Simulation Of Dispersion Research Articles

High-Resolution Spatial Forecasting of Hourly Air Quality: A Fast Method for a Better Representation of Industrial Plumes and Traffic Emissions Contributions

Efficiently mapping hourly air quality at a fine scale (25 m) remains a computational challenge. This difficulty is heightened when aiming to accurately capture industrial plumes and time-varying traffic emissions. This paper presents a method for generating hourly pollutant concentration maps across an entire region for operational applications. Our approach assumes that concentration maps can be decomposed into three components: traffic concentrations, industrial concentrations and a residual “background” concentrations component. The background concentration is estimated using established fine-scale mapping methods involving ADMS-Urban dispersion simulations. Meanwhile, the traffic and industrial layers are derived using a KNN-based approach applied to a sample of hourly ADMS-Urban simulations. This method enhances the representation of industrial plumes and the temporal variability in traffic emissions while maintaining computational efficiency, making it suitable for the operational production of hourly air quality maps in the Hauts-de-France region (France).

Thermoelectric and Optical Properties of HfSi2N4 and HfGe2N4: A First‐Principles Investigation

AbstractThis study explores the thermoelectric and optoelectronic properties of HfSi₂N₄ and HfGe₂N₄ monolayers (ML) through first‐principles calculations. Both materials exhibit excellent structural stability, as confirmed by phonon dispersion and ab initio molecular dynamics simulations. HfSi₂N₄ demonstrates superior power factors and higher thermal conductivity, while HfGe₂N₄ achieves a remarkable thermoelectric figure of merit () of 0.92 at 900 K under p‐type doping, surpassing many 2D materials. The inclusion of spin‐orbit coupling further enhances the thermoelectric performance, especially for HfGe₂N₄. The electronic properties reveal indirect bandgaps of 2.89 eV for HfSi₂N₄ and 2.75 eV for HfGe₂N₄, with strong optical absorption peaks in the visible range, making them suitable for optoelectronic applications. The materials exhibit high carrier mobility, with HfSi₂N₄ reaching 582 cm2V⁻¹s⁻¹ and HfGe₂N₄ achieving an impressive 1870 cm2V⁻¹s⁻¹ for holes. Thermal conductivity analysis reveals that HfGe₂N₄ has significantly lower values than HfSi₂N₄, favoring thermoelectric efficiency. The synergy of high Seebeck coefficients (S), tunable thermal conductivity, and optical properties makes these monolayers promising candidates for advanced thermoelectric devices and visible‐light optoelectronics. This study provides a comprehensive comparison, offering valuable insights into their applicability in next‐generation energy conversion and optoelectronic technologies.

Going with the flow: Leveraging reef‐scale hydrodynamics for upscaling larval‐based restoration

AbstractAnthropogenic pressures are impacting coastal marine ecosystems, necessitating large‐scale interventions to accelerate recovery. Propagule‐based restoration holds the potential for restoring shallow coastal systems at hectare scales by harnessing natural dispersal. However, predicting propagule dispersal remains challenging due to the complex hydrodynamic nature of coastal marine ecosystems and the complex behaviors of marine propagules. To improve predictions of fine‐scale larval dispersal patterns, we developed a 3D reef‐scale (~30‐m resolution) dispersal model for Lizard Island, Australia, with the aim to predict the effect of island‐scale hydrodynamics on the distribution of coral spawn slicks and larvae. Using in situ field observations and dispersal simulations, we assessed the model's capability to (1) forecast hydrodynamic conditions, (2) predict coral spawn slick convergence zones for collection efforts, and (3) identify optimal locations and timeframes where high particle residence time may enhance local settlement following larval delivery to damaged reefs. Predictions of convergence zones in the upper water column aligned well with field observations of coral spawn slicks. At the reef benthos, the model captured variability in current speed and direction at ~58% of studied locations. At other locations, the model did not resolve hydrodynamic conditions due to sheltering effects and associated hydrodynamic processes occurring at a scale below 50 m. At locations where the model performed well, propagules could remain within a 1‐ha area around the delivery site for 5–15 h depending on locations and the timing of larval release. These high retention conditions were infrequent but occurred at least once at 15 of the 25 studied sites. Observations of local currents a posteriori confirmed model predictions, showing periods of little water movement lasting from 6.5 to 15 h. Overall, our study highlights fine‐scale dispersal modeling as a key tool for scaling up larval‐based reef restoration, while also acknowledging the need for better predictions of local conditions in complex, shallow environments. Applications of fine‐scale modeling, coupled with local knowledge of reproductive timing and larval behavioral ecology, assist with the mass collection of propagules upon release and in identifying areas and times of optimal larval deployment to achieve the greatest impact.

Simulation of subsurface mechanical dispersion (SSMD) of oil by a water jet.

Simulation of subsurface mechanical dispersion (SSMD) of oil by a water jet.

Physical modeling for emergency planning support: Gas dispersion simulations in urban and rural areas

Physical modeling for emergency planning support: Gas dispersion simulations in urban and rural areas

High-density multicore fiber with single-mode cores and low-mode crosstalk for visible light applications between 565nm and 650nm.

This study presents what we believe to be a novel 37-core multicore fiber designed for the visible range (565nm … 650nm), featuring a hexagonal arrangement of identical cores, single-mode guidance, low intercore crosstalk, low-mode attenuation (< 0.1 dB/m), and high-core density (1.2 × 10-3). Experimental characterizations, including intercore coupling, mode attenuation, core positioning accuracy (<120 nm), bending loss, group velocity dispersion, and mode field diameter, combined with supermode dispersion simulations, uncover the fiber performance. These results highlight the potential of visible-wavelength multicore fibers for advancing high-resolution imaging, optical trapping, and minimally invasive diagnostics.

Multiphase Flow Simulations of Dispersions in Microfiltration

Multiphase Flow Simulations of Dispersions in Microfiltration

Combining Hierarchical Distribution Models With Dispersal Simulations to Predict the Spread of Invasive Plant Species

ABSTRACTAimPredicting the future distribution of invasive species is a current challenge for biodiversity assessment. Species distribution models (SDMs) have long been the state‐of‐the‐art to evaluate suitable areas for new invasions, but they may be limited by truncated niches and the uncertainties of species dispersal. Here, we developed a framework based on hierarchical SDMs and dispersal simulations to predict the future distribution and spread of invasive species at the ecoregion level.LocationCantabrian Mixed Forests Ecoregion (SW Europe) with global distribution data.Time Period1950–2063.Major Taxa StudiedVascular plants.MethodsWe used occurrence data from 102 invasive species to fit SDMs with machine‐learning algorithms and to simulate species dispersal. We combined habitat suitability models based on species' global climatic niches together with regional models including local variables (topography, landscape features, human activity, soil properties) in a hierarchical approach. Then, we simulated species dispersal across suitable areas over the next 40 years, considering species dispersal limitations and climate change.ResultsGlobal climatic niches retained a strong contribution in the hierarchical models, followed by local factors such as human population density, sand content and soil pH. In general, the highest suitability was predicted for warm and humid climates close to the coastline and urbanised areas. The inclusion of dispersal abilities identified different trajectories of geographic spread for individual species, predicting regional hotspots of species invasion. The predictions were more dependent on global suitability and species dispersal rather than climatic warming scenarios.Main ConclusionsThis study provides a comprehensive framework for predicting the regional distribution of invasive species. While hierarchical modelling combines non‐truncated global climatic niches with regional drivers of species invasions, the integration of dispersal simulations allows us to anticipate invasibility in new areas. This framework can be useful to assess the current and future distribution of invasive species pools in biogeographical regions.

Eulerian RANS simulation of pollutant dispersion in atmospheric boundary layer considering anisotropic and near-source diffusivity behavior

Eulerian RANS simulation of pollutant dispersion in atmospheric boundary layer considering anisotropic and near-source diffusivity behavior

A Fractional Hybrid Staggered-Grid Grünwald–Letnikov Method for Numerical Simulation of Viscoelastic Seismic Wave Propagation

The accurate and efficient simulation of seismic wave energy dissipation and phase dispersion during propagation in subsurface media due to inelastic attenuation is critical for the hydrocarbon-bearing distinction and improving the quality of seismic imaging in strongly attenuating geological media. The fractional viscoelastic equation, which quantifies frequency-independent anelastic effects, has recently become a focal point in seismic exploration. We have developed a novel hybrid staggered-grid Grünwald–Letnikov (HSGGL) finite difference method for solving the fractional viscoelastic equation in the time domain. The proposed method achieves accurate and computationally efficient solutions by using a staggered grid to discretize the first-order partial derivatives of the velocity–stress equations, combined with Grünwald–Letnikov finite difference discretization for the fractional-order terms. To improve the computational efficiency, we employ a preset accuracy to truncate the difference stencil, resulting in a compact fractional-order difference scheme. A stability analysis using the eigenvalue method reveals that the proposed method confers a relaxed stability condition, providing greater flexibility in the selection of sampling intervals. The numerical experiments indicate that the HSGGL method achieves a maximum relative error of no more than 0.17% compared to the reference solution (on a finely meshed domain) while being significantly faster than the conventional global FD method (GFD). In a 500 × 500 computational domain, the computation times for the proposed methods, which meet the specified accuracy levels used, are only approximately 4.67%, 4.47%, 4.44%, and 4.42% of that of the GFD method. This indicates that the novel HSGGL method has the potential as an effective forward modeling tool for understanding complex subsurface structures by employing a fractional viscoelastic equation.

Blended natural gas/hydrogen fuel gas systems: An evaluation of risk

AbstractThe addition of renewably produced (“green”) hydrogen to existing natural gas pipeline systems presents an effective means of transmitting energy with a reduced overall carbon footprint while granting end‐users access to federal incentives, a product of recent climate legislation. Although the concept of blended hydrogen/natural gas infrastructure is not new, it presents a host of engineering challenges that merit attention before being put into practice. In consideration of dissimilarities in physical properties and combustion characteristics between natural gas and hydrogen, the safe implementation of converted utility systems demands a comprehensive assessment of risks involved, including both the probability of accidental leak (infrastructure durability, pipeline embrittlement, and increased leakage rate through permeable elastomer seals) and the impact following the release of material. In this article, hazard analysis considering the effects of loss of containment for natural gas/hydrogen blend composition scenarios (0–30% H2 by volume) is undertaken, specifically examining jet fire thermal radiation, flammable vapor dispersion, and vapor cloud explosions for fixed leak sizes. This investigation applies analytical techniques to evaluate the consequences of gas release behavior through vapor cloud dispersion and mixture deflagration simulation. The work aims to identify and quantify hazard severity and risk associated with system retrofitting for hydrogen blending within existing natural gas distribution networks.

Systematic Simulations of Structural Stability, Phonon Dispersions, and Thermal Expansion in Zinc-Blende ZnO.

Zinc oxide (ZnO) has recently gained considerable attention due to its exceptional properties, including higher electron mobility, good thermal conductivity, high breakdown voltage, and a relatively large exciton-binding energy. These characteristics helped engineers to develop low dimensional heterostructures (LDHs)-based advanced flexible/transparent nanoelectronics, which were then integrated into thermal management systems. Coefficients of thermal expansion αT, phonon dispersions ωj(q→), and Grüneisen parameters γjq→ can play important roles in evaluating the suitability of materials in such devices. By adopting a realistic rigid-ion model in the quasi-harmonic approximation, this work aims to report the results of a methodical study to comprehend the structural, lattice dynamical, and thermodynamic behavior of zinc-blende (zb) ZnO. Systematic calculations of ωj(q→), γjq→, and αT have indicated negative thermal expansion (NTE) at low T. Soft transverse acoustic shear mode gammas γTA at critical points offered major contributions to NTE. Our results of ωj(q→) at ambient pressure compare reasonably well with Raman scattering spectroscopy measurements and first-principles calculations. By adjusting the layers of materials with positive and negative thermal expansion, it is possible to create LDHs with near-zero αT. Such a nanostructure might experience a minimal dimensional change with T fluctuations, making it ideal for devices where precise dimensional stability is crucial.

Simulation of carbon monoxide dispersion released from a fleet in urban environment

Simulation of carbon monoxide dispersion released from a fleet in urban environment

Multiscale simulation and experimental investigation of nanoparticles dispersion during laser surface remelting of SiC/Mg-9Al composites

Multiscale simulation and experimental investigation of nanoparticles dispersion during laser surface remelting of SiC/Mg-9Al composites

Comprehensive evaluation of constant and variable turbulent Schmidt numbers for CFD simulation of near-field air pollutant dispersion

Comprehensive evaluation of constant and variable turbulent Schmidt numbers for CFD simulation of near-field air pollutant dispersion

Non-negligible impact of Stokes drift and wave-driven Eulerian currents on simulated surface particle dispersal in the Mediterranean Sea

Abstract. Numerical simulations of marine surface particle dispersal are a crucial tool for addressing many outstanding issues in physical oceanography of societal relevance, such as marine plastic pollution. However, the quality of these Lagrangian simulations depends on the ability of the underlying numerical model to represent prevailing ocean circulation features. Here, we investigate how simulated marine surface particle dispersal changes if the – often omitted or only approximated – impact of wind-generated surface waves on upper-ocean circulation is considered. We use velocity fields from a high-resolution coupled ocean–wave model simulation and a complementary stand-alone ocean model simulation for the Mediterranean Sea to answer the following questions: (1) how does the explicit representation of waves impact simulated surface particle dispersal, and what is the relative impact of Stokes drift and wave-driven Eulerian currents? (2) How accurately can the wave impact be approximated by the commonly applied approach of advecting particles with non-wave-driven Eulerian currents and Stokes drift from stand-alone ocean and wave models? We find that the representation of surface waves tends to increase the simulated mean Lagrangian surface drift speed in winter through the dominant impact of Stokes drift and tends to decrease the mean Lagrangian surface drift speed in summer through the dominant impact of wave-driven Eulerian currents. Furthermore, simulations that approximate the surface wave impact by including Stokes drift (but ignoring wave-driven Eulerian currents) do not necessarily yield better estimates of surface particle dispersal patterns with explicit wave impact representation than simulations that do not include any surface wave impact. Our results imply that – whenever possible – velocity fields from a coupled ocean–wave model should be used for surface particle dispersal simulations.

3D modelling and simulation of thermal effects and dispersion of particles carrying infectious respiratory agents in a railway transport coach

Even though the COVID-19 pandemic now belongs to the long history of infectious diseases that have struck humanity, pathogenic biological agents continue to pose a recurring threat in private places, but also and mainly in places where the public congregates. In our recent research published in this journal in 2022 and 2023, we considered the illustrative example of a commuter train coach in which a symptomatic or asymptomatic passenger, assumed to be infected with a respiratory disease, sits among other travellers. The passenger emits liquid particles containing, for example, COVID-19 virions or any other pathogen. The size spectrum of particles varies depending on whether they are produced during breathing, speaking, coughing or sneezing. More specifically, droplets associated with breathing are in the range of 1–10 µm in aerodynamic diameter, while at the other end of the spectrum, drops associated with coughing can reach 100–1000 µm. In the first part of our research, we used Computational Fluid Dynamics (CFD) to model and simulate in 3D the transport and dispersion of particles from 1 µm to 1 mm in the turbulent flow generated by the ventilation of the railway coach. We used both the Eulerian approach and the Lagrangian approach and showed that the results were strictly similar and illustrated the very distinct aerodynamics, on one hand, of the aerosol of droplets suspended in the air and, on the other hand, of the drops falling or behaving like projectiles depending on their initial speed. In the second part of our research, we developed a model of filtration through a typical surgical mask and possible leaks around the mask if it is poorly adjusted. We resumed the twin experiment of the railway coach and compared the distribution of droplets depending on whether the passengers (including the infected one) wear masks or not and whether the masks are perfectly fitted or worn loosely. Our method made it possible to quantify the particles suspended in the air of the railway coach depending on whether the infected passenger wore their mask more or less well. In this third article, we specifically explore how thermal effects due to the presence of passengers influence the spatio-temporal distribution in the railway coach of aerosols produced by the breathing infected person. We demonstrate that the influence of thermal effects on aerodynamics is very significant and can be very favourable for air decontamination if the ventilation system is judiciously configured. Beyond its application to a commuter train, our work confirms the value of validated CFD tools for describing the airflow and dispersion of particles in complex spaces that do not always allow experimentation. The models that we have developed are applicable to any other semi-confined, ventilated public place, such as a classroom, a hospital room or a performance hall, and they enable the objective assessment of whether the occupation of these spaces could be critical with regard to infectious contamination and of how to limit this ubiquitous risk.

The Effect of Stellar Evolution on Dispersal of Protoplanetary Disks: Disk Fraction in Star-forming Regions

Abstract We study the effect of stellar evolution on the dispersal of protoplanetary disks by performing one-dimensional simulations of long-term disk evolution. Our simulations include viscous disk accretion, magnetohydrodynamic winds, and photoevaporation as important disk dispersal processes. We consider a wide range of stellar mass of 0.1–7 M ⊙ and incorporate the luminosity evolution of the central star. For solar-mass stars, stellar evolution delays the disk dispersal time as the far-ultraviolet (FUV) luminosity decreases toward the main sequence. In the case of intermediate-mass stars, the FUV luminosity increases significantly over a few million years, driving strong photoevaporation and enhancing disk mass loss during the later stages of disk evolution. This highlights the limitations of assuming a constant FUV luminosity throughout a simulation. Photoevaporation primarily impacts the outer regions of the disk and is the dominant disk dispersal process in the late evolutionary stage. Based on the results of a large set of simulations, we study the evolution of a population of star–disk systems and derive the disk fraction as a function of time. We demonstrate that the inclusion of stellar luminosity evolution can alter the disk fraction by several tens of percent, bringing the simulations into closer agreement with recent observations. We argue that it is important to include the stellar luminosity evolution in simulations of the long-term dispersal of protoplanetary disks.

Weak coupling of observed surface PM2.5 in Delhi-NCR with rice crop residue burning in Punjab and Haryana

Air pollution impacts on human health are of serious concern in northern India, and over the Delhi National Capital Region (NCR) in particular. The Kharif crop residue burning (CRB) is often blamed for degradation of Delhi-NCR’s seasonal air quality. However, the concentration of fine particulate matter (PM2.5) remained stable in Delhi, while the fire detection counts (FDCs) from satellites over Punjab and Haryana declined by 50% or more during 2015–2023. We measured PM2.5, carbon monoxide (CO) and related parameters over Delhi-NCR, Haryana and Punjab from a network of 30 low-cost sensors (CUPI-Gs) in a selected period (September–November) of 2022 and 2023. Measured PM2.5 showed lower concentration in 2023 compared to 2022 at Punjab and Haryana sites, in compliance with FDC reductions. Using the CUPI-G measurements, airmass trajectories, particle dispersion and chemical-transport model simulations, we show that the CRB emissions over Punjab contributed only a meagre ~14% to the overall PM2.5 over Delhi-NCR during October-November 2022. This indicates that there exists only a very weak coupling between PM2.5 mass over Delhi-NCR and the CRB over Punjab, highlighting the effectiveness of the Graded Response Action Plan (GRAP) in controlling air pollution in the region.

High fidelity simulations of contaminant dispersion in an urban environment with comparison to magnetic resonance imaging measurements

The dispersion of a contaminant in an urban environment has the potential to impact a large population of people. In this work, a complex urban canopy flow based on the Oklahoma City downtown business district circa 2003 is studied using Magnetic Resonance Imaging (MRI) and high-fidelity Large Eddy Simulations (LES). MRI is a novel experimental technique that can provide high-resolution measurements in four dimensions (three spatial and temporal) for lab scale models. The experiments and simulations use the same geometry and boundary conditions providing a one-to-one comparison of the two methods. Results are presented on the time-averaged velocity and concentration fields, the temporal dynamics of the concentration plumes for a transient release, and a novel Cloud Identification Algorithm that can separate plumes produced by periodic contaminant releases used for ensemble averaging over many releases. The MRI and LES datasets both include millions of measurement voxels and the comparisons highlight the complex 3D nature of the flow including strong vertical velocities in spanwise street canyons and flow acceleration in streamwise street canyons. The concentration fields are qualitatively similar albeit the LES shows larger dispersion. A quantitative analysis with performance measures compares the datasets pointwise and demonstrates that the two 3D datasets are similar with respect to many measures including a fractional bias of 0.02 (ideal=0.0), correlation coefficient of 0.87 (ideal = 1.0), and the fraction points within a factor of 2 is 0.98 (ideal = 1.0). Plume analysis compares the arrival and residence time of contaminant and is found to vary significantly with location within the urban environment with arrival times between 0 and 1.25 and differences within the contaminant cloud less than 10% at most locations.