Water Model Research Articles

Distribution of microplastics between ice and water in aquatic systems: The influence of particle properties, salinity and freshwater characteristics

Microplastics (MPs) are an anthropogenic emerging pollutant, with global contamination of both marine and freshwater systems extensively documented. The interplay of MP particle properties and environmental conditions needs to be understood in order to assess the environmental fate and evaluate mitigation measures. In cold climate, ice formation has appeared to significantly affect the distribution of MPs, but so far, limited research is available comparing different aquatic systems, especially freshwater. Experiments often rely on artificial water and specific MP model particles. This study used laboratory tests to investigate the ice-water distribution of a variety of environmentally relevant MP particle types (PP, PE, PS and PVC fragments (25–1000 μm), PET fibers (average length 821 μm, diameter 15 μm)) across different water types, including artificial water of high and low salinity, as well as natural water from a lake and a treatment wetland. Overall, ice entrapment of MPs occurred in almost all tests, but the ice-water distribution of MPs differed across the different water types tested. Among the tests with artificial water, salinity clearly increased MP concentrations in the ice, but it cannot be resolved whether this is caused by increased buoyancy, changes in ice structure, or thermohaline convection during freezing. In the natural freshwater tests, the partition of MPs was shifted towards the ice compared to what was seen in the artificial freshwater. The influence of different types of dissolved and particulate substances in the different waters on MPs fate should be considered important and further explored. In this study, the higher content of suspended solids in the lake water might have enhanced MP settling to the bottom and thereby contributed to the absence of MPs in the ice of the lake test, compared to the wetland test with low suspended solids and considerably more MPs in the ice. Furthermore, the higher negative charge in the lake water possibly stabilized the negatively charged MPs in suspension, and reduced ice entrapment. Regarding particle properties, shape had a distinct effect, with fibers being less likely incorporated into ice than fragments. No fibers were found in freshwater ice. However, it became clear that ice entrapment of MPs depends on factors other than the particles' buoyancy based on density differences and particle size and shape alone.

Mechanism of Instantaneous High-Strength Sand–Water Inrush in Steeply Inclined Mining of Soft Coal Seam under Disturbed Rock–Soil Overburden

Abstract Water and sand inrush pose significant threats to underground geotechnical engineering, including shallow buried resource extraction and tunnel construction. To understand the mechanisms behind these phenomena, a mud collapse accident in Chaider Coal Mine was comprehensively investigated through field exploration and laboratory-based testings. Using numerical simulation experiments, we analyzed the failure patterns and seepage characteristics of overlying strata in steeply inclined coal seam mining under various working conditions. We established a structural instability model for water and sand inrush and identified the critical conditions for sand collapse occurrence. Our research indicates that the backfill in the surface mining pit provided a substantial material source for the accident. The overall destabilization of the top coal, due to its insufficient thickness and strength, created a pathway for sand collapse. Furthermore, frequent rainfall during the flood season and the inadequate arrangement of pumping equipment acted as triggers for the sudden water collapse. Preventative measures, such as limiting the mining height, enhancing the shear strength of the top coal, and altering the working face layout, can effectively control the development height of the water-conducting fracture zone. Additionally, timely evacuation and lowering of the aquifer water level, weakening its seepage effect in the top coal area, reducing the moisture content of the bottom soil, and improving its shear strength can mitigate water and sand inrush accidents in the backfill areas of open-pit mines.

Hybrid Quantum Mechanical, Molecular Mechanical, and Machine Learning Potential for Computing Aqueous-Phase Adsorption Free Energies on Metal Surfaces.

Performing reliable computer simulations of elementary processes occurring at metal-water interfaces is pivotal for novel catalyst design in sustainable energy applications. Computational catalyst design hinges on the ability to reliably and efficiently compute the potential energy surface (PES) of the system. Due to the large system sizes needed for studying processes at liquid water-metal interfaces, these systems can currently not be described using density functional theory (DFT). In this work, we used a hybrid quantum mechanical, molecular mechanical, and machine learning potential for studying the adsorption behavior of phenol, atomic hydrogen, 2-butanol, and 2-butanone on the (0001) facet of Ru under reducing conditions when Ru is not oxidized. Specifically, we describe the adsorbate and the surrounding metal atoms at the DFT level of theory. Here, we also considered the electrostatic field effect of the water molecules on adsorbate-metal interactions. Next, for the water-water and water-adsorbate interactions, we used established classical force fields. Finally, for the water-Ru surface interaction, for which no reliable force fields have been published, we used Behler-Parrinello high-dimensional neural network potentials (HDNNPs). Employing this setup, we used our explicit solvation for metal surface (eSMS) approach to compute the aqueous-phase effect on the low-coverage adsorption of selected molecules and atoms on the (0001) facet of Ru. In agreement with previous experimental and computational studies of oxygenated molecules over transition metal facets, we found that liquid water destabilizes the tested adsorbates on Ru(0001). Interestingly, our findings indicate that adsorbates on Ru are less affected by the presence of an aqueous phase than on other transition metals (e.g., Pt), highlighting the necessity of experimental investigations of Ru-based catalytic systems in liquid water.

Two-Way Coupling of the National Water Model (NWM) and Semi-Implicit Cross-Scale Hydroscience Integrated System Model (SCHISM) for Enhanced Coastal Discharge Predictions

This study addresses the limitations of and the common challenges faced by one-dimensional river-routing methods in hydrological models, including the National Water Model (NWM), in accurately representing coastal regions. We developed a two-way coupling between the NWM and the Semi-implicit Cross-scale Hydroscience Integrated System Model (SCHISM). The approach demonstrated improvements in modeling coastal river dynamics, particularly during extreme events like Hurricane Matthew. The coupled model successfully captured tidal influences, storm surge effects, and complex river–river interactions that the standalone NWM missed. The approach revealed more accurate representations of peak discharge timing and magnitude as well as water storage and release in coastal floodplains. However, we also identified challenges in reconciling variable representations between hydrological and hydraulic models. This work not only enhances the understanding of coastal–riverine interactions but also provides valuable insights for the development of next-generation hydrological models. The improved modeling capabilities have implications for flood forecasting, coastal management, and climate change adaptation in vulnerable coastal areas.

Dressing a Nonpolarizable Force Field for OH- in TIP4P/2005 Aqueous Solutions with Corrected Hirshfeld Charges.

We present a rigid model for the OH- ion parametrized for binary mixtures with TIP4P/2005-type water molecules. Li+, Na+ and K+ were selected as counterions, hence mimicking the important and widely used solutions of soluble alkaline hydroxides. The optimized atomic charge distributions were obtained by scaling in a factor of 0.85 those derived from the atomic dipole corrected Hirshfeld approach. The agreement between experimental and Molecular Dynamics simulation results is remarkable for a set of properties, namely, the dependence of the density of the solutions on the hydroxide concentration and on temperature, the structure (i.e., positions of the atom-to-atom radial distribution functions and coordination numbers), the viscosity coefficients, the surface tension, or the freezing point depression. The proposed optimized potential parameters for OH- thus enlarge the set of models comprised within the Madrid-2019 force field and widen the potential applicability of the TIP4P/2005 water model in basic environments.

System dynamic model of water, energy and food nexus for policy implementation

In this study, a spatiotemporal disaggregated simulation model was developed based on water–food–energy (WFE) nexus approach to assess water and food supply security considering ecosystem provisioning services. The main components of the developed model in this study (SD-WFE model) are population, water, agriculture, and energy modules. The model, which was developed using system dynamics (SD) approach, was utilized to simulate effectiveness of sectoral municipal, industrial, and agricultural water and energy consumption management and environmental protection policies in improving ecosystem provisioning services during a 20-year period. Through sensitivity analysis utilizing the Monte Carlo model, the study addresses the formulation of sustainable water resource policies across four main categories: water demand management, water supply management, food resource management, and energy resource demand management. Additionally, it explores the integration of policies within an optimal framework. The simulation of proposed solutions revealed that a combination of water demand management and food resource management yielded the most promising outcome. Specifically, the recommended solution entails enhancing water irrigation efficiency by 18% through the expansion of pressurized irrigation network coverage, adjusting cropping patterns by 14%, reducing agricultural product losses by 8% via improved food supply management, minimizing food demand by 9% due to reduced food consumption losses, and achieving an annual 10% increase in crop performance. These selected policies form the foundation for sustainable water resource management strategies.

Advancing regional flood mapping in a changing climate: A HAND‐based approach for New Jersey with innovations in catchment analysis

AbstractRegional flood mapping poses computational and spatial heterogeneity challenges, exacerbated by climate change‐induced uncertainties. This study focuses on creating a state‐wide flood mapping solution with enhanced accuracy and computational speed to support regional flooding hazard analysis and the assessment of climate change, using New Jersey as a case study. The Height Above Nearest Drainage (HAND) framework was employed for large‐scale flood mapping. The model was validated against high water marks (HWMs) collected after Hurricane Irene. Based on the National Water Model (NWM), synthetic rating curves in HAND were calibrated by tuning Manning's roughness, aligning the predicted and observed flood depths. The roughness values were generalized across the state from the validated water basins to the ungauged ones, using a multivariate regression with the hydrologic and geographic information. To map the future climate‐change‐induced flooding, a correlation between NOAA historical precipitation totals and NWM flow data from 2010 to 2020 was established to link precipitation and runoff. This study also invented a novel method for correcting catchment discontinuities, inherent in the HAND model, based on a computer vision scheme, the Sobel filter. The modeling results show that average and worst‐case storm events have the potential to increase 10%–50% in the state, where mountain areas and major river banks would be exposed to this impact more significantly.

MODELLING THE CONDITIONS OF CIRCULATING WATER SUPPLY FOR A COPPER ORE PROCESSING PLANT

There is carried out a quantitative assessment of the changes in the circulating water composition under the influence of its conditioning method in a circulating water supply system of the Balkhash Concentrator Plant. Research objects are circulating water model mixtures which are reuse in copper ores flotation after clarification in a tailings dam. They are obtained in a laboratory because of modelling the mixing and storage conditions of enrichment tailings from the Balkhash Concentrator Plant and acid effluents neutralization sludge from the Balkhash Copper Smelter Plant with industrial effluents from other enterprises in Balkhash region. There is considers two schemes for conditioning of recycle water in the process water supply system: by mixing clarified water obtained during the combined or separate waste storage (enrichment tailings and acid effluents neutralization sludge). Studies haveshown that after mixing these flows in the tail collector and their combined storage in the tailings dam chemical and physico-chemical processes occur that contribute to the removal of several pollutants (copper, arsenic, iron, zinc, cadmium, and nickel) from circulating water, which can be explained by the binding of cations these elements into insoluble compounds. Based on the results obtained, it is recommended to use a combined waste storage technology for the circulating water conditioning.

Force Field Limitations of All-Atom Continuous Constant pH Molecular Dynamics.

All-atom constant pH molecular dynamics simulations offer a powerful tool for understanding pH-mediated and proton-coupled biological processes. As the protonation equilibria of protein sidechains are shifted by electrostatic interactions and desolvation energies, pK a values calculated from the constant pH simulations may be sensitive to the underlying protein force field and water model. Here we investigated the force field dependence of the all-atom particle mesh Ewald (PME) continuous constant pH (PME-CpHMD) simulations of a mini-protein BBL. The replica-exchange titration simulations based on the Amber ff19SB and ff14SB force fields with the respective water models showed significantly overestimated pK a downshifts for a buried histidine (His166) and for two glutamic acids (Glu141 and Glu161) that are involved in salt-bridge interactions. These errors (due to undersolvation of neutral histidines and overstabilization of salt bridges) are consistent with the previously reported pK a's based on the CHARMM c22/CMAP force field, albeit in larger magnitudes. The pK a calculations also demonstrated that ff19SB with OPC water is significantly more accurate than ff14SB with TIP3P water, and the salt-bridge related pK a downshifts can be partially alleviated by the atom-pair specific Lennard-Jones corrections (NBFIX). Together, these data suggest that the accuracies of the protonation equilibria of proteins from constant pH simulations can significantly benefit from improvements of force fields.

Ecological compensation mechanism controlled by both river ecological water demand and regional water rights

River ecological protection and rational utilization of water resources provide an important support for the sustainable development for human beings and nature. In view of the lack of ecological compensation research on river ecological water demand and socio-economic water demand, a mechanism and methodology for ecological compensation based on the synergistic control of river ecological water demand and river water rights allocation is proposed. The variable monthly flow method and the improved dynamic calculation method are applied to obtain the river basic and suitable ecological water demands as the river protection threshold. A two-layer decision model for water rights allocation is established, which realizes the cascading allocation of initial water rights from city to counties to sectors, and the socio-economic water usage threshold for each level is obtained based on the model. Developing compensation discrimination guidelines under the dual-threshold synergistic control and using the unilateral water resources value by sub-sector as the compensation standard, realize the quantification and sharing of compensation funds. The Nanyang section of the Bai River basin in China is used as an example. The ecological compensation value for wet year (2011), normal year (2012), and dry years (2014–2013) are 0, 15.09 × 108 and 12.04 × 108 (average value for dry years) RMB. The adoption of suitable ecological water demand thresholds in 2012 increases the ecological protection requirements thus leading to an internal compensation situation between Nanyang County and Xinye County. From 2014 to 2016, river runoff continued to be low, and excessive water intake from upstream lead to a chain of compensation situations in the midstream and downstream. It is essential to establish a basin and regionally nested ecological compensation mechanism. The research results are conducive to improving the eco-compensation theory and provide scientific references for water resources management and high-quality development in the basin.

Tuning the interfacial reaction environment via pH-dependent and induced ions to understand C–N bonds coupling performance in NO3− integrated CO2 reduction to carbon and nitrogen compounds over dual Cu-based N-doped carbon catalyst

Dual atomic catalysts (DAC), particularly copper (Cu2)-based nitrogen (N) doped graphene, show great potential to effectively convert CO2 and nitrate (NO3−) into important industrial chemicals such as ethylene, glycol, acetamide, and urea through an efficient catalytical process that involves C–C and C–N coupling. However, the origin of the coupling activity remained unclear, which substantially hinders the rational design of Cu-based catalysts for the N-integrated CO2 reduction reaction (CO2RR). To address this challenge, this work performed advanced density functional theory calculations incorporating explicit solvation based on a Cu2-based N-doped carbon (Cu2N6C10) catalyst for CO2RR. These calculations are aimed to gain insight into the reaction mechanisms for the synthesis of ethylene, acetamide, and urea via coupling in the interfacial reaction micro-environment. Due to the sluggishness of CO2, the formation of a solvation electric layer by anions (F−, Cl−, Br−, and I−) and cations (Na+, Mg2+, K+, and Ca2+) leads to electron transfer towards the Cu surface. This process significantly accelerates the reduction of CO2. These results reveal that *CO intermediates play a pivotal role in N-integrated CO2RR. Remarkably, the Cu2-based N-doped carbon catalyst examined in this study has demonstrated the most potential for C–N coupling to date. Our findings reveal that through the process of a condensation reaction between *CO and NH2OH for urea synthesis, *NO3− is reduced to *NH3, and *CO2 to *CCO at dual Cu atom sites. This dual-site reduction facilitates the synthesis of acetamide through a nucleophilic reaction between NH3 and the ketene intermediate. Furthermore, we found that the I− and Mg2+ ions, influenced by pH, were highly effective for acetamide and ammonia synthesis, except when F− and Ca2+ were present. Furthermore, the mechanisms of C–N bond formation were investigated via ab-initio molecular dynamics simulations, and we found that adjusting the micro-environment can change the dominant side reaction, shifting from hydrogen production in acidic conditions to water reduction in alkaline ones. This study introduces a novel approach using ion-H2O cages to significantly enhance the efficiency of C–N coupling reactions.

Run-Up of a Vortex Hydrodynamic Bore onto the Shore

The run-up of a vortex hydrodynamic bore onto an inclined beach is the subject of this study. To theoretically analyze this problem, we use the Benny equations, which, within the shallow water model, allow us to take into account the distribution of horizontal fluid velocity along the depth of the fluid layer. We show that the presence of a shear flow behind a bore significantly modifies the different regimes of bore motion toward the shoreline depending on its strength. The subsequent collapse of the bore near the shoreline with the release of a high-speed run-up jet onto the dry shore is also significantly modulated by the degree of vorticity of the fluid flow. The maximum flooding length and run-up height increase significantly with increasing vorticity of the fluid flow. We use a theoretical model based on the characteristic Whitham rule for a bore, supplemented by the laws of conservation of mass and the momentum of a liquid crossing a shock wave. It is assumed that the wave run-up that appears after the “collapse” of the bore is determined by gravity. As a result, the maximum value of the wave run-up, its speed, the influence of flow vorticity, and its structure as a whole are estimated. The acceptable agreement of the simulation results with experimental data can serve as a justification for the applicability of our model to the calculation of the bore run-up onto a sloping beach.

Benchmark of computational hydraulics models for open-channel flow with lateral cavities

Computational models in hydro-environmental engineering are diverse in their background formulation and span from two-dimensional depth-averaged shallow water models, to complex fully three-dimensional turbulence models resolving large-eddy simulation with surface capturing techniques, and to Lagrangian particle-based methods. This paper presents a first-of-its-kind comparison of six different computational hydraulics fluid dynamics models, namely Iber+, HO-SWM, GBVC, OpenFOAM (RANS), Hydro3D (LES) and DualSPHysics (SPH), in the prediction of mean velocities and free-surface dynamics in two benchmarks involving open-channel flows with symmetric lateral cavities. Results show that shallow-water models capture relatively well the main large-scale coherent structures of the in-cavity flow, with wider shear layers compared to three-dimensional models, and higher velocities in the main channel. Three-dimensional RANS, LES and SPH yield improved predictions of mean velocities compared with experimental data. Computational cost has been quantified for all models with a logarithmic growth when increasing model complexity. The transverse standing wave is captured by most models, with the shallow-water ones matching the theoretical value, while the three-dimensional models overestimate it slightly.

A Godunov-type scheme for the Saint-Venant-Exner equations with a moving steady states

The Saint-Venant-Exner system is widely used in industrial codes to model the transport of bed sediments. In practice, most of the methods used for its numerical resolution suffer from significant stability problems due to the fact that they are mainly guaranteed by separation techniques which allow weak coupling between hydraulic and morphodynamic software. The search for an adequate alternative method to this problem is a focus towards which several approaches converge. Recently, many authors have proposed acceptable methods but they are not so trivial to implement in an industrial context and some do not take into account all aspects such as mobile steady states. In this work, we derive a well-balanced scheme that takes into account all stable states, to approach weak solutions of the sediment transport model in shallow waters. We demonstrate that it captures exactly all regular steady solutions with non-evanescent velocities, retains water level positivity and is able to degenerate to a classical shallow water model when the sedimentary transport flow is null. A number of numerical test cases are also presented to illustrate these properties.

Molecular Dynamics Calculation of Interfacial Tension in a Two-Phase Liquid Hydrocarbon–Water–Surfactant System: From Rarefied to Superdense Surfactant Monolayer

A method is proposed for calculating low interfacial tension (IFT) based on molecular dynamics simulation of systems with superdense packing of surfactant molecules at the water–liquid hydrocarbon interface. The interfacial tension was calculated by the molecular dynamics method using the all-atom and coarse-grained models in water–alkane (decane, dodecane) two-phase systems in the presence of various individual surfactants. The following ionic and nonionic surfactants were considered: sodium dodecyl sulfate (SDS), cetyltrimethylammonium chloride (CTAC), sodium dodecylbenzenesulfonate (SDBS), sodium decet-6 sulfate C10E6SO4Na, hexaethylene glycol monodecyl ether (C10E6), triethylene glycol monononadecyl ether (C19E3), and octapropoxypentaethylene glycol monododecyl ether (C12P8E5). It was shown that the interfacial tension decreases to zero when surfactant adsorption increases to the limiting values.

Analysis of Inherent Frequencies to Mitigate Liquid Sloshing in Overhead Double-Baffle Damper

A disco-rectangular volume-fraction-of-fluid (VOF) model tank of a prismatic size is considered here for investigating the severe effect of overhead baffles made of three different materials, nylon, polyamide, and polylactic acid. In this work, the overdamped, undamped, and nominal damped motion of baffles and their effect are studied. In this research, the behaviour of different material baffles based on the sloshing effect and natural frequency of each baffle excited in damped, undamped, and overdamped cases is studied. VOF modelling is carried out in moving Yeoh model mesh with fluid–structure interaction between the water models for various baffle plates. The results of the water volume distribution and baffle displacement operating between a sloshing time of 0 and 1 s are recorded. Also, a strong investigation is carried out for the water volume suspended on overhead baffles by three different material selections.

Assignment of a Physical Energy Scale for the Dimensionless Interaction Energies within the PRIME20 Peptide Model.

We present a calibration scheme to determine the conversion factors from a coarse-grained stochastic approximation Monte Carlo approach using the PRIME20 peptide interaction model into atomistic force-field interaction energies at full explicit aqueous solvation. The conversion from coarse-grained to atomistic structures was done according to our previously established inverse coarse-graining protocol. We provide a physical energy scale for both the backbone hydrogen bonding interactions and the sidechain interactions by correlating the dimensionless energy descriptors of the PRIME20 model with the energies averaged over molecular dynamics simulations. The conversion factor for these interactions turns out to be around 2kJ/mol for the backbone interactions, and zero for the sidechain interactions. We discuss these surprisingly small values in terms of their molecular interpretation.

Ab initio electronic absorption spectra of para-nitroaniline in different solvents: Intramolecular charge transfer effects.

Intramolecular charge transfer (ICT) effects of para-nitroaniline (pNA) in eight solvents (cyclohexane, toluene, acetic acid, dichloroethane, acetone, acetonitrile, dimethylsulfoxide, and water) are investigated extensively. The second-order algebraic diagrammatic construction, ADC(2), ab initio wave function is employed with the COSMO implicit and discrete multiscale solvation methods. We found a decreasing amine group torsion angle with increased solvent polarity and a linear correlation between the polarity and ADC(2) transition energies. The first absorption band involves π → π* transitions with ICT from the amine and the benzene ring to the nitro group, increased by 4%-11% for different solvation models of water compared to the vacuum. A second band of pNA is characterized for the first time. This band is primarily a local excitation on the nitro group, including some ICT from the amine group to the benzene ring that decreases with the solvent polarity. For cyclohexane, the COSMO implicit solvent model shows the best agreement with the experiment, while the explicit model has the best agreement for water.

Density functional modeling of ternary Am(III) hydroxo complexes with Ca or Mg counterions. Do Mg stabilized species exist?

We carried out density functional computations to investigate experimentally suggested ternary Ca–Am(III)–OH and possible Mg–Am(III)–OH complexes in water. We confirmed the experimental stoichiometry for the Ca complexes and their relative stability. For the Mg complexes, we find comparable or weaker complexation. This finding is in agreement with experimental observations. We demonstrate that explicit solvation of counterions is important when comparing Ca and Mg species. For the Ca complexes this has a minimal effect on their relative stability. Contrariwise, Mg complexes exhibit a lower stability and are highly sensitive to explicit short-range solvation effects. Explicit Mg2+ solvation significantly altered both absolute and relative formation energies compared to a simpler model. These findings highlight the crucial role of incorporating explicit short-range solvation effects in accurate computational modeling when small and highly charged ions are treated.

Role of the structural order of the hydration layer in regulating the heterogeneous ice nucleation efficiency

Understanding the complex microscopic mechanisms of heterogeneous ice nucleation is crucial across diverse fields from cloud science to microbiology. In this work, we examined the ability of solid surfaces to promote ice nucleation as a function of the structural order of interfacial water, including the first and second hydration layers. Comprehensive all-atom molecular dynamics simulations using the TIP4P/ice water model were conducted on a water film atop a modeled surface inspired by the (0001) surface of AgI crystal, with varying surface charges. These simulations revealed non-monotonic nucleation rates. The first hydration layer formed a hexagonal hydrogen-bond network resembling ice structures, exhibiting low mobility essential for inducing ice nucleation. Notably, the second hydration layer, acting as a key-point bridge, displayed varying degrees of orientational preference facilitated by inter-layer hydrogen bonds. The calculation of fluctuation parameters indicated that the greater structural order of the second layer significantly enhances the surface’s ice-forming capabilities. Unlike previous studies that focused primarily on the role of the first layer of interfacial water, our findings demonstrate that the second layer provides a more accurate indicator of ice nucleation capabilities.