Particle Tracking Model Research Articles

Three-dimensional microscale simulation of colloidal particle transport and deposition in model porous media with converging/diverging geometries

The microscale simulation of colloidal particle transport and deposition in porous media was achieved with a novel colloidal particle tracking model, called 3D-PTPO (Three-Dimensional Particle Tracking model by Python® and OpenFOAM®), using a Lagrangian method. Simulations were performed by considering the elementary pore structure as a capillary tube with converging/diverging geometries (tapered pipe and venturi tube). The particles are considered as a mass point during transport in the flow and their volume is reconstructed when they are deposited. The main feature of this novel model is to renew the flow field by reconstructing the pore structure by taking the volume of the deposited particles into account. The influence of the particle Péclet number (Pe) and the pore shape on the particle deposition therein is investigated. The results are analyzed in terms of deposition probability and dimensionless surface coverage as a function of the number of injected particles for a vast range of Péclet numbers thus allowing distinguishing the behavior in diffusion dominant and advection dominant regimes. Finally, the maximum dimensionless surface coverage Γfinal/ΓRSA is studied as a function of Pe. The declining trend observed for high Pe is in good agreement with experimental and simulation results found in the literature.

Analysis of seasonal characteristics of water exchange in Beibu Gulf based on a particle tracking model

The seasonal characteristics of water exchange in Beibu Gulf are investigated based on a particle tracking model. The gulf is divided into six sub-regions in order to better understand the exchange processes and water movement in the gulf. The residence time is computed for each sub-region, and the results show that the whole gulf has a small seasonal variation, with 66 days in winter and 71 days in summer, while the sub-regions exhibit a large seasonal difference with short residence times in summer. Water exchange curves indicate water movement in the gulf follows the circulation patterns. In winter, the water particles move cyclonically and accumulate near the western coast of the gulf. The current flows entering the gulf are dominated by the westward flow from the Qiongzhou Strait. The influence area of this flow can extend to the Vietnam coast. In summer, water particles from the coastal area tend to move offshore and undergo strong mixing in the center of the gulf. The northward current flow from the south opening becomes the dominant flow, with a large influence area in the eastern part of the gulf.

Particle Focusing in Microchannel with Multi-Parallel Channels or Porous Orifice

The sheathless particle focusing in a microchannel installing one set of multi-parallel channels or one porous orifice is proposed in this study. Numerical calculations have been carried out by the Lagrange two-phase model (i.e. the particle tracking model) in PHOENICS software for the microchannel including the porous orifice, in simulating both the channels installing the multi-parallel channels and the porous orifice. It becomes clear from calculation results that the particle focusing may be achieved at lower inlet velocities by using the porous orifice. Low velocities correspond to reduction in the sample flow including particles (i.e. cells). It also becomes obvious that the particle focusing is improved if the porous orifice with taper shape is used. Furthermore, particle focusing experiments have been conducted in the channel including the multi-parallel channels. It becomes clear that the particle focusing may be achieved by using the multi-parallel channels.

Numerical investigation of pollution transport and environmental improvement measures in a tidal bay based on a Lagrangian particle-tracking model

In view of the severity of oceanic pollution, based on the finite volume coastal ocean model (FVCOM), a Lagrangian particle-tracking model was used to numerically investigate the coastal pollution transport and water exchange capability in Tangdao Bay, in China. The severe pollution in the bay was numerically simulated by releasing and tracking particles inside it. The simulation results demonstrate that the water exchange capability in the bay is very low. Once the bay has suffered pollution, a long period will be required before the environment can purify itself. In order to eliminate or at least reduce the pollution level, environmental improvement measures have been proposed to enhance the seawater exchange capability and speed up the water purification inside the bay. The study findings presented in this paper are believed to be instructive and useful for future environmental policy makers and it is also anticipated that the numerical model in this paper can serve as an effective technological tool to study many emerging coastal environment problems.

One-Dimensional Particle Tracking with Streamline Preserving Junctions for Flows in Channel Networks

A pseudo-three-dimensional particle tracking model of drifter paths has been developed to study the movement of scalars through a complex network of tidal channels and junctions. To better simulate dispersion caused by bifurcation and merging at junctions, a localized model is proposed in which particles move along potential flow streamlines through junctions. The model is applied to the Sacramento–San Joaquin Delta in the California Central Valley, and the approach reproduces the observed ultimate fate of the endangered native fish Delta smelt more accurately than a model that fully randomizes particle positions at junctions. The new model also reproduces the very large dispersion that has been previously inferred from Delta-wide heat balances; this large dispersion appears to be associated with flow splits at junctions. Overall, the streamline-following model is likely to be more accurate for long-term planning and management simulations of such complex estuaries than more commonly used cross-sectionally averaged Lagrangian transport equation solvers, which randomize concentration distributions of scalars at junctions, and thereby do not reproduce the increased dispersion mechanisms.

Interannual variability of Danube waters propagation in summer period of 1992–2015 and its influence on the Black Sea ecosystem

The propagation of the Danube River plume has strong interannual variability that impacts the local balance of nutrients and the thermohaline structure in the western Black Sea. In the present study, we use a particle-tracking model based on satellite altimetry measurements and wind reanalysis data, as well as satellite measurements (SeaWiFS, MODIS), to investigate the interannual variability in the Danube plume pathways during the summer from 1993 to 2015. The wind conditions largely define the variability in the Danube water propagation. Relatively low-frequency variability (on periods of a week to months) in the wind stress curl modulates the intensity of the geostrophic Rim Current and related mesoscale eddy dynamics. High-frequency offshore wind-drift currents transport the plume across isobaths and provide an important transport link between shelf and offshore circulation. Inherent plume dynamics play an additional role in the near-mouth transport of the plume and its connection with offshore circulation. During the years with prevailing northeast winds (~ 30% of studied cases), which are usually accompanied by increased wind curl over the Black Sea and higher Danube discharge, an alongshore southward current at the NorthWestern Shelf (NWS) is formed near the western Black Sea coast. Advected southward, the Danube waters are entrained in the Rim Current jet, which transports them along the west coast of the basin. The strong Rim Current, fewer eddies and downwelling winds substantially decrease the cross-shelf exchange of nutrients. During the years with prevailing southeastern winds (~ 40%), the Rim Current is less intense. Mesoscale eddies effectively trap the Danube waters, transporting them to the deep western part of the basin. The low- and high-frequency southeastern wind-drift currents contribute significantly to cross-isobath plume transport and its connection with offshore circulation. During several years (~ 15%), the Danube waters moved eastward to the west coast of Crimea. They were transported on the north periphery of the mesoscale anticyclones due to prevailing eastward wind-drift currents. During the years with hot summers, a monsoon effect induced the formation of a strong anticyclonic wind cell over the NorthWestern Shelf (NWS), and the plume moved northward (~ 15%). Anticyclonic wind circulation leads to the Ekman convergence of brackish surface waters in the centre of the shelf and the formation of a baroclinic geostrophic anticyclone north of the NWS. This anticyclone traps the Danube waters and forces them to remain on the shelf for a long period of time. The impact of the propagation of the plume on the variability in chlorophyll a chlorophyll a in the NWS and the western Black Sea is analysed in this study based on satellite data.

Aerosol deposition predictions in computed tomography-derived skeletons from severe asthmatics: A feasibility study

BackgroundThe authors numerically investigated the correlation between airway skeletons of severe asthmatic human subjects and predicted aerosol deposition to shed light on the effect of environmental factors on asthma risk. We hypothesized that there are asthmatic subjects whose airway skeletal structure can expose the subject to a risk of higher local aerosol deposition compared to subjects with a more common/normal branching pattern. MethodsFrom a population of severe asthmatics studied at total lung capacity via computed tomography we randomly selected 8 subjects whose Forced Expiratory Volume in 1s, percent predicted fell below 45% predicted. To simulate aerosol motion in the human lungs, we employed in-house three-dimensional eddy-resolving computational fluid dynamics and particle tracking models utilizing 3 of the 8 severe asthmatic subjects. One of the 3 subjects was found to have a distinct, localized airway narrowing chosen for further investigation. In the simulation, we controlled flow rate and luminal area, i.e., Reynolds and Stokes numbers, in each branch of the computed tomography-derived airway skeletons. FindingsWe found a distinct enhancement of aerosol deposition associated with the narrowed branches of one subject even when the luminal area was numerically adjusted from its narrowed state to that of a non-asthmatic subject. The branching angle, freed of luminal narrowing persisted in demonstrating a marginally significant increase in local particle deposition compared with the subjects without the initial constriction. InterpretationThese results demonstrate the possibility that inherent airway structure may influence localized constriction found in severe asthmatics.

Complex effect of projected sea temperature and wind change on flatfish dispersal.

Climate change not only alters ocean physics and chemistry but also affects the biota. Larval dispersal patterns from spawning to nursery grounds and larval survival are driven by hydrodynamic processes and shaped by (a)biotic environmental factors. Therefore, it is important to understand the impacts of increased temperature rise and changes in wind speed and direction on larval drift and survival. We apply a particle-tracking model coupled to a 3D-hydrodynamic model of the English Channel and the North Sea to study the dispersal dynamics of the exploited flatfish (common) sole (Solea solea). We first assess model robustness and interannual variability in larval transport over the period 1995-2011. Then, using a subset of representative years (2003-2011), we investigate the impact of climate change on larval dispersal, connectivity patterns and recruitment at the nursery grounds. The impacts of five scenarios inspired by the 2040 projections of the Intergovernmental Panelon Climate Change are discussed and compared with interannual variability. The results suggest that 33% of the year-to-year recruitment variability is explained at a regional scale and that a 9-year period is sufficient to capture interannual variability in dispersal dynamics. In the scenario involving a temperature increase, early spawning and a wind change, the model predicts that (i) dispersal distance (+70%) and pelagic larval duration (+22%) will increase in response to the reduced temperature (-9%) experienced by early hatched larvae, (ii) larval recruitment at the nursery grounds will increase in some areas (36%) and decrease in others (-58%) and (iii) connectivity will show contrasting changes between areas. At the regional scale, our model predicts considerable changes in larval recruitment (+9%) and connectivity (retention -4% and seeding +37%) due to global change. All of these factors affect the distribution and productivity of sole and therefore the functioning of the demersal ecosystem and fisheries management.

Environmental control of harmful dinoflagellates and diatoms in a fjordic system

Fjordic coastlines provide an ideal protected environment for both finfish and shellfish aquaculture operations. This study reports the results of a cruise to the Scottish Clyde Sea, and associated fjordic sea lochs, that coincided with blooms of the diarrhetic shellfish toxin producing dinoflagellate Dinophysis acuta and the diatom genus Chaetoceros, that can generate finfish mortalities. Unusually, D. acuta reached one order of magnitude higher cell abundance in the water column (2840cellsL−1) than the more common Dinophysis acuminata (200cellsL−1) and was linked with elevated shellfish toxicity (maximum 601±237μg OA eq/kg shellfish flesh) which caused shellfish harvesting closures in the region. Significant correlations between D. acuta abundance and that of Mesodinium rubrum were also observed across the cruise transect potentially supporting bloom formation of the mixotrophic D. acuta. Significant spatial variability in phytoplankton that was related to physical characteristics of the water column was observed, with a temperature-driven frontal region at the mouth of Loch Fyne being important in the development of the D. acuta, but not the Chaetoceros bloom. The front also provided important protection to the aquaculture located within the loch, with neither of the blooms encroaching within it. Analysis based on a particle-tracking model confirms the importance of the front to cell transport and shows significant inter-annual differences in advection within the region, that are important to the harmful algal bloom risk therein.

Understanding the separation of particles in a hydrocyclone by force analysis

The multiphase flow in a hydrocyclone is studied using computational fluid dynamics (CFD). The Reynolds stress model (RSM) is used to describe the turbulent characteristics of the gas-liquid flow. The motions of particles are simulated by the Lagrangian particle tracking model (LPT). By the numerical simulation, the forces on particles are obtained and their spatial and statistical distributions are analyzed. The separation mechanisms of different sized particles are proposed based on the analysis. The results show that for small particles the main force is the fluid drag force. As the particle size increases, the fluid drag force decreases exponentially, while the effects of the centrifugal force and pressure gradient force are enhanced. The fluid drag forces in the axial and tangential directions are both rather random, while with the increase of particle size the randomness of the radial force gradually decreases. The particle motion is governed by the inward pressure gradient force, the outward centrifugal force and the fluid drag force with strong randomness. For different sized particles, the value of the outward centrifugal force is essentially about 2.5 times of the inward pressure gradient force, so that large particles get into the downstream and are collected in the spigot. As particle size decreases, the magnitude of the fluid drag force increases. In addition, the direction of the fluid drag force becomes more random, though it is generally inward. Under the inward drag force, a portion of particles are pushed to the central axis and escape through upstream. When the particle size is smaller than a certain value, the fluid drag force is significantly greater than the centrifugal force and pressure gradient force. In such case, the movements of particles are largely random, and the particles in different directions are uniformly distributed.

Using biological-physical modelling for informing sea lice dispersal in Loch Linnhe, Scotland.

Sea lice are a constraint on the sustainable growth of Scottish marine salmonid aquaculture. As part of an integrated pest management approach, farms coordinate procedures within spatial units. We present observations of copepodids being at relatively greater density than nauplii in upper waters, which informs the development of surface layer sea lice transmission modelling of Loch Linnhe, Scotland, for informing farm parasite management. A hydrodynamic model is coupled with a biological particle-tracking model, with characteristics of plankton sea lice. Simulations are undertaken for May and October 2011-2013, forced by local wind data collected for those periods. Particles are continually released from positions representing farm locations, weighted by relative farm counts, over a 2-week period and tracked for a further 5days. A comparison is made between modelled relative concentrations against physical and biological surveys to provide confidence in model outputs. Connectivity between farm locations is determined in order to propose potential coordination areas. Generally, connectivity depends on flow patterns in the loch and decreases with increased farm separation. The connectivity indices are used to estimate the origins of the sea lice population composition at each site, which may influence medicinal regimens to avoid loss of efficacy.

Numerical Simulation of Suspended Sediment Transportation Based on Particle Tracking Model

Coastal engineering that carried out on the muddy seabed were always accompanied by diffusion of suspended sediment, and that would impact on the surrounding marine environment. A 2-D tidal flow mathematical model of the Yueqing Bay was established based on the Lagrange particle tracking model, the diffusion of suspended sediment in pile foundation construction process of a new wharf in the Yueqing Bay was simulated through a continuous moving points method, the calculation results were compared with the one calculated by the traditional convection diffusion method, it showed that the results calculated from the two different methods were similar, therefore it proved the suitability of the Lagrange particle tracing model in the suspended sediment diffusion problems.

The role of subduction and gravitational sinking in particle export, carbon sequestration, and the remineralization length scale in the California Current Ecosystem

AbstractParticles and aggregates created in the surface layers of the ocean are transported not only by gravity, but also by the horizontal and vertical advection of the surrounding water. Subduction, in particular, can transport organic matter from the surface ocean to the mesopelagic in a manner that is not likely to be detected by typical in situ carbon export measurements (e.g., sediment traps and 238U‐234Th disequilibrium). To assess the importance of subduction to the biological pump, we combined in situ sediment trap, thorium, primary productivity, and particulate organic carbon (POC) measurements with a data‐assimilative physical circulation model and a Lagrangian particle tracking model. We develop a simple parameterization of two alternative particle sinking processes (Phytoplankton‐Fecal Pellet [PFP] and Aggregation) using results from 13 extensively sampled water parcels in the California Current Ecosystem. Both parameterizations suggested that subduction is an important, at times dominant, mechanism of POC vertical export in the region (median 44% and 23% contribution to total POC export for PFP and Aggregate parameterizations at the 100‐m depth horizon). The percentage contribution of subduction was highly variable across water parcels (ranging from 7% to 90%), with subduction typically more important in offshore, oligotrophic regions. On average the fate of particles that are passively transported out of the surface layer by advection is different from that of particles that sink across the 100‐m depth horizon. Subducted particles were predominantly remineralized shallower than 150 m, while approximately 50% of gravitationally exported POC was remineralized at depths > 500 m.

The bottom water exchange between the Singapore Strait and the West Johor Strait

As a part of the border between Singapore and Malaysia, the West Johor Strait (WJS) suffered newly from harmful algal blooms. There is no previous study showing the source of the nutrients in the WJS. This paper is investigating the possible water exchange between the water in the WJS and the bottom water in Singapore Strait.This paper adopts a two-level nesting atmosphere-ocean coupled models to downscale the global atmosphere-ocean model into the Singapore coastal water, keeping the large-scale and long-term ocean and climate circulation signals and the advantages of the high-resolution. Based on the high-resolution ocean circulation fields, a Lagrangian particle tracking model is used to trace the Singapore Strait's bottom water movement and the water mixing in the WJS.The results showed that the numerical models well resolved the Singapore coastal water regional circulation. There is a small but significant bottom water (1.25%) transport from the Singapore Strait to the WJS, which occurs from the southwest coastline of Singapore. The bottom water in the Singapore Strait prefers to enter the WJS during the spring tide and the flood period, and stay in Johor Strait for 6.4 days. The spring tide is the first-order factor for the water vertical mixing in the WJS, the wind is also very important for the vertical mixing especially in neap tide condition. An overall very important factor is the light perturbation. With the strongest vertical mixing of nutrients and bottom sediments due to the spring tide, the latter ones may inhibit the light penetration during the spring tide and reduce the algal bloom. The light penetration otherwise is greater during the neap tide, when the winds are the most important factor and hence favor the algal bloom. With the strongest wind in February and the longest permanence time in June and the sufficient nutrient supply in February and June, the most serious algal blooms may happen in February and June in the WJS.

Circulation, dispersion and hydrodynamic connectivity over the Scotian Shelf and adjacent waters

A nested-grid ocean circulation modelling system is used in this study to examine the circulation of surfacewaters over the Scotian Shelf and its adjacent coastal water bodies. The modelling system consists of acoarse-resolution (1/12°) barotropic storm surge (outer) model covering the northwest Atlantic Ocean, and afine-resolution (1/16°) baroclinic (inner) model covering the Gulf of St. Lawrence, Scotian Shelf, and Gulf of Maine.The three-dimensional model currents are used to track trajectories of particles using a Lagrangian particle-trackingmodel. The simulated particle movements and distributions are used to examine the dispersion, retention, andhydrodynamic connectivity of surface waters over the study region. The near-surface dispersion is relatively high overwestern Cabot Strait, the inner Scotian Shelf, and the shelf break of the Scotian Shelf. The dispersion is relatively low inNorthumberland Strait. A process study is conducted to examine the physical processes affecting the surface dispersion,including tidal forcing and local wind forcing. The model results show that the tidal currents significantly influence thedispersion of surface waters in the Bay of Fundy.

Modelling larval dispersal dynamics of common sole (Solea solea) along the western Iberian coast

Individual-based coupled physical-biological models have become the standard tool for studying ichthyoplankton dynamics and assessing fish recruitment. Here, common sole (Solea solea L.), a flatfish of high commercial importance in Europe was used to evaluate transport of eggs and larvae and investigate the connectivity between spawning and nursery areas along the western Iberian coast as spatio-temporal variability in dispersal and recruitment patterns can result in very strong or weak year-classes causing large fluctuations in stock size. A three-dimensional particle tracking model coupled to Regional Ocean Modelling System model was used to investigate variability of sole larvae dispersal along the western Iberian coast over a five-year period (2004–2009). A sensitivity analysis evaluating: (1) the importance of diel vertical migrations of larvae and (2) the size of designated recruitment areas was performed. Results suggested that connectivity patterns of sole larvae dispersal and their spatio-temporal variability are influenced by the configuration of the coast with its topographical structures and thus the suitable recruitment area available as well as the wind-driven mesoscale circulation along the Iberian coast.

Numerical analysis of particle dispersion and combustion characteristics on a piloted coaxial pulverized coal jet flame

A numerical simulation was performed and validated on a piloted coaxial pulverized coal jet flame by means of large eddy simulation (LES) in which the dynamic Smagorinsky SGS model and the Lagrangian particle tracking model were employed. In the devolatilization process, a postulate substance, CaHbOc, was considered as the devolatilized gas. For gaseous phase reactions, a simple two-step global kinetic mechanism was implemented. For a solid phase reaction, a two-step char oxidation reaction was installed. Results were compared to an experimental result in terms of particle distribution, gaseous temperature, gas composition, and particle velocity. The particle distribution result shows that particle dispersion for the combustion case is narrower than that for the non-combustion case. This phenomena is discussed by observing an axial interphase momentum transfer. The axial momentum of fluids can be maintained as high or similar to the particles by combustion, so momentum transfer is limited in the combustion case. It is also confirmed in the particle and gas velocity results. Time-averaged temperature and mole fractions of gases capture the featured characteristics of the experiment well. From these results, an effect of devolatilized gas combustion on particle dispersion and stream flow are discussed. And it is revealed from instantaneous results that particles tends to form groups following the edge of the devolatilized gas combustion.

Modeling the Fate and Distribution of Floating Litter Particles in the Aegean Sea (E. Mediterranean)

A circulation model is coupled to a Lagrangian particle-tracking model to transport floating litter particles in the Aegean Sea, Greece (Eastern Mediterranean). Considering different source regions and release dates, simulations were carried out to explore the fate and distribution of floating litter over 1990-2009, taking into account the seasonal and interannual variability of surface circulation. Model results depicted recurrently high concentrations of floating litter particles in the North Aegean plateau, the Saronikos Gulf, and along Evia and Crete islands. Modelled transport pathways of floating litter demonstrated that source regions are interconnected, with Saronikos Gulf being a main receptor of litter from other sources. Notably higher percent of litter exit (~35%) than enter the model domain (~7%) signified that Aegean Sea seems to act as a source rather than receptor of floating litter pollution in the Eastern Mediterranean Sea. Beached litter was found around 10%, mostly located in the western part of the Aegean Sea. This is the first modelling study to explore the transport of floating marine litter in Greek waters.

Use of Particle Tracking to Determine Optimal Release Dates and Locations for Rehabilitated Neonate Sea Turtles

Sea turtles found stranded on beaches are often rehabilitated before being released back into the wild. The location and date of release is largely selected on an informal basis, which may not maximise the chance of survival. As oceanic conditions have a large influence on the movements of neonate sea turtles, this study aimed to identify the best locations and months to release rehabilitated sea turtles that would assist in their transport by ocean currents to the habitat and thermal conditions required for their survival. A particle tracking model, forced by ocean surface velocity fields were used to simulate the dispersal pathways of millions of passively drifting particles released from different locations in Western Australia. The particles represented rehabilitated, neonate turtles requiring oceanic habitats (green (Chelonia mydas), hawksbill (Eretmochelys imbricata) and loggerheads (Caretta caretta)) and flatback turtles (Natator depressus) which require neritic habitats. The results clearly identified regions and months where ocean currents were more favourable for transport to suitable habitats. Tantabiddi, near Exmouth on the north-west coast, was consistently the best location for release for the oceanic species, with dominant offshore-directed currents and a very narrow continental shelf reducing the time taken for particles to be transported into deep water. In contrast, release locations with more enclosed geography, wide continental shelves, and/or proximity to cooler ocean temperatures were less successful. Our results produced a decision support system for the release of neonate marine turtles in Western Australia and our particle tracking approach has global transferability.

Fate of microplastics and mesoplastics carried by surface currents and wind waves: A numerical model approach in the Sea of Japan

A numerical model was established to reproduce the oceanic transport processes of microplastics and mesoplastics in the Sea of Japan. A particle tracking model, where surface ocean currents were given by a combination of a reanalysis ocean current product and Stokes drift computed separately by a wave model, simulated particle movement. The model results corresponded with the field survey. Modeled results indicated the micro- and mesoplastics are moved northeastward by the Tsushima Current. Subsequently, Stokes drift selectively moves mesoplastics during winter toward the Japanese coast, resulting in increased contributions of mesoplastics south of 39°N. Additionally, Stokes drift also transports micro- and mesoplastics out to the sea area south of the subpolar front where the northeastward Tsushima Current carries them into the open ocean via the Tsugaru and Soya straits. Average transit time of modeled particles in the Sea of Japan is drastically reduced when including Stokes drift in the model.