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This paper presents a model to characterize the distribution of non-uniform sediment in suspension above erodible sediment beds in turbulent flow under non-equilibrium conditions. The modeling process incorporates three crucial features of sediment-laden flow: mixing length, stratification, and settling velocity. The advection–diffusion equation for the k -th grain-size class is modified accordingly. The model's calculations encompass the determination of reference height and reference concentration, accounting for the presence of different-sized particles in the flow. The numerical solution of the model effectively captures concentration variations for distinct particle sizes in streamwise and vertical directions, as well as temporal changes. As experimental data under non-equilibrium conditions with different sediment sizes are unavailable, the study focuses on specific experiments involving various sediment beds with a mixture of different grain sizes under equilibrium conditions. The current findings reveal that the concentration magnitude decreases downstream with time for all grain sizes, eventually reaching an equilibrium state. This behavior is consistent with variations in downstream distance at a specific time. The mixing length which is concentration-dependent, first increases the suspension concentration for all grain sizes at smaller downstream distance and then the effect reverses for all grain sizes at larger downstream distance. A similar trend is observed when considering both stratification and mixing length. An error analysis evaluates the model's performance, indicating that the least error corresponds to datasets incorporating all considered effects. [ABSTRACT FROM AUTHOR]

Settling basins are one of the structures required for removing excess sediment entering irrigation or power canals diverting water from a river. A numerical model is needed to simulate the flow and sedimentation pattern in settling basins. In the current research, a depth-averaged two-dimensional numerical model of flow and sediment is developed using the finite volume method and based on the time-splitting scheme, which also allows for simulating sediment in a non-equilibrium state. The simulation of flow and sedimentation is done by the numerical model in a decoupled method. Sensitivity analysis was applied to estimate the effects of non-equilibrium parameters and the settling velocity on the numerical results. The results revealed that Maleki and Khan's formula and Zhang and Xie's formula are suitable for estimating the suspended load adaptation coefficient and the sediment settling velocity in the numerical simulations. Investigation of the formulas for the bed adaptation length indicated that all three methods considered in the current research had almost equal accuracy in predicting the sediment concentration distribution in the settling basin. The developed model has been verified against two experimental tests, showing a good fit between observed data and the simulated results. [ABSTRACT FROM AUTHOR]

This study assesses the settling dynamics of suspended sediments along the hyper‐turbid Gironde Garonne fluvial‐estuarine system, with an innovative optical SCAF instrument (System of Characterization of Aggregates and Flocs). Two fields campaigns were carried out to determine the settling velocity and properties of suspended sediments during a semi‐diurnal tidal cycle, as well as hydrodynamic conditions and water properties. The two sampling stations were representative of two regions: a tidal river dominated by fresh water and an estuary affected by salty or brackish waters. A high spatial variability of the settling velocity was observed along the fluvial‐estuarine system and vertically along the water column. Settling velocities ranged from 0.02 to 0.4 mm/s. This study confirms that in hyper‐turbid systems, the suspended sediment concentration (SSC) is predominantly driving the settling dynamics of suspended sediment. Threshold concentrations have been defined for the flocculation and hindered regimes where the settling velocity may vary by one order of magnitude. Although in natural environments it is difficult to distinguish between the effects of SSC and turbulence (as they are correlated), in the Gironde‐Garonne system the turbulent shear G seems to affect the settling of suspended sediment to a lower extent. Settling velocity variations cannot be directly correlated to salinity or organic matter content. Despite differences in hydrodynamic and environmental conditions in fluvial and estuarine regions, a common prediction law has been found to estimate settling velocity of suspended sediment as a function of suspended sediment concentration. Plain Language Summary: Estuaries and rivers are biotically rich environments strongly impacted by human activities. Mud trapping capacity of such systems has a major influence on water quality by reducing light availability, promoting oxygen depletion and by trapping adsorbed contaminants, bacteria and nutrients. A key dynamical parameter impacting the trapping of mud is the sediment settling velocity. Sediment settling is influenced by a wide range of environmental factors such as salinity, sediment concentration, turbulence of the flow and organic matter. This manuscript presents sediment settling data from field surveys carried out along the Garonne River—Gironde Estuary system (France), where large quantities of mud are trapped during the dry season. It highlights the driving role of sediment concentration on the settling dynamics along the entire system, despite the hydrodynamics and water properties of riverine waters differing from the estuarine waters. The turbulence of the flow appeared to be of secondary importance. An unique empirical prediction law has been established for the whole system contrary to other systems around the world. An improved understanding of sediment fluxes contributes to effective waterways management and the preservation of essential ecological environments. Key Points: In such hyper‐turbid system, the suspended sediment concentration predominantly drives the settling dynamics of suspended sedimentThe turbulent shear appeared to be a control parameter of secondary importanceA common prediction law can be found for the whole system [ABSTRACT FROM AUTHOR]

We investigate the settling velocity change of weakly inertial particles, whose density ratio to fluid ranges from 1.35 to 1.38, in vertical water flow. To assess the effect of turbulence, we experimentally examine the dependence of modifications of velocity on physical scales, including time, velocity, and length, between particles and turbulence. It is observed that the settling velocity is either enhanced or hindered by the turbulence compared to stagnant conditions. The change in settling velocity is observed to be responsive to both the inertia of particles and the turbulence intensity. In cases of weak turbulence or with larger particles, the settling velocity exhibits small changes and even decreases. Conversely, the change in settling velocity is more pronounced for smaller particles and in more intense turbulence, reaching a maximum increase at S t ≈ O (1 0 − 3). We compare our experimental results with existing studies conducted in solid–liquid two-phase flow, finding a consistent tendency. In both prior research and the present study, the length scale parameter, S t S v , has consistently been important in discerning inertial conditions that determine the change in settling velocity under turbulent conditions. [Display omitted] • Settling velocity of inertial particles with a density ratio ranging from 1.35 to 1.38 was examined under vertical mean flow conditions. • As the particle Reynolds numbers decrease, the modifications in settling velocity broaden in response to turbulent conditions. • The length scale parameter, S t S v , shows significance in discerning inertial conditions of settling particles. [ABSTRACT FROM AUTHOR]

Residual dosage has a significant impact on the settling characteristics of coal slurry flocs and the sedimentation efficiency of coal slurry. This study conducted sedimentation stirring experiments to measure the supernatant grayscale, floc size, settling velocity, and residual anionic polyacrylamide (APAM) under varying energy inputs. The investigation focused on the correlation between different levels of APAM residual and the settling characteristics of coal slurry flocs. The results show that having APAM residuals in the first three stages helps with sedimentation. This leads to lower residual levels, higher grayscale in the supernatant, bigger floc sizes, and better settling velocities. However, in the fourth stage, as APAM residual levels increased once more, the supernatant grayscale decreased linearly, floc breakup became severe, and settling velocities neared stagnation. In the second stage, a correlation was noticed between higher APAM residual levels and better settling properties of coal slurry flocs. By studying residual dosage and energy input, guidance on how to optimize the sedimentation efficiency of the thickener and reduce dosage can be provided. [ABSTRACT FROM AUTHOR]

The hydrotransport of settling particles using laminar flow as opposed to the more energy‐ and water‐intensive turbulent flow has remained a tentative option for industries due to the complexity in characterizing particle settling dynamics in opaque non‐Newtonian fluids under sheared conditions. To provide insight into this unknown physics, this study focused on viscoelastic shear‐thinning fluids and developed a semi‐empirical model to characterize the batch‐settling dynamics of dilute suspensions (<5 vol% solids concentration) experiencing a shear field. These suspensions consisted of spherical glass microparticles in aqueous xanthan gum solutions. Settling profiles were measured with Electrical Resistance Tomography (ERT) while a motorized belt generated a cross‐shear field. The data acquired by the ERT showed that introducing cross‐shear fields into such suspensions increased settling rates when compared with static settling contexts. Then, a semi‐empirical model describing the "acceleration phase" of the settling process was developed and validated at accuracies between 81% and 97%. [ABSTRACT FROM AUTHOR]

The terminal settling velocity of microplastics plays a vital role in the physical behavior of microplastics, and is related to the migration and fate of these microplastics in the ocean. At present, the terminal settling velocity is mostly calculated by formulae, which also leads to a fewer studies on the use of machine-learning models to predict its settling velocity in this field. This study fills this gap by studying the prediction of the settling velocity by machine-learning models and compares it with the traditional formula calculation method. This study evaluates three machine-learning models, namely, random forest, linear regression, and the back propagation neural network. The results of this study show that the prediction results of the three machine-learning models are more accurate than those of traditional formula calculations, with an accuracy increase of 12.79% (random forest), 9.3% (linear regression), and 13.92% (back propagation neural network), respectively. At the same time, according to the results of this study, random forest is better than the other models in the mean absolute error and root mean square error evaluation indicators, which are only 0.0036 and 0.0047. This paper proposes three machine-learning methods to prove that the prediction effect of machine learning is much better than traditional formula calculations, thereby improving the shortcomings in this field. At the same time, it also provides reliable data support for studying the migration behavior of microplastics in water bodies. [ABSTRACT FROM AUTHOR]

Retention of plastics in estuaries and storage in sediments likely contributes to the mass imbalance between the amount of ocean plastic debris and input from land. A sediment transport model, coupled with a hydrodynamic and wave model, was employed to analyze how microplastics of varying settling velocities behave under non-storm conditions and during extreme storm events in Galveston Bay, USA. The model was informed by measured concentrations of microplastics in a main tributary (Buffalo Bayou), which flows through the highly populated Houston-metro area. Under non-storm conditions, concentrations of neutrally buoyant particles are highest near the source location. In contrast, negatively buoyant particles are highest near the bay mouth where bed shear stress, and thus the potential for erosion/resuspension, is highest. Simulation of Hurricane Harvey, an unpreceded 1000-year flood event, shows a drastic increase of overall microplastic levels in Galveston Bay, approximately 5x that of non-storm conditions, and an increase in corresponding flux of microplastics to the Gulf of Mexico. The differences are attributed both to increases in microplastic loading and erosion of microplastics from bed sediments during Harvey. Differences in concentration between storm and non-storm conditions are most clear in the upper bay, where shear stress is low under normal conditions but shows a significant increase during storms due to wave-enhanced stress. Following Harvey, negatively buoyant particles levels return to normal in less than a week, but neutrally buoyant particle concentrations remain elevated over several months. Use of a sediment transport model that simulates erosion/resuspension to understand particle behavior lends further understanding of processes of microplastics not explored through previous use of particle tracking models that do not account for erosion/resuspension. This is of upmost importance for simulation of negatively buoyant particles, which have more potential to interact with the sediment bed layer. Variation of critical shear stress for erosion, erosion rate, and use of a wave model, all show significant impacts on particle behavior. Future parameterization of microplastic behavior in sediments will enhance our understanding of estuarine retention and export ability.

The purpose of the study was to develop a simple and rapid method for measuring the average settling velocity of particles in stormwater ponds. Water samples with suspended particles were collected from the bottom of a stormwater pond in Lund, Sweden. The absorbance in various samples was measured over 24 h (at 600 nm wavelength) and then translated into total solids concentrations. A one-dimensional model based on the Mason–Weaver equation was coded in Python and solved. The absorbance measurements were used to calibrate the model, thereby quantifying settling velocities and dispersion coefficients for samples from different zones of the stormwater pond. The quantified settling velocities ranged from 40 to 200 mm/h for fast-settling particles and from 2 to 8 mm/h for slow-settling particles. The developed methodology provided a mass estimate of the two modelled particle groups (i.e., fast- and slow-settling particles). Based on the model estimates, fast-settling particles dominated all samples, constituting 70–90% of the total solid mass. Due to its simplicity and inexpensiveness, this methodology is a potential alternative to more demanding and complicated methodologies used for measuring particle velocities in sedimentation systems. HIGHLIGHTS Convection–dispersion equation was adapted to represent particle sedimentation.; Absorbance data (at 600 nm) were used to calibrate the convection–dispersion model.; Calibrated parameters are estimates of particle settling velocity and dispersion.; Settling characteristics of two or more groups of particles can be quantified.; The methodology is inexpensive and fast, thus suitable for the frequent use.;

Efficient transport in vertical pipeline hydraulic lifting systems is vital for coarse-grained ore, necessitating a deep comprehension of the settling traits of coarse mineral particles. In this study, we conducted a series of settling experiments on individual coarse particles in Newtonian fluids with varying viscosities, employing a self-designed and manufactured settling apparatus. A total of 133 sets of experimental data on the free settling of coarse particles in Newtonian fluids were obtained by recording the particle settling process with a high-speed camera and applying image processing techniques. A mechanical model was employed to perform statistical analysis on the experimental data and establish a predictive model for the drag coefficient and an explicit predictive model for the settling terminal velocity of coarse-grained ore in Newtonian fluids. The average relative errors between the predicted values and experimental values of the drag coefficient and settling terminal velocity models are 4.26% and 7.34%, respectively. This confirms the reliability of the provided predicted model, providing a theoretical foundation for determining the hydraulic lifting speed of coarse mineral particles in vertical pipelines for deep mining. [ABSTRACT FROM AUTHOR]

In petroleum engineering, accurately predicting particle settling velocity during various stages of a well's life cycle is vital. This study focuses on settling velocities of both spherical and non-spherical particles in Newtonian and non-Newtonian fluids. Utilizing a dataset of 931 experimental observations, an artificial neural network (ANN) model with a 7-42-1 architecture is developed (one input layer, one hidden layer with 42 neurons, and one output layer). This model effectively incorporates particle settling orientation and the inclusion of the settling area ratio, enhancing its predictive accuracy. Achieving an average absolute relative error (AARE) of 8.51%, the ANN model surpasses traditional empirical correlations for settling velocities in both Newtonian and power-law fluids. Key influencing factors, such as the consistency index and particle equivalent diameter, were identified. This approach in ANN model construction and data analysis represents a significant advancement in understanding particle dynamics. [ABSTRACT FROM AUTHOR]

The prediction of the stability of ceramic suspensions with multiple particles is limited depend on classical DLVO theory or Stokes equation. The mechanical effect of particles settling in suspension was studied, and a simplified mechanical equilibrium model of particles was proposed, shown as follows: u = Δ ρ g d 2 18 η − τ y d 36 η. The sedimentation of particles is mainly influenced by the density difference between particles and fluid Δ ρ , particle size d , suspension viscosity η , as well as shear yield stress τ y. For a given suspension, Δ ρ , d and η are constants, and τ y can be directly measured through rheological methods. When calculated settling velocity of particles approaches infinitely small values, the suspensions can be considered stable. The expression derived in this work had been verified by the experimental data. In addition, correlation between the results from improved settlement height method and the calculated settling velocity was established. To further investigate the impact of additives on suspensions stability, the Kelvin-Voigt rheological model was employed to characterize viscoelastic properties during oscillation, and a coefficient K (K= τ y − G ' γ c τ y) was proposed to quantitatively determine the contribution of the "dashpot" component in influencing the yield stress τ y. The regulation strategy for additives in suspensions was established based on experiments: a K value exceeding 0.274 indicates excessive additives concentration and necessitates reduction, whereas a K value below 0.274 suggests an insufficient additives concentration and requires additional dosage. In summary, the above model is helpful to predict the stability of ceramic suspensions. [ABSTRACT FROM AUTHOR]

[Objective] The classification of sediment particles and the accompanying distribution characteristics of carbon, nitrogen and salt in the process of soil thawing layer by layer under snowmelt runoff scenario were analyzed in order to identify the mechanism of soil freeze-thaw erosion and the induced micro-environmental effects on eroding slopes. [Methods] Soil samples were obtained from an eroding slope in the mollisol region of Northeastern China. Air-dried soil was used to fill columns that were subjected to three treatments: non-freeze-thaw, full freeze-full thaw, and gradual progressive thawing after freezing. The soil columns were completely immersed in a water bath so that thawing occurred from outside to inside. All soil samples were then fractionated by settling velocity, and the electrical conductivity (EC), pH value, soil organic carbon (SOC), and total nitrogen (TN) of each particle size were determined and analyzed. [Results] ① The freeze-thaw process reduced the proportion of the soil particles >500 μm and ≤125 μm, but increased the proportion of soil particles between 125 μm and 500 μm. Larger particles had higher EC, but lower SOC and TN. ② Across gradual progressively thawed layers, the outer layer (thawed earlier) had fewer particles ≤63 μm, and the inner layer (thawed later) had more particles between 125 μm and 500 μm. More specifically, EC, SOC, and TN were higher in the larger fractions from the outer layer. ③ Compared with the original soil, 64.8% of the dissolved solids were lost from the soil that experienced gradual progressive thawing, but the loss rate of SOC and TN was only 4.08% and 2.72%, respectively. The loss of dissolved solids and organic matter was greater from the inner layer than from the outer layer. [Conclusion] After freezing and thawing, the degree of fragmentation of the outer layer of soil was large, and the soil particles on the slope tended to become homogenized. Organic matter content varied significantly between particle size classes, and its distribution was more stable in small-grained soils. Salts and organic matter migrated from the inner layer of the soil to the outer layer during the freeze-thaw process, resulting in loss.

In the ballasted flocculation, high-speed sedimentation of suspensions is achieved using a microsand as a ballast material and a polymer flocculant combined with microflocs made of polyaluminum chloride (PAC) as an inorganic coagulant. In this study, three turbid water samples containing kaolin clay (kaolin concentration: 20, 200, and 500 mg/L) were treated by coagulation–sedimentation and ballasted flocculation. The effects of pH and PAC dosage, which are the controlling parameters for coagulation, and the microsand (silica sand) and polymer dosages, which are the controlling parameters for ballasted treatment, on the treatment efficiency and floc settling velocity were examined. The floc settling velocity under the optimum conditions was 17 times higher than that of the conventional coagulation–sedimentation process using PAC. The turbidity was 0.54 turbidity unit (TU) (TU as the kaolin standard), and its removal efficiency was 99.7%. Furthermore, turbid water samples with different kaolin concentrations (20 and 500 mg/L) were treated via the ballasted flocculation. In this study, fundamental information on the optimization of each dosage condition of coagulant, ballast, and polymer and pH condition in ballasted flocculation was obtained, and the removal mechanisms under optimal, underoptimistic and overoptimistic conditions were proposed. HIGHLIGHTS Conditions for ultrahigh-speed ballast flocculation were investigated.; Floc settling velocity increased and showed a peak at 10 g/L of microsand.; Excess addition of microsand significantly reduced the floc settling velocity.; Hugh floc settling velocity was achieved in the treatment of high-turbidity water.;

The flocculation of cohesive sediment particles is a function of the collision efficiency of sediment particles, which is mainly influenced by local flow hydrodynamics. A detailed study on local hydrodynamic characteristics in a novel stirred tank was done to measure the flow field of a turbulent flow. Instantaneous flow velocity fields were obtained and processed, and the average flow field was computed. Particle image velocimetry (PIV) results measuring the hydrodynamic characteristics (expressed as turbulent kinetic energy (TKE), local dissipation rate of TKE, velocity gradient or shear rate, turbulent shear stress, etc.) were analyzed and discussed. Particle tracking and automated image processing techniques were utilized to analyze the impact of the hydrodynamic conditions on the floc and settling properties. The differences in floc properties under the two turbulent shear states (i.e., steady-state (SS) and unsteady-state (US)) hydrodynamic conditions were examined. The results show that floc size and floc size distribution (FSD) of pure kaolin clay flocs are significantly influenced by the local dissipation rate of TKE and the turbulent intensity states. The floc size, d f, 84 , at local dissipation rate of TKE of 11 × 10−4, 29 × 10−4, 44 × 10−4, 83 × 10−4, and 142 × 10−4 m2/s3 is 97, 108, 107, 124, and 150 μm, respectively. It was found that by increasing the local dissipation rate of TKE, the FSD was skewed left. The US shear condition generated larger flocs (and in higher proportions) relative to the SS condition. The settling velocity and flux settling velocities of flocs formed under SS conditions are higher than those formed under US conditions. The fractal dimension of SS flocs also is higher than the fractal dimension of US flocs. These results highlight a significant impact of the states of hydrodynamics on floc properties such as floc size and FSD as well as the settling and morphological properties of flocs. [ABSTRACT FROM AUTHOR]

In fluvial sediment transport, the sediment threshold parameter Movability Number, which is the ratio of the shear velocity and the settling velocity of a sediment particle, is seen as a potential replacement for the traditional Shields parameter. Until now, the studies carried out on Movability Number have been mostly empirical or crudely analytical. In the current study, a mathematical modeling approach is attempted. Steady unidirectional flow is considered and the mode of entrainment is taken as that of rolling, with a compact sediment bed. The mathematical relationships developed here express the Movability Number as a function of either shear Reynolds number or dimensionless grain diameter. Comparisons are made with both experimental data and previous empirical formulae. The developed model is a novel approach to study the Movability Number, which bears satisfactory nearness to the previous studies. The deviation produced in terms of underestimation is due to the rolling mode of motion, which requires the least disturbing energy. The developed model can be improved by the consideration of turbulence in future studies. [ABSTRACT FROM AUTHOR]

Floating treatment islands (FTIs) offer effective solutions for stormwater management, providing flood attenuation and pollutant removal capabilities. However, there remains a knowledge gap concerning their performance, specifically in terms of pollutant removal and sediment deposition. To address this gap, the present study employs computational fluid dynamics (CFD) modeling to investigate the intricate interactions within FTI systems. Various FTI configurations are analyzed, considering mass removal through FTIs and sediment deposition, the first time where these two processes were considered together in a CFD environment. The findings demonstrate that FTIs have a significant influence on flow patterns and mass removal. Notably, FTIs enhance mass removal compared to the control case, with larger sediment particles exhibiting higher removal rates. The correlation between the short-circuit index and sedimentation in FTI ponds highlights the potential of FTIs as indicators of treatment efficiency. Furthermore, the study focuses on mass removal exclusively through the FTI root zones. The positioning of FTIs within the pond has a considerable impact, resulting in differences of up to 20% in mass removal. Moreover, the FTI configuration exerts a more pronounced influence on mass removal through FTIs than through sediment deposition alone. In cases where both processes occur simultaneously, the presence of FTIs lead to higher mass removal, primarily attributed to the FTIs themselves, particularly in the initial segment. Remarkably, certain FTI configurations enable mass removal exceeding 70% for large sediment particles, even with a pond length less than half of the original. [ABSTRACT FROM AUTHOR]

During the drilling process, cuttings settle under the action of gravity, which easily results in the formation of a cuttings bed, which then results in wellbore cleaning problems. The settling law of cuttings in drilling fluid is essentially a problem of solid–liquid two-phase settling. This study analyzes and summarizes the effects of the wall effect, the rheology of the fluid, particle shape irregularity, and particle concentration on the settling rate of particles and clarifies the problems faced by current research on the settling rate of particles and the development direction. Studies have shown that walls exert additional blocking effects on particles, thus reducing their settling velocity. The shear thinning effect of non-Newtonian fluids such as power-law fluids and Herschel–Bulkley fluids will reduce the viscosity of the liquid, thus increasing the settling velocity of the particles. Compared with spherical particles, irregular particles will obtain higher resistance in the fluid, leading to a decline in the particle settling velocity. The mutual interference between particles will result in an increase in the drag force on the particles and a decline in the settling velocity. However, when the particles are aggregated, the settling velocity will increase. This study can provide theoretical guidance for predicting the migration law of cuttings during the drilling of horizontal wells, and it has important significance for enriching the theory of solid–liquid two-phase flow. [ABSTRACT FROM AUTHOR]

Particle transport and deposition in turbidity currents is governed by the balance between turbulent suspension and gravitational settling, with settling velocity becoming dominant during the final rain‐out phases of decelerated turbidity currents on lobes. Differential particle settling velocities play a role in the sorting of grains in turbidity currents; there is a preference of grains with higher settling velocities to be deposited first, yielding a settling‐velocity gradient in vertical and longitudinal cross‐sections through turbidite beds. If sediments contain little variation in particle shape and density (for example, siliciclastics), then settling velocity is dominantly controlled by grain size. Carbonate sediments, in contrast, are composed of non‐skeletal and skeletal grains with various growth structures, producing a wide distribution of particle shapes (from spheroidal to platy, bladed and elongated forms). The present paper aims to constrain the extent to which shape‐dependent differential settling velocities influence sorting mechanisms in carbonate turbidity currents. Experiments using natural skeletal sand were conducted to investigate the settling of carbonate grains in: (i) isolation; (ii) suspension clouds; and (iii) turbidity currents. Size, density and shape parameters, including Corey Shape Factor and Zingg diagrams, were analysed using high‐resolution micro‐computed tomography. The slower settling of non‐spheroidal shapes was quantified. In the sinking suspensions, a sorting mechanism operated through differential velocities yielding an abundance of spheroidal grains at the base and enrichment in less‐spheroidal grains towards the top of suspension deposits. This trend was also observed longitudinally in carbonate turbidity currents, for which enhanced advection lengths caused less spheroidal grains to be transported farther into the basin. The effect of particle shape becomes increasingly significant as grain size increases, in particular above medium sand. Carbonate turbidites may therefore be more poorly sorted than siliciclastic turbidites, which is expected to result in lower primary porosity in calciturbidites compared to siliciclastic turbidites. [ABSTRACT FROM AUTHOR]

Background: Particle size distribution (PSD) is a fundamental soil measurement that is crucial for agriculture, engineering, hydrological, and environmental applications as well as in basic research such as in developing water release curves in flow and transport modeling. The accurate determination of PSD, particularly clay content, is especially critical in ascertaining the magnitude and rates of many physical, chemical, and hydrological processes in soils. The accuracy of the hydrometer method for PSD, which relies on the settling velocity of soil particles in a soil suspension, could be affected by the density of the suspension, which in turn, depends on the initial sample mass, texture, and mineralogy of the soil. Aims: We hypothesized that (1) initial mass determines the concentration and the physical interaction of particles in a soil suspension and affects particle settlement, recovery, and the accuracy of the hydrometer method, and (2) the widely used initial air‐dry mass of 50 g underestimates the clay percentage of medium to heavy textured tropical soils. The objective of this study was to investigate the effect of mass and KCl on clay recovery in tropical soils with varying texture and mineralogy using the hydrometer method. Methods: The experiment comprised seven soils, four soil masses (10, 20, 30, 50 g), and two KCl treatments in a 7 × 4 × 2 factorial design replicated three times. Results: Results showed a general trend of increasing estimates of clay % as the soil mass decreased from 50 to 10 g and the KCl concentration increased from 0 to 0.0025 M. This implies that using an initial sample mass of 50 g in sedimentation methods, underestimates, and 10 g overestimates the clay % in predominantly medium to heavy textured tropical soils. Interestingly, there was a drastic change in texture for most of the soils as the sample mass decreased to 10 g. Conclusions: We conclude that the initial air‐dry mass affects the clay recovery of medium to heavy textured humid tropical soils. Results suggest that the ideal initial mass for these soils lies between 20 and 30 g. Furthermore, the mechanistic pathway that drives the observed decrease in clay recovery as soil sample mass increase could be due to the flocculating tendency of KCl. [ABSTRACT FROM AUTHOR]

The gravitational settling of a flexible, permeable circular and planktonic particle drenched in a fluid which is assumed to be Newtonian and incompressible along with being viscous was studied. A mathematical formulation and numerical simulations of the studied problem were done by applying the Immersed Boundary Method (IBM) in a two-dimensional fluid domain. Parametric studies were done for analyzing the impact of varying flexibilities and permeabilities with reference to settling velocity (terminal velocity) and shape deformation of the particle. The terminal velocity and permeability of the particle are directly proportional. It was observed that for fixed permeability, the terminal velocity increases when increasing the flexibility of the particle. [ABSTRACT FROM AUTHOR]

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Flocculent settling widely exists in various processes of tailings disposal.It bears significance for the accurate calculation of the flocculent settling velocity in engineering, such as tailings backfilling and surface disposal.This paper studied the structural characteristics of tailings flocs from the perspective of the fractal theory, and established the mathematical relationship between tailings particle size, geometry size of floc and fractal dimension.It analyzed the influence of buoyancy effect, reflux effect and viscosity effect on floc settling, and deduced a calculation formula of tailings flocculent settling velocity.This study carried out a tailings flocculent settling test observed the changes in geometric morphology of flocs by focused beam reflectance measurement technology(FBRM), and carried out validation analysis between testing data and model calculation value.The results showed that the settling velocity increased with the equivalent grain size of flocs, which could be divided into three stages, namely accelerated settling, uniform settling and compaction settling.The equivalent grain size of flocs of test tailings were 140~350 μm, and the settling velocity calculated by the formula were 1.3~2.0 mm/s when the fractal dimension was 2.25, which demonstrates significant correlation with the testing value, and had certain practical application value.

Following the final biological treatment, the oil wastewater is intended for reuse in factory floor cleaning. However, the presence of varying concentrations of oil-in-iron characteristic wastewater has led to a sudden surge in sludge SV to 90%, adversely affecting water treatment efficiency. In this study, we conducted an analysis of microbial community structure and selected pepA and 16S rRNA primers to assess the proportions of zoogloea and total bacteria in sludge bulking. Iron concentration plays a pivotal role, and it should be maintained at or 0.6 mgL−1. By selective discharging of sludge to maintain 1,700 mgL−1, we minimized iron enrichment, thereby enhancing the sludge settling performance. Maintaining dissolved oxygen (DO) at 3.5 mgL−1 supports the aerobic sludge's ability to replenish iron in its system, while the oil content should be controlled at 145.33 mgL−1 to reduce the release of iron into the water. The order of significance is as follows: sludge concentration > Fe amount > DO > oil content. Implementing this approach was applied in the field for 1 week and effectively reduced the SV from 90% to approximately 43%. The interaction between quorum sensing molecules related to sludge bulking and iron, leading to the formation of complexes, underscores the significance of controlling iron levels. This study offers a valuable case for practical application of quorum quenching technology in oil wastewater, presenting a rapid, efficient, and cost-effective solution to address the issue of sludge bulking.

The object of research is the process of dewatering oil emulsions by using a hydrocyclone with forced flow rotation taking into account rheological properties. The problem solved in the work is related to production, primary preparation and transportation of oils. The process of oil extraction is accompanied by saturation of the product with water, salts, mechanical particles and light fractions, which requires primary preparation of oil through multi-stage, sometimes long-term, low-productivity processing in order to separate the above-mentioned components. The water content of some deposits, especially marine deposits, is 80%, which makes the process of oil dehydration particularly important for preparing oil for transportation. Among the known methods of dewatering oil emulsions, such as settling, heat treatment, chemical treatment, electrodehydration and centrifugation, the last one allows to significantly influence the separation processes. The essence of the centrifugation process, consists in increasing the rotational speed of the particles of the dispersed phase by replacing the natural force of gravity with a more powerful centrifugal force. The density of water and mechanical impurities is higher than the density of oil, and particles under the action of centrifugal force are pressed against the wall and, coagulating, are removed through the flow separator. In the course of the work, the main regularities of the process were determinedcentrifugation, namely the rate of sedimentation of the water fraction from the rheological parameters of the emulsion and the kinematic characteristics of the hydrocyclone with forced rotation of the flow. It was established that the dependence of the volume of the water fraction of the oil emulsion is a power function of the second order, and the rate is linear. The settling of a water particle has a linear dependence on the size of the particle. Speed The set speed of settling of water particles of an oil emulsion allows you to calculate the length of the turbine depending on the required performance, speed of rotation and rheological properties. The developed theoretical provisions of the process of dewatering oil emulsions by using a hydrocyclone with forced rotation of the flow, taking into account the rheological properties, allow designing machines of this type for various conditions of oil production.

Clay-rich flocculated suspended sediments are an important constituent of estuarine and coastal systems globally. They are responsible for the host, movement and deposition of a variety of pollutants, contaminants and sediment itself. Accurate modelling of the movement of these sediments is crucial for a number of industries including fisheries, aquaculture, shipping and waste management. This requires an accurate and reliable measurements of the physical properties of flocs and their behaviour. Porosity is a key element in floc structures, and this research provides updated 3D quantified porosity and pore space morphological data in relation to influences on floc settling behaviour. We report the questionable relationship between floc size and settling velocity, and explore alternative influences such as floc composition, porosity and pore morphology. These outcomes suggest that a shift in focus from floc size to a combination of factors is necessitated to understand the complex movement behaviour of flocculated suspended sediments.

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In this communication, the solution of the differential Riccati equation is shown to provide a closed analytical expression for the transient settling velocity of arbitrary non-spherical particles in a still, unbounded viscous fluid. Such a solution is verified against the numerical results of the integrated differential equation, establishing its accuracy, and validated against previous experimental, theoretical and numerical studies, illustrating the effect of particle sphericity. The developed closed analytical formulae are simple and applicable to general initial velocity conditions in the Stokes, transitional and Newtonian regimes, extending the range of application of former published analytical approximate solutions on this subject. [ABSTRACT FROM AUTHOR]

Particle heterogeneity is one of the key indicators to estimate the variability in the soil properties and compositions. This study aims to explore the effects of the soil particles settling and bedding on the greenhouse gas emissions from the depositional area. The layer-specific physicochemical properties were also considered during this time. Specifically, one type of Mollisol (local people named as the black soil) was sampled from a typical eroding slope in the northeastern China. Then six classes were fractionated by their respective settling velocities. Six structures were obtained to bed the differently-sized soil particles in sequence: S1 was the thinnest structure with only > 500 μm particles L1, whereas S6 was the thickest structure with the six particle classes being layered in sequence from the coarsest particles L1 at the bottom to the finest particles L6 on top. The emissions of greenhouse gases CO2, N2O and CH4 were finally collected from the incubated structures on a daily basebasis. The results showed that: 1) The coarse particles settled first (L1) on the bottom, whereas, the fine particles settled the last and then covered on the top (L6). The porosity gradually decreased from 23.79% of coarse layer L1 to 1.0% of fine layer L6. By contrast, the soil water content increased generally at the highest moisture content of 68.78%, as the soil particles were settled with the L5. 2) Carbon and nitrogen were rich in the L2-L4 layer, where the soil organic carbon and total nitrogen were peaked in the L2 layer (with 27.34 and 2.35 g/kg, respectively), and the maximum dissolved organic carbon and nitrogen appeared in the L3 and L4 layer (with 519.31, and 19.69 mg/kg, respectively). 3) The average greenhouse gas emission rates decreased significantly during the seven incubation days, as the sedimentary layers were thicker (P<0.05). Correspondingly, there was no increase in the gas flux with the thickening of the sedimentary soil layer. The layer-by-layer deposition process was separated from the coarse and fine particles, where the coarse particles were preferentially deposited as the lower layers, while the fine ones were stacked over forming upper layers. Consequently, there was a gradual decrease trend of the porosity and relative diffusion coefficient of gas from the bottom to the top. As such, it is expected to effectively inhibit the transfer of greenhouse gases via the depositional profile. Overall, the layer-by-layer settling and bedding can be used to reconstruct the deposition process in the field, and then to effectively capture the potential impacts of depositional layer structure on greenhouse gas emissions. The finding can overcome the limitations of traditional sampling, indicating the outstanding variations of small-scale layers and bedding. The settling and bedding patterns can also be characterized to quantify the greenhouse gas emissions from different depositional settings. [ABSTRACT FROM AUTHOR]

Knowledge of the hydrodynamic behavior of carbonate bioclasts is essential for solving coastal morphodynamic problems in marine carbonate depositional environments. Marine carbonate grains are produced within the sedimentary system itself and are deformed by subsequent hydrodynamics, resulting in particle densities, sizes and shapes that are distinct from those of terrigenous sediments. In this study, we investigated the shapes and settling characteristics of gravel‐size natural coral debris collected from the coasts of Okinawa Prefecture, Japan. Based on the shape parameters and settling velocities obtained using image analysis techniques and settling tube experiments, respectively, a correlation model for predicting the settling velocity of coral gravel particles was developed by extending the previous formula of Dietrich (1982, https://doi.org/10.1029/wr018i006p01615) over particle Reynolds number values ranging from 384.23 to 4439.76. The model determines the settling velocity as a function of particle nominal diameter, form, roundness, and surface texture parameters that were selected after examining several other shape descriptors. Compared with other models, the proposed model showed better settling velocity predictive skills for coral gravel particles classified into four shape types. The proposed model also determines how the drag coefficient of coral gravel particles should be modified from that for spherical particles, by accounting for the abovementioned coral gravel particle shape parameters. The obtained data set of settling velocity and modification of the drag coefficient can be used for quantitative interpretation of suspension, transport, and sedimentation processes in marine carbonate depositional environments. Plain Language Summary: Coral coasts, formed by the accumulation of carbonate bioclasts, are suffering severe erosion and inundation threats due to global climate change. Understanding how these loose materials on top of coral reef platforms move under complex hydrodynamics is essential for morphodynamic predictions and developing coastal protection measures. As highly heterogeneous sediment particles, coral fragments exhibit properties distinct from those of terrestrial source sediments in terms of size, shape and density. In this work, we focused on coral debris samples collected at Okinawa Prefecture, Japan, to clarify their settling characteristics. A better prediction of the settling velocity of coral gravel particles was achieved by considering as many parameters as possible, including particle size, density, form, roundness and surface texture effects. Moreover, the drag coefficient equation for coral gravel particles was modified from that for spherical particles by accounting for particle form, roundness and surface texture effects. These findings are essential for the successful quantitative interpretation of suspension, transport, and sedimentation processes in coral reef systems. Key Points: The variabilities in the skeletal porosity, density, and shape of coral debris were found to be distinct from those of siliciclastic sedimentsThe settling velocity of coral gravels can be better predicted by accounting for the effects of particle form, roundness and surface textureWe provide a way to define the drag coefficient of coral gravels by incorporating particle shape effects into that of a sphere [ABSTRACT FROM AUTHOR]

In petroleum engineering, accurately predicting particle settling velocity during various stages of a well’s life cycle is vital. This study focuses on settling velocities of both spherical and non-spherical particles in Newtonian and non-Newtonian fluids. Utilizing a dataset of 931 experimental observations, an artificial neural network (ANN) model with a 7-42-1 architecture is developed (one input layer, one hidden layer with 42 neurons, and one output layer). This model effectively incorporates particle settling orientation and the inclusion of the settling area ratio, enhancing its predictive accuracy. Achieving an average absolute relative error (AARE) of 8.51%, the ANN model surpasses traditional empirical correlations for settling velocities in both Newtonian and power-law fluids. Key influencing factors, such as the consistency index and particle equivalent diameter, were identified. This approach in ANN model construction and data analysis represents a significant advancement in understanding particle dynamics.

Pollen from a naturally occurring population of the forest grass species Diarrhena obovata was successfully captured in a series of pollen traps to understand the timing of anthesis and the dispersal mechanics of wind pollination in an example of the flowering plant family Poaceae. Scanning electron microscopy was used to identify the pollen surface ornamentation as microechinate-areolate. The spherical grains have a diameter of 38.74 μm. The settling velocity calculated by Stoke’s Law was 4.48 cm s-1, but physical measurement by drop tower experiments resulted in 3.77 ± 0.15 cm s-1 (sd). The surface ornamentation observed in D. obovata pollen is not expected to alter drag forces considerably but the reduction of settling velocity may be a result of species-specific pollen grain density. In forest grasses an improvement in settling velocity may be adaptive in overcoming dispersal constraints in an environment where trees obstruct wind speeds and create more turbulence.

Transport of estuarine sediment have a highly complex method, which is the combined effects result of periodically reciprocating flow, ocean waves, and the electrochemical characteristic of sea water [1]. Settling velocity (SV) is such a parameter fundamental for sediment researchers so that its accurate resolution has been regarded as a top priority in correcting modelling numerical and conceptual understanding of fine sediment dynamics [2] [3]. The goal of this study is to analyze the effect of salinity levels on the settling velocity of fine sediment grains in the Ciliwung estuary, Jakarta. The method used is direct measurement using the hydrometer analysis method. The result of experiment shows salinity levels affect the settling velocity of fine sediment grains in the Ciliwung estuary. The higher salinity, more faster the settling velocity of fine sediment grains. The average settling velocity at distilled water salinity 0 ppt is 1.083 mm/minute, sea water with salinity 0.3 ppt is 1.537 mm/minute, and sea water with salinity of 0.6 ppt of 1.561 mm/minute.

Ionic surfactants are easily adsorbed by silt and clay particles, thus affecting the flocculation characteristics and settling behavior. The settling velocity, typical size, Zeta potential and surface tension of silt flocs were measured in the presence of two different kinds of ionic surfactants. The results indicated that the cetyltrimethylammonium bromide (CTAB, a typical cationic surfactant) can dramatically accelerate the settling of slit particles, while the linear alkylbenzene sulfonate (LAS, a typical anionic surfactant) slightly retarded silt sedimentation to some extent. In still water, the representative settling velocity dramatically increased from 0.36 cm s−1 to 0.43 cm s−1 with the increase of CTAB concentration, which increased by more than 20%. Oppositely, the sedimentation rate decreased from 0.36 cm s−1 to 0.33 cm s−1 with the increase of LAS concentration. In flowing water, as the flow rate increased from 0 to 20 cm s−1 and the ionic surfactant concentration increased from 0 to 10 mg L−1, the sedimentation rate decreased to 57% and 89% in the presence of CTAB and LAS respectively, which was due to an enhanced dispersion of silt particles and a breaking of flocs. The SEM image test shows that the floc particle size increased 1.5 times of the primary particle size under the high CTAB concentration. The flocculation induced by ionic surfactants greatly influences the sediment size as well as the law of settling velocity. The intrinsic influence mechanism was also discussed based on the variations of silt particle properties. This systematic study can be used for further development of flocculation models and particle size distribution of fine-grained soil.

Microplastics (MPs) are found to be omnipresent in marine environments and their production and disposal are constantly increasing. In order to control and mitigate their negative effects on the environment, it is important to understand the processes involved in their transport and sinking. Most of the conducted experimental studies on MP in water have focused on exploring the settling behavior of MP particles under static flow conditions. This paper presents the results of an experimental study of MP particles in a horizontal stream of water. A series of laboratory experiments were carried out to measure the drag coefficient of quasi-radially-symmetric MP particles with different shapes (spheres, cubes, and crosses) and sizes (1.5 to 3.0 mm). In the study, the relationship between the drag coefficient and flow conditions represented by the local Reynolds number is investigated. The experimental procedure was validated, and a total of 400 measurements were performed. Values of the measured drag coefficient ranged from 0.8 to 2.5 for the values of Re from 40 to 300. The results show that the shape of MP particles in the water stream considerably influences the particle drag coefficient, with a rather complex relationship between the drag coefficient and flow conditions. [ABSTRACT FROM AUTHOR]

This study presents morphological data and estimates of the settling velocity and drag coefficient of sea stars (Asterias rubens) caught in the Limfjord, Denmark. A geometric model describing the sea star is presented and the thickness and arm width are determined as linear functions of arm length. The volume and mass of the sea stars is well predicted by the geometric model and is in agreement with the experimental measurements. The mean sea star density is determined to be 1095 kg/m3, the mean drag coefficient is estimated to be 2.3 and the settling velocity is shown to vary with the square root of the its size. [ABSTRACT FROM AUTHOR]

In environmental flows, field and laboratory measurements of suspended sediments show two kinds of concentration profiles. For coarse sediments, a near-bed upward convex profile is observed beneath the main upward concave profile. In this study, we consider two 1-DV models, namely, the classical advection–diffusion equation (ADE) based on the gradient diffusion model, and the kinetic model. Both need sediment diffusivity, which is related to the eddy viscosity, and an y-dependent β-function (i.e., the inverse of the turbulent Schmidt number). Our study shows that the kinetic model reverts to the classical ADE with an "apparent" settling velocity or sediment diffusivity. For the numerical resolution of the ADE, simple and accurate tools are provided for both the sediment diffusivity and hindered settling. The results for the concentration profiles show good agreement with the experimental data. An interpretation of the concentration profiles is provided by two "criteria" for shapes. The main for steady open-channel flows shows that the shape of the concentration profiles in the Cartesian coordinate depends on the vertical distribution of the derivative of R (the ratio between the sediment diffusivity and the settling velocity of the sediments): dR/dy > −1 for the upward concave concentration profile while dR/dy < −1 for the near-bed upward convex profile. A generalization is proposed for oscillatory flows over sand ripples, where the time-averaged concentration profiles in the semi-log plots are interpreted by a relation between the second derivative of the logarithm of the concentration and the derivative of the product between the sediment diffusivity and an additional parameter related to the convective sediment entrainment process. [ABSTRACT FROM AUTHOR]

Microplastics (MPs) have become pervasive in marine ecosystems, potentially causing environmental degradation, impacting ecological function, and posing a serious public health risk. Despite the widespread distribution of MPs, their vertical transport within a water column has limited understanding, representing a key knowledge gap in the development of water quality models to minimize these risks. In this study, 6152 individual particles of six common types of MPs were observed through water column experiments to examine a range of drivers of the vertical velocity of MPs, including particle density and size, biofilm growth, water temperature, and salinity. The experimental results revealed that the vertical velocity of MPs obeyed Stokes' law under laminar conditions; increasing salinity decreased the settling tendency of the particles. Moreover, biofilm attachment induced notable alterations in particle characteristics within 60 days, resulting in slower settling velocities (up to a 21.9% change for non-buoyant MPs) and even a reversed vertical direction (up to several times for buoyant particles). Furthermore, a lattice Boltzmann model could predict the vertical velocity of MPs with reasonable accuracy, especially for small particles. This work facilitates the development of sophisticated models/formulas that integrate particle morphology, hydrodynamics, and biological factors to enhance the understanding of MP transport through the river-to-coastal continuum. [Display omitted] • The settling and rising of different microplastics (MPs) were investigated. • Biofilm attachment altered the movement directions of certain non-buoyant MPs. • The shape factor is critical to exist empirical equations for settling velocity. • The lattice Boltzmann model can reasonably predict the terminal velocities of MPs. [ABSTRACT FROM AUTHOR]