe the potential effect of geomorphology. Results highlight the great contribution of geomorphology, to both air blast initiation and propagation. Collapsed rock mass with a free fall motion is prone to generate significant air blasts when colliding with the slope surface. Tremendous energy was transferred to the surrounding air at the moment. Compared with falling straight down, air blasts resulting from an airborne trajectory case show a longer propagation because the collapsed materials impart air a higher initial momentum parallel to the slope surface. In addition, air blast propagation in wide distribution areas in comparison to narrow valleys shows greater attenuation. This study will aid in understanding the mechanism of a rock collapse-induced air blast as well as the forward simulation of similar events for risk assessment.HighlightsDEM-CFD coupled method provides good performance in simulating the air blast dynamics.Large rock collapse with a free fall motion is prone to generate powerful air blasts when colliding with the slope surface.Geomorphology is greatly influential in both air blast initiation and propagation.

The two-phase solid-liquid flow in the computational fluid dynamic (CFD) method is generally analyzed by treating the solid particles as a quasi-fluid element, but this does not take into account the effects of the physical features of the solid particles and collisions among the particles. In this study, the discrete element method (DEM) was coupled with the CFD method in order to analyze the transient two-phase solid-liquid flow in a single-stage centrifugal pump with consideration for the particle-particle and particle-structure interactions. The numerical simulation process involving EDEM and FLUENT is described. Simulations were performed for the water at 25℃ at the continuous phase together with 15% of the volume as spherical solid particles (density ρ = 1500 kg/m 3 ) with the diameter ranging from 1 to 3 mm in a random order. The results illustrate the motion of the solid particles in the pump and their effect on the flow performance of the pump in terms of time variation in the head. The velocity fields for the two-phase flow together with the volume fraction distributions and trajectories of the solid particles in the centrifugal pump are also presented.

This paper presents three dimensional numerical investigations of batch sedimentation of spherical particles in water, by analyses performed by the discrete element method (DEM) coupled with computational fluid dynamics (CFD). By employing this model, the features of both mechanical and hydraulic behaviour of the fluid-solid mixture system are captured. Firstly, the DEM–CFD model is validated by the simulation of the sedimentation of a single spherical particle, for which an analytical solution is available. The numerical model can replicate accurately the settling behaviour of particles as long as the mesh size ratio D m e s h / d and model size ratio W / D m e s h are both larger than a given threshold. During granular batch sedimentation, segregation of particles is observed at different locations in the model. Coarse grains continuously accumulate at the bottom, leaving the finer grains deposited in the upper part of the granular assembly. During this process, the excess pore water pressure initially increases rapidly to a peak value, and then dissipates gradually to zero. Meanwhile, the compressibility of the sediments decreases slowly as a soil layer builds up at the bottom. Consolidation of the deposited layer is caused by the self-weight of grains, while the compressibility of the sample decreases progressively.

In mechanized rice harvesting, the performance of the cleaning device is one of the important factors that affect the overall efficiency of the combine-harvester. To study the influence of different parameters on the cleaning efficiency, the influence of airflow velocity and the inclination angle on the cleaning effect was analyzed. Both simulation and experimental results prove that the increase of airflow velocity and the inclination angle will reduce the impurity rate of rice and increase the entrainment loss rate. The addition of a vibrating sieve to the device reduces the trash rate of rice, but the entrained loss rate increases accordingly. After tilting the sieve surface by 10°, a reduction in both the impurity rate and the entrainment loss rate of rice was found in combination with the force analysis of the particles on the sieve surface. The effect of the device structure on the internal flow field distribution was analyzed by comparing the eddy viscosity and velocity flow lines inside the three scavenging device structures. Simulation after calibration of rice moisture content revealed that humid rice cleaning was not effective.

During the landslide mobility process, there is a dynamic interaction between the sliding main body and the different surrounding media. This affects the mobility characteristics of the landslide, particularly the friction force and contact force, which play the significant roles of dissipating and transferring energy in the sliding main body, respectively. In order to analyze the dynamic characteristics of rapid and long-runout landslides, the discrete element method solver of EDEM software and the computational fluid dynamics code of ANSYS-Fluent solver for a two-phase flow-like landslide, combined with flume tests and a field case, were used to research the following points: (1) When the liquid volume fraction is large enough during the mobility process of a two-phase flow-like landslide, the liquid phase provides a certain drag force relative to the solid phase. (2) The drag force was determined from the volume fraction of the liquid, the solid–liquid velocity difference, and the viscosity coefficient of the liquid, which together affect the characteristics of the landslide’s mobility and accumulation. (3) According to the back analysis of the Xianchi Reservoir landslide, fluid drag force plays an important role in the actual landslide mobility process. Therefore, it is necessary to consider the influence of the fluid drag force in hazard zoning and the post-failure mobility process analysis of large-scale flow-like landslides.

On April 9, 2018, a massive rock avalanche hit the area of Karimabad, Hunza. Approximately 2Mm3 of rock mass detached from the source area and traveled a total of 4.88 km. The rock mass deposited along 2000 m length and destroyed the Ultar meadows. The avalanche killed three tourists and resulted in a vast dust cloud that engulfed the entire town of Karimabad in a few seconds. In this paper, we have analyzed the dynamic characteristics of the Ultar rock avalanche and subsequent airblast using a coupled three-dimensional discrete element modeling and computational fluid dynamics approach. Two-way coupling was carried out using an application programming interface that transferred the data between models to simulate the avalanche movement and induced airblast. We have also analyzed the formation and propagation of induced dust clouds based on field investigation, captured video, and climatic conditions. The study concludes that the Ultar rock avalanche’s movement lasted 148 s. The average velocity of sliding material was found to be 26.35 m/s. The dynamics of induced airblast were studied along the entire runout path. The maximum velocity of generated airblast along different sections of the runout path was found to be 40 m/s and 35 m/s, respectively, whereas the relative pressure of the blast wave was found to be 0.6 kPa. Furthermore, the results revealed that a low-pressure dust cloud traveled a long distance due to the continuous fragmentation of the sliding material along a steep runout path. The induced dust cloud engulfed the entire town of Karimabad, Hunza, for several hours. This study is expected to help scientists further explore the dynamics of the airblast. It will also help understand the formation and propagation of dust clouds induced by rock avalanches involving excessive fragmentation.

Seepage erosion is one of the main reasons for the local collapse or instability of embankments. To investigate the characteristics and mechanism of seepage erosion for cohesionless soils, model tests using an independently developed seepage erosion device and numerical simulations based on a discrete element method-computational fluid dynamics (DEM-CFD) coupling model were carried out. The results show that the seepage erosion process of cohesionless soil could be characterized by four stages: stable seepage, upward migration of fine particles, boiling of sand samples, and erosion damage. The skeleton structure of a soil sample under seepage flow was continually changed due to the loss of fine soil particles, which resulted in a significant decrease in the sample strength and could, ultimately, lead to the failure of the sample. The results of this study can provide references and bases for the design, construction, and long-term service of embankments or earth dams under complex seepage conditions, reducing the risk of seepage erosion.