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With the increasing demand for efficient and accurate numerical simulations of spray combustion in jet engines, the necessity for robust models to enhance the capabilities of spray models has become imperative. Existing approaches often rely on ad hoc determinations or simplifications, resulting in information loss and potentially inaccurate predictions for critical spray characteristics, such as droplet diameters, velocities, and positions, especially under extreme operating conditions or temporal fluctuations. In this study, we introduce a novel approach to modeling multivariate spray characteristics using Gaussian mixture models (GMM). By applying this approach to spray data obtained from numerical simulations of the primary atomization in air-blast atomizers, we demonstrate that GMMs effectively capture the spray characteristics across a wide range of operating conditions. Importantly, our investigation reveals that GMMs can handle complex non-linear dependencies by increasing the number of components, thereby enabling the modeling of more complex spray statistics. This adaptability makes GMMs a versatile tool for accurately representing spray characteristics even under extreme operating conditions. The presented approach holds promise for enhancing the accuracy of spray combustion modeling, offering an improved injection model that accurately captures the underlying droplet distribution. Additionally, GMMs can serve as a foundation for constructing meta models, striking a balance between the efficiency of low-order approaches and the accuracy of high-fidelity simulations.

In this study, we developed a transport model for typical pollutants in the Yellow Sea using the Lagrangian particle tracking method to analyze the trajectories of fish feed, a common pollutant in the Yellow Sea. The model incorporates the influence of ocean currents and surface winds on pollutant transport and utilizes a series of numerical experiments to simulate pollutant transport. Through statistical analysis of the numerical experiment results, we identified characteristic circles that represent the pollutant distribution patterns. Furthermore, based on the current and wind information within these characteristic circles, we derived an empirical formula to describe pollutant distribution. This formula enables us to predict the spatial distribution of pollutants using available current and wind data. Using this empirical formula, we designed an effective path to avoid pollutant contamination. This approach not only optimizes the utilization of computational resources within the study area but also contributes to the rational planning of navigation routes for aquaculture vessels. Overall, our study provides valuable insights into the transport behavior of fish feed pollutants in the Yellow Sea. The establishment of the empirical formula and the design of effective routes to avoid pollution contribute to the efficient management of pollution and facilitate the planning of marine activities in the region.

In this work we compare the DNS results (Fabregat et al. 2021, Fabregat et al. 2021) for a mild cough already reported in the literarure with those obtained with a compressible URANS equations with a k-ϵ turbulence model. In both cases, the dispersed phase has been modelled as spherical Lagrangian particles using the one-way coupling assumption. Overall, the URANS model is capable of reproducing the observed tendency of light particles under 64 µm in diameter to rise due to the action of the drag exerted by the buoyant puff generated by the cough. Both DNS and URANS found that particles above 64 µm will tend to describe parabolic trajectories under the action of gravitational forces. Grid independence analysis allows to qualify the impact of increasing mesh resolution on the particle cloud statistics as flow evolves. Results suggest that the k-ϵ model overpredicts the horizontal displacement of the particles smaller than 64 µm while the opposite occurs for the particles larger than 64 µm. [ABSTRACT FROM AUTHOR]

Understanding how ocean currents affect larval transport is crucial for understanding population connectivity in sessile marine invertebrates whose primary dispersal opportunity occurs during the pelagic larval stage. This study used Lagrangian particle tracking experiments to examine population connectivity in New Zealand green-lipped mussels (Perna canaliculus) at the national scale. Predicted patterns of larval dispersal were compared to published multi-locus microsatellite data of observed population genetic structure. Estimates of oceanographic circulation correlated significantly with FST, and we conclude that hydrodynamic processes are important in driving genetic connectivity. However, no evidence was found for an oceanographic barrier to gene flow south of Cook Strait, an important feature of genetic structure observed across several marine invertebrate species. Discrepancies between genetic and biophysical data may be explained by several factors including the different timescales of connectivity described by the two methods and the impact of localised ecological conditions and corresponding adaptations in genetic structure not captured by the bipohysical model. Population genetic analyses provide empirical data on realised connectivity and Lagrangian particle tracking experiments reveal information about directionality and asymmetry of connections that often cannot be determined by molecular analyses alone, thus a multidisciplinary approach is recommended.

The large, habitat-forming bubblegum coral, Paragorgia arborea, is a vulnerable marine ecosystem indicator with an antitropical distribution. Dense aggregations of the species have been protected from bottom-contact fishing in the Scotian Shelf bioregion off Nova Scotia, Canada in the northwest Atlantic Ocean. Recently, basin-scale habitat suitability ensemble modeling has projected an alarming loss of 99% of suitable habitat for this species across the North Atlantic by 2100. Here, a regional reassessment of the predicted distribution of this species in the bioregion, using both machine learning (random forest) and generalized additive model (GAM) frameworks, including projection to 2046−2065, was undertaken. Extrapolation diagnostics were applied to determine the degree to which the models projected into novel covariate space (i.e., extrapolation) in order to avoid erroneous inferences. The best predictors of the species’ distribution were a suite of temporally-invariant terrain variables that identified suitable habitat along the upper continental slope. Additional predictors, projected to vary with future ocean climatologies, identified areas of the upper slope in the eastern portion of the study area that will remain within suitable ranges for P. arborea at least through to the mid-century. Additionally, 3-D Lagrangian particle tracking simulations indicated potential for both connectivity among known occurrence sites and existing protected areas, and for colonization of unsurveyed areas predicted to have suitable habitat, from locations of known occurrence. These results showed that extirpation of this iconic species from the Scotian Shelf bioregion is unlikely over the next decades. Potential climate refugia were identified and results presented in the context of protected area network design properties of representativity, connectivity, adequacy, viability and resilience.

A Lagrangian particle tracking module within a hydrodynamic model in Environmental Fluid Dynamic Code Plus (EFDC+) was used to track the movements of large floating marine carcasses. This research used data from six GPS-tagged drifters collected in April 2017 by NOAA to conduct a sensitivity analysis and calibration on the Lagrangian particle tracking module. These analyses investigate the influence of specific parameters, notably wind drag and number of vertical layers in the model. Changing these parameters resulted in observable changes in the trajectories of tracked particles. The results of the sensitivity experiments were compared using the Skill Score statistic. Adding wind drag to the LPT was a pivotal alteration, augmenting the model predictive capabilities by increasing the Skill Score value from 0.23 to 0.47. Further tests examined the impact of varying wind drag coefficients (A and B) which are the slope and y-intercept of a linear equation used to describe overall drag coefficient (CD) as a function of wind velocity. These coefficients are employed in EFDC + software and altering them revealed that coefficient A has a larger impact on the model predictions compared to coefficient B. Finally, the transition from a 2D to a 3D model had a more significant impact on the results compared to increasing the number of vertical layers in the 3D configuration. However, the findings indicated that changing the model from 2D to 3D may not yield a large enough improvement in accuracy that would justify the additional computational demands associated with a 3D model when running long periods of time (several years). The study results have valuable implications for developing accurate and precise models of hydrodynamic systems emphasizing the importance of wind in LPT models and the efficiency of 2D vs 3D models for LPT simulations in the Mississippi Sound area. [Display omitted] • Lagrangian Particle tracking (LPT) was used to simulate the movement of drifters. • Sensitivity and calibration on LPT were performed. • LPT was very sensitive to the wind existence. • Changing the 2D model into 3D offered marginal improvement in accuracy. [ABSTRACT FROM AUTHOR]

Particle solar receivers promise economical and operational advantages compared to the molten salt-based solar receivers. In this study, an experiment is designed to observe the particle flow characteristics in the Centrifugal Particle Solar Receiver. A set of experiments for various receiver rotational speeds and particle mass flowrates is conducted, and experimentally obtained raw results are post-processed by means of an Image Processing Routine based on 4BestEstimate algorithm. The axial advance of the particles in one receiver rotation, the particle film thickness, and the ratio of the length of the stationary zone to the receiver circumference is measured to be later used in the validation study of the discrete element method-based numerical model. [ABSTRACT FROM AUTHOR]

Cardiac resynchronization therapy is a valuable tool to restore left ventricular function in patients experiencing dyssynchronous ventricular activation. However, the non-responder rate is still as high as 40%. Recent studies suggest that left ventricular torsion or specifically the lack thereof might be a good predictor for the response of cardiac resynchronization therapy. Since left ventricular torsion is governed by the muscle fiber orientation and the heterogeneous electromechanical activation of the myocardium, understanding the relation between these components and the ability to measure them is vital. To analyze if locally altered electromechanical activation in heart failure patients affects left ventricular torsion, we conducted a simulation study on 27 personalized left ventricular models. Electroanatomical maps and late gadolinium enhanced magnetic resonance imaging data informed our in-silico model cohort. The angle of rotation was evaluated in every material point of the model and averaged values were used to classify the rotation as clockwise or counterclockwise in each segment and sector of the left ventricle. 88% of the patient models (n = 24) were classified as a wringing rotation and 12% (n = 3) as a rigid-body-type rotation. Comparison to classification based on in vivo rotational NOGA XP maps showed no correlation. Thus, isolated changes of the electromechanical activation sequence in the left ventricle are not sufficient to reproduce the rotation pattern changes observed in vivo and suggest that further patho-mechanisms are involved. [ABSTRACT FROM AUTHOR]

Cardiac resynchronization therapy is a valuable tool to restore left ventricular function in patients experiencing dyssynchronous ventricular activation. However, the non-responder rate is still as high as 40%. Recent studies suggest that left ventricular torsion or specifically the lack thereof might be a good predictor for the response of cardiac resynchronization therapy. Since left ventricular torsion is governed by the muscle fiber orientation and the heterogeneous electromechanical activation of the myocardium, understanding the relation between these components and the ability to measure them is vital. To analyze if locally altered electromechanical activation in heart failure patients affects left ventricular torsion, we conducted a simulation study on 27 personalized left ventricular models. Electroanatomical maps and late gadolinium enhanced magnetic resonance imaging data informed our in-silico model cohort. The angle of rotation was evaluated in every material point of the model and averaged values were used to classify the rotation as clockwise or counterclockwise in each segment and sector of the left ventricle. 88% of the patient models (n = 24) were classified as a wringing rotation and 12% (n = 3) as a rigid-body-type rotation. Comparison to classification based on in vivo rotational NOGA XP maps showed no correlation. Thus, isolated changes of the electromechanical activation sequence in the left ventricle are not sufficient to reproduce the rotation pattern changes observed in vivo and suggest that further patho-mechanisms are involved.

A shortage of dissolved oxygen in seawater can adversely impact marine life and ecosystems. Low oxygen conditions at depth occur in many coastal regions, driven by both local productivity and remote changes in the source waters. A low‐oxygen dense pool of water is observed every summer over the mid‐shelf off southwest Vancouver Island in the Juan de Fuca Eddy region. We trace the dense pool waters back to their source using Lagrangian Particle tracking in an ocean model. The model accuracy is evaluated against a set of dense observations collected in August 2013. Only locations where the model represents water properties well are used as starting locations for the tracking. These locations are selected using a K‐Means clustering algorithm. Tracking particles backwards in time showed that the low oxygen dense pool is primarily composed of water from the California Undercurrent, shallower water from further offshore of the Washington shelf, and offshore water. Waters from the northern shelf were not a primary source even though summer currents are from the north. Correspondingly, the water primarily arrived in the south Vancouver Island region in spring, months before the cruise. A kernel density estimate shows the final water properties of the dense pool are well represented by this mixture. The dense water pathways up and onto the shelf are primarily through coastal submarine canyons in early summer. Combining high spatial resolution observations, a carefully evaluated numerical model, Lagrangian tracking, and statistical techniques reveal detailed answers not obtainable through a single method. Plain Language Summary: A shortage of dissolved oxygen in seawater can adversely impact marine life and ecosystems. A low‐oxygen dense pool of water is observed every summer over the mid‐shelf off southwest Vancouver Island. The dense pool waters are traced back to their source by tracking particles backwards in time using ocean currents from a numerical model. The California Undercurrent, shallower water from the south from further offshore of the Washington shelf, and offshore water contribute the most volume to the dense pool waters. Though summer currents are from the north in the region, they are not a major contributing source. The dense water pathways up and onto the shelf are primarily through the coastal submarine canyons and occur in early summer. Key Points: Using an evaluated numerical model, backward Lagrangian tracking, and kernel density estimation illuminates water mass originPrincipal pathways of the deep, low oxygen summer water onto the shelf are through the submarine canyonsLow‐oxygen deep summer water on the Vancouver Island shelf originates from the south, opposite to summer shelf currents [ABSTRACT FROM AUTHOR]

Background: Larval connectivity between distinct benthic populations is essential for their persistence. Although connectivity is difficult to measure in situ, it can be predicted via models that simulate biophysical interactions between larval behaviour and ocean currents. The blue mussel (Mytilus Edulis L.) is widespread throughout the northern hemisphere and extensively commercialised worldwide. In the Irish Sea, this industry represents ~ 50% of Welsh shellfisheries, where cultivation is mainly based on wild spat. However, the main sources and amount of spat varied interannually (1100 tonnes harvest in 2014 against zero in 2018). The aim of this study is to characterise the structure and dynamics of the blue mussel metapopulation within the northern part of the Irish Sea. Methods: We develop a Lagrangian particle tracking model, driven by a high-resolution (from 30 to 5000 m) validated unstructured coastal hydrodynamic model of the Irish Sea, to simulate spatial and temporal variability of larval dispersal and connectivity between distinct mussel populations and potential settlement areas. Results: Our results showed that: (1) larvae positioned near the surface were strongly influenced by wind-driven currents suggesting that connectivity networks had the potential to span hundreds of kilometres; (2) in contrast, larvae positioned deeper in the water column were driven by tidal currents, producing intricate spatial patterns of connectivity between mussel beds over tens of kilometres that were consistent over time. Conclusions: Dispersal of mussel larvae in the tidally energetic Irish Sea during the April–May spawning season is potentially driven by wind-driven surface currents, as confirmed by fisherman observations of inter-annual variability in wild spat collection. These results have important implications for metapopulation dynamics within the context of climate change and sustainable shellfisheries management (i.e. gain and loss of populations and harvest areas according to wind conditions). [ABSTRACT FROM AUTHOR]

Multidimensional numerical simulations are performed to investigate the evolution and formation of unburned fuels for a shock-fuel jet interaction scenario. A full set of Navier-Stokes equations with detailed chemical mechanisms are solved, and the results are analyzed through the Lagrangian method with the goal of improving combustion efficiency in supersonic flows. The flame morphology of a two-dimensional (2-D) non-premixed reactive shock-bubble interaction is first simulated and studied, in which unburned hydrogen is found to prevent efficient combustion. By applying the Lagrangian particle tracking method, most of the unburned hydrogen wrapped into the primary vortex turns out to be initially located upon the symmetry line of the bubble. Motivated by the idea of breaking the primary vortex, this study designs a novel geometry of a concentric bubble, which improves combustion efficiency to 94.4% in contrast to a solid fuel bubble (74%) due to multivortex interaction and a thick bridge structure. With the consistency between qualitative and quantitative 2-D and three-dimensional (3-D) flow dynamics, the idea of a 2-D concentric-bubble configuration is effectively extended to a 3-D coaxial jet interacting with oblique shock despite the existence of Kelvin-Helmholtz instability. [ABSTRACT FROM AUTHOR]

The aerodynamic, elastic, and inertial components in Collar's triangle of forces acting on a flexible wing with span width s=1.75 m and chord c=0.25 m are determined based on integrated optical measurements of the structural and aerodynamic response to steady and unsteady periodic inflow conditions at a chord-based Reynolds number of 2.3×105. The measurement device is a coaxial volumetric velocimeter mounted on a robotic arm, which is used to perform optical measurements of fiducial markers on the wing surface, and helium-filled soap bubbles, which are used as flow tracers. The optical measurements of the structural markers and the flow tracers are both processed with the Lagrangian particle tracking algorithm Shake-the-Box. Subsequently, physical models are used to determine the inertial and elastic forces of the aeroelastic interaction from the marker tracking results, and to determine the unsteady aerodynamic lift force from the flow velocity fields. The results of this integrated aeroelastic characterization approach are in physical agreement with each other according to the equilibrium of forces in Collar's triangle and good agreement with external reference measurements. [ABSTRACT FROM AUTHOR]

The Antarctic toothfish (Dissostichus mawsoni) is an important fishery species widely distributed in the Southern Ocean, especially in areas covered by sea ice. Understanding fish distributions and life cycles, including the transport and survival of eggs and larvae, is essential for the assessment and sustainable management of the fishery. However, owing to difficulties with in situ winter observations, information on the early life stages of D. mawsoni is lacking. Here, we investigated the transport pathways of fish eggs and larvae through a particle tracking study, using satellite‐derived ocean surface velocities in the East Antarctic region, which includes important D. mawsoni habitats and exploratory fisheries. Our results indicate that particles released from continental slopes are more likely to be successfully transported to suitable settlement grounds than those released from the BANZARE Bank (the southern region of the Kerguelen Plateau), which is situated further north and has been hypothesized to be a potential spawning ground for D. mawsoni. This study demonstrates successful source–settlement connections in relation to ocean recirculation and suggests important settlement regions for D. mawsoni larvae in the East Antarctic region. [ABSTRACT FROM AUTHOR]

[Display omitted] • Novel Hydrocyclone with circular rings introduced • CFD simulations with LES-WALE turbulence model was established to provide accurate predictions • Extensive CFD simulations done to predict performance improvements in novel hydrocylone • Attractive reductions in the bypass of fines and sharper classification observed • Number, location, size, orientation can be optimization variables for further improvements Hydrocylones offer a process intensified environment for rapid, high-throughput and relatively sharp particle classification or phase separation. One of the main performance limitations of hydrocyclone is bypassing of fines to the underflow. To address this limitation, a novel design modification of fitting thin concentric rings to the cylindro-conical section has been proposed. The Computational Fluid Dynamics (CFD) modeling based methodology has been adopted to validate the hypothesis. Predictions using Realizable k - ε , Reynolds Stress Model (RSM), and Large Eddy Simulation Wall Adopting Local Eddy viscosity (LES-WALE) turbulence models has revealed that LES-WALE matched better with the experimental observations. The experimental data included overall performance parameters and detailed observations of axial and tangential velocity profiles across the hydrocyclone. The validated CFD model and the methodology was then used to predict the behavior of the proposed designs. They established that the modifications held promise in reducing the bypass with additional benefits of sharper separation curve and finer D 50. [ABSTRACT FROM AUTHOR]

The region where the East Australian Current (EAC) separates from the coast is dynamic and the shelf circulation is impacted by the interplay of the western boundary current and its eddy field with the coastal ocean. This interaction can drive upwelling, retention or export. Hence understanding the connection between offshore waters and the inner shelf is needed as it influences the productivity potential of valuable coastal rocky reefs. Near urban centres, artificial reefs enhance fishing opportunities in coastal waters, however these reefs are located without consideration of the productivity potential of adjacent waters. Here we identify three dominant modes of mesoscale circulation in the EAC separation region (~31.5−34.5°S); the ‘EAC mode’ which dominates the flow in the poleward direction, and two eddy modes, the ‘EAC eddy mode’ and the ‘Eddy dipole mode’, which are determined by the configuration of a cyclonic and anticyclonic eddy and the relationship with the separated EAC jet. We use a Lagrangian approach to reveal the transport pathways across the shelf to understand the impact of the mesoscale circulation modes and to explore the productivity potential of the coastal waters. We investigate the origin (position and depth) of the water that arrives at the inner-mid shelf over a 21-day period (the plankton productivity timescale). We show that the proportion of water that is upwelled from below the euphotic zone varies spatially, and with each mesoscale circulation mode. Additionally, shelf transport timescales and pathways are also impacted by the mesoscale circulation. The highest proportion of upwelling (70%) occurs upstream of 32.5°S, associated with the EAC jet separation, with vertical displacements of 70–120 m. From 33 to 33.5°S, water comes from offshore above the euphotic layer, and shelf transport timescales are longest. The region of highest retention over the inner shelf is immediately downstream of the EAC separation region. The position of the EAC jet and the location of the cyclonic eddy determines the variability in shelf-ocean interactions and the productivity of shelf waters. These results are useful for understanding productivity of temperate rocky reefs in general and specifically for fisheries enhancements along an increasingly urbanised coast.

The accumulation of plastic debris on land and coastlines and in waterways and garbage patches is one of the greatest ecological concerns of the 21st century. In that context, the sources and pathways of plastic marine debris (PMD) have been increasingly studied in the past ten years. The purpose of this communication was to analyze, thanks to the tracks of two drifting buoys released in May–June 2019 in the North-East Pacific, two features encountered within the Great Pacific Garbage Patch (GPGP): a surface convergence, which could lead to the formation of plastic hotspots, and the persistency of the floating material in this area of the ocean. The evolution of the distance between the buoys was compared with the local circulation field divergence, a Lagrangian plastic dispersal model and sea-level anomalies (SLAs). These analyses highlighted the link between the converging behavior of the drifters and a persistent negative velocity divergence as well as a higher than average-encountered modelled plastic surface density (MPSD). The persistence of the material within the GPGP was observed thanks to the trajectory of the longest persisting drifter in comparison with the trajectory of the GPGP center and extent.

Intraluminal thrombus (ILT) in abdominal aortic aneurysms (AAA) has potential implications to aneurysm growth and rupture risk; yet, the mechanisms underlying its development remain poorly understood. Some researchers have proposed that ILT development may be driven by biomechanical platelet activation within the AAA, followed by adhesion in regions of low wall shear stress. Studies have investigated wall shear stress levels within AAA, but platelet activation potential (AP) has not been quantified. In this study, patient-specific computational fluid dynamic (CFD) models were used to analyze stress-induced AP within AAA under rest and exercise flow conditions. The analysis was conducted using Lagrangian particle-based and Eulerian continuum-based approaches, and the results were compared. Results indicated that biomechanical platelet activation is unlikely to play a significant role for the conditions considered. No consistent trend was observed in comparing rest and exercise conditions, but the functional dependence of AP on stress magnitude and exposure time can have a large impact on absolute levels of anticipated platelet AP. The Lagrangian method obtained higher peak AP values, although this difference was limited to a small percentage of particles that falls below reported levels of physiologic background platelet activation.

The dispersal of marine organisms is a critical process for the maintenance of biodiversity and ecosystem functioning across a seascape. Understanding the patterns of habitat connectivity that arise from the movement of multiple species can highlight the role of regional processes in maintaining local community structure. However, quantifying the probability and scale of dispersal for marine organisms remains a challenge. Here, we use a biophysical model to simulate dispersal, and we conduct a network analysis to predict connectivity patterns across scales for the community of invertebrates associated with seagrass habitat in British Columbia, Canada. We found many possible connections and few isolated habitat meadows, but the probability of most connections was low. Most habitat connections occurred within 3 days of dispersal time over short distances, indicating potential limits to long distance dispersal and little effect of species-specific dispersal abilities on the potential spatial extent of habitat connectivity. We then highlight the different roles that individual seagrass meadows can play in maintaining network connectivity. We also identify clusters of connected meadows and use these clusters to estimate the spatial scale of community dynamics. The connectivity patterns generated by our dispersal simulations highlight the importance of considering marine communities in their broad seascape context, with applications for the prioritization and conservation of habitat that maintains connectivity.

Offshore oil exploration and production in deepwater are associated with environmental risks to marine ecosystems. This research introduces DWOSM (Deep Water Oil Spill Model), a three-dimensional Lagrangian model, which is developed to simulate the transport and fate of oil spills resulting from subsea blowouts. DWOSM comprises three interconnected modules: DWOSM-DSD, which predicts the oil droplet size distribution from a blowout release; DWOSM-NearField, simulating plume dynamics and tracking oil droplets within the plume region; and DWOSM-FarField, modeling the evolution of dispersed oil beyond the near-field. Compared to other oil spill models, this integrated approach improves the transition between near and far fields using a near-field particle tracking algorithm. It also employs the thermodynamic models to enable the prediction of oil properties under varying deep water pressure and temperature. To gauge the reliability and efficacy of DWOSM, a hypothetical case situated within a North American context is employed for model testing. The DWOSM and its each module are juxtaposed with other established oil spill models. The outcomes indicate that DWOSM yields comparable results to these models by providing reasonable predictions of a deepwater blowout. The model's verification through case scenario testing and comparison underscores its potential as a decision tool for assessing and managing the potential environmental impacts of offshore petroleum activities. [Display omitted] • A new integrated deepwater oil spill model is developed in this study. • The model numerically captures the intricate dynamics of deep-sea oil blowouts. • Thermodynamic, physical, and chemical evolution of oil droplets are considered. • The coupling of near- and far-field models is tested through field scenarios. • New model excels other toolkits in systematically assessing Deepsea explorations. [ABSTRACT FROM AUTHOR]

Penetration of droplets in fully-developed turbulent pipe flows (vertical configuration) was studied numerically. Two Reynolds numbers (R e D = 37,700 and 11,700) based on the pipe diameter were used in the simulations. Statistics used in the single-phase flow characterization (mean velocities, root mean square fluctuation velocities, and turbulence dissipation rate) were obtained from the law of the wall relationships in addition to curve-fitting from direct numerical simulation (DNS) data found in the literature. The droplet phase was simulated using a one-way coupling Lagrangian random-walk eddy interaction model (EIM). Monodispersed droplets, ranging from 1.78 to 26. 83 μ m , were released separately in the pipe-flow computational domain. A modified eddy lifetime, based on local turbulent Reynolds numbers (R e λ T ) and velocity fluctuations perpendicular to the walls, is proposed. Simulation results of droplet penetration show relatively good agreement against experimental data obtained from the literature. • In-depth analysis of droplet penetration in turbulent pipe flows was performed. • One-way coupling Lagrangian random-walk EIM (eddy interaction model) was employed. • Two Reynolds numbers and their effect on droplet penetration were investigated. • Conventional modelling of eddy velocity and time scales has limitations. • Innovative semi-empirical time scales based on Taylor microscales were proposed. [ABSTRACT FROM AUTHOR]

Particle deposition dynamics in a fully developed turbulent channel flow at a friction Reynolds number of R e τ = 180 for two Stokes numbers (S t = 1 and 10) are investigated using the point particle-direct numerical simulation (PP-DNS) method, considering dilute system and thus, one-way coupling. In particular, the interplay between particle size, particle property (density) and deposition at the same Stokes number has been investigated. It turns out that the dimensionless particle relaxation time (the Stokes number) alone does not provide enough information to capture the deposition dynamics, and particle size (diameter) and density need to be considered to obtain a more comprehensive understanding of deposition process. Furthermore, we demonstrate that gravity significantly alter the deposition patterns of particles with different size and density differently, even if the Stokes number does not change, and therefore the results from zero gravity cannot be extrapolated to non-zero gravity settings, even for small particles. Finally, our results suggest that wall-normal particle velocity variance at the wall plays an integral role in the deposition process, as it approaches a finite value (significantly larger than particle mean velocity) at the wall. [Display omitted] • Lif and gravity could significantly alter the particle deposition dynamics. • Results from zero-gravity settings cannot be extrapolated to non-zero gravity. • Stokes number alone does not provide enough data to describe deposition dynamics. • Particle velocity variance at the wall is the major mechanism in deposition. [ABSTRACT FROM AUTHOR]

The transport of virus-laden particles was investigated numerically in an archetypical supermarket configuration of area 1,200 m2 and ceiling height of 4.5 m. The particles were tracked using a Lagrangian particle tracking code coupled with the computational fluid dynamics (CFD) model Ansys Fluent. Air transport was assumed to occur due to indoor ventilation. Flow dynamics were simulated using the Reynolds-averaged Navier Stokes (RANS) approach. The movement and spreading of 5- and 20-μm particles were studied with 0%, 25%, and 100% attachment efficiencies on surfaces in the supermarket. We found that the indoor airflows can significantly enhance the transport of particles (e.g., >15 m for 5 μm , and >5 m for 20 μm); therefore, the 6-ft (2.0 m) social distance recommended by health experts would not be sufficient to prevent the transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). We found that the attachment on surfaces reduces the transport of particles significantly within the supermarket, and that an attachment efficiency of 25% results in transport similar to that resulting from 100% efficiency. This suggests that the type of surfaces is not crucial in terms of air transport of particles. We support the existing approaches for reducing exposure between people through the adoption of one-way movement within an aisle. However, we also propose placing display shelves within the aisles in a staggered way to form baffles that would both increase the surface area and block the transport of airborne particles. We found that virus-laden particles could be sucked into the ventilation system through return vents, and could pose potential infection risks for the buildings connected to the same ventilation system. Hence, high-efficiency particulate air (HEPA) filters and pleated filters with a minimum efficiency reporting value (MERV) greater than 12 are recommended. [ABSTRACT FROM AUTHOR]

The dispersion of oil droplets in rivers was numerically investigated for uniform flow in a hypothetical wide river with a depth of 3.0 m. The river hydrodynamics profile was used in conjunction with the VDROP model to produce the oil droplet size distribution (DSD), whereas the NEMO3D model was used to track the movement of the oil droplets. Results suggest that the gradient of eddy diffusivity significantly affected the upward-normal (i.e., quasi-vertical) transport of the droplets, and caused them to mix rapidly through the depth. We also found that an increase in buoyancy resulted in a decrease in the streamwise variance and spreading coefficient. Oil droplets broke up due to the relatively large energy dissipation rates in the river at approximately 1.0 m below the surface and deeper. The droplet breakup varies DSD in the river water column, which may subsequently affect other chemo-physical processes (e.g., oil-particle aggregation). The breakup efficiency is affected by a system-dependent parameter Kb , which reflects the uncertainty of a system. The steady-state DSD was bimodal for the case Kb=0.05 , whereas it was unimodal for larger Kb values (i.e., Kb=1.0 and 0.25), respectively. More small-sized droplets were generated and persisted in the deep-water column with larger Kb values. The droplet breakup also enhanced the streamwise spreading of the plume. The effect of droplet entrainment on oil dispersion was studied by assuming constant entrainment probabilities of surface oil droplets. The oil DSD varied with different droplet entrainment probabilities, and the number of oil droplets generated in the water column decreased significantly with a decrease in the entrainment probability of the oil droplets. [ABSTRACT FROM AUTHOR]

Simulations of spray breakup are challenging due to a wide range of different length and time scales. While Volume-of-Fluid (VoF) is suited for the primary breakup, the secondary breakup and the dilute spray cloud is better resolved using a Lagrangian particle tracking (LPT) method. This publication proposes a 3D coupling between both models using the CFD software OpenFOAM to resolve the complete process of spray atomization. Combined with adaptive mesh refinement, the computational cost can be reduced significantly. The simulation of a fuel jet in crossflow demonstrates the accuracy and speedup of the proposed method.

A major challenge in the operation and development of the high-head water resources, especially in the mountains with high sediment yield, is the erosion of Pelton turbine components. In this work, a numerical study was carried out based on sediment properties measured in field conditions, such as particle distributions and concentrations, to analyze the erosion mechanism of a prototype Pelton turbine injector. The Volume of Fluid (VOF) method was combined with a Lagrangian particle tracking approach to simulate the air-water-sediment flow, followed by the application of Mansouri's model to estimate the erosion. The predicted erosion patterns were in good agreement with field observations, especially in physically reproducing the asymmetrical erosion distribution on the needle surface. To elucidate this asymmetry, fundamental analysis of the flow patterns including the vortex structures and the secondary flow on the particle behaviors was carried out. Interestingly results were found about the secondary flow induced by the von Kármán vortex shedding, which increased the particle separations, and consequently, enhanced the erosion in shedding areas. The current work may provide important engineering insights to reduce erosion of components with inner obstructions. • Numerically reproduced the asymmetrical erosion on Pelton turbine injectors. • Erosion was enhanced by stronger particles separations in the vortex shedding areas. • The secondary flow from von Kármán vortex shedding increased particle separations. [ABSTRACT FROM AUTHOR]

Oil dispersion under a deep-water plunging breaker of height 0.15 m was studied by coupling the Lagrangian particle tracking code (NEMO3D) with the population balance model (VDROP). The wave hydrodynamics obtained in Part I (Cui et al. in Environ Fluid Mech 2020 (in press)) was used as input. It was observed that droplet inertia and major forces on droplets significantly impacted the transport of oil droplets under wave conditions, and neglecting it caused less entrainment into the water column and horizontal spread of oil plume. For droplets less than 400 microns, the droplet size distribution (DSD) tended to follow a power-law distribution with an exponent close to − 2.3, which was consistent with earlier experimental observations by Delvigne and Sweeney (Oil Chem Pollut 4(4):281–310, 1988). The distribution of large size droplets evolved with time and showed agreement with a power-law distribution having an exponent of − 9.7 about 20 s after the passage of the wave train. Reducing the interfacial tension enhanced droplets breakup and increased the exponent of power-law distribution to − 6.1 for droplets smaller than 400 microns. It was also found that neglecting the vertical gradient of eddy diffusivity led to the accumulation of oil droplets in low eddy diffusivity regions at the bottom part of the wave breaker. The investigation herein could be used to obtain design values for breakers that could be used in oil spill models to predict the oil droplet size distribution. [ABSTRACT FROM AUTHOR]

The multi-phase Rayleigh–Bènard convection has been weakly investigated, even though it plays a leading role in the theoretical and applied physics of the heat transfer enhancement. For the case of moderate turbulent convection, a rather unexpected result is an unusual kind of wind reversal, in the sense that the fluid is found to be strongly influenced by the bubbles, whereas the bubbles themselves appear to be little affected by the fluid, despite the relative smallness of the Stokes numbers. The wind reversal induced by the bubbles dispersed in the fluid is a new and remarkable phenomenon in multi-phase flows that provides further perspectives in understanding the complex physics leading the enhancement of thermal convection. For this reason, the fundamental research proposed in this paper aimed to identify a space of control parameters and the physical mechanisms responsible for the wind reversal induced by dispersed bubbles in a confined convective flow. The strength of the following description lies in an innovative numerical approach, based on the multi-scale physics induced by the coupling of the local thermal and mechanical mechanisms arising between each bubble and the surrounding fluid. The continuous phase has been solved numerically using the direct numerical simulation (DNS) technique and each bubble has been tracked by means of a particle Lagrangian model. [ABSTRACT FROM AUTHOR]

In this paper, we present a generic, scalable and adaptive load balancing parallel Lagrangian particle tracking approach in Wiener type processes such as Brownian motion. The approach is particularly suitable in problems involving particles with highly variable computation time, like deposition on boundaries that may include decay, when particle lifetime obeys exponential distribution. At first glance, Lagranginan tracking is highly suitable for a distributed programming model due to the independence of motion of separate particles. However, the commonly employed Decomposition Per Particle (DPP) method, where each process is in charge of a certain number of particles, actually displays poor parallel efficiency due to the high particle lifetime variability when dealing with a wide set of deposition problems that optionally include decay. The proposed method removes DPP defects and brings a novel approach to discrete particle tracking. The algorithm introduces master/slave model dubbed Partial Trajectory Decomposition (PTD), in which a certain number of processes produce partial trajectories and put them into the shared queue, while the remaining processes simulate actual particle motion using previously generated partial trajectories. Our approach also introduces meta-heuristics for determining the optimal values of partial trajectory length, chunk size and the number of processes acting as producers/consumers, for the given total number of participating processes (Optimized Partial Trajectory Decomposition, OPTD). The optimization process employs a surrogate model to estimate the simulation time. The surrogate is based on historical data and uses a coupled machine learning model, consisting of classification and regression phases. OPTD was implemented in C, using standard MPI for message passing and benchmarked on a model of 220 Rn progeny in the diffusion chamber, where particle motion is characterized by an exponential lifetime distribution and Maxwell velocity distribution. The speedup improvement of OPTD is approximatelly 320% over standard DPP, reaching almost ideal speedup on up to 256 CPUs. [ABSTRACT FROM AUTHOR]

• Model nano-particle deposition in Laminar annular pipe flows. • Develop a new corrolation for particle deposition based on CFD simulations. • 3D simulation of Brownian diffusion of ultrafine particles. • Study on the effect of geometrical parameters, flow rate and particle size. The transport and deposition of nano-particles in annular pipe flows under laminar conditions were studied. The Lagrangian particle tracking method was used to simulate the Brownian diffusion of ultrafine solid particles in a three-dimensional domain. The effects of nano-particle size, flow rate, inner and outer pipe diameters, pipe length, and temperature were studied. The computational models for the deposition of nano-particles in tubular, as well as annular pipe flows, were validated. Furthermore, using the CFD simulations and the Lagrangian particle tracking results, a new correlation for evaluating the deposition fraction of nano-particles in annular pipe flows was developed. The presented results could provide guidelines for evaluating nano-particle transport and deposition in annular pipes. [ABSTRACT FROM AUTHOR]

The polar cod (Boreogadus saida) in the Barents Sea is one of the main stocks of this species in the Arctic, reaching a total biomass of almost 2 million tonnes in some years. It has been fluctuating considerably in abundance, and in recent years, it has been at a low level. Only small catches have been taken from the stock over the last four decades, and consequently, the observed variation in abundance must be caused by natural (environmental and/or biological) changes in the ecosystem. Sea temperatures have been rising in the Barents Sea in recent years, possibly causing changes to the living conditions of this true Arctic stock. Consequently, there is a need for investigating how the observed changes might affect polar cod in this area. One important aspect of the environmental impact on the stock is possible effect on the recruitment, which has been varying considerably from year to year. In this modelling study, we thus recreate and analyse the environmental and developmental histories of the observed 0-group individuals in the Barents Sea (young of the year), with emphasis on the importance of ice cover, ice breakup time, maximum temperature, and spawning stock biomass. Our simulations indicate that the environmental conditions experienced by individuals successfully "recruited" to the 0-group are characterized by high ice concentration well into summer, and low temperatures throughout the pelagic juvenile phase, and any perturbations from the Arctic ocean climate typically found in the northern and eastern Barents Sea appears to be detrimental to stock recruitment. In light of the projected warming of the Barents Sea in the next decades and the potential reduction in ice cover, this will entail, the mechanisms investigated herein might lead to future marginalization of polar cod in the Barents Sea. [ABSTRACT FROM AUTHOR]

The three-dimensional hydrodynamic model was established based on FVCOM, coupled with the Lagrangian particle tracking module to study the water exchange ability of 15 drain outlets of North and South Changshan Island. Meanwhile, the 30-day influence distance was introduced to quantify the water exchange ability. The drain outlets with a strong water exchange capacity are mainly located in the east of North and South Changshan Islands and the southwest corner of South Changshan Island, and those with a weak water exchange capacity are mainly located in the northwest corner of North Changshan Island, joint of South Changshan Island and the tombolo dyke and inside the Changdao Harbor. The 30-day influence range of the 15 drain outlets of North and South Changshan Islands is significantly affected by monsoon. East Asian monsoon accelerates the dispersion of the pollutants in the south sea areas of Bohai Strait. [ABSTRACT FROM AUTHOR]

In a recently conducted study, we developed a nano-particle sizer (NPS) that consists of a multi-port differential mobility analyzer (MP-DMA) and two multi condensation particle counters (M-CPCs) for achieving fast measurements of aerosol particles; however, the performance of MP-DMA was not detailed in the study. Therefore, the objective of this study is to perform numerical simulations to obtain the transfer function of each port in the MP-DMA, which is the main component of the NPS. We observed good agreement between the numerically obtained central particle size of each port and the experimental data under the same operating conditions. The transmission probability and resolution of each port were determined and analyzed under various conditions using the transfer function. The findings of this study shall help in understanding the advantages of NPS. Unlabelled Image • Simulations on the MP-DMA in the newly developed real-time NPS were conducted. • A Lagrangian particle tracking with a flow rate weighted method was used. • Transfer functions of the MP-DMA were obtained for the performance evaluation. • Numerical transmission probability decreases with the increasing port number. • Increasing half-width of transfer function due to reducing aerosol/sheath ratio. [ABSTRACT FROM AUTHOR]

The transport of oil droplets following a surface oil spill was investigated using a uniform vertical eddy diffusivity model and the K‐profile parameterization model, which assumes a maximum K value at 1/3 depth of the mixed layer. The initial droplet size distribution was obtained based on the Delvigne and Sweeney (1988, https://doi.org/10.1007/s13131‐013‐0364‐7) model. Using a uniform eddy diffusivity Kave, an exact analytical solution was used to produce the transient and steady state profile of the concentration of droplets of all sizes. It was found that the concentration at the surface is proportional to the droplet rise velocity and inversely proportional to Kave. Thus, small droplets (smaller than 100 μm) do not persist at the water surface. It was found that K‐profile parameterization produces smaller concentrations at the water surface than the uniform K model. The impact of waves was introduced into the K‐profile parameterization model through a roughness height, zo, that is comparable to the wave height. The investigation herein reveals that the Delvigne and Sweeney approach, commonly used in oil spill modeling, is not sufficient to predict the oil droplet size distribution, and that one needs to use a vertical eddy diffusivity to accurately predict the transport in the following hours and days. A new dimensionless formulation was provided to generalize the results, and showed that transport depends on three major parameters, the water friction speed, the mixed layer depth, and the droplet diameter. Plain Language Summary: Oil slicks at sea form oil droplets that get transported into the water column based on their size (buoyancy) and the vertical mixing at sea, as governed by the eddy diffusivity (K) profile. We explored using a uniform K and the well‐known K‐profile parameterization model. The uniform K profile provided fundamental relations between the size of each droplet and the level of turbulence. It was found that the concentration of a given oil droplet size is proportional to the rise velocity and inversely proportional to K. Based on the Stokes' laws, the concentration at the sea surface is proportional to the square of the droplet diameter. Therefore, the concentration of 5‐μm droplets (for example) is 100 times smaller than the concentration of 50‐μm droplets. The K‐profile parameterization model was found incapable of transporting droplets below the surface due to turbulence, which is not realistic; hence, a parameter is applied to the amended model to account for the impact of waves. A dimensionless formulation was introduced and it shows that two sea systems of various wind speeds, mixed layer depth, and droplet size could be equivalent. Therefore, one could use it to design experiments and/or to interpret sea observations. Key Points: The oil droplet distribution at the ocean surface is proportional to the rise velocity and inversely proportional to the eddy diffusivityThe KPP model provides smaller concentrations at the water surface compared to uniform K. The impact of wave roughness was consideredA dimensionless formulation was provided to generalize the results [ABSTRACT FROM AUTHOR]

Lagrangian particle tracking and Large-Eddy simulation were used to assess the effect of different fuels on spray characteristics. In such a two-way coupled modeling scenario, spray momentum accelerates the gaseous phase into an intense, multiphase jet near the nozzle. To assess fuel property effects on liquid spray formation, the non-reacting Engine Combustion Network Spray A baseline condition was chosen as the reference case. The validated Spray A case was modified by replacing n -dodecane with diesel, methanol, dimethyl ether, or propane assuming 150 MPa injection pressure. The model features and performance for various fuels in the under-resolved near-nozzle region are discussed. The main findings of the paper are as follows. (1) We show that, in addition to the well-known liquid penetration (L liq) , and vapor penetration (L vap) , for all the investigated fuels, the modeled multiphase jets exhibit also a third length scale L core , with discussed correspondence to a potential core part common to single phase jets. (2) As a characteristic feature of the present model, L core is noted to correlate linearly with L liq and L vap for all the fuels. (3) A separate sensitivity test on density variation indicated that the liquid density had a relatively minor role on L liq . (4) Significant dependency between fuel oxygen content and the equivalence ratio (Φ) distribution was observed. (5) Repeated simulations indicated injection-to-injection variations below 2% for L liq and 4% for L vap . In the absence of experimental and fully resolved numerical near-nozzle velocity data, the exact details of L core remain as an open question. In contrast, fuel property effects on spray development have been consistently explained herein. [ABSTRACT FROM AUTHOR]

Numerous dolphins are found dead on beaches and waterways of the Gulf of Mexico and Mississippi Sound every year. In 2019 an unusual mortality event (UME) occurred when 337 deceased bottlenose dolphins were stranded between Louisiana, Mississippi, Alabama, and Florida. According to NOAA, based on observations of skin lesions or distinct ulcerative dermatitis and other internal pathologic findings and the environmental conditions during that period of time, the identified cause of this UME was determined to be protracted exposure to low salinity waters. Dolphin carcasses are often found stranded on beaches days after they die. Consequently, their initial place of death is unknown. In this study, an existing 2D hydrodynamic model (EFDC+ 11.2) of the Mississippi Sound simulated by Armandei et al. (2021) was used to track dolphin carcass movement and to simulate salinity at the time and location of each predicted dolphin's death. Particles within the Lagrangian particle tracking module were used to represent the movement of 19 dolphin carcasses. A large number of particles (virtual dolphin carcasses) were seeded throughout the model domain and tracked for five days. These results were used to hindcast each dolphin's original location of death. The results indicate that the most likely place of death for 12 dolphins stranded on the beaches of Mississippi, along with the two found on Ship and Horn Islands, was west of their stranding location., For both of the dolphins stranded on Dauphin Island, the most likely place of death was in the Mobile Bay area north of where they were found. The remaining three dolphins found dead on barrier islands, most likely originally died in close proximity to their stranding locations. The average simulated salinity of all the dolphins' most probable original place of death was below five except for two cases. These results are compared to the salinity of the Mississippi Sound during Bonnet Carré spillway opening and non-opening dates. The results highlight the significant impact of the spillway's opening on the reduction of salinity and its association with dolphin mortality. [Display omitted] • A 2D hydrodynamic and water quality model of the Mississippi Sound and Mobile Bay region simulated in EFDC+ was used. • Lagrangian Particle tracking was employed to hindcast freshly dead dolphins origins of death in 2019. • The average simulated salinity of the origins of dead was obtained to analyze the effect of salinity on dolphins mortality. • Analysis was carried out to evaluate how the BC spillway opening affected the salinity levels at the origins of death. [ABSTRACT FROM AUTHOR]

• Freshwater plume from four bays along the Texas-Louisiana coast were reproduced. • Wind induced volume/salt fluxes through four bays were calculated and compared. • Hurricane Harvey resulted in a maximum of 5000 m3/s more water volume fluxes. • Particles released from bays were blown further eastward by up to 170 km to the max. • Vermilion Bay has the longest residence time of 34 days pre-, and 5 days post-Harvey. Hurricane Harvey (2017) delivered an extraordinarily large amount of freshwater, sediment, and pollutants to the Texas-Louisiana (TX-LA) coastal ocean. While the impact of extreme precipitation and river discharge on the freshwater plumes has been investigated, the role of winds has rarely been addressed. Using a 3D creek-to-ocean mode, SCHISM, we conducted numerical experiments including/excluding wind effects and quantitatively assessed the wind impacts on the freshwater plumes from four estuarine bays along the TX-LA coast including Galveston Bay, Sabine Lake, Calcasieu Lake, and Vermilion Bay. Our results indicate the important role of wind in shaping the freshwater plumes and circulations around the four bays, and highlight the wind induced circulations in the four bays under varying wind conditions during Hurricane Harvey from August 26 to September 2, 2017. In addition, the volume and salt fluxes between these bays and the coastal ocean are compared between the experiments with or without wind. In addition, a Lagrangian particle tracking is used to track pollutants released from these bays. The wind is found to exert a great impact on the trajectories of the particles released from Galveston Bay, Sabine Lake, and Calcasieu Lake, extending the particles 10–50 km further southward (seaward) and 50–100 km westward compared to the case without wind. For Vermilion Bay, particles would not have been transported outside of the bay without wind but were transported 170 km westward away from the bay with wind. Lastly, the residence times in the four bays are calculated. Vermilion Bay has the longest residence time pre- (∼34 days) and post-Hurricane (∼5 days). Our results demonstrate that the wind associated with Hurricane Harvey had a significant impact on the exchange between the estuarine bays and the coastal ocean along the TX-LA coast. [ABSTRACT FROM AUTHOR]

• The presence of solid beds in turbulent pipe flows results in secondary fluid motions which impacts particle transport dynamics. • Streamwise vorticity due to corners in the cross-sectional plane of pipes is increased as the pipe bed height increases. • Particles are influenced by the secondary flows, with particles in a half-pipe less likely to concentrate near the upper walls. • The secondary flows also modify the deposition and resuspension rates of particles, particularly near the corners of the bed. Turbulent particle-laden flows in pipes can result in particle deposition leading to the formation of solid beds. The presence of such beds modifies the flow field, resulting in secondary motions in the plane of the pipe cross-section, which in turn impact particle transport. In this work turbulent pipe flows with equal mass flow rates and solid beds of height H b = 0 (full pipe), 0.5 R (three-quarter pipe), and R (half pipe) are predicted using direct numerical simulation, with the beds represented simplistically as flat surfaces. The particulate phase is one-way coupled to the flow at a volume fraction of 10−3 and particle motion is solved for using a Lagrangian point-particle approach. The Reynolds numbers computed based on bulk velocity and equivalent pipe diameter for the full, ¾ and, ½ pipes are 5,300, 5,909 and 7,494, respectively. The same particle size is used in all the simulations and their respective Stokes numbers, based on the shear timescale, are 0.5, 1.2 and 1.9, respectively. The results for flows with beds show that the fluid flow exhibits secondary vortices and an increase in the mean streamwise vorticity caused by corners in the cross-sectional plane of the pipes, with their intensity near the upper curved wall increasing with H b. However, the upper vortices remain relative weak compared to those in lower regions of the pipes. The increase in mean streamwise vorticity in the half pipe is larger than that in the three-quarter pipe near the upper curved wall, while similar near the flat pipe floor due to the resistance of the curved wall to secondary motions. The movement of the particles in the cross-sectional plane is consistent with that of the secondary flows, but with slightly lower velocities. In regions near the wall away from the pipe corners, particle concentration in the half pipe is lower than in the three-quarter pipe, most likely due to its thinner boundary layer. This is reversed for concentration maxima near the pipe corners because of the magnitude of the secondary flows. Finally, the secondary flow changes the deposition or resuspension rate of the particles, particularly near the pipe corners, but these are always less than equivalent rates in the full pipe flow, which is likely caused by the magnitude of the wall unit. [Display omitted] [ABSTRACT FROM AUTHOR]

A number of studies have illustrated the utility of environmental DNA (eDNA) for detecting marine vertebrates. However, little is known about the fate and transport of eDNA in the ocean, thus limiting the ability to interpret eDNA measurements. In the present study, we explore how fate and transport processes affect oceanic eDNA in Monterey Bay, CA, United States (MB). Regional ocean modeling predictions of advection and mixing are used for an approximately 10,000 km2 area in and around MB to simulate the transport of eDNA. These predictions along with realistic settling rates and first-order decay rate constants are applied as inputs into a particle tracking model to investigate the displacement and spread of eDNA from its release location. We found that eDNA can be transported on the order of tens of kilometers in a few days and that horizontal advection, decay, and settling have greater impacts on the displacement of eDNA in the ocean than mixing. The eDNA particle tracking model was applied to identify possible origin locations of eDNA measured in MB using a quantitative PCR assay for Northern anchovy (Engraulis mordax). We found that eDNA likely originated from within 40 km and south of the sampling site if it had been shed approximately 4 days prior to sampling.

• Turbophoresis results in particles accumulating in areas near the wall and channel center. • Turbophoresis leads to the complex distribution of radioactive decay. • The radioactivity loss due to deposition and decay was obtained for different nuclides. This paper aims at radiation monitoring and activity inversion when radionuclides are transported in duct or a pipe. The Lagrangian trajectory model was established, and a quick numerical method was used to simulate radioactive aerosols transport and radioactive decay in a wall-bounded flow. Total 12 cases were studied in the simulation according to the particle diameter and density. The dimensionless deposition velocity has been validated by comparing with Wood's predictions and the experienced gravitational settling velocity. The results show that turbophoresis has a significant effect on particle transport in the wall-bounded flow, leading to particles migration and concentrating near the wall or channel center. It will cause particles to move with different velocities in the streamwise direction, so that their residence times in channel will be complexly distributed. In addition, the gravity settling will enhance the disequilibrium of particle distribution. The activity losses are obtained in detail including particle deposition ratio and radioactive decay. One radionuclide with half-life 7 s was employed in simulation, and the activity error between the estimated and initial values is up to about 40%. The activity error decreases if the half-life becomes large. When the half-life is 7.5 and 0.5 times larger than the mean time spent by airflow through the channel if the gravity is considered or not respectively, the final activity error will be less than ±5% in the present simulation setup. [ABSTRACT FROM AUTHOR]

Hydropower projects have changed the physical habitat of rivers, which has a serious impact on the survival of local fish. The reproduction of fish producing semi-buoyant eggs requires a specific hydrodynamic condition. To predict the influence of cascade hydropower development on the reproductive process of fish with semi-buoyant eggs, a MIKE 21 Flow Model was applied. Lagrangian particle tracking was used to simulate the movement of semi-buoyant eggs and larvae using the Agent-based Modeling (ABM) lab module. The calibrated model showed good agreement between the simulated and observed data for the hydrodynamic process in the reservoir. Twelve scenarios were defined to fully understand whether fish with semi-buoyant eggs can reproduce naturally. The results showed the following: (1) It is difficult to form a fish migration passage in the reservoir in all potential scenarios. (2) Semi-buoyant eggs and larvae sank to the bottom and perished before they hatched and were old enough to survive, since the hydrodynamic conditions could not meet the minimum flow velocity required to keep them in the drift. (3) Even if the hydrodynamic conditions can keep them in the drift in impossible high-discharge conditions, there was not enough drifting time and distance in the reservoir. The results implied that fishes with semi-buoyant eggs cannot reproduce naturally in the main stream, but it is possible that they can reproduce successfully after the protection of the tributary. The method is transferrable to other locations via establishment of models with relevant data to a particular area. Unlabelled Image • It is difficult to form a fish migration passage in the reservoir in all potential scenarios. • Semi-buoyant eggs and larvae sank to the bottom and perished before they hatched and were old enough to survive. • It is possible that fish with semi-buoyant eggs can reproduce successfully after the protection of the tributary. [ABSTRACT FROM AUTHOR]