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1
Tirabassi, Tiziano, Daniela Buske, Davidson M. Moreira, and Marco T. Vilhena. "A Two-Dimensional Solution of the Advection–Diffusion Equation with Dry Deposition to the Ground." Journal of Applied Meteorology and Climatology 47, no. 8 (August 1, 2008): 2096–104. http://dx.doi.org/10.1175/2008jamc1674.1.
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Abstract A mathematical scheme is developed to simulate the vertical turbulent dispersion of air pollution that is absorbed or deposited to the ground. The scheme is an exact analytical solution of the atmospheric diffusion equation, without any restriction to the vertical profile of wind speed and eddy diffusivities, and taking into account the dry deposition by a boundary condition of a nonzero flux to the ground. The performances of the solution, with a proper parameterization of the vertical profiles of the wind and eddy diffusivities, were evaluated against the dataset from the Hanford (Washington) diffusion experiment, in which two tracers (one depositing and one nondepositing) were released simultaneously. In addition, the solution derived in this work is compared with four different models, with deposition at the ground, found in the literature.
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Niemimäki, Ossi, and Stefan Kurz. "Quasi 3D modelling and simulation of axial flux machines." COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering 33, no. 4 (July 1, 2014): 1220–32. http://dx.doi.org/10.1108/compel-11-2012-0352.
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Purpose – The purpose of this paper is to investigate the theoretical foundation of the so-called quasi 3D modelling method of axial flux machines, and the means for the simulation of the resulting models. Design/methodology/approach – Starting from the first principles, a 3D magnetostatic problem is geometrically decomposed into a coupled system of 2D problems. Genuine 2D problems are derived by decoupling the system. The construction of the 2D simulation models is discussed, and their applicability is evaluated by comparing a finite element implementation to an existing industry-used model. Findings – The quasi 3D method relies on the assumption of vanishing radial magnetic flux. The validity of this assumption is reflected in a residual gained from the 3D coupled system. Moreover, under a modification of the metric of the 2D models, an axial flux machine can be presented as a family of radial flux machines. Research limitations/implications – The evaluation and interpretation of the residual has not been carried out. Furthermore, the inclusion of eddy currents has not been detailed in the present study. Originality/value – A summary of existing modelling and simulation methods of axial flux machines is provided. As a novel result, proper mathematical context for the quasi 3D method is given and the underlying assumptions are laid out. The implementation of the 2D models is approached from a general angle, strengthening the foundation for future research.
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Mukhartova, Iuliia, Alexander Krupenko, Polina Mangura, and Alexander Olchev. "Mathematical Modeling of Vegetation Heterogeneity and Complex Topography Effects on Turbulent Exchange of GHG within the Atmospheric Surface Layer." Proceedings 2, no. 20 (October 17, 2018): 1310. http://dx.doi.org/10.3390/proceedings2201310.
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The local-scale 2D and 3D models of greenhouse gases (GHG) exchange between a non-uniform land surface and the atmosphere were developed. They are based on solution of the system of averaged Navier-Stokes, continuity and diffusion-advection equations. For numerical solution of the differential equations the stable finite-difference schemes were suggested. The models were applied to derive effects of complex topography and vegetation heterogeneity on 2D-3D air flow patterns, as well as on CO2 exchange within the atmospheric surface layer. Several numerical experiments were also provided to describe the air-flow re-establishing after its interaction with some obstacle (e.g., forest edge). Quantitative criteria for selection of the experimental sites for continuous eddy covariance flux measurements characterized by minimum effects of horizontal advection on measured fluxes were suggested.
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Grinstein, F. F., and C. Fureby. "Recent Progress on MILES for High Reynolds Number Flows." Journal of Fluids Engineering 124, no. 4 (December 1, 2002): 848–61. http://dx.doi.org/10.1115/1.1516576.
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A promising large-eddy simulation (LES) approach is monotonically integrated LES (MILES) which involves solving the Navier-Stokes equations using high-resolution monotone algorithms. In MILES, the subgrid scale (SGS) flow physics is provided by intrinsic, nonlinear, high-frequency filters built into the discretization and implicit SGS models. Mathematical and physical aspects of implicit SGS modeling using nonlinear flux-limiters are addressed using a formalism based on the modified LES equations approach. Detailed properties of the implicit subgrid model are related to the flux limiter, which in turn depends on the specifics of the numerical scheme; we illustrate how the latter properties can directly affect their potential in the MILES framework. Major unresolved issues relevant to LES of complex practical turbulent flows are discussed in this context, including some aspects of boundary condition modeling and overall computational model validation.
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Saenz, Juan A., Qingshan Chen, and Todd Ringler. "Prognostic Residual Mean Flow in an Ocean General Circulation Model and its Relation to Prognostic Eulerian Mean Flow." Journal of Physical Oceanography 45, no. 9 (September 2015): 2247–60. http://dx.doi.org/10.1175/jpo-d-15-0024.1.
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AbstractRecent work has shown that taking the thickness-weighted average (TWA) of the Boussinesq equations in buoyancy coordinates results in exact equations governing the prognostic residual mean flow where eddy–mean flow interactions appear in the horizontal momentum equations as the divergence of the Eliassen–Palm flux tensor (EPFT). It has been proposed that, given the mathematical tractability of the TWA equations, the physical interpretation of the EPFT, and its relation to potential vorticity fluxes, the TWA is an appropriate framework for modeling ocean circulation with parameterized eddies. The authors test the feasibility of this proposition and investigate the connections between the TWA framework and the conventional framework used in models, where Eulerian mean flow prognostic variables are solved for. Using the TWA framework as a starting point, this study explores the well-known connections between vertical transfer of horizontal momentum by eddy form drag and eddy overturning by the bolus velocity, used by Greatbatch and Lamb and Gent and McWilliams to parameterize eddies. After implementing the TWA framework in an ocean general circulation model, the analysis is verified by comparing the flows in an idealized Southern Ocean configuration simulated using the TWA and conventional frameworks with the same mesoscale eddy parameterization.
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Arshad, Salman, Bo Kong, Alan Kerstein, and Michael Oevermann. "A strategy for large-scale scalar advection in large eddy simulations that use the linear eddy sub-grid mixing model." International Journal of Numerical Methods for Heat & Fluid Flow 28, no. 10 (October 1, 2018): 2463–79. http://dx.doi.org/10.1108/hff-09-2017-0387.
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PurposeThe purpose of this numerical work is to present and test a new approach for large-scale scalar advection (splicing) in large eddy simulations (LES) that use the linear eddy sub-grid mixing model (LEM) called the LES-LEM.Design/methodology/approachThe new splicing strategy is based on an ordered flux of spliced LEM segments. The principle is that low-flux segments have less momentum than high-flux segments and, therefore, are displaced less than high-flux segments. This strategy affects the order of both inflowing and outflowing LEM segments of an LES cell. The new splicing approach is implemented in a pressure-based fluid solver and tested by simulation of passive scalar transport in a co-flowing turbulent rectangular jet, instead of combustion simulation, to perform an isolated investigation of splicing. Comparison of the new splicing with a previous splicing approach is also done.FindingsThe simulation results show that the velocity statistics and passive scalar mixing are correctly predicted using the new splicing approach for the LES-LEM. It is argued that modeling of large-scale advection in the LES-LEM via splicing is reasonable, and the new splicing approach potentially captures the physics better than the old approach. The standard LES sub-grid mixing models do not represent turbulent mixing in a proper way because they do not adequately represent molecular diffusion processes and counter gradient effects. Scalar mixing in turbulent flow consists of two different processes, i.e. turbulent mixing that increases the interface between unmixed species and molecular diffusion. It is crucial to model these two processes individually at their respective time scales. The LEM explicitly includes both of these processes and has been used successfully as a sub-grid scalar mixing model (McMurtry et al., 1992; Sone and Menon, 2003). Here, the turbulent mixing capabilities of the LES-LEM with a modified splicing treatment are examined.Originality/valueThe splicing strategy proposed for the LES-LEM is original and has not been investigated before. Also, it is the first LES-LEM implementation using unstructured grids.
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Majda, Andrew J. "New Multiscale Models and Self-Similarity in Tropical Convection." Journal of the Atmospheric Sciences 64, no. 4 (April 1, 2007): 1393–404. http://dx.doi.org/10.1175/jas3880.1.
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Abstract One of the unexplained striking features of tropical convection is the observed statistical self-similarity in clusters, superclusters, and intraseasonal oscillations through complex multiscale processes ranging from the mesoscales to the equatorial synoptic scales to the intraseasonal/planetary scales. Here new multispatial-scale, multitime-scale, simplified asymptotic models are derived systematically from the equatorial primitive equations on the range of scales from mesoscale to equatorial synoptic to planetary/intraseasonal, which provide a useful analytic framework for addressing these issues. New mesoscale equatorial synoptic dynamical (MESD) models and balanced MESD (BMESD) models are developed for the multitime, multispace interaction from mesoscales to equatorial synoptic scales; new multitime versions of the intraseasonal planetary equatorial synoptic dynamics (IPESD) models are developed for multiple spatiotemporal interactions on equatorial synoptic scales and planetary scales. The mathematical character derived below for all these simplified models explicitly demonstrates that the main nonlinear interactions across scales are quasi-linear where eddy flux divergences of momentum and temperature from nonlinear advection from the smaller-scale spatiotemporal flows as well as mean source effects accumulate in time and drive the waves on the successively larger spatiotemporal scales. Furthermore, these processes that transfer energy to the next larger, longer, spatiotemporal scales are self-similar in a suitable sense established here. On the other hand, the larger scales set the environment for this transport through processes such as mean advection of the smaller scales.
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van Heerwaarden, Chiel C., and Juan Pedro Mellado. "Growth and Decay of a Convective Boundary Layer over a Surface with a Constant Temperature." Journal of the Atmospheric Sciences 73, no. 5 (May 1, 2016): 2165–77. http://dx.doi.org/10.1175/jas-d-15-0315.1.
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Abstract The growth and decay of a convective boundary layer (CBL) over a surface with a constant surface temperature that develops into a linear stratification is studied, and a mathematical model for this system is derived. The study is based on direct numerical simulations with four different Reynolds numbers; the two simulations with the largest Reynolds numbers display Reynolds number similarity, suggesting that the results can be extrapolated to the atmosphere. Because of the interplay of the growing CBL and the gradually decreasing surface buoyancy flux, the system has a complex time evolution in which integrated kinetic energy, buoyancy flux, and dissipation peak and subsequently decay. The derived model provides characteristic scales for bulk properties of the CBL. Even though the system is unsteady, self-similar vertical profiles of buoyancy, buoyancy flux, and velocity variances are recovered. There are two important implications for atmospheric modeling. First, the magnitude of the surface buoyancy flux sets the time scale of the system; thus, over a rough surface the roughness length is a key variable. Therefore, the performance of the surface model is crucial in large-eddy simulations of convection over water surfaces. Second, during the phase in which kinetic energy decays, the integrated kinetic energy never follows a power law, because the buoyancy flux and dissipation balance until the kinetic energy has almost vanished. Therefore, the applicability of power-law decay models to the afternoon transition in the atmospheric boundary layer is questionable; the presented model provides a physically sound alternative.
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Karthaus, Jan, Benedikt Groschup, Robin Krüger, and Kay Hameyer. "Mechanical stress distribution and the utilisation of the magneto-elastic effect in electrical machines." COMPEL - The international journal for computation and mathematics in electrical and electronic engineering 38, no. 4 (July 1, 2019): 1085–97. http://dx.doi.org/10.1108/compel-10-2018-0387.
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Purpose Due to the increasing amount of high power density high-speed electrical machines, a detailed understanding of the consequences for the machine’s operational behaviour and efficiency is necessary. Magnetic materials are prone to mechanical stress. Therefore, this paper aims to study the relation between the local mechanical stress distribution and magnetic properties such as magnetic flux density and iron losses. Design/methodology/approach In this paper, different approaches for equivalent mechanical stress criteria are analysed with focus on their applicability in electrical machines. Resulting machine characteristics such as magnetic flux density distribution or iron are compared. Findings The study shows a strong influence on the magnetic flux density distribution when considering the magneto-elastic effect for all analysed models. The influence on the iron loss is smaller due to a high amount of stress-independent eddy current loss component. Originality/value The understanding of the influence of mechanical stress on dimensions of electrical machines is important to obtain an accurate machine design. In this paper, the discussion on different equivalent stress approaches allows a new perspective for considering the magneto-elastic effect.
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Wu, Zheng, and Thomas Reichler. "Surface Control of the Frequency of Stratospheric Sudden Warming Events." Journal of Climate 32, no. 15 (July 3, 2019): 4753–66. http://dx.doi.org/10.1175/jcli-d-18-0801.1.
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AbstractThe frequency of stratospheric sudden warming events (SSWs) is an important characteristic of the coupled stratosphere–troposphere system. However, many modern climate models are unable to reproduce the observed SSW frequency. A previous study suggested that one of the reasons could be the momentum damping at the surface. The goal of the present study is to understand what determines the climatological SSW frequency and how the surface damping comes into play. To this end, we conduct a parameter sweep with an idealized model, using a wide range of values for the surface damping. It is found that the SSW frequency is a strong and nonlinear function of the surface damping. Various tropospheric and stratospheric factors are identified to link the surface damping to the SSW frequency. The factors include the magnitude of the surface winds, the meridional and vertical wind shear, the synoptic eddy activity in the troposphere, the transient wave activity flux at the lower stratosphere, and the strength of the stratospheric polar vortex. Mathematical–statistical modeling, informed by the parameter sweep, is used to quantify how the different factors relate to each other. This successfully reproduces the complex variations of the SSW frequency with the surface damping seen in the parameter sweep. The results may help in explaining some of the difficulties that climate models have in simulating the observed SSW frequency.
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Gaskell, P. H., M. D. Savage, J. L. Summers, and H. M. Thompson. "Modelling and analysis of meniscus roll coating." Journal of Fluid Mechanics 298 (September 10, 1995): 113–37. http://dx.doi.org/10.1017/s0022112095003247.
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Three mathematical models are developed for meniscus roll coating in which there is steady flow of a Newtonian fluid in the narrow gap, or nip, between two contrarotating rolls in the absence of body forces.The zero flux model predicts a constant pressure gradient within the central core and two eddies, each with an inner structure, in qualitative agreement with observation. The small flux model takes account of a small inlet flux and employs the lubrication approximation to represent fluid velocity as a combination of Couette and Poiseuille flows. Results show that the meniscus coating regime is characterized by small flow rates (λ [Lt ] 1) and a sub-ambient pressure field generated by capillary action at the upstream meniscus. Such flows are found to exist for small modified capillary number, Ca(R/H0)1/2 [lsim ] 0.15, where Ca and R/H0 represent capillary number and the radius to semi-gap ratio, respectively.A third model incorporates the full effects of curved menisci and nonlinear free surface boundary conditions. The presence of a dynamic contact line, adjacent to the web on the upper roll, requires the imposition of an apparent contact angle and slip length. Numerical solutions for the velocity and pressure fields over the entire domain are obtained using the finite element method. Results are in accord with experimental observations that the flow domain consists of two large eddies and fluid transfer jets or ‘snakes’. Furthermore, the numerical results show that the sub-structure of each large eddy consists of a separatrix with one saddle point, two sub-eddies with centres, and an outer recirculation.Finally finite element solutions in tandem with lubrication analysis establish the existence of three critical flow rates corresponding to a transformation of the pressure field, the emergence of a ‘secondary snake’ (another fluid transfer jet) and the disappearance of a primary snake.
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Masmoudi, Asma, and Ahmed Masmoudi. "Iron loss in FSPMM: 2D FEA-based comparative study between single and double-layer topologies." COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering 34, no. 1 (January 5, 2015): 61–75. http://dx.doi.org/10.1108/compel-10-2014-0244.
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Purpose – The purpose of this paper is to compare the study between two topologies of fractional-slot permanent-magnet machines such that: double-layer topology and single-layer one. The comparison considers the assessment of the iron loss in the laminated cores of the magnetic circuit as well as in the permanent magnets (PMs) for constant torque and flux weakening ranges. Design/methodology/approach – The investigation of the hysteresis and eddy-current loss has been carried out using 2D transient FEA models. Findings – It has been found that the stator iron losses are almost the same for both topologies. Whereas, the single-layer topology is penalized by higher iron loss especially the eddy-current ones taking place in the PMs. This is due to their denser harmonic content of the armature air gap MMF spatial repartition. Originality/value – The analysis of the iron loss maps in different parts of each machine including stator and rotor laminations as well as the PMs, in one hand, and the investigation of their variation with respect to the speed, in the other hand, represent the major contribution of this work.
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Sarigiannidis, Athanasios, Minos Beniakar, and Antonios Kladas. "Computationally efficient permanent magnet traction motor loss assessment." COMPEL - The international journal for computation and mathematics in electrical and electronic engineering 37, no. 6 (November 5, 2018): 2093–108. http://dx.doi.org/10.1108/compel-08-2017-0326.
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Purpose This paper aims to introduce a computationally efficient hybrid analytical–finite element (FE) methodology for loss evaluation in electric vehicle (EV) permanent magnet (PM) traction motor applications. In this class of problems, eddy current losses in PMs and iron laminations constitute an important part of overall drive losses, representing a key design target. Design/methodology/approach Both surface mounted permanent magnet (SMPM) and double-layer interior permanent magnet (IPM) motor topologies are considered. The PM eddy losses are calculated by using analytical solutions and Fourier harmonic decomposition. The boundary conditions are based on slot opening magnetic field strength tangential component in the air gap in the SMPM topology case, whereas the numerically evaluated normal flux density variation on the surface of the outer PM is implemented in the IPM case. Combined analytical–loss evaluation technique has been verified by comparing its results to a transient magnetodynamic two-dimensional FE model ones. Findings The proposed loss evaluation technique calculated the total power losses for various operating conditions with low computational cost, illustrating the relative advantages and drawbacks of each motor topology along a typical EV operating cycle. The accuracy of the method was comparable to transient FE loss evaluation models, particularly around nominal speed. Originality/value The originality of this paper is based on the development of a fast and accurate PM eddy loss model for both SMPM and IPM motor topologies for traction applications, combining effectively both analytical and FE techniques.
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Akhatov, S. T., V. G. Solonenko, N. M. Makhmetova, S. A. Kosenko, N. V. Ivanovtseva, and A. A. Malik. "APPLICATION OF LINEAR ASYNCHRONOUS MOTORS FOR HIGH-SPEED GROUND TRANSPORT." Series of Geology and Technical Sciences 2, no. 446 (April 15, 2021): 31–36. http://dx.doi.org/10.32014/2021.2518-170x.31.
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Magnetic suspension in high-speed ground transport systems is an alternative to the rail wheel. The successful solution to the development of high-speed ground transport is largely determined by the creation of operationally efficient linear motors, the main task of which is to convert electrical energy into mechanical energy and create tractive force to ensure the movement of the crew according to a given program in the range of operating speeds. The article investigates linear asynchronous motors with longitudinal closure of magnetic flux of single-ended design. As a result of investigation of physical processes in linear motors caused by edge problems it was found that the cause of the transverse edge effect is the finite width dimensions of the reactive bus, the change of which causes closure of eddy currents within the active area of inductor, leads to weakening of magnetic field in the central zone and to reduction of tractive force. The discrepancy between the calculated and experimental indicators of physical processes in linear asynchro- nous motors due to significant idealization of mathematical models led to the development of a three-dimensional theory, brought to the calculation programs. The developed calculation program of electromechanical characteristics of linear induction motors with inductor and reactive bus layout, as well as their geometrical and physical parameters allows to determine the necessary integral motor characteristics in the form of a levitation function.
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Jaszczur, Marek. "Large eddy simulation of a fully developed non-isothermal turbulent channel flow." International Journal of Numerical Methods for Heat & Fluid Flow 24, no. 4 (April 29, 2014): 861–72. http://dx.doi.org/10.1108/hff-02-2013-0043.
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Purpose – The purpose of this paper is to numerically study heated channel flow using direct numerical simulation (DNS) and large eddy simulation (LES) method. Using different domain size and different grid resolution it is show that filtering procedure is influenced and may results in very different solutions. Design/methodology/approach – Turbulent non-isothermal fully developed channel flow has been investigated using LES. The filtered Navier-stokes and energy equations were numerically solved with dynamic subgrid scale (SGS) model, standard Smagorinsky model or without additional model for the turbulent SGS stress and heat flux required to close the governing equations. Findings – The numerical LES results in comparison with the DNS data demonstrate that the LES computations may not always offers a reliable prediction of non-isothermal turbulent flow in open channel. It has been found that, even though the models reproduces accurately results for the flow field the thermal field computed using LES do not necessary match the DNS results. Introducing SGS model for scalar do not always show large improvement. One of the reason is thickness of hydrodynamic and thermal boundary layer. In the cases when boundary layers are very different it is not easy optimally set up control volumes in the domain. Originality/value – This is one of the first instance in which a results of numerical computations for different grid resolution, different stretching, SGS model is employed for non-isothermal turbulent channel flow. It shows that in the cases when boundary layers hydrodynamic and thermal are very different it is hardly find optimal grid resolution or stretching
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Burger, Loïc, Christophe Geuzaine, Francois Henrotte, and Benoît Vanderheyden. "Modelling the penetration of magnetic flux in thin superconducting films with shell transformations." COMPEL - The international journal for computation and mathematics in electrical and electronic engineering 38, no. 5 (September 2, 2019): 1441–52. http://dx.doi.org/10.1108/compel-11-2018-0488.
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Purpose Finite element (FE) models are considered for the penetration of magnetic flux in type-II superconductor films. A shell transformation allows boundary conditions to be applied at infinity with no truncation approximation. This paper aims to determine the accuracy and efficiency of shell transformation techniques in such non-linear eddy current problems. Design/methodology/approach A three-dimensional H – ϕ formulation is considered, where the reaction field is calculated in the presence of a uniform applied field. The shell transformation is used in the far-field region, and the uniform applied field is introduced through surface terms, so as to avoid infinite energy terms. The resulting field distributions are compared against known solutions for different geometries (thin disks and thin strips in the critical state, square thin films). The influence of the shape, size and mesh quality of the far-field regions are discussed. Findings The formulation is shown to provide accurate results for a number of film geometries and shell transformation shapes. The size of the far-field region has to be chosen in such a way to properly capture the asymptotic decay of the fields, and a practical procedure to determine this size is provided. Originality/value The importance of the size of the far-field region in a shell transformation and its proximity to the conducting domains are both highlighted. This paper also provides a numerical way to apply a constant magnetic field in a given region, while the source, on which only the far-field behaviour of the applied field depends, is excluded from the model.
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Taler, Dawid. "Semi-empirical heat transfer correlations for turbulent tube flow of liquid metals." International Journal of Numerical Methods for Heat & Fluid Flow 28, no. 1 (January 2, 2018): 151–72. http://dx.doi.org/10.1108/hff-09-2017-0367.
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Purpose The purpose of this paper is to develop new semi-empirical heat transfer correlations for turbulent flow of liquid metals in the tubes, and then to compare these correlations with the experimental data. The Prandtl and Reynolds numbers can vary in the ranges: 0.0001 ≤ Pr ≤ 0.1 and 3000 ≤ Re ≤ 106. Design/methodology/approach The energy conservation equation averaged by Reynolds was integrated using the universal velocity profile determined experimentally by Reichardt for the turbulent tube flow and four different models for the turbulent Prandtl number. Turbulent heat transfer in the circular tube was analyzed for a constant heat flux at the inner surface. Some constants in different models for the turbulent Prandtl number were adjusted to obtain good agreement between calculated and experimentally obtained Nusselt numbers. Subsequently, new correlations for the Nusselt number as a function of a Peclet number was proposed for different models of the turbulent Prandtl number. Findings The inclusion of turbulent Prandtl number greater than one and the experimentally determined velocity profile of the fluid in the tube while solving the energy conservation equation improved the compatibility of calculated Nusselt numbers, with Nusselt numbers determined experimentally. The correlations proposed in the paper have a sound theoretical basis and give Nusselt number values that are in good agreement with the experimental data. Research limitations/implications Heat transfer correlations proposed in this paper were derived assuming a constant heat flux at the inner surface of the tube. However, they can also be used for a constant wall temperature, as for the turbulent flow (Re > 3,000), the relative difference between the Nusselt number for uniform wall heat flux and uniform wall temperature is very low. Originality/value Unified, systematic approach to derive correlations for the Nusselt number for liquid metals was proposed in the paper. The Nusselt number was obtained from the solution of the energy conservation equation using the universal velocity profile and eddy diffusivity determined experimentally, and various models for the turbulent Prandtl number. Four different relationships for the Nusselt number proposed in the paper were compared with the experimental data.
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Heywood, Karen J., Sunke Schmidtko, Céline Heuzé, Jan Kaiser, Timothy D. Jickells, Bastien Y. Queste, David P. Stevens, et al. "Ocean processes at the Antarctic continental slope." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 372, no. 2019 (July 13, 2014): 20130047. http://dx.doi.org/10.1098/rsta.2013.0047.
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The Antarctic continental shelves and slopes occupy relatively small areas, but, nevertheless, are important for global climate, biogeochemical cycling and ecosystem functioning. Processes of water mass transformation through sea ice formation/melting and ocean–atmosphere interaction are key to the formation of deep and bottom waters as well as determining the heat flux beneath ice shelves. Climate models, however, struggle to capture these physical processes and are unable to reproduce water mass properties of the region. Dynamics at the continental slope are key for correctly modelling climate, yet their small spatial scale presents challenges both for ocean modelling and for observational studies. Cross-slope exchange processes are also vital for the flux of nutrients such as iron from the continental shelf into the mixed layer of the Southern Ocean. An iron-cycling model embedded in an eddy-permitting ocean model reveals the importance of sedimentary iron in fertilizing parts of the Southern Ocean. Ocean gliders play a key role in improving our ability to observe and understand these small-scale processes at the continental shelf break. The Gliders: Excellent New Tools for Observing the Ocean (GENTOO) project deployed three Seagliders for up to two months in early 2012 to sample the water to the east of the Antarctic Peninsula in unprecedented temporal and spatial detail. The glider data resolve small-scale exchange processes across the shelf-break front (the Antarctic Slope Front) and the front's biogeochemical signature. GENTOO demonstrated the capability of ocean gliders to play a key role in a future multi-disciplinary Southern Ocean observing system.
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Younis, Bassam A., Charles G. Speziale, and Timothy T. Clark. "A rational model for the turbulent scalar fluxes." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 461, no. 2054 (February 8, 2005): 575–94. http://dx.doi.org/10.1098/rspa.2004.1380.
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The paper reports on an alternative approach to modelling the turbulent scalar fluxes that arise from time averaging the transport equation for a scalar. In this approach, a functional relationship between these fluxes and various tensor quantities is constructed with guidance from the exact equations governing the transport of fluxes. Results from tensor representation theory are then used to obtain an explicit relationship between the fluxes and the terms in the assumed functional relationship. Where turbulence length– and time–scales are implied, these are determined from two scalar quantities: the turbulence kinetic energy and its rate of dissipation by viscous action. The general representation is then reduced by certain justifiable assumptions to yield a practical model for the turbulent scalar fluxes that is explicit and algebraic in these quantities and one that correctly reflects their dependence on the gradients of mean velocity and on the details of the turbulence. Examination of alternative algebraic models shows most to be subsets of the present proposal. The new model is calibrated using results from large–eddy simulations (LESs) of homogeneous turbulence with passive scalars and then assessed by reference to benchmark data from heated turbulent shear flows. The results obtained show the model to correctly predict the anisotropy of the turbulent diffusivity tensor. The asymmetric nature of this tensor is also recovered, but only qualitatively, there being significant quantitative differences between the model predictions and the LES results. Finally, comparisons with data from benchmark two–dimensional free shear flows show the new model to yield distinct improvements over other algebraic scalar–flux closures.
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Peussa, Tommi, and Anouar Belahcen. "Coupled wave-equation and eddy-current model for modelling and measuring propagating stress-waves." Archives of Electrical Engineering 64, no. 2 (June 1, 2015): 215–26. http://dx.doi.org/10.1515/aee-2015-0018.
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AbstractThe coupling of the propagating stress wave with the eddy current model is presented. The applied stress produces magnetization in the sample that can be measured outside the sample by measuring the resulting magnetic flux density. The stress and flux density measurements are made on a mechanically excited steel bar. The problem is modelled with the finite element method for both the propagating wave and the eddy current. Three aspects are considered: eddy current model using magnetization from the measurements, coupled wave and eddy current models, and coupled different dimensions in the wave model. The measured stress can be reproduced from the measured flux density by modelling. The coupled models work both for stress and flux couplings as well as for the different dimensionality couplings.
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Ichii, K., T. Suzuki, T. Kato, A. Ito, T. Hajima, M. Ueyama, T. Sasai, et al. "Multi-model analysis of terrestrial carbon cycles in Japan: limitations and implications of model calibration using eddy flux observations." Biogeosciences 7, no. 7 (July 2, 2010): 2061–80. http://dx.doi.org/10.5194/bg-7-2061-2010.
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Abstract. Terrestrial biosphere models show large differences when simulating carbon and water cycles, and reducing these differences is a priority for developing more accurate estimates of the condition of terrestrial ecosystems and future climate change. To reduce uncertainties and improve the understanding of their carbon budgets, we investigated the utility of the eddy flux datasets to improve model simulations and reduce variabilities among multi-model outputs of terrestrial biosphere models in Japan. Using 9 terrestrial biosphere models (Support Vector Machine – based regressions, TOPS, CASA, VISIT, Biome-BGC, DAYCENT, SEIB, LPJ, and TRIFFID), we conducted two simulations: (1) point simulations at four eddy flux sites in Japan and (2) spatial simulations for Japan with a default model (based on original settings) and a modified model (based on model parameter tuning using eddy flux data). Generally, models using default model settings showed large deviations in model outputs from observation with large model-by-model variability. However, after we calibrated the model parameters using eddy flux data (GPP, RE and NEP), most models successfully simulated seasonal variations in the carbon cycle, with less variability among models. We also found that interannual variations in the carbon cycle are mostly consistent among models and observations. Spatial analysis also showed a large reduction in the variability among model outputs. This study demonstrated that careful validation and calibration of models with available eddy flux data reduced model-by-model differences. Yet, site history, analysis of model structure changes, and more objective procedure of model calibration should be included in the further analysis.
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Grinstein, Fernando F., and Christer Fureby. "On Flux-Limiting-Based Implicit Large Eddy Simulation." Journal of Fluids Engineering 129, no. 12 (July 19, 2007): 1483–92. http://dx.doi.org/10.1115/1.2801684.
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Recent progress in understanding the theoretical basis and effectiveness of implicit large eddy simulation (ILES) is reviewed in both incompressible and compressible flow regimes. We use a modified equation analysis to show that the leading-order truncation error terms introduced by certain hybrid high resolution methods provide implicit subgrid scale (SGS) models similar in form to those of conventional mixed SGS models. Major properties of the implicit SGS model are related to the choice of high-order and low-order scheme components, the choice of a flux limiter, which determines how these schemes are blended locally depending on the flow, and the designed balance of the dissipation and dispersion contributions to the numerical solution. Comparative tests of ILES and classical LES in the Taylor–Green vortex case show robustness in capturing established theoretical findings for transition and turbulence decay.
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Lachmy, Orli, and Tiffany Shaw. "Connecting the Energy and Momentum Flux Response to Climate Change Using the Eliassen–Palm Relation." Journal of Climate 31, no. 18 (September 2018): 7401–16. http://dx.doi.org/10.1175/jcli-d-17-0792.1.
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Coupled climate models project that extratropical storm tracks and eddy-driven jets generally shift poleward in response to increased CO2 concentration. Here the connection between the storm-track and jet responses to climate change is examined using the Eliassen–Palm (EP) relation. The EP relation states that the eddy potential energy flux is equal to the eddy momentum flux times the Doppler-shifted phase speed. The EP relation can be used to connect the storm-track and eddy-driven jet responses to climate change assuming 1) the storm-track and eddy potential energy flux responses are consistent and 2) the response of the Doppler-shifted phase speed is negligible. We examine the extent to which the EP relation connects the eddy-driven jet (eddy momentum flux convergence) response to climate change with the storm-track (eddy potential energy flux) response in two idealized aquaplanet model experiments. The two experiments, which differ in their radiation schemes, both show a poleward shift of the storm track in response to climate change. However, the eddy-driven jet shifts poleward using the sophisticated radiation scheme but equatorward using the gray radiation scheme. The EP relation gives a good approximation of the momentum flux response and the eddy-driven jet shift, given the eddy potential energy flux response, because the Doppler-shifted phase speed response is negligible. According to the EP relation, the opposite shift of the eddy-driven jet for the different radiation schemes is associated with dividing the eddy potential energy flux response by the climatological Doppler-shifted phase speed, which is dominated by the zonal-mean zonal wind.
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Fox-Kemper, Baylor. "Reevaluating the Roles of Eddies in Multiple Barotropic Wind-Driven Gyres." Journal of Physical Oceanography 35, no. 7 (July 1, 2005): 1263–78. http://dx.doi.org/10.1175/jpo2743.1.
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Abstract Multiple-gyre ocean models have a weaker mean subtropical circulation than single-gyre calculations with the same viscosity and subtropical forcing. Traditionally, this reduction in circulation is attributed to an intergyre eddy vorticity flux that cancels some of the wind input, part of which does not require a Lagrangian mass exchange (theory of dissipative meandering). Herein the intergyre eddy vorticity flux is shown to be a controlling factor in barotropic models at high Reynolds number only with exactly antisymmetric gyres and slip boundary conditions. Almost no intergyre flux occurs when no-slip boundary conditions are used, yet the subtropical gyre is still significantly weaker in multiple-gyre calculations. Sinuous modes of instability present only in multiple gyres are shown here to vastly increase the eddy vorticity transport efficiency. This increase in efficiency reduces the mean circulation necessary for equilibrium. With slip boundary conditions, the intergyre eddy transport is possibly much larger. However, with wind forcing relevant for the ocean—two unequal gyres—a mean flow flux of vorticity rather than an eddy flux between the regions of opposing wind forcing is increasingly important with increasing Reynolds number. A physical rationalization of the differing results is provided by diagnosis of the equilibrium vorticity budget and eddy transport efficiency. Calculations varying 1) boundary conditions, 2) sources and sinks of vorticity, 3) eddy transport efficiency, and 4) the degree of symmetry of the gyres are discussed.
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Richardson, Andrew D., Bobby H. Braswell, David Y. Hollinger, Prabir Burman, Eric A. Davidson, Robert S. Evans, Lawrence B. Flanagan, et al. "Comparing simple respiration models for eddy flux and dynamic chamber data." Agricultural and Forest Meteorology 141, no. 2-4 (December 2006): 219–34. http://dx.doi.org/10.1016/j.agrformet.2006.10.010.
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Tsubokura, Makoto. "Subgrid Scale Modeling of Turbulence for the Dynamic Procedure Using Finite Difference Method and Its Assessment on the Thermally Stratified Turbulent Channel Flow." Journal of Applied Mechanics 73, no. 3 (October 14, 2005): 382–90. http://dx.doi.org/10.1115/1.2150236.
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Previously proposed methods for subgrid-scale (SGS) stress modeling were re-investigated and extended to SGS heat-flux modeling, and various anisotropic and isotropic eddy viscosity/diffusivity models were obtained. On the assumption that they are used in a finite-difference (FD) simulation, the models were constructed in such a way that they are insensitive to numerical parameters on which calculated flows are strongly dependent in the conventional Smagorinsky model. The models obtained, as well as those previously proposed, were evaluated a priori in a stably stratified open channel flow, which is considered to be a challenging application of large eddy simulation and suitable for testing both SGS stress and heat-flux models. The most important feature of the models proposed is that they are insensitive to the discretized test filtering parameter required in the dynamic procedure of Germano et al. (1991, Phys. Fluids, 3, pp. 1760–1765) in FD simulation. We also found in SGS heat-flux modeling that the effect of the grid (resolved)-scale (GS) velocity gradient plays an important role in the estimation of the streamwise heat flux, and an isotropic eddy diffusivity model with the effect of the GS velocity is proposed.
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Eden, Carsten. "Anisotropic Rotational and Isotropic Residual Isopycnal Mesoscale Eddy Fluxes." Journal of Physical Oceanography 40, no. 11 (November 1, 2010): 2511–24. http://dx.doi.org/10.1175/2010jpo4397.1.
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Abstract In the generalized temporal residual mean (TRM-G) framework, the diapycnal rotational eddy fluxes are defined such that the residual divergent diapycnal eddy flux is related to irreversible changes of buoyancy, that is, diapycnal mixing (or temporal changes of variance and higher order moments) only. Here, it is discussed that for the isopycnal eddy fluxes a similar physically meaningful property exists: rotational isopycnal eddy fluxes can be defined in TRM-G such that the residual divergent part of the flux is related to removal of mean available potential energy and transfer to eddy energy only, that is, to the classical picture of eddy activity. In two idealized eddying models, both featuring strong mesoscale eddy-driven zonal jets, large isopycnal eddy fluxes are circulating at the flanks of the jets. The residual isopycnal eddy fluxes, however, are predominantly meridional and thus downgradient, indicating vanishing anisotropic mixing of isopycnal thickness, consistent with the classical picture of eddy-driven overturning by baroclinic instability in jets. Using isotropic thickness mixing—standard in ocean models—appears therefore as sufficient in this model diagnosis.
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Guermond, J. L., J. T. Oden, and S. Prudhomme. "Mathematical Perspectives on Large Eddy Simulation Models for Turbulent Flows." Journal of Mathematical Fluid Mechanics 6, no. 2 (June 1, 2004): 194–248. http://dx.doi.org/10.1007/s00021-003-0091-5.
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Lu, Jian, Gang Chen, and Dargan M. W. Frierson. "The Position of the Midlatitude Storm Track and Eddy-Driven Westerlies in Aquaplanet AGCMs." Journal of the Atmospheric Sciences 67, no. 12 (December 1, 2010): 3984–4000. http://dx.doi.org/10.1175/2010jas3477.1.
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Abstract The sensitivity of the midlatitude storm track and eddy-driven wind to the sea surface temperature (SST) boundary forcing is studied over a wide range of perturbations using both simple and comprehensive general circulation models over aquaplanet lower boundary conditions. Under the single-jet circulation regime similar to the conditions of the present climate in the Northern Hemisphere winter or the Southern Hemisphere summer, the eddy-driven jet shifts monotonically poleward with both the global mean and the equator-to-pole gradient of the SST. The eddy-driven jet can have a reverse relationship to the gradient if it is well separated from the subtropical jet and Hadley cell boundary in a double-jet circulation regime. A simple scaling is put forward to interpret the simulated sensitivity of the storm-track/eddy-driven westerly wind position within the single-jet regime in both models. The rationale for the scaling is based on the notion that the wave activity flux can propagate horizontally away from the source region, resulting in a broader distribution of eddy potential vorticity (PV) flux in the upper troposphere than that of the flux in the opposite direction in the lower troposphere. As a consequence, the position of the maximum of the eddy-driven westerlies tends to be controlled by the profile of the relatively sharp-peaked low-level PV flux, which is dominated by the eddy heat flux component of the Eliassen–Palm (EP) flux. Thus, the position of the eddy-driven surface westerlies may be inferred from the vertical EP flux coming out of the lower troposphere. The vertical EP flux can be parameterized by a measure of baroclinicity, whose latitudinal variations show a linear relationship with the meridional displacement of the eddy-driven westerlies and the storm track. This relationship still holds well within the single-jet regime, even when only the variation of static stability is taken into consideration in estimating the baroclinicity (the temperature gradient component of which is fixed). To the extent that the static stability is deterministically constrained by and hence can be predicted from the given SST conditions through a moist scaling for the midlatitude stratification, one may, given SST perturbations, predict which way the storm track and eddy-driven wind should shift with respect to a chosen reference climate state. The resultant anomaly-wise scaling turns out to be valid for both the idealized and comprehensive models, regardless of the details in the model physics. By corollary, it can be argued that the poleward shift of storm track found in the global warming simulations by fully coupled climate models may be attributed, at least partially, to the increase in the subtropical and midlatitude static stability with global warming.
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Cessi, Paola. "An Energy-Constrained Parameterization of Eddy Buoyancy Flux." Journal of Physical Oceanography 38, no. 8 (August 1, 2008): 1807–19. http://dx.doi.org/10.1175/2007jpo3812.1.
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Abstract A parameterization for eddy buoyancy fluxes for use in coarse-grid models is developed and tested against eddy-resolving simulations. The development is based on the assumption that the eddies are adiabatic (except near the surface) and the observation that the flux of buoyancy is affected by barotropic, depth-independent eddies. Like the previous parameterizations of Gent and McWilliams (GM) and Visbeck et al. (VMHS), the horizontal flux of a tracer is proportional to the local large-scale horizontal gradient of the tracer through a transfer coefficient assumed to be given by the product of a typical eddy velocity scale and a typical mixing length. The proposed parameterization differs from GM and VMHS in the selection of the eddy velocity scale, which is based on the kinetic energy balance of baroclinic eddies. The three parameterizations are compared to eddy-resolving computations in a variety of forcing configurations and for several sets of parameters. The VMHS and the energy balance parameterizations perform best in the tests considered here.
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Jiang, Nan, William Layton, Michael McLaughlin, Yao Rong, and Haiyun Zhao. "On the Foundations of Eddy Viscosity Models of Turbulence." Fluids 5, no. 4 (September 29, 2020): 167. http://dx.doi.org/10.3390/fluids5040167.
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Zhang, Yuman, Gang Dou, Zhao Sun, Mei Guo, and Yuxia Li. "Establishment of Physical and Mathematical Models for Sr0.95Ba0.05TiO3Memristor." International Journal of Bifurcation and Chaos 27, no. 09 (August 2017): 1750148. http://dx.doi.org/10.1142/s0218127417501486.
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The Sr[Formula: see text]Ba[Formula: see text]TiO3(SBT) memristor is prepared using the monolayer Sr[Formula: see text]Ba[Formula: see text]TiO3nano-film structure. In order to apply it into the nonlinear circuit design, the SBT memristor is modeled in the paper. The voltage-controlled physical model of the SBT memristor is established based on its working mechanism. Due to the difficulty in determining the accurate parameters of the voltage-controlled physical model, a flux-controlled mathematical model of the SBT memristor is proposed, and its equivalence relation with the voltage-controlled physical model is proved. Moreover, the parameters of the flux-controlled mathematical model are determined by means of the quadratic polynomial interpolation method using the experimentally measured voltage and current data of the SBT memristor. The simulated [Formula: see text]–[Formula: see text] characteristic curve using the flux-controlled mathematical model coincides well with the measured [Formula: see text]–[Formula: see text] characteristic curves. The result indicates that the flux-controlled mathematical model with the definite parameters can be used to characterize the behaviors of the physical SBT memristor and guide its application to nonlinear circuit design.
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Chor, Tomas, James C. McWilliams, and Marcelo Chamecki. "Diffusive–Nondiffusive Flux Decompositions in Atmospheric Boundary Layers." Journal of the Atmospheric Sciences 77, no. 10 (October 1, 2020): 3479–94. http://dx.doi.org/10.1175/jas-d-20-0093.1.
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AbstractEddy diffusivity models are a common method to parameterize turbulent fluxes in the atmospheric sciences community. However, their inability to handle convective boundary layers leads to the addition of a nondiffusive flux component (usually called nonlocal) alongside the original diffusive term (usually called local). Both components are often modeled for convective conditions based on the shape of the eddy diffusivity profile for neutral conditions. This assumption of shape is traditionally employed due to the difficulty of estimating both components based on numerically simulated turbulent fluxes without any a priori assumptions. In this manuscript we propose a novel method to avoid this issue and estimate both components from numerical simulations without having to assume any a priori shape or scaling for either. Our approach is based on optimizing results from a modeling perspective and taking as much advantage as possible from the diffusive term, thus maximizing the eddy diffusivity. We use our method to diagnostically investigate four different large-eddy simulations spanning different stability regimes, which reveal that nondiffusive fluxes are important even when trying to minimize them. Furthermore, the calculated profiles for both diffusive and nondiffusive fluxes suggest that their shapes change with stability, which is an effect that is not included in most models currently in use. Finally, we use our results to discuss modeling approaches and identify opportunities for improving current models.
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Gutierrez-Villanueva, Manuel O., Teresa K. Chereskin, and Janet Sprintall. "Upper-Ocean Eddy Heat Flux across the Antarctic Circumpolar Current in Drake Passage from Observations: Time-Mean and Seasonal Variability." Journal of Physical Oceanography 50, no. 9 (September 1, 2020): 2507–27. http://dx.doi.org/10.1175/jpo-d-19-0266.1.
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AbstractEddy heat flux plays a fundamental role in the Southern Ocean meridional overturning circulation, providing the only mechanism for poleward heat transport above the topography and below the Ekman layer at the latitudes of Drake Passage. Models and observations identify Drake Passage as one of a handful of hot spots in the Southern Ocean where eddy heat transport across the Antarctic Circumpolar Current (ACC) is enhanced. Quantifying this transport, however, together with its spatial distribution and temporal variability, remains an open question. This study quantifies eddy heat flux as a function of ACC streamlines using a unique 20-yr time series of upper-ocean temperature and velocity transects with unprecedented horizontal resolution. Eddy heat flux is calculated using both time-mean and time-varying streamlines to isolate the dynamically important across-ACC heat flux component. The time-varying streamlines provide the best estimate of the across-ACC component because they track the shifting and meandering of the ACC fronts. The depth-integrated (0–900 m) across-stream eddy heat flux is maximum poleward in the south flank of the Subantarctic Front (−0.10 ± 0.05 GW m−1) and decreases toward the south, becoming statistically insignificant in the Polar Front, indicating heat convergence south of the Subantarctic Front. The time series provides an uncommon opportunity to explore the seasonal cycle of eddy heat flux. Poleward eddy heat flux in the Polar Front Zone is enhanced during austral autumn–winter, suggesting a seasonal variation in eddy-driven upwelling and thus the meridional overturning circulation.
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He, Ren, and Donghai Hu. "Physical Mechanism of Eddy Current Demagnetizing Effect for Eddy Current Brake." Journal of Computational and Theoretical Nanoscience 13, no. 10 (October 1, 2016): 6810–22. http://dx.doi.org/10.1166/jctn.2016.5632.
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This article researches both the mathematical relation between the braking force of eddy current brake and the speed of the moving conductor and the relationship between the average air-gap flux density and the velocity of the moving conductor respectively which result in the ambiguity of the physical mechanism of eddy current demagnetizing effect. The theoretical methods for obtaining the distribution of the excitation magnetic field, the eddy current magnetic field and the air gap magnetic field of eddy current brake were presented. Then the impacts of the excitation magnetic field and eddy current magnetic field on the distribution of air gap magnetic field were got through contrastive analysis and then the physical mechanism of eddy current demagnetizing effect is obtained. Finally, the influence of the eddy current demagnetizing effect on the design and control of eddy current brake was discussed in depth. The correctness of these theoretical calculations was validated by experiments on the retarder synthetic performance test bench or the finite element numerical calculation.
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Chumakov, Sergei, and Christopher J. Rutland. "Dynamic Structure Models for Scalar Flux and Dissipation in Large Eddy Simulation." AIAA Journal 42, no. 6 (June 2004): 1132–39. http://dx.doi.org/10.2514/1.10416.
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Hogg, Andrew Mc C., Michael P. Meredith, Jeffrey R. Blundell, and Chris Wilson. "Eddy Heat Flux in the Southern Ocean: Response to Variable Wind Forcing." Journal of Climate 21, no. 4 (February 15, 2008): 608–20. http://dx.doi.org/10.1175/2007jcli1925.1.
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Abstract The authors assess the role of time-dependent eddy variability in the Antarctic Circumpolar Current (ACC) in influencing warming of the Southern Ocean. For this, an eddy-resolving quasigeostrophic model of the wind-driven circulation is used, and the response of circumpolar transport, eddy kinetic energy, and eddy heat transport to changes in winds is quantified. On interannual time scales, the model exhibits the behavior of an “eddy saturated” ocean state, where increases in wind stress do not significantly change the circumpolar transport, but instead enhance the eddy field. This is in accord with previous dynamical arguments, and a recent observational study. The instantaneous response to increased wind stress is to cool temperatures through increased northward Ekman transport of cool water. But, in the longer term, the enhanced eddy state is more efficient at transporting heat, leading to a warming of the ocean. The total eddy heat flux response is greater than the Ekman transport heat flux in this model by a factor of 2, indicating that coarse (non eddy resolving) models may fail to adequately capture the key processes. The authors also test the model response to long-term changes in wind forcing, including steadily increasing circumpolar wind strength over a 30-yr period. The model shows a response in eddy heat flux, and a change in ocean temperature not dissimilar from observed Southern Ocean warming. These findings suggest that eddy heat flux, energized by increasing wind stress, may be a significant contributor to the observed warming of the Southern Ocean.
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Toro, Ivan Mauricio Cely, Ricardo Acosta Gotuzzo, Débora Regina Roberti, and Jackson Ernani Fiorin. "Avaliação de modelos de footprint para análise de fluxos obtidos por Eddy-Covariance em pequenas-áreas." Ciência e Natura 40 (March 22, 2018): 93. http://dx.doi.org/10.5902/2179460x30701.
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Two models for footprint calculations are compared employing flux measurements in the planetary boundary layer. The calculationsare based on the analytical models by Kormann e Meixner (2001) [An analytical footprint model for non-neutral stratification.Boundary-Layer Meteorology 99, 207–224] and by Schuepp et al. (1990) [Footprint prediction of scalar fluxes from analytical solutions of the difussion equation. Boundary-Layer Meteorology 50, 355-373]. The footprint density functions of a flux sensor are determined using eddy-covariance data. Those functions are integrated over surfaces given by quadrangular rectangles, in this case an agricultural field. This work ilustrates the features of each footprint model employing flux measurements with an eddy-covariance system of the SULFLUX network, installed on a agricultural field. Finally, it is presented the model that describes in a better way the flux measurements in small fields.
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Drijfhout, S. S. "What Sets the Surface Eddy Mass Flux in the Southern Ocean?" Journal of Physical Oceanography 35, no. 11 (November 1, 2005): 2152–66. http://dx.doi.org/10.1175/jpo2776.1.
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Abstract The Ocean Circulation and Climate Advanced Modelling (OCCAM) global, eddy-permitting ocean general circulation model has been used to investigate the surface eddy mass flux in the Southern Ocean. The isopycnal eddy mass flux in the surface layer is almost uniformly poleward and scales well with the local Ekman transport. This seems at odds with other models and observations suggesting topographic localization of the eddy fluxes with locally, large rotational components. Integrated over the thermocline depth the eddy fluxes do show such topographic localization. The surface eddy mass flux is mainly a consequence of the intermittent deepening of the mixed layer with the seasonal cycle, which redistributes the Ekman transport over the stack of layers that eventually become ventilated. Baroclinic instability gives rise to much smaller eddy-induced transports. Independent of the framework in which the residual mean flow is analyzed (isopycnal or geometric), the eddy-induced transport that opposes the wind-driven Ekman flow only partially compensates the Deacon cell. The associated overturning cell is about 5 Sv (where 1 Sv ≡ 106 m3 s−1), responsible for a cancellation of the Deacon cell of 30%. In geometric coordinates, a strong signature (14 Sv) of the Deacon cell remains for the residual mean flow. Only after transformation to density coordinates is a further reduction with 10 Sv obtained. Zonal tilting of isopycnals makes along-isopycnal recirculations appear as vertical overturning cells in geometric coordinates. These cells disappear in the isopycnal framework without any eddy-induced transport being involved.
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Wang, Z. J., and Yanan Li. "A Mathematical Analysis of Scale Similarity." Communications in Computational Physics 21, no. 1 (December 5, 2016): 149–61. http://dx.doi.org/10.4208/cicp.131015.110416a.
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AbstractScale similarity is found in many natural phenomena in the universe, from fluid dynamics to astrophysics. In large eddy simulations of turbulent flows, some sub-grid scale (SGS) models are based on scale similarity. The earliest scale similarity SGS model was developed by Bardina et al., which produced SGS stresses with good correlation to the true stresses. In the present study, we perform a mathematical analysis of scale similarity. The analysis has revealed that the ratio of the resolved stress to the SGS stress isγ2, whereγis the ratio of the second filter width to the first filter width, under the assumption of small filter width. The implications of this analysis are discussed in the context of large eddy simulation.
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Huang, Junji, Jorge-Valentino Bretzke, and Lian Duan. "Assessment of Turbulence Models in a Hypersonic Cold-Wall Turbulent Boundary Layer." Fluids 4, no. 1 (February 26, 2019): 37. http://dx.doi.org/10.3390/fluids4010037.
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In this study, the ability of standard one- or two-equation turbulence models to predict mean and turbulence profiles, the Reynolds stress, and the turbulent heat flux in hypersonic cold-wall boundary-layer applications is investigated. The turbulence models under investigation include the one-equation model of Spalart–Allmaras, the baseline k - ω model by Menter, as well as the shear-stress transport k - ω model by Menter. Reynolds-Averaged Navier-Stokes (RANS) simulations with the different turbulence models are conducted for a flat-plate, zero-pressure-gradient turbulent boundary layer with a nominal free-stream Mach number of 8 and wall-to-recovery temperature ratio of 0.48 , and the RANS results are compared with those of direct numerical simulations (DNS) under similar conditions. The study shows that the selected eddy-viscosity turbulence models, in combination with a constant Prandtl number model for turbulent heat flux, give good predictions of the skin friction, wall heat flux, and boundary-layer mean profiles. The Boussinesq assumption leads to essentially correct predictions of the Reynolds shear stress, but gives wrong predictions of the Reynolds normal stresses. The constant Prandtl number model gives an adequate prediction of the normal turbulent heat flux, while it fails to predict transverse turbulent heat fluxes. The discrepancy in model predictions among the three eddy-viscosity models under investigation is small.
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Jansen, Malte, and Raffaele Ferrari. "The Vertical Structure of the Eddy Diffusivity and the Equilibration of the Extratropical Atmosphere." Journal of the Atmospheric Sciences 70, no. 5 (April 23, 2013): 1456–69. http://dx.doi.org/10.1175/jas-d-12-086.1.
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Abstract Observations suggest that the time- and zonal-mean state of the extratropical atmosphere adjusts itself such that the so-called “criticality parameter” (which relates the vertical stratification to the horizontal temperature gradient) is close to one. T. Schneider has argued that the criticality parameter is kept near one by a constraint on the zonal momentum budget in primitive equations. The constraint relies on a diffusive closure for the eddy flux of potential vorticity (PV) with an eddy diffusivity that is approximately constant in the vertical. The diffusive closure for the eddy PV flux, however, depends crucially on the definition of averages along isentropes that intersect the surface. It is argued that the definition favored by Schneider results in eddy PV fluxes whose physical interpretation is unclear and that do not satisfy the proposed closure in numerical simulations. An alternative definition, first proposed by T.-Y. Koh and R. A. Plumb, is preferred. A diffusive closure for the eddy PV flux under this definition is supported by analysis of the PV variance budget and can be used to close the near-surface zonal momentum budget in idealized numerical simulations. Following this approach, it is shown that O(1) criticalities are obtained if the eddy diffusivity decays from its surface value to about zero over the depth of the troposphere, which is likely to be the case in Earth’s atmosphere. Large criticality parameters, however, are possible if the eddy diffusivity decays only weakly in the vertical, consistent with results from quasigeostrophic models. This provides theoretical support for recent numerical studies that have found supercritical mean states in primitive equation models.
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Berselli, Luigi C., Roger Lewandowski, and Dinh Duong Nguyen. "Rotational Forms of Large Eddy Simulation Turbulence Models: Modeling and Mathematical Theory." Chinese Annals of Mathematics, Series B 42, no. 1 (January 2021): 17–40. http://dx.doi.org/10.1007/s11401-021-0243-z.
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WANG, BING-CHEN, EUGENE YEE, DONALD J. BERGSTROM, and OAKI IIDA. "New dynamic subgrid-scale heat flux models for large-eddy simulation of thermal convection based on the general gradient diffusion hypothesis." Journal of Fluid Mechanics 604 (May 14, 2008): 125–63. http://dx.doi.org/10.1017/s0022112008001079.
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Three new dynamic tensor thermal diffusivity subgrid-scale (SGS) heat flux (HF) models are proposed for large-eddy simulation of thermal convection. The constitutive relations for the proposed modelling approaches represent the most general explicit algebraic formulations possible for the family of SGS HF models constructed using the resolved temperature gradient and SGS stress tensor. As a result, these three new models include a number of previously proposed dynamic SGS HF models as special cases. In contrast to the classical dynamic eddy thermal diffusivity SGS HF model, which strictly requires the SGS heat flux be aligned with the negative of the resolved temperature gradient, the three new models proposed here admit more degrees of freedom, and consequently provide a more realistic geometrical and physical representation of the SGS HF vector. To validate the proposed models, numerical simulations have been performed based on two benchmark test cases of neutrally and unstably stratified horizontal channel flows.
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Zurita-Gotor, Pablo, Javier Blanco-Fuentes, and Edwin P. Gerber. "The Impact of Baroclinic Eddy Feedback on the Persistence of Jet Variability in the Two-Layer Model." Journal of the Atmospheric Sciences 71, no. 1 (December 27, 2013): 410–29. http://dx.doi.org/10.1175/jas-d-13-0102.1.
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Abstract Although it is well known that the persistence of extratropical jet shifts is enhanced by a positive eddy feedback, the dynamics of this feedback is still debated. Two types of mechanisms have been proposed: barotropic mechanisms rely on changes in upper-level propagation and baroclinic mechanisms rely on the coupling between barotropic and baroclinic flow. Recent studies have suggested that barotropic models can capture key aspects of the observed jet variability but the role of baroclinic dynamics has been less explored. This study investigates the temporal relations between barotropic and baroclinic anomalies and their eddy forcings during the internal variability of the simple two-layer quasigeostrophic model. A large correlation is found between barotropic and baroclinic anomalies and between the meridional and vertical components of the Eliassen–Palm divergence, especially at low frequency. The low-frequency variability is consistent with the baroclinic mechanism: persistent upper-level eddy momentum convergence is associated with (and precedes) persistent anomalies in the poleward eddy heat flux. In contrast, at high frequency, poleward heat flux anomalies are associated with eddy momentum divergence aloft and both eddy forcings have same-sign contributions to the upper-level eddy potential vorticity (PV) flux. In this limit the eddy PV flux is associated with wave activity transience as effective diffusivity is too small to dissipate the wave–mean flow interaction term. The large correlation between barotropic and baroclinic anomalies implies that the low-frequency variability of barotropic flow may be affected by thermal damping when this damping is sufficiently strong. For example, zonal index persistence drops drastically in our model when baroclinicity shifts are prevented by strong thermal restoration.
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Horiuti, Kiyosi. "Assessment of two-equation models of turbulent passive-scalar diffusion in channel flow." Journal of Fluid Mechanics 238 (May 1992): 405–33. http://dx.doi.org/10.1017/s0022112092001769.
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Models for the transport of passive scalar in turbulent flow were investigated using databases derived from numerical solutions of the Navier—Stokes equations for fully developed plane channel flow, these databases being generated using large-eddy and direct numerical simulation techniques. Their reliability has been established by comparison with the experimental measurements of Hishida. Nagano & Tagawa (1986). The present paper compares these simulations and calculations using the Nagano & Kim (1988) ‘two-equation’ model for the scalar variance (kθ) and scalar variance dissipation (εθ). This model accounts for the dependence of flow quantities on the Prandtl number by expressing eddy diffusivity in terms of the ratio of the timescales of velocity and scalar fluctuations. However, the statistical analysis by Yoshizawa (1988) showed that there was an inconsistency in the definition of the isotropic eddy diffusivity in the Nagano—Kim model, the implications of which are clearly demonstrated by the results of this paper where large-eddy simulation and direct numerical simulation (LES/DNS) databases are used to compute the quantities contained in both models. An extension of the Nagano-Kim model is proposed which resolves these inconsistencies, and a further development of this model is given in which the anisotropic scalar fluxes are calculated. Near a rigid surface, a third-order ‘anisotropic representation’ of scalar fluxes may be used as an alternative model for reducing the eddy diffusivity, instead of the conventional ‘damping functions’. This model is similar but distinct from the algebraic scalar flux model of Rogers, Mansour & Reynolds (1989). A third aspect of this paper is the use of the LES/DNS databases to evaluate certain coefficients (those for modelling the pressure-scalar gradient terms) of another model of a similar type, namely the algebraic scalar flux model of Launder (1975).
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Chávez, JoséL, Christopher M. U. Neale, Lawrence E. Hipps, John H. Prueger, and William P. Kustas. "Comparing Aircraft-Based Remotely Sensed Energy Balance Fluxes with Eddy Covariance Tower Data Using Heat Flux Source Area Functions." Journal of Hydrometeorology 6, no. 6 (December 1, 2005): 923–40. http://dx.doi.org/10.1175/jhm467.1.
Full textAbstract:
Abstract In an effort to better evaluate distributed airborne remotely sensed sensible and latent heat flux estimates, two heat flux source area (footprint) models were applied to the imagery, and their pixel weighting/integrating functionality was investigated through statistical analysis. Soil heat flux and sensible heat flux models were calibrated. The latent heat flux was determined as a residual from the energy balance equation. The resulting raster images were integrated using the 2D footprints and were compared to eddy covariance energy balance flux measurements. The results show latent heat flux estimates (adjusted for closure) with errors of (mean ± std dev) −9.2 ± 39.4 W m−2, sensible heat flux estimate errors of 9.4 ± 28.3 W m−2, net radiation error of −4.8 ± 20.7 W m−2, and soil heat flux error of −0.5 ± 24.5 W m−2. This good agreement with measured values indicates that the adopted methodology for estimating the energy balance components, using high-resolution airborne multispectral imagery, is appropriate for modeling latent heat fluxes. The method worked well for the unstable atmospheric conditions of the study. The footprint weighting/integration models tested indicate that they perform better than simple pixel averages upwind from the flux stations. In particular the flux source area model (footprint) seemed to better integrate the resulting heat flux image pixels. It is suggested that future studies test the methodology for heterogeneous surfaces under stable atmospheric conditions.
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Suga, K., M. Nagaoka and, and N. Horinouchi. "Application of a Higher Order GGDH Heat Flux Model to Three-Dimensional Turbulent U-Bend Duct Heat Transfer." Journal of Heat Transfer 125, no. 1 (January 29, 2003): 200–203. http://dx.doi.org/10.1115/1.1532018.
Full textAbstract:
A higher order version of the generalized gradient diffusion hypothesis (HOGGDH) for turbulent heat flux is applied to predict heat transfer in a square-sectioned U-bend duct. The flow field turbulence models coupled with are a cubic nonlinear eddy viscosity model and a full second moment closure. Both of them are low Reynolds number turbulence models. The benefits of using the HOGGDH heat flux model are presented through the comparison with the standard GGDH.
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Huang, Hsin-Yuan, Alex Hall, and Joao Teixeira. "Evaluation of the WRF PBL Parameterizations for Marine Boundary Layer Clouds: Cumulus and Stratocumulus." Monthly Weather Review 141, no. 7 (July 1, 2013): 2265–71. http://dx.doi.org/10.1175/mwr-d-12-00292.1.
Full textAbstract:
Abstract The performance of five boundary layer parameterizations in the Weather Research and Forecasting Model is examined for marine boundary layer cloud regions running in single-column mode. Most parameterizations show a poor agreement of the vertical boundary layer structure when compared with large-eddy simulation models. These comparisons against large-eddy simulation show that a parameterization based on the eddy-diffusivity/mass-flux approach provides a better performance. The results also illustrate the key role of boundary layer parameterizations in model performance.
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Wu, L. M., Nan Hui Lai, and G. T. Wang. "Measurement and Simulation of Automotive Eddy Current Retarder Based on Virtual Reality." Key Engineering Materials 392-394 (October 2008): 93–97. http://dx.doi.org/10.4028/www.scientific.net/kem.392-394.93.
Full textAbstract:
Structure and working principles of eddy current retarder (ECR) are discussed, as well as performance requirements of real-time virtual testing and simulation. On the basis of hardware testing platform, virtual models of vehicle and retarder are embedded into application program. In the testing system, Vega API function library is used for second development to control the 3D models, and Visual C++ is used for mathematical models call from MATLAB to simulate the working condition. Integrated with virtual instrument and virtual environment, the limitation of former simulation is broken through. Monitoring and testing on eddy current retarder are achieved efficiently and visually. Besides, the virtual test data is not only compared with the practical vehicle test data to correct the technical parameter of eddy current retarder, but also compared with the simulation of mathematical models for further study. The testing system gives evaluation on the performance of the retarder in different vehicles, so it expands application range and heightens testing efficiency.