Shear Velocity Research Articles

Resolution-based comparative analysis of 4D-phase-contrast magnetic resonance images and hemodynamic simulations of the aortic arch

Abstract Introduction: In this study, phase-contrast magnetic resonance imaging (PC-MRI) 4D flow data for patients with bicuspid aortic valve (BAV) were analyzed based on the spatial resolution of the images. BAV is a congenital heart defect characterized by the presence of two cusps in the aortic valve, leading to various complications. PC-MRI is a noninvasive imaging technique used to assess the hemodynamics in patients. However, interpretation of PC-MRI data can be challenging due to complex hemodynamics, which makes numerical simulations necessary to complement the results. Methods:Within this study PC-MRI 4D flow data in the aortic arch (AA) were compared with hemodynamic numerical simulations based on the MRI resolution for six patient-specific AAs with BAV. First, the segmentations were reconstructed and divided into three groups based on the resolution. Second, the numerical simulations were performed and resulting hemodynamics compared to PC-MRI results at three time points in the cardiac cycle using velocity and wall shear stress. Results: Results from group 1 (highest resolution) show an overestimation of wall shear stress (WSS) values during peaksystole in the three arteries and along the AA and descending aorta (DAo). Nevertheless, velocity mean values show an overall good agreement. Group 2 shows higher velocity magnitudes in the simulation than in PC-MRI. Within group 3, velocity values differ from the measurements. Conclusion: The study shows that with a low resolution, flow patterns can already be evaluated based on PC-MRI, but to get an insight into the flow quantitatively a higher resolution is necessary.

A High‐Resolution Shear Velocity Model of the Crust and Uppermost Mantle Beneath Westernmost Mediterranean Including Radial Anisotropy

AbstractUsing seismic data from 1,186 stations deployed across the westernmost Mediterranean, we construct a high‐resolution 3‐D radially anisotropic model from a joint inversion of receiver functions and Rayleigh and Love wave dispersions. The Rayleigh and Love data are extracted from both ambient noise interferograms and earthquake waveforms, and a new three‐station ambient noise interferometry method is used to further improve the data coverage. The obtained crustal thickness map reproduces independently the Moho depth maps compiled from previous data, showing crustal roots beneath the Pyrenean‐Cantabrian range and the Gibraltar Arc and thicker crust beneath the Variscan Iberian Massif than in the area affected by Alpine orogenesis. The Vsv crustal model outlines the Iberian Massif as a high shear wave velocity block and shows extremely low velocities in the Gulf of Cadiz and Gibraltar Arc. At mantle levels, a sharp boundary between the Aquitanean Basin and the Massif Central is imaged, with low Vsv beneath the Massif Central probably reflecting a remaining signature of the magma. To the south of Iberia, the geometry of the Alboran slab is captured by the model, while beneath the Atlas Mountains, widespread low Vsv and positive radial anisotropy is observed, favoring the edge‐driven convection model explaining the lithospheric thinning. The most relevant contribution of this work is mapping, for the first time at this scale, the radial anisotropy anomalies at crustal level, with higher values observed in the Alpine Iberia, dominated by present‐day extensional tectonics.

Interannual eddy variability in the eastern Ryukyu Island chain

Interannual eddy variability in the eastern Ryukyu Island chain (RIC) was analyzed based on eddy trajectories and assimilation data. Analysis of the eddy trajectory data suggested a predominance of eddies originating near the study area. The occurrence frequency of eddies has interannual variability, but it demonstrates a different tendency with eddy kinetic energy (EKE): few eddies appear when EKE is high; however, they are strong with fast rotation speeds and increase in size. The EKE variability was correlated with the baroclinic conversion rates, suggesting a vital role of baroclinic instability in the study area. Baroclinic instability was found to be affected by the North Equatorial Current (NEC), during which more NEC water entered the eastern RIC, intensifying the vertical velocity shear between the upper and lower oceans. Consequently, baroclinic instability in the study area was enhanced.

Robust low-rank learning multi-output regression for incipient sediment motion in sewer pipes

The existing incipient sediment motion models typically apply conventional regression methods considering either velocity or shear stress. In the current study, incipient sediment motion is analyzed through a simultaneous and joint analysis of velocity and shear stress using the robust low-rank learning (RLRL) multi-output regression technique. Moreover, the experimental data compiled from five different channels are utilized to develop a generic incipient sediment motion model valid for a channel of any cross-sectional shape. The efficiency of the developed method is examined and compared against the available conventional regression models. The experimental results indicate that the RLRL model yields better results than its counterparts. In particular, while cross-section specific models fail to provide accurate estimates for shear stress or velocity for other cross sections, the proposed model provides satisfactory results for all channel shapes. The better performance of the recommended approach can be attributed to the joint modeling of the shear stress and the velocity which is realized by capturing the correlation between these parameters in terms of a low rank output mixing matrix which enhances the prediction performance of the approach.

One-dimensional regional shear velocity structure from joint inversion of fundamental mode group velocity dispersion measurements of Love and Rayleigh waves: application to the Uttarakhand Himalaya

One-dimensional regional shear velocity structure from joint inversion of fundamental mode group velocity dispersion measurements of Love and Rayleigh waves: application to the Uttarakhand Himalaya

Numerical Simulation on Insoluble Surfactant Mass Transfer on Deformable Bubble Interface in a Couette Flow by Phase-Field Lattice Boltzmann Method-Finite-Difference Method Hybrid Approach.

Elaborate management on bubble shape and transportations depends on the balance between multiple physical behaviors for two-phase flow with Marangoni stress and the interface mass transfer. In this paper, a new model combining PFLBM (phase-field lattice Boltzmann method) and FDM ( finite-difference method) coupling with the ghost-cell method was built. The PFLBM-FDM was validated for the high accuracy, less computational cost, and low mass loss compared to other methods. Based on the PFLBM-FDM, a surfactant-laden bubble deformed and transported in a laminar Couette flow was investigated. The deformation ratio and transportation velocity were explored with different density ratios, surface tensions, shear velocities, and diffusion coefficients. The numerical results showed that the equilibrium state of the bubble deformation was decided only by the dimensionless numbers when the Sh number was higher than 100. Moreover, the transportation velocity of the bubble can be controlled by the balance between the Marangoni stress and shear velocity. When the Sh is lower than 100, the Marangoni stress from the surfactant is not a long-range force, which only works at the early flow. Otherwise, the Marangoni stress will be a long-range force that provides a persistent force to accelerate the bubble by ∼10%. Increasing ReH will further intensify the effect. Based on all the data, a correlation of the bubble deformation including with the densities of two fluids was obtained and the error range is less 5%.

Turbulence modelling for depth-averaged velocity and boundary shear stress of a dense rigid grass bed open channel

Abstract The present research focusses on a comparison of experimental and numerical approaches for flow over fixed artificial rigid grass bed channels. Various flow parameters like longitudinal velocity, depth-averaged velocity (DAV), boundary shear stress (BSS) and secondary current are analysed and compared with seven numerical models: standard, realizable and renormalization group (RNG) k–ε models and standard, shear stress transport (SST), generalized k–ω (GEKO) and Baseline (BSL) k–ω models. To evaluate the strength of the seven applied models, the error analysis has been performed. It is found that the RNG k–ε and SST k–ω models provided better results for both the DAV and BSS prediction, but the RNG k–ε model is found to be the most suitable for predicting the DAV and the SST k–ω model for BSS as compared to the other models. For the longitudinal velocity profiles, both the RNG k–ε and SST k–ω models are found to provide good agreement with experimental results at the centre of the channel, whereas the SST k–ω model is more accurate near the wall. Overall, the SST k–ω model has predicted the results with good accuracy for all the flow parameters considered in the present study.

Molecular simulation of the effect of dioctyl phthalate on the properties of nitrile rubber

The mechanical and tribological properties of pure nitrile rubber (NBR) and dioctyl phthalate/nitrile rubber (DOP/NBR) composite materials with mass ratios of 5/95, 10/90, 15/85, 20/80, 25/75, and 30/70 were studied through molecular dynamics simulations at the molecular level. The root mean square displacement (RMSD) and gyration radius of the composite materials were investigated to explore the mechanism of DOP plasticizing NBR. Different models of pure NBR and DOP/NBR composite materials with different mass ratios were established, and the mechanical properties of the materials were calculated by using the constant strain method. The tribological properties of the materials were studied by applying shear velocity on the surface of the materials. The research results showed that the shear resistance of the DOP/NBR composite material increased and then decreased with the increase of the DOP mass ratio, and the same pattern was observed for the shear modulus. Compared with pure NBR materials, DOP/NBR composite materials demonstrated better mobility and flexibility, and the RMSD and gyration radius of the material increased and then decreased with the increase of the DOP mass ratio. The DOP plasticization of NBR reduced the intermolecular interaction forces and changed the molecular conformation, increasing the softness and plasticity of the polymer chains.

Wind tunnel simulation of wind erosion and dust emission processes, and the influences of soil texture

Dust emission caused by wind erosion of soil is an important surface process in arid and semi-arid regions. However, existing dust emission models pay insufficient attention to the impacts of aerodynamic entrainment of particles. In addition, studies of wind erosion processes do not adequately account for the dynamics of wind erosion rates and dust emission fluxes, or for the impact of soil texture on dust emission. Our wind tunnel simulations of wind erosion and dust emission showed that the soil texture, wind erosion duration, and shear velocity are major factors that affect the dynamics of wind erosion and dust emission. Because of the limited supply of surface sand and the change in surface erosion resistance caused by surface coarsening during erosion, the wind erosion rate and the flux of particles smaller than 10 μm (PM10) caused by aerodynamic entrainment decreased rapidly with increasing erosion duration, which suggests that surface wind erosion and dust emission occur primarily during the initial stage of wind erosion. The PM10 emission efficiency decreased with increasing shear velocity following a power function, and finer textured sandy loam soils had greater PM10 emission efficiency than loamy sand soils.

Characterization of small abdominal aortic aneurysms' growth status using spatial pattern analysis of aneurismal hemodynamics

Aneurysm hemodynamics is known for its crucial role in the natural history of abdominal aortic aneurysms (AAA). However, there is a lack of well-developed quantitative assessments for disturbed aneurysmal flow. Therefore, we aimed to develop innovative metrics for quantifying disturbed aneurysm hemodynamics and evaluate their effectiveness in predicting the growth status of AAAs, specifically distinguishing between fast-growing and slowly-growing aneurysms. The growth status of aneurysms was classified as fast (≥ 5 mm/year) or slow (< 5 mm/year) based on serial imaging over time. We conducted computational fluid dynamics (CFD) simulations on 70 patients with computed tomography (CT) angiography findings. By converting hemodynamics data (wall shear stress and velocity) located on unstructured meshes into image-like data, we enabled spatial pattern analysis using Radiomics methods, referred to as "Hemodynamics-informatics" (i.e., using informatics techniques to analyze hemodynamic data). Our best model achieved an AUROC of 0.93 and an accuracy of 87.83%, correctly identifying 82.00% of fast-growing and 90.75% of slowly-growing AAAs. Compared with six classification methods, the models incorporating hemodynamics-informatics exhibited an average improvement of 8.40% in AUROC and 7.95% in total accuracy. These preliminary results indicate that hemodynamics-informatics correlates with AAAs' growth status and aids in assessing their progression.

Numerical simulation of aortic coarctations of different grades of severity: Flow features and importance of outlet boundary conditions

Numerical simulations of the blood flow inside a patient-specific thoracic aorta in presence of coarctation are considered. Different grades of severity of the coarctation are obtained by constructing parametric geometries in which the coarctation section is circular with varying diameter values. The impact of a fine-tuning of the Windkessel model resistances, at each outlet, is also investigated. A stochastic approach based on the generalized Polynomial Chaos (gPC) is used to carry out a systematic analysis. It allows obtaining continuous response surfaces of the quantities of interest in the parameter space from a limited number of simulations. Two parameters are selected: the vessel diameter, D, at the coarctation plane and a non-dimensional parameter, α, through which it is possible to calibrate the resistance offered by organs and vessels downstream the thoracic aorta. The value of the coarctation diameter has the strongest impact on all the flow features, i.e., flow rate, pressure, velocity, and wall shear stresses. It is also shown that, as the value of D increases, the dependence on α decreases. This means that the more the geometry of the thoracic aorta approaches a healthy shape, the less significant it is to perform a fine-tuning of the Windkessel model resistances to match the patient-specific pressure waveform, whereas it should be done in cases of severe coarctations.

Modelling the wall friction coefficient for a simple shear granular flow in view of the degradation mechanism

A steady granular flow experiment was performed in a confined annular shear cell to examine how the wall friction coefficient $\mu _w$ degrades from the intrinsic sliding friction coefficient $f$ between the grains and the container wall. Two existing models are invoked to examine the decay trend of $\mu _w/f$ in view of the ratio of shear velocity to the square root of granular temperature $\chi$ (Artoni &amp; Richard, Phys. Rev. Lett., vol. 115, 2015, 158001) and the ratio of grain angular and slip velocities $\varOmega$ (Yang &amp; Huang, Granul. Matt., vol. 18, issue 4, 2016, p. 77), respectively. As both models correlate $\mu _w/f$ to different flow properties, a hidden relation is speculated between $\chi$ and $\varOmega$ , or equivalently, between the granular temperature and the grain rotation speed. We used experiment data to confirm and reveal this hidden relation. From there, a unified $\mu _w/f-\chi$ model is proposed with physical meanings for the model coefficients and to show general agreement with the measured trend. Hence we may conclude that both the fluctuations in grain translations and their mean rotation are the crucial yet equivalent mechanisms to degrade $\mu _w/f$ .

Patient-specific computational fluid dynamics for hypertrophic obstructive cardiomyopathy

BackgroundThe heterogeneous morphologic and functional expression of hypertrophic obstructive cardiomyopathy (HOCM) is evidenced by established imaging, multimodality imaging is essential for a comprehensive assessment but may remain uncertain. This study aimed to develop a patient-specific hemodynamics assessment with cardiac computed tomography angiography (CCTA) based computational fluid dynamics (CFD) and prove its usability in cohorts of HOCM patients. MethodsA retrospective study was performed on eight HOCM patients with septal myectomy who had both preoperative and postoperative CCTA as well as transthoracic echocardiography (TTE). The three-dimensional models were reconstructed from CCTA data, following which patient-specific CFD simulations were performed to estimate the blood velocity, pressure gradient, and wall shear stress. The simulation output was compared with TTE. Based on CFD simulations, retrospective and blinded virtual myectomy was also performed, to predict the minimum resected volume for improving obstruction in patients. ResultThe complex HOCM anatomy was successfully reconstructed for all 8 patients. The CFD simulation accurately assessed the pressure gradient, flow velocity. There was a good correlation between the peak pressure gradient measured by CFD and TTE in the pre- and post-operative assessments (r = 0.87 and 0.84, respectively), and the flow velocity (r = 0.87 and 0.90, respectively). The volumes of minimal resection myocardium predicted by CFD and virtual myectomy were consistent with the actual resection volumes. ConclusionCCTA-based CFD for HOCM patients may play a unique role in the assessment of patient-specific morphology and hemodynamics. Combination with virtual myectomy might allow for optimizing therapy planning in septal myectomy. Clinical perspectiveCFD based CCTA may emerge as a complement to established imaging strategies, with accurate three-dimensional reconstruction and hemodynamic simulation of the left ventricle in this retrospective study. Combined with virtual myectomy, CFD simulation might allow for predicting the volume of resected myocardium for septal myectomy. Moving forward, this technology may be used by clinicians to better assess the conditions of HOCM patients, and guide the extent and depth of resection during septal myectomy. Therefore, further prospective clinical evaluation is clearly warranted.

Significance of body acceleration and gold nanoparticles through blood flow in an uneven/composite inclined stenosis artery: A finite difference computation

Stenosis is a tiny plaque-like structure that builds up in the arterial wall owing to the sediment of cholesterol, fats, and pearly substances. Such inward proliferation in arteries significantly inhibits blood flow, which leads to a lack of nutrients and oxygen in the organs. Therefore, exploring the transport characteristics of blood fluid flow in stenosis arteries plays a prominent role in enhancing blood transportation. As a result, the present mathematical model is devoted to scrutinizing the flow of Sutterby gold blood nanofluid in two distinct stenosis arteries with periodic body acceleration. It is observed that the Sutterby rheology model is treated as blood, and the single-phase model is used for exposing the nanofluid behaviour. Dimensional non-linear PDEs of the current model are reduced to the set of dimensionless PDEs with the help of non-similar variables. A finite-difference approach is manipulated to compute the dimensionless PDEs. The physical features of governing flow parameters on the Sutterby nanofluid velocity, temperature, resistance impedance, flow rate, and wall shear stress are exposed through graphs. It is found that the composite stenosis has a lower wall shear stress than the irregular stenosis. Sutterby blood nanofluid velocity is elevated with the rising of nanoparticle volume fraction. When employing a gold nanofluid containing 5% volume fraction, the temperature in the irregular artery rises by 26.004% compared to the base fluid (blood). Similarly, in the composite artery, utilizing the same 5% volume fraction of the gold nanofluid leads to a temperature increase of 32.6207%. The blood flow pattern exhibits a 0.2340% higher in the irregular artery as compared to the composite artery.

New formulations for the mean wall-normal velocity and Reynolds shear stress in a turbulent boundary layer under zero pressure gradient

In this study, a novel analytical solution is derived rigorously for the mean wall-normal velocity in a turbulent boundary layer (TBL) under zero pressure gradient (ZPG), without relying on any a priori assumptions regarding the mean streamwise velocity. By neglecting the higher-order terms in the exact solution, an approximate formulation for the mean wall-normal velocity is obtained. The accuracy of this approximation is then validated through a comparison with data from direct numerical simulations (DNS). Drawing upon the distinct behaviours of force balance in the inner and outer regions of the ZPG TBL, simplified approximate mean momentum equations are derived by decomposing the Reynolds shear stress into inner and outer parts. The inner and outer Reynolds shear stresses are then obtained through integration of the corresponding approximate mean momentum equations. The outer Reynolds shear stress is revealed to exhibit a strong connection to the mean wall-normal velocity. Specifically, it is observed that $R_{uv-{out}}/u^2_\tau \approx 1 - UV/(U_e V_e)$ , where $u_\tau$ represents the friction velocity, and $U_e$ and $V_e$ denote the mean streamwise and wall-normal velocities at the boundary layer edge, respectively. Finally, an approximate formulation for the Reynolds shear stress across the entire TBL is developed by synthesizing the inner and outer parts. Extensive validation against both DNS and experimental data, spanning a wide range of Reynolds numbers, demonstrates the excellent agreement achieved.

Experimental and calculation investigations of hydrodynamics and heat exchange in liquid metal turbulent flows in fast reactor fuel assemblies

The formation of velocity and temperature fields in the fuel assemblies of fast reactor core occurs under the influence various factors. It is shown, that the most important factors include a complex multiply connected geometry, subject to deformation during the campaign under the influence of temperature non-uniformity and radiation effects. The results of studies of the velocity fields and shear stress, turbulence microstructure are presented. An intensification of turbulent momentum transfer in channels in azimuthal and radial directions in the area of gaps between the rods is demonstrated. The performed analysis is indicate that there are a significant difference between the experimental dependences for turbulent momentum transfer coefficients in the radial and azimuthal directions and calculated within the framework of semi-empirical models of turbulent momentum transfer as well as the anisotropy coefficients of the turbulent momentum transfer in rod bundles. The results of benchmark on the fuel assembly thermohydraulics showed that the common commercial codes describe experimental data only approximately. It is shown, that the intensification of turbulent momentum transfer in the channels of rod bundles is due to the appearance of large-scale turbulent momentum transfer (secondary flows). The contribution of large-scale turbulent momentum transfer to the turbulent momentum transfer coefficients in the channels of rod bundles is calculated. The dependence for coefficient of inter-channel turbulent exchange of momentum is obtained and the intensification of inter-channel turbulent exchange in close-packed rod lattices is explained. A dependence for the dissimilarity coefficients of forced inter-channel convective exchange of momentum and mass, as well as energy and mass in rod bundles spaced by wire winding is obtained. The calculation methods and the numerical modeling results for temperature regime of fuel assemblies with randomly distributed initial parameters by the Monte Carlo method are presented as well as the thermomechanical analysis of the temperature field in the fuel assemblies during the campaign. An idea about the equilibrium configuration of a rod bundle in a hexagonal jacket during irradiation, the stress–strain state of an individual fuel rod and a fuel assembly jacket is obtained. The tasks of further investigations discussed.

Mechanism-informed constitutive modeling of molecular crystal cyclotetramethylene tetranitramine (β-HMX)

Molecular crystals are of importance in many applications including energetic materials and pharmaceuticals. Here we focus on the energetic material cyclotetramethylene tetranitramine (β-HMX) whose plastic deformation plays an important role in reaction initiation and detonation. While constitutive modeling of monatomic crystals is well established, the development of models for molecular crystals is less advanced. We present a mechanism-based constitutive formulation for β-HMX crystals, and an equivalent Reuss averaged homogenized model, which are based on a wealth of information about the physics of plastic deformation collected from the literature and developed in this work. We use atomistic models to evaluate the dislocation velocity vs. resolved shear stress relation in multiple slip systems and at various pressures up to 20 GPa, while accounting for slip asymmetry. We use this data to evaluate the strain rate sensitivity on the crystal scale and calibrate all constitutive parameters of the thermally activated and dislocation drag regimes. The resulting crystal plasticity model is then Reuss averaged to produce a homogenized version. The model is perfectly plastic, strongly pressure-dependent and rate sensitive. Further, we observe that strain localization takes place at large enough strain rates and propose a criterion for the occurrence of localization. The formulation can be used to advance the state of the art of continuum modeling of microstructure-dependent initiation in HMX.

A committee machine-based estimation of shear velocity log by combining intelligent systems and rock-physics model using metaheuristic algorithms

Estimation of reservoir parameters such as porosity, lithology and determination of elastic moduli is based on well-logging data and seismic velocity information. However, the lack of shear velocity log in many wells, and the high costs of its acquisition have led to developing different approaches for shear velocity estimation. Currently, shear velocity estimation is accomplished by common industrial methods such as empirical equations, regression analysis, intelligent methods and rock-physics models (RPMs). The current study proposes that robust, accurate and cost-effective intelligent methods coupled with suitable RPM provide reasonable estimations of the shear velocity in an optimal processing time. Hybridizing intelligent models with RPMs in the framework of a committee machine is an optimal solution for shear velocity estimation of carbonate reservoirs. The intelligent methods used in this study include neural network (NN), fuzzy logic (FL) and an adaptive-neuro fuzzy inference system (ANFIS). In this research, for each individual intelligent model and a developed RPM, the optimal weights were allocated by Metaheuristic optimization algorithms including genetic algorithm (GA), ant colony optimization routing (ACOR) and simulated annealing (SA)). To obtain the best results with the lowest mean squared error (MSE), a total of 9408, 10801 and 12288 models were created and tested in MATLAB to optimally parametrize the GA, ACOR and SA, respectively. The results showed that the combination of the applied intelligent models with the developed RPMs leads to a higher correlation coefficient with reference to the measured Shear velocity in test dataset. The use of a combination of intelligent methods in the form of committee-machine instead of individual methods has led to a reduction in error and improved the results by up to 2% Considering the high sensitivity of shear wave velocity in geomechanical and reservoir characterization studies, even small improvements in its estimation can significantly reduce error in the characterization of hydrocarbon reservoirs.

Joint Action and Competition between Centrifugal, Magnetorotational, and Magnetic Buoyancy Instabilities

Instabilities driven by some combination of rotation, velocity shear, and magnetic field in a stratified fluid under gravity play an important role in many astrophysical settings. Of particular note are the centrifugal instability, the magnetorotational instability, and magnetic buoyancy instability. Here, we consider a Cartesian model of an equatorial region incorporating all the physical ingredients necessary to study their competition. We investigate the linear instability to interchange (“axisymmetric”) modes of an inviscid, perfectly conducting, isothermal gas, including the effects of rotation, velocity shear, and poloidal and toroidal magnetic fields. The stability problem can be reduced to a second-order boundary value problem, with the growth rate as the eigenvalue. We can make analytic progress through consideration of the physically relevant regime in which the transverse horizontal wavenumber k ≫ 1. Via a perturbation analysis, with 1/k as the small parameter, we can derive the growth rate and the spatial dependence of the eigenfunctions: the unstable modes are strongly localized in the vertical direction, being either wall modes (localized near a boundary of the domain) or body modes (localized in the interior). We describe the conditions under which the joint action of the separate instability mechanisms leads to enhancement or suppression of the instability. Our analytical results are supplemented by numerical solutions of the stability problem. The most unstable mode found analytically is typically in excellent agreement with that found numerically through consideration of a wide range of wavenumbers. Finally, we discuss how our results relate to the solar tachocline.

Sedimentation in particle-laden flows with and without velocity shear

The vertical transport of sediment from particle-laden flows in marine settings can be enhanced by a settling-driven convective instability. The presence of a horizontal velocity shear can further influence this vertical transport. We conduct numerical simulations to investigate the vertical sediment transport in the presence and absence of shear. We show how this transport is determined by a competition between the growth of the settling-driven convective instability (Rayleigh–Taylor) and the stratified shear instability (Kelvin–Helmholtz). In the absence of shear, the Rayleigh–Taylor instability drives enhanced vertical sediment transport; this effect increases with the Stokes settling velocity of the particles and decreases with the stratification strength. In the presence of shear, there are two regimes of effective settling. When the Kelvin–Helmholtz instability grows rapidly and suppresses the Rayleigh–Taylor instability, the effective settling velocity is significantly reduced. On the other hand, if the Rayleigh–Taylor instability dominates and completely inhibits the Kelvin–Helmholtz instability, the effective settling velocity is enhanced due to the additional energy input by shear. We explore the parameter space of these regimes and interpret their physics.