Search

Neurological complexities resulting from surgery requiring cardiopulmonary bypass (CPB) remain a major concern, encompassing a spectrum of complications including thromboembolic stroke and various cognitive impairments. Surgical manipulation during CPB is considered the primary cause of these neurological complications. This study addresses the overall lack of knowledge concerning CPB hemodynamics within the aorta, employing a combined experimental-computational modeling approach, featuring computational fluid dynamics simulations validated with an in vitro CPB flow loop under steady conditions. Parametric studies were systematically performed, varying parameters associated with CPB techniques (pump flow rate and hemodiluted blood viscosity) and properties related to formed emboli (size and density). This represents the first comprehensive investigation into the individual and combined effects of these factors. Our findings reveal critical insights into the operating conditions of CPB, indicating a positive correlation between pump flow rate and emboli transport into the aortic branches, potentially increasing the risk of stroke. It was also found that larger emboli were more often transported into the aortic branches at higher pump flow rates, while smaller emboli preferred lower flow rates. Further, as blood is commonly diluted during CPB to decrease its viscosity, more emboli were found to enter the aortic branches with greater hemodilution. The combined effects of these parameters are captured using the non-dimensional Stokes number, which was found to positively correlate with emboli transport into the aortic branches. These findings contribute to our understanding of embolic stroke risk factors during CPB and shed light on the complex interplay between CPB parameters. [ABSTRACT FROM AUTHOR]

By adopting FVCOM-simulated 3-D physical field and based on the biological processes of chub mackerel (Scomber japonicus) in its early life history from the individual-based biological model, the individual-based ecological model for chub mackerel at its early transport dynamics in the Yellow Sea was constructed through coupling the physical field from April to August with the biological model by the method of Lagrange particle tracking.The results showed that the model can accurately simulate the transport path、density and retention distribution of eggs and larvae of chub mackerel in the spawning ground in Qingdao Shidao offshore in the Yellow Sea.The study found that under average climate conditions, chub mackerelin the spawning ground in Qingdao Shidao offshore was overall transported to the southern part of Shandong Peninsula after spawning, eggs and larvae of chub mackerel were finally distributed in the range of 32°N-37°N and 121°E-124°E, and had a large distribution in the waters of the provisional measures of the China-Korea Fisheries Agreement(hereinafter referred to as the waters of the Agreement). Since spawning in April, some eggs and larvae of chub mackerel have begun to enter the waters of the Agreement, and from July to August, 50% of the super-individuals have entered the 40-80 m isobath in the waters of the Agreement and have been stranded for more than 300 hours, illustrating the spawning ground in Qingdao Shidao offshore contributes significantly to the replenishment of chub mackerel resources in the waters of the Agreement.The biopatch density and retention area of eggs and larvae of chub mackerel were mainly concentrated in the sea area of 33.5°N-37.5°N and 121°E-124.5°E, and this sea area was determined to be the main fattening ground for larvae of chub mackerel in the Yellow Sea, and 3/5 of the fattening ground was in the waters of the Agreement, indicating that the physical environment of the waters of the Agreement had a great impact on the replenishment of chub mackerel resources in the spawning ground in Qingdao Shidao offshore. There were obvious differences in the transport distribution of eggs and larvae of chub mackerel in different years, and the main dynamic reason for the interannual difference in the transport distribution of chub mackerel in the Yellow Sea is the location of the cold center of the Yellow Sea Cold Water Mass. [ABSTRACT FROM AUTHOR]

Habitat suitability modeling is a commonly used methodology to plan and assess in‐stream habitat enhancement in rivers, such as for the key fish life stages spawning and juvenile development. However, their use only allows modeling the spatial distribution of habitats, but not their connectivity. By integrating micro‐scale habitat modeling and a larval drift model, we assess the functional connectivity between spawning and larval nursery habitats for four rheophilic and litophilic fish species in a channelized and hydropower impacted reach of the lower Inn River (Bavaria, Germany), in which two restoration measures, a bypass channel and an island side‐channel system, have been constructed to improve longitudinal connectivity and habitat conditions. The study aims to (a) map spawning and larval nursery habitats, (b) quantify their connectivity, and (c) optimize functional habitat connectivity through an alternative bypass channel location. Results show that the channel's morphological complexity influences quantity and quality of available spawning and nursery habitats and their connectivity. Despite the presence of nursery habitats across the analyzed channel, the slow lateral larval dispersion during drift limits their accessibility to only the left river bank, making only 33% of available habitats useable. The degree of functional connectivity and hence the percentage of useable habitats can however be increased up to 95.3 % when considering different spatial configurations of habitats, which were explored in two alternative restoration scenarios. The results demonstrate the importance of considering functional habitat connectivity in habitat assessments and restoration planning. Key Points: Spawning to nursery functional habitat connectivity was quantified using a larval drift modelMorphological complexity affects habitat availability and functional connectivityConnectivity can be improved by optimizing spatial distribution of spawning sites [ABSTRACT FROM AUTHOR]

The Paluch diagram is a widely used tool for interpreting aircraft measurements of shallow cumulus clouds. A prior study conducted by Heus et al. (2008, https://doi.org/10.1175/2008jas2572.1) concluded that the source levels of in‐cloud air inferred from the Paluch diagram exhibit biases, sometimes of several hundred meters, in comparison to those derived from Lagrangian particle tracking. In this short study we revisit this comparison. The results indicate that the upper source levels of in‐cloud air determined from the Lagrangian Particle Tracking and the Paluch diagram are consistent, and the choice of statistical methods is crucial. The significance of this research lies in confirming the reliability of the Paluch analysis, enabling its confident application to aircraft data. Plain Language Summary: The Paluch diagram is a commonly used tool for studying clouds using aircraft data. Earlier studies showed differences in upper source levels of in‐cloud air estimated from the Paluch diagram and another method called Lagrangian particle tracking. The current study rechecked this and found that both methods agree on inferring upper source levels of in‐cloud air. This confirmation is important because it demonstrates that we can rely on the Paluch diagram for studying clouds using aircraft data. Key Points: Prior research highlighted discrepancies in source level estimation of in‐cloud air using Paluch diagram versus Lagrangian Particle TrackingWe re‐examined and found consistent alignment of in‐cloud air's upper source levels using Lagrangian Tracking and the Paluch diagramSelecting the appropriate statistical methods is vital for accurately determining upper source levels of in‐cloud air [ABSTRACT FROM AUTHOR]

Introduction: Bivalve aquaculture is an important pillar of China's fisheries, with over 1 million tonnes of scallop shells produced annually. However, most of these shells are directly discarded into the sea, leading to continuous pollution of the marine and coastal environments, especially the coast of Yantai in the Bohai Sea where a large number of discarded scallop shell have accumulated. Methods: To trace the fate of scallop shells in the ocean, this study established a model for the transport of scallop shells, coupling a two-dimensional tidal current model using the adjoint method with a Lagrangian particle model. By simulating nested tidal models, the distribution of tidal residual current in the Yantai coastal region was obtained. Then, a Lagrangian particle model was used to track the transport pathways of pollutants in the sea. Results: Driven by the residual current calculated from the tidal model with the actual situation, possible pollutant release areas were inferred. The results of Lagrangian particle tracking experiments indicate that pollutants were released from the upstream accumulation area, specifically the area near Penglai Hulushan, confirming previous speculation. Discussion: The scallop shells transport model can accurately simulate the spatiotemporal profile of scallop shells, which is helpful for managing scallop shell resources and improving the level of shell reuse. [ABSTRACT FROM AUTHOR]

Route planning to evade potential pollution holds critical importance for aquaculture vessels. This study establishes a fish-feed pollutant drift model based on the Lagrangian particle tracking algorithm and designs four sets of sensitivity experiments in the East China Sea. The research investigates the impact of model input uncertainties on the drift trajectory, centroid position, and sweeping area of the fish-feed pollutants. Numerical results indicate that the uncertainty in the background flow field significantly affects the uncertainty in the centroid position and sweeping area in the numerical simulations. Specifically, when a 35% random error is added to the background flow field, the centroid shift distance reaches its maximum, and the sweeping area also attains its largest value. The uncertainty in the background wind field affects the centroid position of particles but to a much lesser extent compared to the background flow field. When considering only the uncertainty of the background wind field, the sweeping area does not significantly differ from the control experiment as the uncertainty of the background wind field increases. The initial release position has little effect on the drift direction of the fish-feed pollutants but does affect the drift distance; it has minimal impact on the trajectory but significantly affects the final position of the pollutant centroid. By analyzing the model uncertainties, this study reveals the key factors influencing the drift of fish-feed pollutants. This information is crucial for aquaculture vessels in planning routes, considering environmental factors, and reducing potential pollution risks. [ABSTRACT FROM AUTHOR]

Complex flows are often characterized using the theory of Lagrangian coherent structures (LCS), which leverages the motion of flow-embedded tracers to highlight features of interest. LCS are commonly employed to study fluid mechanical systems where flow tracers are readily observed, but they are broadly applicable to dynamical systems in general. A prevailing class of LCS analyses depends on reliable computation of flow gradients. The finite-time Lyapunov exponent (FTLE), for example, is derived from the Jacobian of the flow map, and the Lagrangian-averaged vorticity deviation (LAVD) relies on velocity gradients. Observational tracer data, however, are typically sparse (e.g. drifters in the ocean), making accurate computation of gradients difficult. While a variety of methods have been developed to address tracer sparsity, they do not provide the same information about the flow as gradient-based approaches. This work proposes a purely Lagrangian method, based on the data-driven machinery of regression, for computing instantaneous and finite-time flow gradients from sparse trajectories. The tool is demonstrated on a common analytical benchmark to provide intuition and demonstrate performance. The method is seen to effectively estimate gradients using data with sparsity representative of observable systems.

As a lunar lander attempts to make a soft landing on the moon, the supersonic exhaust plumes from the descent engine can liberate a large quantity of regolith grains off the ground surface. In this work, we investigate the particle–particle collision phenomenon inside this regolith spray with the soft sphere method — an alternate to the generally used hard sphere approach. Individual collisions are resolved by generating spring and damping forces at the contact point of particles that are already moving under fluid drag and buoyancy. To reduce the computational burden, a 1:100 scale model of the real flow domain is used. We insert 60,000 numerically representative regolith particles through random locations on the ground to yield an initial solid grain density of ∼ 1 0 8 particles/m3. Three different particle diameters, ranging from small to moderately large, are considered to account for the wide size variation of lunar regolith, and observe the relationship between inter-particle collisions and particle size. The coefficient of restitution is varied to model completely inelastic collisions to highly elastic collisions. Results indicate that collisions between larger regolith grains with high elasticity cause a significant portion of particles to reach high elevations inside the domain and leave at large angles. However, the majority of the ejecta spray is bound within a shallow region (< 3°) above ground where they move slowly due to weak plume-generated forces. On the other hand, inelastic collisions tend to significantly decrease the maximum particle height within the domain, but the main particle stream is more uniformly distributed in the flow domain and average particle speed increases. Maximum particle speed shows an inverse relation with energy depletion in collisions, but this relation becomes less remarkable for larger (100 and 150 μ m) grains. Overall, particle trajectory results in this work align with the 1–3° angles measured for the visible regolith sheet in Apollo landing videos. However, the possibility of many grains ejecting at much higher angles due to collisions is also revealed. These high-angle particles can be problematic for relying on berms on the lunar surface to block the regolith spray. • Collisions inside plume-driven lunar regolith are studied with the soft sphere method. • Highly elastic collisions between large grains decrease their average speed. • The same collisions increase maximum particle height and speed in the flow domain. • Trajectories of small particles are not significantly affected by collisions. [ABSTRACT FROM AUTHOR]

High Reynolds number turbulent reacting flows poses a modeling challenge due to the multi-regime, mixed-mode nature of the combustion processes. This study presents a novel unified index that includes the description of both premixed and nonpremixed combustion regimes and the occurrences of local extinction and re-ignition. This classifier is applied to large eddy simulations of the Darmstadt multi-regime burner for the nominal cases 18b and 26b. Lagrangian particles are transported along with the flow in order to monitor the evolution of the local flow-chemistry interaction. The simulations are validated against experimental data, and the Lagrangian properties are compared against the traditional premixed model in progress variable space and a generalized multi-modal manifold model in mixture fraction and generalized progress variable space. The comparison reveals that minor radical species are sensitive to the generalized progress variable dissipation rates, and the multi-modal manifold model is more suitable to reproduce the multi-regime flame structure. Using the multi-modal framework, the regime index is simply defined by the slope of the Lagrangian particle trajectory in the phase space and is able to detect the evolution of the combustion regimes and the occurrence of extinction events. Consistent with the previous experimental findings, the statistics of the regimes reveals that the leaner case 18b is more susceptible to extinction and re-ignition and the regime is predominantly premixed, while the richer 26b case is more pronounced in the nonpremixed regime. [ABSTRACT FROM AUTHOR]

This study presents a comprehensive analysis of contaminant transport in estuarine environments, focusing on the impact of tidal creeks and flats. The research employs advanced hydrodynamic models with irregular grid systems and conducts a detailed residual current analysis to explore how these physical features influence the movement and dispersion of contaminants. The methodology involves simulating residual currents and Lagrangian particle trajectories in both 'Creek' and 'No Creek' cases, under varying tidal conditions. The results indicate that tidal creeks significantly affect particle retention and transport, with notable differences observed in the dispersion patterns between the two scenarios. The 'Creek' case demonstrates enhanced material retention along the creek pathways, while the 'No Creek' case shows broader dispersion, potentially leading to increased sedimentation in open sea areas. The discussion highlights the implications of these findings for sediment dynamics, contaminant transport, and estuarine ecology, emphasizing the role of tidal creeks in modulating flow and material transport. The research underlines the necessity of incorporating detailed environmental features in estuarine models for accurate contaminant transport prediction and effective estuarine management. This study contributes to a deeper understanding of estuarine hydrodynamics and offers valuable insights for environmental policy and management in coastal regions. [ABSTRACT FROM AUTHOR]

The Eastern Shore Islands (ESI) archipelago on the Scotian Shelf supports a rich variety of biogenic habitats and associated diversity of coastal species. The unique and complex geometry of the ESI coastline has a significant impact on circulation and, correspondingly, influences the dispersal of nearshore organisms. For many coastal areas, the ability to accurately resolve the dispersal processes is contingent on the availability of oceanographic models that can resolve fine-scale coastal boundary conditions, including coastlines and bathymetric features. We applied a high-resolution ocean circulation model and Lagrangian particle tracking in the ESI to simulate dispersal of nearshore organisms. Our results revealed predominant southwest–northeast transport that was associated with a nearshore reversal flow. While transport among different zones of the study region is mainly determined by residual currents over the long term, tidal currents dominate patterns of particle dispersal over shorter time scales. An analysis of Lagrangian coherent structures found that they were consistently associated with the mouths of bays, demonstrating that the islands and associated oceanographic processes promote self-retention. These results highlight how complex coastlines and associated oceanographic processes promote retention and underline the need to resolve these fine-scale physical and oceanographic features when estimating biophysical dispersal in the coastal environment. [ABSTRACT FROM AUTHOR]

Route planning to evade potential pollution holds critical importance for aquaculture vessels. This study establishes a fish-feed pollutant drift model based on the Lagrangian particle tracking algorithm and designs four sets of sensitivity experiments in the East China Sea. The research investigates the impact of model input uncertainties on the drift trajectory, centroid position, and sweeping area of the fish-feed pollutants. Numerical results indicate that the uncertainty in the background flow field significantly affects the uncertainty in the centroid position and sweeping area in the numerical simulations. Specifically, when a 35% random error is added to the background flow field, the centroid shift distance reaches its maximum, and the sweeping area also attains its largest value. The uncertainty in the background wind field affects the centroid position of particles but to a much lesser extent compared to the background flow field. When considering only the uncertainty of the background wind field, the sweeping area does not significantly differ from the control experiment as the uncertainty of the background wind field increases. The initial release position has little effect on the drift direction of the fish-feed pollutants but does affect the drift distance; it has minimal impact on the trajectory but significantly affects the final position of the pollutant centroid. By analyzing the model uncertainties, this study reveals the key factors influencing the drift of fish-feed pollutants. This information is crucial for aquaculture vessels in planning routes, considering environmental factors, and reducing potential pollution risks.

The Lombok Strait (LS), Ombai Strait (OS), and Timor Passage (TP) are three major outlets of the Indonesian Throughflow to the Indian Ocean. Here, sources and pathways of the LS, OS, and TP outflows are explored by a Lagrangian particle tracking analysis based on a ~3 km regional ocean model simulation. The Makassar Strait transport contributes to ~80%, ~75%, and ~45% of the LS, OS, and TP outflows, respectively. However, ~41% and ~19% of the TP and OS outflows stem from the Lifamatola Passage, which largely feeds the upper and intermediate layers of the outflows. The role of Karimata Strait is quite limited and restricted to the upper layer. It takes 1-2 years and 2-6 years for the Makassar Strait water to reach the OS and TP, respectively, whereas the Lifamatola Passage water passes through the OS (2-6 years) and TP (3-9 years) on a prolonged transit time. In the Banda Sea, the western boundary current is the main pathway toward the OS, while the waters to the TP tend to take a basin interior route. [ABSTRACT FROM AUTHOR]

We study experimentally the statistical properties and evolution of circulation in a turbulent flow passing through a smooth 2-D contraction. The turbulence is generated with active grids to reach $ Re_{\lambda } \simeq ~220 $ R e λ ≃ 220 at the inlet to the 2.5:1 contraction. We employ time-resolved 3-D Lagrangian Particle Tracking technique with the Shake-The-Box algorithm to obtain volumetric velocity fields which we use to calculate the simultaneous circulation in three perpendicular planes. Forming a circulation vector and studying the PDFs of the relative strength of its components, we can quantify how the mean strain enhances and orients coherent vortical structures with the streamwise direction. This is further studied with streamwise space and time correlations of the circulations over a range of loop sizes. The streamwise component of the circulation, over same-size square loops, shows increased integral length, while the other two components are less affected. The circulation around the compressive direction weakens and reaches prominent negative correlation values, suggesting buckling or sharp reorientation of transverse vortices. The PDFs of circulation transit from non-Gaussian to Gaussian behaviour as the loop size is increased from dissipative to large scales. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Microfluidic flows feature typically fully three-dimensional velocity fields. However, often the optical access for measurements is limited. Astigmatism or defocus particle tracking velocimetry is a technique that enables the 3D position determination of individual particles by the analysis of astigmatic/defocused particle images. The classification and position determination of particles is a task well suited to deep neural networks (DNNs). In this work, two DNNs are used to extract the class and in-plane position (object detection) as well as the depth position (regression). The performance of both DNNs is assessed by the position uncertainties as well as the precision of the size classes and the amount of recalled particles. The DNNs are evaluated on a synthetic dataset and establish a new benchmark of DNNs in defocus tracking applications. The recall is higher than compared to classic methods and the in-plane errors are always subpixel accurate. The relative uncertainty in the depth position is below 1% for all examined particle seeding concentrations. Additionally, the performance on experimental images, using four different particle sizes, ranging from 1.14 μ m to 5.03 μ m is analyzed. The particle images are systematically rearranged to produce comprehensive datasets of varying particle seeding concentrations. The distinction between particles of similar size is more challenging but the DNNs still show very good results. A precision above 96% is reached with a high recall above 95%. The error in the depth position remains below 1% and the in-plane errors are subpixel accurate with respect to the labels. The work shows that first, DNNs can be trained with artificially rearranged data sets based on individual experimental images and are therefore easily adaptable to various experimental setups and applicable by non-experts. Second, the DNNs can be successfully adapted to determine additional variables as in this case the size of the suspended particles. [ABSTRACT FROM AUTHOR]

In turbulent boundary layers, streamwise elongated regions of high- and low-momentum in the log-law layer that can extent up to several boundary layer thicknesses are often referred to as turbulent superstructures. These structures contain a relatively large portion of the layer's turbulent kinetic energy and have been shown to interact with the near-wall flow structures. In the last few decades extensive research on zero-pressure gradient (ZPG) turbulent boundary layers has been done, however by comparison, the structural characteristics for adverse pressure gradient turbulent (APG) boundary layer flows are much less studied despite their strong significance aero-hydrodynamic vehicle design. Therefore, the three-dimensional dynamics of turbulent superstructures in a turbulent boundary layer flow are investigated in the Atmospheric Wind Tunnel Munich (AWM) using a multi-camera 3D time-resolved Lagrangian particle tracking approach. In this study, Lagrangian and Eulerian statistics will be used to characterize the dynamics and interaction of turbulent superstructures within a zero pressure gradient (ZPG) turbulent boundary layer at Re τ = 5000 or Re θ = 14 000 that then flows over a curved plate subjected to a favorable (FPG) and strong adverse (APG) pressure gradient, which eventually separates. An Eulerian analysis, using multi-point correlations of 3D velocity fields, found that the average superstructure topology is modulated by decelerating flow in the APG region when compared to the ZPG region, however the basic shape and spanwise pattern is preserved. Looking into the behavior of individual trajectories, it was found that the dispersion of single particles along trajectories in the log-law layer are capable of moving more than the average Eulerian superstructure spacing in the spanwise direction. Furthermore, the mean square of the single particle dispersion indicates that the maximum dispersion in the spanwise direction comes from particles released at the wall-normal location corresponding to the so-called "second-peak/plateau" region in the streamwise normal Reynolds stress. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The ability to predict particle dispersion, interaction, and deposition in turbulent pipes is of value in improving the transport and process efficiency of high concentration particulate flows. In this work, the settling and deposition behavior of suspensions of dense particles in a cylindrical pipe has been studied using direct numerical simulation coupled with Lagrangian particle tracking, with the influence of Stokes number on deposition behavior examined. From the analysis performed, it can be concluded that particle deposition is sensitive to Stokes number. In particular, the dispersion function and mean vertical displacement of the particles are demonstrated to decrease considerably faster with time at the higher Stokes number. Particle migration towards the lower wall regions of the pipe also shows the formation of a solid bed of these particles, whilst over the same time period only dune‐like structures are produced at the lower Stokes number. Further analysis of the particle dynamics confirms these findings and generates insight into the particle dynamics within the deposition regions. [ABSTRACT FROM AUTHOR]

Direct numerical simulation, facilitated by the spectral element method, has been used to study collisions and agglomeration in particle‐laden fluid flows through a channel at shear Reynolds number. The particulate phase is simulated by deterministic Lagrangian particle tracking alongside a stochastic technique to resolve collisions. Interestingly, the implementation of agglomeration in the deterministic approach caused a major reduction in the particle collision rate. To determine the cause of this effect, analysis of the collision rate and location across the channel for different particle properties was performed. For systems without agglomeration, collisions between particles tend to be located on consistent streamlines, occurring between single pairs of particles. A numerical analysis of this effect confirmed the result, where inter‐particle collisions across the channel mostly took place between consistent particle pairs in close proximity. Repeat collisions are shown to be almost eliminated with the addition of the agglomeration mechanism. The impact and implications of this effect on the accuracy of the stochastic technique is discussed, and modifications are suggested to offer improvements while accounting for the repeat collisions. [ABSTRACT FROM AUTHOR]

The first part of the research reported here consists of an experimental campaign to study the scouring of a granular bed (glass beads, sand) induced by a dam break in an open channel. Two configurations are considered: with and without cylinders. In the second part of this study, the volume of fluid method coupled with the shear stress transport turbulent model and the lagrangian particle tracking method is used to simulate the local scour processes. The four-way coupling is realized by considering the drag force and collisions between particles. Using a vortex map and velocity profiles, the flow dynamics and scour pattern can be studied. The current research also focuses on the profiles of the erodible particle bed and the sediment transport rate to study the effects of a cylinder on local scour. The presence of the cylinder increases the experimental erosion depth by up to 42%. It was found that for relatively close particle diameters (2 and 3 mm), a granular bed with larger porosity (larger diameter) erodes the most. Experimentally and numerically it was found that the center of the granular bed experiences more erosion compared to the channel sides. In the last part of the research, comparisons between the numerical results and the experimental data allowed risk areas to be identified and the roles of porosity, sediment density, and flow dynamics on erosion to be identified. [ABSTRACT FROM AUTHOR]

Due to the density stratification of sea water, the dispersed oil droplets and gas bubbles with small diameters, as well as the dissolved components, may remain in some specific depths. The double-plume Lagrangian particle tracking model for bubbly plumes in vertical density stratified environments is improved and applied to predict the underwater pollutants in a blowout. This model considers the different properties and dissolution processes of components in crude oil and focuses on their behavior and stratification differences in the plume. The crude oil components are divided into several groups and the dissolution of oil and gas is also considered. The model is applied to simulate the "Deepwater Horizon" oil spill accident in the Gulf of Mexico in 2010. The results show several enrichment layers of oil and gas at different depth and the differences in concentration between components, which corresponds to the distribution of petroleum pollutants in the in-situ observation. [ABSTRACT FROM AUTHOR]

Previous studies have shown the presence of strong mesoscale eddy activities in the Indonesian Seas and their influence on the transport and water mass properties of the Indonesian Throughflow (ITF), a mean flow from the Pacific Ocean to the Indian Ocean through the Indonesian Archipelago. This study explores the effects of these eddy activities, or high‐frequency flow variability (HFFV), on residence time and pathway of the ITF by conducting Lagrangian particle tracking experiments using a velocity field from an eddy‐resolving ocean general circulation model. Particles are released at key locations in the western and eastern routes of the ITF and tracked both backward and forward in time. To assess the effects of flow variability that has a time scale longer than a day but shorter than a month, the definition of HFFV in this study, we conduct parallel experiments using daily and monthly averaged velocity fields. Particle trajectories reveal the contrasting circulation characteristics of the Sulawesi and Banda Seas. HFFV in the Sulawesi Sea (in the western route) is high, causing water to circulate longer over a broader area. The longer residence time in the Sulawesi Sea helps the upwelling of the inflowing Pacific waters, especially the intermediate water masses, to rise above 300 m at the Makassar Strait, and also has the potential to allow mixing processes to modify the water mass properties of the ITF. In contrast, HFFV is much lower in the Banda Sea and has minimal effects on the ITF. Plain Language Summary: As part of the world ocean general circulation, warm water in the upper layer flows from the Pacific Ocean to the Indian Ocean through the Indonesian Archipelago. The flow through the archipelago, known as the Indonesian Throughflow (ITF), is neither a steady one nor a single stream. The ITF experiences fluctuation and turbulence while navigating through the various seas, straits, and passages. In this study, using the velocity field generated by an ocean circulation model, we explore the roles that the flow variability plays in the ITF pathway and its transit time through the major seas. We find that flow variability in the Sulawesi Sea is high, causing water to circulate longer over a broader area and to rise from the intermediate depth to near the surface, thus providing the potential for turbulence to modify the water properties of the ITF. On the other hand, flow variability is low in the Banda Sea and has minimal effects on the ITF. Key Points: Residence time and pathways of the Indonesian Throughflow are examined using virtual particles advected in an eddy‐resolving modeled velocity fieldHigh‐frequency flow variability increases residence time and supports the upwelling of the inflowing Pacific water, especially in the Sulawesi SeaThere is a need for adequate representation of mixing processes (including tidal and shear‐induced) occurring in the Indonesian Seas in ocean models [ABSTRACT FROM AUTHOR]

Open-cell metal foams are often used in applications where particulate and/or droplet capture is important. Here a Computational Fluid Dynamics (CFD) modelling approach is described which models the metal foam at both the pore-scale and the macroscopic scale. At the pore-scale, the detailed internal geometry of the foam is included and the flow field and droplet tracking and capture is modelled explicitly. At this scale, a coefficient is found for each metal foam that relates the distance a droplet can freely travel through the foam to both the droplet diameter and the Darcian velocity in the porous medium. Then, at the macroscopic scale, the coefficient from the pore-scale droplet capture simulations is used in a novel stochastic particle extinction model. Here, the droplets travel through a porous zone and are removed from the model, the probability of which is determined by the coefficient from the pore-scale modelling. A test case is described in which the macroscopic model is verified against the pore-scale model with acceptable levels of accuracy. Article Highlights: Single phase CFD and Lagrangian particle tracking are carried out in a range of open-cell metal foams at the pore-scale. A capture probability of the droplets as a function of droplet diameter and Reynolds number for each metal foam is found. The probability of capture is used in a new macroscale droplet capture model, based on Lagrangian particle tracking. [ABSTRACT FROM AUTHOR]

A three-dimensional stochastic Lagrangian particle tracking sediment transport model is developed to solve the discrete advection–dispersion equation using a combination of empirical dispersion equations. The performance of three widely-used longitudinal dispersion coefficient equations was examined to select one of them as the primary dispersion equation term in the developed model. Also, a conditional empirical equation was used to consider the effect of vertical dispersion term in top layers near the water surface. The performance of particle tracking model (PTM) to calculate the sediment concentration was evaluated for various sediment classes (very fine sand, fine sand, and medium sand) using available laboratory dataset. Multiple statistical measures were calculated using the Taylor diagram for each dispersion equation. Based on the result, the developed particle tracking model estimated the suspended sediment concentration in a rectangular open channel with a correlation coefficient (R) of 0.96, standard deviation (STD) of 0.262, and root mean square deviation (RMSD) of 0.06 for three different sediment classes proving the acceptable accuracy of the developed model for different range of sediment gradations. In addition, the accuracy of PTM was compared to recently developed models. Comparison between the particle tracking model and the analytical solution of the advection–dispersion equation showed that the developed model predicted the maximum concentration of suspended sediment 6% and 9.4% lower than the analytical solution result for 30 and 50 s simulation time in the straight channel, respectively. However, there was a good agreement between the longitudinal and transverse sediment concentration distribution from the model and the analytical solution approach. The result of the sensitivity analysis and validation process showed that the model could be used to simulate sediment transport in open channel flows. [ABSTRACT FROM AUTHOR]

The Virgin Islands basin (VIB) includes several Marine Protected Areas (MPAs) of interest as biologically unique spawning aggregation sites. The ecological structure in and around these MPAs is regulated by several factors, including changes in near‐surface water properties. Anomalously low near‐surface salinity is observed in the VIB during April 2009/2011, and March 2010, with a salinity signature consistent with Amazon plume waters. Other low salinity events in the region are found during 2007–2017 using output from an ocean reanalysis. The reanalysis shows that horizontal salinity advection explains near‐surface salinity variability in the VIB to a high degree, including events observed in the in situ measurements. We use a Lagrangian Particle tracking model to track particles over the 2007–2017 period and identify the source and pathways of water imports to the VIB. We describe three pathways. The northernmost one is often associated with advection of salty Atlantic waters. The two southernmost paths are associated with advection of low salinity waters from the Amazon into the VIB. The latter two pathways arrive to the Caribbean Sea as described in previous studies on low salinity advection to the wider Caribbean from the Amazon River; we find that once in the Caribbean Sea, the low salinity water makes its way into the VIB when steered northward by mesoscale features. This results in Amazon River waters regulating salinity variability in the VIB during April–November. During December–March, when mesoscale activity is at its minimum, the Atlantic inflow regulates the salinity variability within the VIB instead. Plain Language Summary: The Virgin Islands basin (VIB) is an ecologically important region of the northeastern Caribbean Sea. Changes in upper‐ocean properties affect the regional biology. Measurements of water properties in the VIB during April 2009/2011 and March 2010 show low salinity waters near the surface consistent with salinity from the Amazon River plume. Similar events are found during the 2007–2017 period using outputs from an ocean model. We show that salinity in the region is driven by the horizontal transport of salt via ocean currents. We then track the origin of the waters arriving to the VIB. A path from the east/north‐east transports salty ocean waters into the VIB during December–March. Two other paths from the south/south‐east are instead associated with the transport of low salinity waters into the VIB from the Amazon River area and occur frequently during April–November. Key Points: Salinity variability in the Virgin Islands basin (VIB) is primarily driven by horizontal salinity advectionThree paths dominate the import of waters into the VIB: two paths linked with Amazon plume waters and the third with Atlantic inflowMesoscale features steer low salinity waters from the southeastern Caribbean toward the VIB [ABSTRACT FROM AUTHOR]

Latitudinal range limits for mangroves on high‐energy, wave‐dominated coasts are controlled by geomorphological features and estuarine dynamics. Mangroves reach a southern global range limit along the South African coastline, but the distribution is patchy, with stands occurring in only 16% of the estuaries in the region. Yet, the persistence of forests planted >50 years ago beyond the natural distribution limit suggests that additional estuaries could support mangroves. Understanding regional drivers is necessary to inform global‐scale estimates for how this important ecosystem is predicted to respond to climate change.Here, we combine species distribution modelling (MaxEnt), Lagrangian particle tracking using an eddy‐ and tide‐resolving numerical ocean model, and connectivity matrices, to identify suitable mangrove habitats along the South African coastline at present, as well as under the IPCC RCP4.5 and RCP8.5 climate scenarios.Within the current South African distribution range (±900 km), eight more estuaries were identified to be suitable under contemporary conditions. When considering potential range extension (±110 km), an additional 14 suitable estuaries were identified. Connectivity matrices suggest limited long‐distance dispersal, stranding mostly at or near the release location, and a decreased probability of connectivity towards the range limit. Under both future climate scenarios, 30% of estuaries currently supporting mangroves are predicted to become unsuitable, while an additional six estuaries beyond the current distribution are predicted to become suitable. However, there is limited connectivity between these new sites and established forests.Synthesis. This study shows that dispersal substantially limits mangrove distribution at the southern African range limit and highlights the importance of including this process in species distribution models. Ultimately, our results provide new insight into mangrove conservation and management at range limits that are not controlled predominantly by temperature, as it has been assumed that mangroves will largely expand to higher latitudes under climate change. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

We propose a novel, demonstrably effective, utmost versatile and computationally highly efficient pseudo-rigid body approach for tracking the barycenter and shape dynamics of soft, i.e. non-linearly deformable micro-particles dilutely suspended in viscous flow. Pseudo-rigid bodies are characterized by affine deformation and thus represent a first-order extension to the kinematics of rigid bodies. Soft particles in viscous flow are ubiquitous in nature and sciences, prominent examples, among others, are cells, vesicles or bacteria. Typically, soft particles deform severely due to the mechanical loads exerted by the fluid flow. Since the shape dynamics of a soft particle - a terminology that shall here also include its orientation dynamics - also affects its barycenter dynamics, the resulting particle trajectory as a consequence is markedly altered as compared to a rigid particle. Here, we consider soft micro-particles of initially spherical shape that affinely deform into an ellipsoidal shape. These kinematic conditions are commensurate with i) the affine deformation assumption inherent to a pseudo-rigid body and ii) the celebrated Jeffery-Roscoe model for the traction exerted on an ellipsoidal particle due to creeping flow conditions around the particle. Without loss of generality, we here focus on non-linear hyperelastic particles for the sake of demonstration. Our novel numerical approach proves to accurately capture the particular deformation pattern of soft particles in viscous flow, such as for example tank-treading, thereby being completely general regarding the flow conditions at the macro-scale and, as an option, the constitutive behavior of the particle. Moreover, our computational method is highly efficient and allows straightforward integration into established Lagrangian tracking algorithms as employed for the point-particle approach to track rigid particles in dilute viscous flow. [ABSTRACT FROM AUTHOR]

Marine debris, particularly microplastics, is an important environmental problem for Indonesia, impacting vast coastline and diverse marine ecosystems. However, little is known about the microplastics flux to the seafloor in the Indonesian Seas. This study employs HYCOM data and Lagrangian particle tracking model to analyze the distribution of microplastics flux to the seafloor from 68 rivers in Indonesia. Microplastics accumulation can be found in coastal waters near major islands, typically within 50–100 km of the coast. Accumulation regions within the Fisheries Management Area (FMA) in Indonesia are mostly located in Karimata Strait, Java Sea and South Java. This study highlights the importance of understanding sinking particles behavior for effective waste management strategies, as well as for mitigating environmental impacts in Indonesian waters. • With particle tracking bottom microplastic flux from Indonesian rivers was estimated. • The bottom microplastic flux closely resembles surface microplastic concentration. • The majority of benthic plastics are situated within 50–100 km of the coastline. • The bottom fluxes are higher over the southwestern part of Indonesian Seas. • The Karimata Strait, Java Sea and South Java are affected most. [ABSTRACT FROM AUTHOR]

• Aerosol particle deposition in wavy pipes during turbulent flow is investigated. • Finite volume method and Eulerian-Lagrangian tracking are used for numerical simulation. • Large pipe diameter and low flow velocity enhance deposition efficiency. • Higher wave amplitude contributes significantly to particle deposition. • Optimal wave frequency ensures the required deposition efficiency. This paper demonstrates a numerical simulation study to understand particle deposition phenomena in wavy pipe configurations comprehensively. The research investigates the intricate dynamics of particle deposition within wavy pipes by utilizing the RNG k - ε turbulence model with enhanced wall treatment for fluid flow simulation and employing a Lagrangian particle tracking model. The finite volume approach is adopted to solve the mathematical model of the current problem. The rate of aerosol particle deposition within a wavy pipe under turbulent flow conditions is systematically explored by varying the size of particles (1 ≤ d p (μm) ≤ 30), Reynolds numbers (5000 ≤ Re ≤ 10,000), and other parameters like wave frequency (3 ≤ f ≤ 7), wave amplitude (5 ≤ a (mm) ≤ 15), and diameter of the pipe (10 ≤ D (mm) ≤ 30). The findings reveal significant correlations between these parameters and deposition efficiency, shedding light on the complex interplay between geometric factors and flow characteristics within the wavy pipe configurations. Notably, larger pipe diameters and higher wave amplitudes are found to enhance deposition rates, while the optimal wave frequencies exist at intermediate values. Additionally, alterations in flow velocity exhibit an inverse relationship with deposition efficiency. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract 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).

A numerical simulation of aerosol particle deposition in a horizontal circular pipe with a corrugated wall under turbulent flow has been carried out in this research. This paper uses the RNG k-ε turbulence model with Enhanced Wall Treatment to simulate fluid flow. Furthermore, the Lagrangian particle tracking model simulates particle deposition in the corrugated pipe. Air-particle interaction is influenced by Stokes number, surface roughness, flow velocity, particle diameter, and pipe diameter. For the parametric simulation, particle diameter varies from 1 to 30 μm, whereas the Reynolds number ranges from 5000 to 10,000. The effect of corrugation height and pipe diameter on deposition efficiency is also investigated. This study shows that corrugation height significantly increases particle deposition compared to the smooth wall pipe. As the pipe diameter decreases, keeping the corrugation ratio constant, deposition efficiency also increases. Moreover, high flow velocity enhances deposition efficiency for particle diameters lower than 5 μm.

The outbreak of nuclear power cooling water system (NPCS) disaster-causing organisms has become more frequent, causing huge economic losses. Therefore, it is necessary to understand the aggregation mechanism of disaster-causing organisms for the risk prevention and control of NPCS. Hence, this study applied the Lagrangian flow network (LFN) to analyze the aggregation mechanism of Acetes near NPCS, as such a complex network can describe the interconnections between massive nodes and has already been used for modeling complex nonlinear systems, revealing how the mechanisms of such novel processes emerge. In this study, the degree and probability paths in the network were used to reveal the transport pathway and aggregation area of Acetes. The experimental results highlighted that the sea area of the nuclear power plant is the key node with a large in-degree of the LFN, where the material easily accumulated. The Acetes near the NPCS mainly originated from the east along two critical paths. Overall, this study demonstrates that the LFN is a feasible approach to predicting the transport and the accumulation of the NPCS disaster-causing plankton.

Larval dispersal and connectivity have important implications for fisheries management, especially for species with life cycles influenced by ocean boundary currents. Giant Mud Crab (Scylla serrata) and Blue Swimmer Crab (Portunus armatus) are two estuarine portunid crabs (Family: Portunidae) that support significant commercial and recreational harvest in eastern Australia. Giant Mud Crab migrate to coastal waters to spawn, and while Blue Swimmer Crab spawn primarily within estuaries they occasionally migrate to coastal waters to spawn, followed by larval dispersal in the East Australian Current (EAC). Here, we coupled a high‐resolution oceanographic model with a Lagrangian particle tracking framework to simulate larval dispersal and determine the extent of population connectivity in this region. Our simulations indicate broad‐scale connectivity (~40–400 km), characterised by high inter‐estuary connectivity. Overall, our results suggest a north‐to‐south source‐sink structure for both species, with contributions of particles from the north ranging from 51% to 99%. Recruitment to a given estuary is dependent on the proximity of mesoscale oceanographic features of the EAC. Most notably, the EAC separation acts as a barrier to recruitment between spawning and settlement to the north/south of this region. This significantly limits interjurisdictional connectivity for these species, especially Blue Swimmer Crab, likely due to a shorter pelagic larval duration than Giant Mud Crab. Our results provide evidence to inform the assessment and management of these species. [ABSTRACT FROM AUTHOR]

Sustainability solutions to water quality management problems, many generated by human activities, require knowledge and understanding of circulation patterns and transport rates that govern water quality conditions. This research demonstrates approaches to frame and implement estuary investigations with the purpose of quantifying hydrodynamics influencing estuary water pollution residence time and transport rates governed by freshwater flows and estuary tidal dynamics. The study area is a coastal location with connected estuaries in the Gulf of Maine, USA, near Acadia National Park where complex coastal morphometry controls on estuary hydrodynamics and pollution problems have been observed. A Lagrangian particle tracking study is implemented to examine particle transport patterns and timescales to identify the conditions and mechanisms that influence them. Conservative virtual particles are released and tracked in hydrodynamic simulations over month-long periods with a range of conditions specified by freshwater flow input, tide range, and varied density gradients. Results show that residual eddy size surpasses the tidal excursion length and transport behavior is controlled by the residual flow rather than the tide in wide and geometrically simple estuaries with a simple bed profile and few complications from localized geomorphological features. Estuaries with similar characteristics are pre-disposed to suppression of the estuary water density gradient, a primary driver of residual flow, producing an order of magnitude increase in residence time under conditions comparable to those simulated by our analysis. Narrow channels and the presence of complex geomorphic features such as islands and constrictions limit the length of residual eddies and increase the tidal excursion. Transport timescales in estuaries with these conditions are more sensitive to variations in the tidal range than to changes in residual flow. Explorations of the relations between residual eddy length estimated as the estuary aspect ratio and a normalized tidal excursion provide a practical way for managers to identify controls on particle transport and pollution dynamics in estuaries and determine appropriate management actions to monitor and respond to coastal water pollution problems. [ABSTRACT FROM AUTHOR]

Particulate flow in closed space is involved in many engineering applications. In this paper, the prediction of particle removal is investigated in a thermally driven 3D cavity at turbulent Rayleigh number Ra = 109 using Coarse Large Eddy Simulation (CLES). The depletion dynamics of SiO2 aerosol with aerodynamic diameters between 1.4 and 14 µm is reported in an Euler/Lagrange framework. The main focus of this work is therefore to assess the effect of the subgrid-scale motions on the prediction of the particulate flow in a buoyancy driven 3D cavity flow when the mesh resolution is coarse and below optimal LES standards. The research is motivated by the feasibility of modeling more complex particulate flows with reduced CPU cost. The cubical cavity of 0.7 m side-length is set to have a temperature difference of 39 K between the two facing cold and hot vertical walls. As a first step, the carrier fluid flow was validated by comparing the first and second-moment statistics against both previous well-resolved LES and experimental databases [Kalilainen (J. Aero Sci. 100:73–87, 2016); Dehbi (J. Aero. Sci. 103:67–82, 2017)]. First moment Eulerian statistics show a very good match with the reference data both qualitatively and quantitatively, whereas higher moments show underprediction due to the lesser spatial resolution. In a second step, six particle swarms spanning a wide range of particle Stokes numbers were computed to predict particle depletion. In particular, predictions of 1.4 and 3.5 µm particles were compared to LES and available experimental data. Particles of low inertia i.e. dp < 3.5 µm are more affected by the SGS effects, while bigger ones i.e. dp = 3.5–14 µm exhibit much less grid-dependency. Lagrangian statistics reported in both qualitative and quantitative fashions show globally a very good agreement with reference LES and experimental databases at a fraction of the CPU power needed for optimal LES. [ABSTRACT FROM AUTHOR]

A new white-light volumetric flow measurement technique is presented that can be used in large-scale facilities. The technique enables large volumes to be measured with high temporal and spatial resolution and without the need for a class-4 laser. This LED-based Lagrangian particle tracking velocimetry is demonstrated by measuring the tip vortex formation and the near wake of a 1.2 m diameter tidal turbine in a 25 m diameter, 2 m deep tank. Seven streamwise-distributed volumes of interest are combined, each 334 mm long, 244 mm wide and 140 mm deep, reaching up to one diameter downstream of the turbine. The system does not require re-calibration when moved. By assuming a periodic flow field, a phase-averaged flow field was reconstructed with a temporal resolution of 3.9 ms and a spatial resolution of 5.4 mm. The large volume and high time and spatial resolution could enable key research questions to be addressed on high-Reynolds-number flows and could provide valuable benchmark data for numerical model development and code validation. [ABSTRACT FROM AUTHOR]

Complex flows are often characterized using the theory of Lagrangian coherent structures (LCS), which leverages the motion of flow-embedded tracers to highlight features of interest. LCS are commonly employed to study fluid mechanical systems where flow tracers are readily observed, but they are broadly applicable to dynamical systems in general. A prevailing class of LCS analyses depends on reliable computation of flow gradients. The finite-time Lyapunov exponent (FTLE), for example, is derived from the Jacobian of the flow map, and the Lagrangian-averaged vorticity deviation (LAVD) relies on velocity gradients. Observational tracer data, however, are typically sparse (e.g. drifters in the ocean), making accurate computation of gradients difficult. While a variety of methods have been developed to address tracer sparsity, they do not provide the same information about the flow as gradient-based approaches. This work proposes a purely Lagrangian method, based on the data-driven machinery of regression, for computing instantaneous and finite-time flow gradients from sparse trajectories. The tool is demonstrated on a common analytical benchmark to provide intuition and demonstrate performance. The method is seen to effectively estimate gradients using data with sparsity representative of observable systems., Competing Interests: We declare we have no competing interests., (© 2024 The Author(s).)

Firebrand impingement is a leading cause of home ignitions from wildland fire. The use of porous fencing has recently been proposed as a potential method for mitigating firebrand impingement on homes. A porous fence can act as a windbreak to alter the near-surface flow and induce particle deposition, as demonstrated in other applications, such as the use of snow fences to protect roadways from drifting snow. Conservation advocates have proposed the use of fire-resistant vegetation to act as a fence upwind of homes or subdivisions. Porous fences could also be constructed from fire-resistant materials such as metal, rock, or composites. This numerical investigation of the effectiveness of porous fencing to reduce firebrand impingement on homes conducted a series of experiments to explore the effect of porous fencing on the near-surface flow field and firebrand transport downwind of the fence. We also evaluated the sensitivity of the results to various fence, flow, and firebrand properties, including fence height, fence porosity, wind speed, firebrand source location, and firebrand size. To our knowledge, this is the first study to investigate the concept of using a fence to induce firebrand deposition upwind of homes. Our results showed that porous fencing can reduce firebrand impingement on homes by up to 35% under certain conditions; however, fencing can also increase impingement on homes. The mitigation effectiveness depended on the proximity of the firebrand source, distance between the fence and home as a function of fence height, wind speed, and firebrand size. A series of key findings and recommendations are provided.

The New Guinea Coastal Undercurrent (NGCUC) is considered a bottleneck in the western tropical Pacific (WTP), carrying upper-to-intermediate waters from the south to the northwestern Pacific, thereby playing a fundamen tal role in the interhemispheric water mass exchange. However, how the NGCUC links to the circulation in the WTP was insufficiently studied. This work explores the destination of NGCUC waters, its spatiotemporal changes, and possible physical processes linked with the downstream NGCUC using ocean reanalysis for 22 years (1994 – 2015). Lagrangian particle tracking discloses eight major destinations of the NGCUC: The Equatorial Undercurrent (EUC, 35.26%), the North Equatorial Countercurrent (NECC, 12.3%), the North (13.33%) and South (8.85%) Subsurface Countercurrents, the Equatorial Deep Jet (11.49%), the Mindanao Undercurrent (13.24%), and the Indonesian (3.47%) and Halmahera (0.86%) Throughflows. The NGCUC waters are distributed mainly to the east (81.65%) and their dissemination varies markedly with depth. These destinations exhibit significant variations on seasonal and interannual time scales. The NGCUC strengthens (weakens) during summer (winter) and more NGCUC waters are distributed westward and northeastward (eastward). Interannually, the distribution of the NGCUC water is influenced by El Niño-Southern Oscillation, in which most of its eastward-distributed waters shift northward (equatorward) in El Niño (La Niña) phase joining the strengthened NECC (EUC). Changes in the NGCUC water destination can transform the water mass properties in the WTP. The findings of this study also emphasize the fundamental role of eddies in trapping and redistributing the NGCUC waters and linking the currents in the WTP.

Connectivity, the exchange of individuals and genes among geographically separated marine populations, plays a key role in coral reef biodiversity and resilience. The Red Sea is a semi-enclosed basin with dynamic circulation and abundant coral reefs, making it a natural laboratory for coral reef connectivity research. Previous studies broadly investigated Red Sea connectivity, but were spatially restricted to regional or sparsely-distributed reef sites. Here, using hydrodynamic and particle tracking models, a high-resolution circulation-driven physical connectivity atlas covering every Red Sea coral reef, including seasonality, was simulated and further validated against available in-situ genetic datasets. The simulation was conducted without incorporating larval traits to isolate and quantify the connectivity contributed by circulation. Our validation experiment suggests the importance of circulation in shaping the genetic structure of Red Sea reef species, supporting the Isolation By Circulation (IBC) theory in the Red Sea seascape genetics. The simulated atlas reveals that reefs in the northern Red Sea are better sources and destinations than those in the southern basin, regardless of season. The east-west connections between the southern reefs are identified to be weak. Complex circulation dynamics drive a regional-specific seasonality, e.g., the Farasan Islands reefs are better sources during summer while the nearby Bab-Al-Mandeb strait reefs are better sources during winter. The west-coast reefs are generally winter-intensified sources whereas the east-coast reefs are generally summer-intensified sources. The revealed seasonality of physical connectivity is important for larval dispersal processes as reef species may spawn in different seasons. This physical connectivity atlas provides a reference for designing marine conservation strategies from a circulation perspective and easy-to-access physical connectivity datasets for the future Red Sea seascape genetic studies.