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The influence of particle concentration on the drag force of a particle deserves attention when using the Lagrangian Particle Tracking methods for the prediction of industrial type gas-solid flows. The Lagrangian approach is best suited to applications where the solids volume fraction is low, and the effect of particle concentration can be ignored. In the present work, a 3D time dependent numerical analysis is performed to study the effect of Lagrangian model improvements to replicate experimental studies of straight horizontal pipe flow and flow through a 90° horizontal-to-vertical bend. The present predictions are compared with published experimental data of Tsuji and Morikawa (1982) , and Yilmaz (1997). Special attention is paid to influence of particle mass-flow rates and conveying velocity on the particle motion within the system. This study used a CFX-4 package, where the ability to modify the code was necessary to include particle model improvements. These improvements included implementing a newly drag force model developed as a part of this research work. Particle-wall collision and particle-particle collision models developed by Sommerfeld (1992) , and Sommerfeld (2001) are also implemented in the CFD model. The standard k–ε dispersed turbulence model was utilized as the predictions for the gas phase only gave similar predicted axial velocity compared to the more computationally demanding Reynolds stress model. The results showed that the inclusion of the various improvements lead to reasonable predicted particle velocities in both the upper and lower regions of the straight horizontal pipe which denote the dilute and dense regions respectively. It was also found that the inclusion of the rough-wall particle wall collision model decreases the axial particle velocity in the lower region where the bulk of the particle wall collisions occur. While the inclusion of the particle collision models tends to disperse the particles away from the lower region resulting in a less dense lower section and a distinctly more homogenous particle distribution compared with the standard model predictions. Further, the increase in particle concentration leads to a reduction in axial velocity due to a loss of momentum through particle-wall and particle-particle collisions. Finally, the improved CFD model best predicted both the reduction and increase in the particle velocities in the different regions. [ABSTRACT FROM AUTHOR]

Summary: Windstorms are a primary natural hazard affecting Europe that are commonly linked to substantial property and infrastructural damage and are responsible for the largest spatially aggregated financial losses. Such extreme winds are typically generated by extratropical cyclone systems originating in the North Atlantic and passing over Europe. Previous statistical studies tend to model extreme winds at a given set of sites, corresponding to inference in an Eulerian framework. Such inference cannot incorporate knowledge of the life cycle and progression of extratropical cyclones across the region and is forced to make restrictive assumptions about the extremal dependence structure. We take an entirely different approach which overcomes these limitations by working in a Lagrangian framework. Specifically, we model the development of windstorms over time, preserving the physical characteristics linking the windstorm and the cyclone track, the path of local vorticity maxima, and make a key finding that the spatial extent of extratropical windstorms becomes more localized as its magnitude increases irrespective of the location of the storm track. Our model allows simulation of synthetic windstorm events to derive the joint distributional features over any set of sites giving physically consistent extrapolations to rarer events. From such simulations improved estimates of this hazard can be achieved in terms of both intensity and area affected. [ABSTRACT FROM AUTHOR]

In the present study, numerical simulations are carried out to understand the combustion characteristics of lifted spray flames for various coflow conditions. Flame structure, lift-off characteristics, and droplet dynamics of kerosene spray flames in various coflow conditions are studied. Numerical results are validated with experimental results. Three different coflow conditions are considered; cold flow, cold flow with N2 dilution, and simultaneous preheating and dilution. A solid cone fuel spray characteristic is modeled in this present numerical study. The numerical simulations are performed using Reynolds averaged Navier-Stokes approach with standard k-ε turbulence model. Liquid droplets are tracked using Discrete Phase Model. In the current work, non-premixed equilibrium combustion model with the probability density function (PDF) is utilized to model the combustion process. Transport equation for the scalar mixture fraction (Y) is solved using pre-calculated variables and results are stored in a look-up PDF table. Isolines of OH distribution are studied to understand the distribution of the reaction zone for different operating conditions. Maximum temperature of the flame and emissions for different coflow conditions are also presented. Numerical results of all cases are very well validated with experimental results. [ABSTRACT FROM AUTHOR]

In September 2017, numerous measurement stations recorded large surface concentrations of Ru 106 in Europe. This event was well recorded by various monitoring stations worldwide and offer a valuable framework to compare the modelling strategies deployed to quickly evaluate where the plume goes and with what concentrations. In general, the source and its intensity are not known and hypotheses have to be done. Models have to be fast and accurate: Lagrangian and Eulerian are often used but rarely compared. In this study, the FLEXPART Lagrangian model and the WRF-CHIMERE Eulerian models are used to simulate the emissions, transport and deposition of this source of Ru 106. First, it is shown that the hypothesis of location, timing and intensity of the source is realistic, by comparison to surface measurements. Second, sensitivity analysis performed with the Eulerian model and several transport scheme showed that this model may provide better results than the Lagrangian one. It opens the door to further development, including chemistry and mixing with other pollutants during these specific events. • Long range atmospheric transport in CHIMERE and FLEXPART models yield similar behaviors. • Numerous worldwide measurements allowed the comparison of CHIMERE and FLEXPART at various ranges. • Confusion matrices indicate that CHIMERE performs overall better than FLEXPART on this case. • Numerical diffusion in CHIMERE can be reduced with newly implemented numerical transport schemes. • Conjoint use of both CHIMERE and FLEXPART could be beneficial in future work. [ABSTRACT FROM AUTHOR]

A computationally efficient source inversion algorithm was developed and applied with the Lagrangian atmospheric dispersion model DIPCOT. In the process of source location estimation by minimizing a correlation-based cost function, the algorithm uses only the values of the time-integrated concentrations at the monitoring stations instead of all of the individual measurements in the full concentration-time series, resulting in a significant reduction in the number of integrations of the backward transport equations. Following the source location estimation the release start time, duration and emission rate are assessed. The developed algorithm was verified for the conditions of the ETEX-I (European Tracer Experiment—1st release). Using time-integrated measurements from all available stations, the distance between the estimated and true source location was 108 km. The estimated start time of the release was only about 1 h different from the true value, within the possible accuracy of estimate of this parameter. The estimated release duration was 21 h (the true value was 12 h). The estimated release rate was 4.28 g/s (the true value was 7.95 g/s). The estimated released mass almost perfectly fitted the true released mass (323.6 vs. 343.4 kg). It thus could be concluded that the developed algorithm is suitable for further integration in real-time decision support systems.

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ATLAS-1.0 (ATmospheric LAgrangian diSpersion) is a new atmospheric dispersion and sedimentation Lagrangian model tailored to volcanic tephra/ash. The model solves the Advection–Diffusion–Sedimentation equation across multiple scales (from regional to global) and can be driven off-line by different numerical weather prediction models in combination. For example, meteorological data from the mesoscale Weather Research Forecast (WRF) model can be combined with data from the Global Forecast System (GFS) so that ATLAS automatically selects the highest resolution data available in any part of the computational domain. ATLAS can be used in forward mode to forecast ash dispersal from a volcano (or from extended sources) or in backward mode to integrate trajectories backwards in time and constrain unknown source term characteristics. Multiple source terms can be defined, e.g. to simulate several eruption phases with different granulometric characteristics on a single model execution. We validate the implementation of the model using the 2011 Cordón Caulle and the 2015 Calbuco eruptions and compare the results with previous simulations performed with the FALL3D model. The code has been designed from scratch to facilitate future parallelization, inclusion of ash resuspension schemes, and ensemble-based probabilistic forecast assimilating data from satellite retrievals. • ATLAS simulates the atmospheric dispersion of volcanic ash particles. • ATLAS admits different particles emission sources and grain size distributions. • ATLAS reads global and regional meteorological files. • ATLAS is validated using Cordón Caulle 2011 and Calbuco 2015 eruptions. • Convergence analysis indicate 1M to 1.5M particles (puff) to simulate eruptions. [ABSTRACT FROM AUTHOR]

Fast simulation tools for the prediction of transient particle transport are critical in designing the air distribution indoors to reduce the exposure to indoor particles and associated health risks. This investigation proposed a combined fast fluid dynamics (FFD) and Markov chain model for fast predicting transient particle transport indoors. The solver for FFD-Markov-chain model was programmed in OpenFOAM, an open-source CFD toolbox. This study used two cases from the literature to validate the developed model and found well agreement between the transient particle concentrations predicted by the FFD-Markov-chain model and the experimental data. This investigation further compared the FFD-Markov-chain model with the CFD-Eulerian model and CFD-Lagrangian model in terms of accuracy and efficiency. The accuracy of the FFD-Markov-chain model was similar to that of the other two models. For the two studied cases, the FFD-Markovchain model was 4.7 and 6.8 times faster, respectively, than the CFD-Eulerian model, and it was 137.4 and 53.3 times faster than the CFD-Lagrangian model in predicting the steady-state airflow and transient particle transport. Therefore, the FFD-Markov-chain model is able to greatly reduce the computing cost for predicting transient particle transport in indoor environments. [ABSTRACT FROM AUTHOR]

• Major requirements for lagrangian modelling of droplet collisions in sprays. • Review of experiments on collision outcomes with collision maps, i.e. B = f (We). • Collection and correlation of data for characteristic points in the collision maps. • Generalisation of boundary lines with regard to fluid properties and validation. • Experiments and modelling of droplet collisions for various size ratios and liquids. The present article summarises the requirements for modelling droplet binary collisions in the frame of a Lagrangian point-particle tracking approach. The essential ingredients of such a collision model are the collision detection, done in a deterministic or stochastic way, the consideration of the impact efficiency (i.e. small droplets might move around larger ones with the relative flow), and the prediction of the droplet collision outcome based on the well-known collision maps (i.e. B = f (We), We is the Weber-number and B the non-dimensional impact parameter, both defined below). The different approaches used in Euler/Lagrange spray calculations for prescribing such collision maps with single or composite boundary lines are briefly reviewed. Then available experimental studies providing full collision maps including all possible collision outcomes with boundary lines are reviewed with special emphasis on higher liquid viscosities; however both droplets have the same fluid, and different sizes of colliding droplets. Most important for modelling the collision outcomes (i.e. in the lower We-regime up to about 150 – 200 these are bouncing, coalescence, stretching and reflexive separation) are physically-based theoretical boundary lines between the regimes which are not specific for certain boundary conditions (i.e. liquid properties, ambient gas conditions and droplet size ratio). The most commonly used correlations for boundary lines are presented and analysed with respect to their performance (i.e. effect of size ratio, liquid properties and included model constants or parameters). In this study the shift of boundary lines and characteristic points in the collision maps due to changes of fluid properties (i.e. the Ohnesorge-number) and size ratio are used as a modelling framework. Specifically, these are the critical Weber-number location (i.e. beginning of reflexive separation) and the triple-point (i.e. location where bouncing, coalescence and reflexive separation come together). Numerous available experiments on these characteristic point locations are collected showing that they very well correlate with the Ohnesorge-number (i.e. depending only of liquid properties and droplet size). For generalisation, the model of Jiang et al. (Jiang, Y. J., Umemura, A. and Law, C.K.: Journal of Fluid Mechanics, Vol. 234, 171–190, 1992) including viscous dissipation is used for the stretching separation-coalescence boundary and for the beginning of reflexive separation the Ashgriz and Poo (Ashgriz, N. and Poo, J.Y.: Journal of Fluid Mechanics, Vol. 221, 183–204, 1990) approach is applied. This boundary line is just shifted according to the critical Weber-number obtained from an elaborated correlation We C = f (Oh). The Jiang et al. (1992) boundary could be very well adapted for different liquids through the involved constants which again depend on the Ohnesorge-number, differentiating between pure fluids and solutions. It is demonstrated that the suggested novel models capture the two boundaries extremely well for a variety of different liquids and also solutions. Eventually, the effect of droplet size ratio on the collision outcome is considered. Additional experiments were conducted for a polymer-water solution and a high viscous sunflower oil by varying the size ratio of colliding droplets in a wider range of 1.0 < Δ < 0.35 and for We < ≈ 200. The proposed reflexive separation boundary model using the shift due to different fluid properties, i.e. We C , and including the size ratio compares very well with these measurements. For the boundary stretching separation-coalescence the Jiang et al. (1992) and the Brazier-Smith et al. (Brazier-Smith, P. R., Jennings, S. G. and Latham, J.: Proc. R. Soc. Lond. A, Vol. 326, 393–408, 1972) boundaries were combined to capture both influences, namely the liquid property and size ratio. The model parameters were adapted in the same way as done in the model only accounting for the type of liquid. For upper values of the size ratio, range of 1.0 < Δ < 0.5, the agreement with the measurements was found to be excellent. Image, graphical abstract [ABSTRACT FROM AUTHOR]

• The LB-CA model is developed to investigate the flow and soot loading. • Non-virtual porous structure wall is considered in the filtration process. • The effects of upstream velocities on flow field and soot distribution are studied. • The distribution of soot particles is also simulated by LB-Lagrangian model. • The deposited particles dynamic evolution and its effect on flow field are studied. A two-dimensional mesoscopic gas-solid two-phase flow model has been developed to investigate the flow and soot loading in the micro-channel of diesel particulate filters. Soot particle size examined is in the range of 10 nm–1 µm. The flow is solved by an incompressible lattice Boltzmann model and the transport of solid particles is described by the cell automation probabilistic model. The lattice Boltzmann-cell automation probabilistic model (LB-CA model) is validated with the results of previous studies. The effects of different upstream velocities on the flow field in channels are investigated. The distribution and deposition of soot particles with different sizes in clean channels are simulated based on the LB-CA method and the LB-Lagrangian method respectively. The effects of deposited soot particles on flow field are evaluated in real soot particle capture process. The results show that the distributions of velocity field and pressure field in the channel are significantly affected by the upstream velocity. Compared with the effect of the particle size, the upstream velocity is more influential on the particle deposition distributions. The profiles of deposition distribution from the LB-CA method are in close agreement with those from the LB-Lagrangian method. The deposition distributions of particles with different diameters at the top of the porous wall are similar to the distributions of wall velocity along the channel length. Generally, the deposited soot particles increase the axial pressure and decrease the axial velocity in the inlet channel. The evolution trend of the areas where wall velocity undergoes changes is consistent with that of the solid nodes made of the captured soot particles. [ABSTRACT FROM AUTHOR]

In order to understand the main driving factors of ozone (O 3) deposition we tested the hypothesis that sky conditions (cloudy, partly cloudy, and clear sky) modulate O 3 flux in forest ecosystems via stomatal regulation. The hypothesis is based on the fact that complex microclimate conditions under cloudy sky usually stimulate stomatal conductance. O 3 fluxes were inferred from a concentration gradient in a mountainous Norway spruce forest in the Czech Republic (Central Europe) for years 2012–2016 and measured directly by eddy-covariance during the summer of 2017. Daily and seasonal O 3 depositions were calculated separately for days with cloudy, partly cloudy, and clear sky conditions. The data show unequivocally that more O 3 is taken up under cloudy and partially cloudy skies. Moreover, we found significant interactive effects of sky conditions and season on O 3 flux. Though there are other mechanisms and pathways involved in the transport of O 3 to the plant-soil system, the highest O 3 deposition was associated to the highest stomatal conductance during partly cloudy and cloudy sky conditions in all seasons, while lower O 3 ecosystem fluxes were observed under clear sky conditions despite the highest O 3 concentrations at this time. These findings suggest that forests growing at sites where conditions are predominantly cloudy are expected to deposit higher extent of O 3 than less-cloudy forests being thus more threatened by phytotoxic O 3. Unlabelled Image • Sky conditions, not only ozone concentration, influence the rate of its uptake. • More O 3 is taken up under cloudy and partially cloudy skies. • Strong dependence of O 3 uptake on stomatal conductance was demonstrated. • Cloudy mountain forests could be more threatened by O 3 than less-cloudy forests. [ABSTRACT FROM AUTHOR]

Abstract In this work, we propose and evaluate a one-particle Lagrangian stochastic model for the assessment of the concentration-fluctuation variance, which is often used to predict odour hours for example. The main challenge is to provide a suitable parameterisation for the concentration-variance dissipation time scale. While the particle mass is conserved along the particle trajectory, the concentration variance dissipates. The concentration variance in a Lagrangian particle model evolves according to the same Langevin equation used for the simulation of the turbulent dispersion resulting in a mean concentration field. The variance dissipation is taken into account via a decay term with a finite time scale. We herein discuss and compare different parameterisations of the variance-dissipation time scale against observations from a field experiment. It was found that best results are obtained prescribing the ratio between the concentration-variance dissipation time scale and the Lagrangian time scale, which depends on the travel time. Highlights • A new approach for the evaluation of the odour hour is presented and discussed. • Concentration distribution 90th percentile is given by the concentration variance. • The concentration variance is calculated by means of a Lagrangian model. • Different parameterisation fo the concentration variance dissipation are compared. [ABSTRACT FROM AUTHOR]

Highlights • Experimental and numerical investigation of particle deposition in ECS components. • The particle deposition fraction increased with particle size. • RNG k-ε model with near-wall correction provided the most accurate prediction. • The particle deposition distributions were obtained with the CFD method. • A suitable tool was identified for studying particle deposition in the ECS. Abstract As most airplanes do not have HEPA filters for filtering outside air, particulate matter in the outdoor air can deposit on the environmental control systems (ECS) of the airplanes. The particles that accumulate on the various surfaces of the ECS components can affect their thermal performance and may lead to component failures. This study experimentally and numerically investigated the particle deposition on a heat exchanger and a turbocharger, which are key components of ECS with complex geometry. A test rig was built to obtain the monodisperse particle deposition fractions by measuring the particle concentration upstream and downstream of the components with the weighing method. The tested particles ranged from 1 to 8 μm in diameter. Different Reynolds-averaged Navier-Stokes (RANS) models, together with a modified Lagrangian method, were used to predict the total particle deposition fractions in the tested components. The computed particle deposition was compared with the experimental data. The results showed that the RNG k-ε model with near-wall correction provided the most accurate prediction of the particle deposition fraction on the heat exchanger and turbocharger. The particle deposition fraction increased significantly with the particle size. CFD simulation provided detailed information about the particle deposition distribution inside the heat exchanger and turbocharger. The location and number of deposited particles depended mainly on the particle size and air velocity. This investigation identified a suitable tool for studying particle deposition in the ECS of commercial airplanes. [ABSTRACT FROM AUTHOR]

In the framework of the Urban Dispersion International Evaluation Exercise (UDINEE) project coordinated by the European Commission's Joint Research Centre, a case study was conducted of the Joint Urban 2003 (JU2003) experimental campaign in the central area of Oklahoma City, USA. The UDINEE project concerned the cases of puff dispersion of the JU2003 campaign, which are of special interest to scenarios related to security studies, such as explosions of radiological dispersal devices. Starting from the fact that puff-dispersion variability is substantial, especially in complex urban areas, even for puffs released under similar meteorological conditions, a methodology is presented for assessing this variability, which is applied to the dispersion of puffs in two of the intensive operation periods of the JU2003 campaign. Lagrangian and Eulerian dispersion models are applied for the simulations. For the Lagrangian model, variability is assessed by repeating the computations a large number of times. For the Eulerian model, variability is assessed by constructing probability density functions of concentrations on the basis of the dispersion-model results. Peak concentrations, dosages, puff-arrival times and puff durations are considered. Percentiles calculated by the Lagrangian model for all the above quantities and by the Eulerian model for peak concentrations and dosages are compared with the measurements. The results are encouraging since in several cases the measured and computed ranges of values overlap. [ABSTRACT FROM AUTHOR]

The Indonesian Seas receive one of the largest amounts of rainfall around the globe. Part of this freshwater disperses to the Indian Ocean through the Indonesian Throughflow (ITF), the Pacific and Indian interocean exchange flow, making the Indonesian Seas a major source of freshwater, and plays an important part of the global hydrological cycle. By using a Lagrangian particle tracking model, we examine the pathways behind the dispersion of freshwater that the Indonesian Seas receive through precipitation. The model suggests that the dispersion from the near‐surface water of the Indonesian Seas occurs in about 6 months, primarily through advection to the surrounding seas, followed by evaporation, entrainment, and vertical mixing. The Lombok Strait and the Timor Strait are the major outflowing straits, and the freshwater exiting through these straits are found to originate from limited areas and seasons. The sources for the Lombok Strait outflow are the Java Sea precipitated freshwater during boreal fall and winter, while the sources for the Timor Strait outflow are the Flores‐Banda Seas and Arafura Sea precipitated freshwater during winter and spring. Mixing with the thermocline water is found to occur when the monsoonal winds induce upwelling events in winter and summer, along the shelf breaks and steep coastlines surrounding the Flores‐Banda Seas. Vertical mixing provides a pathway for the surface freshwater to enter the ITF thermocline, and our model suggests that it is the Java Sea precipitated freshwater during winter that is entering the ITF thermocline along its main pathway. Key Points: The fate of precipitated origin freshwater of the Indonesian Seas is examined using a Lagrangian particle tracking modelFreshwater outflows from the Indonesian Seas to the Indian Ocean near the surface occur mostly through the Lombok and Timor StraitsVertical mixing to the Indonesian Throughflow thermocline water occurs along shelf breaks and coastlines during the upwelling seasons [ABSTRACT FROM AUTHOR]

Most ocean climate models do not represent ice shelf calving in a physically realistic way, even though the calving of icebergs is a major component of the mass balance for Antarctic ice shelves. The infrequency of large calving events together with the difficulty of placing observational instruments around icebergs means that little is known about how calving icebergs affect the ocean. In this study we present a novel model of an ice shelf coupled to an ocean circulation model, where the ice shelf is constructed of Lagrangian elements that allow simulation of iceberg calving. The Lagrangian ice shelf model is used to simulate the flow beneath a static idealized ice shelf, to verify that it can reproduce the results of an existing Eulerian model simulation with an identical configuration. The Lagrangian model is then used to simulate the ocean's response to a calved iceberg drifting away from the ice shelf. The results show how a calving event and subsequent iceberg drift affect the ocean. At the ice front, the calving event leads to a warming of the ocean surface and cooling of the water column at depth, allowing cooler waters to enter the ice shelf cavity, leading to reduced melt rates within the cavity. A Taylor column is observed below the iceberg, which moves with the iceberg as it drifts into the open ocean. As the iceberg drifts further from the ice shelf, the circulation within the ice shelf cavity tends toward a new steady state, consistent with the new ice shelf geometry. Key Points: A novel modeling framework is developed to simulate ice shelves calving icebergs using Lagrangian elements, held together by numerical bondsAfter an iceberg calves away from an ice shelf, a complex interaction is observed between the iceberg motion and ocean hydrographyA Taylor column, subsurface cooling at the ice front, and reduced melt rates within the ice‐shelf cavity are observed after iceberg calving [ABSTRACT FROM AUTHOR]

A single particle Lagrangian Stochastic model has been developed and applied with the purpose of simulating the concentration fluctuations dispersion. This model treats concentration variance as a quantity whose motion is driven by an advection-diffusion process so that it can be studied by a single particle model. A parameterization for both velocity standard deviations and Lagrangian time-scales is required as input to the model. The paper is focused on the estimation of the best parameterization needed to simulate both mean and standard deviation concentrations in a case study. We consider the FFT-07 field experiment. The trials took place at Dugway Proving Ground, UTAH (USA) and consist of a dispersion analysis of a gas emitted from a point-like source in different atmospheric conditions with a continuous emission technique. The very small spatial scales (a few hundred meters) and short duration (about 10 min) that characterize the trials make the comparison with model results very challenging, since traditional boundary layer parameterizations fail in correctly reproducing the turbulent field and, as a consequence, the dispersion simulation yields unsatisfactorily results. We vary the coefficients of the turbulence parameterization to match the small-scale turbulence. Furthermore, we show that the parameterization for the variance dissipation time-scale, already tested in neutral conditions, can be used also in stable and unstable conditions and in low-wind speed conditions. The model gives good results as far as mean concentration is concerned and rather satisfactory results for the concentration standard deviations. Comparison between model results and observation is shown through both statistical and graphical analyses.

The constitutive model and its pertinent set of parameters are important input data in finite element modeling to define the behavior of Ti6Al4V during machining process. The present work focusses on comparing different constitutive models and the parameters sets available in literatures and investigating the quality of the predictions when varying uncut chip thickness (40 µm, 60 µm, 100 µm and 280 µm). In addition, temperature-dependent strain hardening factor along with strain softening phenomenon based reconstructed material model is proposed. The results from the numerical simulations are compared with experimental results available in literature. The comparison shows that the force values are highly influenced by constitutive models and the choice of parameters sets, whereas the chip morphologies are mainly influenced by the uncut chip thickness and constitutive models. This work justifies the need for an appropriate set of parameters and constitutive model that replicate the machining behavior of Ti6Al4V alloy for different cutting conditions.

A cost-effective particle-tracking model was implemented to study the transport and landing of sargassum in the Mexican Caribbean. Sensitivity analyses were performed to quantify the change in landing percentages varying some model factors: 1) windage factor, 2) the horizontal distribution of sargassum, 3) monthly variability of currents and winds, 4) sargassum growth, 5) thickness of the transporting ocean layer, 6) wind data source, and 7) ocean data source. The windage factor had the greatest effect on landing estimates: as it increased, the sargassum landing percentage increased by 19%. In second place, differences in the initial horizontal distribution of sargassum caused the landing percentage to change by ∼10%. In third place, the monthly variability of currents and winds changed the landing percentage by 6%. The northern shoreline of Mexican Caribbean (between 20.25°N and 20.75°N) was the most prone to sargassum landings. At the regional scale, this condition is related with a) the shoreline orientation in that region, which more clearly faces the northward flow of the Yucatán Current, and b) the position of Cozumel Island, which acts as an offshore barrier capturing sargassum. Most of landed sargassum in the Mexican Caribbean had floated 0–40 km east and south of Chinchorro Bank, within 18.25°N and 18.75°N (southern Mexican Caribbean), and then spread along the shore. Monitoring, containment, and collection of sargassum east and south of Chinchorro Bank could help predict and mitigate sargassum landings about 5 days in advance. [Display omitted] • Sargassum in the Mexican Caribbean flows with the Yucatan Current and is pushed shoreward by trade winds. • Transport models are very sensitive to the windage factor and initial sargassum conditions. • The northern shoreline of Mexican Caribbean (20.25°N–20.75°N) is more prone to sargassum landings. • The region east Chinchorro B. provides outstanding sargassum amounts to Mexican shores in 4–5 days. • Sargassum in the northeastern Mexican Caribbean is less likely to land in the region. [ABSTRACT FROM AUTHOR]

Computational modeling allows studying the air quality problems in depth and provides the best solution reducing the population risks. This research demonstrates the Graz Lagrangian model effectiveness for assessing emission sources contributions to the air pollution: particles tracking and accumulation estimate. The article describes model setting up parameters and datasets preparation for the analysis. The experiment simulated the dispersion from the main groups of emission sources for real weather conditions during 96 h of December 2018, when significant excess of NO2, CO, SO2, PM10, and benzo(a)pyrene concentrations were observed in the Krasnoyarsk surface atmospheric layer. The computational domain was a parallelepiped of 40 × 30 × 2.5 km, which was located deep inside the Eurasian continent on a heterogeneous landscape exaggerated by high-rise buildings, with various pollutions sources and the ice-free Yenisei River. The results demonstrated an excellent applicability of the Lagrange model for hourly tracking of particle trajectories, taking into account the urban landscape. For values

Air distribution systems generally focus on diluting contaminants and distributing conditioned air. However, this strategy has a potential for spreading particulate matter or bioaerosols. Thus, it is considered to be useful to create a non-uniform indoor environment to prevent such dispersion of particulate matter or bioaerosols, and an air curtain could serve for this purpose. This study investigates the effects of an air curtain system in a ventilated office to prevent the dispersion of expiratory droplets that are generated locally, while also considering thermal comfort. Droplets dispersion was modelled with computational fluid dynamics (CFD) with the Lagrangian method. In the CFD simulations, an air curtain system was installed in the middle of an office with varied factors of design, orientation and jet velocity of the air curtain system. Numerical results showed that unless there was an independent inlet and outlet for each region, the air curtain system alone could not create a non-uniform thermal environment; however, it was effective in removing and preventing dispersion of the expiratory droplets. The droplet removal performance of an air curtain system was not proportional to its jet velocity, but a velocity of 3 m/s was found to be feasible for this office. The air curtain system showed better performance than an air cleaner used to exhaust and filter the expiratory droplets. [ABSTRACT FROM AUTHOR]

Collisions between cold pools are generally acknowledged to be important processes through which new convective cells are triggered. Yet relatively little has been done to characterize these processes in detail, quantify their impact on the life cycle of cold pools, and include them in convective parameterizations. We use a combination of Eulerian and Lagrangian models to investigate how much cold pools are affected by collisions. Results from simulations in radiative‐convective equilibrium suggest that collisions represent a first‐order process in the dynamics of cold pools, the median time of first collision being under 10 min since cold pool birth. Through a Lagrangian tracking algorithm, it is also shown that cold pools are significantly deformed by collisions and lose the circular shapes they would have if in isolation only a few minutes after birth. Finally, it is suggested that cold pools happen in clusters, and associated spatial and temporal scales are presented. Plain Language Summary: While collisions between cold pools are known to be key processes in the formation of new convective clouds, they are overlooked by many studies and most parameterizations. We find that collisions have a significant impact on the life and the dynamics of cold pools, affecting their propagations in the boundary layer already few minutes after their birth. Contrary to many conceptual models, our results suggest that cold pools lose circular symmetry already when still young. Finally, we show that cold pools are not randomly distributed in space and time but tend to appear in clusters. Key Points: Collisions represent first‐order processes in cold pool dynamicsCold pools lose circular shape shortly after birthCold pools appear in clusters [ABSTRACT FROM AUTHOR]

Abstract The aim of this study is to develop a large-eddy simulation (LES)-coupled Lagrangian snow transport model. This model consists of an LES for turbulent flow fields, and a particle transport simulation model based on Newton's equations of motion. Particles are treated as point masses for turbulent flow fields in this study. The interactions of momentum exchange between a fluid and particles are considered. The particle transport simulation includes three physical sub-processes on the snow surface: aerodynamic entrainment, rebound, and splash. Then, we simulated particle transport within a turbulent boundary layer under the low-wind condition in which saltation intermittently occurs. This simulation was calculated with high frequency and high resolution to capture the fine turbulent structures. The initial stage of saltation mainly related to sweeps, and particles were ejected through the process of aerodynamic entrainment. These ejected particle induced more saltating particles, and the number of saltating particles transported through the processes of splash and rebound increased and became dominant as time proceeds. In such processes of splash and rebound under low-wind conditions, the particle transport might be unaffected by turbulent structures. Highlights • We developed a large-eddy-simulation-coupled Lagrangian snow transport model. • We simulated particle transport within a turbulent boundary layer. • Sweeps occurred just before the drifting snow density increased. • Almost all particles were maintained through the process of rebound. • Turbulent structure hardly affected rebound and splash particles under low wind. [ABSTRACT FROM AUTHOR]

The amount of concentration and distribution length of air pollutant discharged from industrial area has consequences for fluctuations in ambient air. The objective of the research was to figure out the alteration of ambient air in Cilegon city. To achieve this objective, the research was conducted by analyzing the emission and circulation of SO2 and dust pollutants emitted from the industrial estate. Hence, the researchers analyzed the distribution of industrial pollutants using Screen3 software whereas the distribution used is Lagrangian model. To validate the change of ambient air in Cilegon city, the measurement completed on 18 samples points. The results confirm that the amount of concentration of SO2 pollutants had an impact on the change of ambient air in Taman Sari Village, Pulomerak District. Meanwhile, the impact of dust pollution changes the ambient air in Kotabumi village, the district of Purwakarta and Gerem Village in Grogol District. [ABSTRACT FROM AUTHOR]

Abstract Accumulated pollen sequences are used to infer temporal changes in vegetation composition. Pollen transport and dispersal by winds introduce large biases in the interpretation of pollen records. In order to calibrate the models used to infer past species distributions, human activities or climate, contemporary time series of pollen records are assessed and modelled. The Gaussian plume model assumes that pollen transport takes place in a neutral atmosphere and pollen contribution is even from all directions (isotropy). In this study, we analyse these assumptions with airborne pollen measurements of Weinmannia trichosperma , a forest tree which grows mainly on the western slopes of the Andes, along with other characteristic species of the steppe which develops in eastern Patagonia. Instead of the Gaussian plume mixing model that is usually employed in the theory of pollen analysis, we apply a full 3D Lagrangian dispersion model, which allows calculation of potential source distributions (footprint) from modelled backward trajectories of airborne pollen observations. Results show that neutral atmospheric conditions are properly assumed for the region. The footprint calculated from the modelled trajectories of a five-year record is consistent with the location of pollen sources but the footprint shape showed that pollen contribution is uneven due to the influence of transient weather systems. Highlights • Assumptions of pollen transport model affects paleoenvironmental reconstructions. • Gauss plume model properly assume neutral atmosphere condition for North Patagonia. • Pollen contribution is uneven due to transient weather systems in North Patagonia. [ABSTRACT FROM AUTHOR]

The periodic cellular topology characterizing the microscale structure of a heterogeneous material may allow the finest functional customization of its acoustic dispersion properties. The paper addresses the free propagation of elastic waves in micro-structured cellular materials. Focus is on the alternative formulations suited to describe the wave propagation in the material, according to the classic canons of solid or structural mechanics. Adopting the centrosymmetric tetrachiral microstructure as prototypical periodic cell, the frequency dispersion spectrum resulting from a synthetic lagrangian beam-lattice formulation is compared with its counterpart derived from different continuous models (high-fidelity first-order heterogeneous and equivalent homogenized micropolar continuum). Asymptotic perturbation-based approximations and numerical spectral solutions are cross-validated. Adopting the low-frequency band gaps of the material band structures as functional targets, parametric analyses are carried out to highlight the descriptive limits of the synthetic models and to explore the enlarged parameter space described by high-fidelity models. The final tuning of the mechanical properties of the cellular microstructure is employed to successfully verify the wave filtering functionality of the tetrachiral material. [ABSTRACT FROM AUTHOR]

Lagrangian models of sea ice dynamics have several advantages over Eulerian continuum models. Spatial discretization on the ice floe scale is natural for Lagrangian models and offers exact solutions for mechanical nonlinearities with arbitrary sea ice concentrations. This allows for improved model performance in ice‐marginal zones, where sea ice is fragmented. Furthermore, Lagrangian models can explicitly simulate jamming processes that occur when sea ice moves through narrow confinements. While difficult to parameterize in continuum formulations, jamming emerges spontaneously in dense granular systems simulated in a Lagrangian framework. Here we present a flexible discrete element framework for approximating Lagrangian sea ice mechanics at the ice floe scale, forced by ocean and atmosphere velocity fields. Our goal is to evaluate the potential of models simpler than the traditional discrete element methods for granular dynamics. We demonstrate that frictionless contact models based on compressive stiffness alone are unlikely to produce jamming and describe two different approaches based on Coulomb friction and cohesion which both result in increased bulk shear strength of the granular assemblage. The frictionless but cohesive contact model displays jamming behavior which is similar to the more complex model with Coulomb friction and ice floe rotation at larger scales and has significantly lower computational cost. Key Points: Abrupt strengthening under dense ice‐packing configurations induces granular jammingCohesive bonds can provide similar behavior as Coulomb frictional parameterizationsA probabilistic model characterizes the likelihood of jamming over time [ABSTRACT FROM AUTHOR]

In this work the decrease in the number of particles due to decrease in the size of the detection window on particle diffusion is investigated with the use of a numerical model of saltating grains. In order to formulate the problem, the available experimental data of particle diffusion are presented and discussed. Five different detection window sizes are investigated, showing that in both transverse and longitudinal directions the calculated dispersion of the particles noticeably decreases with the decrease in the window size. This highlights the “window” effect on the calculated variance of particle positions. The results indicate that the interpretation of the experimental data may be biased due to the “window” effect leading to potentially false conclusions about the regime of the diffusion of particles. [ABSTRACT FROM AUTHOR]

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A numerical model, previously validated with other radionuclides, was applied to simulate the dispersion of 236 U released from European nuclear fuel reprocessing plants in the North Atlantic and Shelf Seas using a published reconstruction of Sellafield and La Hague releases. Model results are in better agreement with observations if the lowest estimation of such releases are used. This implies that approximately 40 kg of 236 U has been discharged from Sellafield. It was found that adsorption of 236 U on bed sediments of the shallow European Shelf Seas plays an essential role in its dispersion patterns. This contrasts strongly with the more conservative behaviour of 129 I in the same area. This has two important implications in the use of 236 U as oceanographic tracer; i) special care must be taken in coastal areas, as sediments might act as sinks and sources of 236 U; ii) the annual input function of 236 U into the Arctic is not directly controlled by the annual discharges from Sellafield and La Hague, since sediments from the Irish, Celtic and North Sea modulate and smooth the signal. Only 52% of the total releases enter into the Arctic Ocean. [ABSTRACT FROM AUTHOR]

Magnetic nano drug targeting, with an external magnetic field, can potentially improve the drug absorption in specific locations of the body. However, the effectiveness of the procedure can be reduced due to the limitations of the magnetic field intensity. This work investigates this technique with the Computational Fluid Dynamics (CFD) approach. A single rectangular coil generates the external magnetic field. A patient-specific geometry of the Trachea, with its primary and secondary bronchi, is reconstructed from Digital Imaging and Communications in Medicine (DICOM) formatted images, throughout the Vascular Modelling Tool Kit (VMTK) software. A solver, coupling the Lagrangian dynamics of the magnetic nanoparticles with the Eulerian dynamics of the air, is used to perform the simulations. The resistive pressure, the pulsatile inlet velocity and the rectangular coil magnetic field are the boundary conditions. The dynamics of the injected particles is investigated without and with the magnetic probe. The flow field promotes particles adhesion to the tracheal wall. The particles volumetric flow rate in both cases has been calculated. The magnetic probe is shown to increase the particles flow in the target region, but at a limited extent. This behavior has been attributed to the small particle size and the probe configuration. [ABSTRACT FROM AUTHOR]

The transmission of airborne infectious diseases in enclosed environments has become a significant public health issue. Far-ultraviolet C (UVC) lights can be used safely and effectively to disinfect bioaerosols and reduce the risk of airborne infectious disease transmission. To ensure proper use of far-UVC systems, an improved Lagrangian method for predicting the dispersion, deposition, and far-UVC disinfection of bioaerosols was proposed. First, an improved Lagrangian model considering the probability of bioaerosol survival was developed for predicting the UVC disinfection of airborne bioaerosols in enclosed environments. The UVC disinfection of surfaces with deposited bioaerosols was implemented into the deposition module of the Lagrangian model by introducing the concept of equivalent deposition number. Experimental data on far-UVC disinfection of E. Coli in the air and on the surfaces in a ventilated chamber were used to validate the proposed model. The validation results show that the proposed model can predict the bioaerosol dispersion, deposition, and far-UVC disinfection reasonably well. The validated model was then employed to calculate the far-UVC disinfection of airborne and surface SARS-CoV-2 bioaerosols in a Mass Transit Railway (MTR) train compartment in Hong Kong. According to the calculation results, the far-UVC lamps are effective in reducing the passengers' exposure to SARS-CoV-2 bioaerosols. • A novel Lagrangian model was developed for predicting UV disinfection of bioaerosols. • The proposed Lagrangian model was validated by experimental data. • Far-UVC disinfection of SARS-CoV-2 bioaerosols in a train compartment was investigated. [ABSTRACT FROM AUTHOR]

In this paper, a review of the Lagrangian stochastic models developed in the last decades for the simulation of the concentration−fluctuation dispersion is presented. The main approaches available in the literature are described and their ability in reproducing the higher order moments of the probability density function is discussed. Then, the Lagrangian approaches for evaluating of the odor annoyance are presented. It is worth to notice that, while Lagrangian stochastic models for mean concentrations are well-known and their ability in correctly reproducing the observation is well assessed, concerning concentration fluctuations the approaches are often new and unknown for most of the scientific community.