Homogeneous Fluxes Research Articles

Role of rotational and divergence effects induced by wind turbines wakes on near-ground air warming

Various studies, involving numerical simulations, satellite measurements, and field measurement campaigns, have demonstrated that wind turbine wakes can lead to changes in near-ground air temperature. To investigate these phenomena an Actuator Disk with Rotation (ADR) is implemented within the LES non-hydrostatic atmospheric model Meso-NH and validated using the NewMEXICO wind tunnel measurements and the VERTEX field measurement campaign. The NewMEXICO case allows the aerodynamic validation of the approach, especially the effect of the wake on wind speed components. On the VERTEX case, meteorological effects of wind turbines are studied under various atmospheric stability conditions through the application of homogeneous sensible heat fluxes at the ground level. Results show wake-related warming and cooling near the ground for stable and unstable conditions respectively, and no significant change for neutral conditions. These results show a good tendency agreement with the VERTEX campaign’s measurements. The comparison between an Actuator Disk with No Rotation (ADNR) and an ADR simulation show the dual contribution of the rotation of the wake and the growth of the stream tube on the temperature change in the wake but also on the near-ground air temperature.

Superdense Lithium Deposition via Mixed Ionic/Electronic Conductive Interfaces Implanted In Vivo/Vitro for Stable Lithium Metal Batteries

AbstractLithium metal batteries specialize in energy density, while the immoderate dendrite growth and solid electrolyte interphase (SEI) proliferation have been impeding their practical application. The key is the regulation of Li+ diffusion/nucleation behaviors toward a dense deposition. Herein, Li9Al4/Li3N energized mixed ionic/electronic conductive (MIEC) interfaces are pre‐implanted in both the surface and bulk of the lithium metal anode. Such MIEC interfaces are activated from the in situ conversion and nano‐alloying reactions between AlN and metallic Li and are uniformly dispersed via facile mechanical kneading. In vitro, MIEC interfaces participate in the formation of an inorganic‐enriched SEI that balances ionic transport, electron blocking, and mechanical strength to guarantee homogeneous ion fluxes and structural integrity. In vivo, a unique nanorod‐array architecture enables a released internal stress and rapid diffusion kinetics, affording a dense and large granular plating manner. As a result, the symmetric cell delivers a striking cumulative capacity of >120000 mAh cm−2 at 20 mA cm−2@20 mAh cm−2 with a prolonged lifespan of over 6000 h. The improved machinability also enables a scalable fabrication of ultrathin foil to achieve a stable high‐areal‐capacity full cell for 320 cycles with enhanced energy density characteristics both gravimetrically and volumetrically.

Elliptic deformations of the AdS3 × S3 × T4 string

Abstract With the aim of investigating the existence of an integrable elliptic deformation of strings on AdS3 × S3 × T4, we compute the tree-level worldsheet S-matrix of the elliptically-deformed bosonic sigma model on AdS3 × S3 in uniform light-cone gauge. The resulting tree-level S-matrix is compatible with the integrability of the model and has interesting features, including a hidden U(1) symmetry not manifest in the Lagrangian. We find that it cannot be embedded in the known exact integrable R-matrices describing deformations of the undeformed AdS3 × S3 × T4 light-cone gauge S-matrix including fermions. Therefore, we construct embeddings of the deformed 6-d metric in type II supergravity with constant dilaton and homogeneous fluxes. The simplicity of these solutions suggests they are promising candidates to lead to an integrable string sigma model including fermions.

Analysis of flux footprints in fragmented, heterogeneous croplands

An accurate quantification of fluxes from heterogeneous sites and further bifurcation into contributing homogeneous fluxes is an active field of research. Among such sites, fragmented croplands with varying surface roughness characteristics pose formidable challenges for footprint analysis. We conducted two flux monitoring experiments in fragmented croplands characterized by two dissimilar surfaces with objectives to: (i) evaluate the performance of two analytical footprint models in heterogeneous canopy considering aggregated roughness parameters and (ii) analyze the contribution of fluxes from individual surfaces under changing wind speed. A set of three eddy covariance (EC) towers (one each capturing the homogenous fluxes from individual surfaces and a third, high tower capturing the heterogeneous mixed fluxes) was used for method validation. High-quality EC fluxes that fulfill stationarity and internal turbulence tests were analyzed considering daytime, unstable conditions. In the first experiment, source area contribution from a surface is gradually reduced by progressive cut, and its effect on high-tower flux measurements is analyzed. Two footprint models (Kormann and Meixner ‘KM’; analytical solution to Lagrangian model ‘FFP’) with modified surface roughness parameters were applied under changing source area contributions. FFP model has consistently over predicted the footprints (RMSEFFP = 0.31 m−1, PBIASFFP = 19.00), whereas KM model prediction was gradually changed from over prediction to under prediction towards higher upwind distances (RMSEKM = 0.02 m−1, PBIASKM = 8.50). Sensitivity analysis revealed that the models are more sensitive to turbulent conditions than surface characteristics. This motivated to conduct the second experiment, where the fractional contribution of individual surfaces (α and β) to the heterogeneous fluxes measured by the high tower (T3) was estimated using the principle of superposition (FT3 = α FT1 + β FT2). Results showed that α and β are dynamic during daylight hours and strongly depend on mean wind speed (U) and friction velocity (u*). The contribution of fluxes from adjoining fields [1 − (α + β)] is significant beyond 80% isopleth. Our findings provide guidelines for future analysis of fluxes in heterogeneous, fragmented croplands.

Thermal and mechanical stresses in a solar central receiver

Failure in the tubes of the solar receiver is a problem that should be studied. This failure is caused by the combined action of the high temperature, stresses and corrosion. Commonly, the calculation of the stresses in the receiver tubes is carried out in the crossed sections, taking into account the radial and the circumferential variation of the temperature. However, the temperature gradient along the tube length has been ignored. In this study a new model for the stress calculation in the receiver tubes has been developed. This model includes the temperature gradient in circumferential, radial, and longitudinal direction, taking into account the movement restrictions. The results show that the mechanical boundary conditions have a large effect in the stresses of the tube, being 3 times higher than the stress when no movement restrictions have been imposed. Moreover, the stress profile is highly dependent on the temperature gradient and hence on the incident solar flux on the receiver. Homogeneous solar fluxes are then more suitable than lower levels of solar fluxes with important gradients.

Effects of Horizontal Resolution, Domain Size, Boundary Conditions, and Surface Heterogeneity on Coarse LES of a Convective Boundary Layer

Abstract Atmospheric properties in a convective boundary layer vary over a wide range of spatial scales and are commonly studied using large-eddy simulations (LES) in various configurations. We examine how the boundary layer depth and distribution of variability across scales are affected by LES grid spacing, domain size, inhomogeneity of surface properties, and external forcing. Two different setups of the Weather Research and Forecasting (WRF) model are analyzed. A semi-idealized configuration uses a periodic domain, flat surface, prescribed homogeneous surface heat fluxes, and horizontally uniform profiles of large-scale advective tendencies. A nested LES setup employs a larger domain and realistic initial and boundary conditions, including an interactive land surface model with representative topography and vegetation and soil types. Subdomains of identical size are analyzed for all simulations. Characteristic structure sizes are quantified using the variability scales L50 and L95, defined such that features smaller than that contain 50% and 95% of the total variance, respectively. Progressive increase in L50 from vertical velocity to temperature and moisture structures is systematically reproduced in all simulation configurations. This dependence of L50 on the considered variable complicates the development of scale-aware parameterizations for models with grid spacing in the “terra incognita”. In simulations using a larger domain with heterogeneous surface properties, the development of internal mesoscale patterns significantly affects variance distributions inside analyzed subdomains. Sizes of boundary layer structures also strongly depend on the LES grid spacing and, in case of heterogeneous surface and topography, on location of the subdomain inside a larger computational domain.

ECR discharge sustained by millimeter waves as a source of dense plasma flux

The results of the investigation of the dense ECR discharge hydrogen plasma flux formation in the single solenoid magnetic field are presented in this work. The transversal flux profile obtained at the optimal system parameters is shown. The possibility of the formation of homogeneous plasma fluxes with density of 750 mA/cm2 and total current of 5 A is demonstrated. The results of the first experiments of the hydrogen ion beam extraction from the ECR discharge plasma in the single magnetic coil are presented. The record values of the ion current density higher than 1.5 A/cm2 were obtained. The results of the research presented in this paper show the prospects of the proposed system for applications of the neutral beam injector development for the plasma heating in the controlled thermonuclear fusion installations.

Characterizing the shape and heat production of open vertical cracks in burst vibrothermography experiments

We present a quantitative characterization of the heat flux distribution generated at open vertical cracks in burst vibrothermography experiments. We use a stabilized inversion algorithm that is able to retrieve both homogeneous and inhomogeneous fluxes from surface temperature data generated by open cracks. The performance of the algorithm is checked by inverting both synthetic data with added random noise and experimental data taken on samples containing calibrated heat sources. The results show that it is possible to characterize simultaneously the geometry and the absolute value of the heat flux distribution generated at the crack and therefore, the total emitted thermal power.

Long‐Time Behavior, Invariant Measures, and Regularizing Effects for Stochastic Scalar Conservation Laws

AbstractWe study the long‐time behavior and regularity of the pathwise entropy solutions to stochastic scalar conservation laws with random‐in‐time spatially homogeneous fluxes and periodic initial data. We prove that the solutions converge to their spatial average, which is the unique invariant measure of the associated random dynamical system, and provide a rate of convergence, the latter being new even in the deterministic case for dimensions higher than 2. The main tool is a new regularization result in the spirit of averaging lemmata for scalar conservation laws, which, in particular, implies a regularization by noise‐type result for pathwise quasi‐solutions.© 2016 Wiley Periodicals, Inc.

A comparison of Monte Carlo methods for neutron leakage at assembly level

The treatment of neutron leakage at assembly level is an essential step in the generation of few-group cross section data for reactor calculations. This work compares methods used for the characterization of assembly leakage in the framework of Monte Carlo cross section generation, using nearly-critical colorset configurations in order to obtain approximate reference values. The B1 fundamental mode approximation and the albedo-search method are compared in terms of eigenvalue, multi-group homogeneous scalar fluxes and maximum pin power differences for several cell types. The performance of a novel heterogeneous leakage method is also tested. Whereas B1 corrections provide the best agreement in homogeneous fluxes, the new method furnishes the best consistence in terms of pin powers, whilst providing rich spectral information and reducing computational overheads associated with colorset calculations. Future investigations are suggested in order to test the performance of these methods in the calculation of few-group, leakage-corrected assembly cross sections and discontinuity factors.

Thermohaline residual circulation of the Wadden Sea

In this study, we present estuarine circulation driven by horizontal density gradients generated by spatially homogeneous surface buoyancy fluxes over sloping bathymetry as a dynamical feature in the coastal zone being potentially relevant for cross-coastal transports. A combination of downward buoyancy flux (net precipitation, net heating) together with tidal mixing may generate a classical estuarine circulation with landward near-bottom residual currents. The Wadden Sea of the south-eastern North Sea is a prototype for such a coastal regime. It is characterised by extensive inter-tidal flats along the coast separated from the open sea by barrier islands. Here, we present long-term observations from the Wadden Sea covering the years 2006–2011. We investigated the statistics of the density gradients. Typical values for the landward density gradient were ∂xρ≈−3⋅10−5 kg m−4 and maximum values were ∂xρ≈−6.5⋅10−5 kg m−4. The magnitude of the density gradient resulted from the magnitude of the salinity gradient, with some modifications by the positive (towards the coast, in spring) or negative (towards the sea, in autumn) temperature gradient. To explain the generation of estuarine circulation by the surface buoyancy flux, we construct an analytical model representing the geometry and dynamics of a Wadden Sea Basin. With downward buoyancy flux, a weak classical estuarine circulation due to gravitational forcing results, whereas upward buoyancy flux drives inverse estuarine circulation. Finally, a two-dimensional (vertical-longitudinal) numerical model was set up for the idealised geometry, including tidally asymmetric turbulent mixing. This results in significantly stronger estuarine circulation due to the presence of tidal straining. The model assesses the circulation due to neutral and upward surface buoyancy fluxes. We conclude that these mechanisms may be important in many coastal areas and may substantially contribute to coast-to-sea exchange in these areas.

Applicability of angular flux discontinuity factor preserving region-wise leakage for integro-differential transport equation

In the current core analysis, spatial homogenization is utilized to reduce the computational time. The discontinuity factor (DF) is one of the effective correction factors to reduce spatial homogenization error. The DF in diffusion equation is widely used; on the other hand the DF in transport equation has not been put to practical use although several efforts have been carried out. In this paper, the angular flux discontinuity factor (AFDF) as the DF for the integro-differential transport equation (e.g., the discrete-ordinate method, the method of characteristics) is theoretically described and its applicability is discussed. The AFDF is used to preserve the region-wise neutron leakage at each spatial mesh and defined as a ratio of heterogeneous and homogeneous angular fluxes at the homogenized region surface. In a homogeneous calculation with the AFDF, the angular flux is discontinuous at the region surface. In this paper the applicability of the AFDF to fuel pin cell homogenization is verified for one-dimensional slab geometry. As a result of this verification, it is confirmed that the AFDF has the capability to reduce the spatial homogenization error of fuel pin cell homogenization.

Atmospheric Deposition of Inorganic Elements and Organic Compounds at the Inlets of the Venice Lagoon

The Venice Lagoon is subjected to long-range transport of contaminants via aerosol from the near Po Valley. Moreover, it is an area with significant local anthropogenic emissions due to the industrial area of Porto Marghera, the urban centres, and the glass factories and with emissions by ships traffic within the Lagoon. Furthermore, since 2005, the Lagoon has also been affected by the construction of the MOSE (Modulo Sperimentale Elettromeccanico—Electromechanical Experimental Module) mobile dams, as a barrier against the high tide. This work presents and discusses the results from chemical analyses of bulk depositions, carried out in different sites of the Venice Lagoon. Fluxes of pollutants were also statistically analysed on PCA with the aim of investigating the spatial variability of depositions and their correlation with precipitations. Fluxes of inorganic pollutants depend differently on precipitations, while organic compounds show a more seasonal trend. The statistical analysis showed that the site in the northern Lagoon has lower and almost homogeneous fluxes of pollutants, while the other sites registered more variable concentrations. The study also provided important information about the annual trend of pollutants and their evolution over a period of about five years, from 2005 to 2010.

Axial discontinuity factors for the nodal diffusion analysis of high conversion BWR cores

High conversion LWRs concepts typically rely on a heterogeneous core configuration, where fissile zones are interspersed with fertile blanket zones in order to achieve a high conversion ratio. Modeling such a heterogeneous structure of these cores represents a significant challenge to the conventional reactor analysis methods. It was recently suggested to overcome such difficulties, in particular, for the case of axially heterogeneous reduced moderation BWRs, by introducing an additional set of discontinuity factors in axial direction at the interfaces between fissile and fertile fuel assembly zones. However, none of the existing nodal diffusion core simulators have the capability of accounting for discontinuity of homogeneous nodal fluxes in axial direction since the fuel composition of conventional LWRs is much more axially uniform. In this work, we modified the nodal diffusion code DYN3D by introducing such a capability. The new version of the code was tested on a series of reduced moderation BWR cases with Th–U233 and U–Pu–MA fuel. The library of few-group homogenized cross sections and the data required for the calculation of discontinuity factors were generated using the Monte Carlo transport code Serpent. The results obtained with the modified version of DYN3D were compared with the reference Monte Carlo solutions and were found to be in good agreement. The current analysis demonstrates that high conversion LWRs can in principle be modeled using existing nodal diffusion core simulators.

Distribution of the coal flow in the mill-duct system of the As Pontes Power Plant using CFD modeling

The efficiency of a Power Plant is affected by the distribution of the pulverized coal within the furnace. The coal, which is pulverized in the mills, is transported and distributed by the primary gas through the mill-ducts to the interior of the furnace. This is done with a double function: dry and enter the coal by different levels for optimizing the combustion in the sense that a complete combustion occurs with homogeneous heat fluxes to the walls. The mill-duct systems of a real Power Plant are very complex and they are not yet well understood. In particular, experimental data concerning the mass flows of coal to the different levels are very difficult to measure. CFD modeling can help to determine them. An Eulerian/Lagrangian approach is used due to the low solid–gas volume ratio.

The effect of dynamic–thermodynamic icebergs on the Southern Ocean climate in a three-dimensional model

Melting icebergs are a mobile source of fresh water as well as a sink of latent heat. In most global climate models, the spatio-temporal redistribution of fresh water and latent heat fluxes related to icebergs is parameterized by an instantaneous more or less arbitrary flux distribution over some parts of the oceans. It is uncertain if such a parameterization provides a realistic representation of the role of icebergs in the coupled climate system. However, icebergs could have a significant climate role, in particular during past abrupt climate change events which have been associated with armada’s of icebergs. We therefore present the interactive coupling of a global climate model to a dynamic thermodynamic iceberg model, leading to a more plausible spatio-temporal redistribution of fresh water and heat fluxes. We show first that our model is able to reproduce a reasonable iceberg distribution in both hemispheres when compared to recent data. Second, in a series of sensitivity experiments we explore cooling and freshening effects of dynamical icebergs on the upper Southern Ocean and we compare these dynamic iceberg results to the effects of an equivalent parameterized iceberg flux. In our model without interactive icebergs, the parameterized fluxes are distributed homogeneously South of 55°S, whereas dynamic icebergs are found to be concentrated closer to shore except for a plume of icebergs floating North–East from the tip of the Antarctic Peninsula. Compared to homogeneous fluxes, the dynamic icebergs lead to a 10% greater net production of Antarctic bottom water (AABW). This increased bottom water production involves open ocean convection, which is enhanced by a less efficient stratification of the ocean when comparing to a homogeneous flux distribution. Icebergs facilitate the formation of sea-ice. In the sensitivity experiments, both the fresh water and the cooling flux lead to a significant increase in sea-ice area of 12% and 6%, respectively, directly affecting the highly coupled and interactive air/sea/ice system. The consequences are most pronounced along the sea-ice edge, where this sea-ice facilitation has the greatest potential to affect ocean stratification, for example by heat insulation and wind shielding, which further amplifies the cooling and freshening of the surface waters.

An Empirical Orthogonal Function Iteration Approach for Obtaining Homogeneous Radiative Fluxes from Satellite Observations

Abstract Conventional observations of climate parameters are sparse in space and/or time, and the representativeness of such information needs to be optimized. Observations from satellites provide improved spatial coverage over point observations; however, they pose new challenges for obtaining homogeneous coverage. Surface radiative fluxes, the forcing functions of the hydrologic cycle and biogeophysical processes, are now becoming available from global-scale satellite observations. They are derived from independent satellite platforms and sensors that differ in temporal and spatial resolution and in the size of the footprint from which information is derived. Data gaps, degraded spatial resolution near boundaries of geostationary satellites, and different viewing geometries in areas of satellite overlap could result in biased estimates of radiative fluxes. In this study will be discussed issues related to the sources of inhomogeneity in surface radiative fluxes as derived from satellites, development of an approach to obtain homogeneous datasets, and application of the method to the widely used International Satellite Cloud Climatology Project data that currently serve as a source of information for deriving estimates of surface and top-of-the-atmosphere radiative fluxes. Introduced is an empirical orthogonal function (EOF) iteration scheme for homogenizing the fluxes. The scheme is evaluated in several ways, including comparison of the inferred radiative fluxes with ground observations, both before and after the EOF approach is applied. On the average, the latter reduces the RMS error by about 2–3 W m−2.

On nonlinear structure of electrical noise generated by slow discharge

Nonlinear structure of electrical noise of slow electrochemical discharge is analyzed within theory of integral random homogeneous fluxes with independent increments. It is shown that the degree of deviation of a flux of elementary acts from the Poissonian flux is defined by the magnitude of the factor of symmetry of slow discharge. An equation that links polyspectra of slow discharge of first, second, and third orders is derived.

Microscopic thermodynamic basis of normality structure of inelastic constitutive relations

The essential content of plasticity theory is the normality of plastic strain increments to the yield or flow potential surface at smooth points. The corresponding microscopic thermodynamic mechanism has been explored by Rice [Rice, J.R., 1971. Inelastic constitutive relations for solids: an integral variable theory and its application to metal plasticity. Journal of the Mechanics and Physics of Solids 19, 433; Rice, J.R., 1975. Continuum mechanics and thermodynamics of plasticity in relation to microscale deformation mechanisms, in: Argon, A.S. (Ed.), Constitutive Equations in Plasticity. MIT Press, Cambridge, MA, p. 23] in his thermodynamic framework with internal variables. Rice’s kinetic rate laws of local internal variables, with each rate being stress dependent only via its conjugate thermodynamic force, directly lead to a unifying normality structure and represent a wide class of inelastic behaviors. The aim of this paper is to reveal the underlying physical mechanism and basis of Rice’s kinetic rate laws. It is shown that Onsager fluxes which satisfy the so-called non-linear Onsager reciprocal relations Edelen [Edelen, D.G.B., 1972. A non-linear Onsager theory of irreversibility. International Journal of Engineering Science 10, 481; 1973. Asymptotic stability, Onsager fluxes and reaction kinetics, International Journal of Engineering Science 11, 819], can ensure the existence of the flow potential function and lead to the normality structure, and Rice’s kinetic rate laws of local internal variables are just certain specific Onsager fluxes. It is also shown that the convexity of the entropy production rate can ensure the convexity of the flow potential function based on homogeneous Onsager fluxes.

Hydromechanical properties and alteration of natural fracture surfaces in the Soultz granite (Bas-Rhin, France)

Natural fractures are characterized by rough surfaces and complex fluid flows. A large distribution of apertures (residual voids) within their walls and the presence of contact points (in situ normal loads) produce heterogeneous flows (channeling). The resulting permeabilities, porosities or fluid–rock exchange surfaces cannot be realistically modeled by parallel and smooth plate models. Four natural fractures are sampled at different depths and degrees of alteration in the Soultz sandstone and granite (EPS1 drillhole, Soultz-sous-Forêts, Bas-Rhin, France). The fracture surfaces are measured with mechanical profilometry and maps of asperity heights ( XYZ). Resulting local apertures ( XYe) are then calculated. A statistical study of the surface profiles ( XZ) show that the fractures are more or less rough and tortuous according to the types of alteration. Altered samples are characterized by smoother surfaces of fractures. Such differences imply that (i) the average fracture aperture is not representative for the whole fracture and that (ii) the different local apertures should be integrated in hydraulic and mechanical models. A hydraulic model (finite difference calculations) of fluid flow, taking into account the elastic closure (Hertz contact theory) of fractures with depth, is used. Maps of contact points and relative local loads within the fracture planes are compared to flow maps. They show different channeling of fluid flows. Strongly altered fractures are characterized by homogeneous fluxes despite the presence of numerous contact zones during the closure of fracture. By contrast, fresh fractures develop, increasing fluid flow channels with depth. Fracture closure (increasing normal stress) does not systematically increase the channeling of fluid flow. There is evidence for a general smoothing out of the irregularities of the fracture walls due to precipitation of secondary minerals, indicating that the cubic law can be commonly valid, also at great crustal depth but this validity depends on the degree of fracture alteration. Mineralogical and geochemical observations, thus, should be taken into account to perform more accurate permeability calculations and models of fluid circulation in fracture networks.