Entrainment Model Research Articles

A study of a flowslide with significant entrainment in loess areas in China

AbstractFlowslides are a frequent type of natural disaster in loess areas and may result in the significant loss of properties and/or casualties. The Dagou flowslide is a typical event in a loess area and is accompanied by significant sediment entrainment. To analyze the mechanisms responsible for flowslides and to obtain the parameters for a runout analysis, a field investigation was conducted. Specimens were sampled on site to carry out laboratory tests, including a triaxial test, sieve analysis, and chemical component analysis. The parameters were used in the runout study employing an energy‐based runout model. An analytical entrainment model was adopted to calculate the entrainment after considering physical properties and the mechanism of the entrainment process of the loess. Finally, the entrainment model was incorporated into the runout model to simulate the post‐failure process of this case. Energy dissipation due to the deformation of slices was considered as it was thought to be important for a slide with a significant deformation. The simulation results were compared with the measurements, including runout distance, total volume, erosion depth, deposition height at different sections, and velocities at specific locations. The results indicate that the energy‐based runout model, together with the entrainment model, can capture the kinematic characteristics of the Dagou flowslide. Therefore, it is feasible to use this model to predict the runout characteristics of flowslides in similar areas. Copyright © 2017 John Wiley & Sons, Ltd.

Debris-flow modeling at Meretschibach and Bondasca catchments, Switzerland: sensitivity testing of field-data-based entrainment model

Abstract. Debris-flow volumes can increase due to the incorporation of sediment into the flow as a consequence of channel-bed erosion along the flow path. This study describes a sensitivity analysis of the recently introduced RAMMS (Rapid Mass Movements) debris-flow entrainment model, which is intended to help solve problems related to predicting the runout of debris flows. The entrainment algorithm predicts the depth and rate of erosion as a function of basal shear stress based on an analysis of erosion measurements at the Illgraben catchment, Switzerland (Frank et al., 2015). Starting with a landslide-type initiation in the RAMMS model, the volume of entrained sediment was calculated for recent well-documented debris-flow events at the Bondasca and the Meretschibach catchments, Switzerland. The sensitivity to the initial landslide volume was investigated by systematically varying the initial landslide volume and comparing the resulting debris-flow volume with estimates from the field sites. In both cases, the friction coefficients in the RAMMS runout model were calibrated using the model, whereby the entrainment module was (1) inactivated to find plausible values for general flow properties by adjusting both coefficients (ξ and μ) and then (2) activated to further refine coefficient μ, which controls erosion (patterns). The results indicate that the model predicts plausible erosion volumes in comparison with field data. By including bulking due to entrainment in runout models, more realistic runout patterns are predicted in comparison to starting the model with the entire debris-flow volume (initial landslide plus entrained sediment). In particular, lateral bank overflow – not observed during these events – is prevented when using the sediment entrainment model, even in very steep (≈ 60–65 %) and narrow (4–6 m) torrent channels. Predicted sediment entrainment volumes are sensitive to the initial landslide volume, suggesting that the model may be useful for both reconstruction of historical events and the modeling of scenarios as part of a hazard analysis.

Inclined gravity currents filling basins: the impact of peeling detrainment on transport and vertical structure

Transport of dense fluid by an inclined gravity current can control the vertical density structure of the receiving basin in many natural and industrial settings. A case familiar to many is a lake fed by river water that is dense relative to the lake water. In laboratory experiments, we pulsed dye into the basin inflow to visualise the transport pathway of the inflow fluid through the basin. We also measured the evolving density profile as the basin filled. The experiments confirmed previous observations that when the turbulent gravity current travelled through ambient fluid of uniform density, only entrainment into the dense current occurred. When the gravity current travelled through the stratified part of the ambient fluid, however, the outer layers of the gravity current outflowed from the current by a peeling detrainment mechanism and moved directly into the ambient fluid over a large range of depths. The prevailing model of a filling box flow assumes that a persistently entraining gravity current entrains fluid from the basin as the current descends to the deepest point in the basin. This model, however, is inconsistent with the transport pathway observed in visualisations and poorly matches the stratifications measured in basin experiments. The main contribution of the present work is to extend the prevailing filling box model by incorporating the observed peeling detrainment. The analytical expressions given by the peeling detrainment model match the experimental observations of the density profiles more closely than the persistently entraining model. Incorporating peeling detrainment into multiprocess models of geophysical systems, such as lakes, will lead to models that better describe inflow behaviour.

Mathematical Modeling of Liquid Slag Layer Fluctuation and Slag Droplets Entrainment in a Continuous Casting Mold Based on VOF-LES Method

Abstract The slag behaviors, directly relating with the qualities of the final cast products, are influenced by the transient surface flow of liquid steel in a continuous casting mold. A one-half scale model is used to investigate the slag behaviors and their droplets entrainment. The model based on Volume of Fluid (VOF) multiphase coupled with Large Eddy Simulation (LES) is established to further illuminate the phenomena of the liquid oil layer fluctuation, the slag “eye” regions, and the slag entrainment observed in water experiment. The effects of casting speeds on the slag behaviors and their entrained droplets are investigated. The results show that the fluctuation of the oil layer is influenced by the transient flow. The calculations for the oil layer profile, the accumulation, and protrusions of oil layer are consistent with the water experiment. The asymmetry of the slag “eye” regions is also influenced by the asymmetry of free surface and transient turbulent flow. The “eye” regions near the narrow wall show distinct asymmetric change at different casting speeds. At a lower casting speed, the slag “eye” regions change irregularly and display the alternate process of open and collapse at the two sides of the narrow walls of the model. While at a relative higher casting speed, the slag layer gathers toward the nozzle, and the slag “eye” regions gradually grow and always open. The simulation model can reveal that the mechanism of the slag entrainment includes two main modes: the cutting or dragging mode and shear layer instability. The average diameter and amount of the entrained droplets are calculated through the UDF codes of ANSYS FLUENT software, and the size distribution of the entrained droplets is also counted. When the casting speed is lower, the dominant diameters of the entrained droplets range between 2 and 3 mm. With casting speed increase, the distribution of the droplets becomes wider, and there is a gradually increase in the percentage of larger droplets with a size of 4–6 mm.

Contrasting aerosol refractive index and hygroscopicity in the inflow and outflow of deep convective storms: Analysis of airborne data from DC3

AbstractWe examine three case studies during the Deep Convective Clouds and Chemistry (DC3) field experiment when storm inflow and outflow air were sampled for aerosol subsaturated hygroscopicity and the real part of refractive index (n) with a Differential Aerosol Sizing and Hygroscopicity Probe (DASH‐SP) on the NASA DC‐8. Relative to inflow aerosol particles, outflow particles were more hygroscopic (by 0.03 based on the estimated κ parameter) in one of the three storms examined. Two of three “control” flights with no storm convection reveal higher κ values, albeit by only 0.02, at high altitude (> 8 km) versus < 4 km. Entrainment modeling shows that measured κ values in the outflow of the three storm flights are higher than predicted values (by 0.03–0.11) based on knowledge of κ values from the inflow and clear air adjacent to the storms. This suggests that other process(es) contributed to hygroscopicity enhancements such as secondary aerosol formation via aqueous‐phase chemistry. Values of n were higher in the outflow of two of the three storm flights, reaching as high as 1.54. More statistically significant differences were observed in control flights (no storms) where n decreased from 1.50–1.52 (< 4 km) to 1.49–1.50 (> 8 km). Chemical data show that enhanced hygroscopicity was coincident with lower organic mass fractions, higher sulfate mass fractions, and higher O:C ratios of organic aerosol. Refractive index did not correlate as well with available chemical data. Deep convection is shown to alter aerosol radiative properties, which has implications for aerosol effects on climate.

Modelling of air entrainment during pouring of metal castings

Air entrainment during mould filling is major source of oxide inclusions in metal castings. A model is developed to predict the location and rate of air entrainment as part of a standard mould filling simulation. The local air entrainment rate is calculated as a function of the turbulent kinetic energy and the magnitude of the normal velocity gradient of the liquid metal at the liquid–air interface. The model is validated through comparisons with experimental air entrainment measurements for a plunging water jet. It is then applied to study the effect of gating system design and pouring parameters on air entrainment in steel casting. Air entrainment is found to be reduced for a metal stream from the ladle that is centred above the pouring cup or the use of an offset step pouring basin, low head heights, high flow rates, a pressurised gating system and bottom ingates.

An algorithm for modeling entrainment and naturally and chemically dispersed oil droplet size distribution under surface breaking wave conditions

A surface oil entrainment model and droplet size model have been developed to estimate the flux of oil under surface breaking waves. Both equations are expressed in dimensionless Weber number (We) and Ohnesorge number (Oh, which explicitly accounts for the oil viscosity, density, and oil-water interfacial tension). Data from controlled lab studies, large-scale wave tank tests, and field observations have been used to calibrate the constants of the two independent equations. Predictions using the new algorithm compared well with the observed amount of oil removed from the surface and the sizes of the oil droplets entrained in the water column. Simulations with the new algorithm, implemented in a comprehensive spill model, show that entrainment rates increase more rapidly with wind speed than previously predicted based on the existing Delvigne and Sweeney's (1988) model, and a quasi-stable droplet size distribution (d<~50μm) is developed in the near surface water.

Characterization of liquid entrainment in a counter flowing gas using Phase Doppler Interferometry

An 8inch ID spray column was used to characterize the entrainment of water droplets into counter flowing air. The ability of Phase Doppler Interferometry (PDI) to measure the size and velocity distributions of entrained droplets resulting from a single full cone Bete® nozzle was proven, and the total volume of liquid entrained was gravimetrically quantified. The experimental setup consisted of a variable speed pump and air blower which allowed for droplet measurements over a range of gas and liquid rates. This work illustrates the effect of nozzle supply pressure and air rate on the entrainment rates and PDI measured droplet size distributions. The magnitude of the droplet size distribution, as well as the rate of entrainment, increased with the liquid spray rate, but the unimodal distribution peak diameter remained consistent. The same conclusion was true at an increased gas rate, in addition to an overall decrease in entrained droplet Sauter mean diameter and an increase in the total liquid entrained. The use of a theoretical entrainment model with PDI measured droplet diameters was explored. Applying the measured PDI diameters was found to significantly decrease the estimated entrainment from the theoretical entrainment based on a droplet buoyancy concept. This effect was further explored by comparing the sizing of a de-entrainment mesh pad for both cases.

Models development of liquid drops entrainment at a T-junction with a large vertical up branch

The liquid entrainment process at the vertical up tee branch is widespread in mass and heat transfer applications. Existing liquid entrainment models mainly apply to T-junctions with small diameter ratios of branch to main line (d/D), which are unable to predict the liquid entrainment under large d/D conditions. The models of liquid entrainment onset and entrainment rate are developed under reasonable assumptions. The entrainment onset model was developed based on the wave theory, force analysis and potential flow theory. The Bond number is innovatively introduced into the model to represent the effect of surface tension acting on the entrainment onset. The model is compared against the relevant experimental data which shows good agreement. In the modeling of the entrainment rate, the key parameters are obtained by nondimensionalizing the conservation equations governing the liquid entrainment process, and the constants in the model are determined by genetic algorithm. The model agrees well with existing experimental data.

Jets of SS 433 on scales of dozens of parsecs

The radio nebula W50 harbours the relativistic binary system SS433, which is a source of the powerful wind and jets. The origin of W50 is wrapped in the interplay of the wind, supernova remnant and jets. The evolution of the jets on the scales of the nebula is a Rosetta stone for its origin. To disentangle the roles of these components, we study physical conditions of the jets propagation inside W50, and determine deceleration of the jets. The morphology and parameters of the interior of W50 are analyzed using the available observations of the eastern X-ray lobe, which traces the jet. In order to estimate deceleration of this jet, we devised a simplistic model of the viscous interaction, via turbulence, of a jet with the ambient medium, which would fit mass entrainment from the ambient medium into the jets of the radio galaxy 3C31, the well studied case of continuously decelerating jets. X-ray observations suggest that the eastern jet persists through W50 as hollow one, and is recollimated to the opening $\sim 30^\circ$. From the thermal emission of the eastern X-ray lobe, we determine a pressure of $P \sim 3\cdot 10^{-11}$ erg/cm$^3$ inside W50. In the frame of a theory of the dynamics of radiative supernova remnants and stellar wind bubbles, this pressure in combination with other known parameters restricts W50's origin to a supernova happened $\sim 100\,000$ yr ago. Also, this pressure in our entrainment model gives a deceleration of the jet by $\sim 60\%$ in the bounds of W50's spherical component, of radius $\sim 40$ pc. In this case, the age of the jet should be $\ll 27\,000$ yr so as to satisfy the sphericity of W50. The entrainment model comes to the viscous stress in a jet of a form $\sigma = \alpha P$, where the viscosity parameter $\alpha$ is predefined by the model.

Generalization of droplet entrainment rate correlation for annular flow considering disturbance wave properties

A full knowledge of the interfacial disturbance wave effects on droplet entrainment is crucial for accurately predicting entrainment rate in annular flow. However, most entrainment models in literatures do not account for interfacial properties but only consider global flow parameters than precise wave characteristics. In view of this, based on the shearing-off mechanism of disturbance wave crest, a comprehensive model of droplet entrainment rate for annular flow has been established considering the characteristics of disturbance wave. Effects of hydraulic parameters on the instability of disturbance wave and their relationship with the droplet entrainment rate are presented. Results reveal that the gas and liquid flow rate, hydraulic diameter, surface tension and pressure have a great influence on the wave properties, i.e., critical wavelength, wave amplitude and wave velocity, and hence the droplet entrainment rate. Taking these influencing factors into account, a more accurate and reasonable formula for entrainment rate in annular flow is proposed. Comparison of the present correlation with the existing empirical correlations reveals that the new developed correlation can be correlated reasonably well with the experimental data within ±25% deviation for both air-water and steam-water annular flow.

Energy‐ and momentum‐conserving model of splash entrainment in sand and snow saltation

AbstractDespite being the main sediment entrainment mechanism in aeolian transport, granular splash is still poorly understood. We provide a deeper insight into the dynamics of sand and snow ejection with a stochastic model derived from the energy and momentum conservation laws. Our analysis highlights that the ejection regime of uniform sand is inherently different from that of heterogeneous sand. Moreover, we show that cohesive snow presents a mixed ejection regime, statistically controlled either by energy or momentum conservation depending on the impact velocity. The proposed formulation can provide a solid base for granular splash simulations in saltation models, leading to more reliable assessments of aeolian transport on Earth and Mars.

Neural mechanisms of rhythm-based temporal prediction: Delta phase-locking reflects temporal predictability but not rhythmic entrainment.

Predicting the timing of upcoming events enables efficient resource allocation and action preparation. Rhythmic streams, such as music, speech, and biological motion, constitute a pervasive source for temporal predictions. Widely accepted entrainment theories postulate that rhythm-based predictions are mediated by synchronizing low-frequency neural oscillations to the rhythm, as indicated by increased phase concentration (PC) of low-frequency neural activity for rhythmic compared to random streams. However, we show here that PC enhancement in scalp recordings is not specific to rhythms but is observed to the same extent in less periodic streams if they enable memory-based prediction. This is inconsistent with the predictions of a computational entrainment model of stronger PC for rhythmic streams. Anticipatory change in alpha activity and facilitation of electroencephalogram (EEG) manifestations of response selection are also comparable between rhythm- and memory-based predictions. However, rhythmic sequences uniquely result in obligatory depression of preparation-related premotor brain activity when an on-beat event is omitted, even when it is strategically beneficial to maintain preparation, leading to larger behavioral costs for violation of prediction. Thus, while our findings undermine the validity of PC as a sign of rhythmic entrainment, they constitute the first electrophysiological dissociation, to our knowledge, between mechanisms of rhythmic predictions and of memory-based predictions: the former obligatorily lead to resonance-like preparation patterns (that are in line with entrainment), while the latter allow flexible resource allocation in time regardless of periodicity in the input. Taken together, they delineate the neural mechanisms of three distinct modes of preparation: continuous vigilance, interval-timing-based prediction and rhythm-based prediction.

Modeling of Slag Entrainment and Interfacial Mass Transfer in Gas Stirred Ladles

Modeling of Slag Entrainment and Interfacial Mass Transfer in Gas Stirred Ladles

Numerical and physical modelling of tundish slag entrainment in the steelmaking process

CITATION: Mabentsela, A., Akdogan, G. & Bradshaw, S. 2017. Numerical and physical modelling of tundish slag entrainment in the steelmaking process. Journal of the Southern African Institute of Mining and Metallurgy, 117(5):469-483, doi:10.17159/2411-9717/2017/v117n5a9.

Распределение жидкости между ядром и жидкой пленкой в газокапельных потоках при высоких приведенных давлениях

The aim of the study is to develop an approximate but well-grounded model of droplet entrainment and deposition processes in annular two-phase flows at high reduced pressures. Very scarce experimental data are available for these conditions except for the indicators obtained by Nakazatomi and Sekoguchi (1996), who studied the distribution of liquid between the core and liquid film in a two-phase flow of air--water mixture at high pressures up to 20 MPa. These data feature an abnormally high fraction of entrained liquid in the flow core at pressures above 10 MPa and manifest very strong deviation from any known empirical correlations, including the Cioncolini and Thome's procedure published in 2012. The proposed droplets entrainment model takes into consideration the experimental observations according to which a liquid film becomes thin and smooth at high reduced pressures. A plenty of tiny droplets detach from the liquid film surface at the points the mutual spacing of which is determined by the Weber number for steam flow. This spacing and the liquid film thickness are the parameters governing the detached droplet diameter. An equation for calculating the entrainment intensity at high reduced pressures was constructed proceeding from these assumptions. However, it is rather difficult to verify this equation directly against experimental data because only the integral effect (i.e., the liquid flow rate in the film at dynamic equilibrium between entrainment and deposition) is usually measured in the experiments. The balance between the droplet entrainment and deposition flows due to turbulent diffusion corresponds to the dynamic equilibrium. The equation obtained proceeding from this balance contains one unknown numerical multiplier and allows one to calculate the liquid flow rate in the film. A comparison between the calculation results and the experimental data for a water–air flow at high reduced pressures has shown their good agreement at the universal value of a numerical constant in case of using an additional dimensionless parameter reflecting the ratio of phase densities.

Неисчерпаемые проблемы теплообмена

The article considers the heat transfer problems studied by the researchers of the MPEI Department of Engineering Thermal Physics (DETP) during the last five years. Modes involving low-frequency temperature pulsations have been revealed during heat transfer with liquid metals under the conditions of turbulence being suppressed by magnetic field; these pulsations, which are caused by thermo-gravity convection, present potential danger for the liquid metal cooling systems used in nuclear power engineering and in nuclear fusion installations. The facilities available at the joint laboratory of the Joint Institute for High Temperatures (JIHT) of the Russian Academy of Sciences and the Moscow Power Engineering Institute, which was established on the JIHT territory, have opened the possibilities for studying magnetic hydrodynamics and heat transfer for combinations of parameters close to the conditions under which real liquid metal-cooled systems operate. Numerical investigations of heat transfer, including direct numerical simulation (DNS) of single-phase turbulent flows or processes in heterogeneous systems, are used as an efficient tool for studying the mechanisms governing the relevant phenomena. Along with this, they open the possibility to solve applied problems, also within the framework of commercial agreements. Numerical techniques were used to optimize the metal hydride-based hydrogen cleaning and compressing systems and to study the fluid dynamics and heat transfer in air-cooled condensers. The processes taking place in the experimental section of an air-cooled condenser were for the first time simulated in the conjugated statement with taking into account the performance characteristics of gas removal devices. Solution of the natural convection problem in large-scale closed volumes at high Rayleigh numbers is an example of successful combined application of approximate analytical and numerical analysis methods. Hydrodynamics and heat transfer in two-phase media are widely studied at the Department. A few series of experiments on condensation of ethanol and water vapor mixtures with the mass fraction of alcohol ranging 0.8 to 16% on the surface of horizontal and vertical tubes have been conducted. It has been shown that the heat transfer intensity for such mixtures can increase by more than a factor of 4 as compared with condensation of pure steam. The specific features pertinent to boiling in microchannels on a smooth surface and on a surface microstructured by depositing nanoparticles have been studied. For annular two-phase flows, droplet entrainment and deposition models have been developed, and equations for predicting the distribution of droplets between the liquid film and flow core have been proposed. Comprehensive investigations of film boiling for subcooled liquid have been carried out. A unique array of experimental data on the cooling conditions of high-temperature spheres made of three different metals in four different liquids at pressures ranging from 0.1 to 1.0 MPa in a wide range of subcooling values has been created. A hypothesis about the conditions under which an intensive heat transfer mode may appear during film boiling of subcooled liquid, in which the heat transfer intensity is 20 to 30 times higher than it is during saturated film boiling. Experimental and theoretical investigations of sonoluminescence and hydroluminescence accompanying cavitation in liquids are conducted. Work is underway on developing methods for simulating macroscopically permeable phase interface boundaries in numerically solving heat and mass transfer problems under the conditions of phase transformations.

Interplay between the endocrine and circadian systems in fishes.

The circadian system is responsible for the temporal organisation of physiological functions which, in part, involves daily cycles of hormonal activity. In this review, we analyse the interplay between the circadian and endocrine systems in fishes. We first describe the current model of fish circadian system organisation and the basis of the molecular clockwork that enables different tissues to act as internal pacemakers. This system consists of a net of central and peripherally located oscillators and can be synchronised by the light-darkness and feeding-fasting cycles. We then focus on two central neuroendocrine transducers (melatonin and orexin) and three peripheral hormones (leptin, ghrelin and cortisol), which are involved in the synchronisation of the circadian system in mammals and/or energy status signalling. We review the role of each of these as overt rhythms (i.e. outputs of the circadian system) and, for the first time, as key internal temporal messengers that act as inputs for other endogenous oscillators. Based on acute changes in clock gene expression, we describe the currently accepted model of endogenous oscillator entrainment by the light-darkness cycle and propose a new model for non-photic (endocrine) entrainment, highlighting the importance of the bidirectional cross-talking between the endocrine and circadian systems in fishes. The flexibility of the fish circadian system combined with the absence of a master clock makes these vertebrates a very attractive model for studying communication among oscillators to drive functionally coordinated outputs.

An entrainment model for lazy turbulent plumes

An entrainment model for lazy turbulent plumes is proposed, the resulting solutions of the plume conservation equations are developed and the implications for plume behaviour are considered and compared with the available experimental data. Indeed, the applicability of the classic solutions of the conservation equations subject to source conditions that produce lazy plumes, i.e. those with suitably high source Richardson number, contains an essential weakness: the underlying assumption of a constant entrainment coefficient. While entrainment models prescribing the dependence of the entrainment coefficient on the local Richardson number have been proposed for forced plumes, corresponding formulations for lazy plumes have not until now been considered. In the context of saline plumes, the model is applied directly. For hot gaseous plumes, we use a modified definition of buoyancy flux to recover a constant buoyancy flux in a non-stratified environment, despite the specific heat varying with the temperature. After a brief review of existing forced-plume formulations of entrainment, a power-law variation is adopted for the lazy plume. The plume equations are solved for the parameter $0\leqslant \unicode[STIX]{x1D714}&lt;1$, where $\unicode[STIX]{x1D714}$ denotes the exponent of the power law. The cases of pure plumes and lazy plumes are then analysed in more detail; to the best of our knowledge this represents the first modelling of variable entrainment for lazy plumes. Specifically, it is shown that classic plume theory is recovered for $\unicode[STIX]{x1D714}=0$, while for $\unicode[STIX]{x1D714}=1/5$ the plume equations may be solved using usual functions (notably polynomials) only. The results of the models for these cases are very similar, which advocates the idea of selecting systematically $\unicode[STIX]{x1D714}=1/5$, instead of $\unicode[STIX]{x1D714}=0$, for cases where the effect of variation of entrainment is weak, since the new model leads to simple calculations. In the case of very lazy plumes, it is shown that, provided that a relevant value of $\unicode[STIX]{x1D714}$ is chosen, the new model reproduces the available experimental results well.

A probabilistic model for sediment entrainment: The role of bed irregularity

A generalized probabilistic model is developed in this study to predict sediment entrainment under the incipient motion, rolling, and pickup modes. A novelty of the proposed model is that it incorporates in its formulation the probability density function of the bed shear stress, instead of the near-bed velocity fluctuations, to account for the effects of both flow turbulence and bed surface irregularity on sediment entrainment. The proposed model incorporates in its formulation the collective effects of three parameters describing bed surface irregularity, namely the relative roughness, the volumetric fraction and relative position of sediment particles within the active layer. Another key feature of the model is that it provides a criterion for estimating the lift and drag coefficients jointly based on the recognition that lift and drag forces acting on sediment particles are interdependent and vary with particle protrusion and packing density. The model was validated using laboratory data of both fine and coarse sediment and was compared with previously published models. The study results show that all the examined models perform adequately for the fine sediment data, where the sediment particles have more uniform gradation and relative roughness is not a factor. The proposed model was particularly suited for the coarse sediment data, where the increased bed irregularity was captured by the new parameters introduced in the model formulation. As a result, the proposed model yielded smaller prediction errors and physically acceptable values for the lift coefficient compared to the other models in case of the coarse sediment data.