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Fluid-based methods for particle sorting demonstrate increasing appeal in many areas of biosciences due to their biocompatibility and cost-effectiveness. Herein, we construct a microfluidic sorting system based on a swirl microchip. The impact of microchannel velocity on the swirl stagnation point as well as particle movement is analyzed through simulation and experiment. Moreover, the quantitative mapping relationship between flow velocity and particle position distribution is established. With this foundation established, a particle sorting method based on swirl induction is proposed. Initially, the particle is captured by a swirl. Then, the Sorting Region into which the particle aims to enter is determined according to the sorting condition and particle characteristic. Subsequently, the velocities of the microchannels are adjusted to control the swirl, which will induce the particle to enter its corresponding Induction Region. Thereafter, the velocities are adjusted again to change the fluid field and drive the particle into a predetermined Sorting Region, hence the sorting is accomplished. We have extensively conducted experiments taking particle size or color as a sorting condition. An outstanding sorting success rate of 98.75% is achieved when dealing with particles within the size range of tens to hundreds of micrometers in radius, which certifies the effectiveness of the proposed sorting method. Compared to the existing sorting techniques, the proposed method offers greater flexibility. The adjustment of sorting conditions or particle parameters no longer requires complex chip redesign, because such sorting tasks can be successfully realized through simple microchannel velocities control. [ABSTRACT FROM AUTHOR]

Systematic atomistic simulations of oblique collisions between spherical crystalline, 6H and 3C, and amorphous SiC nanoparticles (NPs) are performed in the bouncing and fragmentation regimes for the particles with diameters from 8 nm to 30 nm, impact velocities from 100 ms−1 to 5000 ms−1, and in the whole range of the geometric impact parameter. The critical sticking velocity of 6H-SiC NPs reduces from ∼490 ms−1 to ∼150 ms−1 when the NP diameter increases from 10 nm to 30 nm. Below the melting threshold, the collision of crystalline NPs induces the formation of localized zones of densified material, while the remaining parts of NPs are not affected by plastic deformations. The impact of amorphous NPs results in the plastic deformation of significant parts of the NP material and much larger irreversible losses of mechanical energy. The post-collision translational and rotational velocities of crystalline NPs as well as coefficients of restitution (CORs) demonstrate weak dependence on the NP size if the NP diameter is greater than 20 nm. At constant impact velocity, the normal COR only marginally varies for head-on and oblique collisions, when the collision angle is smaller than ∼53°. The tangential center-of-mass and point-of-contact CORs, as functions of the impact parameter, demonstrate extremal behavior with the minima at collision angles from ∼27° to ∼37°. The normal COR exhibits a linear decay as a function of the impact velocity where the slope coefficient is different below and above the melting threshold. The tangential CORs attain the minimum values at the impact velocity of ∼300 ms−1. The obtained results are summarized in the form of fitting equations for CORs as functions of the impact parameter and velocity, which can be readily used to predict the post-collision translational and angular velocities of NPs in large-scale simulations of granular gas flows. [ABSTRACT FROM AUTHOR]

The concentration change of fine suspended solids along a sewage pipe can be influenced by different water inflow patterns, which may cause water quality issues and affect the maintenance operation on sediment management. This study was conducted to explore the migration features of fine suspended solids under the influence of the variable inflow in drainage pipes. A three-dimensional numerical model was constructed to represent a more realistic flow condition and the interaction between water flow and suspended solids. Movement characteristics of fine suspended solids under different inflow conditions were numerically investigated based on the Euler–Lagrange method. The variations of the inflow pattern, particle vertical velocity, and concentration were discussed in detail to obtain the migration-deposition characteristics of fine suspended solids in a drainage pipe. The results show that, with the increase of flow velocity in steady inflow condition, the particles gradually diffuse to the bottom and the largest concentration of suspended solids gradually moves downward. For unsteady inflow condition, the flow change would lead to the change of sectional concentration and particle mass flow. The concentration of suspended solid in the front segment of pipe was more susceptible to the variable flow than the posterior segment. The highest particle concentration and mass flow situation can be influenced for the inflow pattern scenario with advanced flow peak, which means that the front section (at least half the length) is the important area where attention is required during sewer protection and pollution control processes. Besides, advanced flow peak of rainfall may cause more pollutants to accumulate in sewers. [ABSTRACT FROM AUTHOR]

Accurate analysis of the deformation characteristics and the damage destruction mechanism of a rock mass is a prerequisite for the evaluation of the stability of the surrounding rock in tunnel engineering. This paper proposes a combination of numerical simulation techniques based on microstructure analysis and physical model experimental methods, which allows for the microscale interpretation of macroscale experimental phenomena and provides new insights for further summarizing the instability and failure patterns of rocks under unloading paths. To investigate the macroscopic and microscopic failure mechanisms as well as the damage deterioration patterns of granite under unloading conditions, physical model tests were conducted using stress paths of conventional triaxial and constant axial pressure unloading confining pressure. The experiments encompassed unloading paths, and the associated mechanical responses were finely simulated using the particle flow code method coupled with digital image processing techniques. The results reveal that at lower unloading rates, granite predominantly undergoes shear failure, with the destabilizing mechanism attributed to the formation of an "X"-shaped conjugate failure surface under the influence of tension–shear coupling. As the unloading rate increases, tensile forces progressively take precedence, leading to more pronounced brittle failure characteristics in granite. The ratio of the confining pressure reduction to the initial confining pressure at the point of specimen failure increases with the unloading rate and decreases with the initial confining pressure. Faster unloading rates correspond to a more rapid increase in Poisson's ratio, and the unloading path primarily influences the lateral strain variation during the initial stages of unloading. Additionally, under unloading conditions, the internal friction angle of granite increases, while the cohesion decreases. The impact of unloading rate and path on cohesion becomes more pronounced. The findings of this research have certain reference value for further optimizing the methods for assessing the stability of rock masses surrounding tunnels. [ABSTRACT FROM AUTHOR]

In granular media, the crushing of individual particles is influenced by the number of contacts with neighbouring particles. This well-known phenomenon of "cushioning" shields the individual particles from crushing when the number of contacts is high. However, in open systems that involve extensive granular flow and bulk motion, like those found in industrial mills, the neighbouring particles continually exchange positions due to segregation and mixing, thereby altering the number of neighbouring contacts and their sizes, affecting the crushing of individual particles. Therefore, a critical challenge for properly modelling comminution in such systems lies in tracking the fluxes of the various particle size classes. Here, we explore the physics that governs the mechanisms of segregation and mixing within the multiscale heterarchical modelling paradigm. Building upon the framework developed in Part I, which integrated the heterarchical aspects of the physics of crushing along streamlines, we further account for segregation and mixing, and demonstrate their impact on the comminution efficiency of autogenous grinding mills. In particular, segregation is shown to greatly enhance the extent of particle crushing within the mill. Accordingly, we posit that this mechanism cannot be ignored. In summary, the new model sheds light on previously obscured dynamics within industrial mills, as well as enables the field to predict the time evolution of the particle size distribution at any point in the mill domain. This modelling capability opens the doors to new developments for estimating and improving milling efficiencies. [ABSTRACT FROM AUTHOR]

Particle Tracking Velocimetry (PTV) is a Lagrange-based flow visualization technique that tracks the motion of multiple particles or granules simultaneously. With the widespread application of three-dimensional (3D) particle imaging systems, 3D PTV algorithms have attracted considerable interest, whereas many 3D algorithms are developed from the corresponding 2D algorithms; moreover, compared with 3D algorithms, 2D algorithms are more suitable for real-time flow monitoring in industry. This paper proposes a 2D PTV algorithm based on the Voronoi diagram (VD) that is optimized by the minimum enclosing ellipse (MEE); then a re-matching process based on a homemade method called Quasi-Parallel Correction (QPC) is developed to correct the abnormal results produced by PTV at large inter-frame particle displacement. This PTV is thereby named MQ-PTV. MQ-PTV is then employed for reconstructing a granular flow made of dense polypropylene particles along a declined chute, an aeolian sand flow over sand bed, the migration of a barchans swarm and the motion of stars, thus confirming its practicability in a wide variety of particle motion reconstruction. [ABSTRACT FROM AUTHOR]

The different flow regimes in a two-dimensional silo with a vibrated base are studied in terms of the usual statistical techniques and information theory. The passage of granular material through the mouth of the silo is analyzed by real-time analysis of images captured by a standard video camera. The brightness of these images is measured and recorded at very small time intervals (100 frames per second). The experiment is repeated for different values of the vibration intensity. Data recognizer wlzip directly treats the resulting b(t) files (brightness time series) based on data compressor techniques, yielding the information content measured by the mutability μ function. μ has not previously been considered as part of the conventional treatment of flow in granular media. The results obtained here clearly demonstrate the usefulness of mutability as a tool for distinguishing between different flowing regimes directly from the brightness sequence, with no manipulation of the series. This shows that information theory techniques can provide a complementary description of the discharge of granular materials and its control through data compression algorithms. [ABSTRACT FROM AUTHOR]

Rotary mills aim to effectively reduce the size of particles through a process called comminution. Modelling comminution in rotary mills is a challenging task due to substantial material deformation and the intricate interplay of particle kinematics of segregation, mixing, crushing, and abrasion. Existing particle-based simulations tend to provide predictions that cannot cope with the large number of particles within rotary mills, their wide range of sizes, and the physics dictating the crushing of individual particles. Similarly, there is currently no deterministic modelling means to determine the evolving population of particle sizes at any point in time and space within the mill. The aim of this two-part contribution is to address these gaps by advancing a framework for a novel stochastic comminution model for rotary mills, which has a well-defined deterministic continuum limit and can cope with arbitrarily large numbers of particles. This work describes the basic physics and structure of the new model within a heterarchical framework for ball and autogenous grinding mills. The primary focus of this Part I paper is to develop a computational model for the integration of motion of material along streamlines inside a mill. Coupled to this process is the kinetic physics dictating particle crushing. In a subsequent work, Part II, segregation and mixing will be added to this model such that realistic behaviour from the mill can be observed. [ABSTRACT FROM AUTHOR]

Transport of particles in flows is often modeled in a combined Eulerian–Lagrangian framework. The flow is evaluated on an Eulerian grid, while particles are modeled as Lagrangian points whose positions and velocities are evolved in time, resulting in particle trajectories embedded in the time-dependent flow field. The method essentially resolves the flow field in complex geometries in detail but uses a closure model for the particle dynamics aimed at including the essential particle–fluid interactions at the cost of detailed small-scale physics. Rarefaction effects are usually included through the phenomenological Cunningham correction on the drag force experienced by the particles. In this Lagrangian point-particle approach, any explicit reference to the finite size and the shape of the particles, and their local orientation in the flow field, is typically ignored. In this work we aim to address this gap by deriving, from fully-resolved Direct Simulation Monte Carlo (DSMC) studies, heuristic or closure models for the drag force acting on prolate and oblate spheroidal particles with different aspect ratios, and a fixed orientation, in uniform ambient rarefied flows covering the transition regime between the continuum and free-molecular limits. These closure models predict the drag in the transition regime for all considered parameter settings (validated with DSMC data). The continuum limit is enforced a priori and we retrieve the free-molecular limit with reasonable accuracy (based on comparisons with literature data). We also include in the models the capability to predict effects related to basic gas-surface interactions via the tangential momentum accommodation coefficient. We furthermore assess the validity of the proposed closure model for particle dynamics in proximity to solid walls. This investigation extends our previous work, which focused on small aspect ratio spheroids with exclusively diffusive gas-surface interactions [see Livi et al. (2022)]. The derived models are obtained for isothermal, subsonic flows relevant for particle contamination control in semiconductor manufacturing. • DSMC-enhanced drag force closures for particle tracking under rarefied gas conditions. • The drag force on finite-size spheroids in the transition regime of rarefied flows. • Towards algorithms for particle contamination control in semiconductor manufacturing. • Covering the device-to-nanoparticle scale separation in high-tech equipment. [ABSTRACT FROM AUTHOR]

Sewage pipes are important conduits for microplastics into the natural environment, but previous studies have paid little attention to the hydraulic characteristics of the confluence of pipe and channel, and the distribution of microplastics at the confluence. This study compared the effects of varying flow rates and particle sizes (Including 500 μm, 700 μm, and 900 μm) on microplastic migration and distribution at the confluence of pipe and channel using experimental measurements. The results obtained using flotation method indicate that flow proportions and particle sizes influence the capacity of flow to transport microplastics. Larger microplastic accumulation occurs in scour holes and separation zones characterized by lower flow velocities, while deposition decreases in acceleration zones characterized by higher flow velocities. Increasing the flow rate of the branch pipe influences the volume of each zone at the pipe-channel confluence. The elongated shape of the scour hole and the acceleration zone facilitate the downstream migration of microplastics. Moreover, the hydrophilic nature of microplastics increases after aging, and it is more likely to migrate to downstream with the water flow, making the downstream microplastics account for more proportion. These results provide valuable insights into the migration and distribution of microplastics at the confluence of pipe and channel, with practical implications for microplastic treatment strategies at these confluences. [ABSTRACT FROM AUTHOR]

The influence of silo width on dense granular flow in a two‐dimensional silo is investigated through experiments and simulations. Though the flow rate remains stable for larger silo widths, a slight reduction in silo width results in a significant increase in flow rate for smaller silo widths. Both Beverloo's and Janda's formula accurately capture the relationship between the flow rate and outlet size. Flow characteristics in the regions near the outlet exhibit local self‐similarity, supporting Beverloo and Janda's principles. Moreover, global self‐similarity is analyzed, indicated by the transition in flow state from mass flow in regions far from the outlet to funnel flow near the outlet. The earlier occurrence of this transition favors to enhance the grain velocity and consequently increases the dense flow rate. An exponential scaling law is proposed to describe the dependencies of flow rate, grain velocity, and transition height on silo width. [ABSTRACT FROM AUTHOR]

The fluidized bed magnetizing roasting of low‐grade iron ore fines is employed as a beneficiation technique in iron‐making and steel‐making industries. In the present work, the unreacted shrinking core reaction kinetic model is coupled with the two‐fluid and kinetic theory of granular flow gas–solid flow model to simulate magnetizing roasting of hematite to magnetite in iron ore fines using a fluidized bed reactor. The model is validated with published experimental findings. Thereafter, the influence of different process parameters such as gas temperature, composition, velocity, and particle size on the reduction fraction and rate along with CO2$\left(\text{CO}\right)_{2}$ mass fraction and emission is studied. The reduction rate increases with gas temperature and CO$\text{CO}$ mass fraction while it decreases with particle size. The CO2$\left(\text{CO}\right)_{2}$ emission increases with gas temperature, particle size, and CO$\text{CO}$ mass fraction. However, the influence of gas velocity on these parameters is not significant. The reduction rate and time vary from 0.0010 to 0.0067 s−1 and 65 to 553 s, respectively, at a reduction fraction of 0.5. The CO2$\left(\text{CO}\right)_{2}$ mass fraction and emission range from 0.80 to 0.92  and from 0.63 to 4.14 g kg−1 ore, respectively. [ABSTRACT FROM AUTHOR]

Environmental barrier coating (EBC) can reduce the environmental susceptibility of turbine blades due to the increasing problems of high temperature oxidation and vapor corrosion in heating parts of aeroengine made by SiC/SiC. However, in addition to high-temperature corrosion, EBC may be subject to solid particle erosion (SPE) due to sands and peeled coatings. The erosion mechanism is insufficiently studied, and the impact erosion to SiC/SiC is seldom noticed. In this paper, the SPE behavior of SiC/SiC prepared by chemical vapor infiltration (CVI), which was coated with Si/Yb 2 Si 2 O 7 /Yb 2 SiO 5 rare earth silicate EBC prepared by atmospheric plasma spraying (APS), was studied, and the EBC-SiC/SiC were impacted in normal direction by SiO 2 particles with multiple particle sizes and flow rates. Scanning electron microscope (SEM) was used to observe the damage morphology, and the effects of different flow rates, energies and particle sizes on the SPE behaviors of EBC-SiC/SiC were analyzed. A meso-scale model of progressive damage method - finite element method (PDM-FEM) was built and the SiO 2 particle erosion mechanism for single layer SiC/SiC was simulated, analyzed and compared with the experimental results. [ABSTRACT FROM AUTHOR]

Dense γ-Y 2 Si 2 O 7 /Y 2 O 3 –SiO 2 –Al 2 O 3 glass coatings were prepared on porous Si 3 N 4 ceramics using high-temperature melt-infiltration preparation method to improve their stability in service environments, specifically including water resistance and erosion wear resistance. Evolution of structure and mechanical properties during coating preparation was studied. Damage mechanism in erosion wear process was illustrated by putting the coated samples into a high-speed water flow with quartz particles. Dense double-layer microstructure could be formed when sintering at 1350–1450 °C for 1 h. The proportion of each phase inside the coating material prepared by various sintering temperatures was different, resulting in different elastic modulus and hardness, and ultimately affected the erosion resistance of the coatings. The "plasticity index" (E/H value) of γ-Y 2 Si 2 O 7 /Y 2 O 3 –SiO 2 –Al 2 O 3 glass coating prepared at lower temperature (1350 and 1400 °C) was low, and the erosion failure of the coating was brittleness mode, leading to an obvious decrease on waterproof performance after erosion test. While coating prepared at higher temperature (1450 °C) showed a better erosion resistance. After erosion for 2 h, water absorption of coating surface was changed by only 1.34 %. Micro-morphology of the coating was almost unchanged before and after erosion, maintaining excellent waterproof performance. [ABSTRACT FROM AUTHOR]

ABSTRACT Deep lung delivery is crucial for respiratory disease treatment. Although nano and submicron particles exhibited a good deposition efficiency in deep regions of the lung, powder nonuniformity and particle agglomeration reduce their efficiency. Inhalation of porous particles (PPs) can overcome the mentioned challenges due to their larger size and low‐density. The present study numerically investigates the deposition and penetration efficiency of orally inhaled PPs. A revised drag coefficient was implemented for PP transport. A realistic mouth–throat to the fifth generation of the lung was reconstructed from CT‐scan images. A dilute suspension of uniformly distributed particles was considered at three inhalation flow rates (15, 30, and 45 L/min). Governing equations of the flow field and particle transport are solved using an Eulerian–Lagrangian approach. The results demonstrate that inhaling PPs significantly reduces the total and regional deposition of particles. There was also a critical porosity value under moderate and high inhalation flow rates for large PPs. Below this critical value, PP deposition efficiency substantially decreases. Additionally, it was also found that under low inhalation flow rates, the impact of porosity value is negligible. Almost 95% of the PPs penetrate the lower branches. These findings provide particle engineers and pharmaceutics with profound insight into developing novel inhalation techniques and drug delivery methods for deep lung delivery. [ABSTRACT FROM AUTHOR]

The study of the movement of pollutants through ducts facilitates the assessment and control of ambient air quality problems (AQ). Among other things, understanding the deposition and distribution of particulate matter in elbows is important for practical engineering applications. In this study, the turbulent flow field and particle deposition in a 90° bend is investigated using RANS simulation. The RNG k-ε turbulence model was employed to calculate the airflow flow field and the discrete phase model (DPM) was used to simulate the particle phase motion. Where for the discrete phase, the Discrete Random Wander (DRW) model was considered and the deposition of particles with sizes of 1, 3, 5, 10, 20, and 40 μιτι in the flow field was investigated separately. Grid-independent validation of the models used in the simulations was performed. The effects of inlet velocity, particle size, and direction of gravity on the flow field and particle deposition in the elbow were considered. The results show that the flow field in the bend is strongly influenced by the above parameters. Among them, the turbulent disturbance in the bend section is the most intense, with high turbulent energy value, and it is also the region with the largest energy loss. The inlet velocity is negatively correlated with the deposition rate, and the particle size is positively correlated with the deposition rate. [ABSTRACT FROM AUTHOR]

Rainfall-triggered landslides generally pose a high risk due to their sudden initiation, massive impact force, and energy. It is, therefore, necessary to perform accurate and timely hazard prediction for these landslides. Most studies have focused on the hazard assessment and verification of landslides that have occurred, which were essentially back-analyses rather than predictions. To overcome this drawback, a framework aimed at forecasting landslide hazards by combining UAV remote sensing and numerical simulation was proposed in this study. A slow-moving landslide identified by SBAS-InSAR in Tianjin city of northern China was taken as a case study to clarify its application. A UAV with laser scanning techniques was utilized to obtain high-resolution topography data. Then, extreme rainfall with a given return period was determined based on the Gumbel distribution. The Particle Flow Code (PFC), a discrete element model, was also applied to simulate the runout process after slope failure under rainfall and earthquake scenarios. The results showed that the extreme rainfall for three continuous days in the study area was 151.5 mm (P = 5%), 184.6 mm (P = 2%), and 209.3 mm (P = 1%), respectively. Both extreme rainfall and earthquake scenarios could induce slope failure, and the failure probabilities revealed by a seepage–mechanic interaction simulation in Geostudio reached 82.9% (earthquake scenario) and 92.5% (extreme rainfall). The landslide hazard under a given scenario was assessed by kinetic indicators during the PFC simulation. The landslide runout analysis indicated that the landslide had a velocity of max 23.4 m/s under rainfall scenarios, whereas this reached 19.8 m/s under earthquake scenarios. In addition, a comparison regarding particle displacement also showed that the landslide hazard under rainfall scenarios was worse than that under earthquake scenarios. The modeling strategy incorporated spatial and temporal probabilities and runout hazard analyses, even though landslide hazard mapping was not actually achieved. The present framework can predict the areas threatened by landslides under specific scenarios, and holds substantial scientific reference value for effective landslide prevention and control strategies. [ABSTRACT FROM AUTHOR]

To assess connections between these notches throughout fracture formation under stress, the mechanical performance of granite specimens with two non-parallel notches underwent a biaxial compression test. The first notch had a 45° angle, whereas the second had a variable angle (0°, 45°, 90°, 130°, and 180°). Three ligament angles (0°, 45°, and 90°) were measured between the inner tips of two notches and the horizontal axis. The ligament length, distance between the inner tips of the two notches, and both notch lengths were each 2 cm. These samples were examined at 0, 1, and 3 MPa confining pressures. By using the particle flow code (PFC), simulated results of the evaluations were run after the trials. It was discovered that the specimens' failure strengths were influenced by the notch's geometric characteristics, which in turn impacted the failure mechanism as well as fracture geometry. The number of tensile fractures had an impact on the specimens' failure strengths. Whilst also increasing the ligament angle, more induced tensile cracks were produced. In the early stages of loading, just a few AE events were found, but after that, they multiplied quickly before approaching the peak stress. By raising the confining pressure, the AE hits were increased and delay failure was occured. The failure strength and AE hits are significantly impacted by the second notch's angle. In constant ligament angel, the compressive strength of models containing overlapped joint were more than that with non-overlapped joints. In models containing non-overlapped notches, the model with ligament angles of 0° and 45° had maximum and minimum compressive strength, respectively. In models containing overlapped notches, the model with ligament angles of 90° and 45° had maximum compressive strength and minimum compressive strength, respectively. In all ligament angles, minimum compressive strength was occurred when the upper joint angle was 45°. Both the computational and experimental methodologies showed that the specimens' failure pattern and compressive strength were very comparable. [ABSTRACT FROM AUTHOR]

The wall-attached structure characteristics of flow and dust concentration fields are investigated in this study based on high-Reynolds-number ($Re_{\tau } \sim O(10^{6})$) synchronous multiphase observations from the Qingtu Lake observation array site (recorded by Liu et al. , J. Fluid Mech. , vol. 957, 2023, A14). The results show that not only the particle-free flow field but also the particle-laden flow and dust concentration field contain wall-attached structures. The linear coherence spectrum, as a data-driven filter, is adopted to separate the wall-attached portions from the premultiplied spectra. The decomposed spectra for wall-attached structures in streamwise velocity fluctuations under particle-free and particle-laden conditions show obvious outer-scaling and wall-scaling at large-scale and medium-scale ranges, respectively, but the spectra of dust concentration exhibit only wall-scaling rather than outer-scaling. The streamwise length of the most significant wall-attached dust clustering structures in the logarithmic region is approximately five times the boundary layer thickness, and does not change significantly with height. Furthermore, the streamwise turbulence intensity for wall-attached portions follows the universal Townsend–Perry constant, without particle mass loading effect. Correspondingly, the wall-attached portions of the dust concentration also exhibit universal logarithmic decay slope. The remaining non-attached portions for the turbulent velocity and dust concentration have significant dependence on the particle mass loading. [ABSTRACT FROM AUTHOR]

The Basset–Boussinesq force is often perfunctorily neglected when studying small inertial particles in turbulence. This force arises from the diffusion of vorticity from the particles and, since it depends on the particles' history, complicates the dynamics by transforming their equations of motion into integrodifferential equations. However, this force is of the same order as other viscous forces acting on the particles, and beyond convenience, the reasons for neglecting it are unclear. This study addresses the following question: Under what conditions can the Basset–Boussinesq force be neglected in light particles in geophysical flows? We derive strict bounds for the magnitude of the Basset–Boussinesq force in stably stratified flows, in contexts of interest for geophysical turbulence. The bounds are validated by direct numerical simulations. The Basset–Boussinesq force is negligible when a buoyancy Stokes number Sb = N τ p is small, where N is the flow Brunt–Väisälä frequency and τ p is the particle's Stokes time. Interestingly, for most oceanic particles this force may be negligible. Only for very strong stratification, or for particles with very large inertia, this force must be considered in the dynamics. [ABSTRACT FROM AUTHOR]

A novel model is proposed for analyzing high-concentration granular flow systems comprising equally sized spherical particles within vertical, long straight pipelines. This model is specifically tailored for simulating the vertical hydraulic transport of ore particles in marine mining projects. The proposed model treats the granular system akin to a pseudo-fluid and operates through three mechanisms. First, fluid characteristics of the granular system are derived from particle–particle collisions. Second, the resistance exerted by the pipe wall on the granular system is calculated based on the momentum loss of particles during particle–wall collisions. Third, the interaction between individual particles and the surrounding fluid is transformed into an interaction between the carrier fluid and the pseudo-fluid. Additionally, the present work develops a dedicated numerical format and iterative method for solving the one-dimensional two-fluid governing equations. The one-dimensional (1D) model notably enhances computational efficiency and facilitates accurate tracking of high-concentration particles over extended distances within straight pipelines. Notably, the proposed 1D model demonstrates a high degree of predictive accuracy when compared against experimental data as well as results from computational fluid dynamics and discrete element method simulations. [ABSTRACT FROM AUTHOR]

The response of spherical particles to oscillatory fluid flow forcing at finite Reynolds numbers exhibits significant deviations from classical analytical predictions due to nonlinear convective contributions. This study employs finite element simulations to explore the long-term (stationary) behavior of such particles across a wide range of conditions, including various external and particle Reynolds numbers, Strouhal numbers, and fluid-to-particle density ratios. Key contributions of this work include determining the range of validity of Tchen's equation of motion for infinitesimal and finite Reynolds numbers and correlating particle response for a wide range of density ratios and flow conditions at high frequency oscillations. This work introduces a modified form of the history drag term in a newly proposed Lagrangian equation of motion. The new equation incorporates a parameter-dependent fractional-order derivative tailored to accommodate nonlinearities due to convective effects. These novel correlations not only extend the operational range of existing model equations but also provide accurate estimates of particle response under a range of external flow conditions, as validated by comparison with numerical solutions of the Navier–Stokes flow around the particles. [ABSTRACT FROM AUTHOR]

Double-row hydraulic collectors are extensively utilized for deep-sea polymetallic nodule harvesting. Understanding the movement behavior of particles within the flow field is crucial for evaluating the efficiency collection system and guiding the design of deep-sea hydraulic collectors. This study first investigates the settling characteristics of particles in various deep-sea environments to assess the effects of high-pressure and low-temperature conditions on particle motion. Subsequently, the motion and force characteristics of particles under different double-row jet parameters were measured and analyzed in the laboratory using high-speed imaging. The results indicate that ambient pressure has a negligible effect on particle motion when the ambient temperature is considered. Particle is mainly lifted in an irregular spiral path by the turbulence of the upper fountain. The lifting height or force of a particle in the vertical direction is positively correlated with the frequency of horizontal fluctuations and inversely related to the average amplitude of these fluctuations. Finally, a neural network was constructed to predict the particle motion characteristics, demonstrating strong generalization and providing a reference for further use of artificial intelligence in extracting physical information of particles from the jet field. This study offers potential benefits for optimizing the design of the double-row jet collectors. [ABSTRACT FROM AUTHOR]

The transport of non-spherical particles on bed is significantly influenced by flow dynamics and particle shape. To study the impact of changes in the flatness of isolated bed particles on the surrounding flow characteristics, we prefabricated three isovolumetric particles with varying levels of flatness and analyzed the flow field around them using two-dimensional particle image velocimetry measurement methods. The results show that the presence of the particles significantly alters the turbulence parameters of the surrounding flow. Specifically, the influence extends up to 1D upstream of the particles, 0.5D above the particle tops, and throughout most of the downstream region, where D represents the equivalent particle diameter. The particles cause a reduction in Reynolds stress and turbulent kinetic energy in the near-bed upstream region, with a more pronounced effect observed for particles with lower flatness. Increased particle flatness is associated with a smaller difference in the longitudinal time-averaged velocity between upstream and downstream regions. In the wake region, particle flatness shows a negative correlation with Reynolds stress, longitudinal turbulence intensity, and turbulent kinetic energy, with this effect being more pronounced closer to the particles. Quadrant analysis indicates that ejection (Q2) and sweep (Q4) quadrant events remain dominant in the presence of particles, while particle flatness positively correlates with the frequency of outward (Q1) and inward (Q3) events in the wake region and negatively correlates with the frequency of Q2 and Q4 events. This study enhances our understanding of particle-fluid interactions, particularly the response relationship between non-spherical particles and turbulent mechanisms. [ABSTRACT FROM AUTHOR]

The measurement of particle volume fraction in flow fields is of great significance in scientific research and engineering applications. As one of the particle detection techniques, the light extinction method is widely used in measuring nano-particles volume fraction in flow fields due to its simplicity and non-contact nature. In particular, in complex reactive flow fields like combustion reactions, the volume fraction of soot particulate and other particles can be accurately measured and reconstructed via the light extinction method that based on the Beer–Lambert law. This is crucial for exploring combustion phenomena, understanding their internal mechanisms, and reducing pollutant emissions. However, due to the enormous computational burden, current algebra reconstruction techniques struggle to achieve high-precision three-dimensional (3D) reconstruction of particles. Therefore, this paper originally proposes a 3D reconstruction algorithm based on the Beer–Lambert law physical information neural networks (LB-PINNs). By incorporating physical information as constraints into the particle reconstruction process, it is possible to achieve high-precision 3D reconstruction of particles in complex flow field environments with low computational cost. Meanwhile, to address the trade-off issues of reconstruction accuracy and smooth noise resistance in previous reconstruction algorithms, i.e., Tikhonov regularization, this paper employs dynamically adjusted regularization parameters in the LB-PINN algorithm. This approach ensures smooth noise-resistant processing while maintaining reconstruction accuracy, significantly reducing computation time and resource consumption. According to the experimental results, LB-PINNs demonstrate superior performance compared to previous reconstruction algorithms when reconstructing the soot volume fraction in complex reacting flow fields, i.e., combustion flame scenarios. [ABSTRACT FROM AUTHOR]

Due to their simple geometric configuration and involved rich physics, rotating drums have been widely used to elaborate granular flow dynamics, which is of significant importance in many scientific and engineering applications. This study both numerically and experimentally investigates dry and wet mono-dispersed granular flows in a rotating drum, concentrating on the effects of relative densities, ρ s − ρ f , and rotating speeds, ω. In our numerical model, a continuum approach based on the two-phase flow and μ I theory is adopted, with all material parameters calibrated from experimental measurements. It is found that, in the rolling and cascading regimes, the dynamic angle of repose and the flow region depth are linearly correlated with the modified Froude number, F r * , introducing the relative density. At the pore scale, flow mobility can be characterized by the excess pore pressure, p f . To quantify the variance of the local p f , it is specifically nondimensionalized as a pore pressure number, K , and then manifested as a function of porosity, 1 − ϕ s . We find K (ϕ s) approximately follow the same manner as the Kozeny–Carman equation, K ∝ ϕ s 2 / 1 − ϕ s 3 . Furthermore, we present the applicability of the length-scale-based rheology model developed by Ge et al. ["Unifying length-scale-based rheology of dense suspensions," Phys. Rev. Fluids 9, L012302 (2024)], which combines all the related time scales in one dimensionless number G , and a power law between G and 1 − ϕ s / ϕ c is confirmed. This work sheds new lights not only on the rigidity of implementing continuum simulations for two-phase granular flows, but also on optimizing rotating drums related engineering applications and understanding their underlying mechanisms. [ABSTRACT FROM AUTHOR]

Compressible particle-laden systems are widely present in various natural phenomena and engineering applications. This study focuses on developing a compressible semi-resolved computational fluid dynamics-discrete element method (CFD-DEM) coupling model with heat transfer. The model can simulate gas–solid and liquid–solid systems across a range of dilute to dense patterns. A semi-resolved model is developed by combining the diffusion-based smoothing method and the volume-averaged weighted function interpolation method, removing the restriction of the grid size to particle diameter ratio in unresolved models. The volume-averaged Navier–Stokes equation is introduced for variable density flows in the fluid phase. All closed terms and assumptions are discussed. Special attention is paid to the improved energy conservation equation for the fluid phase and the modified pressure Poisson equations that are suitable for high-speed thermal particulate flows. Particle motion is tracked using DEM, which considers the translation, rotation, collision, and heat transfer processes of the particles. The numerical simulation results are compared with several experimental findings, validating the effectiveness of the compressible CFD-DEM coupling model. The proposed model introduces new ideas and methods for investigating the mechanisms and engineering applications of compressible fluid–solid systems. [ABSTRACT FROM AUTHOR]

A mixed charge structure is composed of several different types of particles to achieve performance indicators that cannot be achieved by a single particle and usually need to be adjusted and evaluated to determine the parameters in the chamber according to different demand. To balance the accuracy and efficiency, and obtain more calculation parameters, the solid phase is modeled by the particle element method, while the fluid phase is modeled by a computational fluid dynamics solver based on the fifth-order weighted essentially non-oscillatory scheme. In the mixed charge structure of different granular propellant, different particles in different areas are classified and particle elements are divided, and the particle interface position is tracked and captured to form the particle element distribution with different sizes. In the mixed charge structure with central tubular propellant, the granular and the tubular propellants are calculated separately by different types of particle elements, and the source term is used in coupling simulation. Comparing with the calculation results of experiment, the velocity error is less than 1%, and the maximal breech pressure error is less than 3%. In the mixed granular charge structure, due to the differences in combustion rates and movement velocities of the particles, the distribution state of the particles within the chamber is significantly different from that of single particle charge. Additionally, the standard deviation of the porosity is greater in mixed granular charge (0.051: 0.0086). In the mixed charge structure with central tubular propellant, the porosity of tubular and particle distribution in the chamber is discontinuous, and the pressure distribution is effectively predicted. The calculation results show that the perfect consistency of ignition in the chamber, which shows the superior flame-spreading performance of the central tubular propellant. The particle element method can provide a powerful tool for the rapid modeling and simulation of two-phase flow. [ABSTRACT FROM AUTHOR]

The motion characteristics of Janus in the flow are studied numerically using the lattice Boltzmann method based on the squirmer model. The effects of velocity ratio J on the right and left hemisphere surface of Janus, particle Reynolds number Rep, flow Reynolds number Rec, initial orientation angle φ0 on Janus trajectory, and lateral equilibrium position yeq/H are analyzed. The results showed that, for the motion of Janus in stationary power-law fluids in a channel, Janus moves randomly in a small space in shear-thickening fluids when Rep is low and exhibits three motion modes at Rep = 5. The larger the J value, the easier it is for Janus to reach yeq/H. The higher the Rep, the closer the yeq/H is to the lower wall. In shear-thinning fluids, the motion of Janus exhibits significant randomness at Rep = 0.5 and 1, reaches the same yeq/H at Rep = 2 and 3, and tends toward yeq/H near the centerline and along the upper wall, respectively, at Rep = 4 and 5. For the motion of Janus particles in a channel flow of power-law fluids, in shear-thinning fluids, no matter what value J is, Janus reaches yeq/H on the centerline. The lower the Rep, the closer the yeq/H is to the wall. Two particles move toward yeq/H when Rep ≥ 1. The higher the Rep, the closer the yeq/H is to the centerline. The two particles will exhibit the upstream mode at Rep = 2. Two particles eventually reach yeq/H at different Rec. When φ0 > 0°, the two particles first eventually tend toward yeq/H = 0.2 and 0.8. When the value of φ0 is negative, the larger the absolute value of φ0 and higher the Rep, the more likely particles are to exhibit upstream mode. [ABSTRACT FROM AUTHOR]

The double-row hydraulic sluicing model is widely used in deep-sea mining collecting systems. However, there has been limited research focusing on its flow contributions and the relationship with particle motions. In this paper, a double-row hydraulic sluicing collector with high pickup efficiency is designed. The flow characteristics, the mechanics of the flow field, and the movement of particles in the collector are analyzed in detail through numerical calculations and experiments. The flow contributions and the collecting mechanism are clearly highlighted through aspects such as the frequency of pressure fluctuations and flow-induced vortices. The high-speed jet rolls upward after hitting the ground, forming a high-pressure area on the ground. The upwelling in the collection area is generated by the combination of the high-pressure area and the upward rolling of fluid. Regarding the particles, it is observed that particle motion can be divided into two main stages, rapid acceleration, followed by slow deceleration. Some particles may fall back when rising. Additionally, the analysis of fluid forces on the particles indicates that drag force and pressure gradient force have significant influence on particle motion. [ABSTRACT FROM AUTHOR]

In the study of fluid turbulence, the Lagrangian frame of reference represents the most appropriate methodology for investigating transport and mixing. This necessitates the tracking of particles advected by the flow over space and time at high resolution. In the past, the purely spatial counterpart, the Eulerian frame of reference, has been the subject of extensive investigation utilizing hot wire anemometry that employs Taylor's frozen flow hypotheses. Measurements were reported for Taylor scale Reynolds number Rλ > 104 in atmospheric flows, which represent the highest strength of turbulence observed on Earth. The inherent difficulties in accurately tracking particles in turbulent flows have thus far constrained Lagrangian measurements to Taylor scale Reynolds numbers up to approximately Rλ = 103. This study presents the Lagrangian particle tracking setup in the Max Planck Variable Density Turbulence Tunnel (VDTT), where Taylor scale Reynolds numbers between 100 and 6000 can be reached. It provides a comprehensive account of the imaging setup within the pressurized facility, the laser illumination, the particles used, and the particle seeding mechanism employed, as well as a detailed description of the experimental procedure. The suitability of KOBO Cellulobeads D-10 particles as tracers within the VDTT is illustrated. The results demonstrate that there is no significant charge exhibited by the particles and that the impact of their inertia on the results is negligible across a wide range of experimental conditions. Typical data are presented, and the challenges and constraints of the experimental approach are discussed in detail. [ABSTRACT FROM AUTHOR]

This study presents a numerical investigation of turbulent crude oil flows in circular curved pipelines, with a focus on the deposition patterns of solid particles within the fluid. Simulations were conducted using the Reynolds–Averaged Navier–Stokes equations coupled with the k–ε turbulence model to examine the influence of structural characteristics, such as bend curvature angle and bend curvature radius, on flow dynamics and particle deposition. The results reveal that the complex flow patterns generated by these geometric features significantly affect pressure gradients and particle trajectories. Specifically, the study shows that turbulent flows within bends exhibit intricate behaviors, with deposition patterns being strongly influenced by the pipeline's geometric parameters. Sand particles, commonly present in petroleum flows, are found to be more effectively transported in pipes with larger curvature angles, while they exhibit a higher propensity to settle at smaller curvature angles and larger bend curvature radii. Furthermore, the simulations indicate that the majority of deposited particles accumulate on the inner wall immediately downstream of the elbow entrance. [ABSTRACT FROM AUTHOR]

Cruise-type aquaculture on deep-sea aquaculture vessels is an important direction for developing of modern marine fisheries. The article explored the effect of transverse rolling motion on the flow field characteristics in the tank based on FLOW-3D software, and calculated the removal of waste particles in the flow field under different transverse rolling conditions on this basis. The results showed that when controlling the period of transverse rolling, the flow velocity in the aquaculture tank increased slightly as the amplitude of the transverse rolling angle increased from 0° to 2°. When the amplitude of the transverse rolling angle was increased from 2° to 7º, the flow velocity in the aquaculture tank showed a large increase, and the v50% increased from 0.171 m/s to 0.477 m/s; the increase of the transverse rolling angle also made the overall distribution of the flow velocity more discrete. The flow uniformity index of the conditions with the transverse rolling angle amplitude of 2° or less is mainly concentrated in 0.8-0.85, while when the transverse rolling angle amplitude is increased to 3º, the flow uniformity of the aquaculture tank decreases significantly. The flow uniformity indices of the water in the aquaculture tank are all less than 0. 8. When the amplitude of the transverse rolling angle is certain, the transverse rolling period is shortened, the flow velocity in the aquaculture tank increases sharply, and the v50% of the flow velocity of each condition and the other quartiles show a linear growth trend while the uniformity of the flow of the water in the tank does not change significantly. For the removal of waste solid particles in the aquaculture tank, the whole process is divided into two phases with opposite effects when the period of transverse rolling and the properties of particles themselves are certain. From the time when the particles were released into the flow field to the 1000 s after the release, the smaller the amplitude of the transverse rolling angle was, the higher the removal rate was; thereafter, until the end of the calculation of the whole example, the larger the transverse rolling angle was, the higher the removal rate of the particles was. The period of transverse rolling did not effect the removal of particles in the aquaculture tanks, and the time to reach the standard for particles removal was very close for each condition. [ABSTRACT FROM AUTHOR]

The dynamic interaction between granular flowing masses and rigid obstacles is a complex phenomenon characterised by both large displacements and high strain rates. In case the flowing mass is modelled as a continuum, its numerical simulation requires both advanced computational tools and constitutive relationships capable of predicting the mechanical behaviour of the same material under both fluid and solid regimes. In this paper, the authors employed the open‐source ANURA3D code, based on the Material Point Method (MPM), and a multi‐regime constitutive model. A series of impacts characterised by different velocities, initial void ratios, front inclinations and impacting mass lengths have been simulated. The MPM numerical results are critically compared with those obtained by using a Discrete Element Method (DEM) numerical code. The model capability of simulating material regime transitions, from fluid to solid and vice versa, is shown to be crucial for reproducing the mechanical response of the flowing mass put in evidence by DEM data. [ABSTRACT FROM AUTHOR]

We propose a constitutive model for both the solid-like and fluid-like behavior of granular materials by decomposing the stress tensor into quasi-static and collisional components. A hypoplastic model is adopted for the solid-like behavior in the quasi-static regime, while the viscous and dilatant behavior in the fluid-like regime is represented by a modified μ (I) rheology model. This model effectively captures the transition between solid-like and fluid-like flows. Performance and validation of the proposed model are demonstrated through numerical simulations of element tests. [ABSTRACT FROM AUTHOR]

The discrete element method (DEM) has emerged as an essential computational tool in geotechnical engineering for the simulation of granular materials, offering significant advantages over traditional continuum-based methods such as the finite element method (FEM) and the finite difference method (FDM). The DEM's ability to model particle-level interactions, including contact forces, rotations, and particle breakage, allows for a more precise understanding of granular media behavior under various loading conditions. However, accurate DEM simulations require meticulous calibration of input parameters, such as particle density, stiffness, and friction, to effectively replicate real-world behavior. This study proposes a simplified calibration procedure, intended to be conducted prior to any granular material flow DEM modeling, based on three fundamental physical tests: bulk density, surface friction, and angle of repose. The ability of these tests, conducted on dry quartz sand, to accurately determine DEM micromechanical parameters, was validated through numerical simulation of cylinder tests with varying height-to-radius ratios. The results demonstrated that this calibration approach effectively reduced computational complexity while maintaining high accuracy, with validation errors of 0% to 12%. This research underscores the efficacy of simplified DEM calibration methods in enhancing the predictive reliability of simulations, particularly for sand modeling in geotechnical applications. [ABSTRACT FROM AUTHOR]

Expanded polystyrene (EPS) particle-based lightweight soil, which is a type of lightweight filler, is mainly used in road engineering. The stability of subgrades under dynamic loading is attracting increased research attention. The traditional method for studying the dynamic strength characteristics of soils is dynamic triaxial testing, and the discrete element simulation of lightweight soils under cyclic load has rarely been considered. To study the meso-mechanisms of the dynamic failure processes of EPS particle lightweight soils, a discrete element numerical model is established using the particle flow code (PFC) software. The contact force, displacement field, and velocity field of lightweight soil under different cumulative compressive strains are studied. The results show that the hysteresis curves of lightweight soil present characteristics of strain accumulation, which reflect the cyclic effects of the dynamic load. When the confining pressure increases, the contact force of the particles also increases. The confining pressure can restrain the motion of the particle system and increase the dynamic strength of the sample. When the confining pressure is held constant, an increase in compressive strain causes minimal change in the contact force between soil particles. However, the contact force between the EPS particles decreases, and their displacement direction points vertically toward the center of the sample. Under an increase in compressive strain, the velocity direction of the particle system changes from a random distribution and points vertically toward the center of the sample. When the compressive strain is 5%, the number of particles deflected in the particle velocity direction increases significantly, and the cumulative rate of deformation in the lightweight soil accelerates. Therefore, it is feasible to use 5% compressive strain as the dynamic strength standard for lightweight soil. Discrete element methods provide a new approach toward the dynamic performance evaluation of lightweight soil subgrades. [ABSTRACT FROM AUTHOR]

The natural non-penetrated openings in natural rock masses due to weathering and erosion and the artificial non-penetrated openings formed in deep mining and tunneling have significant effects on the stability and safety of rock engineering. Hence, the uniaxial compression test, 3D particle flow code (PFC3D) simulation, and digital image correlation (DIC) method are used to systematically investigate the influence of the opening penetration ratio (OPR) on the mechanical behaviors and fracture characteristics of rocks containing the non-penetrated opening. Further, the maximum principal strain/stress distributions around the opening on both sides of the specimen are compared to quantitatively analyze the effect of OPR on the crack initiation mechanism from the microscopic perspective. The results show that as OPR increases, the uniaxial compressive strength (UCS) and elastic modulus (E) of sandstone/numerical specimens show a linearly decrease law, and the failure mode exhibits a law of shear failure to tensile-shear mixed failure and then to shear failure. The fracture process analyses show that the two sides of specimens containing non-penetrated opening have different cracking characteristics and belong three-dimensional failure, while the specimen containing penetrated opening are two-dimensional failure. The stress/strain distribution around the opening is altered by the support effect in the non-opening part of specimens. Therefore, as the OPR increases, the crack initiation stress level decreases and the crack initiation crack type around the opening changes from the tensile-shear to tensile. Finally, implications of the study for fracture prevention in underground excavation engineering and early warning of instability in rock engineering are given. These findings enrich the study on the failure mechanism of rock masses containing defects, which is of great importance for rock engineering safety. Highlights: The uniaxial compression strength and elastic modulus of sandstones decrease linearly with increasing opening penetration depth. The cracking behaviors of sandstone with non-penetrated opening are three-dimensional. The pre-existing defect surface of sandstone with non-penetrated opening is cracking first and failure first. The changes in stress/strain distribution around the opening on both sides make differences in the crack initiation mechanism and initiation stresses. The findings are instructive for fracture prevention in underground excavation engineering and early warning of instability in rock engineering. [ABSTRACT FROM AUTHOR]

In this paper, a novel three-dimensional grain-based model based on particle flow code (PFC3D-GBM) is used to reconstruct the crystalline structure of granite, which enables the grouping and filling of minerals. Some contacts in the numerical sample are grouped separately and then calibrated with lower microparameters, which represent mesoscopic defects within natural granites. In addition, considering the heterogeneity of the levels of force chain networks in different structures of granites, a multilevel classification of the entire force chain network is accomplished. A uniaxial compression test is conducted to quantify the effect of the microtensile strength σD and volume proportion VD of mesoscopic defects on the macroscopic mechanical behaviour of granites at various points of the force chains. Both the strength and modulus of the sample increase as σD increases. The mean, sum and maximum of the general force chains of the intact structures and defect structures increase with increasing σD. The bearing capacity of various structures also increases. Both the strength and modulus of the sample decrease as VD increases, and the strength of the overall force chain network decreases. The mean, sum and maximum values of the general force chains of the intact structures decrease. Although the number of force chains in the corresponding defect structures greatly increases, the average level of the force chain network decreases. The bearing capacity of the various structures decreases as VD increases. Highlights: A three-dimensional grain-based model is proposed, which enables the multilevel classification and quantitative analysis of the force chain network. The mesoscopic defects within natural granites are reproduced by grouping "weak contacts" with low microstrengths. The influence of the microstrength and volume proportion of defects on granites is explored based on the multilevel force chain network. The bearing capacity of granites is proportional to the microstrength of defects and is inversely proportional to the volume proportion. [ABSTRACT FROM AUTHOR]

In this study, a realistic model of the respiratory tract obtained from CT medical images was used to solve the flow field and particle motion using the Eulerian–Lagrangian approach to obtain the maximum particle deposition in the bronchial tree for the main purpose of optimizing the performance of drug delivery devices. The effects of different parameters, including particle diameter, particle shape factor, and air velocity, on the airflow field and particle deposition pattern in different zones of the lung were investigated. In addition, a genetic algorithm was employed to obtain the maximum particle deposition in the bronchial tree and the effect of the aforementioned parameters on particle deposition. Reverse flow, vortex formation, and laryngeal jet all affect the airflow structure and particle deposition pattern. The mouth–throat region had the highest deposition fraction at various flow rates. A change in the deposition pattern with an increased deposition fraction in the throat was observed owing to the increased diameter and shape factor of the particles, resulting from the higher inertia and drag force, respectively. The particle deposition analysis showed that three parameters, shape factor, diameter, and velocity, are directly related to particle deposition, and the diameter is the most effective parameter for particle deposition, with an effect of 60% compared to the shape factor and velocity. Finally, the prediction of the genetic algorithm reported a maximum particle deposition in the bronchial tree of 17%, whereas, based on the numerical results, the maximum particle deposition was reported to be 16%. Therefore, there is a 1% difference between the prediction of the genetic algorithm and the numerical results, which indicates the high accuracy of the prediction of the genetic algorithm. [ABSTRACT FROM AUTHOR]

The bidirectional composite vibratory finishing (BCVF), which is a novel high efficiency collaborative surface finishing technology of structure shape and surface integrity, is expected to solve the problem of poor machinability in grooves, slits, corners, and intricate profiles of the workpiece. The basic research was carried out to expand its engineering applications. Based on the discrete element method (DEM), the particle flow behavior and velocity distribution were analyzed, it is found that the particle temperature can explain the changes of the normal and tangential cumulative contact energy on the workpiece surface. In addition, the normal contact force on the container sidewall and the pressure distribution on the workpiece surface were measured under different process parameters. The comparison with the simulations reveals that DEM model accurately predicted the particle–wall normal contact force frequency content, and the dominant frequencies are the container driving frequency and its multiplication. Meanwhile, the pressure-sensitive film can intuitively demonstrate the integrated action behavior of particles, including normal impact, inclined impact, rolling, scratching, and ploughing. Moreover, the axial uniformity and machining efficiency were enhanced by the rise in the frequencies and amplitudes of both horizontal and vertical vibration. For the combined effect of vibration frequency and amplitude, it was verified that the dimensionless vibration velocity amplitude was linearly and positively correlated with the normal contact force and the tangential cumulative contact energy on the workpiece surface. As a result, the simulations using spherical particles can predict some critical properties in non-spherical processing, and provide reference for the popularization of the BCVF process. [ABSTRACT FROM AUTHOR]

Carbon particles, a primary component of diesel engine emissions, cause persistent erosion in the exhaust piping system, inevitably leading to performance degradation. This erosion can result in reduced fuel economy and increased emissions. The effects of three key parameters including solid particle size, turbine U/C operating conditions and rotational speed on the erosion characteristics of the flow channels of a radial turbine for vehicle diesel engine applications and their impact on performance were investigated through numerical simulations in the study. The findings indicate that larger particle size and higher rotational speed can significantly lead to the higher erosion rate density of the volute channel and casing wall surfaces. Reducing U/C does not substantially affect the distribution of erosion rate density. Centrifugal force will play an important role in the variation of erosion distribution characteristics. Compared to U/C, the other two key parameters are sensitive factors affecting turbine performance degradation. Under the same condition for operating 5000 h, 10 μm particles cause a 7.5-fold increase in efficiency loss change rate compared to 0.5 μm particles. The efficiency loss at 140 krpm is 16 times greater than that at 40 krpm. [ABSTRACT FROM AUTHOR]

A dual-jet collecting device is highly efficient at picking up small-sized polymetallic nodules; however, its performance is not as effective for large nodules in deep-sea mining. To address this problem, numerical simulations have been conducted to thoroughly investigate the flow characteristics and particle motions during the collection of larger nodules. The collection performance of the enhanced device is analyzed across varying front jet velocities (Vf), suction pressures (Pout), and nozzle heights (h/d). The results reveal that increasing Vf improves the drag force and particle velocity in the jet impingement and upwelling zones, facilitating nodule lifting movement and transport. However, increasing Pout reduces the drag forces in these zones while increasing the particle velocity in the upwelling zone. A large Pout is not conducive to nodule initiation but has benefits for transport. Increasing h/d reduces the drag force in the anti-gravity direction in the jet impingement zone. The improved collecting device attains a pick-up efficiency that exceeds 80% for large-sized nodules when h/d < 1.3. The pick-up efficiency with suction pressure, which remains 40%, is higher than that without suction pressure when h/d > 1.3. The research findings may shed light on the design of more efficient dual-jet collection systems. [ABSTRACT FROM AUTHOR]

This research aims to experimentally characterize cooling, clogging and jamming of a dry granular flow in a chute partially obstructed by a stopping wall with two slits adjacent to the side walls. We ensemble‐average velocities, determined with Particle Tracking Velocimetry, and its fluctuations, to compute mean flow and granular temperature fields. Full chute‐wide jamming is triggered by the formation of stable arch‐like clogging structures in front of the slits. The statistical distribution of the clogging instant is not heavy‐tailed, which indicates that clogging occurs only when the flow through the slits is liquid‐like. An upstream‐progressing jamming wave eventually forms, similar to that observed in fully obstructed chutes. There is no triple point anywhere, since the flow cools down to a granular liquid before jamming. We identified three main stages of jamming wave propagation. The initial buildup is characterized by high values of the upstream Froude number, slow progression, and transformation of kinetic into potential energy. This occurs with significant granular head losses, as particles attempt to flow over the jam. In the second stage, accretion becomes dominant, characterized by smaller head losses and, consequently, higher values of the jamming wave celerity. In the third stage, the jamming wave propagates against a cooler but faster flow that pushes against the jam, slightly increasing the wave strength. Accretion is the main mechanism of jammed mass increase, justifying a further increase of wave acceleration. The macroscopic aspects of the jamming wave dynamics can be described, as a first approximation, by shallow‐water theory. Key Points: The flow through the slits enters the clogging regime as it cools down. Chute‐wide generalized jamming results from cloggingThere are no triple points in the system. Jamming only incorporates particles that have cooled to liquid‐like behaviorThe dynamics of the jamming wave exhibit three stages, with different roles of accretion and upward dissipative modes of jamming [ABSTRACT FROM AUTHOR]

Taking a four-stage transonic compressor as the research object, the Lagrange particle tracking method was used to simulate the multiphase flow by considering the particle fragmentation, collision and evaporation models, and the influence of different inlet conditions (raindrop diameter, velocity, temperature and flow rate) on the compressor's performance and stable working range was studied. The results show that inlet rain absorption can weaken the clearance leakage vortex make the shock wave move downstream, thus increasing the inlet flow rate, resulting in a decrease in stability margin and the highest efficiency point moving in the direction of flow increase. With the decrease in raindrop diameter, the pressure ratio and wet compression efficiency increase, and the stability margin decreases. With the increase in inlet raindrop velocity, the degree of pneumatic breakage increases and the raindrop diameter becomes smaller, which leads to the decrease in pressure ratio and efficiency. The influence of the mass flow rate of imported raindrops on the stable working range is significant. When the mass flow rate of imported raindrops accounts for 5% of the design flow, the stable working range can be reduced by more than half. Rain absorption increases the reaction force of the compressor and increases the load of the rotor blade. [ABSTRACT FROM AUTHOR]

Tunnel Boring Machines (TBMs) are integral to modern underground engineering construction, offering enhanced safety and efficiency. However, TBMs often face challenges in complex geological conditions, such as composite strata, resulting in reduced advancement speed and increased cutter wear. This study investigates the rock-breaking characteristics of TBM disc cutters in composite strata through numerical simulations using the Particle Flow Code (PFC) 5.0 software. Focusing on the Jinan Metro Line 6, the research analyzes cutter forces, rock crack propagation, and the impact of cutter edge shapes on rock-breaking efficiency. The discrete element method (DEM) is employed to simulate microscopic behaviors of rocks, providing insights into crack formation, expansion, and failure. This study's findings reveal that cutter design and operational parameters can significantly influence cutter lifespan and efficiency. By modifying cutter spacing and penetration depth, enhancing rock-breaking efficiency, and grouting softer layers, TBMs can maintain effective excavation in composite strata. The study establishes a comprehensive understanding of the interplay between TBM cutters and complex geological conditions, offering actionable strategies to enhance TBM performance and mitigate cutter damage. [ABSTRACT FROM AUTHOR]

Copyright of Chinese Journal of High Pressure Physics is the property of Chinese Journal of High Pressure Physics Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Chinese Journal of High Pressure Physics is the property of Chinese Journal of High Pressure Physics Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Investigating the shear characteristics of the contact surface between tunnel surrounding rock and lining under different normal stresses and roughness conditions has significant theoretical and engineering importance for further research on the interaction between tunnel surrounding rock and lining, as well as the stability of rock mass. To consider roughness conditions, fractal theory was adopted to generate five different contact surfaces by changing the fractal dimension D and fractal roughness G in the fractal formula. Based on the two-dimensional particle flow code (PFC2D ), a numerical shear model of the contact surface with dimensions of 150 mm x 150 mm was established. Numerical shear tests were carried out for the same contact surface under different normal stresses and for different contact surfaces under the same normal stress. In order to verify the reliability of the numerical simulation, shear stress-shear displacement curves obtained from a typical numerical shear test were compared with those obtained from the laboratory shear test. The research results showed that: (1) The cracks generated by shear failure in the numerical model were mainly concentrated at the middle contact surface, with stress after failure mainly concentrated at points with the greatest contact surface roughness. The failure cracks could be divided into shear cracks and tensile cracks, with tensile cracks being predominant. (2) Shear stress-shear displacement curves exhibited three stages: climbing, cutting and sliding, with obvious peak strength and residual strength. Normal displacement increased with increasing shear displacement, resulting in dilatancy effect. (3) With the increase of normal stress, the number of shear and tensile cracks increased, failure phenomena became more pronounced. Peak strength and residual strength increased, and the dilatancy effect decreased. (4) With increasing roughness undulation, i. e., an increase in fractal dimension D or a decrease in fractal roughness G, the number of failure cracks increased, especially tensile cracks, as well as peak strength and residual strength. The dilatancy effect also intensified. [ABSTRACT FROM AUTHOR]

Multi-scale assessment of shear behavior in the tunnel carbonaceous slate is critical for evaluating the stability of the surrounding rock. In this study, direct shear tests were conducted on carbonaceous slates from the Muzhailing Tunnel, considering five bedding dip angles (β) and four normal stresses (σn). The micro-mechanism was also examined by combining acoustic emission (AE) and energy rate with PFC2D Version 5.0 (particle flow code 2D Version 5.0 software) numerical simulations. The results showed a linear relationship between peak shear stress and normal stress, with the rate of increase inversely related to β. Cohesion increased linearly with β, while internal friction angle and AE activity decreased; the energy release rate is 3.92 × 108 aJ/s at 0° and 1.93 × 108 aJ/s at 90°. Shearing along the preset fracture plane was the main failure mode. Increased normal stress led to lateral cracks perpendicular to or intersecting the shear plane. Cracks along the bedding plane formed a broad shear band with concentrated compressive force, and inclined bedding was accompanied by a dense tension chain along the bedding plane. [ABSTRACT FROM AUTHOR]