Fluid Coupling Research Articles

Inlet baffle structural optimization and reforming performance of exhaust gas-fuel reformer for marine LNG engine

The structural and boundary conditions are pivotal factors influencing the performance of the reformer. However, previous research primarily relied on tailored theoretical boundary conditions specific to the research requirements, often conducted in low airspeed conditions ranging from 700 ℃ to 1000 ℃. There is a lack of research focused on the complex and dynamic process of reforming hydrogen production process in reformers that handle exhaust gas components with high flow rates, high dilution, complex compositions, and low to medium temperatures (300 °C–600 °C) as boundary conditions. The objective of this study is to optimize the structure of the reformation reactor while exploring its hydrogen reforming characteristics. Therefore, this study focused on the simulation-based optimization design of an EGR reformer for marine natural gas engines. A comprehensive model was developed by coupling fluid flow, heat transfer, and surface reactions on a nickel-based catalyst. The accuracy of the model was validated through experimental data from a single-tube fixed-bed catalytic reforming experiment. The results highlighted the importance of the reformer design, with the optimal configuration incorporating two baffle plates positioned at angles of 15° and 35°. This design achieved the most uniform flow field and minimal pressure drop among the six investigated configurations. Furthermore, the study emphasized the significance of reforming gas composition in achieving high performance. The optimal reforming gas composition was found to have an M/O value of approximately 2 and an S/M value of approximately 1. This resulted in an outlet hydrogen concentration of approximately 18.8%, hydrogen yield of approximately 46.1%, methane conversion rate of approximately 66.2%, and an energy efficiency of 71%. It was observed that increasing the EGR rate led to a decrease in performance indicators, with a more pronounced effect observed at an M/O value of 1. This study provides valuable insights into the performance optimization of EGR reformers for marine natural gas engines. The findings offer guidance on selecting operational parameters to enhance efficiency and hydrogen production.

Two-way coupling fluid–structure interaction analysis on dynamic response of offshore wind turbine

The monopile-supported offshore wind turbines (OWTs) are subjected to the wave and current loadings. Affected by currents and waves, monopile-supported OWTs are also vulnerable to scour. However, the effect of scour and currents on the dynamic behavior of the monopile are not fully appreciated. This study conducted the model tests to evaluate the effect of scour depth and flow velocity on the lateral responses of support structure. Furthermore, the two-way (T-W) coupling fluid–structure interaction (FSI) method was proposed to evaluate the dynamic responses of piles in sand. The support structure is modeled using ABAQUS, a finite-element models software package, by considering the nonlinear soil–structure interaction effects, STAR-CCM + tools has been employed to model the FSI which are fed into ABAQUS to predict the structure’s dynamic response. Using the proposed method, a parametric study has been conducted to evaluate the effects of scour depths, flow velocities on the dynamic responses of OWTs. The results indicate that scour altered the fundamental frequency of OWT, causing resonance. An increase in scour depth and flow velocity increased the dynamic responses of support structure, which are detrimental for the safety and stability of the OWT system.

Accelerating hypersonic reentry simulations using deep learning-based hybridization (with guarantees)

In this paper, we are interested in the acceleration of numerical simulations. We focus on a hypersonic planetary reentry problem whose simulation involves coupling fluid dynamics and chemical reactions. Simulating chemical reactions takes most of the computational time but, on the other hand, cannot be avoided to obtain accurate predictions. We face a trade-off between cost-efficiency and accuracy: the numerical scheme has to be sufficiently efficient to be used in an operational context but accurate enough to predict the phenomenon faithfully. To tackle this trade-off, we design a hybrid numerical scheme coupling a traditional fluid dynamic solver with a neural network approximating the chemical reactions. We rely on their power in terms of accuracy and dimension reduction when applied in a big data context and on their efficiency stemming from their matrix-vector structure to achieve important acceleration factors (×10 to ×18.6). This paper aims to explain how we design such cost-effective hybrid numerical schemes in practice. Above all, we describe methodologies to ensure accuracy guarantees, allowing us to go beyond traditional surrogate modeling and to use these schemes as references.

Study on Condensed Matter Simulated by Multiphase Fluid-Solid Coupling Fluid Mechanics

The hydrodynamic characteristics of a three-phase gas-liquid-solid turbulent bed with light particle flow and intermittent liquid feeding were numerically simulated by CFD program Fluent6.3. The axial and radial motion of particles in a three-phase gas-liquid-solid turbulent bed and the variation of particle concentration in the bed are studied. The results show that the size and frequency of cavitation increase with the increase of the distance from the axis of the air distribution disk and the distance from the bed surface to the central region. The void varied from narrow to wide, while the void changed in the opposite direction. The bubble lift rate and bubble size are basically the same in axial and radial direction. With the increase of the surface gas velocity and the viscosity of the liquid phase, the average particle content in the bed decreases.

The porous structure induced heterogeneous and localized failure of the biofilm in microfluidic channels.

Understanding the mechanism of biofilm distribution and detachment is very important to effectively improve water treatment and prevent blockage in porous media. The existing research is more related to the local biofilm evolving around one or few microposts and the lack of the integral biofilm evolution in a micropost array for a longer growth period. This study combines microfluidic experiments and mathematical simulations to study the distribution and detachment of biofilm in porous media. Microfluidic chips with an array of microposts with different sizes are designed to simulate the physical pore structure of soil. The research shows that the initial formation and distribution of biofilm are influenced by bacterial transport velocity gradients within the pore space. Bacteria prefer to aggregate areas with smaller microposts, leading to the development of biofilm in those regions. Consequently, impermeable blockage structures form in this area. By analyzing experimental images of biofilm structures at the later stages, as well as coupling fluid flow and porous medium, and the finite element simulation, we find that the biofilm detachment is correlated with the morphology and permeability (kb) (from 10-15 to 10-9 m2) of the biofilm. The simulations show that there are two modes of biofilm detachment, such as internal detachment and external erosion.

Modeling a Fluid-Coupled Single Piezoelectric Micromachined Ultrasonic Transducer Using the Finite Difference Method.

A complete model was developed to simulate the behavior of a circular clamped axisymmetric fluid-coupled Piezoelectric Micromachined Ultrasonic Transducer (PMUT). Combining Finite Difference and Boundary Element Matrix (FD-BEM), this model is based on the discretization of the partial differential equation used to translate the mechanical behavior of a PMUT. In the model, both the axial and the transverse displacements are preserved in the equation of motion and used to properly define the neutral line position. To introduce fluid coupling, a Green's function dedicated to axisymmetric circular radiating sources is employed. The resolution of the behavioral equations is used to establish the equivalent electroacoustic circuit of a PMUT that preserves the average particular velocity, the mechanical power, and the acoustic power. Particular consideration is given to verifying the validity of certain assumptions that are usually made across various steps of previously reported analytical models. In this framework, the advantages of the membrane discretization performed in the FD-BEM model are highlighted through accurate simulations of the first vibration mode and especially the cutoff frequency that many other models do not predict. This high cutoff frequency corresponds to cases where the spatial average velocity of the plate is null and is of great importance for PMUT design because it defines the upper limit above which the device is considered to be mechanically blocked. These modeling results are compared with electrical and dynamic membrane displacement measurements of AlN-based (500 nm thick) PMUTs in air and fluid. The first resonance frequency confrontation showed a maximum relative error of 1.13% between the FD model and Finite Element Method (FEM). Moreover, the model perfectly predicts displacement amplitudes when PMUT vibrates in a fluid, with less than 5% relative error. Displacement amplitudes of 16 nm and 20 nm were measured for PMUT with 340 µm and 275 µm diameters, respectively. This complete PMUT model using the FD-BEM approach is shown to be very efficient in terms of computation time and accuracy.

Abstract 16610: A New Left Ventricle Vortex Formation Time for Clinical Assessment of Diastolic Filling Efficiency Based on Direct Mechanical Ventricular-Vascular Coupling: Evaluation in Heart-Failure and Healthy Cohort

Introduction: The mechanical coupling of the left ventricle (LV) and aorta creates the apical motion of the atrioventricular plane (AVP), resembling a piston-cylinder system, impacting early diastolic filling (J Am Heart Assoc. 2017;6:e004903). Furthermore, several clinical studies have suggested the vortex formation time (VFT) as an indicator of LV diastolic function (Eur. Heart J. Cardiovasc. Imaging. 2012;13(5):385-93). However, conflicting results exist in previous clinical studies, potentially due to deviations from the original fluid dynamics definition of VFT in a piston-in-cylinder setting. In this study, we propose a new VFT approach to assess LV diastolic filling performance based on direct mechanical ventricular-vascular coupling. Methods: Cardiac MRI was used on 69 healthy individuals and 19 heart failure (HF) patients. The clinical cohort (37% women) had a mean age of 46 [± 17.5] years and BMI of 24.8 [±4.5]. LV valvular diseases were excluded. VFT was assessed using the original L/D definition, where L represents ascending aortic recoil motion (piston displacement) and D represents the mitral valve orifice. Aortic displacement was measured on the three and four-chamber MRI scans by tracing the AVP. Mitral valve orifice was determined as the average of commissure distance (short-axis images) and the leaflet tip distance (three-chamber view). Results: The new VFT approach yielded a mean[± std.] of 4.73[±0.89] for the healthy group, and considerably lower values (3.24±0.83) for the patients with HF (figure 1). Conclusions: The proposed VFT based on the mechanical ventricular-vascular coupling and original fluid dynamic formulation, demonstrates a theoretical optimal value of approximately 4 in healthy individuals, while significantly lower in HF. This novel VFT has the potential to address existing discrepancies regarding the clinical significance of VFT and establish it as a promising indicator of left ventricular filling efficiency.

A comprehensive numerical study based on topology optimization for cooling plates thermal design of battery packs

This article focuses on the problem of fluctuating cooling system flow caused by different working states such as acceleration and braking during the actual operation of electric vehicles, which prevents the system from effectively dissipating heat from the battery for a long time. In the past, liquid cooling heat dissipation schemes designed based on structural parameters often relied on the experience of CFD engineers. There is no in-depth study of the heat propagation characteristics. At present, research on the application of topology optimization method in cooling plate design mainly focuses on the relative positions of single inlet and outlet, objective functions, and constraint conditions. There are very few studies evaluating the adaptability of different cooling plate structures at different flow rates. In this perspective, this work proposes a two-dimensional topology optimization method for obtaining the cooling plates with different topological structures such as the series of cooling plate structures with dual entrances and exits. The method comprises of a comprehensive study on variations of the inlet flow rate under different average fluid volume fraction, outlet width, and temperature weight conditions. The results indicate that setting an excessive inlet flow rate can actually lead to an increase in the average temperature of the optimized cooling plate. Subsequently, the cooling plate structure obtained through topology optimization at inlet flow rates of 0.015 m/s, 0.02 m/s, and 0.025 m/s was selected, and a three-dimensional electrothermal fluid coupling model was established based on its two-dimensional channel structure. Its cooling performance, flow characteristics, and heat transfer characteristics were analyzed, and compared with two straight channel reference models. The results indicate that the optimized cooling plate structure under low flow conditions has better heat dissipation performance. At a flow rate of 0.56 × At 10-6m3/s, compared to traditional cooling plates(CASE D, CASE E), the highest temperature of the battery using topology optimized cooling plates (CASE A) decreased by 3.5 K and 1.79 K, respectively, and the standard deviation of temperature decreased by 48% and 14%, respectively. Under the same inlet flow velocity, the area of the fluid region increases with the increase of the mean fluid volume fraction, and the width of the flow channel increases gradually and the branches increase significantly, from the concentrated solid region to the dispersed isolated region. At a low flow rate, the normalized temperature of the cooling plate increases with the increase of the flow rate of the coolant inlet, and when the flow rate reaches a certain value, in order to reduce the power loss of the cooling plate, the flow path is gradually concentrated on both sides of the cooling plate. This leads to the decline of the normalized temperature of the cooling plate.

Stokes number and coupling effects on particle interaction behavior in turbulent channel flows

The effects of Reynolds number (Reτ=180 and 300), particle Stokes number (St+=0.5, 50, and 92), and fluid–solid phase coupling level (one-way, two-way, and four-way) on particle behavior in turbulent channel flows has been investigated using direct numerical simulation and Lagrangian particle tracking. Previous studies have used all these levels of coupling, but in terms of those employing four-way coupling, no consideration is given as to how emergent phenomena due to collision dynamics within a flow affect the way in which particles impart feedback to the continuous phase. In the present work, we relate the particle–particle interaction to particle–fluid coupling, as well as in assessing its relation to the Stokes number. As the Reynolds number increases and the turbulent region narrows, fewer particles retain their velocity as they migrate to the wall-region leading to reduced streamwise velocity fluctuations and preferential concentration. It is also evident that low Stokes number particles are capable of minor wall-accumulation at Reτ=300. At this increased Reynolds number, four-way coupled simulations performed with moderate Stokes number particles (St+=50) are shown to diminish the effects of particle–fluid feedback, leading to similar fluid and particle statistics as the one-way coupled simulations. It is concluded that turbophoretic and preferential concentration effects are responsible for this phenomenon, since the increased collision rates due to larger concentrations of particles and velocity fluctuations in the wall-region correlate directly with the impact on the two-way coupling flow modifications. Analysis of the collision dynamics also indicates particles colliding with increased relative velocities and angles, which cause larger momentum transfer and directional redistribution, increasing and redirecting slip velocities. It is concluded that for midrange Stokes numbers, four-way coupling is imperative to increase simulation accuracy beyond that obtained assuming one-way coupling.

The thermal-fluid-mechanical (TFM) coupling method based on discrete element method (DEM) and the application of CO2 fracturing analysis

Due to the challenges of the complex temperature, fluid and mechanical coupling phenomenon during CO2 fracturing, a new thermal-fluid-mechanical (TFM) coupling method is proposed by using PFC2D fish code. This method utilizes the PFC2D fish code and combines the heat transfer difference algorithm with Cundall's fluid-mechanical coupling algorithm to establish a TFM model for CO2 fracturing. Subsequently, the validation of the TFM coupling model is conducted using the analytical solution provided by the plane strain Khristianovic Geertsma-de Klerk (KGD) model. The reservoir temperature variation, pore pressure and crack propagation are studied considering many involved factors, such as injection fluid temperature, injection flow rate, in-situ stress and formation temperature. Crack number and length would increase with the increasing temperature difference between fracturing CO2 and reservoir temperature. The breakdown pressure reduces when there are large injection flow rate or temperature differences between fracturing CO2 and reservoir temperature, which can be optimized in the CO2 fracturing operation. Even CO2 fracturing could create complex fracture network, we must pay attention to the in-situ stress distribution and injection flow rate. Our simulation suggests that pore pressure and heat could prevent the fracture from initiating and propagating in the direction of the minimum principal stress, and the temperature influencing has contributed to the extra pressure increment in the pore domain, which could not be ignored in CO2 fracturing. From the above research, it is expected to offer a novel method to simulate the complex TFM coupling phenomenon and enhance our understanding of CO2 fracturing.

Observation of Alfvén Ion Cyclotron Waves in ICME Magnetic Clouds at 1 au

Waves in plasma play an essential role in the energy transfer and plasma-heating processes. This article discusses the in situ observation of Alfvén ion cyclotron (AIC) waves and their characteristics within interplanetary coronal mass ejection (ICME) flux ropes. We analyzed 401 ICME flux ropes, observed by WIND spacecraft from 1995 to 2021 at 1 au. We found only five ICME flux ropes that show an explicit presence of AIC waves; two have normalized magnetic helicity σ m ≤ −0.5, and the remaining three show σ m ≥ 0.5 polarization. The angle between velocity and magnetic field (θ VB) for σ m ≤ −0.5 is <40°, whereas for σ m ≥ 0.5, θ VB > 140°. This result supports the existence of quasi-parallel and quasi-antiparallel left-handed polarized AIC waves within ICME flux ropes. We suggest that AIC waves are possibly triggered by (i) proton temperature anisotropy Tp ⊥/Tp ∥ > 1 driven by cyclotron instability and (ii) low-frequency Alfvén waves through the magnetohydrodynamic turbulent cascade. This study shows evidence of fluid and kinetic scales coupling in the ICME flux rope.

Energy harvesting analysis of the magneto-electric and fluid-structure interaction parametric excited system

This research proposes an innovative design of a fluid-solid coupling vibration energy harvesting system (VEH system) that includes a downstream waterwheel driven by the flow field, which, in turn, drives gears and connecting rods to rotate a wheel equipped with magnets to generate electricity by changing the magnetic field. A piezoelectric patch (PZT) is installed upstream of the pipeline with a magnet attached to it. The repulsive force between the magnet on the wheel and the magnet on the PZT generates additional force while also creating vibration through fluid-solid coupling of the pipeline. The study derives a theoretical model of the nonlinear vibrating beam and couples it with the piezoelectric and magneto-electric equations to simulate the vibration of the fixed-fixed elastic pipe. The method of multiple scales (MOMS), fixed points plots, phase plots, and Poincaré maps are employed to verify the theoretically predicted parametric excitation properties of the system. The study uses the Biot-Savart Law to calculate the theoretical magnetic force and combines it with the fluid-conveying nonlinear beam and the PZT to create a magneto-electric coupling fluid pipeline vibration energy harvesting model. The study conducts a simple experiment to verify the feasibility of the theoretical model and demonstrates that the repulsive force of the magnet significantly enhances the electric generation benefit of the system. Regardless of whether the PZT is located in the curved or flat area (straight part) of the nonlinear beam, the addition of magnets to the system significantly increases voltage generation efficiency by more than 190 % when compared to systems without magnets.

Stable monolithic immersed boundary projection method for particle sedimentation with heat transfer at density ratios near unity

This study proposes a highly stable and efficient monolithic immersed boundary projection method with staggered time discretization for particle sedimentation with heat transfer at density ratios near unity. To achieve the implicit coupling of fluid and solid motion, the proposed method uses a monolithic approach that incorporates temperature, fluid velocities, particle velocities, momentum forcing, energy forcing, and pressure. Subsequently, a two-step approximate lower–upper decomposition is used to decouple the complex large system. Two-dimensional and three-dimensional (3D) single particle sedimentation at various Grashof numbers and density ratios verifies the ability of the proposed method to handle particle sedimentation at density ratios near unity. Moreover, the proposed method demonstrates its clear advantages by successfully addressing both stability issues and spurious oscillations. Furthermore, simulation with the proposed method was performed for 3D two- and multi-particle sedimentation with heat transfer to demonstrate the robustness of the proposed method. The investigation of the effects of density ratio and Grashof numbers on particle sedimentation reveals a significant influence of buoyancy force, particularly for relatively lighter particles. An increase in the drag coefficient for multi-particle sedimentation is observed, owing to interactions between particles, and the Grashof number exerts a pronounced influence, particularly at low-density ratios.

Practical design guidelines for heat transfer enhancement of condensers

Enhanced condensation is of great practical interest to further improve and miniaturize power generation and refrigeration systems. Studies in the literature that investigate enhanced condensation focus on increasing the heat flux at high vapor qualities; however, many thermodynamic cycles such as vapor compression and the Rankine cycle require complete condensation for cycle operation, and in such cases, low-quality condensation can be the limiting factor. Performance evaluation criteria (PEC) can be used to assess the relative improvement achieved by different enhancement methods, but most PEC are only applicable to single-phase flows. The present study therefore develops local design guidelines for condensing flows to determine the regions of the condenser that most need heat transfer enhancement. This is achieved by comparing the relative benefits and penalties associated with enhancing low-quality, medium-quality, and high-quality condensation equally. The effects of varying heat transfer coefficient, frictional pressure drop, temperature reduction due to pressure drop, driving temperature difference, and coupling fluid thermal resistance are considered. Three enhancement techniques are then analyzed with these approaches to determine their relative benefits and disadvantages. Cases that consider fixed geometries, fixed flow areas, and variable flow area are considered, along with comparing the relative benefits of size reduction, increased heat duty, and reduced temperature difference. Results show that heat transfer enhancement is achieved when the increase in heat exchanger conductance exceeds the reduction in the heat exchanger temperature difference induced by condensation pressure drop. Additionally, it is found that enhancement is typically most needed in the low vapor quality region of the condenser, except in situations where temperature pinching occurs along the heat exchanger.

Investigation of dynamic characteristics in the hydraulic shock absorber based on different FSI FEA methods

Two three-dimensional fluid-structure interaction (FSI) finite element analysis (FEA) models with different fluid cells and coupling solution methods of a gas-pressured hydraulic shock absorber is constructed, and the results are partially verified experimentally. Models with FCBI fluid cell and direct FSI solution method or FCBI-C fluid cell and iterative FSI solution method provide good simulation results of the FSI system of the hydraulic damper.

Multi-Physics Simulation of Tar-Rich Coal In Situ Pyrolysis with a Multiregion Homogenization Treatment.

The macroscopic multi-physics simulation of tar-rich coal in situ pyrolysis (TCISP) is conducted, in the fractured porous zone, by coupling heat transfer, fluid flow, and chemical reaction. A novel TCISP pattern of gas injection between fractured zones is proposed by treating the fractured porous zone as a homogeneous porosity gradient descending region. In this case, nearly 11,500 kg of oil can be produced within 6 months from a 10*10*1 m3 area. The influence of the fractured zone and porosity are investigated. The results indicated that gas injection between fractured zones is more conducive to rapid production, compared with the traditional case where the gas injection is in the center. The temperature field is more uniform, which is conducive to maintaining the same reaction conditions and producing appropriate products. Inlet velocity has a positive effect on the increase of heat transfer rate but has a negative effect on heat transfer uniformity. There is an optimal inlet temperature of 973 K for the fastest heating rate. With the increase in temperature, the heat transfer uniformity gets worse. Increasing the height of the fractured zone is beneficial for the heating rate and heat transfer uniformity.

Multi-Scale Simulations of Bubble Transport in an Alkaline Water Electrolyzer

The existence of bubbles can lead to the loss of performance by decreasing the electrochemically active surface area and disrupting the transport of hydroxide ions. These effects caused by the bubbles have yet to be sufficiently clarified. A comprehensive understanding of the mechanisms of dynamics inside an electrolyzer from the molecular scale up to the whole electrolyzer scale is needed. Furthermore, establishing relations between these dynamics at a wide range of scales is important. In this study, numerical simulations of bubble transport coupling fluid dynamics, mass transport and electrochemical reactions were conducted on micro and macro scales, respectively. The micro scale bubble simulation (Fig. 1(a)) incorporates the concentration field of the chemical species into the numerical model and deals with how bubbles grow on and detach from an electrode. In this model, the chemical species generated by the electrochemical reactions dissolve into the liquid phase, and their transfer into the gas phase leads to bubble growth. Since the spatial size distribution of the bubbles can be one of the factors that affect electrolysis performance, in the macro scale bubble simulation (Fig. 1(b)), we study how different sizes of bubbles are transported and distributed inside the electrolyzer. To simulate this phenomenon, a four-phase flow analysis is performed in which small, medium, and large diameters are selected as representatives of bubble diameters, and each is treated as a different phase.[Acknowledgements]This study was based on results obtained from the Development of Fundamental Technology for Advancement of Water Electrolysis Hydrogen Production in Advancement of Hydrogen Technologies and Utilization Project (P14021) commissioned by the New Energy and Industrial Technology Development Organization (NEDO).Fig. 1 Simulation systems of bubble transport at (a) micro scale and (b) macro scale. Figure 1

A Study on the Influence of Double Tunnel Excavations on the Settlement Deformation of Flood Control Dikes

This article combines numerical simulation and field monitoring methods to study the stability of the overlying Liuyang River embankment in the tunnel crossing between Huaqiao Station and Rice Museum Station of Changsha Metro’s Line 6. Using AutoCAD, 3Dmine, and COMSOL Multiphysics, a calculation model of the entire subway tunnel section crossing the flood control embankment under the coupling of fluids and solids was established. The process of tunnel-crossing the embankment and the variation in spatial displacement and plastic strain in different geological layers were analyzed from the perspective of time evolution and spatial distribution. The research results show that during the process of crossing the embankment, the deformation of the east bank is greater than that of the west bank, and crossing the west bank is the relatively riskier stage of the entire project. Moreover, during the process of crossing the embankment, the overlying soil layer will produce a plastic strain zone, and only a small amount of plastic strain is generated in the surrounding sandstone layer of the tunnel walls. In terms of the magnitude of plastic strain, the plastic strain area produced by the leading tunnel’s surrounding rocks is larger than that of the following tunnel. As the excavation progresses, a funnel-shaped settlement displacement gradually forms during the passage of the leading tunnel, and this settlement funnel gradually expands during the passage of the following tunnel, with the maximum settlement point transitioning from directly above the leading tunnel to the middle position between the two tunnels. Using the jitter filter algorithm and the adjacent average method to process the field monitoring data, the results show that the monitored deformation results well match the simulated settlement results.

Investigation of rainfall intensity on the slope failure process using GPU-accelerated coupled MPM

Rainfall-induced slope failure is a common geo-hazard, which can cause catastrophic damages to human life and properties. In order to prevent the occurrence of catastrophes, understanding the mechanism of rainfall-induced slope failure and estimating its failure process is of significant importance. This paper presents a solid–fluid coupling material point method (MPM) in simulating the rainfall-induced slope failure process, and meanwhile, the influence of rainfall intensities on the slope failure process is explored. The solid–fluid coupling MPM is enhanced with a cubic B-spline shape function, rainfall infiltration boundary condition and GPU-accelerated framework, so that a computationally efficient and numerically stable simulation can be realized. One-dimensional consolidation, infiltration and two-dimensional slumping block tests are firstly simulated to test the effectiveness and capability of the solid–fluid coupling MPM in simulating large deformation hydro-mechanical problems. Thereafter, an in-door rainfall-induced slope failure experiment is simulated, where a consistent failure pattern is reproduced. Finally, the influence of rainfall intensity on the slope failure process is studied. Deep-seated and shallow surface failures are two major failure patterns corresponding to small and large rainfall intensities, respectively. Further analyses prove that different evolutions of pore pressure fields and seepage channels play important roles in forming the different failure patterns.

The Effect of the Aeration Condition on the Liquid–Solid Material Mixing in a Stirred Tank with a Single-Layer Impeller

In order to increase industrial production quality and efficiency, it is essential to understand how the aeration and no-aeration condition affects liquid and solid material mixing in the stirred tank. Due to complicated shear flows, the related mass-transfer mechanism confronts numerous difficulties. This paper put forward an improved computational fluid dynamics and discrete element method (CFD–DEM) modeling approach to explore the effect mechanism of aeration conditions on liquid–solid material mixing. Firstly, a mass-transfer dynamic model is set up with a volume of fluid and piecewise linear interface construction (VOF–PLIC) coupling strategy to explore flow modes and vorticity evolution trends under aeration control. Then, a self-developed interphase coupling interface is utilized to modify the coupling force and porosity of the porous media model in the DEM module, and random dispersion properties of the particle phase under non-aeration and aeration are obtained. Results show that the aeration and flow-blocking components transform fluid tangential speeds into axial and radial speeds, which can improve the material mixing quality and efficiency. The mixed flow field can reach a greater turbulent process under the impeller rotation, making the particles have an intensive disorder and complex flow patterns. The enhanced motion efficiency of the vortex clusters encourages their nesting courses and improves cross-scale mixed transport. It can serve as some reference for the three-phase flow mixing mechanism, vorticity distribution law, and particle motion solution and has a general significance for battery homogeneous mixing, biopharmaceutical processes, and chemical process extraction.