Littérature scientifique sur le sujet « Lagrangian dispersal models »
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Articles de revues sur le sujet "Lagrangian dispersal models"
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Kim, Moonil, Seonghun Lee, Songhee Lee, Koong Yi, Hyung-Sub Kim, Sanghoon Chung, Junmo Chung, Hyun Seop Kim et Tae Kyung Yoon. « Seed Dispersal Models for Natural Regeneration : A Review and Prospects ». Forests 13, no 5 (23 avril 2022) : 659. http://dx.doi.org/10.3390/f13050659.
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Natural regeneration in forest management, which relies on artificial planting, is considered a desirable alternative to reforestation. However, there are large uncertainties regarding the natural regeneration processes, such as seed production, seed dispersal, and seedling establishment. Among these processes, seed dispersal by wind must be modeled accurately to minimize the risks of natural regeneration. This study aimed to (1) review the main mechanisms of seed dispersal models, their characteristics, and their applications and (2) suggest prospects for seed dispersal models to increase the predictability of natural regeneration. With improving computing and observation systems, the modeling technique for seed dispersal by wind has continued to progress steadily from a simple empirical model to the Eulerian-Lagrangian model. Mechanistic modeling approaches with a dispersal kernel have been widely used and have attempted to be directly incorporated into spatial models. Despite the rapid development of various wind-dispersal models, only a few studies have considered their application in natural regeneration. We identified the potential attributes of seed dispersal modeling that cause high uncertainties and poor simulation results in natural regeneration scenarios: topography, pre-processing of wind data, and various inherent complexities in seed dispersal processes. We suggest that seed dispersal models can be further improved by incorporating (1) seed abscission mechanisms by wind, (2) spatiotemporally complex wind environments, (3) collisions with the canopy or ground during seed flight, and (4) secondary dispersal, long-distance dispersal, and seed predation. Interdisciplinary research linking climatology, biophysics, and forestry would help improve the prediction of seed dispersal and its impact on natural regeneration.
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Reynolds, A. M. « Incorporating Sweeps and Ejections into Lagrangian Stochastic Models of Spore Trajectories Within Plant Canopy Turbulence : Modeled Contact Distributions Are Heavy-Tailed ». Phytopathology® 102, no 11 (novembre 2012) : 1026–33. http://dx.doi.org/10.1094/phyto-01-12-0002.
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The turbulent dispersal of fungal spores within plant canopies is very different from that within atmospheric boundary-layers and closely analogous to dispersal within turbulent mixing-layers. The process is dominated by the presence of large coherent flow structures, high-velocity downdrafts (sweeps) and updrafts (ejections), that punctuate otherwise quiescent flow. Turbulent dispersion within plant canopies is best predicted by Lagrangian stochastic (particle-tracking) models because other approaches (e.g., diffusion models and similarity theory) are either inappropriate or invalid. Nonetheless, attempts to construct such models have not been wholly successful. Accounting for sweeps and ejections has substantially worsened rather than improved model agreement with experimental dispersion data. Here we show how this long-standing difficulty with the formulation of Lagrangian stochastic models can be overcome. The new model is shown to be in good agreement with data from a carefully controlled, well-documented wind-tunnel study of scalar dispersion within plant canopy turbulence. Equally good agreement with this data is obtained using Thomson's (1987) Gaussian model. This bolsters confidence in the application of this simple model to the prediction of spore dispersal within plant canopy turbulence. Contact distributions—the probability distribution function for the distance of viable fungal spore movement until deposition—are predicted to have “heavy” inverse power-law tails. It is known that heavy-tailed contact distributions also characterize the dispersal of spores which pass through the canopy turbulence and enter into the overlying atmospheric boundary-layer. Plant disease epidemics due to the airborne dispersal of fungal spores are therefore predicted to develop as accelerating waves over a vast range of scales—from the within field scale to intercontinental scales. This prediction is consistent with recent analyses of field and historical data for rusts in wheat. Such plant disease epidemics are shown to be governed by space-fractional diffusion equations and by Lévy flights.
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Rühs, Siren, Victor Zhurbas, Inga M. Koszalka, Jonathan V. Durgadoo et Arne Biastoch. « Eddy Diffusivity Estimates from Lagrangian Trajectories Simulated with Ocean Models and Surface Drifter Data—A Case Study for the Greater Agulhas System ». Journal of Physical Oceanography 48, no 1 (janvier 2018) : 175–96. http://dx.doi.org/10.1175/jpo-d-17-0048.1.
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AbstractThe Lagrangian analysis of sets of particles advected with the flow fields of ocean models is used to study connectivity, that is, exchange pathways, time scales, and volume transports, between distinct oceanic regions. One important factor influencing the dispersion of fluid particles and, hence, connectivity is the Lagrangian eddy diffusivity, which quantifies the influence of turbulent processes on the rate of particle dispersal. Because of spatial and temporal discretization, turbulence is not fully resolved in modeled velocities, and the concept of eddy diffusivity is used to parameterize the impact of unresolved processes. However, the relations between observation- and model-based Lagrangian eddy diffusivity estimates, as well as eddy parameterizations, are not clear. This study presents an analysis of the spatially variable near-surface lateral eddy diffusivity estimates obtained from Lagrangian trajectories simulated with 5-day mean velocities from an eddy-resolving ocean model (INALT01) for the Agulhas system. INALT01 features diffusive regimes for dynamically different regions, some of which exhibit strong suppression of eddy mixing by mean flow, and it is consistent with the pattern and magnitude of drifter-based eddy diffusivity estimates. Using monthly mean velocities decreases the estimated diffusivities less than eddy kinetic energy, supporting the idea that large and persistent eddy features dominate eddy diffusivities. For a noneddying ocean model (ORCA05), Lagrangian eddy diffusivities are greatly reduced, particularly when the Gent and McWilliams parameterization of mesoscale eddies is employed.
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Theuerkauf, Martin, Anna Kuparinen et Hans Joosten. « Pollen productivity estimates strongly depend on assumed pollen dispersal ». Holocene 23, no 1 (16 juillet 2012) : 14–24. http://dx.doi.org/10.1177/0959683612450194.
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Past plant abundance may be reconstructed from pollen data if dispersal distances of pollen and pollen productivities of each taxon are known. Using surface sediment samples from small and medium sized, closed and near circular lakes from lowland Central Europe, we tested the validity of three pollen dispersal models by comparing empirical pollen data from each lake with simulated pollen data derived from applying various pollen dispersal models to vegetation data from rings situated up to 100 km from each site. Pollen assemblages simulated with a Lagrangian stochastic (LS) model best fit real pollen assemblages, simulations with the commonly used Prentice model on pollen dispersal underestimated the amount of pollen arriving from distances larger than 10 km and overestimated the differences in dispersal distances between lighter ( Pinus) and heavier ( Fagus, Picea) pollen grains. The LS model appeared to provide more appropriate simulations. Pollen productivity estimates (PPEs) calculated for the data set showed that the choice of the dispersal model has great impact on the results. If derived with the Prentice model, PPEs for Fagus and Picea are three times higher than with the LS model. Studies on pollen productivities thus need to consider the apparent limitations of the Prentice model. We suggest an alternative approach, which uses simulations instead of the extended R-value model, to calculate PPEs. The approach is flexible in the use of dispersal functions and produced consistent results for two independent data sets from small and medium sized lakes.
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Stephens, S. A., N. Broekhuizen, A. B. Macdiarmid, C. J. Lundquist, L. McLeod et R. Haskew. « Modelling transport of larval New Zealand abalone (Haliotis iris) along an open coast ». Marine and Freshwater Research 57, no 5 (2006) : 519. http://dx.doi.org/10.1071/mf06020.
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The dispersal and transport of larval New Zealand abalone Haliotis iris was simulated using coupled two-dimensional hydrodynamic and Lagrangian particle-trajectory models. The aim was to estimate pelagic larval dispersal potential along the open coast, as a starting point from which basic management questions can be made for this recreationally and commercially important species. Larval dispersal was simulated from representative spawning sites under a range of representative hydrodynamic conditions, including wave-induced circulation cells. Larval presence over near-shore reef habitat declined as the energy of the flow field and corresponding larval dispersal and transport increased. Thus, spawning during high-energy conditions will promote dispersal and transport but reduce successful recruitment on near-shore reefs. This indicates that seeding of the adjacent coast is likely to be sporadic, with existing populations necessarily being somewhat self-recruiting. Results suggest that an ideal management system would ensure that adult populations were maintained at intervals of 10–30 km along the coast to maintain larval supply to areas in between. Dispersal characteristics were specific to the release site, and the simulations suggest that marine reserves can be positioned to accordingly achieve desired functions: for example, optimal choices can be made for seeding areas, recruitment or self-maintaining areas.
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Seredyn, Tomasz, Adam Dziubiński et Piotr Jaśkowski. « CFD Analysis of the Fluid Particles Distribution by Means of Aviation Technique ». Transactions on Aerospace Research 2018, no 1 (1 mars 2018) : 67–97. http://dx.doi.org/10.2478/tar-2018-0006.
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Abstract The article describes a computational study, using CFD models, of droplet spray dispersal in the wake of a ‘Turbo Kruk’ airplane up to 500 m downstream. The CFD Reynolds-averaged Navier-Stokes (RANS) models use a Lagrangian (droplet phase) and Eulerian (fluid phase) procedure to predict the droplet trajectories trough the turbulent aircraft wake. The methods described in the work have the potential to improve current models for aerial spraying and will help in the development of new spraying procedures. In this study, the CFD models are used to describe the phenomenon of sprays released from atomizers mounted on the plane. A parametric study of the aircraft model examines the effects of crosswind on the aircraft’s vortex structures and the resulting droplet trajectories. The study shows, that such influence is underestimated in the current models. A comparison of the present results to AGDISP predictions is provided.
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Rupolo, Volfango. « A Lagrangian-Based Approach for Determining Trajectories Taxonomy and Turbulence Regimes ». Journal of Physical Oceanography 37, no 6 (1 juin 2007) : 1584–609. http://dx.doi.org/10.1175/jpo3038.1.
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Abstract The use of the ratio between the acceleration and velocity time scales y = Ta/Tυ to separate Lagrangian trajectories in homogeneous classes is proposed. In fact, when analyzing subsurface floats data in the Atlantic Ocean and surface drifters data in the world’s ocean basins, it is observed that trajectories having different values of y are characterized by different shapes, correlation, and dispersal properties. In particular, trajectories having similar values of the acceleration and velocity time scales clearly show the influence of eddies and are characterized by an oscillating velocity correlation function. It is shown here that this trajectory screening is a useful procedure to rationalize the analysis of real Lagrangian trajectories and to avoid a mixture of different regimes, when averaging quantities. The mean statistical quantities computed averaging on quasi-homogeneous datasets put in evidence the role of the coherent structures in the dispersion properties, both in time and in the main oceanic current systems. These results are discussed in the context of the parameterization of eddy diffusivity in general circulation models.
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Nilsson, Jenny A. U., Kristofer Döös, Paolo M. Ruti, Vincenzo Artale, Andrew Coward et Laurent Brodeau. « Observed and Modeled Global Ocean Turbulence Regimes as Deduced from Surface Trajectory Data ». Journal of Physical Oceanography 43, no 11 (1 novembre 2013) : 2249–69. http://dx.doi.org/10.1175/jpo-d-12-0193.1.
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Abstract A large-scale tool for systematic analyses of the dispersal and turbulent properties of ocean currents and the subsequent separation of dynamical regimes according to the prevailing trajectories taxonomy in a certain area was proposed by Rupolo. In the present study, this methodology has been extended to the analysis of model trajectories obtained by analytical computations of the particle advection equation using the Lagrangian open-source software package Tracing the Water Masses of the North Atlantic and the Mediterranean (TRACMASS), and intercomparisons have been made between the surface velocity fields from three different configurations of the global Nucleus for European Modelling of the Ocean (NEMO) ocean/sea ice general circulation model. Lagrangian time scales of the observed and synthetic trajectory datasets have been calculated by means of inverse Lagrangian stochastic modeling, and the influence of the model field spatial and temporal resolution on the analyses has been investigated. In global-scale ocean modeling, compromises are frequently made in terms of grid resolution and time averaging of the output fields because high-resolution data require considerable amounts of storage space. Here, the implications of such approximations on the modeled velocity fields and, consequently, on the particle dispersion, have been assessed through validation against observed drifter tracks. This study aims, moreover, to shed some light on the relatively unknown turbulent properties of near-surface ocean dynamics and their representation in numerical models globally and in a number of key regions. These results could be of interest for other studies within the field of turbulent eddy diffusion parameterization in ocean models or ocean circulation studies involving long-term coarse-grid model experiments.
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Reynolds, Andy M., et Don R. Reynolds. « Aphid aerial density profiles are consistent with turbulent advection amplifying flight behaviours : abandoning the epithet ‘passive’ ». Proceedings of the Royal Society B : Biological Sciences 276, no 1654 (9 septembre 2008) : 137–43. http://dx.doi.org/10.1098/rspb.2008.0880.
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Seminal field studies led by C. G. Johnson in the 1940s and 1950s showed that aphid aerial density diminishes with height above the ground such that the linear regression coefficient, b , of log density on log height provides a single-parameter characterization of the vertical density profile. This coefficient decreases with increasing atmospheric stability, ranging from −0.27 for a fully convective boundary layer to −2.01 for a stable boundary layer. We combined a well-established Lagrangian stochastic model of atmospheric dispersal with simple models of aphid behaviour in order to account for the range of aerial density profiles. We show that these density distributions are consistent with the aphids producing just enough lift to become neutrally buoyant when they are in updraughts and ceasing to produce lift when they are in downdraughts. This active flight behaviour in a weak flier is thus distinctly different from the aerial dispersal of seeds and wingless arthropods, which is passive once these organisms have launched into the air. The novel findings from the model indicate that the epithet ‘passive’ often applied to the windborne migration of small winged insects is misleading and should be abandoned. The implications for the distances traversed by migrating aphids under various boundary-layer conditions are outlined.
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Ospina-Alvarez, A., S. de Juan, J. Alós, G. Basterretxea, A. Alonso-Fernández, G. Follana-Berná, M. Palmer et IA Catalán. « MPA network design based on graph theory and emergent properties of larval dispersal ». Marine Ecology Progress Series 650 (17 septembre 2020) : 309–26. http://dx.doi.org/10.3354/meps13399.
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Despite the recognised effectiveness of networks of marine protected areas (MPAs) as a biodiversity conservation instrument, MPA network design frequently disregards the importance of connectivity patterns. In the case of sedentary marine populations, connectivity stems not only from the stochastic nature of the physical environment that affects dispersal of early life stages, but also from the spawning stock attributes that affect reproductive output (e.g. passive eggs and larvae) and survivorship. Early life stages are virtually impossible to track in the ocean. Therefore, numerical ocean current simulations coupled with egg and larval Lagrangian transport models remain the most common approach for the assessment of marine larval connectivity. Inferred larval connectivity may differ depending on the type of connectivity considered; consequently, the prioritisation of sites for the conservation of marine populations might also differ. Here, we introduce a framework for evaluating and designing MPA networks based on the identification of connectivity hotspots using graph theoretic analysis. As a case study, we used a network of open-access areas and MPAs off Mallorca Island (Spain), and tested its effectiveness for the protection of the painted comber Serranus scriba. Outputs from network analysis were used to (1) identify critical areas for improving overall larval connectivity, (2) assess the impact of species’ biological parameters in network connectivity and (3) explore alternative MPA configurations to improve average network connectivity. Results demonstrate the potential of graph theory to identify non-trivial egg/larval dispersal patterns and emerging collective properties of the MPA network, which are relevant for increasing protection efficiency.
Thèses sur le sujet "Lagrangian dispersal models"
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Ross, Rebecca E. « Investigating the role of larval dispersal models in the development of an 'ecologically coherent' network of deep sea marine protected areas ». Thesis, University of Plymouth, 2016. http://hdl.handle.net/10026.1/6560.
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There is currently worldwide pressure to establish Marine Protected Area (MPA) networks which are self-sustaining and will persistently protect habitats and species. In order for MPA networks to be effective, the species targeted for conservation must be able to disperse between protected areas and maintain a gene-flow necessary for population sustainability and persistence. This warrants new research on how to quantify and map faunal dispersal to ensure that protection will be effective and sustainable. Population genetic methods have merit, with the ability to track parentage and gene flow between areas directly. However the costs, quantity of samples, and time required to genetically quantify dispersal for multiple species make these approaches prohibitive as the only method of assessment, especially in relatively inaccessible offshore waters. Dispersal modelling is now becoming more accessible and may fulfil immediate needs in this field (although ground truthing will be necessary in the future). There have been very few dispersal modelling studies focussed on deep sea or offshore areas, predominantly due to the lack of high resolution hydrodynamic models with sufficient geographic extent away from shore. Current conclusions have been drawn based on shallow water coastal studies, informing offshore MPA network size and spacing. However the differences between these two environments may mean that dispersal abilities are not comparable. Deep water receives less influence from wind and weather, and the scales are vastly different in terms of a) the depth ranges covered, b) the planktonic larval durations (PLDs) of animals, and c) the geographic areas concerned as a consequence. Global hydrodynamic models with reasonable resolution are now becoming more accessible. With the outputs from these models, and freely available particle simulators, it is becoming more practical to undertake offshore deep water dispersal studies. This thesis aims to undertake an analysis of these accessible modelling tools within a deep sea context. The guidelines which are currently available to dispersal modellers are yet to encompass the needs of deep water modellers which may require some additional considerations given the extended depth range covered and the different hydrodynamic drivers away from the air/sea interface. Chapter 1 reviews the larval dispersal process, the factors which may affect dispersal success, and those which should be incorporated into future predictions of dispersal. The current methods for assessing larval dispersal are explored covering genetics, elemental tagging and modelling approaches with an extended look at modelling considerations. Existing marine conservation policy is also touched on in the context of connectivity and larval dispersal. Chapter 2 is designed to inform future deep sea modellers on how to parameterise and understand a dispersal model. As models appear as a ‘black box’ to the majority of users, sensitivity tests can offer a way of scaling model inputs and tempering expectations from model outputs. A commonly used model pairing (the HYCOM hydrodynamic model and the Connectivity Modeling System) is assessed, using parameters which link to the temporal and spatial scales of mixing in the modelled system: timestep of particle tracer, horizontal and vertical positioning of release points, release frequency of larvae, and temporal range of simulation. All parameters were shown to have a decreased sensitivity with depth, with patterns reflecting local watermass structure. Future studies observing similar hydrodynamic conditions seeking to optimise their model set up would be advised to stratify their model release locations with depth. A means to incorporate all sensitivity test results into optimal input parameters for future studies is demonstrated. Chapter 3 investigates whether dispersal models provide any advantage over a “sphere of influence” estimate based on average current speeds and PLDs: there is no use pursuing dispersal modelling if the outputs are too erroneous to provide any advantage over a back-of-the-envelope calculation. This chapter examines the outputs of two dispersal models driven by two different hydrodynamic models in order to observe the variability in prediction between models. This model comparison revealed a greater disparity between hydrodynamic model predictions than has been previously understood by ecologists. The two models compared (POLCOMS and HYCOM) may equally be considered as suitable to promote realism in the study region, but slight differences in resolution and numerical error handling resulted in dispersal predictions from which opposing conclusions can be drawn. This chapter therefore emphasises the necessity for model ground truthing before predictions can be trusted. Chapter 4 assimilates the findings of the previous chapters and applies their advice to a study of MPA network dispersal connectivity. Using the hydrodynamic model which performed best in chapter 3 (HYCOM), a simulation was undertaken for cold water coral (Lophelia pertusa (Linnaeus 1758)) larval dispersal between already established MPAs in the NE Atlantic. As larval characters have only been observed ex situ, dispersal was simulated using two null models (passive and active vertical migration) and averaged to provide an intermediate prediction. A method for assessing dispersal within MPAs and MPA networks is offered based on the intermediate prediction, as well as a network wide assessment of the difference in dispersal patterns for passive and active larvae. It was found that the existing network performs well at supplying larvae to non-networked sites, but performs poorly at supplying other MPAs. The ‘best’ MPAs were central to the network and facilitated the traverse of regional gaps in suitable habitat. The ‘worst’ MPAs were peripheral to the network and small in size. Network-wide passive and active dispersal matrices had no significant difference between them. However site specific variability in the effect of vertical migration was detected subject to variability in local topographic barriers to dispersal, only some of which could be surmounted with vertical migration. All chapters aim to inform future deep sea dispersal modellers, and encourage exploration of this tool in other contexts, as well as marine conservation. The thesis cautions against the transplantation of shallow water assumptions to deep water environments, and advocates region specific studies and mandatory ground truthing of predictions. An upcoming study will ground truth the findings of this thesis with both genetic and oceanographic data, allowing the accuracy of study results to be quantified.
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Guillaumot, Charlène. « Modelling the response of Antarctic marine species to environmental changes. Methods, applications and limitations ». Electronic Thesis or Diss., Bourgogne Franche-Comté, 2021. http://www.theses.fr/2021UBFCK020.
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Parmi les outils qui permettent de mieux comprendre les systèmes naturels, la modélisation écologique a connu un essor particulièrement important depuis une vingtaine d’années. Les modèles écologiques, représentation simplifiée d’une réalité complexe, permettent de mettre en avant les facteurs environnementaux qui déterminent la niche écologique des espèces et de mieux comprendre leur réponse aux changements de l’environnement. Dans le cas des faunes marines antarctiques, la modélisation écologique fait face à plusieurs défis méthodologiques. Les jeux de données de présence des espèces sont très souvent agrégés dans le temps et dans l’espace, à proximité des stations de recherche. Ces données sont souvent trop peu nombreuses pour caractériser l’espace environnemental occupé par les espèces ainsi que leur physiologie. Enfin, les jeux de données environnementales manquent encore de précision pour finement représenter la complexité des habitats marins. Dans ces conditions, est-il possible de générer des modèles performants et justes à l’échelle de l’océan Austral ? Quelles sont les approches possibles et leurs limites ? Comment améliorer les méthodes afin de générer de meilleurs modèles ? Au cours de ce travail de thèse, trois types de modèles ont été étudiés et leurs performances évaluées. (1) Les modèles physiologiques de type DEB (Dynamic Energy Budget) simulent la manière dont l’environnement abiotique influe sur le métabolisme des individus et proposent une représentation de la niche fondamentale des espèces. (2) Les modèles de distribution d’espèces (SDMs pour Species Distribution Models) prédisent la probabilité de distribution des espèces en étudiant la relation spatiale entre données de présence et environnement. Ils proposent une représentation de la niche réalisée des espèces. Enfin (3), les modèles de dispersion de type lagrangien prédisent le mouvement de propagules dans les masses d’eau. Les résultats montrent que les modèles physiologiques réussissent à simuler les variations métaboliques des espèces antarctiques en fonction de l’environnement et à prédire les dynamiques de populations. Cependant, davantage de données sont nécessaires pour pouvoir caractériser finement les différences physiologiques entre populations et évaluer correctement les modèles. Les résultats obtenus pour les SDMs montrent que les modèles générés à l’échelle de l’océan Austral et leurs prédictions futures ne sont pas fiables du fait du manque de données disponibles pour caractériser l’espace occupé par les espèces, du manque de précision des scénarios climatiques futurs et de l’impossibilité d’évaluer les modèles. De plus, les modèles extrapolent sur une très grande proportion de l’espace projeté. L’apport d’information complémentaire sur les limites physiologiques des espèces (observations, résultats d’expériences, sorties de modèles physiologiques) permet de réduire l’extrapolation et d’augmenter la capacité des modèles à décrire la niche réalisée des espèces. L’agrégation spatiale des données, qui influençait les prédictions et l’évaluation des modèles a également pu être corrigée. Enfin, les modèles de dispersion ont montré un potentiel intéressant pour révéler le rôle des barrières géographiques ou à l’inverse, la connectivité spatiale, mais également le lien existant entre distribution, physiologie et histoire phylogénétique des espèces. Ce travail de thèse propose de nombreux conseils et fournit des codes annotés parfois sous forme de tutoriels, afin de constituer une aide utile aux futurs travaux de modélisation sur les espèces marines antarctiquesAmong tools that are used to fill knowledge gaps on natural systems, ecological modelling has been widely applied during the last two decades. Ecological models are simple representations of a complex reality. They allow to highlight environmental drivers of species ecological niche and better understand species responses to environmental changes. However, applying models to Southern Ocean benthic organisms raises several methodological challenges. Species presence datasets are often aggregated in time and space nearby research stations or along main sailing routes. Data are often limited in number to correctly describe species occupied space and physiology. Finally, environmental datasets are not precise enough to accurately represent the complexity of marine habitats. Can we thus generate performant and accurate models at the scale of the Southern Ocean ? What are the limits of such approaches ? How could we improve methods to build more relevant models ? In this PhD thesis, three different model categories have been studied and their performance evaluated. (1) Mechanistic physiological models (Dynamic Energy Budget models, DEB) simulate how the abiotic environment influences individual metabolism and represent the species fundamental niche. (2) Species distribution models (SDMs) predict species distribution probability by studying the relationship between species presences and the environment. They represent the species realised niche. (3) Dispersal lagrangian models predict the drift of propagules in water masses. Results show that physiological models can be developed for marine Southern Ocean species to simulate the metabolic variations in link with the environment and predict population dynamics. However, more data are necessary to highlight detailed physiological contrasts between populations and to accurately evaluate models. Results obtained for SDMs suggest that models generated at the scale of the Southern Ocean and future simulations are not relevant, given the lack of data available to characterise species occupied space, the lack of precision and accuracy of future climate scenarios and the impossibility to evaluate models. Moreover, model extrapolate on a large proportion of the projected area. Adding information on species physiological limits (observations, results from experiments, physiological model outputs) was shown to reduce extrapolation and to improve the capacity of models to estimate the species realised niche. Spatial aggregation of occurrence data, which influenced model predictions and evaluation was also succefully corrected. Finally, dispersal models showed an interesting potential to highlight the role of geographic barriers or conversely of spatial connectivity and also the link between species distribution, physiology and phylogeny history. This PhD thesis provides methodological advices, annoted codes and tutorials to help implement future modelling works applied to Southern Ocean marine species
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Lönnell, Niklas. « Dispersal of bryophytes across landscapes ». Doctoral thesis, Stockholms universitet, Institutionen för ekologi, miljö och botanik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-100064.
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Dispersal, especially long-distance dispersal, is an important component in many disciplines within biology. Many species are passively dispersed by wind, not least spore-dispersed organisms. In this thesis I investigated the dispersal capacity of bryophytes by studying the colonization patterns from local scales (100 m) to landscape scales (20 km). The dispersal distances were measured from a known source (up to 600 m away) or inferred from a connectivity measure (1–20 km). I introduced acidic clay to measure the colonization rates over one season of a pioneer moss, Discelium nudum (I–III). I also investigated which vascular plants and bryophytes that had colonized limed mires approximately 20–30 years after the first disturbance (IV). Discelium effectively colonized new disturbed substrates over one season. Most spores were deposited up to 50 meters from a source but the relationship between local colonization rates and connectivity increased with distance up to 20 km (I–III). Also calcicolous wetland bryophyte species were good colonizers over similar distances, while vascular plants in the same environment colonized less frequently. Common bryophytes that produce spores frequently were more effective colonizers, while no effect of spore size was detected (IV). A mechanistic model that take into account meteorological parameters to simulate the trajectories for spores of Discelium nudum fitted rather well to the observed colonization pattern, especially if spore release thresholds in wind variation and humidity were accounted for (III). This thesis conclude that bryophytes in open habitats can disperse effectively across landscapes given that the regional spore source is large enough (i.e. are common in the region and produce spores abundantly). For spore-dispersed organisms in open landscapes I suggest that it is often the colonization phase and not the transport that is the main bottle-neck for maintaining populations across landscapes.At the time of the doctoral defence the following papesr were unpublished and had a status as follows: Paper 2: Epubl ahead of print; Paper 3: Manuscript; Paper 4: Manuscript
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Goncalves, Juliana Bittencourt. « EMPREGO DE UM MODELO DE DISPERSÃO TURBULENTO NO ESTUDO DA UNIVERSALIDADE DA TAXA DE DISSIPAÇÃO DA ENERGIA ». Universidade Federal de Santa Maria, 2010. http://repositorio.ufsm.br/handle/1/10254.
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Conselho Nacional de Desenvolvimento Científico e TecnológicoThis study employed different autocorrelation functions and Maclaurin series expansions in the derivation of expressions describing the dissipation rate of turbulent kinetic energy. These expressions have the same functional form, but are described in terms of different numerical coefficients. The values obtained for the numerical coefficients were used in a Lagrangian stochastic dispersion model to simulate the dispersion of contaminants in the Planetary Boundary Layer (PBL). The simulation results were compared with concentration data observed in the Copenhagen experiment. The good performance of the parameterization and analysis through statistical indices showed that the mathematical relationships that describe the turbulent dissipation rate present an uncertainty. The analysis developed in this study indicates that there is no a universal functional form describing the dissipation rate of turbulent energy.
Neste estudo foram empregadas diferentes funções de autocorrelação e expansões em série de Maclaurin na derivação de expressões que descrevem a taxa de dissipação da energia cinética turbulenta. Estas expressões apresentam a mesma forma funcional, porém são descritas em termos de diferentes coeficientes numéricos. Os valores obtidos para os coeficientes numéricos foram empregados em um modelo de dispersão estocástico Lagrangiano para simular a dispersão de contaminantes na Camada Limite Planetária (CLP). Os resultados das simulações foram comparados com dados de concentração do experimento de Copenhagen. O bom desempenho da parametrização e a análise através de índices estatísticos permitiram concluir que as relações matemáticas que descrevem a taxa de dissipação da turbulenta, apresentam uma incerteza. A análise desenvolvida nesse estudo permite concluir que não existe uma forma funcional universal descrevendo a taxa de dissipação de energia turbulenta.
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Riffel, Morgana Silva Franco. « Simulação da dispersão de poluentes por modelo lagrangeano em condições de vento fraco ». reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2007. http://hdl.handle.net/10183/12011.
Texte intégralRésumé :
Neste trabalho, a partir de dados rotineiramente medidos em estações meteorológicas de superfície, estimamos os parâmetros de escala da Camada Limite Planetária (CLP) do experimento OLAD (Over Land Atmospheric Dispersion). Esses parâmetros são muito importantes no processo de dispersão, especialmente no cálculo das parametrizações para os modelos de dispersão atmosférica. Simular o processo de dispersão de poluentes na atmosfera sob a condição de vento fraco é uma tarefa difícil. Nesse sentido, realizamos a implementação e avaliação de um modelo de partícula lagrangeano semi-analítico, denominado ILS-LW (Iterative Langevin Solution for Low Wind) para investigar o processo de dispersão atmosférica em situações de vento fraco. A avaliação foi feita mediante comparação entre os resultados das simulações numéricas e os dados de concentração obtidos no experimento OLAD. Os dados experimentais foram coletados em um sítio experimental localizado no West Desert Test Center (WDTC), Utah, nos Estados Unidos, com a colaboração do exército americano e supervisões do National Oceanic and Atmospheric Administration (NOAA) e Air Resources Laboratory Field Research Division (ARLFRD), em setembro de 1997. Concluímos que o modelo ILS-LW reproduz satisfatoriamente o conjunto de dados testado.In this work, we present estimates for Boundary Layer Planetary's scaling parameters for the data obtained by superficial meteorological stations of the Over Land Atmospheric Dispersion (OLAD) experimento These parameters are very important, specially for the estimate of parametrizations for the atmospheric dispersion models. The simulation of the atmospheric pollutant dispersion under low wind speed is not a trivial task. We have tested and evaluated a semi-analytic model with lagrangean particles, that we refer to as the Iterative Langevin Solution for Low Wind (ILS-LW), in order to investigate the atmospheric dispersion process in low wind speed conditions. The evaluation was done by comparing the results generated by the numerical simulations and the concentration dataset from OLAD experimento The experimental data were obtained on an experimental site at the West Desert Test Center (WDTC), Utah, USA, under colaboration ofthe american army and supervision by the National Oceanic and Atmospheric Administration (NOAA) and Air Resources Laboratory Field Research Division (ARLFRD) in September, 1997. We conclude that the model ILS-LW reproduces reasonably the tested data.
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Zacharias, Daniel Constantino. « Desenvolvimento do STFM (Spill, Transport and Fate Model) : Modelo computacional lagrangeano de transporte e degradação de manchas de óleo ». Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/14/14133/tde-08052018-192547/.
Texte intégralRésumé :
Os derramamentos de petróleo são consequência inevitável e indesejável da produção e transporte do petróleo e seus derivados. A maioria desses derramamentos são relativamente pequenos, mas alguns deles são grandes o suficiente para causar significativo impacto ambiental. Nessas situações, os modelos computacionais são ferramentas importantes para estimar a trajetória, dimensionamento e comportamento do óleo derramado no ambiente marinho, sendo determinantes na elaboração de planos de ação e trabalho das equipes de resposta. O transporte e destino de óleo offshore derramado são regidos majoritariamente, no curto período, por processos de transporte e de transformação físico-químicos e no longo período por processos de degradação biológica, de acordo com as condições ambientais locais (oceânicas e atmosféricas). Os principais processos que atuam sobre as manchas de óleo offshore incluem, no curto período, advecção, difusão turbulenta, espalhamento superficial, evaporação, dissolução, emulsificação, sedimentação e a interação de mancha de óleo com a linha da costa. O STFM (Spill, Transport and Fate Model) foi o modelo computacional desenvolvido nesse trabalho. Os algoritmos foram desenvolvidos com base em formulações físico-químicas propostas na literatura, sendo testadas as proposições de diversos autores e selecionadas as equações que apresentaram melhores resultado para integrar o conjunto físico-químico que compõe o STFM. Os resultados do trabalho mostraram que o STFM apresentou desempenho superior aos demais modelos testados na descrição do espalhamento e difusão dando mais estabilidade à mancha por utilizar a derivação de Dodge para a proposta de espalhamento de Fay e substituir o método usual de Randon Walk por Randon Flight (avançado no tempo) na forma canônica dada por Lynch. O algoritmo do STFM também traz outra evolução importante ao incluir um modelo de evaporação baseado nas equações empíricas de Fingas, substituindo as atuais parametrizações baseadas no ADIOS2 e nos métodos de pseudocomponentes.Oil and its by-products spills are an inevitable and undesirable consequence of their production and transportation. Even though these spills are relatively small, some of them are large enough to cause significant environmental impact. Taken this into account, the computational models are important tools to estimate the trajectory, dimensioning and behavior of the oil spilled in the marine environment, being also determinants to elaborate action plans for response teams work. The transportation and fate of oil spills are governed in the short term by physical-chemical transport and transformation processes and in the long term by biological degradation processes, according to local environmental conditions (oceanic and atmospheric). The main processes that act on offshore oil spills include, in the short term, advection, turbulent diffusion, surface scattering, evaporation, dissolution, emulsification, sedimentation and the interaction of oil slick according to the coast line. The Spill, Transport and Fate Model (STFM) was the computational model developed in this work. The algorithms were developed based on physicochemical formulations proposed in literature, being the propositions of several authors tested and the equations which presented the best results were selected to integrate the physical-chemical set that makes up the STFM. The STFM results presented superior performance, giving more stability to the stain, compared to the other models tested in the scattering and diffusion description, by using the Dodge derivation for the Fay spreading proposal and by replacing the usual \"Randon Walk\" method by \"Randon Flight\" (advanced in time) in the canonical form given by Lynch. The STFM algorithm also brings forward another important evolution by including an evaporation model based on Fingas empirical equations, replacing the current parameterizations based on ADIOS2 and pseudo component methods.
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Sallet, Marieli, et Marieli Sallet. « Desenvolvimento de um modelo lagrangeano para dispersão de poluentes em condições de vento fraco ». Universidade Federal de Pelotas, 2007. http://repositorio.ufpel.edu.br/handle/ri/2183.
Texte intégralRésumé :
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Previous issue date: 2007-02-23Currently, the search for analytical solutions for the dispersion problems is one of the main research subjects in the pollutant dispersion modeling. These solutions become important due to the intention to obtain dispersion models that generate reliable results in a small computational time, which are of great interest for regulatory air quality applications. Lagrangian particle models are an important and effective tool to simulate the atmospheric dispersion of airborne pollutants. These models are based on the Langevin equation, which is derived from the hypothesis that the velocity is given by the combination between a deterministic term and a stochastic term. In this work is presented a new Lagrangian particle model to simulate the pollutant dispersion in low wind speed conditions. During low wind speed, the diffusion of a pollutant in the planetary boundary layer (PBL) is indefinite and it has been observed that the plume is subject to a great deal of horizontal undulations, which are called plume meandering. The method proposed leads to a stochastic integral equation whose solution has been obtained through the Method of Successive Approximations or Picard s Iteration Method. The integral equation is written in terms of the real and imaginary parts of the complex function before performing the multiplication of the integrating factor, expressed by the Euler formula, inside and outside of the integral solution. To take account the meandering effect, the Frenkiel s Eulerian autocorrelation functions for low wind conditions is included naturally in the model. The new approach has been evaluated through the comparison with experimental data and other different dispersion models. Particularly, the results obtained by the model agree very well with the experimental data, indicating the model represents the dispersion process correctly in low wind speed conditions. It is also possible to verify that the new model results are better than ones obtained by the other models. The analytical feature of the technique and the natural inclusion of the Frenkiel s Eulerian autocorrelation function become the model more accurate than other models.
Atualmente, a busca por soluções analíticas para os problemas de dispersão é um dos principais assuntos de pesquisa na modelagem da dispersão de poluentes. Estas soluções tornam-se importantes devido à intenção de obter modelos de dispersão que geram resultados confiáveis em um tempo computacional pequeno, que são de grande interesse para aplicações no controle da qualidade do ar. Modelos de partícula Lagrangeano são uma ferramenta importante e eficaz para simular a dispersão atmosférica de poluentes do ar. Esses modelos são baseados na equação de Langevin, que é derivada da hipótese que a velocidade é dada por uma combinação entre um termo determinístico e um termo estocástico. Neste trabalho é apresentado um novo modelo de partícula Lagrangeano para simular a dispersão de poluentes em condições de velocidade de vento fraco. Durante a velocidade de vento fraco, a difusão de um poluente na Camada Limite Planetária (CLP) é indefinida e tem sido observado que a pluma está sujeita a grandes ondulações horizontais, que são chamadas meandro do vento. O método proposto leva a uma equação integral estocástica cuja solução é obtida através do Método das Aproximações Sucessivas ou Método Iterativo de Picard. A equação integral é escrita em termos das partes real e imaginária da função complexa antes de realizar a multiplicação do fator integrante, expresso pela fórmula de Euler, dentro e fora da solução integral. Para considerar o efeito do meandro, as funções de autocorrelação Euleriana de Frenkiel para condições de vento fraco são incluídas naturalmente no modelo. A nova aproximação foi avaliada através da comparação com dados experimentais e outros diferentes modelos de dispersão. Particularmente, os resultados obtidos pelo modelo concordam muito bem com os dados experimentais, indicando que o modelo representa o processo de dispersão corretamente em condições de velocidade de vento fraco. Também é possível verificar que os resultados do novo modelo são melhores do que os obtidos pelos outros modelos. A característica analítica da técnica e a inclusão natural da função de autocorrelação Euleriana de Frenkiel tornam o modelo mais exato que os outros modelos.
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Stefanello, Michel Baptistella. « Desenvolvimento de um modelo lagrangiano para estimar a dispersão de escalares passivos em condições de meandro do vento horizontal ». Universidade Federal de Santa Maria, 2017. http://repositorio.ufsm.br/handle/1/12408.
Texte intégralRésumé :
The description of the effects of the wind meandering in the scalar dispersion is a challenging
task, since this type of flow represents a physical state characterized by multiple
scales. In this study, a Lagrangian stochastic diffusion model is derived to describe the
scalar transport during the horizontal wind meandering phenomenon, occurring in a PBL.
The model is derived from the linearization of the Langevin equation and employs a heuristic
functional form, which represents the autocorrelation functions of the meandering. The
new solutions, which describe the longitudinal and lateral wind components, were used to
simulate two experiments of contaminants dispersion in low-wind conditions, INEL (USA)
and GRAZ (Austria). The results of the comparison indicate that the new model reproduces
fairly well the observed concentrations of contaminants and, therefore, satisfactorily describes
the enhanced dispersion due to the presence of meandering.Descrever os efeitos provocados pelo meandro do vento na dispersão de escalares é uma tarefa desafiadora, uma vez que este tipo de escoamento representa um estado físico caracterizado por múltiplas escalas. Neste trabalho, deriva-se um modelo estocátisco Lagrangiano para descrever a dispersão de escalares, na camada limite planetária, durante o fenômeno de meandro do vento horizontal. O modelo é derivado a partir da linearização da equação de Langevin e emprega uma forma funcional heurística, que representa as funções de autocorrelação do meandro. As novas soluções, que descrevem as componentes longitudinais e laterais do vento, foram empregadas para simular dois experimentos de dispersão de contaminantes em condições de vento fraco, INEL (USA) e GRAZ (Áustria). Os resultados das comparações indicam que o novo modelo pode ser usado para reproduzir as concentrações observadas de contaminantes e, portanto descreve de forma satisfatória a difusão reforçada provocada pelo meandro do vento.
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Arbage, Maria Cristina Andres. « Características estatísticas turbulentas associadas ao fenômeno do vento norte no sul do Brasil : aplicação ao problema da difusão de contaminantes ». Universidade Federal de Santa Maria, 2008. http://repositorio.ufsm.br/handle/1/3892.
Texte intégralRésumé :
Coordenação de Aperfeiçoamento de Pessoal de Nível SuperiorA parameterization for the transport processes in a shear driven planetary boundary layer (PBL) has been established, employing turbulent statistical quantities measured during the north wind phenomenon in southern Brazil. Therefore, observed one-dimensional turbulent energy spectra are compared with a spectral model based on the Kolmogorov arguments. The good agreement obtained from this comparison leads to well defined formulations for the turbulent velocity variances, local decorrelation time scale and eddy diffusivities. Furthermore, for vertical regions in which the wind shear forcing is relevant, the eddy diffusivity derived from the north wind data presents a similar profile as those obtained from the non-extensive statistical mechanics theory. Finally, a validation for the present parameterization has been accomplished, using a Lagrangian stochastic dispersion model. Twind speed, is simulated. The analysis developed in this study shows that the turbulence parameterization constructed from wind data for north wind flow cases is able to describe the diffusion in a high wind speed, shear-dominated PBL.he Prairie Grass data set, which presents high mean
Foi realizada uma parametrização para os processos de transporte em uma camada limite planetária (CLP) dominada pela turbulência mecânica, empregando quantidades estatísticas turbulentas medidas durante eventos do Vento Norte no Sul do Brasil. Assim, espectros observados de energia turbulenta unidimensionais são comparados com um modelo espectral baseado na hipótese de Kolmogorov válida para uma turbulência desenvolvida. A boa concordância obtida a partir desta comparação permite derivar formulações para as variâncias de velocidade turbulenta, escala de tempo de decorrelação local e para os coeficientes de difusão. Além disso, o coeficiente de difusão vertical derivado a parir dos dados de vento norte apresenta um perfil semelhante àquele obtido dos conceitos da mecânica estatística não-extensiva. Finalmente, a validação da presente parametrização foi realizada utilizando-se um modelo de dispersão estocástico Lagrangeano. São simuladas as concentrações medidas ao nível do solo no experimento clássico de Prairie-Grass sob condições de vento forte. A análise desenvolvida no presente estudo mostra que a parametrização da turbulência, construída a partir de dados de casos de Vento Norte, é capaz de descrever a difusão em condições de vento forte, em uma CLP gerada pela turbulência mecânica.
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SANTIAGO, D. I. « "Aplicação de um modelo lagrangiano de trajetória de partículas para modelagem da dispersão em águas rasas e simulação da dispersão no canal de acesso ao porto de Vitória, ES" ». Universidade Federal do Espírito Santo, 2007. http://repositorio.ufes.br/handle/10/3873.
Texte intégralRésumé :
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Previous issue date: 2007-02-26Nesta pesquisa um Modelo Lagrangiano de Partículas de Deslocamento Aleatório (MLPDA) desenvolvido para a modelagem da dispersão em águas rasas é acoplado ao modelo hidrodinâmico DIVAST (Depth Integrated Velocity and Solute Transport) para estudar as características dispersivas na região do canal de acesso ao Porto de Vitória. Inicialmente o modelo DIVAST é utilizado na avaliação da hidrodinâmica induzida pela maré astronômica no canal de acesso ao Porto de Vitória. O DIVAST se fundamenta nas equações não-lineares de águas rasas e considera além do efeito de fricção da vegetação de mangue na hidrodinâmica, o alagamento e a secagem de planícies de marés cobertas com vegetação de mangue. A grade computacional elaborada representa adequadamente a geometria e as ilhas no interior da região de estudo. As condições de contorno fornecidas ao modelo numérico foram elevação no contorno leste e correntes no contorno oeste, que foram obtidas de um modelo global para o complexo estuarino da ilha de Vitória. A validação dos resultados do modelo DIVAST foi realizada pela comparação com dados experimentais de velocidade e com dados numéricos de elevação da superfície da água, mostrando uma boa concordância com os mesmos e indicando que o modelo representa satisfatoriamente a hidrodinâmica da região do canal de acesso ao Porto de Vitória. A observação dos campos de escoamento simulados pelo DIVAST possibilitou identificar e analisar diferentes padrões de escoamento associados a interação do escoamento com a geometria do canal. O MLPDA se fundamenta nas equações de deslocamento aleatório. O MLPDA foi validado a partir da simulação e comparação com experimentos numéricos sugeridos por Heemink (1995). Os resultados do MLPDA reproduziram bem os experimentos numéricos e demostraram que o modelo é uma ferramenta adequada para a simulação do transporte de solutos. O MLPDA acoplado ao DIVAST foi aplicado para a região do canal de acesso ao Porto de Vitória e demonstrou a capacidade de simular os processos dispersivos em pequena e grande escala. Identificaram-se diferentes zonas na região modelada, observando-se áreas mais dispersivas e áreas que favorecem o acúmulo de constituintes.
Chapitres de livres sur le sujet "Lagrangian dispersal models"
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Guerrini, Federica. « Data-Informed Models for the Coupled Dispersal of Microplastics and Related Pollutants Applied to the Mediterranean Sea ». Dans Special Topics in Information Technology, 3–14. Cham : Springer International Publishing, 2022. http://dx.doi.org/10.1007/978-3-031-15374-7_1.
Texte intégralRésumé :
AbstractMicroplastic pollution is a ubiquitous environmental threat, in particular to the oceans. In the marine environment, microplastics are not just passively transported by sea currents, but often get contaminated with organic pollutants during the journey. The uptake of chemicals onto microplastics can worsen the adverse effects of microplastics to marine organisms; however, investigation on this urgent phenomenon is hampered by the impossibility of monitoring and tracking such small plastic fragments during their motion at sea. This work aims at addressing the need for an effective modelling of the advection–diffusion processes jointly involving microplastics and the pollutants they carry to further our understanding of their spatiotemporal patterns and ecological impacts, focusing on the Mediterranean Sea. Here we present the conceptual design, methodological settings, and modelling results of a novel, data-informed 2D Lagrangian–Eulerian modelling framework that simultaneously describes (i) the Lagrangian dispersal of microplastic on the sea surface, (ii) the Eulerian advection–diffusion of selected organic contaminants, and (iii) the gradient-driven chemical exchanges between microplastic particles and chemical pollutants in the marine environment in a simple, yet comprehensive way. Crucial to the realism of our model is exploiting the wide variety and abundance of data linked with drivers of Mediterranean marine pollution by microplastics and chemicals, ranging from national censuses to satellite data of surface water runoff and GPS ship tracking, other than the use of oceanographic reanalyses to inform microplastics’ motion at sea. The results of our method applied to a multi-year simulation contribute to a first basin-wide assessment of the role of microplastics as a vehicle of other pollutants of concern in the marine environment. The framework proposed here is intended as a flexible tool to help advance knowledge towards a comprehensive description of the multifaceted threat of marine plastic pollution and an informed support to targeted mitigation policies.
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Brenerman, M. H., et A. R. Kessel. « Stochastic Geometric Model of Combustion in Two-Phase Turbulent Flow ». Dans Mathematics of Heat Transfer, 115–24. Oxford University PressOxford, 1998. http://dx.doi.org/10.1093/oso/9780198503583.003.0013.
Texte intégralRésumé :
Abstract The universally accepted continuous mixture (CM) models are valid for describing two-phase flows (TPF) with inhomogenities, whose characteristic size is much less than the scale of the problem. Generally speaking, TPF characterized by large-scale inhomogeneities cannot be described by CM models. A combined Eulerian-Lagrangian mathematical model of combustion in TPF with large-scale inhomogenities is presented here. It treats the kinetics of the carrying phase as a random process and the kinetics of the dispersed phase as a random walk (macro-scale Lagrangian approach). The interaction between the particles and the carrying phase is chosen in a classical form (micro-scale Eulerian approach). Differential equations are replaced by a random walk simulation scheme. This approach takes into account some phenomenological details of TPF and explains the effect of incomplete burning, which contradicts CM models.
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Brenerman, M. H., et A. R. Kessel. « Random Walk Trajectory Model of Interphase Heat Exchange in Turbulent Two-Phase Flow ». Dans Mathematics of Heat Transfer, 125–30. Oxford University PressOxford, 1998. http://dx.doi.org/10.1093/oso/9780198503583.003.0014.
Texte intégralRésumé :
Abstract The universally accepted continuous mixture (CM) models are valid for describing two-phase flows (TPF) when the inhomogeneities have a characteristic size which is much less than the scale of the problem. There is a great interest in creating alternative models. Here a combined EulerianLagrangian mathematical model of heat transfer in TPF with large-scale inhomogeneities is presented. It treats the kinetics of the carrying phase as a random process and that of the dispersed phase as a random walk (Lagrangian approach on a macro scale). The interaction between the particles and the carrying phase is chosen in a classical form (Eulerian approach on a micro scale). Differential equations are replaced by a random walk simulation scheme. This approach incorporates some phenomenological details of TPF and is simple for numerical simulation.
Actes de conférences sur le sujet "Lagrangian dispersal models"
1
Rollin, Bertrand, et Marie Desenlis. « Interaction of a Shock Wave With a Dense Corrugated Particle Curtain ». Dans ASME 2017 Fluids Engineering Division Summer Meeting. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/fedsm2017-69562.
Texte intégralRésumé :
A numerical experiment studying the gas-particle variant of the Richtmyer-Meshkov instability is presented. Using an Eulerian-Lagrangian approach, namely point particle simulations, we track trajectories of computational particles composing an initially corrugated particle curtain, after the curtain’s interaction with a shock wave. We solve the compressible multiphase Euler equations in a two-dimensional planar geometry and use state-of-the-art particle force models, including unsteady forces, for the gas-particle coupling. However, additional complexities associated with compaction of the curtain of particles to random close packing limit and beyond are avoided by limiting the simulations to relatively modest initial volume fraction of particles. At a fixed Mach number, we explore the effects of the initial perturbation amplitude, initial particle volume fraction and initial shape on the dispersal of the particle curtain. For this shock strength, our simulations suggests that the amplitude of the initial perturbation does not play a significant role in the late time particle dispersal, contrary to the volume fraction. Higher initial particle volume fraction tend to faster particles dispersal. Finally, higher frequency initial perturbations seem to be absorbed by lower frequency initial perturbations.
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Lei, Kangbin, Kiwamu Kase, Nobuyuki Oshima et Toshio Kobayashi. « A Disperse-Phase Dynamic SGS Coupling Model for Particle-Laden Turbulent Flows ». Dans ASME/JSME 2007 5th Joint Fluids Engineering Conference. ASMEDC, 2007. http://dx.doi.org/10.1115/fedsm2007-37059.
Texte intégralRésumé :
In order to study the effects of turbulence sub-grid-scale (SGS) fluctuation on particle Lagrangian motion in turbulent flows, a dynamic random walk (DRW) SGS coupling model based on an Eulerian-Lagrangian approach was developed. The advantage of the new model is that the Gaussian statistical distribution and local isotropic properties of turbulence SGS fluctuation can be parameterized by Germano’s (1991) Eulerian dynamic procedure. Using the present model, large eddy simulation (LES) was performed for downward channel flow at a Reynolds number of 180, as in the direct numerical simulation (DNS) done by Rouson & Eaton in 1997. Through a comparing of the statistical properties of particle diffusion with DNS, the capabilities and limitations of the present DRW SGS model were verified. Moreover, it was found that turbulence SGS fluctuation was strongly associated with particle motion, because preferred particles were affected by the preferred length scale of the eddy structure around. It was also found that turbulence SGS fluctuations are indispensable in calculating particles’ Lagrangian trajectories in LES even when the particle Stokes number is high.
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Nili, Samaun, Chanyoung Park, Raphael T. Haftka, Sivaramakrishnan Balachandar et Nam H. Kim. « Sensitivity Analysis of Force Models for a Four-Way Coupled Eulerian-Lagrangian Dispersed Multiphase Flow ». Dans 23rd AIAA Computational Fluid Dynamics Conference. Reston, Virginia : American Institute of Aeronautics and Astronautics, 2017. http://dx.doi.org/10.2514/6.2017-3800.
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Boyde, J. M., P. Le Clercq, M. Di Domenico, M. Rachner, G. C. Gebel, T. Mosbach et M. Aigner. « Validation of an Ignition and Flame Propagation Model for Multiphase Flows ». Dans ASME 2011 Turbo Expo : Turbine Technical Conference and Exposition. ASMEDC, 2011. http://dx.doi.org/10.1115/gt2011-45104.
Texte intégralRésumé :
This paper presents a numerical investigation of a generic lab scale combustor with focus on the ignition characteristics. The test case has been examined thoroughly in a comprehensive measurement campaign to provide a detailed set of boundary conditions and a profound data base of results. The experimental setup comprises five parallel-aligned mono-disperse droplet chains which are ignited, using a focused laser beam. One aspect of the experimental study is the ignitability with respect to the imposed boundary conditions. The second covers the growth and the propagation of the flame after the establishment of an initial kernel. The outcome of the numerical simulations is compared to the experimental results which allows an in-depth assessment of the employed numerical models. The chemistry and, thus, the flame propagation behavior is captured by a turbulent flame speed closure approach with an adaptation to render the model suitable to multiphase flows. For the dispersed phase a Lagrangian particle tracking scheme is employed in combination with a continuous thermodynamics fuel model for the evaporation. The overall good agreement demonstrates the capability of a multiphase flow CFD solver in the field of ignition modeling.
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Vance, Marion W., et Kyle D. Squires. « An Approach to Parallel Computing in an Eulerian-Lagrangian Two-Phase Flow Model ». Dans ASME 2002 Joint U.S.-European Fluids Engineering Division Conference. ASMEDC, 2002. http://dx.doi.org/10.1115/fedsm2002-31225.
Texte intégralRésumé :
An approach to parallel solution of an Eulerian-Lagrangian model of dilute gas-solid flows is presented. Using Lagrangian treatments for the dispersed phase, one of the principal computational challenges arises in models in which inter-particle interactions are taken into account. Deterministic treatment of particle-particle collisions in the present work pose the most computationally intensive aspect of the simulation. Simple searches lead to algorithms whose cost is O(N2p) where Np is the particle population. The approach developed in the current effort is based on localizing collision detection neighborhoods using a cell-index method and spatially distributing those neighborhoods for parallel solution. The method is evaluated using simulations of the gas-solid turbulent flow in a vertical channel. The instantaneous position and the velocity of any particle is obtained by solving the equation of motion for a small rigid sphere assuming that the resulting force induced by the fluid reduces to the drag contribution. Binary particle collisions without energy dissipation or inter-particle friction are considered. The carrier flow is computed using Large Eddy Simulation of the incompressible Navier-Stokes equations. The entire dispersed-phase population is partitioned via static spatial decomposition of the domain to maximize parallel efficiency. Simulations on small numbers of distributed memory processors show linear speedup in processing of the collision detection step and nearly optimal reductions in simulation time for the entire solution.
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Ajmi, S., M. Boutet, A. Bennis et J. Dauvin. « Influence of the turbulent wake downstream offshore wind turbines on larval dispersal : development of a new Lagrangian-Eulerian model ». Dans 8th European Congress on Computational Methods in Applied Sciences and Engineering. CIMNE, 2022. http://dx.doi.org/10.23967/eccomas.2022.147.
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Traore´, Ph, C. Herbreteau et R. Bouard. « An Eulerian-Lagrangian Approach for the Numerical Simulation and Visualization of Two-Dimensional Fluidized Beds ». Dans ASME 2002 International Mechanical Engineering Congress and Exposition. ASMEDC, 2002. http://dx.doi.org/10.1115/imece2002-33114.
Texte intégralRésumé :
This paper deals with an Eulerian-Lagrangian model for dispersed multiphase flow in which all the interactions of any kind are taking into account. The fluid phase and particles interactions are two way coupled while all the collisions between the particles or between the particles and the walls are calculated. The Navier-Stokes equations (fluid phase continuity and momentum equations including exchange from the particle to the fluid is modeled to simulate the effect of the presence of the particles in the fluid phase) are solved on a staggered Eulerian grid by a finite volume discretisation type method. The originality of the Lagrangian approach used here for the particles motion, lies in the way of managing the collisions which are calculated using simple mechanical models such as a spring, dashpot and friction slider at the contact points following the Distinct Element Method DEM [1]. In the Lagrangian stage, motion’s calculation of each discrete particle including collisions effects is generally time consuming. In the context of this paper we shall show how to optimized the contacts tracking algorithm in an efficient way to increase significantly the capability of the DEM.
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Huilier, Daniel. « Why Are Relationships Between Lagrangian and Eulerian Scales Necessary for Gas-Particle Flow Modeling ? » Dans ASME/JSME 2003 4th Joint Fluids Summer Engineering Conference. ASMEDC, 2003. http://dx.doi.org/10.1115/fedsm2003-45727.
Texte intégralRésumé :
Simulation of Gas-Particle flows can be fulfilled by Lagrangian modeling of the dispersed phase. Each type of Lagrangian method, Monte-Carlo/Eddy Interaction or Markov Chain models, needs the knowledge of Lagrangian scales associated with the turbulent flow under consideration and the type of particle dispersing in the gas carrier flow. Unfortunately, Lagrangian quantities (as well the interesting moving Eulerian time scale, that given by a sensor which would move with the mean fluid velocity) are still difficult to be obtained directly by most experimental measurement techniques (except by very recent techniques such as PIV.PTV.), contrary to Eulerian scales scales, such as those classically obtained from a fixed hot-wire or LDA control volume. It is therefore of great importance to have available accurate relationships between Eulerian and Lagrangian scales, based on fluid flow properties as well as particle characteristics.
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Fiveland, W. A., K. L. Parker et R. F. Gansman. « Parallel Computing Strategies for a Disperse Phase Flow and Combustion Model ». Dans ASME 1997 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 1997. http://dx.doi.org/10.1115/imece1997-0927.
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Abstract Flow and combustion models are being used to evaluate new designs and retrofit options for various industrial combustion systems. Combustion models being used today are often very modular and, since they apply serial algorithms, require long run times to produce results. It is common for solutions to take several days, and the use of finite rate chemistry and Lagrangian based particle models can lengthen run times to a week or more. The modularity of these methods makes them candidates for parallel computing. This paper presents results for a distributed computing algorithm using the PVM software, which is applied to the finite rate chemistry and particle transport modules. It is based on a master-slave algorithm in which the master doles work to a number of independent processors. A load balancing scheme is used to account for the variability in the time the slaves complete their work. PVM was successfully used for parallel computations in the finite rate chemistry and particle modules. Significant speedups were found for both modules, but the work clearly indicates the need to control granularity and the need to optimize the algorithm specifically for the processors being used. Future work is planned to improve the algorithms presented here as well as extending the work to other parts of the combustion model.
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Lipowsky, Justus, et Martin Sommerfeld. « Time-Dependent Simulation of a Swirling Two Phase Flow Using an Anisotropic Turbulent Dispersion Model ». Dans ASME 2005 Fluids Engineering Division Summer Meeting. ASMEDC, 2005. http://dx.doi.org/10.1115/fedsm2005-77210.
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Time-dependent simulations of a particle-laden swirl flow in a pipe expansion based on the Euler-Lagrange approach are presented. Two equation and Reynolds Stress Models were used in the calculation of turbulent quantities in the continuous phase. Additional attention was payed to the influence of particle dispersion. The instantaneous fluid velocities seen by the particles was reconstructed by different dispersion models. To come to a time dependant solution for the Euler-Lagrange approach, a quasi-unsteady approach is taken. This results in a calculational scheme where one Eulerian time-step is divided in a number of Lagrangian steps. Particle source term are sampled which represent the influence of the disperse phase on the flow field. which call for additional coupling within one Eulerian time step. The effect of inter-particle collisions on the movement of the disperse phase is accounted for using a stochastic inter-particle collision model. Special interest of this study was the formation of dust ropes which are observed in such flows.