Nitrogen (N) contamination within agricultural‐karst landscapes and aquifers is widely reported; however, the complex hydrological pathways of karst make N fate difficult to ascertain. We developed a ...hydrologic and N numerical model for agricultural‐karst, including simulation of soil, epikarst, phreatic, and quick flow pathways as well as biochemical processes such as nitrification, mineralization, and denitrification. We tested the model on four years of nitrate (NO3−) data collected from a phreatic conduit and an overlying surface channel in the Cane Run watershed, Kentucky, USA. Model results indicate that slow to moderate flow pathways (phreatic and epikarst) dominate the N load and account for nearly 90% of downstream NO3− delivery. Further, quick flow pathways dilute NO3− concentrations relative to background aquifer levels. Net denitrification distributed across soil, epikarst, and phreatic water removes approximately 36% of the N inputs to the system at rates comparable to nonkarst systems. Evidence is provided by numerical modeling that NO3− accumulation via evapotranspiration in the soil followed by leaching through the epikarst acts as a control on spring NO3− concentration and loading. Compared to a fluvial‐dominated immature karst system, mature‐karst systems behave as natural detention basins for NO3−, temporarily delaying NO3− delivery to downstream waters and maintaining elevated NO3− concentrations for days to weeks after hydrologic activity ends. This study shows the efficacy of numerical modeling to elucidate complex pathways, processes, and timing of N in karst systems.
Key Points
Slow (epikarst and phreatic) flows account for nearly 90% of nitrate loading in an agricultural‐karst system
Nitrate accumulation and subsequent leaching dominate pathway processes
Agricultural‐karst systems act as detention basins of nitrate and, during flood recession, drain storm‐derived nitrate more gradually compared to poorly karstified systems
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
•Blast effects on reinforced concrete slabs used for civil buildings.•Experimental tests on reinforced concrete slab samples subjected to contact explosions induced by different charges.•Damage ...produced in the slabs analyzed in terms of the extension and the shape of the crater and of the hole.•Numerical modeling of blast wave generation and propagation.•Validation of constitutive models for describing the slab structural elements.
In this work, a numerical model for analyzing the mechanical behavior of a reinforced concrete slab subjected to a direct contact explosion was developed, using the explicit finite element code LS-DYNA and facing the following issues: generation and propagation of the blast wave, interaction with the solid structure, and mechanical behavior of the slab. The different elements that constitutes the slab were modeled as deformable bodies and the constitutive model coefficients for each material, when not directly measured, were calibrated by comparison with experimental measures. To this purpose, a reinforced concrete slab used for civil buildings was loaded with three different charge of EXEM 100: 2.1, 6.3, and 10.5 kg. For each test, the blast wave pressure-time profile was measured at two different locations and the damage extension in concrete and reinforcing elements was estimated. Using the same sets of material dependent parameters, a good agreement between experimental and numerical results was found for all tested configurations. The validated numerical model provided insight into the role of different structural elements on the failure mechanisms into the slab and is a useful tool for investigating alternative loading configurations and designing potential reinforcement solutions.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•We simulate SWI in simplified, discretely fractured aquifers.•Fracture orientation, location and density can affect seawater extent.•EPM models cannot infer seawater distribution in most discrete ...fracture cases.
Despite that fractured coastal aquifers are widespread, the influence of fracture characteristics on seawater intrusion (SWI) has not been explored in previous studies. This research uses numerical modelling in a first step towards understanding the influence of fracture orientation, location and density on the extent of seawater and accompanying patterns of groundwater discharge in an idealised coastal aquifer. Specifically, aquifers containing single fractures or networks of regularly spaced fractures are studied using modified forms of the Henry SWI benchmark problem. The applicability of equivalent porous media (EPM) models for representing simple fracture networks in steady-state simulations of SWI is tested. The results indicate that the influence of fractures on SWI is likely to be mixed, ranging from enhancement to reduction in seawater extent and the width of the mixing zone. For the conceptual models considered here, vertical fractures in contact with the seawater wedge increase the width of the mixing zone, whereas vertical fractures inland of the wedge have minimal impact on the seawater distribution. Horizontal fractures in the lower part of the aquifer force the wedge seaward, whereas horizontal fractures located within the zone of freshwater discharge enhance the wedge. Inclined fractures roughly parallel to the seawater-freshwater interface increase the landward extent of seawater and fractures perpendicular to the interface inhibit the wedge. The results show that EPM models are likely inadequate for inferring salinity distributions in most of the fractured cases, although the EPM approach may be suitable for orthogonal fracture networks if fracture density is high and appropriate dispersivity values can be determined.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Investigating the equilibrium profile of a sandy beach is important to evaluate the beach response to natural forces. Empirical or semi-empirical relationships among beach states, wave climates and ...sediments properties have been established in various studies. In this study, detailed physical insights of hydrodynamics and sediment transport patterns on a quasi-equilibrium beach profile are provided using a process-based model. Model results show that during the beach profile transition to equilibrium, both the magnitude and the cross-shore gradient of sediment transport rate decrease. The total net sediment transport in surfzone is mainly affected by the balance/imbalance between offshore-directed current-related suspended sediment transport and onshore-directed bedload transport, both of which showing a decreasing tendency during the transition to equilibrium. The former is due to the decreasing undertow velocity and sediment concentration, and the latter is due to the decrease of peak bedload transport rate near the intra-wave crest phase. The wave-related suspended sediment transport is relatively small compared to the other two transport components. Based on the entropy concept, a dimensionless parameter representing the spatial uniformity of wave energy dissipation rate is proposed as an indicator of the equilibrium degree of a beach profile. Results suggest that a quantitative relationship can be established between this parameter and the overall characteristics of sediment transport on a beach profile.
•Beach profile evolutions are reproduced by a process-based numerical model.•Analysis of hydrodynamics and sediment transport on a quasi-equilibrium profile.•Each sediment transport component decreases during transition to equilibrium.•Retrieving sediment transport into an intra-wave time scale.•An entropy paramter is proposed to reflect the equilibrium degree of a beach.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
ABSTRACT
The Holocene Storegga tsunami, 8120–8175 cal a bp, resulted in run‐up heights of up to 3–6 m around mainland UK and coincided with a suggested large population decline in the coastally ...focused Mesolithic population in Northern Britain. At Howick, Northumberland, the site of a Mesolithic settlement, a nearby sediment deposit may be of tsunamigenic origin, but this is uncertain. Here, a numerical model was used to simulate the Storegga tsunami in Northumberland. Two scenarios of relative sea‐level change, and a third incorporating high tide, were simulated with mortality estimated within the intertidal zone for the Mesolithic sites in the region. The results showed that only with the addition of high tide could the sediment deposit site have been inundated by the tsunami. At Howick, mortality estimates varied but were up to 100% within the resource‐rich intertidal zone. The tsunami inundated a large area and would have led to the loss of key resources such as hazelnuts prior to the winter months. These combined effects would have probably been replicated throughout coastal settlements in Northern Britain, possibly leading to the contemporary population decline estimated to have occurred at this time.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Corona discharge, as a partial self-sustaining discharge phenomenon under extremely uneven electric field, has been widely concerned in dc transmission projects. However, the research on the ...transition mechanism of corona discharge at different stages is not in-depth at present, which leads to the inadequacy of the basic development theory of corona discharge. This article focuses on the research of direct current corona discharge in air and establishes a numerical simulation model of corona discharge fluid plasma in air. The simulation model focuses on the needle-plate discharge model, with an environmental temperature set at 293.15 K and pressure at 101.325 kPa. The curvature radius of the needle electrode is 60 <inline-formula> <tex-math notation="LaTeX">\mu</tex-math> </inline-formula>m, and the discharge gap is set to 4.5 mm for positive corona and 5 mm for negative corona. The simulation covers the transition of positive corona discharge from the initial discharge stage, through the initial glow discharge stage, ultimately reaching the glow discharge stage as the needle electrode voltage increases from 2 to 4 kV. Similarly, for negative corona discharge, the simulation captures the evolution from the initial discharge stage to the Trichel pulse discharge stage and finally to the no-pulse discharge stage as the needle electrode voltage changes from <inline-formula> <tex-math notation="LaTeX">-</tex-math> </inline-formula>2 to <inline-formula> <tex-math notation="LaTeX">-</tex-math> </inline-formula>4.2 kV. This article also analyzes the transition mechanism between different stages in positive and negative corona processes. The transition of negative corona at different stages is a process where the nominal electric field and spatial charge electric field mutually constrain each other and reach equilibrium with the participation of secondary electrons. The transition of positive corona discharge at different stages is mainly determined by the nominal electric field and the secondary electrons produced by the collision of positive ion clusters with the needle electrode. Finally, the simulated model was validated by measuring the current and spectral signals during the discharge process in the experiments.
This study evaluated the assumption that back-filled excavated areas of old mine workings can be modeled as porous media, where groundwater flow is governed by Darcy's law. The Yatani mine, located ...in Yamagata Prefecture, Japan, was selected for this study because several mining methods were used during its operation and detailed drawings of the excavated areas of the mine are available. The model was calibrated using combinations of hydraulic conductivities (k), with the best-matched case being selected by comparing calculated and measured AMD fluxes. Modeled AMD fluxes along the drainage tunnel (−2 L level) were consistent with measured data when the excavated areas were considered to be porous media with a specific hydraulic conductivity, and the presence of faults and permeability were taken into account. The model also successfully predicted the increasing trend of AMD flux from the shaft to adit mouth. In the numerical model, the back-filled excavated areas were assumed to behave as porous media, which was shown to be a valid assumption in this mine. The model demonstrated that back-filling the excavated areas and drainage tunnel with low permeability materials could reduce the flux of Zn in AMD by up to 61%.
•The Yatani mine in Japan has been generating acid mine drainage.•A numerical model was constructed based on hydrological properties.•The modeled and measured acid mine drainage flux along drainage tunnel agree.•Back-filling excavated areas lowers the flux of Zn in AMD by up to 61%.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•Opposed-flow flame spread on discrete fuel beds was studied by numerical model.•Relationship between opposed-flow flame spread and gap size was studied.•Results of numerical model were validated ...with analytical model.•Flame jump effect and heat transfer on discrete fuel beds were analyzed.
Flame spread over solid fuel is a common phenomenon in fire scenes. This work looks into the relationship between the flame spread and the gap length between fuel beds at different opposed-flow velocities. An unsteady numerical model is developed to study the opposed-flow flame spread over discrete fuels. The influence of the gap size between the discrete fuels and the opposed-flow velocity on the opposed-flow flame spread is investigated, and the results are validated with an analytical model. The characteristics of solid burning, gas fuel and flame spread rates are examined. The results of temperature and gas fuel distribution show that the heat transfer from the flame to the discrete fuels decreases as the gap size increase. The pyrolysis front lags behind the leading position of gas thermal structure because the discrete fuels behind the flame front can provide fuel gas to the flame front by diffusion for combustion. The mass diffusion plays a significant role in the flame spread across the gaps. The average flame spread rate increase first and then decreases with the increase of gap size, because of the competition mechanism between the flame jump effect and the heat transfer. Besides, the flame cannot spread across to the next discrete fuel if the gap size increases to a critical value. The analytical and numerical results showed that the critical gap size is proportional to the reciprocal of opposed-flow. This work should be significant to predict the fire growth of discrete fuels and its potential hazards.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Thermoelectric power generation is a renewable energy conversion technology that can directly convert heat into electricity. In recent years, a great number of theoretical models have been ...established to predict and optimize the performance of both thermoelectric generators and thermoelectric generator systems. In this work, a comprehensive review of theoretical models is given with a specific focus on the different modeling approaches and different application scenarios. Firstly, the basic principles of theoretical models of the thermoelectric generator are presented, including the thermal resistance model, thermal-electric numerical model, and analogy model. Then, the theoretical models of the thermoelectric generator system are reviewed in detail, including the thermal resistance-based analytical model, computational fluid dynamics models, and fluid-thermal-electric multiphysics field coupled numerical model. The methods to improve the accuracy of theoretical models are also discussed. Furthermore, the transient thermal-electric numerical model of the thermoelectric generator and the transient fluid-thermal-electric multiphysics field coupled numerical model of the thermoelectric generator system are introduced, which can take into account the dynamic characteristics of the heat source, and may remain a hot research field in the upcoming years. Generally, thermal resistance models can quickly obtain the performance of the thermoelectric generator and thermoelectric generator system under different parameters, but suffer from relatively large errors; while it is the opposite for numerical models. To design a comprehensive thermoelectric generator system for practical application, it is suggested to combine the advantages of different models, to shorten the development time and ensure optimal performance at the same time.
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GEOZS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPUK, ZAGLJ, ZRSKP
A transient Mixed Lubrication-Wear coupling model (MLW coupling model) is developed to investigate the mixed lubrication and wear performances of journal bearings, and a wear experiment for journal ...bearing is performed to support the validity of the developed numerical model. In the coupling numerical model, the transient interaction between the behaviour of mixed lubrication and wear is considered by incorporating the wear depth distribution, which is determined by the developed friction fatigue wear model, into the film gap equation. The evolutions of the worn surface profile, wear rate, fluid pressure and asperity contact pressure over operating time are calculated by the developed numerical model. The simulated results demonstrate that the transient wear process affects the distribution trend of lubrication performances significantly, and a worn surface profile may exist that provides an optimal tribology performance of journal bearings. The simulated results also demonstrate that there are two wear stages, identified by initial and steady wear stage, of journal bearings under mixed lubrication condition. Furthermore, the effects of the input parameters, including the radius clearance(C), surface roughness (σ), asperity curvature radius (β) and boundary friction coefficient(μc), on the predicted mixed lubrication and wear performance are evaluated.
•A transient Mixed Lubrication-Wear coupling model (MLW coupling model) for journal bearings is developed.•The effects of transient mixed lubrication performance on the wear are considered by a developed fatigue wear model.•The evolution of the lubrication and wear performance over operating time is determined.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZRSKP
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