CFD-DEM Coupling Research Articles

Numerical simulation of ice loading characteristics of ships in a wave-current environment in a broken ice area

A numerical simulation technique with CFD-DEM coupling is used to simulate a full-scale KCS model sailing in the pancake ice region. Based on the actual polar information, the Stokes fifth-order wave model is selected. The pancake ice particle of two scales is established based on the DEM, and the corresponding broken-ice region is generated. The contact and collision problems of ice-ice and ice-wall (ship) were analyzed by solving the Hertz-Mindlin model, and the monitored data were processed and summarized. The results show that the ice load on the ship is a repetitive “loading-unloading” process, and the peak ice load curve is characterized by segmented and concentrated fluctuations. In terms of ice parameters, the pancake diameter has a great degree of influence on the crushed ice loads, and the size of the crushed ice loads increases with the diameter of the crushed ice particles.

DEM-CFD coupling verification and analysis of a sand control medium structure with weakened particle blockage performance

This study addresses the prominent contradiction between solid phase control and production capacity release during the exploitation of natural gas hydrate in fine silty sand reservoirs. A novel mechanical sand control medium structure incorporating the filter slots/nets (referred to as the sand control component, SCC) and the cylindrical/spherical structures placed outside the SCC (referred to as the blockage control component, BCC) has been designed. Concurrently, a DEM-CFD sand-retaining numerical model is developed, and the traditional/new structural screens have been separately simulated for sand retention. Through the spatiotemporal evolution of DEM and CFD characteristic model parameters during simulation, the blockage mechanism and characteristics of fine particles are obtained. Compared to the traditional screen structure without a BCC, the existence of a BCC effectively evacuates particles within the accumulated sand body towards the wellbore, reducing the compactness and stress level within the sand body; while the pressure loss generated by fluid flow through the sand body decreases, significantly improving the porous and permeable conditions within the sand body. The degree of influence of a BCC on different DEM and CFD characteristic model parameters is further determined and ranked. A comprehensive blockage optimization index is introduced to quantify the performance of weakening sand blockage by the BCC and optimize the spatial position of the BCC. The BCC enables the design of sand control schemes to reduce the filter aperture of the SCC to a sufficiently small size to effectively control the fine silty sand production, while avoiding gradually severe blockage as production progresses.

A novel CFD-DEM coupling method with moving boundary for simulating one-dimensional consolidation test

The conventional CFD-DEM coupling method fails to dynamically modify the position of the drainage boundary during the simulation of one-dimensional consolidation tests (1d CT), resulting in inaccuracies in the numerical results. In this study, a novel CFD-DEM coupling method with moving boundaries is proposed to simulate 1d CT where the fluid boundary adaption and internal mesh reconstruction are implemented with reference to the real-time morphology of the consolidation specimen. Additionally, the convective terms in Navier-Stokes equations are modified to account for the moving drainage boundary and the equation of state (EOS) is introduced to consider fluid compressibility. A series of 1d CTs based on the traditional fixed boundary and the moving boundary are subsequently conducted for comparison. Moreover, the influence of fluid compressibility and mesh coarseness on the consolidation characteristics is briefly discussed. The proposed method is verified to serve well in revealing the underlying microscopic mechanism of the Mandel-Cryer effect and complementing the traditional consolidation theories.

Numerical investigations of the restriction effects on a ship navigating in pack-ice channel

This paper adopts Computational Fluid Dynamics (CFD) method and Discrete Element Method (DEM) to simulate a ship navigating in pack-ice channel considering the effects of channel restriction. First, from the simulations of the ship sailing in open-water channel by CFD, it is found that the effects of channel width on water resistance is more pronounced than the impacts by level-ice thickness. Then, based on the stable and converged flow field obtained by CFD simulations, the CFD-DEM coupling method is applied to reveal the effects of channel width and level ice thickness on ship-ice-water interactions and ice resistances at different ship speeds. The results indicate that as the channel width decreases, the accumulation of pack ice in the areas of bow and midship intensifies. The ice resistances on the bow and midship increase notably, and the lateral ice forces exhibit pronounced asymmetric and random characteristics. In extremely narrow pack-ice channels, lower ship speed results in lager ice resistance and lateral ice force on the ship. In addition, as the level ice thickness decreases, the pack ice is more easily squeezed below the level ice, resulting in the decreases of ice resistance and lateral ice force.

Micro-mechanical behavior of stone-blowing in ballast maintenance using DEM-CFD coupling method

Stone-blowing restores the track geometry by blowing small crushed stones into the bottom of the sleeper, extending the maintenance period. In this study, ballast and filling stones were modelled using discrete element method (DEM), while the air blowing was simulated using computational fluid dynamics (CFD). The DEM-CFD coupled model has been used to simulate the stone-blowing process and investigate the optimal operation parameters from a micro view.The disturbance of ballast bed during stone-blowing process was analyzed. Meanwhile, the effect of air velocity and tube layouts on the stone-blowing, as well as the sleeper settlement after stone-blowing were discussed. The results show that the maximum disturbance occurs in the inserting area between sleepers, and the disturbance increased with faster insertion speed. It was suggested that the inserting speed of the tube is 0.4 m/s. When the air velocity of stone-blowing was not less than 20 m/s, the blowing quality meets the requirement. Furthermore, the four-tubed stone-blowing approach distributed filling stones more evenly under the sleeper, and reduced the risk of tube blockage. After stone-blowing, the contact number between the bottom of the sleeper and the ballast is greatly increased, reaching 217.9 % after double cross tubes, and 245 % after four tubes stone-blowing. The crushed stone blown in greatly improves the stress distribution of the ballast bed and makes the load transfer more uniform. Overall, this study provides valuable insights into the stone-blowing process and can help optimize the stone-blowing parameters for efficient and effective track maintenance.

Scour mechanism around a pipeline under different current-wave conditions using the CFD-DEM coupling model

Understanding the pipeline scour mechanism under different conditions is essential for protection measures. The computational fluid dynamics (CFD) and discrete element method (DEM) are coupled for the simulations. To reduce the computational effort, the coarse-grained method is applied, and the Darcy-Forchheimer porous model is used to replace the far field elements. Both of the porous medium and particles-fluid interaction model are validated by comparison between simulation results and theories. The scouring simulation results show a good agreement with the experiments conducted with single-diameter spherical particles under different current-wave conditions. Further, the flow around the pipeline, the seepage in the sediment bed and the force acting on the particles are analyzed. The vortex shedding exists downstream under current but the vortex moves around under waves. The seepage depends on the pressure, influenced by the pipeline and the water depth, and the variation of the seepage is discussed. The force acting on the particles is not uniform along bed and the distribution is analyzed.This paper provides an insight into scour mechanics from the aspects including seepage and flow-particle interaction. Different methods are used for modification, giving a reference for the usage of CFD-DEM model in the analysis of scour process.

Constructing a cut-off dam inside a water-filled circular tunnel with backfill grouting

This study employs laboratory model tests for backfill grouting and numerical analyses (coupled analysis of the discrete element method and computational fluid dynamics, DEM-CFD coupling analysis) to investigate the feasibility of constructing a cut-off dam inside a water-filled circular tunnel using the backfill grouting method from the ground surface. Several improved backfill methods were studied to enhance the effectiveness of the cut-off dam. These methods include: (a) adding an additional backfill grouting hole between the double-row cut-off dam and applying pressurized grouting; (b) adjusting the number of backfill grouting holes per row of the cut-off dam; (c) simultaneously grouting the double-row cut-off dams to minimize the formation of interface fissures and voids; (d) adjusting the grout hole spacing of the double-row cut-off dams to reduce the volume of backfill material. Additionally, pressurized mortar grouting is a critical mass to ensure the water tightness of the cut-off dam. The implementation of these backfilling arrangements improves the effectiveness and watertight of the cut-off dam, thereby reducing the construction time and cost. The findings of this study can serve as a reference for water-filled tunnels and subsequent rehabilitation works in the future.

Sand control mechanism of radial well filled with phase change material in hydrate reservoir

Radial well filled with phase change material has been proposed as a novel sand control method for hydrate exploitation. In order to reveal the sand control mechanism, CFD-DEM coupling method is applied to simulate the migration, settlement, and blockage processes of sand particles in the radial well. The obtained results indicate that three scenarios have been recognized for sand particles passing through sand control medium, based on the diameter ratio of sand control medium to sand particle (Dd): fully passing (Dd = 8.75–22.5), partially passing and partially blocked (Dd = 3.18–5.63), and completely blocked (Dd = 2.18–3.21). After being captured by the sand control medium, sand particles can block pores, which increases fluid flow resistance and causes a certain pressure difference in the radial well. The pressure in the radial well should be lower than the hydrate phase equilibrium pressure during sand control design, for the purpose of promoting hydrate decomposition, and sand capture. The length of the radial well should be optimized based on the reservoir pore pressure, production pressure difference, bottom hole pressure, and the pressure gradient in the radial well. It should be noticed that the sand control medium leads to a decrease in permeability after sand particles captured. Even the permeability is reduced to several hundred millidarcy, it is still sufficient to ensure the effective flow of gas and water after hydrate decomposition. Increasing fluid velocity reduces the blocking capacity of the sand control medium, mainly because of deterioration in bridging between sand particles.

Study on flow characteristics of vertical pneumatic conveying of stiff shotcrete materials based on CFD-DEM

In view of the vertical pneumatic transportation process of stiff shotcrete materials (SSM), the method of CFD-DEM coupling numerical simulation was used to analyze the flow characteristics of the SSM. In this aspect, the flow characteristics of SSM transported by vertical pipe pneumatically under different solid-gas ratios were studied. Among them, the accuracy of the simulation results was verified through SSM particle parameter calibration and field testing. The research results show that during the process of vertical pneumatic transportation, full pipe flow, annular flow, and suspended flow can be clearly observed in the pipe. The cross-sectional particle volume fraction increases as the feeding rate increases, and the conveying stability becomes worse. As the air velocity increases, and the conveying stability becomes better. This study can provide support for research on vertical pneumatic conveying, thereby effectively reducing energy loss during the process of spraying

Investigation of vibration on rheological behavior of fresh concrete using CFD-DEM coupling method

Vibration can increase the flow ability of fresh concrete and may cause segregation. The rheology behavior of fresh concrete after vibration is different from that in the unvibrated state. In this paper, a CFD-DEM coupling method was developed to investigate the rheological behavior of fresh concrete before and after vibration. The Bingham model and Hershcel-Bulkley were respectively used as the constitutive relationship of fresh concrete in unvibrated and vibrated state. The Hertz-Mindlin with bonding bond is employed to describe the interaction between coarse aggregate. To analyze the effect of vibration on the rheological behavior of fresh concrete, the rheometer test was conducted. The relationship of shear stress and shear strain rate is linear before vibration and is nonlinear after vibration. Vibration reduces the yield stress and plastic viscosity of concrete. The shear zone decreases when fresh concrete is vibrated.

Studying particle transport characteristics in centrifugal pumps under external vibration using CFD-DEM simulation

Centrifugal pumps play a crucial role in deep-sea mining systems. In the marine environment, external vibrations induced by ocean currents and waves can impact the particle transport characteristics of centrifugal pumps in mining systems. CFD-DEM coupling simulations were conducted to simulate operating conditions with external vibration frequencies of 5, 10, and 15 Hz. The study reveals that in the suction chamber, with increasing vibration frequency, the dynamic number of particles decreased, and the percentage of particles with greater velocities than the fluid velocity increased. In the impeller channel, with increasing vibration frequency, the number of collisions among particles and pressure surface of the impeller decreased, and the average energy loss per collision increased. Therefore, external vibrations provide additional kinetic energy for particles, reduce the deposition effects of particles, and improve the pass-ability of particles. This paper can provide theory and engineering support for operation of deep-sea mining centrifugal pumps.

Fluid–Solid Mixing Transfer Mechanism and Flow Patterns of the Double-Layered Impeller Stirring Tank by the CFD-DEM Method

The optimization design of the double-layered material tank is essential to improve the material mixing efficiency and quality in chemical engineering and lithium battery production. The draft tube structure and double-layered impellers affect the flow patterns of the fluid–solid transfer process, and its flow pattern recognition faces significant challenges. This paper presents a fluid–solid mixing transfer modeling method using the CFD-DEM coupling solution method to analyze flow pattern evolution regularities. A porous-based interphase coupling technology solved the interphase force and could be used to acquire accurate particle motion trajectories. The effect mechanism of fluid–solid transfer courses in the double-layered mixing tank with a draft tube can be obtained by analyzing key features, including velocity distribution, circulation flows, power, and particle characteristics. The research results illustrate that the draft tube structure creates two major circulations in the mixing transfer process and changes particle and vortex flow patterns. The circulating motion of the double-layered impellers strengthens the overall fluid circulation, enhances the overall mixing efficiency of the fluid medium, and reduces particle deposition. Numerical results can offer technical guidance for the chemical extraction course and lithium battery slurry mixing.

Research on the cuttings discharge in air cushion chamber of slurry shield based on CFD-DEM coupling method

The rapid discharge of cuttings from the air cushion chamber is crucial for the construction safety and excavation efficiency of the slurry shield. Previous studies have mainly focused on the transport characteristics of cuttings in the slurry discharge pipe, while the complete process of cuttings entering the slurry discharge pipe from the air cushion chamber until they are discharged was often overlooked. Based on the CFD-DEM coupling method and combined with actual engineering, this paper established a numerical model that can more completely reflect the cuttings discharge process during slurry shield tunneling, and the effects of the slurry velocity at slurry gate and scouring pipes, inclination angle of slurry discharge pipe, cuttings diameter and shape coefficient were investigated by analyzing the variation in the mass flow rate, mass of discharged cuttings, and discharged ratio. The results revealed that increasing the slurry velocity can promote the discharge of cuttings. To keep the discharged rate at a high level, it is recommended that the slurry velocity at the slurry gate should be greater than 0.15 m/s. Reducing the inclination angle of the discharge pipe is conducive to the rapid discharge of cuttings. Cuttings with large diameter or small shape coefficient are more prone to accumulate in the air cushion chamber and cause clogging risk. The research results not only help to improve engineers' understanding of cuttings discharge in slurry shield, but also provide practical guidance for formulating relevant construction measures.

Numerical Simulation of Proppant Transport in Major and Branching Fractures Based on CFD-DEM.

This research investigated the effect of branching fracture, proppant, and fracturing fluid on proppant transport based on the CFD-DEM coupling model. The obtained results show that the balance height of embankment in the major fracture decreases gradually with increasing angle between major and branching fractures, while it increases gradually in the branching fracture. This is because the additional resistance of fracturing fluid flow at the joint increases with increasing angle, leading to the decrease of the fracturing fluid velocity. The proppant is prone to settling in branching fractures, resulting in the increase of embankment height in the branching fracture. At angles of 45, 60, and 90°, as the diameter of the proppant increases from 0.8 to 1.1 mm, the balance height of embankment increases slightly in the major fracture, while it decreases in the branching fracture. The frictional resistance of the fracture wall enhances the difficulty of large proppant entering the branching fracture, resulting in a decrease in the amount of proppant entering the branching fracture and a decrease of the balance height of embankment in the branching fracture. In the low-viscosity fracturing fluid, the proppant quickly deposits at the bottom of the fracture as it enters the fracture. Improving the viscosity of the fracturing fluid can significantly enhance its ability to transport the proppant. The proppant is less likely to quickly settle in high-viscosity fracturing fluids, especially when the fracturing fluid viscosity exceeds 50 mPa·s.

Four-way CFD-DEM coupling to simulate concrete pipe flow: Mechanism of formation of lubrication layer

This study introduced a four-way CFD-DEM coupling approach to simulate the shear-induced particle migration (SIPM) mechanism leading to formation of the lubrication layer (LL) during concrete pumping. The CFD-DEM simulations considered the coupled effect of concentration (10 %–40 %) and wide size distribution (1–17 mm) of aggregate and rheology of the mortar for forces between the suspending matrix and the particles (and vice versa), as well as force transmission directly between particles (and the pipe wall). The formation of the LL was successfully simulated through a more realistic understanding the SIPM mechanism and rheological evaluation across the pipe with comparable calculation times compared to the one-way coupled DEM approach, especially for high concentrations. The simulated LL thicknesses of 0.8–2.7 mm compared well with experimental values. The flow rate and rheological heterogeneity of pumped concrete, and rheology of the LL, were found mostly controlled by the granular-skeleton characteristics rather than the suspending-matrix rheology.

Study on the diffusion and deposition law of pore slurry in gangue filling zone based on CFD-DEM coupling.

In this study, the slurry diffusion in a cavity filled with coal gangue was studied by combining experimental and numerical simulation methods. By calibrating slurry and particle materials, the grouting process in coal gangue filling area is simulated successfully, and the change of slurry diffusion flow field and particle movement and settling process in different dimensions are deeply analyzed. Both experimental and numerical simulation results show that the particle settlement presents a bell-shaped curve, which is of great significance for understanding the particle movement and settlement behavior in the filling cavity. In addition, it is found that the grouting speed has a significant effect on the particle settlement during the slurry diffusion process. When the grouting speed increases from 0.1m /s to 0.2m /s, the particle settlement and diffusion range increases about twice. In the plane flow field, it is observed that the outward diffusion trend and speed of grouting are more obvious. It is worth noting that in the whole process of grouting, it is observed that with the increase of grouting distance and depth, both the velocity of slurry and particles show a trend of rapid initial decline and gradually slow down, and the flow velocity of slurry near the grouting outlet at a flow rate of 0.2m/s is 2-4 times that of 0.1m/s. This provides important enlightenment for the porous seepage effect at different grouting speeds.

Influence of guide vane on dispersion of aggregates near the guide vane in a turbo air classifier

Ultra-fine particles are prone to agglomeration, limiting the preparation of ultra-fine powder. The aggregates' disaggregation mechanism is studied, and the proposal of improving the guide vane of a turbo air classifier is contributed to strengthen powder disaggregation based on CFD-DEM coupling and the novel local fluid domain extraction method. The results show the cylindrical tail of guide vane is conducive to the disaggregation, and the powder dispersion near the guide vane is improved. When the inlet air velocity vin is <18 m·s−1, the cylindrical tail of guide vane can significantly improve the powder dispersion. When the cylinder diameter is larger than or equal to 2 mm, the effect of the increase of the cylinder diameter on powder dispersion is significant. However, the increase of cylinder diameter will lead to the increase of energy consumption, so the cylinder diameter should not be too large.

Study of the water cleaning process by using CFD-DEM method: A case study of coarse filter material

In this paper, the CFD-DEM coupling method was utilized to study the water cleaning and regeneration process of fibrous filter material. The effects of cleaning flow rate, time and adhesion force on the particle removal process were simulated. The results showed that the particle removal rate had a diminishing marginal effect with the increasing of cleaning flow rate. More than 80% of the particles were removed in the initial period, and then tended to stabilize. The higher the flow rate, the shorter the time needed to achieve stability. For G4 filter material, the function between the particle removal rate and the cleaning flow rate and time was given, and the best cleaning flow rate was 1.2 m/s while the cleaning time was 30 seconds. The surface energy of the fibers plays a dominant role in the cleaning process, and the reduction 1/4 of the surface energy of the particles can effectively improve the cleaning and regeneration performance.

Numerical analysis of snow distribution on greenhouse roofs using CFD–DEM coupling method

Numerical analysis of snow distribution on greenhouse roofs using CFD–DEM coupling method

Numerical simulations of sand‐screen performance in unconsolidated prepacked gravel screen

AbstractThis work addresses the ongoing challenge of optimizing sand control screens, attributed to a limited understanding of screen blocking. A novel one‐way computational fluid dynamics and discrete element method (CFD–DEM) coupling technique is presented to analyze the structural parameters of unconsolidated prepacked gravel screens (PPGS). CFD–DEM involves systematically investigating the width of the punched slot on the outer protective screen, the size of the gravel, and the efficiency of gravel packing to improve the antiblocking capability of unconsolidated PPGS. Results from numerical simulations reveal that under conditions of effective sand control, the amount of sand entering the gravel layer to the bridge (referred to as the sand pass rate) is positively correlated with the antilocking ability (referred to as oil productivity index) for unconsolidated PPGS. The efficiency of gravel packing has the most substantial effect on the antilocking performance of unconsolidated PPGS. The data suggest that appropriately reducing the efficiency of gravel packing can enhance the antilocking capability of unconsolidated PPGS. To design an unconsolidated PPGS with enhanced antilocking capability, the efficiency of gravel packing be determined first. Then, the gravel size is designed based on this efficiency, and the width relative to the gravel size is decided. This contemporary design principle diverges considerably from previous design principles for gravel‐packed sand control screens. Supporting validation experiments agree with simulation outcomes, suggesting the established one‐way CFD–DEM coupling method in this paper is suitable for analyzing the plugging mechanism of unconsolidated PPGS. Thus, the CFD–DEM coupling method improves the design of such screens for improved antiblocking performance.