Frontiers of chaotic advection
Aref, Hassan; Budišić, Marko; Cartwright, Julyan H E; Clercx, Herman J H; Feudel, Ulrike; Golestanian, Ramin; Gouillart, Emmanuelle; Guer, Yves Le; van Heijst, GertJan F; Krasnopolskaya, Tatyana S; MacKay, Robert S; Meleshko, Vyacheslav V; Metcalfe, Guy; Mezić, Igor; de Moura, Alessandro P S; Omari, Kamal El; Piro, Oreste; Speetjens, Michel F M; Sturman, Rob; Thiffeault, Jean-Luc; Tuval, Idan
2014-01-01
We review the present position of and survey future perspectives in the physics of chaotic advection; the field that emerged three decades ago at the intersection of fluid mechanics and nonlinear dynamics, which encompasses a range of applications with length scales ranging from micrometers to hundreds of kilometers, including systems as diverse as mixing and thermal processing of viscous fluids, micro-fluidics, biological flows, and large-scale dispersion of pollutants in oceanographic and atmospheric flows.
A generalized advection dispersion equation
Indian Academy of Sciences (India)
Abdon Atangana
2014-02-01
This paper examines a possible effect of uncertainties, variability or heterogeneity of any dynamic system when being included in its evolution rule; the notion is illustrated with the advection dispersion equation, which describes the groundwater pollution model. An uncertain derivative is defined; some properties of the operator are presented. The operator is used to generalize the advection dispersion equation. The generalized equation differs from the standard equation in four properties. The generalized equation is solved via the variational iteration technique. Some illustrative figures are presented.
Instabilities of advection-dominated accretion flows
Chen, X
1996-01-01
Accretion disk instabilities are briefly reviewed. Some details are given to the short-wavelength thermal instabilities and the convective instabilities. Time-dependent calculations of two-dimensional advection-dominated accretion flows are presented.
Turbulent dynamo with advective magnetic helicity flux
Del Sordo, Fabio; Brandenburg, Axel
2012-01-01
Many astrophysical bodies harbor magnetic fields that are thought to be sustained by dynamo processes. However, it has been argued that the production of large-scale magnetic fields by a mean-field dynamo is strongly suppressed at large magnetic Reynolds numbers owing to the conservation of magnetic helicity. This phenomenon is known as catastrophic quenching. Advection of magnetic field toward the outer boundaries and away from the dynamo is expected to alleviate such quenching. Examples are stellar and galactic winds. Such advection might be able to overcome the constraint imposed by the conservation of magnetic helicity, transporting a fraction of it outside the domain in which the dynamo operates. We study how the dynamo process is affected by advection. In particular, we study the relative roles played by advective and diffusive fluxes of magnetic helicity. We do this by performing direct numerical simulations of a turbulent dynamo of alpha^2 type driven by forced turbulence in a Cartesian domain in the ...
Discrete Lie Advection of Differential Forms
Mullen, P; Pavlov, D; Durant, L; Tong, Y; Kanso, E; Marsden, J E; Desbrun, M
2009-01-01
In this paper, we present a numerical technique for performing Lie advection of arbitrary differential forms. Leveraging advances in high-resolution finite volume methods for scalar hyperbolic conservation laws, we first discretize the interior product (also called contraction) through integrals over Eulerian approximations of extrusions. This, along with Cartan's homotopy formula and a discrete exterior derivative, can then be used to derive a discrete Lie derivative. The usefulness of this operator is demonstrated through the numerical advection of scalar fields and 1-forms on regular grids.
Optically-thick accretion discs with advection
Institute of Scientific and Technical Information of China (English)
陈林红; 吴枚; 尚仁成
2002-01-01
The structures of optically-thick accretion discs with radial advection have been investigated by the iteration and integration algorithms. The advective cooling term changes mostly the inner part of disc solution, and even results in an optically-thick advection-dominated accretion flow (ADAF). Three distinct branches-the outer Shakura-Sunyaev disc (SSD), the inner ADAF and the middle transition layer-are found for a super-Eddington disc. The SSD-ADAF transition radius can be estimated as 18(M/ME)RG where RG is the Schwarzschild radius, M is the mass accretion rate and ME is the Eddington accretion rate. SSD solutions calculated with the iteration and integration methods are identical, while ADAF solutions obtained by these two methods differ greatly. Detailed algorithms and their differences have been analysed. The iteration algorithm is not self-consistent, since it implies that the dimensionless advection factor ξ is invariant, but in the inner ADAF region the variation of ξ is not negligible. The integration algorithm is always effective for the whole region of an optically-thick disc if the accretion rate is no smaller than 10-4ME. For optically-thin discs, the validity of these two algorithms is different. We suggest that the integration method be employed to calculate the global solution of a disc model without assuming ξ to be a constant. We also discuss its application to the emergent continuum spectrum in order to explain observational facts.
On the tensorial nature of advective porosity
Neuman, Shlomo P.
2005-02-01
Field tracer tests indicate that advective porosity, the quantity relating advective velocity to Darcy flux, may exhibit directional dependence. Hydraulic anisotropy explains some but not all of the reported directional results. The present paper shows mathematically that directional variations in advective porosity may arise simply from incomplete mixing of an inert tracer between directional flow channels within a sampling (or support) volume ω of soil or rock that may be hydraulically isotropic or anisotropic. In the traditional fully homogenized case, our theory yields trivially a scalar advective porosity equal to the interconnected porosity ϕ, thus explaining neither the observed directional effects nor the widely reported experimental finding that advective porosity is generally smaller than ϕ. We consider incomplete mixing under conditions in which the characteristic time tD of longitudinal diffusion along channels across ω is much shorter than the characteristic time tH required for homogenization through transverse diffusion between channels. This may happen where flow takes place preferentially through relatively conductive channels and/or fractures of variable orientation separated by material that forms a partial barrier to diffusive transport. Our solution is valid for arbitrary channel Peclet numbers on a correspondingly wide range of time scales tD ⩽ t ≪ tH. It shows that the tracer center of mass is advected at a macroscopic velocity which is generally not collinear with the macroscopic Darcy flux and exceeds it in magnitude. These two vectors are related through a second-rank symmetric advective dispersivity tensor Φ. If the permeability k of ω is a symmetric positive-definite tensor, so is Φ. However, the principal directions and values of these two tensors are generally not the same; whereas those of k are a fixed property of the medium and the length-scale of ω, those of Φ depend additionally on the direction and magnitude of the
Asymmetric spreading in highly advective, disordered environments
Carpenter, John H.; Dahmen, Karin A.
2005-01-01
Spreading of bacteria in a highly advective, disordered environment is examined. Predictions of super-diffusive spreading for a simplified reaction-diffusion equation are tested. Concentration profiles display anomalous growth and super-diffusive spreading. A perturbation analysis yields a crossover time between diffusive and super-diffusive behavior. The time's dependence on the convection velocity and disorder is tested. Like the simplified equation, the full linear reaction-diffusion equat...
Distributed Parallel Particle Advection using Work Requesting
Energy Technology Data Exchange (ETDEWEB)
Muller, Cornelius; Camp, David; Hentschel, Bernd; Garth, Christoph
2013-09-30
Particle advection is an important vector field visualization technique that is difficult to apply to very large data sets in a distributed setting due to scalability limitations in existing algorithms. In this paper, we report on several experiments using work requesting dynamic scheduling which achieves balanced work distribution on arbitrary problems with minimal communication overhead. We present a corresponding prototype implementation, provide and analyze benchmark results, and compare our results to an existing algorithm.
High Order Semi-Lagrangian Advection Scheme
Malaga, Carlos; Mandujano, Francisco; Becerra, Julian
2014-11-01
In most fluid phenomena, advection plays an important roll. A numerical scheme capable of making quantitative predictions and simulations must compute correctly the advection terms appearing in the equations governing fluid flow. Here we present a high order forward semi-Lagrangian numerical scheme specifically tailored to compute material derivatives. The scheme relies on the geometrical interpretation of material derivatives to compute the time evolution of fields on grids that deform with the material fluid domain, an interpolating procedure of arbitrary order that preserves the moments of the interpolated distributions, and a nonlinear mapping strategy to perform interpolations between undeformed and deformed grids. Additionally, a discontinuity criterion was implemented to deal with discontinuous fields and shocks. Tests of pure advection, shock formation and nonlinear phenomena are presented to show performance and convergence of the scheme. The high computational cost is considerably reduced when implemented on massively parallel architectures found in graphic cards. The authors acknowledge funding from Fondo Sectorial CONACYT-SENER Grant Number 42536 (DGAJ-SPI-34-170412-217).
Vertical structure of Advection dominated Accretion Flows
Zeraatgari, Fateme Zahra
2015-01-01
We solve the set of hydrodynamic (HD) equations for optically thin Advection Dominated Accretion Flows (ADAFs) by assuming radially self-similar in spherical coordinate system $ (r, \\theta, \\phi) $. The disk is considered to be steady state and axi-symmetric. We define the boundary conditions at the pole and the equator of the disk and to avoid singularity at the rotation axis, the disk is taken to be symmetric with respect to this axis. Moreover, only the $ \\tau_{r \\phi} $ component of viscous stress tensor is assumed and we have set $ v_{\\theta} = 0 $. The main purpose of this study is to investigate the variation of dynamical quantities of the flow in the vertical direction by finding an analytical solution. As a consequence, we found that the advection parameter, $ f^{adv} $, varies along the $ \\theta $ direction and reaches to its maximum near the rotation axis. Our results also show that, in terms of no-outflow solution, thermal equilibrium still exists and consequently advection cooling can balance vis...
Advective turbulent transport in the fluid plasma
Min, Byung-Hoon; An, Chan-Yong; Kim, Chang-Bae
2013-10-01
The Hasegawa-Wakatani model (HWM) has been employed in pedagogical analyses of the physics behind the behavior of the tokamak plasmas. In addition to the geometric simplicity HWM has an appealing feature of sustaining autonomous quasi-steady state, unstable modes providing the power that is being transported by the nonlinear interactions and is eventually dissipated by the collisional damping at small scales. Emergence of the zonal flow out of the turbulence is a main candidate to cause the transition from the low plasma confinement to the high mode. In the study of such LH transition with the HWM, the adiabaticity parameter has been shown to play an important role in forcing the zonal flow that results in the regulation of the drift-wave turbulence. Instead of concentrating on the physics of the feedback loop between the turbulence and the zonal flow the present study focuses on the presence of the advective transport of the energy. Numerical simulations of HWM are performed and the connections between the advective transport and the zonal flow will be presented. This work was supported by the Supercpmputing Center/Korea Institute of Science and Technology Information with supercomputing resources including technical support (KSC-2013-C1-009).
A Computational Method for Sharp Interface Advection
Roenby, Johan; Jasak, Hrvoje
2016-01-01
We devise a numerical method for passive advection of a surface, such as the interface between two incompressible fluids, across a computational mesh. The method is called isoAdvector, and is developed for general meshes consisting of arbitrary polyhedral cells. The algorithm is based on the volume of fluid (VOF) idea of calculating the volume of one of the fluids transported across the mesh faces during a time step. The novelty of the isoAdvector concept consists in two parts: First, we exploit an isosurface concept for modelling the interface inside cells in a geometric surface reconstruction step. Second, from the reconstructed surface, we model the motion of the face-interface intersection line for a general polygonal face to obtain the time evolution within a time step of the submerged face area. Integrating this submerged area over the time step leads to an accurate estimate for the total volume of fluid transported across the face. The method was tested on simple 2D and 3D interface advection problems ...
Thermal instability of advection-dominated disks against local perturbations
Kato, S; Chen, X; Kato, Shoji; Abramowicz, Marek Artur; Chen, Xingming
1995-01-01
Thermal instability is examined for advection-dominated one-temperature accretion disks. We consider axisymmetric perturbations with short wavelength in the radial direction. The viscosity is assumed to be sufficiently small for the vertical hydrostatic balance to hold in perturbed states. The type of viscosity is given either by the \\alpha-viscosity or by a diffusion-type stress tensor. Optically thick disks are found to be in general more unstable than optically thin ones. When the thermal diffusion is present, the optically thin disks become stable, but the optically thick disks are still unstable. The instability of the advection-dominated disks is different from that of the geometrically thin disks without advection. In the case of no advection, the thermal mode behaves under no appreciable surface density change. In the case of advection-dominated disks, however, the thermal mode occurs with no appreciable pressure change (compared with the density change), when local perturbations are considered. The v...
Predicting salt advection in groundwater from saline aquaculture ponds
Verrall, D. P.; Read, W. W.; Narayan, K. A.
2009-01-01
SummaryThis paper predicts saltwater advection in groundwater from leaky aquaculture ponds. A closed form solution for the potential function, stream function and velocity field is derived via the series solutions method. Numerically integrating along different streamlines gives the location (or advection front) of saltwater throughout the domain for any predefined upper time limit. Extending this process produces a function which predicts advection front location against time. The models considered in this paper are easily modified given knowledge of the required physical parameters.
Contribution of Advective and Non-advective Heat Fluxes to the Heat Budget of a Shallow Lagoon
Directory of Open Access Journals (Sweden)
Rodríguez-Rodríguez Miguel
2005-01-01
Full Text Available The heat budget in a shallow lagoon has been established from field measurements at a bihourly scale. Information on the main advective and non-advective heat fluxes were collected during year 2003 at Nueva lagoon (AlmerÃa, Southern Spain. Heat storage data was obtained from a thermistor chain located in the deepest part of the lagoon and meteorological information was acquired using an automatic meteorological station placed near the lagoon's shore. In addition, estimation of evaporation was inferred from climatic approaches. Inputs of heat energy were dominated by radiative fluxes, with received net radiation accounting on average for around 95% of the non-advective total gains and radiation losses accounting for around 70% of the non-advective total losses. Sensible heat transfer from/to the atmosphere constituted the second energy input (4% and output (20%, although heat losses by evaporation were also significant. Conduction of heat into the sediments was a relatively constant form of energy loss but constitutes a minor contribution on the overall heat budget. Considerable variability was evident in non-advective heat fluxes at different time scales, from diel to seasonal. In relation to advective heat fluxes, groundwater and irrigation surpluses added to the heat storage of Nueva lagoon, whereas heat advected via precipitation was negligible.
New complex variable meshless method for advection-diffusion problems
Institute of Scientific and Technical Information of China (English)
Wang Jian-Fei; Cheng Yu-Min
2013-01-01
In this paper,an improved complex variable meshless method (ICVMM) for two-dimensional advection-diffusion problems is developed based on improved complex variable moving least-square (ICVMLS) approximation.The equivalent functional of two-dimensional advection-diffusion problems is formed,the variation method is used to obtain the equation system,and the penalty method is employed to impose the essential boundary conditions.The difference method for two-point boundary value problems is used to obtain the discrete equations.Then the corresponding formulas of the ICVMM for advection-diffusion problems are presented.Two numerical examples with different node distributions are used to validate and investigate the accuracy and efficiency of the new method in this paper.It is shown that ICVMM is very effective for advection-diffusion problems,and has a good convergent character,accuracy,and computational efficiency.
Anomalous scaling of a scalar field advected by turbulence
Energy Technology Data Exchange (ETDEWEB)
Kraichnan, R.H. [Robert H. Kraichnan, Inc., Santa Fe, NM (United States)
1995-12-31
Recent work leading to deduction of anomalous scaling exponents for the inertial range of an advected passive field from the equations of motion is reviewed. Implications for other turbulence problems are discussed.
Advection around ventilated U-shaped burrows: A model study
Brand, Andreas; Lewandowski, JöRg; Hamann, Enrico; Nützmann, Gunnar
2013-05-01
Advective transport in the porous matrix of sediments surrounding burrows formed by fauna such as Chironomus plumosus has been generally neglected. A positron emission tomography study recently revealed that the pumping activity of the midge larvae can indeed induce fluid flow in the sediment. We present a numerical model study which explores the conditions at which advective transport in the sediment becomes relevant. A 0.15 m deep U-shaped burrow with a diameter of 0.002 m within the sediment was represented in a 3-D domain. Fluid flow in the burrow was calculated using the Navier-Stokes equation for incompressible laminar flow in the burrow, and flow in the sediment was described by Darcy's law. Nonreactive and reactive transport scenarios were simulated considering diffusion and advection. The pumping activity of the model larva results in considerable advective flow in the sediment at reasonable high permeabilities with flow velocities of up to 7.0 × 10-6 m s-1 close to the larva for a permeability of 3 × 10-12 m2. At permeabilities below 7 × 10-13 m2 advection is negligible compared to diffusion. Reactive transport simulations using first-order kinetics for oxygen revealed that advective flux into the sediment downstream of the pumping larva enhances sedimentary uptake, while the advective flux into the burrow upstream of the larvae inhibits diffusive sedimentary uptake. Despite the fact that both effects cancel each other with respect to total solute uptake, the advection-induced asymmetry in concentration distribution can lead to a heterogeneous solute and redox distribution in the sediment relevant to complex reaction networks.
A spatial SIS model in advective heterogeneous environments
Cui, Renhao; Lou, Yuan
2016-09-01
We study the effects of diffusion and advection for a susceptible-infected-susceptible epidemic reaction-diffusion model in heterogeneous environments. The definition of the basic reproduction number R0 is given. If R0 globally asymptotically stable. Asymptotic behaviors of R0 for advection rate and mobility of the infected individuals (denoted by dI) are established, and the existence of the endemic equilibrium when R0 > 1 is studied. The effects of diffusion and advection rates on the stability of the DFE are further investigated. Among other things, we find that if the habitat is a low-risk domain, there may exist one critical value for the advection rate, under which the DFE changes its stability at least twice as dI varies from zero to infinity, while the DFE is unstable for any dI when the advection rate is larger than the critical value. These results are in strong contrast with the case of no advection, where the DFE changes its stability at most once as dI varies from zero to infinity.
Institute of Scientific and Technical Information of China (English)
HUANG Rui Xin
2014-01-01
Gravitational Potential Energy (GPE) change due to horizontal/isopycnal eddy diffusion and advection is examined. Horizontal/isopycnal eddy diffusion is conceptually separated into two steps:stirring and sub-scale diffusion. GPE changes associated with these two steps are analyzed. In addition, GPE changes due to stirring and subscale diffusion associated with horizontal/isopycnal advection in the Eulerian coordinates are analyzed. These formulae are applied to the SODA data for the world oceans. Our analysis indicates that horizontal/isopycnal advection in Eulerian coordinates can introduce large artificial diffusion in the model. It is shown that GPE source/sink in isopycnal coordinates is closely linked to physical property distribution, such as temperature, salinity and velocity. In comparison with z-coordinates, GPE source/sink due to stir-ring/cabbeling associated with isopycnal diffusion/advection is much smaller. Although isopycnal coordi-nates may be a better choice in terms of handling lateral diffusion, advection terms in the traditional Eule-rian coordinates can produce artificial source of GPE due to cabbeling associated with advection. Reducing such numerical errors remains a grand challenge.
Features of a rare advection-radiation fog event
Institute of Scientific and Technical Information of China (English)
2008-01-01
To investigate effects of atmospheric pollutants on fog nature, a comprehensive in situ observation project was implemented in the northern suburb of Nanjing, in December of 2006. For December 24-27 there occurred a heavy fog lasting 4 d in succession. This event is of rare characteristics, namely long persistence, high concentration, tall fog top, acid fog water and explosive growth. Detailed analysis along with the causes of the fog was presented. The evidence suggests that the fog was generated by nighttime radiative cooling, maintained and developed under effects of warm, wet advection. As a result, it is an advection-radiation fog event.
Fast multigrid solution of the advection problem with closed characteristics
Energy Technology Data Exchange (ETDEWEB)
Yavneh, I. [Israel Inst. of Technology, Haifa (Israel); Venner, C.H. [Univ. of Twente, Enschede (Netherlands); Brandt, A. [Weizmann Inst. of Science, Rehovot (Israel)
1996-12-31
The numerical solution of the advection-diffusion problem in the inviscid limit with closed characteristics is studied as a prelude to an efficient high Reynolds-number flow solver. It is demonstrated by a heuristic analysis and numerical calculations that using upstream discretization with downstream relaxation-ordering and appropriate residual weighting in a simple multigrid V cycle produces an efficient solution process. We also derive upstream finite-difference approximations to the advection operator, whose truncation terms approximate {open_quotes}physical{close_quotes} (Laplacian) viscosity, thus avoiding spurious solutions to the homogeneous problem when the artificial diffusivity dominates the physical viscosity.
Simulating magnetised plasma with the versatile advection code
Keppens, R.; Toth, G.; Palma, J. M. L.; Dongarra, J.; Hernandez, V.
1999-01-01
Matter in the universe mainly consists of plasma. The dynamics of plasmas is controlled by magnetic fields. To simulate the evolution of magnetised plasma, we solve the equations of magnetohydrodynamics using the Versatile Advection Code (VAC). To demonstrate the versatility of VAC, we present calcu
Theory of advection-driven long range biotic transport
We propose a simple mechanistic model to examine the effects of advective flow on the spread of fungal diseases spread by wind-blown spores. The model is defined by a set of two coupled non-linear partial differential equations for spore densities. One equation describes the long-distance advectiv...
Consistency Problem with Tracer Advection in the Atmospheric Model GAMIL
Institute of Scientific and Technical Information of China (English)
ZHANG Kai; WAN Hui; WANG Bin; ZHANG Meigen
2008-01-01
The radon transport test,which is a widely used test case for atmospheric transport models,is carried out to evaluate the tracer advection schemes in the Grid-Point Atmospheric Model of IAP-LASG (GAMIL).TWO of the three available schemes in the model are found to be associated with significant biases in the polar regions and in the upper part of the atmosphere,which implies potentially large errors in the simulation of ozone-like tracers.Theoretical analyses show that inconsistency exists between the advection schemes and the discrete continuity equation in the dynamical core of GAMIL and consequently leads to spurious sources and sinks in the tracer transport equation.The impact of this type of inconsistency is demonstrated by idealized tests and identified as the cause of the aforementioned biases.Other potential effects of this inconsistency are also discussed.Results of this study provide some hints for choosing suitable advection schemes in the GAMIL model.At least for the polar-region-concentrated atmospheric components and the closely correlated chemical species,the Flux-Form Semi-Lagrangian advection scheme produces more reasonable simulations of the large-scale transport processes without significantly increasing the computational expense.
Advective and diffusive cosmic ray transport in galactic haloes
Heesen, Volker; Krause, Marita; Beck, Rainer; Stein, Yelena
2016-01-01
We present 1D cosmic ray transport models, numerically solving equations of pure advection and diffusion for the electrons and calculating synchrotron emission spectra. We find that for exponential halo magnetic field distributions advection leads to approximately exponential radio continuum intensity profiles, whereas diffusion leads to profiles that can be better approximated by a Gaussian function. Accordingly, the vertical radio spectral profiles for advection are approximately linear, whereas for diffusion they are of `parabolic' shape. We compare our models with deep ATCA observations of two edge-on galaxies, NGC 7090 and 7462, at $\\lambda\\lambda$ 22 and 6 cm. Our result is that the cosmic ray transport in NGC 7090 is advection dominated with $V=150^{+80}_{-30}~\\rm km\\,s^{-1}$, and that the one in NGC 7462 is diffusion dominated with $D=3.0\\pm 1.0 \\times 10^{28}E_{\\rm GeV}^{0.5}~\\rm cm^2\\,s^{-1}$. NGC 7090 has both a thin and thick radio disc with respective magnetic field scale heights of $h_{\\rm B1}=0...
Fractional gradient and its application to the fractional advection equation
D'Ovidio, M; Garra, R.
2013-01-01
In this paper we provide a definition of fractional gradient operators, related to directional derivatives. We develop a fractional vector calculus, providing a probabilistic interpretation and mathematical tools to treat multidimensional fractional differential equations. A first application is discussed in relation to the d-dimensional fractional advection-dispersion equation. We also study the connection with multidimensional L\\'evy processes.
Institute of Scientific and Technical Information of China (English)
HUANG Rui Xin
2014-01-01
Gravitational potential energy (GPE) source and sink due to stirring and cabbeling associated with sigma dif-fusion/advection is analyzed. It is shown that GPE source and sink is too big, and they are not closely linked to physical property distribution, such as temperature, salinity and velocity. Although the most frequently quoted advantage of sigma coordinate models are their capability of dealing with topography;the exces-sive amount of GPE source and sink due to stirring and cabbeling associated with sigma diffusion/advec-tion diagnosed from our analysis raises a very serious question whether the way lateral diffusion/advection simulated in the sigma coordinates model is physically acceptable. GPE source and sink in three coordinates is dramatically different in their magnitude and patterns. Overall, in terms of simulating lateral eddy diffu-sion and advection isopycnal coordinates is the best choice and sigma coordinates is the worst. The physical reason of the excessive GPE source and sink in sigma coordinates is further explored in details. However, even in the isopycnal coordinates, simulation based on the Eulerian coordinates can be contaminated by the numerical errors associated with the advection terms.
Cellwise conservative unsplit advection for the volume of fluid method
DEFF Research Database (Denmark)
Comminal, Raphaël; Spangenberg, Jon; Hattel, Jesper Henri
2015-01-01
We present a cellwise conservative unsplit (CCU) advection scheme for the volume of fluid method (VOF) in 2D. Contrary to other schemes based on explicit calculations of the flux balances, the CCU advection adopts a cellwise approach where the pre-images of the control volumes are traced...... improvements of the VOF method with the use of more precise interface representation techniques and the future extension of the CCU scheme to 3D are discussed. ©2014 Elsevier Inc. All rights reserved.......-order Runge–Kutta method, where intermediate velocities along pathlines are determined with quadratic temporal and bicubic spatial interpolations. The volumes of the donating regions are corrected in order to fulfill the discrete continuity of incompressible flows. Consequently, the calculation produces non...
The multifractal structure of chaotically advected chemical fields
Neufeld, Z; Hernández-García, E; Tél, T; Neufeld, Zoltan; Lopez, Cristobal; Hernandez-Garcia, Emilio; Tel, Tamas
1999-01-01
The structure of the concentration field of a decaying substance produced by chemical sources and advected by a smooth incompressible two-dimensional flow is investigated. We focus our attention on the non-uniformities of the Hölder exponent of the resulting filamental chemical field. They appear most evidently in the case of open flows where irregularities of the field exhibit strong spatial intermittency as they are restricted to a fractal manifold. Non-uniformities of the Hölder exponent of the chemical field in closed flows appears as a consequence of the non-uniform stretching of the fluid elements. We study how this affects the scaling exponents of the structure functions, displaying anomalous scaling, and relate the scaling exponents to the distribution of finite-time Lyapunov exponents of the advection dynamics. Theoretical predictions are compared with numerical experiments.
Advection equation analysed by two-timing method
Vladimirov, V A
2016-01-01
The aim of this paper is to study and classify the multiplicity of distinguished limits and asymptotic solutions for the advection equation with a general oscillating velocity field with the systematic use of the two-timing method. Our results are: (i) the dimensionless advection equation contains two independent small parameters, which represent the ratio of two characteristic time-scales and the spatial amplitudes of oscillations; the scaling of the variables and parameters contains Strouhal number; (ii) an infinite sequence of distinguished limits has been identified; this sequence corresponds to the successive degenerations of a drift velocity; (iii) we have derived the averaged and oscillatory equations for the first four distinguished limits; derivations are performed up to the forth orders in small parameters; (v) we have shown, that each distinguish limit solution generates an infinite number of parametric solutions; these solutions differ from each other by the slow time-scale and the amplitude of pr...
Features of a rare advection-radiation event
Institute of Scientific and Technical Information of China (English)
PU MeiJuan; ZHANG GuoZheng; YAN WenLian; LI ZiHua
2008-01-01
To investigate effects of atmospheric pollutants on fog nature,a comprehensive in situ observation project was implemented in the northern suburb of Nanjing,in December of 2006. For December 24-27 there occurred a heavy fog lasting 4 d in succession. This event is of rare characteristics,namely long persistence,high concentration,tall fog top,acid fog water and explosive growth. Detailed analysis along with the causes of the fog was presented. The evidence suggests that the fog was generated by nighttime radiative cooling,maintained and developed under effects of warm,wet advection. As a result,it is an advection-radiation fog event.
Oceanic heat advection to the Arctic in the last Millennium
Spielhagen, Robert F.; Werner, Kirstin; Aagaard-Sørensen, Steffen; Zamelczyk, Katarzyna; Kandiano, Evguenia; Budeus, Gereon; Husum, Katrine; Marchitto, Thomas M.; Hald, Morten
2011-01-01
EGU2011-8738 At present, the Arctic is responding faster to global warming than most other areas on earth, as indicated by rising air temperatures, melting glaciers and ice sheets and a decline of the sea ice cover. As part of the meridional overturning circulation which connects all ocean basins and influences global climate, northward flowing Atlantic Water is the major means of heat and salt advection towards the Arctic where it strongly affects the sea ice distribution. Records of its ...
Lattice Boltzmann method for the fractional advection-diffusion equation.
Zhou, J G; Haygarth, P M; Withers, P J A; Macleod, C J A; Falloon, P D; Beven, K J; Ockenden, M C; Forber, K J; Hollaway, M J; Evans, R; Collins, A L; Hiscock, K M; Wearing, C; Kahana, R; Villamizar Velez, M L
2016-04-01
Mass transport, such as movement of phosphorus in soils and solutes in rivers, is a natural phenomenon and its study plays an important role in science and engineering. It is found that there are numerous practical diffusion phenomena that do not obey the classical advection-diffusion equation (ADE). Such diffusion is called abnormal or superdiffusion, and it is well described using a fractional advection-diffusion equation (FADE). The FADE finds a wide range of applications in various areas with great potential for studying complex mass transport in real hydrological systems. However, solution to the FADE is difficult, and the existing numerical methods are complicated and inefficient. In this study, a fresh lattice Boltzmann method is developed for solving the fractional advection-diffusion equation (LabFADE). The FADE is transformed into an equation similar to an advection-diffusion equation and solved using the lattice Boltzmann method. The LabFADE has all the advantages of the conventional lattice Boltzmann method and avoids a complex solution procedure, unlike other existing numerical methods. The method has been validated through simulations of several benchmark tests: a point-source diffusion, a boundary-value problem of steady diffusion, and an initial-boundary-value problem of unsteady diffusion with the coexistence of source and sink terms. In addition, by including the effects of the skewness β, the fractional order α, and the single relaxation time τ, the accuracy and convergence of the method have been assessed. The numerical predictions are compared with the analytical solutions, and they indicate that the method is second-order accurate. The method presented will allow the FADE to be more widely applied to complex mass transport problems in science and engineering.
NUMERICAL SIMULATIONS OF SEA ICE WITH DIFFERENT ADVECTION SCHEMES
Institute of Scientific and Technical Information of China (English)
LIU Xi-ying
2011-01-01
Numerical simulations are carried out for sea ice with four different advection schemes to study their effects on the simulation results.The sea ice model employed here is the Sea Ice Simulator (SIS) of the Geophysical Fluid Dynamics Laboratory (GFDL) Modular Ocean Model version 4b (MOM4b) and the four advection schemes are, the upwind scheme originally used in the SIS, the Multi-Dimensional Positive Advection (MDPA) scheme, the Incremental Remapping Scheme (IRS) and the Two Step Shape Preserving (TSSP) scheme.The latter three schemes are newly introduced.To consider the interactions between sea ice and ocean, a mixed layer ocean model is introduced and coupled to the SIS.The coupled model uses a tri-polar coordinate with 120×65 grids,covering the whole earth globe, in the horizontal plane.Simulation results in the northern high latitudes are analyzed.In all simulations, the model reproduces the seasonal variation of sea ice in the northern high latitudes well.Compared with the results from the observation, the sea ice model produces some extra sea ice coverage in the Greenland Sea and Barents Sea in winter due to the exclusion of ocean current effects and the smaller simulated sea ice thickness in the Arctic basin.There are similar features among the results obtained with the introduced three advection schemes.The simulated sea ice thickness with the three newly introduced schemes are all smaller than that of the upwind scheme and the simulated sea ice velocities of movement are all smaller than that of the upwind scheme.There are more similarities shared in the results obtained with the MPDA and TSSP schemes.
Cellwise conservative unsplit advection for the volume of fluid method
Comminal, Raphaël; Spangenberg, Jon; Hattel, Jesper Henri
2015-02-01
We present a cellwise conservative unsplit (CCU) advection scheme for the volume of fluid method (VOF) in 2D. Contrary to other schemes based on explicit calculations of the flux balances, the CCU advection adopts a cellwise approach where the pre-images of the control volumes are traced backwards through the flow map. The donating regions of the fluxes are calculated via the streaklines of the grid intersections, represented as polygonal chains whose vertices are determined by backward tracing of particles injected in the flow at different times. High order accuracy is obtained from the fourth-order Runge-Kutta method, where intermediate velocities along pathlines are determined with quadratic temporal and bicubic spatial interpolations. The volumes of the donating regions are corrected in order to fulfill the discrete continuity of incompressible flows. Consequently, the calculation produces non-overlapping donating regions and pre-images with conforming edges to their neighbors, resulting in the conservativeness and the boundedness (liquid volume fraction inside the interval [ 0 , 1 ]) of the CCU advection scheme. Finally, the update of the liquid volume fractions is computed from the intersections of the pre-image polygons with the reconstructed interfaces. The CCU scheme is tested on several benchmark tests for the VOF advection, together with the standard piecewise linear interface calculation (PLIC). The geometrical errors of the CCU compare favorably with other unsplit VOF-PLIC schemes. Finally, potential improvements of the VOF method with the use of more precise interface representation techniques and the future extension of the CCU scheme to 3D are discussed.
Oscillatory convection in binary mixtures: thermodiffusion, solutal buoyancy, and advection
Jung, D.; Matura, P.; Luecke, M.
2005-01-01
The role of thermodiffusive generation of concentration fluctuations via the Soret effect, their contribution to the buoyancy forces that drive convection, the advective mixing effect of the latter, and the diffusive homogenisation are compared and elucidated for oscillatory convection. Numerically obtained solutions of the field equations in the form of spatially extended relaxed traveling waves, of standing waves, and of the transient growth of standing waves and their transition to traveli...
Lattice Boltzmann method for the fractional advection-diffusion equation
Zhou, J. G.; Haygarth, P. M.; Withers, P. J. A.; Macleod, C. J. A.; Falloon, P. D.; Beven, K. J.; Ockenden, M. C.; Forber, K. J.; Hollaway, M. J.; Evans, R.; Collins, A. L.; Hiscock, K. M.; Wearing, C.; Kahana, R.; Villamizar Velez, M. L.
2016-04-01
Mass transport, such as movement of phosphorus in soils and solutes in rivers, is a natural phenomenon and its study plays an important role in science and engineering. It is found that there are numerous practical diffusion phenomena that do not obey the classical advection-diffusion equation (ADE). Such diffusion is called abnormal or superdiffusion, and it is well described using a fractional advection-diffusion equation (FADE). The FADE finds a wide range of applications in various areas with great potential for studying complex mass transport in real hydrological systems. However, solution to the FADE is difficult, and the existing numerical methods are complicated and inefficient. In this study, a fresh lattice Boltzmann method is developed for solving the fractional advection-diffusion equation (LabFADE). The FADE is transformed into an equation similar to an advection-diffusion equation and solved using the lattice Boltzmann method. The LabFADE has all the advantages of the conventional lattice Boltzmann method and avoids a complex solution procedure, unlike other existing numerical methods. The method has been validated through simulations of several benchmark tests: a point-source diffusion, a boundary-value problem of steady diffusion, and an initial-boundary-value problem of unsteady diffusion with the coexistence of source and sink terms. In addition, by including the effects of the skewness β , the fractional order α , and the single relaxation time τ , the accuracy and convergence of the method have been assessed. The numerical predictions are compared with the analytical solutions, and they indicate that the method is second-order accurate. The method presented will allow the FADE to be more widely applied to complex mass transport problems in science and engineering.
Energy Technology Data Exchange (ETDEWEB)
NONE
1998-12-31
This conference day was jointly organized by the `university group of thermal engineering (GUT)` and the French association of thermal engineers. This book of proceedings contains 7 papers entitled: `energy spectra of a passive scalar undergoing advection by a chaotic flow`; `analysis of chaotic behaviours: from topological characterization to modeling`; `temperature homogeneity by Lagrangian chaos in a direct current flow heat exchanger: numerical approach`; ` thermal instabilities in a mixed convection phenomenon: nonlinear dynamics`; `experimental characterization study of the 3-D Lagrangian chaos by thermal analogy`; `influence of coherent structures on the mixing of a passive scalar`; `evaluation of the performance index of a chaotic advection effect heat exchanger for a wide range of Reynolds numbers`. (J.S.)
Ancey, Christophe; Bohorquez, Patricio; Heyman, Joris
2016-04-01
The advection-diffusion equation arises quite often in the context of sediment transport, e.g., for describing time and space variations in the particle activity (the solid volume of particles in motion per unit streambed area). Stochastic models can also be used to derive this equation, with the significant advantage that they provide information on the statistical properties of particle activity. Stochastic models are quite useful when sediment transport exhibits large fluctuations (typically at low transport rates), making the measurement of mean values difficult. We develop an approach based on birth-death Markov processes, which involves monitoring the evolution of the number of particles moving within an array of cells of finite length. While the topic has been explored in detail for diffusion-reaction systems, the treatment of advection has received little attention. We show that particle advection produces nonlocal effects, which are more or less significant depending on the cell size and particle velocity. Albeit nonlocal, these effects look like (local) diffusion and add to the intrinsic particle diffusion (dispersal due to velocity fluctuations), with the important consequence that local measurements depend on both the intrinsic properties of particle displacement and the dimensions of the measurement system.
Subsurface barrier design alternatives for confinement and controlled advection flow
International Nuclear Information System (INIS)
Various technologies and designs are being considered to serve as subsurface barriers to confine or control contaminant migration from underground waste storage or disposal structures containing radioactive and hazardous wastes. Alternatives including direct-coupled flood and controlled advection designs are described as preconceptual examples. Prototype geotechnical equipment for testing and demonstration of these alternative designs tested at the Hanford Geotechnical Development and Test Facility and the Hanford Small-Tube Lysimeter Facility include mobile high-pressure injectors and pumps, mobile transport and pumping units, vibratory and impact pile drivers, and mobile batching systems. Preliminary laboratory testing of barrier materials and additive sequestering agents have been completed and are described
Waste dissolution with chemical reaction, diffusion and advection
International Nuclear Information System (INIS)
This paper extends the mass-transfer analysis to include the effect of advective transport in predicting the steady-state dissolution rate, with a chemical-reaction-rate boundary condition at the surface of a waste form of arbitrary shape. This new theory provides an analytic means of predicting the ground-water velocities at which dissolution rate in a geologic environment will be governed entirely to the chemical reaction rate. As an illustration, we consider the steady-state potential flow of ground water in porous rock surrounding a spherical waste solid. 3 refs., 2 figs
Chaotic advection in 2D anisotropic porous media
Varghese, Stephen; Speetjens, Michel; Trieling, Ruben; Toschi, Federico
2015-11-01
Traditional methods for heat recovery from underground geothermal reservoirs employ a static system of injector-producer wells. Recent studies in literature have shown that using a well-devised pumping scheme, through actuation of multiple injector-producer wells, can dramatically enhance production rates due to the increased scalar / heat transport by means of chaotic advection. However the effect of reservoir anisotropy on kinematic mixing and heat transport is unknown and has to be incorporated and studied for practical deployment in the field. As a first step, we numerically investigate the effect of anisotropy (both magnitude and direction) on (chaotic) advection of passive tracers in a time-periodic Darcy flow within a 2D circular domain driven by periodically reoriented diametrically opposite source-sink pairs. Preliminary results indicate that anisotropy has a significant impact on the location, shape and size of coherent structures in the Poincare sections. This implies that the optimal operating parameters (well spacing, time period of well actuation) may vary strongly and must be carefully chosen so as to enhance subsurface transport. This work is part of the research program of the Foundation for Fundamental Research on Matter (FOM), which is part of Netherlands Organisation for Scientific Research (NWO). This research program is co-financed by Shell Global Solutions International B.V.
Multiple anisotropic collisions for advection-diffusion Lattice Boltzmann schemes
Ginzburg, Irina
2013-01-01
This paper develops a symmetrized framework for the analysis of the anisotropic advection-diffusion Lattice Boltzmann schemes. Two main approaches build the anisotropic diffusion coefficients either from the anisotropic anti-symmetric collision matrix or from the anisotropic symmetric equilibrium distribution. We combine and extend existing approaches for all commonly used velocity sets, prescribe most general equilibrium and build the diffusion and numerical-diffusion forms, then derive and compare solvability conditions, examine available anisotropy and stable velocity magnitudes in the presence of advection. Besides the deterioration of accuracy, the numerical diffusion dictates the stable velocity range. Three techniques are proposed for its elimination: (i) velocity-dependent relaxation entries; (ii) their combination with the coordinate-link equilibrium correction; and (iii) equilibrium correction for all links. Two first techniques are also available for the minimal (coordinate) velocity sets. Even then, the two-relaxation-times model with the isotropic rates often gains in effective stability and accuracy. The key point is that the symmetric collision mode does not modify the modeled diffusion tensor but it controls the effective accuracy and stability, via eigenvalue combinations of the opposite parity eigenmodes. We propose to reduce the eigenvalue spectrum by properly combining different anisotropic collision elements. The stability role of the symmetric, multiple-relaxation-times component, is further investigated with the exact von Neumann stability analysis developed in diffusion-dominant limit.
Toward enhanced subsurface intervention methods using chaotic advection.
Trefry, Michael G; Lester, Daniel R; Metcalfe, Guy; Ord, Alison; Regenauer-Lieb, Klaus
2012-01-01
Many intervention activities in the terrestrial subsurface involve the need to recover/emplace distributions of scalar quantities (e.g. dissolved phase concentrations or heat) from/in volumes of saturated porous media. These scalars can be targeted by pump-and-treat methods or by amendment technologies. Application examples include in-situ leaching for metals, recovery of dissolved contaminant plumes, or utilizing heat energy in geothermal reservoirs. While conventional pumping methods work reasonably well, costs associated with maintaining pumping schedules are high and improvements in efficiency would be welcome. In this paper we discuss how transient switching of the pressure at different wells can intimately control subsurface flow, generating a range of "programmed" flows with various beneficial characteristics. Some programs produce chaotic flows which accelerate mixing, while others create encapsulating flows which can isolate fluid zones for lengthy periods. In a simplified model of an aquifer subject to balanced pumping, chaotic flow topologies have been predicted theoretically and verified experimentally using Hele-Shaw cells. Here, a survey of the key characteristics of chaotic advection is presented. Mathematical methods are used to show how these characteristics may translate into practical situations involving regional flows and heterogeneity. The results are robust to perturbations, and withstand significant aquifer heterogeneity. It is proposed that chaotic advection may form the basis of new efficient technologies for groundwater interventions.
A cryogenic circulating advective multi-pass absorption cell
Stockett, M. H.; Lawler, J. E.
2012-03-01
A novel absorption cell has been developed to enable a spectroscopic survey of a broad range of polycyclic aromatic hydrocarbons (PAH) under astrophysically relevant conditions and utilizing a synchrotron radiation continuum to test the still controversial hypothesis that these molecules or their ions could be carriers of the diffuse interstellar bands. The cryogenic circulating advective multi-pass absorption cell resembles a wind tunnel; molecules evaporated from a crucible or injected using a custom gas feedthrough are entrained in a laminar flow of cryogenically cooled buffer gas and advected into the path of the synchrotron beam. This system includes a multi-pass optical White cell enabling absorption path lengths of hundreds of meters and a detection sensitivity to molecular densities on the order of 107 cm-3. A capacitively coupled radio frequency dielectric barrier discharge provides ionized and metastable buffer gas atoms for ionizing the candidate molecules via charge exchange and the Penning effect. Stronger than expected clustering of PAH molecules has slowed efforts to record gas phase PAH spectra at cryogenic temperatures, though such clusters may play a role in other interstellar phenomena.
Horizontal advection, diffusion and plankton spectra at the sea surface.
Bracco, A.; Clayton, S.; Pasquero, C.
2009-04-01
Plankton patchiness is ubiquitous in the oceans, and various physical and biological processes have been proposed as its generating mechanisms. However, a coherent statement on the problem is missing, due to both a small number of suitable observations and to an incomplete understanding of the properties of reactive tracers in turbulent media. Abraham (1998) suggested that horizontal advection may be the dominant process behind the observed distributions of phytoplankton and zooplankton, acting to mix tracers with longer reaction times (Rt) down to smaller scales. Conversely, Mahadevan and Campbell (2002) attributed the relative distributions of sea surface temperature and phytoplankton to small scale upwelling, where tracers with longer Rt are able to homogenize more than those with shorter reaction times. Neither of the above mechanisms can explain simultaneously the (relative) spectral slopes of temperature, phytoplankton and zooplankton. Here, with a simple advection model and a large suite of numerical experiments, we concentrate on some of the physical processes influencing the relative distributions of tracers at the ocean surface, and we investigate: 1) the impact of the spatial scale of tracer supply; 2) the role played by coherent eddies on the distribution of tracers with different Rt; 3) the role of diffusion (so far neglected). We show that diffusion determines the distribution of temperature, regardless of the nature of the forcing. We also find that coherent structures together with differential diffusion of tracers with different Rt impact the tracer distributions. This may help in understanding the highly variable nature of observed plankton spectra.
OBSERVATION OF MAGNETIC RECONNECTION DRIVEN BY GRANULAR SCALE ADVECTION
Energy Technology Data Exchange (ETDEWEB)
Zeng Zhicheng; Cao Wenda [Center for Solar-Terrestrial Research, New Jersey Institute of Technology, 323 Martin Luther King Blvd., Newark, NJ 07102 (United States); Ji Haisheng [Big Bear Solar Observatory, 40386 North Shore Lane, Big Bear City, CA 92314 (United States)
2013-06-01
We report the first evidence of magnetic reconnection driven by advection in a rapidly developing large granule using high spatial resolution observations of a small surge event (base size {approx} 4'' Multiplication-Sign 4'') with the 1.6 m aperture New Solar Telescope at the Big Bear Solar Observatory. The observations were carried out in narrowband (0.5 A) He I 10830 A and broadband (10 A) TiO 7057 A. Since He I 10830 A triplet has a very high excitation level and is optically thin, its filtergrams enable us to investigate the surge from the photosphere through the chromosphere into the lower corona. Simultaneous space data from the Atmospheric Imaging Assembly and Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory were used in the analysis. It is shown that the surge is spatio-temporally associated with magnetic flux emergence in the rapidly developing large granule. During the development of the granule, its advecting flow ({approx}2 km s{sup -1}) squeezed the magnetic flux into an intergranular lane area, where a magnetic flux concentration was formed and the neighboring flux with opposite magnetic polarity was canceled. During the cancellation, the surge was produced as absorption in He I 10830 A filtergrams while simultaneous EUV brightening occurred at its base. The observations clearly indicate evidence of a finest-scale reconnection process driven by the granule's motion.
Finite amplitude gravity waves: Harmonics, advective steepening, breaking and saturation
Weinstock, J.
1985-01-01
A simple theory is presented which determines details of the breaking and saturation of a gravity wave as it propagates upward in the atmosphere. Breaking and saturation are here due to nonlinear advection analogous to the breaching of a surface wave and to the breaking of a planetary wave. Much simplification is obtained by the assumption that in a wave packet consisting of a primary wave and its harmonics, the primary wave remains dominant. This assumption, referred to a quasi-monochromatic approximation, is suggested by observations. Determined by this approximate theory are: a detailed picture of the waveform as it steepens and breaks; harmonics of the wave; the turbulence generation; and an underlying relationship between superadiabatic lapse rate and saturation by wave-wave interactions.
On the Structure of Advective Accretion Disks At High Luminosity
Artemova, I V; Igumenshchev, I V; Novikov, I D; Artemova, Ioulia V.; Bisnovatyi-Kogan, Gennadi S.; Igumenshchev, Igor V.; Novikov, Igor D.
2001-01-01
Global solutions of optically thick advective accretion disks around blackholes are constructed. The solutions are obtained by solving numerically a setof ordinary differential equations corresponding to a steady axisymmetricgeometrically thin disk. We pay special attention to consistently satisfy theregularity conditions at singular points of the equations. For this reason weanalytically expand a solution at the singular point, and use coefficients ofthe expansion in our iterative numerical procedure. We obtain consistenttransonic solutions in a wide range of values of the viscosity parameter alphaand mass acretion rate. We compare two different form of viscosity: one takesthe shear stress to be proportional to the pressure, while the other uses theangular velocity gradient-dependent stress. We find that there are two singular points in solutions corresponding to thepressure-proportional shear stress. The inner singular point locates close tothe last stable orbit around black hole. This point changes its typ...
Advection of nematic liquid crystals by chaotic flow
O'Naraigh, Lennon
2016-01-01
Consideration is given to the effects of inhomogeneous shear flow (both regular and chaotic) on nematic liquid crystals in a planar two-dimensional geometry. The Landau-de Gennes equation coupled to an externally-prescribed flow field is the basis for the study: this is solved numerically in a periodic spatial domain. The focus is on a limiting case where the advection is passive, such that variations in the liquid-crystal properties do not feed back into the equation of motion for the uid velocity. The numerical simulations demonstrate that the coarsening of the liquid-crystal domains is arrested by the ow. The nature of the arrest is different depending on whether the flow is regular or chaotic. For the specific case where tumbling is important, the flow has a strong effect on the the liquid-crystal morphology: this provides a mechanism for controlling the shape of the liquid-crystal domains.
A high-order splitting scheme for the advection-diffusion equation of pollutants
Institute of Scientific and Technical Information of China (English)
无
2001-01-01
A high-order splitting scheme for the advection-diffusion equation of pollutants is proposed in this paper. The multidimensional advection-diffusion equation is splitted into several one-dimensional equations that are solved by the scheme. Only three spatial grid points are needed in each direction and the scheme has fourth-order spatial accuracy. Several typically pure advection and advection-diffusion problems are simulated. Numerical results show that the accuracy of the scheme is much higher than that of the classical schemes and the scheme can be efficiently solved with little programming effort.
Algebraic dynamics solution to and algebraic dynamics algorithm for nonlinear advection equation
Institute of Scientific and Technical Information of China (English)
2008-01-01
Algebraic dynamics approach and algebraic dynamics algorithm for the solution of nonlinear partial differential equations are applied to the nonlinear advection equa-tion. The results show that the approach is effective for the exact analytical solu-tion and the algorithm has higher precision than other existing algorithms in nu-merical computation for the nonlinear advection equation.
Nucleosynthesis in Advective Accretion Disks Around Galactic and Extra-Galactic Black Holes
Mukhopadhyay, B
1998-01-01
We compute the nucleosynthesis of materials inside advective disks around black holes. We show that composition of incoming matter can change significantly depending on the accretion rate and accretion disks. These works are improvements on the earlier works in thick accretion disks of Chakrabarti, Jin & Arnett (1987) in presence of advection in the flow.
Analytical solution for the advection-dispersion transport equation in layered media
The advection-dispersion transport equation with first-order decay was solved analytically for multi-layered media using the classic integral transform technique (CITT). The solution procedure used an associated non-self-adjoint advection-diffusion eigenvalue problem that had the same form and coef...
Mass loss from advective accretion disc around rotating black holes
Aktar, Ramiz; Nandi, Anuj
2015-01-01
We examine the properties of the outflowing matter from an advective accretion disc around a spinning black hole. During accretion, rotating matter experiences centrifugal pressure supported shock transition that effectively produces a virtual barrier around the black hole in the form of post-shock corona (hereafter, PSC). Due to shock compression, PSC becomes hot and dense that eventually deflects a part of the inflowing matter as bipolar outflows because of the presence of extra thermal gradient force. In our approach, we study the outflow properties in terms of the inflow parameters, namely specific energy (${\\mathcal E}$) and specific angular momentum ($\\lambda$) considering the realistic outflow geometry around the rotating black holes. We find that spin of the black hole ($a_k$) plays an important role in deciding the outflow rate $R_{\\dot m}$ (ratio of mass flux of outflow and inflow), in particular, $R_{\\dot m}$ is directly correlated with $a_k$ for the same set of inflow parameters. It is found that ...
Implementation of Two Component Advective Flow Solution in XSPEC
Debnath, Dipak; Mondal, Santanu
2014-01-01
Spectral and Temporal properties of black hole candidates can be explained reasonably well using Chakrabarti-Titarchuk solution of two component advective flow (TCAF). This model requires two accretion rates, namely, the Keplerian disk accretion rate and the halo accretion rate, the latter being composed of a sub-Keplerian, low angular momentum flow which may or may not develop a shock. In this solution, the relevant parameter is the relative importance of the halo (which creates the Compton cloud region) rate with respect to the Keplerian disk rate (soft photon source). Though this model has been used earlier to manually fit data of several black hole candidates quite satisfactorily, for the first time, we made it user friendly by implementing it into XSPEC software of GSFC/NASA. This enables any user to extract physical parameters of the accretion flows, such as two accretion rates, the shock location, the shock strength etc. for any black hole candidate. We provide some examples of fitting a few cases usin...
Is the accretion flow in NGC 4258 advection-dominated?
Lasota, J P; Chen, X; Krolik, J H; Narayan, R; Yi, I
1995-01-01
The mass of the central black hole in the active galaxy NGC 4258 (M106) has been measured to be M=3.6\\times10^7\\Msun (Miyoshi et al. 1995). The Eddington luminosity corresponding to this mass is L_E=4.5\\times10^{45} erg s^{-1}. By contrast the X-ray luminosity of the nucleus of NGC 4258 between 2-10 keV is (4\\pm 1)\\times10^{40}~{\\rm erg\\,s^{-1}} while the optical/UV luminosity is less than 1.5\\times10^{42} ~{\\rm erg\\,s^{-1}}. The luminosity of NGC 4258 is therefore extremely sub-Eddington, L\\sim10^{-5}L_E in X-rays and L\\sim3\\times10^{-4} L_E even if we take the maximum optical/UV luminosity. Assuming the usual accretion efficiency of 0.1 would imply accretion rates orders of magnitude lower than in Seyfert galaxies and quasars. We show that the properties of the AGN in NGC 4258 can be explained by an accretion flow in the form of a very hot, optically-thin plasma which advects most of the viscously generated thermal energy into the central black hole and radiates only a small fraction of the energy. In this ...
Standing Shock Instability in Advection-Dominated Accretion Flows
Le, Truong; Wolff, Michael T; Becker, Peter A; Putney, Joy
2015-01-01
Depending on the values of the energy and angular momentum per unit mass in the gas supplied at large radii, inviscid advection-dominated accretion flows can display velocity profiles with either pre-shock deceleration or pre-shock acceleration. Nakayama has shown that these two types of flow configurations are expected to have different stability properties. By employing the Chevalier & Imamura linearization method and the Nakayama instability boundary conditions, we discover that there are regions of parameters space where disk/shocks with outflows can be stable or unstable. In region of instability, we find that pre-shock deceleration is always unstable to the zeroth mode with zero frequency of oscillation, but is always stable to the fundamental and overtones. Furthermore, we also find that pre-shock acceleration is always unstable to the zeroth mode, and that the fundamental and overtones become increasingly less stable as the shock location moves away from the horizon when the disk half-height expan...
Round window membrane intracochlear drug delivery enhanced by induced advection.
Borkholder, David A; Zhu, Xiaoxia; Frisina, Robert D
2014-01-28
Delivery of therapeutic compounds to the inner ear via absorption through the round window membrane (RWM) has advantages over direct intracochlear infusions; specifically, minimizing impact upon functional hearing measures. However, previous reports show that significant basal-to-apical concentration gradients occur, with the potential to impact treatment efficacy. Here we present a new approach to inner ear drug delivery with induced advection aiding distribution of compounds throughout the inner ear in the murine cochlea. Polyimide microtubing was placed near the RWM niche through a bullaostomy into the middle ear cavity allowing directed delivery of compounds to the RWM. We hypothesized that a posterior semicircular canalostomy would induce apical flow from the patent cochlear aqueduct to the canalostomy due to influx of cerebral spinal fluid. To test this hypothesis, young adult CBA/CaJ mice were divided into two groups: bullaostomy approach only (BA) and bullaostomy+canalostomy (B+C). Cochlear function was evaluated by distortion product otoacoustic emission (DPOAE) and auditory brainstem response (ABR) thresholds during and after middle ear infusion of salicylate in artificial perilymph (AP), applied near the RWM. The mice recovered for 1week, and were re-tested. The results demonstrate there was no significant impact on auditory function utilizing the RWM surgical procedure with or without the canalostomy, and DPOAE thresholds were elevated reversibly during the salicylate infusion. Comparing the threshold shifts for both methods, the B+C approach had more of a physiological effect than the BA approach, including at lower frequencies representing more apical cochlear locations. Unlike mouse cochleostomies, there was no deleterious auditory functional impact after 1week recovery from surgery. The B+C approach had more drug efficacy at lower frequencies, underscoring potential benefits for more precise control of delivery of inner ear therapeutic compounds.
Verification of Advective Bar Elements Implemented in the Aria Thermal Response Code.
Energy Technology Data Exchange (ETDEWEB)
Mills, Brantley [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
2016-01-01
A verification effort was undertaken to evaluate the implementation of the new advective bar capability in the Aria thermal response code. Several approaches to the verification process were taken : a mesh refinement study to demonstrate solution convergence in the fluid and the solid, visually examining the mapping of the advective bar element nodes to the surrounding surfaces, and a comparison of solutions produced using the advective bars for simple geometries with solutions from commercial CFD software . The mesh refinement study has shown solution convergence for simple pipe flow in both temperature and velocity . Guidelines were provided to achieve appropriate meshes between the advective bar elements and the surrounding volume. Simulations of pipe flow using advective bars elements in Aria have been compared to simulations using the commercial CFD software ANSYS Fluent (r) and provided comparable solutions in temperature and velocity supporting proper implementation of the new capability. Verification of Advective Bar Elements iv Acknowledgements A special thanks goes to Dean Dobranich for his guidance and expertise through all stages of this effort . His advice and feedback was instrumental to its completion. Thanks also goes to Sam Subia and Tolu Okusanya for helping to plan many of the verification activities performed in this document. Thank you to Sam, Justin Lamb and Victor Brunini for their assistance in resolving issues encountered with running the advective bar element model. Finally, thanks goes to Dean, Sam, and Adam Hetzler for reviewing the document and providing very valuable comments.
A diffusive Fisher-KPP equation with free boundaries and time-periodic advections
Sun, Ningkui; Lou, Bendong; Zhou, Maolin
2016-01-01
We consider a reaction-diffusion-advection equation of the form: $u_t=u_{xx}-\\beta(t)u_x+f(t,u)$ for $x\\in (g(t),h(t))$, where $\\beta(t)$ is a $T$-periodic function representing the intensity of the advection, $f(t,u)$ is a Fisher-KPP type of nonlinearity, $T$-periodic in $t$, $g(t)$ and $h(t)$ are two free boundaries satisfying Stefan conditions. This equation can be used to describe the population dynamics in time-periodic environment with advection. Its homogeneous version (that is, both $...
DEFF Research Database (Denmark)
Binning, Philip John; Postma, Diederik Jan; Russel, T.F.;
2007-01-01
at depth in the unsaturated zone, a pressure gradient is created between the reactive zone and the ground surface, causing a substantial advective air flow into the subsurface. To determine the balance between advective and diffusive transport, a one-dimensional multicomponent unsaturated zone gas...... flows at steady state. However, greater pressure gradients are found in low-permeability soils. In transient cases, advective fluxes depend on the initial conditions and can be far greater than diffusive fluxes. In contrast to steady state conditions the transient case is sensitive to other model...
Boundary value problemfor multidimensional fractional advection-dispersion equation
Directory of Open Access Journals (Sweden)
Khasambiev Mokhammad Vakhaevich
2015-05-01
authors first considered the boundary value problem for stationary equation for mass transfer in super-diffusion conditions and abnormal advection. Then the solution of the problem is explicitly given. The solution is obtained by the Fourier’s method.The obtained results will be useful in liquid filtration theory in fractal medium and for modeling the temperature variations in the heated bar.
A Method for Measuring Subcanopy CO2 Advection
Staebler, R. M.; Fitzjarrald, D. R.
2004-12-01
Underestimation of nocturnal CO2 respiration under calm conditions remains an unsolved problem at many forest flux stations, and several groups are currently investigating the direct measurement of horizontal advection of CO2. This presentation will describe a systematic, relatively low-cost methodology developed to determine whether horizontal mean transport of CO2 accounts for the missing CO2 at the Harvard Forest (Petersham, MA). This methodology includes the characterization of subcanopy motions, determining the appropriate size of the subcanopy network required to make the measurements, developing a method of integrating the measurements in the vertical, and determining the required averaging time. Measurements were conducted over 4 years and produced data for 310 nights covering all seasons. Subcanopy flows were decoupled from the flows aloft 75% of the time. Conditions conducive to the generation of negative buoyancy near the forest floor, necessary for drainage flows to develop, were given in 92% of all nights. The occurrence of nocturnal drainage flows correlated well with "missing flux" problems ("deficit nights"), prompting us to propose an improvement on the commonly used friction velocity criterion (which requires u* to be larger than some empirical cut-off for the eddy fluxes to be considered credible). The "negative buoyancy forcing fraction", i.e. negative buoyancy as a fraction of the sum of the dynamic driving forces, can be shown to predict deficit nights significantly better than the u* cut-off. The appropriate horizontal size of the network of wind and CO2 sensors at the Harvard Forest was shown to be on the order of 100 m, ensuring that sensors were generally observing coherent processes on this scale or larger and thus displaying some correlation. Horizontal transport of CO2 was found to be restricted to the bottom ~10 m of the forest, facilitating the development of a method of integrating the horizontal CO2 gradients in the vertical
Clay with Desiccation Cracks is an Advection Dominated Environment
Baram, S.; Kurtzman, D.; Sher, Y.; Ronen, Z.; Dahan, O.
2012-04-01
, indicating deep soil evaporation. Daily fluctuation of the air temperature in the desiccation cracks supported thermally induced air convection within the cracks void and could explain the deep soil salinization process. Combination of all the abovementioned observations demonstrated that the formation of desiccation cracks network in dispersive clay sediments generates a bulk advection dominated environment for both air and water flow, and that the reference to clay sediments as "hydrologically safe" should to be reconsidered.
Advective surface velocity in the north west Pacific derived from NOAA AVHRR images
Digital Repository Service at National Institute of Oceanography (India)
Pankajakshan, T.; Akiyama, M.; Okada, Y.; Sugimori, Y.
Using sequential AVHRR images in November 1983, nearsurface advective velocities are derived in the region Kuroshio south of Japan. For deriving the velocities two methods are used. One is the Method of Cross Correlation (MCC), using image pair...
Rigorous upper bounds for fluid and plasma transport due to passive advection
Energy Technology Data Exchange (ETDEWEB)
Krommes, J.A.; Smith, R.A.; Kim, C.B.
1987-07-01
The formulation of variational principles for transport due to passive advection is described. A detailed account of the work has been published elsewhere. In the present paper, the motivations, philosophy, and implications of the method are briefly discussed. 15 refs.
Computation of Mass-Outflow Rates From Advective Accretion Disks Around Black Holes
Das, T K
1998-01-01
We self-consistently compute the mass outflow rate from a mass inflow using the conditions in the centrifugal barrier of an advective flow. Our detailed result agrees with the theoretical estimates given in Chakrabarti (1997; astro-ph/9801079).
Implicit and semi-implicit schemes in the Versatile Advection Code: numerical tests
Toth, G.; Keppens, R.; Botchev, M. A.
1998-01-01
We describe and evaluate various implicit and semiimplicit time integration schemes applied to the numerical simulation of hydrodynamical and magnetohydrodynamical problems. The schemes were implemented recently in the software package Versatile Advection Code, which uses modern shock capturing meth
Solving the Advection-Diffusion Equations in Biological Contexts using the Cellular Potts Model
Dan, D; Chen, K; Glazier, J A; Dan, Debasis; Mueller, Chris; Chen, Kun; Glazier, James A.
2005-01-01
The Cellular Potts Model (CPM) is a robust, cell-level methodology for simulation of biological tissues and morphogenesis. Both tissue physiology and morphogenesis depend on diffusion of chemical morphogens in the extra-cellular fluid or matrix (ECM). Standard diffusion solvers applied to the cellular potts model use finite difference methods on the underlying CPM lattice. However, these methods produce a diffusing field tied to the underlying lattice, which is inaccurate in many biological situations in which cell or ECM movement causes advection rapid compared to diffusion. Finite difference schemes suffer numerical instabilities solving the resulting advection-diffusion equations. To circumvent these problems we simulate advection-diffusion within the framework of the CPM using off-lattice finite-difference methods. We define a set of generalized fluid particles which detach advection and diffusion from the lattice. Diffusion occurs between neighboring fluid particles by local averaging rules which approxi...
D'Ovidio, Mirko
2012-01-01
We consider fractional directional derivatives and establish some connection with stable densities. Solutions to advection equations involving fractional directional derivatives are presented and some properties investigated. In particular we obtain solutions written in terms of Wright functions by exploiting operational rules involving the shift operator. We also consider fractional advection diffusion equations involving fractional powers of the negative Laplace operator and directional derivatives of fractional order and discuss the probabilistic interpretations of solutions.
Modifying SEBAL ET Algorithm to account for advection by using daily averages of weather data
Mkhwanazi, M. M.; Chavez, J. L.
2013-12-01
The use of Remote Sensing (RS) in crop evapotranspiration (ET) estimation is aimed at improving agricultural water management. The Surface Energy Balance Algorithm for Land (SEBAL) is one of several methods that have been developed for this purpose. This has been a preferred model as it requires minimal climate data. However, it has a noted downside of underestimating ET under advective conditions. This is primarily due to the use of evaporative fraction (EF) to extrapolate instantaneous ET to daily values, with the assumption that EF is constant throughout the day. A modified SEBAL model was used in this study, which requires daily averages of weather data to estimate advection which is then introduced into the 24-hour ET sub-model of SEBAL. The study was carried out in southeastern Colorado, a semi-arid area where afternoon advection is a common feature. ET estimated using the original and modified SEBAL was compared to the lysimeter-measured ET. Results showed that the modified SEBAL algorithm performed better in estimating daily ET in overall, but especially on days when there was advection. On non-advective days, the original SEBAL was more accurate. It is therefore recommended that the modified SEBAL be used only on advective days, and guidelines to help identify such days were proposed.
Diagnosis of a Moist Thermodynamic Advection Parameter in Heavy-Rainfall Events
Institute of Scientific and Technical Information of China (English)
WU Xiandu; RAN Lingkun; CHU Yanli
2011-01-01
A moist thermodynamic advection parameter, defined as an absolute value of the dot product of horizontal gradients of three-dimensional potential temperature advection and general potential temperature, is introduced to diagnose frontal heavy rainfall events in the north of China. It is shown that the parameter is closely related to observed 6-h accumulative surface rainfall and simulated cloud hydrometeors. Since the parameter is capable of describing the typical vertical structural characteristics of dynamic, thermodynamic and water vapor fields above a strong precipitation region near the front surface, it may serve as a physical tracker to detect precipitable weather systems near to a front.A tendency equation of the parameter was derived in Cartesian coordinates and calculated with the simulation output data of a heavy rainfall event. Results revealed that the advection of the parameter by the three-dimensional velocity vector, the covariance of potential temperature advection by local change of the velocity vector and general potential temperature, and the interaction between potential temperature advection and the source or sink of general potential temperature, accounted for local change in the parameter. This indicated that the parameter was determined by a combination of dynamic processes and cloud microphysical processes.
International Nuclear Information System (INIS)
In this paper advected invariants and conservation laws in ideal magnetohydrodynamics (MHD) and gas dynamics are obtained using Lie dragging techniques. There are different classes of invariants that are advected or Lie dragged with the flow. Simple examples are the advection of the entropy S (a 0-form), and the conservation of magnetic flux (an invariant 2-form advected with the flow). The magnetic flux conservation law is equivalent to Faraday's equation. The gauge condition for the magnetic helicity to be advected with the flow is determined. Different variants of the helicity in ideal fluid dynamics and MHD including: fluid helicity, cross helicity and magnetic helicity are investigated. The fluid helicity conservation law and the cross-helicity conservation law in MHD are derived for the case of a barotropic gas. If the magnetic field lies in the constant entropy surface, then the gas pressure can depend on both the entropy and the density. In these cases the conservation laws are local conservation laws. For non-barotropic gases, we obtain nonlocal conservation laws for fluid helicity and cross helicity by using Clebsch variables. These nonlocal conservation laws are the main new results of the paper. Ertel's theorem and potential vorticity, the Hollman invariant, and the Godbillon–Vey invariant for special flows for which the magnetic helicity is zero are also discussed. (paper)
Metamorphism during temperature gradient with undersaturated advective airflow in a snow sample
Ebner, Pirmin Philipp; Schneebeli, Martin; Steinfeld, Aldo
2016-04-01
Snow at or close to the surface commonly undergoes temperature gradient metamorphism under advective flow, which alters its microstructure and physical properties. Time-lapse X-ray microtomography is applied to investigate the structural dynamics of temperature gradient snow metamorphism exposed to an advective airflow in controlled laboratory conditions. Cold saturated air at the inlet was blown into the snow samples and warmed up while flowing across the sample with a temperature gradient of around 50 K m-1. Changes of the porous ice structure were observed at mid-height of the snow sample. Sublimation occurred due to the slight undersaturation of the incoming air into the warmer ice matrix. Diffusion of water vapor opposite to the direction of the temperature gradient counteracted the mass transport of advection. Therefore, the total net ice change was negligible leading to a constant porosity profile. However, the strong recrystallization of water molecules in snow may impact its isotopic or chemical content.
First-Order Hyperbolic System Method for Time-Dependent Advection-Diffusion Problems
Mazaheri, Alireza; Nishikawa, Hiroaki
2014-01-01
A time-dependent extension of the first-order hyperbolic system method for advection-diffusion problems is introduced. Diffusive/viscous terms are written and discretized as a hyperbolic system, which recovers the original equation in the steady state. The resulting scheme offers advantages over traditional schemes: a dramatic simplification in the discretization, high-order accuracy in the solution gradients, and orders-of-magnitude convergence acceleration. The hyperbolic advection-diffusion system is discretized by the second-order upwind residual-distribution scheme in a unified manner, and the system of implicit-residual-equations is solved by Newton's method over every physical time step. The numerical results are presented for linear and nonlinear advection-diffusion problems, demonstrating solutions and gradients produced to the same order of accuracy, with rapid convergence over each physical time step, typically less than five Newton iterations.
Large-eddy Advection in Evapotranspiration Estimates from an Array of Eddy Covariance Towers
Lin, X.; Evett, S. R.; Gowda, P. H.; Colaizzi, P. D.; Aiken, R.
2014-12-01
Evapotranspiration was continuously measured by an array of eddy covariance systems and large weighting lysimeter in a sorghum in Bushland, Texas in 2014. The advective divergence from both horizontal and vertical directions were measured through profile measurements above canopy. All storage terms were integrated from the depth of soil heat flux plate to the height of eddy covariance measurement. Therefore, a comparison between the eddy covariance system and large weighing lysimeter was conducted on hourly and daily basis. The results for the discrepancy between eddy covariance towers and the lysimeter will be discussed in terms of advection and storage contributions in time domain and frequency domain.
Semi-Lagrangian advection-propagation (SLAP) scheme for three-dimensional interface tracking
Aldredge, R. C.
2010-06-01
A fully three-dimensional semi-Lagrangian scheme is developed for computing the evolution of advected self-propagating surfaces (e.g., premixed flames) governed by a level-set advection-propagation equation. The scheme provides third-order spatial accuracy and shape preservation. Example numerical simulations of three-dimensional front propagation are presented to illustrate the capability of the scheme of capturing cusp formation and associated surface-area annihilation as well as the formation and consumption of detached closed-surface pockets behind fronts propagating in highly vortical flow.
Rogers, M. A.
2015-12-01
Using satellite observations from GOES-E and GOES-W platforms in concert with GFS-derived cloud-level winds and a standalone radiative transfer model, an advection-derived forecast for surface GHI over the continental United States, with intercomparison between forecasts for four zones over the CONUS and Central Pacific with SURFRAD results. Primary sources for error in advection-based forecasts, primarily driven by false- or mistimed ramp events are discussed, with identification of error sources quantified along with techniques used to improve advection-based forecasts to approximately 10% MAE for designated surface locations. Development of a blended steering wind product utilizing NWP output combined with satellite-derived winds from AMV techniques to improve 0-1 hour advection forecasts will be discussed. Additionally, the use of two years' of solar forecast observations in the development of a prototype probablistic forecast for ramp events will be shown, with the intent of increasing the use of satellite-derived forecasts for grid operators and optimizing integration of renewable resources into the power grid. Elements of the work were developed under the 'Public-Private-Academic Partnership to Advance Solar Power Forecasting' project spearheaded by the National Center for Atmospheric Research.
Shell model for time-correlated random advection of passive scalars
DEFF Research Database (Denmark)
Andersen, Ken Haste; Muratore-Ginanneschi, P.
1999-01-01
We study a minimal shell model for the advection of a passive scalar by a Gaussian time-correlated velocity field. The anomalous scaling properties of the white noise limit are studied analytically. The effect of the time correlations are investigated using perturbation theory around the white...
Hoedjes, J.C.B.; Zuurbier, R.M.; Watts, J.C.
2002-01-01
Scintillometer measurements were collected over an irrigated wheat field in a semi-arid region in northwest Mexico. Conditions were unstable in the morning and stable during the afternoon, while latent heat fluxes remained high throughout the day. Regional advection was observed during near-neutral
DEFF Research Database (Denmark)
Santos, Isaac R.; Eyre, Bradley D.; Glud, Ronnie N.
2012-01-01
Porewater flow enhances mineralization rates in organic-poor permeable sands. Here, a series of sediment column experiments were undertaken to assess the potential effect of advective porewater transport on denitrification in permeable carbonate sands collected from Heron Island (Great Barrier Reef...
Energy Technology Data Exchange (ETDEWEB)
Gjesdal, Thor
1997-12-31
This thesis discusses the development and application of efficient numerical methods for the simulation of fluid flows, in particular the flow of incompressible fluids. The emphasis is on practical aspects of algorithm development and on application of the methods either to linear scalar model equations or to the non-linear incompressible Navier-Stokes equations. The first part deals with cell centred multigrid methods and linear correction scheme and presents papers on (1) generalization of the method to arbitrary sized grids for diffusion problems, (2) low order method for advection-diffusion problems, (3) attempt to extend the basic method to advection-diffusion problems, (4) Fourier smoothing analysis of multicolour relaxation schemes, and (5) analysis of high-order discretizations for advection terms. The second part discusses a multigrid based on pressure correction methods, non-linear full approximation scheme, and papers on (1) systematic comparison of the performance of different pressure correction smoothers and some other algorithmic variants, low to moderate Reynolds numbers, and (2) systematic study of implementation strategies for high order advection schemes, high-Re flow. An appendix contains Fortran 90 data structures for multigrid development. 160 refs., 26 figs., 22 tabs.
Analytical solutions of the advection-dispersion equation and related models are indispensable for predicting or analyzing contaminant transport processes in streams and rivers, as well as in other surface water bodies. Many useful analytical solutions originated in disciplines other than surface-w...
Implicit and semi-implicit schemes in the Versatile Advection Code : numerical tests
Tóth, G.; Keppens, R.; Botchev, M.A.
1998-01-01
We describe and evaluate various implicit and semi-implicit time integration schemes applied to the numerical simulation of hydrodynamical and magnetohydrodynamical problems. The schemes were implemented recently in the software package Versatile Advection Code, which uses modern shock capturing met
Isoline retrieval: An optimal sounding method for validation of advected contours
Mills, Peter
2012-01-01
The study of chaotic mixing is important for its potential to improve our understanding of fluid systems. Contour advection simulations provide a good model of the phenomenon by tracking the evolution of one or more contours or isolines of a trace substance to a high level of precision. The most accurate method of validating an advected contour is to divide the tracer concentration into discrete ranges and perform a maximum likelihood classification, a method that we term, "isoline retrieval." Conditional probabilities generated as a result provide excellent error characterization. In this study, a water vapour isoline of 0.001 mass-mixing-ratio is advected over five days in the upper troposphere and compared with high-resolution AMSU (Advanced Microwave Sounding Unit) satellite retrievals. The goal is to find the same fine-scale, chaotic mixing in the isoline retrievals as seen in the advection simulations. Some of the filaments generated by the simulations show up in the conditional probabilities as areas o...
Emery, W. J.; Thomas, A. C.; Collins, M. J.; Crawford, W. R.; Mackas, D. L.
1986-11-01
Using cross correlations between sequential infrared satellite images, an objective technique is developed to compute advective sea surface velocities. Cross correlations are computed in 32 × 32 pixel search (second image) and 22 × 22 template (first image) windows from gradients of sea surface temperature computed from the satellite images. Velocity vectors, computed from sequential images of the British Columbia coastal ocean, generally appear coherent and consistent with the seasonal surface current in the region. During periods of strong wind forcing, as indicated by maps of sea level pressure, the image advective velocities are stronger and more coherent spatially and appear to cross surface temperature gradients; when winds are weaker, the advective velocities correspond better with the infrared temperature patterns, suggesting the increased contribution of the geostrophic current to the surface flow. Velocities determined from coincident, near-surface drogued (5-10 m) buoys, positioned every half hour by internal LORAN-C units in mid-June, show excellent agreement with the image advective velocities. In addition, conductivity, temperature, and depth (CTD) measurements (taken during the buoy tracking) confirm the homogeneity of the upper 10 m, and CTD-derived geostrophic currents are consistent with both buoy and sequential image displacement velocities.
Manmoto, T; Kusunose, M
1997-01-01
The global structure of optically thin advection dominated accretion flows which are composed of two-temperature plasma around black holes is calculated. We adopt the full set of basic equations including the advective energy transport in the energy equation for the electrons. The spectra emitted by the optically thin accretion flows are also investigated. The radiation mechanisms which are taken into accout are bremsstrahlung, synchrotron emission, and Comptonization. The calculation of the spectra and that of the structure of the accretion flows are made to be completely consistent by calculating the radiative cooling rate at each radius. As a result of the advection domination for the ions, the heat transport from the ions to the electrons becomes practically zero and the radiative cooling balances with the advective heating in the energy equation of the electrons. Following up on the successful work of Narayan et al. (1995), we applied our model to the spectrum of Sgr A*. We find that the spectrum of Sgr ...
Comparison of different computer platforms for running the Versatile Advection Code
Toth, G.; Keppens, R.; Sloot, P.; Bubak, M.; Hertzberger, B.
1998-01-01
The Versatile Advection Code is a general tool for solving hydrodynamical and magnetohydrodynamical problems arising in astrophysics. We compare the performance of the code on different computer platforms, including work stations and vector and parallel supercomputers. Good parallel scaling can be a
Quantification of numerical diffusivity due to TVD schemes in the advection equation
Bidadi, Shreyas; Rani, Sarma L.
2014-03-01
In this study, the numerical diffusivity νnum inherent to the Roe-MUSCL scheme has been quantified for the scalar advection equation. The Roe-MUSCL scheme employed is a combination of: (1) the standard extension of the original Roe's formulation to the advection equation, and (2) van Leer's Monotone Upwind Scheme for Conservation Laws (MUSCL) technique that applies a linear variable reconstruction in a cell along with a scaled limiter function. An explicit expression is derived for the numerical diffusivity in terms of the limiter function, the distance between the cell centers on either side of a face, and the face-normal velocity. The numerical diffusivity formulation shows that a scaled limiter function is more appropriate for MUSCL in order to consistently recover the central-differenced flux at the maximum value of the limiter. The significance of the scaling factor is revealed when the Roe-MUSCL scheme, originally developed for 1-D scenarios, is applied to 2-D scalar advection problems. It is seen that without the scaling factor, the MUSCL scheme may not necessarily be monotonic in multi-dimensional scenarios. Numerical diffusivities of the minmod, superbee, van Leer and Barth-Jesperson TVD limiters were quantified for four problems: 1-D advection of a step function profile, and 2-D advection of step, sinusoidal, and double-step profiles. For all the cases, it is shown that the superbee scheme provides the lowest numerical diffusivity that is also most confined to the vicinity of the discontinuity. The minmod scheme is the most diffusive, as well as active in regions away from high gradients. As expected, the grid resolution study demonstrates that the magnitude and the spatial extent of the numerical diffusivity decrease with increasing resolution.
Continuous time series of dissolved oxygen (DO) have been used to compute estimates of metabolism in aquatic ecosystems. Central to this open water or "Odum" method is the assumption that the DO time is not strongly affected by advection and that effects due to advection or mixin...
Analytical solutions of the advection-dispersion solute transport equation remain useful for a large number of applications in science and engineering. In this paper we extend the Duhamel theorem, originally established for diffusion type problems, to the case of advective-dispersive transport subj...
Particulate export vs lateral advection in the Antarctic Polar Front (Southern Pacific Ocean)
Tesi, T.; Langone, L.; Ravaioli, M.; Capotondi, L.; Giglio, F.
2012-04-01
The overarching goal of our study was to describe and quantify the influence of lateral advection relative to the vertical export in the Antarctic Polar Front (Southern Pacific Ocean). In areas where lateral advection of particulate material is significant, budgets of bioactive elements can be inaccurate if fluxes through the water column and to the seabed are exclusively interpreted as passive sinking of particles. However, detailed information on the influence of lateral advection in the water column in the southern ocean is lacking. With this in mind, our study focused between the twilight zone (i.e. mesopelagic) and the benthic nepheloid layer to understand the relative importance of lateral flux with increasing water depth. Measurements were performed south of the Antarctic Polar Front for 1 year (January 10th 1999-January 3rd 2000) at 900, 1300, 2400, and 3700 m from the sea surface. The study was carried out using a 3.5 km long mooring line instrumented with sediment traps, current meters and sensors of temperature and conductivity. Sediment trap samples were characterized via several parameters including total mass flux, elemental composition (organic carbon, total nitrogen, biogenic silica, and calcium carbonate), concentration of metals (aluminum, iron, barium, and manganese), 210Pb activity, and foraminifera taxonomy. High fluxes of biogenic particles were observed in both summer 1999 and 2000 as a result of seasonal algal blooms associated with sea ice retreat and water column stratification. During no-productive periods, several high energy events occurred and resulted in advecting resuspended biogenic particles from flat-topped summits of the Pacific Antarctic Ridge. Whereas the distance between seabed and uppermost sediment traps was sufficient to avoid lateral advection processes, resuspension was significant in the lowermost sediment traps accounting for ~60 and ~90% of the material caught at 2400 and 3700 m, respectively. Samples collected during
Directory of Open Access Journals (Sweden)
Mcebisi Mkhwanazi
2015-11-01
Full Text Available The Surface Energy Balance Algorithm for Land (SEBAL is one of the remote sensing (RS models that are increasingly being used to determine evapotranspiration (ET. SEBAL is a widely used model, mainly due to the fact that it requires minimum weather data, and also no prior knowledge of surface characteristics is needed. However, it has been observed that it underestimates ET under advective conditions due to its disregard of advection as another source of energy available for evaporation. A modified SEBAL model was therefore developed in this study. An advection component, which is absent in the original SEBAL, was introduced such that the energy available for evapotranspiration was a sum of net radiation and advected heat energy. The improved SEBAL model was termed SEBAL-Advection or SEBAL-A. An important aspect of the improved model is the estimation of advected energy using minimal weather data. While other RS models would require hourly weather data to be able to account for advection (e.g., METRIC, SEBAL-A only requires daily averages of limited weather data, making it appropriate even in areas where weather data at short time steps may not be available. In this study, firstly, the original SEBAL model was evaluated under advective and non-advective conditions near Rocky Ford in southeastern Colorado, a semi-arid area where afternoon advection is common occurrence. The SEBAL model was found to incur large errors when there was advection (which was indicated by higher wind speed and warm and dry air. SEBAL-A was then developed and validated in the same area under standard surface conditions, which were described as healthy alfalfa with height of 40–60 cm, without water-stress. ET values estimated using the original and modified SEBAL were compared to large weighing lysimeter-measured ET values. When the SEBAL ET was compared to SEBAL-A ET values, the latter showed improved performance, with the ET Mean Bias Error (MBE reduced from −17
Analytical Solutions of the Space-Time Fractional Derivative of Advection Dispersion Equation
Directory of Open Access Journals (Sweden)
Abdon Atangana
2013-01-01
Full Text Available Fractional advection-dispersion equations are used in groundwater hydrology to model the transport of passive tracers carried by fluid flow in porous medium. A space-time fractional advection-dispersion equation (FADE is a generalization of the classical ADE in which the first-order space derivative is replaced with Caputo or Riemann-Liouville derivative of order , and the second-order space derivative is replaced with the Caputo or the Riemann-Liouville fractional derivative of order . We derive the solution of the new equation in terms of Mittag-Leffler functions using Laplace transfrom. Some examples are given. The results from comparison let no doubt that the FADE is better in prediction than ADE.
Object-oriented implementations of the MPDATA advection equation solver in C++, Python and Fortran
Arabas, Sylwester; Jaruga, Anna; Fijałkowski, Maciej
2013-01-01
Three object-oriented implementations of a prototype solver of the advection equation are introduced. Presented programs are based on Blitz++ (C++), NumPy (Python), and Fortran's built-in array containers. The solvers include an implementation of the Multidimensional Positive-Definite Advective Transport Algorithm (MPDATA). The introduced codes exemplify how the application of object-oriented programming (OOP) techniques allows to reproduce the mathematical notation used in the literature within the program code. The introduced codes serve as a basis for discussion on the tradeoffs of the programming language choice. The main angles of comparison are code brevity and syntax clarity (and hence maintainability and auditability) as well as performance. In case of Python, a significant performance gain is observed when switching from the standard interpreter (CPython) to the PyPy implementation of Python. Entire source code of all three implementations is embedded in the text and is licensed under the terms of th...
Wu, Fan; Vainchtein, Dmitri; Ward, Thomas
2015-08-01
A drop translating in the presence of an electric field is studied analytically. The flow is a combination of a Hadamard-Rybczynski and a Taylor circulation due to the translation and electric field, respectively. We consider chaotic advection that is generated by (1) tilting and (2) time-dependent modulation of the electric field. For the analysis we consider small perturbations in time and space to what is otherwise an integrable flow. By using a robust analytical technique we find an adiabatic invariant (AI) for the system by averaging the equations of motion. The chaotic advection is due to quasirandom jumps of the AI after crossing the separatrix of the unperturbed flow. We demonstrate that the asymptotic analysis leads to a set of criteria that can be used to optimize stirring in these systems.
Gal-Chen, T.
1981-01-01
The laws of fluid motion are invariant under a Gallilean transformation. For a perfect observing system, the data analysis should, therefore, also be invariant under a Gallilean transformation. This invariance is often not preserved in practical observing systems. In this connection, it is often advisable to perform mesoscale analysis in a frame moving with respect to the earth's surface. In the present investigation the velocity of such a frame is referred to as an advection velocity. The investigation is concerned with remaining problems regarding the Gallilean transformation. The establishment of a frame of reference for the achievement of maximum coherence is considered, taking into account the case of given nonsimultaneous observations of scalars or Cartesian vectors. It is found that advection speed can be estimated objectively if a scalar or Cartesian vector can be observed directly and if, in addition, the time and position of each observation is approximately known.
Advective-diffusive mass transfer in fractured porous media with variable rock matrix block size.
Sharifi Haddad, Amin; Hassanzadeh, Hassan; Abedi, Jalal
2012-05-15
Traditional dual porosity models do not take into account the effect of matrix block size distribution on the mass transfer between matrix and fracture. In this study, we introduce the matrix block size distributions into an advective-diffusive solute transport model of a divergent radial system to evaluate the mass transfer shape factor, which is considered as a first-order exchange coefficient between the fracture and matrix. The results obtained lead to a better understanding of the advective-diffusive mass transport in fractured porous media by identifying two early and late time periods of mass transfer. Results show that fractured rock matrix block size distribution has a great impact on mass transfer during early time period. In addition, two dimensionless shape factors are obtained for the late time, which depend on the injection flow rate and the distance of the rock matrix from the injection point.
Directory of Open Access Journals (Sweden)
Gurhan Gurarslan
2013-01-01
Full Text Available This study aims to produce numerical solutions of one-dimensional advection-diffusion equation using a sixth-order compact difference scheme in space and a fourth-order Runge-Kutta scheme in time. The suggested scheme here has been seen to be very accurate and a relatively flexible solution approach in solving the contaminant transport equation for Pe≤5. For the solution of the present equation, the combined technique has been used instead of conventional solution techniques. The accuracy and validity of the numerical model are verified through the presented results and the literature. The computed results showed that the use of the current method in the simulation is very applicable for the solution of the advection-diffusion equation. The present technique is seen to be a very reliable alternative to existing techniques for these kinds of applications.
An advection-diffusion model for cross-field runaway electron transport in perturbed magnetic fields
Särkimäki, Konsta; Decker, Joan; Varje, Jari; Kurki-Suonio, Taina
2016-01-01
Disruption-generated runaway electrons (RE) present an outstanding issue for ITER. The predictive computational studies of RE generation rely on orbit-averaged computations and, as such, they lack the effects from the magnetic field stochasticity. Since stochasiticity is naturally present in post-disruption plasma, and externally induced stochastization offers a prominent mechanism to mitigate RE avalanche, we present an advection-diffusion model that can be used to couple an orbit-following code to an orbit-averaged tool in order to capture the cross-field transport and to overcome the latter's limitation. The transport coefficients are evaluated via a Monte Carlo method. We show that the diffusion coefficient differs significantly from the well-known Rechester-Rosenbluth result. We also demonstrate the importance of including the advection: it has a two-fold role both in modelling transport barriers created by magnetic islands and in amplifying losses in regions where the islands are not present.
Improvement of the One-dimensional Vertical Advection-diffusion Model in Seawater
Institute of Scientific and Technical Information of China (English)
王保栋; 单宝田; 战闰; 王修林
2003-01-01
The classical 1-D vertical advection-diffusion model was improved in this work. Themain advantages of the improved model over the previous one are: 1 ) The applicable condition ofthe 1-D model is made clear in the improved model, in that it is substantively applicable only to avertical domain on which two end-member water masses are mixing. 2) The substitution of parame-ter f(z) in the equation of the classical 1-D model with end-member fraction f1 makes the modelmore precisely and easily solved. 3 ) All the terms in the improved model equation have specificphysical meanings, which makes the model easily understood. Practical application of the improvedmodel to predict the vertical profiles of dissolved oxygen and micronutrients in abyssal ocean waterof the North Pacific proved that the improvement of the 1-D advection-diffusion model is successfuland practicable.
A balancing domain decomposition method by constraints for advection-diffusion problems
Energy Technology Data Exchange (ETDEWEB)
Tu, Xuemin; Li, Jing
2008-12-10
The balancing domain decomposition methods by constraints are extended to solving nonsymmetric, positive definite linear systems resulting from the finite element discretization of advection-diffusion equations. A pre-conditioned GMRES iteration is used to solve a Schur complement system of equations for the subdomain interface variables. In the preconditioning step of each iteration, a partially sub-assembled finite element problem is solved. A convergence rate estimate for the GMRES iteration is established, under the condition that the diameters of subdomains are small enough. It is independent of the number of subdomains and grows only slowly with the subdomain problem size. Numerical experiments for several two-dimensional advection-diffusion problems illustrate the fast convergence of the proposed algorithm.
Directory of Open Access Journals (Sweden)
Birol İbiş
2014-01-01
Full Text Available This paper aims to obtain the approximate solution of time-fractional advection-dispersion equation (FADE involving Jumarie’s modification of Riemann-Liouville derivative by the fractional variational iteration method (FVIM. FVIM provides an analytical approximate solution in the form of a convergent series. Some examples are given and the results indicate that the FVIM is of high accuracy, more efficient, and more convenient for solving time FADEs.
Gurhan Gurarslan; Halil Karahan; Devrim Alkaya; Murat Sari; Mutlu Yasar
2013-01-01
This study aims to produce numerical solutions of one-dimensional advection-diffusion equation using a sixth-order compact difference scheme in space and a fourth-order Runge-Kutta scheme in time. The suggested scheme here has been seen to be very accurate and a relatively flexible solution approach in solving the contaminant transport equation for Pe≤5. For the solution of the present equation, the combined technique has been used instead of conventional solution techniques. The accuracy and...
A New Evapotranspiration Model Accounting for Advection and Its Validation during SMEX02
Yongmin Yang; Hongbo Su; Renhua Zhang; Jianjun Wu; Jianwei Qi
2013-01-01
Based on the crop water stress index (CWSI) concept, a new model was proposed to account for advection to estimate evapotranspiration. Both local scale evaluation with sites observations and regional scale evaluation with a remote dataset from Landsat 7 ETM+ were carried out to assess the performance of this model. Local scale evaluation indicates that this newly developed model can effectively characterize the daily variations of evapotranspiration and the predicted results show good agreeme...
Fan, Yi; Schlick, Conor; Isner, Austin; Ottino, Julio; Umbanhowar, Paul; Richard, Lueptow
2014-01-01
Segregation of granular materials composed of different-sized particles has important repercussions in various industrial processes and natural phenomena, but predicting size segregation remains a challenging problem. To address this problem, we have developed a theoretical model that captures the interplay between advection, segregation, and diffusion in size bidisperse granular materials. The fluxes associated with these three driving factors depend on the underlying kinematics, whose chara...
ADVECTION AND DIFFUSION OF POISONOUS GAS CONTAMINANT RELEASED FROM BOTTOM SLUDGE IN OPEN CHANNEL
Institute of Scientific and Technical Information of China (English)
WU Zhou-hu
2004-01-01
In some cases, poisonous contaminants may be released from bottom sludge in open channels. The equation of advection and diffusion for the related problem was analyzed in this paper. The conditions for the definite solution to the equation were given. The analytic solution of poisonous gas concentration distribution was worked out. The reasonableness of this solution was discussed. The result is also of significance for other similar problems.
Carbon dioxide seasonality in dynamically ventilated caves: the role of advective fluxes
Lang, Marek; Faimon, Jiří; Godissart, Jean; Ek, Camille
2016-07-01
The seasonality in cave CO2 levels was studied based on (1) a new data set from the dynamically ventilated Comblain-au-Pont Cave (Dinant Karst Basin, Belgium), (2) archive data from Moravian Karst caves, and (3) published data from caves worldwide. A simplified dynamic model was proposed for testing the effect of all conceivable CO2 fluxes on cave CO2 levels. Considering generally accepted fluxes, i.e., the direct diffusive flux from soils/epikarst, the indirect flux derived from dripwater degassing, and the input/output fluxes linked to cave ventilation, gives the cave CO2 level maxima of 1.9 × 10-2 mol m-3 (i.e., ˜ 440 ppmv), which only slightly exceed external values. This indicates that an additional input CO2 flux is necessary for reaching usual cave CO2 level maxima. The modeling indicates that the additional flux could be a convective advective CO2 flux from soil/epikarst driven by airflow (cave ventilation) and enhanced soil/epikarstic CO2 concentrations. Such flux reaching up to 170 mol s-1 is capable of providing the cave CO2 level maxima up to 3 × 10-2 mol m-3 (70,000 ppmv). This value corresponds to the maxima known from caves worldwide. Based on cave geometry, three types of dynamic caves were distinguished: (1) the caves with the advective CO2 flux from soil/epikarst at downward airflow ventilation mode, (2) the caves with the advective soil/epikarstic flux at upward airflow ventilation mode, and (3) the caves without any soil/epikarstic advective flux. In addition to CO2 seasonality, the model explains both the short-term and seasonal variations in δ13C in cave air CO2.
Advective loss of overwintering Calanus finmarchicus from the Faroe-Shetland Channel
DEFF Research Database (Denmark)
Rullyanto, Arief; Jonasdottir, Sigrun H.; Visser, Andre W.
2015-01-01
, a regionally important secondary producer. Using a high resolution hydrodynamic model, MIKE 3 FM, we simulate the overflow of deep water and estimate the associated loss rate of C. finmarchicus as a function of the water depth strata within which they reside. We estimate a net advective loss from the Norwegian...... is to be entrained into warmer waters of the North Atlantic Basin, a habitat that appears to be unsuitable for successful overwintering. (C) 2015 Elsevier Ltd. All rights reserved....
Gu, Wei-Min
2012-01-01
By taking into account the local energy balance per unit volume between the viscous heating and the advective cooling plus the radiative cooling, we investigate the vertical structure of radiation pressure-supported accretion disks in spherical coordinates. Our solutions show that the photosphere of the disk is close to the polar axis and therefore the disk seems to be extremely thick. However, the profile of density implies that most of the accreted matter exists in a moderate range around the equatorial plane. We show that the well-known polytropic relation between the pressure and the density is unsuitable for describing the vertical structure of radiation pressure-supported disks. More importantly, we find that the energy advection is significant even for slightly sub-Eddington accretion disks. We argue that the non-negligible advection may help to understand why the standard thin disk model is likely to be inaccurate above \\sim 0.3 Eddington luminosity, which was found by some works on the black hole spi...
Chauhan, R. P.; Kumar, Amit
The present work is aimed that out of diffusive and advective transport which is dominant process for indoor radon entry under normal room conditions. For this purpose the radon diffusion coefficient and permeability of concrete were measured by specially designed experimental set up. The radon diffusion coefficient of concrete was measured by continuous radon monitor. The measured value was (3.78 ± 0.39)×10-8 m2/s and found independent of the radon gas concentration in source chamber. The radon permeability of concrete varied between 1.85×10-17 to 1.36×10-15 m2 for the bulk pressure difference fewer than 20 Pa to 73.3 kPa. From the measured diffusion coefficient and absolute permeability, the radon flux from the concrete surface having concentrations gradient 12-40 kBq/m3 and typical floor thickness 0.1 m was calculated by the application of Fick and Darcy laws. Using the measured flux attributable to diffusive and advective transport, the indoor radon concentration for a typical Indian model room having dimension (5×6×7) m3 was calculated under average room ventilation (0.63 h-1). The results showed that the contribution of diffusive transport through intact concrete is dominant over the advective transport, as expected from the low values of concrete permeability.
Advection-condensation of water vapor with coherent stirring: a stochastic approach
Tsang, Yue-Kin; Vanneste, Jacques; Vallis, Geoffrey
2015-11-01
The dynamics of atmospheric water is an essential ingredient of weather and climate. Water vapor, in particular, is an important greenhouse gas whose distribution has a strong impact on climate. To gain insight into the factors controlling the distribution of atmospheric moisture, we study an advection-condensation model in which water vapor is passively advected by a prescribed velocity and condensation acts as a sink that maintains the specific humidity below a prescribed, spatially dependent saturation value. The velocity consists of two parts: a single vortex representing large-scale coherent flow (e.g. the Hadley cell) and a white noise component mimicking small-scale turbulence. Steady-state is achieved in the presence of a moisture source at a boundary. We formulate this model as a set of stochastic differential equations. In the fast advection limit, analytical expression for the water vapor distribution is obtained by matched asymptotics. This allows us to make various predictions including the dependence of total precipitation on the vortex strength. These analytical results are verified by Monte Carlo simulations. This work is supported by the UK EPSRC Grant EP/I028072/1 and the Feasibility Fund from the UK EPSRC Network ReCoVER.
Backward Calculation Based on the Advection and Diffusion of Oil Spills on the Sea Surface
Institute of Scientific and Technical Information of China (English)
LIU Hao; YIN Baoshu; LIN Jianguo
2005-01-01
In the light of the problem of oil pollution brought about by ships, in this paper we present the concept of backward tracing oil spills. In the course of backward calculation of the two-dimensional convection & diffusion equation, on the one hand,the advection term itself has the strong unilateral property, which means information in the upper reaches is transmitted downstream via the advection term; on the other hand,because of the opposite direction of calculation, it is essential for information to be conveyed upstream by means of the advection term. In addition, unlike that in the forward calculation, the diffusion term in the backward calculation is prone to accumulate errors, and thus renders the whole scheme unstable. Therefore, we adopt the central difference to deal with both the convectional term and the diffusion term. By examining two practical examples (1) under the unlimited boundary condition, and (2) under the limited boundary condition, it is proven that this method could achieve fundamentally satisfactory results not only in the open ocean but also in the closed or semi-closed bay.
Künzli, Pierre; Tsunematsu, Kae; Albuquerque, Paul; Falcone, Jean-Luc; Chopard, Bastien; Bonadonna, Costanza
2016-04-01
Volcanic ash transport and dispersal models typically describe particle motion via a turbulent velocity field. Particles are advected inside this field from the moment they leave the vent of the volcano until they deposit on the ground. Several techniques exist to simulate particles in an advection field such as finite difference Eulerian, Lagrangian-puff or pure Lagrangian techniques. In this paper, we present a new flexible simulation tool called TETRAS (TEphra TRAnsport Simulator) based on a hybrid Eulerian-Lagrangian model. This scheme offers the advantages of being numerically stable with no numerical diffusion and easily parallelizable. It also allows us to output particle atmospheric concentration or ground mass load at any given time. The model is validated using the advection-diffusion analytical equation. We also obtained a good agreement with field observations of the tephra deposit associated with the 2450 BP Pululagua (Ecuador) and the 1996 Ruapehu (New Zealand) eruptions. As this kind of model can lead to computationally intensive simulations, a parallelization on a distributed memory architecture was developed. A related performance model, taking into account load imbalance, is proposed and its accuracy tested.
Heat transfer enhancement utilizing chaotic advection in coiled tube heat exchangers
International Nuclear Information System (INIS)
The present study introduced a novel chaotic coil heat exchanger utilizing chaotic advection to enhance heat transfer at low Reynolds numbers. Using Lagrangian tracing of fluid particles and their sensitivity to the initial condition and fluid element calculations, it was shown that mixing was significantly increased due to the chaotic advection. Heat transfer performance in the coil and chaotic configuration was visualized by isotherms contours of temperature in different cross-sections. In order to evaluate the hydraulic-thermal performance of heat exchangers, Nusselt numbers and friction factor were calculated and comparison was made between the two configurations. Numerical calculations revealed that the chaotic coil configuration displayed heat transfer enhancement of 4–26% relative to the fully developed Nusselt numbers in the regular coil with only 5–8% change in the pressure drop. - Highlights: • A novel chaotic coil heat exchanger is introduced in this study. • It is shown that mixing is increased significantly due to the altered chaotic advection mechanism. • By increasing the Reynolds number, results show impressive enhancement in chaotic heat exchanger performance. • Reorientation in chaotic flow leads to higher pressure loss than that in the normal helical coil
Vertical advection and nocturnal deposition of ozone over a boreal pine forest
Directory of Open Access Journals (Sweden)
Ü. Rannik
2008-10-01
Full Text Available Night-time ozone deposition for a Scots pine forest in Southern Finland was studied at the SMEAR II measurement station by evaluating the turbulent eddy covariance (EC, storage change and vertical advection fluxes. Similarly to night-time carbon dioxide flux, the eddy-covariance flux of ozone was decreasing with turbulence intensity (friction velocity, and storage change of the compound did not compensate the reduction (well-known night-time measurement problem. Accounting for vertical advection resulted in invariance of ozone deposition rate on turbulence intensity. This was also demonstrated for carbon dioxide, verified by independent measurements of NEE by chamber systems. The result highlights the importance of advection when considering the exchange measurements of any scalar. Analysis of aerodynamic and laminar boundary layer resistances by the model approach indicated that the surface resistance and/or chemical sink strength was limiting ozone deposition. The possible aerial ozone sink by known fast chemical reactions with sesquiterpenes and NO explain only a minor fraction of ozone sink. Thus the deposition is controlled either by stomatal uptake or surface reactions or both of them, the mechanisms not affected by turbulence intensity. Therefore invariance of deposition flux on turbulence intensity is expected also from resistance and chemical sink analysis.
Some numerical studies of interface advection properties of level set method
Indian Academy of Sciences (India)
A Salih; S Ghosh Moulic
2009-04-01
In this paper, we discuss the results of a series of tests carried out to assess the level set methodology for capturing interfaces between two immiscible ﬂuids. The tests are designed to investigate the accuracy of convection process, the preservation of interface shape, and the mass conservation properties of individual ﬂuids. These test cases involve the advection of interfaces of different shapes exposed to translation, rotation, deformation, and shear ﬂow. Prescribed solenoidal velocity ﬁelds are used and no attempt is made to couple the advection of the level set function with the momentum equations. For the solution of level set equation we have employed ﬁrst-order upwind scheme, MacCormack method, second-order ENO scheme, and ﬁfth-order WENO scheme. Our studies show that the level set method perform well when higher-order schemes are used for the solution of advection equation. However, for certain type of shearing and vortical velocity ﬁelds mass conservation is an issue on coarser meshes even with higher order schemes. Finer mesh must be used in such situations to reduce numerical diffusion.
Energy Technology Data Exchange (ETDEWEB)
Torres Astorga, Romina; Velasco, Hugo; Valladares, Diego L.; Lohaiza, Flavia; Ayub, Jimena Juri; Rizzotto, Marcos [Grupo de Estudios Ambientales. Instituto de Matematica Aplicada San Luis - Universidad Nacional de San Luis - CONICET, San Luis (Argentina)
2014-07-01
{sup 7}Be is a short-lived environmental radionuclide, produced in the upper atmosphere by spallation of nitrogen and oxygen by cosmic rays. After of the production by the nuclear reaction, {sup 7}Be diffuses through the atmosphere until it attaches to atmospheric aerosols. Subsequently, it is deposited on the earth surface mainly as wet fallout. The main physical processes which transport {sup 7}Be in soil are diffusion and advection by water. Migration parameters and measurements confirm that sorption is the main physical process, which confines {sup 7}Be concentration to soil surface. The literature data show that in soils, {sup 7}Be is concentrated near the surface (0-2 cm) as it is adsorbed onto clay minerals after its deposition on the soil surface and does not penetrate deeper into soils due to its short half-life. The maximum mass activity density of {sup 7}Be is found at the point of input of the radionuclide, i.e. at the surface of the soil column, showing a exponential distribution profile typical of a purely diffusive transport. Many studies applying the advection dispersion models have been reported in the literature in order to modelling the transport of {sup 137}Cs in soils. On them, the models are used to achieve information of the mechanisms that govern the transport, i. e. the model is used to explain the soil profile of radionuclide. The effective dispersion coefficient and the apparent advection velocity of radionuclide in soil are also obtained by fitting the analytical solution of the model equation to measured depth distributions of the radionuclide. In this work, the advective dispersive transport model with linear sorption is used to analyze the vertical migration process of {sup 7}Be in soils of undisturbed or reference sites. The deposition history is approximated by pulse-like input functions and time dependent analytical solution of equation model is obtained. The values of dispersion coefficient and apparent advection velocity obtained
Osgood, Kenric E.; Frost, Bruce W.
1996-08-01
The copepodid stage abundances of Calanus marshallae, Calanus pacificus and Metridia pacifica in Dabob Bay, Washington were followed through two years. Based on the species' life histories, vertical distributions, abundances inside and outside the bay, and the hydrographic setting, times when advection was important were explored. During the first study-year, 1973, advection acted to keep the copepod concentrations inside and outside Dabob Bay similar through the early summer. During the summer, a period of very little advective exchange, the copepod concentrations diverged at the two stations. In the fall, when advection picked up again, the copepod concentrations at the two stations once again became similar. During the summer of the other study-year, 1982, flow of deep water into Dabob Bay occurred. This may have caused some of the differences observed in the abundances of the copepods during the summer of 1982 vs 1973. Due in part to the advective events, the seasonal abundance patterns of the copepods could not be predicted based upon their locally expressed life history patterns. The most striking example of this was C. pacificus. Its population decreased during the spring and increased during the fall, despite having its major reproductive peak in the spring. Advective effects clearly contributed to this.
Numerical Modeling of Deep Mantle Convection: Advection and Diffusion Schemes for Marker Methods
Mulyukova, Elvira; Dabrowski, Marcin; Steinberger, Bernhard
2013-04-01
Thermal and chemical evolution of Earth's deep mantle can be studied by modeling vigorous convection in a chemically heterogeneous fluid. Numerical modeling of such a system poses several computational challenges. Dominance of heat advection over the diffusive heat transport, and a negligible amount of chemical diffusion results in sharp gradients of thermal and chemical fields. The exponential dependence of the viscosity of mantle materials on temperature also leads to high gradients of the velocity field. The accuracy of many numerical advection schemes degrades quickly with increasing gradient of the solution, while the computational effort, in terms of the scheme complexity and required resolution, grows. Additional numerical challenges arise due to a large range of length-scales characteristic of a thermochemical convection system with highly variable viscosity. To examplify, the thickness of the stem of a rising thermal plume may be a few percent of the mantle thickness. An even thinner filament of an anomalous material that is entrained by that plume may consitute less than a tenth of a percent of the mantle thickness. We have developed a two-dimensional FEM code to model thermochemical convection in a hollow cylinder domain, with a depth- and temperature-dependent viscosity representative of the mantle (Steinberger and Calderwood, 2006). We use marker-in-cell method for advection of chemical and thermal fields. The main advantage of perfoming advection using markers is absence of numerical diffusion during the advection step, as opposed to the more diffusive field-methods. However, in the common implementation of the marker-methods, the solution of the momentum and energy equations takes place on a computational grid, and nodes do not generally coincide with the positions of the markers. Transferring velocity-, temperature-, and chemistry- information between nodes and markers introduces errors inherent to inter- and extrapolation. In the numerical scheme
Phase mixing versus nonlinear advection in drift-kinetic plasma turbulence
Schekochihin, A. A.; Parker, J. T.; Highcock, E. G.; Dellar, P. J.; Dorland, W.; Hammett, G. W.
2016-04-01
> A scaling theory of long-wavelength electrostatic turbulence in a magnetised, weakly collisional plasma (e.g. drift-wave turbulence driven by ion temperature gradients) is proposed, with account taken both of the nonlinear advection of the perturbed particle distribution by fluctuating flows and of its phase mixing, which is caused by the streaming of the particles along the mean magnetic field and, in a linear problem, would lead to Landau damping. It is found that it is possible to construct a consistent theory in which very little free energy leaks into high velocity moments of the distribution function, rendering the turbulent cascade in the energetically relevant part of the wavenumber space essentially fluid-like. The velocity-space spectra of free energy expressed in terms of Hermite-moment orders are steep power laws and so the free-energy content of the phase space does not diverge at infinitesimal collisionality (while it does for a linear problem); collisional heating due to long-wavelength perturbations vanishes in this limit (also in contrast with the linear problem, in which it occurs at the finite rate equal to the Landau damping rate). The ability of the free energy to stay in the low velocity moments of the distribution function is facilitated by the `anti-phase-mixing' effect, whose presence in the nonlinear system is due to the stochastic version of the plasma echo (the advecting velocity couples the phase-mixing and anti-phase-mixing perturbations). The partitioning of the wavenumber space between the (energetically dominant) region where this is the case and the region where linear phase mixing wins its competition with nonlinear advection is governed by the `critical balance' between linear and nonlinear time scales (which for high Hermite moments splits into two thresholds, one demarcating the wavenumber region where phase mixing predominates, the other where plasma echo does).
Performance Analysis of high-order remap-type advection scheme on icosahedral-hexagonal grid
Mittal, Rashmi; Dubey, Sarvesh; Saxena, Vaibhav; Meurdesoif, Yann
2014-05-01
A comparative performance analysis on computational cost of second order advection schemes FF-CSLAM (Flux form conservative semi-Lagrangian multi-tracer transport scheme) and it's two simplifications on Icosahedral grid has been presented. Tracer transport is one of the main building blocks in atmospheric models and hence their performance greatly determines the overall performance of the model. FF-CSLAM falls in the category of arbitrary Lagrangian Eulerian (ALE) scheme. It exploits the finite volume formulation and therefore it is inherently conservative. Flux-area through edges are approximated with great circle arcs in an upwind fashion. Bi-quadratic sub-grid scale reconstructions using weighted least-squares method is employed to approximate trace field. Area integrals on the overlapped region of flux-area and static Eulerian meshes are evaluated via line-integrals. A brief description of implementation of FF-CSLAM on icosahedral -hexagonal meshes along with and its numerical accuracy in terms of standard test cases will be presented. A comparative analysis of the computational overhead is necessary to assess the suitability of FF-CSLAM for massively parallel and multi-threading computer architectures in comparison to other advection schemes implemented on icosahedral grids. The main focus of this work is to present the implementation of the shared memory parallelization and to describe the memory access pattern of the numerical scheme. FF-CSLAM is a remap-type advection scheme, thus extra calculation are done in comparison to the other advection schemes. The additional computations are associated with the search required to find the overlap area between the area swept through the edge and the underlining grid. But the experiments shows that the associated computational overhead is minimal for multi-tracer transport. It will be shown that for the Courant Number less than one, FF-CSLAM, the computations are not expensive. Since the grid cells are arranged in
Accuracy of spectral and finite difference schemes in 2D advection problems
DEFF Research Database (Denmark)
Naulin, V.; Nielsen, A.H.
2003-01-01
In this paper we investigate the accuracy of two numerical procedures commonly used to solve 2D advection problems: spectral and finite difference (FD) schemes. These schemes are widely used, simulating, e.g., neutral and plasma flows. FD schemes have long been considered fast, relatively easy...... that the accuracy of FD schemes can be significantly improved if one is careful in choosing an appropriate FD scheme that reflects conservation properties of the nonlinear terms and in setting up the grid in accordance with the problem....
Really TVD advection schemes for the depth-integrated transport equation
Mercier, Ch.; Delhez, E. J. M.
This paper explores the use of TVD advection schemes to solve the depth-integrated transport equation for tracers in finite volume marine models. Numerical experiments show that the blind application of the usual TVD schemes and associated flux limiters can lead to non-TVD solutions when applied in complex geometries. Spatial and/or temporal variations of the local bathymetry can indeed break the TVD property of the usual schemes. Really TVD schemes can be recovered by taking into account the local depth and its variations in the formulation of the flux limiters. Using this approach, a generalized superbee limiter is introduced and validated.
Variational Integration for Ideal MHD with Built-in Advection Equations
Energy Technology Data Exchange (ETDEWEB)
Zhou, Yao [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); Qin, Hong [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); Burby, J. W. [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); Bhattacharjee, A. [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
2014-08-05
Newcomb's Lagrangian for ideal MHD in Lagrangian labeling is discretized using discrete exterior calculus. Variational integrators for ideal MHD are derived thereafter. Besides being symplectic and momentum preserving, the schemes inherit built-in advection equations from Newcomb's formulation, and therefore avoid solving them and the accompanying error and dissipation. We implement the method in 2D and show that numerical reconnection does not take place when singular current sheets are present. We then apply it to studying the dynamics of the ideal coalescence instability with multiple islands. The relaxed equilibrium state with embedded current sheets is obtained numerically.
Preconditioned iterative methods for space-time fractional advection-diffusion equations
Zhao, Zhi; Jin, Xiao-Qing; Lin, Matthew M.
2016-08-01
In this paper, we propose practical numerical methods for solving a class of initial-boundary value problems of space-time fractional advection-diffusion equations. First, we propose an implicit method based on two-sided Grünwald formulae and discuss its stability and consistency. Then, we develop the preconditioned generalized minimal residual (preconditioned GMRES) method and preconditioned conjugate gradient normal residual (preconditioned CGNR) method with easily constructed preconditioners. Importantly, because resulting systems are Toeplitz-like, fast Fourier transform can be applied to significantly reduce the computational cost. We perform numerical experiments to demonstrate the efficiency of our preconditioners, even in cases with variable coefficients.
The determination of an unknown source for a space fractional advection dispersion equation
Aldoghaither, Abeer
2014-09-01
In this paper, we are interested in the estimation of the source term for a space fractional advection dispersion equation using concentration and flux measurements at final time. An example of application is the identification of contamination source in groundwater transport. We propose to use the socalled modulating functions method which has been introduced for parameters estimation. This method allows to transfer the estimation problem into solving a system of algebraic equations. Numerical examples are given to illustrate the effectiveness and the robustness of the proposed method. Finally, a comparison between a Tikhonov-based optimization method and the modulating functions approach is presented.
2.5-dimensional solution of the advective accretion disk:a self-similar approach
Institute of Scientific and Technical Information of China (English)
Shubhrangshu Ghosh; Banibrata Mukhopadhyay
2009-01-01
We provide a 2.5-dimensional solution to a complete set of viscous hydrodynamical equations describing accretion-induced outflows and plausible jets around black holes/compact objects. We prescribe a self-consistent advective disk-outflow coupling model, which explicitly includes the information of vertical flux. Inter-connecting dynamics of an inflow-outflow system essentially upholds the conservation laws. We provide a set of analytical family of solutions through a self-similar approach. The flow parameters of the disk-outflow system depend strongly on the viscosity parameter α and the cooling factor f.
Maryshev, Boris; Latrille, Christelle; Néel, Marie-Christine
2016-01-01
Tracer tests in natural porous media sometimes show abnormalities that suggest considering a fractional variant of the Advection Diffusion Equation supplemented by a time derivative of non-integer order. We are describing an inverse method for this equation: it finds the order of the fractional derivative and the coefficients that achieve minimum discrepancy between solution and tracer data. Using an adjoint equation divides the computational effort by an amount proportional to the number of freedom degrees, which becomes large when some coefficients depend on space. Method accuracy is checked on synthetical data, and applicability to actual tracer test is demonstrated.
Convergence to a propagating front in a degenerate Fisher-KPP equation with advection
Alfaro, Matthieu
2011-01-01
We consider a Fisher-KPP equation with density-dependent diffusion and advection, arising from a chemotaxis-growth model. We study its behavior as a small parameter, related to the thickness of a diffuse interface, tends to zero. We analyze, for small times, the emergence of transition layers induced by a balance between reaction and drift effects. Then we investigate the propagation of the layers. Convergence to a free-boundary limit problem is proved and a sharp estimate of the thickness of the layers is provided.
Variational integration for ideal magnetohydrodynamics with built-in advection equations
International Nuclear Information System (INIS)
Newcomb's Lagrangian for ideal magnetohydrodynamics (MHD) in Lagrangian labeling is discretized using discrete exterior calculus. Variational integrators for ideal MHD are derived thereafter. Besides being symplectic and momentum-preserving, the schemes inherit built-in advection equations from Newcomb's formulation, and therefore avoid solving them and the accompanying error and dissipation. We implement the method in 2D and show that numerical reconnection does not take place when singular current sheets are present. We then apply it to studying the dynamics of the ideal coalescence instability with multiple islands. The relaxed equilibrium state with embedded current sheets is obtained numerically
Lester, D. R.; Trefry, M. G.; Metcalfe, G.
2016-11-01
The macroscopic spreading and mixing of solute plumes in saturated porous media is ultimately controlled by processes operating at the pore scale. Whilst the conventional picture of pore-scale mechanical dispersion and molecular diffusion leading to persistent hydrodynamic dispersion is well accepted, this paradigm is inherently two-dimensional (2D) in nature and neglects important three-dimensional (3D) phenomena. We discuss how the kinematics of steady 3D flow at the pore scale generate chaotic advection-involving exponential stretching and folding of fluid elements-the mechanisms by which it arises and implications of microscopic chaos for macroscopic dispersion and mixing. Prohibited in steady 2D flow due to topological constraints, these phenomena are ubiquitous due to the topological complexity inherent to all 3D porous media. Consequently 3D porous media flows generate profoundly different fluid deformation and mixing processes to those of 2D flow. The interplay of chaotic advection and broad transit time distributions can be incorporated into a continuous-time random walk (CTRW) framework to predict macroscopic solute mixing and spreading. We show how these results may be generalised to real porous architectures via a CTRW model of fluid deformation, leading to stochastic models of macroscopic dispersion and mixing which both honour the pore-scale kinematics and are directly conditioned on the pore-scale architecture.
A high order characteristic discontinuous Galerkin scheme for advection on unstructured meshes
Lee, D.; Lowrie, R.; Petersen, M.; Ringler, T.; Hecht, M.
2016-11-01
A new characteristic discontinuous Galerkin (CDG) advection scheme is presented. In contrast to standard discontinuous Galerkin schemes, the test functions themselves follow characteristics in order to ensure conservation and the edges of each element are also traced backwards along characteristics in order to create a swept region, which is integrated in order to determine the mass flux across the edge. Both the accuracy and performance of the scheme are greatly improved by the use of large Courant-Friedrichs-Lewy numbers for a shear flow test case and the scheme is shown to scale sublinearly with the number of tracers being advected, outperforming a standard flux corrected transport scheme for 10 or more tracers with a linear basis. Moreover the CDG scheme may be run to arbitrarily high order spatial accuracy and on unstructured grids, and is shown to give the correct order of error convergence for piecewise linear and quadratic bases on regular quadrilateral and hexahedral planar grids. Using a modal Taylor series basis, the scheme may be made monotone while preserving conservation with the use of a standard slope limiter, although this reduces the formal accuracy of the scheme to first order. The second order scheme is roughly as accurate as the incremental remap scheme with nonlocal gradient reconstruction at half the horizontal resolution. The scheme is being developed for implementation within the Model for Prediction Across Scales (MPAS) Ocean model, an unstructured grid finite volume ocean model.
Effect of advection on variations in zooplankton at a single location near Cabo Nazca, Peru
Energy Technology Data Exchange (ETDEWEB)
Smith, S L; Brink, K H; Santander, H; Cowles, T J; Huyer, A
1980-04-01
Temporal variations in the biomass and species composition of zooplankton at a single midshelf station in an upwelling area off Peru can be explained to a large extent by onshore-offshore advection in the upper 20 m of the water column. During periods of strong or sustained near-surface onshore flow, peaks in biomass of zooplankton were observed at midshelf and typically oceanic species of copepod were collected. In periods of offshore flow at the surface, a copepod capable of migrating into oxygen-depleted layers deeper than 30 m was collected. A simple translocation model of advection applied to the cross-shelf distribution of Paracalanus parvus suggests that the fluctuations in P. pavus observed in the midshelf time-series were closely related to onshore-offshore flow in the upper 20 m. Fluctuations in abundance of the numerically dominant copepod, Acartia tonsa, were apparently affected by near surface flow also. The population age-structure suggests that A. tonsa was growing at maximal rates, due in part to its positive feeding response to the dinoflagellate/diatom assemblage of phytoplankton.
Space-Time Fractional Diffusion-Advection Equation with Caputo Derivative
Directory of Open Access Journals (Sweden)
José Francisco Gómez Aguilar
2014-01-01
Full Text Available An alternative construction for the space-time fractional diffusion-advection equation for the sedimentation phenomena is presented. The order of the derivative is considered as 0<β, γ≤1 for the space and time domain, respectively. The fractional derivative of Caputo type is considered. In the spatial case we obtain the fractional solution for the underdamped, undamped, and overdamped case. In the temporal case we show that the concentration has amplitude which exhibits an algebraic decay at asymptotically large times and also shows numerical simulations where both derivatives are taken in simultaneous form. In order that the equation preserves the physical units of the system two auxiliary parameters σx and σt are introduced characterizing the existence of fractional space and time components, respectively. A physical relation between these parameters is reported and the solutions in space-time are given in terms of the Mittag-Leffler function depending on the parameters β and γ. The generalization of the fractional diffusion-advection equation in space-time exhibits anomalous behavior.
An advective-spectral-mixed method for time-dependent many-body Wigner simulations
Xiong, Yunfeng; Shao, Sihong
2016-01-01
As a phase space language for quantum mechanics, the Wigner function approach bears a close analogy to classical mechanics and has been drawing growing attention, especially in simulating quantum many-body systems. However, deterministic numerical solutions have been almost exclusively confined to one-dimensional one-body systems and few results are reported even for one-dimensional two-body problems. This paper serves as the first attempt to solve the time-dependent many-body Wigner equation through a grid-based advective-spectral-mixed method. The main feature of the method is to resolve the linear advection in $(\\bm{x},t)$-space by an explicit three-step characteristic scheme coupled with the piecewise cubic spline interpolation, while the Chebyshev spectral element method in $\\bm k$-space is adopted for accurate calculation of the nonlocal pseudo-differential term. Not only the time step of the resulting method is not restricted by the usual CFL condition and thus a large time step is allowed, but also th...
Modeling of advection-diffusion-reaction processes using transport dissipative particle dynamics
Li, Zhen; Yazdani, Alireza; Tartakovsky, Alexandre; Karniadakis, George Em
2015-11-01
We present a transport dissipative particle dynamics (tDPD) model for simulating mesoscopic problems involving advection-diffusion-reaction (ADR) processes, along with a methodology for implementation of the correct Dirichlet and Neumann boundary conditions in tDPD simulations. In particular, the transport of concentration is modeled by a Fickian flux and a random flux between tDPD particles, and the advection is implicitly considered by the movements of Lagrangian particles. To validate the proposed tDPD model and the boundary conditions, three benchmark simulations of one-dimensional diffusion with different boundary conditions are performed, and the results show excellent agreement with the theoretical solutions. Also, two-dimensional simulations of ADR systems are performed and the tDPD simulations agree well with the results obtained by the spectral element method. Finally, an application of tDPD to the spatio-temporal dynamics of blood coagulation involving twenty-five reacting species is performed to demonstrate the promising biological applications of the tDPD model. Supported by the DOE Center on Mathematics for Mesoscopic Modeling of Materials (CM4) and an INCITE grant.
Siero, E; Doelman, A; Eppinga, M B; Rademacher, J D M; Rietkerk, M; Siteur, K
2015-03-01
For water-limited arid ecosystems, where water distribution and infiltration play a vital role, various models have been set up to explain vegetation patterning. On sloped terrains, vegetation aligned in bands has been observed ubiquitously. In this paper, we consider the appearance, stability, and bifurcations of 2D striped or banded patterns in an arid ecosystem model. We numerically show that the resilience of the vegetation bands is larger on steeper slopes by computing the stability regions (Busse balloons) of striped patterns with respect to 1D and transverse 2D perturbations. This is corroborated by numerical simulations with a slowly decreasing water input parameter. Here, long wavelength striped patterns are unstable against transverse perturbations, which we also rigorously prove on flat ground through an Evans function approach. In addition, we prove a "Squire theorem" for a class of two-component reaction-advection-diffusion systems that includes our model, showing that the onset of pattern formation in 2D is due to 1D instabilities in the direction of advection, which naturally leads to striped patterns. PMID:25833449
Institute of Scientific and Technical Information of China (English)
HUANG Rui Xin
2014-01-01
Two important nonlinear properties of seawater thermodynamics linked to changes of water density, cab-beling and elasticity (compressibility), are discussed. Eddy diffusion and advection lead to changes in den-sity;as a result, gravitational potential energy of the system is changed. Therefore, cabbeling and elasticity play key roles in the energetics of lateral eddy diffusion and advection. Vertical eddy diffusion is one of the key elements in the mechanical energy balance of the global oceans. Vertical eddy diffusion can be con-ceptually separated into two steps:stirring and subscale diffusion. Vertical eddy stirring pushes cold/dense water upward and warm/light water downward;thus, gravitational potential energy is increased. During the second steps, water masses from different places mix through subscale diffusion, and water density is increased due to cabbeling. Using WOA01 climatology and assuming the vertical eddy diffusivity is equal to a constant value of 2×103 Pa2/s, the total amount of gravitational potential energy increase due to vertical stirring in the world oceans is estimated at 263 GW. Cabbeling associated with vertical subscale diffusion is a sink of gravitational potential energy, and the total value of energy lost is estimated at 73 GW. Therefore, the net source of gravitational potential energy due to vertical eddy diffusion for the world oceans is estimated at 189 GW.
Optimizing zonal advection of the Advanced Research WRF (ARW) dynamics for Intel MIC
Mielikainen, Jarno; Huang, Bormin; Huang, Allen H.
2014-10-01
The Weather Research and Forecast (WRF) model is the most widely used community weather forecast and research model in the world. There are two distinct varieties of WRF. The Advanced Research WRF (ARW) is an experimental, advanced research version featuring very high resolution. The WRF Nonhydrostatic Mesoscale Model (WRF-NMM) has been designed for forecasting operations. WRF consists of dynamics code and several physics modules. The WRF-ARW core is based on an Eulerian solver for the fully compressible nonhydrostatic equations. In the paper, we will use Intel Intel Many Integrated Core (MIC) architecture to substantially increase the performance of a zonal advection subroutine for optimization. It is of the most time consuming routines in the ARW dynamics core. Advection advances the explicit perturbation horizontal momentum equations by adding in the large-timestep tendency along with the small timestep pressure gradient tendency. We will describe the challenges we met during the development of a high-speed dynamics code subroutine for MIC architecture. Furthermore, lessons learned from the code optimization process will be discussed. The results show that the optimizations improved performance of the original code on Xeon Phi 5110P by a factor of 2.4x.
Institute of Scientific and Technical Information of China (English)
2006-01-01
<正>As well known, the methods of remote sensing and Bowen Ratio for retrieving surface flux are based on energy balance closure; however, in most cases, surface energy observed in experiment is lack of closure. There are two main causes for this: one is from the errors of the observation devices and the differences of their observational scale; the other lies in the effect of horizontal advection on the surface flux measurement. Therefore, it is very important to estimate the effects of horizontal advection quantitatively. Based on the local advection theory and the surface experiment, a model has been proposed for correcting the effect of horizontal advection on surface flux measurement, in which the relationship between the fetch of the measurement and pixel size for remote sensed data was considered. By means of numerical simulations, the sensitivities of the main parameters in the model and the scaling problems of horizontal advection were analyzed. At last, by using the observational data acquired in agricultural field with relatively homogeneous surface, the model was validated.
Wilderbuer, Thomas; Duffy-Anderson, Janet T.; Stabeno, Phyllis; Hermann, Albert
2016-05-01
In an effort to better understand the physics of the eastern Bering Sea shelf current as it relates to flatfish advection to favorable near-shore areas, sets of multiple, satellite-tracked, oceanic drifters were released in 2010, 2012 and 2013. The release sites and dates were chosen to coincide with known spawning locations for northern rock sole (Lepidopsetta polyxystra) and known time of larval emergence. The drifters were drogued 5-each at 20 and 40 m in 2010 and 2012, and 4 at 40 m and 2 at 20 m in 2013. The locations of drifters were used to calculate divergence over a 90-day period that corresponds to the larval pelagic duration of Bering Sea shelf northern rock sole. Results indicate that there are alternating periods of positive and negative divergence with an overall trend toward drifter separation after 90 days, roughly the end of the rock sole planktonic larval period. Examination of the drifter behavior at the hourly scale indicates that semi-daily tidal forcing is the primary mechanism of drifter divergence and convergence. Field observations of early-stage northern rock sole larval distributions over the same period indicate that predominant oceanographic advection is northerly over the continental shelf among preflexion stages, though juveniles are predominantly found in nursery areas located ~ 400 km eastward and inshore. Evidence from drifter deployments suggests that behavioral movements during the postflexion and early juvenile larval phases that optimize eastward periodicity of tidal cycles is a viable mechanism to enhance eastward movement of northern rock sole larvae to favorable nursery grounds. A regional ocean modeling system (ROMS) was implemented to track the different rates of dispersion in simulations both with and without tidal forcing, and was used to estimate effective horizontal eddy diffusion in the case of both isobaric (fixed-depth) and Lagrangian (neutrally buoyant) particles. The addition of tidal forcing had a pronounced
Developing a modified SEBAL algorithm that is responsive to advection by using limited weather data
Mkhwanazi, Mcebisi
The use of Remote Sensing ET algorithms in water management, especially for agricultural purposes is increasing, and there are more models being introduced. The Surface Energy Balance Algorithm for Land (SEBAL) and its variant, Mapping Evapotranspiration with Internalized Calibration (METRIC) are some of the models that are being widely used. While SEBAL has several advantages over other RS models, including that it does not require prior knowledge of soil, crop and other ground details, it has the downside of underestimating evapotranspiration (ET) on days when there is advection, which may be in most cases in arid and semi-arid areas. METRIC, however has been modified to be able to account for advection, but in doing so it requires hourly weather data. In most developing countries, while accurate estimates of ET are required, the weather data necessary to use METRIC may not be available. This research therefore was meant to develop a modified version of SEBAL that would require minimal weather data that may be available in these areas, and still estimate ET accurately. The data that were used to develop this model were minimum and maximum temperatures, wind data, preferably the run of wind in the afternoon, and wet bulb temperature. These were used to quantify the advected energy that would increase ET in the field. This was a two-step process; the first was developing the model for standard conditions, which was described as a healthy cover of alfalfa, 40-60 cm tall and not short of water. Under standard conditions, when estimated ET using modified SEBAL was compared with lysimeter-measured ET, the modified SEBAL model had a Mean Bias Error (MBE) of 2.2 % compared to -17.1 % from the original SEBAL. The Root Mean Square Error (RMSE) was lower for the modified SEBAL model at 10.9 % compared to 25.1 % for the original SEBAL. The modified SEBAL model, developed on an alfalfa field in Rocky Ford, was then tested on other crops; beans and wheat. It was also tested on
Advection from the North Atlantic as the Forcing of Winter Greenhouse Effect Over Europe
Otterman, J.; Angell, J.; Atlas, R.; Bungato, D.; Shubert, S.; Starr, David OC.; Susskind, J.; Wu, M.-L. C.
2002-01-01
In winter, large interannual fluctuations in the surface temperature are observed over central Europe. Comparing warm February 1990 with cold February 1996, a satellite-retrieved surface (skin) temperature difference of 9.8 K is observed for the region 50-60 degrees N; 5-35 degrees E. Previous studies show that advection from the North Atlantic constitutes the forcing to such fluctuations. The advection is quantified by Index I(sub na), the average of the ocean-surface wind speed over the eastern North Atlantic when the direction is from the southwest (when the wind is from another direction, it counts as a zero speed to the average). Average I(sub na) for February 1990 was 10.6 m/s, but for February 1996 I(sub na) was only 2.4 m/s. A large value of I(sub na) means a strong southwesterly flow which brings warm and moist air into central Europe at low level, producing a steeper tropospheric lapse rate. Strong ascending motions at 700 mb are observed in association with the occurrence of enhanced warm, moist advection from the ocean in February 1990 producing clouds and precipitation. Total precipitable water and cloud-cover fraction have larger values in February 1990 than in 1996. The difference in the greenhouse effect between these two scenarios, this reduction in heat loss to space, can be translated into a virtual radiative heating of 2.6 W/square m above the February 1990 surface/atmosphere system, which contributes to a warming of the surface on the order of 2.6 K. Accepting this estimate as quantitatively meaningful, we evaluate the direct effect, the rise in the surface temperature in Europe as a result of maritime-air inflow, as 7.2 K (9.8 K-2.6 K). Thus, fractional reinforcement by the greenhouse effect is 2.6/7.2, or 36%, a substantial positive feedback.
Chakrabarti, Sandip K
2016-01-01
An accretion flow around a black hole has a saddle type sonic point just outside the event horizon to guarantee that the flow enters the black hole supersonically. This feature exclusively present in strong gravity limit makes its marks in every observation of black hole candidates. Another physical sonic point is present (as in a Bondi flow) even in weak gravity. Every aspect of spectral or temporal properties of every black hole can be understood using this transonic or advective flow having more than one saddle type points. This most well known and generalized solution with viscosity and radiative transfer has been verified by numerical simulations also. Spectra, computed for various combinations of the standard Keplerian, and advective sub-Keplerian components match accurately with those from satellite observations. Standing, oscillating and propagatory oscillating shocks are produced due to centrifugal barrier of the advective component. The post-shock region acts as the Compton cloud producing the power...
Preconditioned time-difference methods for advection-diffusion-reaction equations
Energy Technology Data Exchange (ETDEWEB)
Aro, C.; Rodrigue, G. [Lawrence Livermore National Lab., CA (United States); Wolitzer, D. [California State Univ., Hayward, CA (United States)
1994-12-31
Explicit time differencing methods for solving differential equations are advantageous in that they are easy to implement on a computer and are intrinsically very parallel. The disadvantage of explicit methods is the severe restrictions placed on stepsize due to stability. Stability bounds for explicit time differencing methods on advection-diffusion-reaction problems are generally quite severe and implicit methods are used instead. The linear systems arising from these implicit methods are large and sparse so that iterative methods must be used to solve them. In this paper the authors develop a methodology for increasing the stability bounds of standard explicit finite differencing methods by combining explicit methods, implicit methods, and iterative methods in a novel way to generate new time-difference schemes, called preconditioned time-difference methods.
Directory of Open Access Journals (Sweden)
Dali Zhang
2012-01-01
Full Text Available This paper deals with an inverse problem for identifying multiparameters in 1D space fractional advection dispersion equation (FADE on a finite domain with final observations. The parameters to be identified are the fractional order, the diffusion coefficient, and the average velocity in the FADE. The forward problem is solved by a finite difference scheme, and then an optimal perturbation regularization algorithm is introduced to determine the three parameters simultaneously. Numerical inversions are performed both with the accurate data and noisy data, and several factors having influences on realization of the algorithm are discussed. The inversion solutions are in good approximations to the exact solutions demonstrating the efficiency of the proposed algorithm.
Advection and diffusion in random media implications for sea surface temperature anomalies
Piterbarg, Leonid I
1997-01-01
The book presents the foundations of the theory of turbulent transport within the context of stochastic partial differential equations. It serves to establish a firm connection between rigorous and non-rigorous results concerning turbulent diffusion. Mathematically all of the issues addressed in this book are concentrated around a single linear equation: stochastic advection-diffusion (transport) equation. There is no attempt made to derive universal statistics for turbulent flow. Instead emphasis is placed on a statistical description of a passive scalar (tracer) under given velocity statistics. An application concerning transport of sea surface temperature anomalies reconciles the developed theory and a highly practical issue of modern physical oceanography by using the newly designed inversion techniques which take advantage of powerful maximum likelihood and autoregressive estimators. Audience: Graduate students and researchers in mathematics, fluid dynamics, and physical oceanography.
Analytical Solutions of a Fractional Diffusion-advection Equation for Solar Cosmic-Ray Transport
Litvinenko, Yuri E.; Effenberger, Frederic
2014-12-01
Motivated by recent applications of superdiffusive transport models to shock-accelerated particle distributions in the heliosphere, we analytically solve a one-dimensional fractional diffusion-advection equation for the particle density. We derive an exact Fourier transform solution, simplify it in a weak diffusion approximation, and compare the new solution with previously available analytical results and with a semi-numerical solution based on a Fourier series expansion. We apply the results to the problem of describing the transport of energetic particles, accelerated at a traveling heliospheric shock. Our analysis shows that significant errors may result from assuming an infinite initial distance between the shock and the observer. We argue that the shock travel time should be a parameter of a realistic superdiffusive transport model.
Analytical solutions of a fractional diffusion-advection equation for solar cosmic-ray transport
Litvinenko, Yuri E
2014-01-01
Motivated by recent applications of superdiffusive transport models to shock-accelerated particle distributions in the heliosphere, we solve analytically a one-dimensional fractional diffusion-advection equation for the particle density. We derive an exact Fourier transform solution, simplify it in a weak diffusion approximation, and compare the new solution with previously available analytical results and with a semi-numerical solution based on a Fourier series expansion. We apply the results to the problem of describing the transport of energetic particles, accelerated at a traveling heliospheric shock. Our analysis shows that significant errors may result from assuming an infinite initial distance between the shock and the observer. We argue that the shock travel time should be a parameter of a realistic superdiffusive transport model.
Advection of pollutants by internal solitary waves in oceanic and atmospheric stable stratifications
Directory of Open Access Journals (Sweden)
G. W. Haarlemmer
1998-01-01
Full Text Available When a pollutant is released into the ocean or atmosphere under turbulent conditions, even a steady release is captured by large eddies resulting in localized patches of high concentration of the pollutant. If such a cloud of pollutant subsequently enters a stable stratification-either a pycnocline or thermocline-then internal waves are excited. Since large solitary internal waves have a recirculating core, pollutants may be trapped in the sclitary wave, and advected large distances through the waveguide provided by the stratification. This paper addresses the mechanisms, through computer and physical simulation, by which a localized release of a dense pollutant results in solitary waves that trap the pollutant or disperse the pollutant faster than in the absence of the waves.
Mignone, A; Stute, M; Kolb, S M; Muscianisi, G
2012-01-01
Explicit numerical computations of super-fast differentially rotating disks are subject to the time-step constraint imposed by the Courant condition. When the bulk orbital velocity largely exceeds any other wave speed the time step is considerably reduced and a large number of steps may be necessary to complete the computation. We present a robust numerical scheme to overcome the Courant limitation by extending the algorithm previously known as FARGO (Fast Advection in Rotating Gaseous Objects) to the equations of magnetohydrodynamics (MHD). The proposed scheme conserves total angular momentum and energy to machine precision and works in Cartesian, cylindrical, or spherical coordinates. The algorithm is implemented in the PLUTO code for astrophysical gasdynamics and is suitable for local or global simulations of accretion or proto-planetary disk models. By decomposing the total velocity into an average azimuthal contribution and a residual term, the algorithm solves the MHD equations through a linear transpor...
Advection Dominated Accretion Flows in the Kerr Metric; 1, Basic Equations
Gammie, C F; Gammie, Charles F.; Popham, Robert
1997-01-01
We write down and solve equations describing steady state, optically thin, advection-dominated accretion onto a Kerr black hole. The mean flow, described by the relativistic fluid equations, is axisymmetric and vertically averaged. The effect of turbulence in the flow is represented by a viscous shear stress. Our treatment differs in several important ways from earlier work: we use a causal prescription for the shear stress, we do not assume the relativistic enthalpy is unity (this is important for rapidly rotating holes), and we use a relativistic equation of state. We present several representative solutions and use them to evaluate the importance of relativistic effects, to check our approximations, and to evaluate the robustness of the input physics. Detailed properties of the solutions are described in an accompanying paper.
Moments Preserving and high-resolution Semi-Lagrangian Advection Scheme
Becerra-Sagredo, Julián; Mandujano, Francisco
2014-01-01
We present a forward semi-Lagrangian numerical method for systems of transport equations able to advect smooth and discontinuous fields with high-order accuracy. The numerical scheme is composed of an integration of the transport equations along the trajectory of material elements in a moving grid and a reconstruction of the fields in a reference regular mesh using a non-linear mapping and adaptive moment-preserving interpolations. The non-linear mapping allows for the arbitrary deformation of material elements. Additionally, interpolations can represent discontinuous fields using adaptive-order interpolation near jumps detected with a slope-limiter function. Due to the large number of operations during the interpolations, a serial implementation of this scheme is computationally expensive. The scheme has been accelerated in many-core parallel architectures using a thread per grid node and parallel data gathers. We present a series of tests that prove the scheme to be an attractive option for simulating advec...
Energy Technology Data Exchange (ETDEWEB)
Richon, Patrick, E-mail: patrick.richon@cea.f [CEA, DAM, DIF, F-91297 Arpajon (France); Equipe Geologie des Systemes Volcaniques, Institut de Physique du Globe, 1 rue Jussieu, F-75238 Paris cedex 05 (France); Universite Paris Diderot, Sorbonne Paris Cite (France); Perrier, Frederic [Equipe de Geomagnetisme, Institut de Physique du Globe, 1 rue Jussieu, F-75238 Paris cedex 05 (France); Universite Paris Diderot, Sorbonne Paris Cite (France), CNRS (UMR 7154) (France); Koirala, Bharat Prasad [National Seismological Centre, Department of Mines and Geology, Lainchaur, Kathmandu (Nepal); Girault, Frederic [Equipe de Geomagnetisme, Institut de Physique du Globe, 1 rue Jussieu, F-75238 Paris cedex 05 (France); Universite Paris Diderot, Sorbonne Paris Cite (France), CNRS (UMR 7154) (France); Bhattarai, Mukunda; Sapkota, Soma Nath [National Seismological Centre, Department of Mines and Geology, Lainchaur, Kathmandu (Nepal)
2011-02-15
Temporal variation of radon-222 concentration was studied at the Syabru-Bensi hot springs, located on the Main Central Thrust zone in Central Nepal. This site is characterized by several carbon dioxide discharges having maximum fluxes larger than 10 kg m{sup -2} d{sup -1}. Radon concentration was monitored with autonomous Barasol{sup TM} probes between January 2008 and November 2009 in two small natural cavities with high CO{sub 2} concentration and at six locations in the soil: four points having a high flux, and two background reference points. At the reference points, dominated by radon diffusion, radon concentration was stable from January to May, with mean values of 22 {+-} 6.9 and 37 {+-} 5.5 kBq m{sup -3}, but was affected by a large increase, of about a factor of 2 and 1.6, respectively, during the monsoon season from June to September. At the points dominated by CO{sub 2} advection, by contrast, radon concentration showed higher mean values 39.0 {+-} 2.6 to 78 {+-} 1.4 kBq m{sup -3}, remarkably stable throughout the year with small long-term variation, including a possible modulation of period around 6 months. A significant difference between the diffusion dominated reference points and the advection-dominated points also emerged when studying the diurnal S{sub 1} and semi-diurnal S{sub 2} periodic components. At the advection-dominated points, radon concentration did not exhibit S{sub 1} or S{sub 2} components. At the reference points, however, the S{sub 2} component, associated with barometric tide, could be identified during the dry season, but only when the probe was installed at shallow depth. The S{sub 1} component, associated with thermal and possibly barometric diurnal forcing, was systematically observed, especially during monsoon season. The remarkable short-term and long-term temporal stability of the radon concentration at the advection-dominated points, which suggests a strong pressure source at depth, may be an important asset to detect
Numerical calculation of tidal current with UTOPIA scheme for advection and application to Osaka Bay
Komoda, Jun; Matsuyama, Masaji
UTOPIA scheme was applied to advection term for the numerical calculation of tide and tidal current to reproduce the strong tidal current realistically. Numerical model is constructed by boundary-fitted coordinate method vertically using Arakawa A grid in space. The new method is designed to suppress a numerical oscillation usually induced by Arakawa A grid. UTOPIA scheme was confirmed to be suitable to express a strong current around complicated topography. This model was applied to the tidal calculation for M2 constituent in Osaka Bay with two narrow straits, i.e., Akashi and Tomogashima straits. The tidal currents obtained in this model agree with them observed at monitoring stations, and the four eddies in the bay were also reproduced as the residual currents, i.e., tide induced transient eddy (TITE). The generation, growth and lifetime of the eddies also were investigated.
Multiscale numerical methods for passive advection-diffusion in incompressible turbulent flow fields
Lee, Yoonsang; Engquist, Bjorn
2016-07-01
We propose a seamless multiscale method which approximates the macroscopic behavior of the passive advection-diffusion equations with steady incompressible velocity fields with multi-spatial scales. The method uses decompositions of the velocity fields in the Fourier space, which are similar to the decomposition in large eddy simulations. It also uses a hierarchy of local domains with different resolutions as in multigrid methods. The effective diffusivity from finer scale is used for the next coarser level computation and this process is repeated up to the coarsest scale of interest. The grids are only in local domains whose sizes decrease depending on the resolution level so that the overall computational complexity increases linearly as the number of different resolution grids increases. The method captures interactions between finer and coarser scales but has to sacrifice some of interactions between different scales. The proposed method is numerically tested with 2D examples including a successful approximation to a continuous spectrum flow.
A self-organizing Lagrangian particle method for adaptive-resolution advection-diffusion simulations
Reboux, Sylvain; Schrader, Birte; Sbalzarini, Ivo F.
2012-05-01
We present a novel adaptive-resolution particle method for continuous parabolic problems. In this method, particles self-organize in order to adapt to local resolution requirements. This is achieved by pseudo forces that are designed so as to guarantee that the solution is always well sampled and that no holes or clusters develop in the particle distribution. The particle sizes are locally adapted to the length scale of the solution. Differential operators are consistently evaluated on the evolving set of irregularly distributed particles of varying sizes using discretization-corrected operators. The method does not rely on any global transforms or mapping functions. After presenting the method and its error analysis, we demonstrate its capabilities and limitations on a set of two- and three-dimensional benchmark problems. These include advection-diffusion, the Burgers equation, the Buckley-Leverett five-spot problem, and curvature-driven level-set surface refinement.
International Nuclear Information System (INIS)
Temporal variation of radon-222 concentration was studied at the Syabru-Bensi hot springs, located on the Main Central Thrust zone in Central Nepal. This site is characterized by several carbon dioxide discharges having maximum fluxes larger than 10 kg m-2 d-1. Radon concentration was monitored with autonomous BarasolTM probes between January 2008 and November 2009 in two small natural cavities with high CO2 concentration and at six locations in the soil: four points having a high flux, and two background reference points. At the reference points, dominated by radon diffusion, radon concentration was stable from January to May, with mean values of 22 ± 6.9 and 37 ± 5.5 kBq m-3, but was affected by a large increase, of about a factor of 2 and 1.6, respectively, during the monsoon season from June to September. At the points dominated by CO2 advection, by contrast, radon concentration showed higher mean values 39.0 ± 2.6 to 78 ± 1.4 kBq m-3, remarkably stable throughout the year with small long-term variation, including a possible modulation of period around 6 months. A significant difference between the diffusion dominated reference points and the advection-dominated points also emerged when studying the diurnal S1 and semi-diurnal S2 periodic components. At the advection-dominated points, radon concentration did not exhibit S1 or S2 components. At the reference points, however, the S2 component, associated with barometric tide, could be identified during the dry season, but only when the probe was installed at shallow depth. The S1 component, associated with thermal and possibly barometric diurnal forcing, was systematically observed, especially during monsoon season. The remarkable short-term and long-term temporal stability of the radon concentration at the advection-dominated points, which suggests a strong pressure source at depth, may be an important asset to detect possible temporal variations associated with the seismic cycle. - Graphical abstract: Radon
Bias adjustment and advection interpolation of long-term high resolution radar rainfall series
DEFF Research Database (Denmark)
Thorndahl, Søren Liedtke; Nielsen, Jesper Ellerbæk; Rasmussen, Michael R.
2014-01-01
known to depend on the changing drop size distribution of the specific rain. This creates a transient bias between the radar rainfall and the ground observations due to seasonal changes of the drop size distribution as well as other atmospheric effects and effects related to the radar observational...... technology. In this study different bias adjustment techniques is investigated, developing a complete 10-year dataset (2002–2012) of high spatio-temporal resolution radar rainfall based on a radar observations from a single C-band radar from Denmark. Results show that hourly adjustment mean field bias...... adjustment outperform daily mean field bias adjustment with regards to estimation of rainfall totals and peak rain rates. Furthermore, it is demonstrated that radar rainfall estimates can be improved significantly by implementation of a novel advection interpolation technique....
Mandal, S; Mandal, Samir; Chakrabarti, Sandip K.
2005-01-01
Centrifugal barrier supported boundary layer (CENBOL) of a black hole affects the spectrum exactly in the same way the boundary layer of a neutron star does. The CENBOL is produced due to standing or oscillating shock waves and these shocks accelerate electrons very efficiently and produce a power-law distribution. The accelerated particles in turn emit synchrotron radiation in presence of the magnetic field. We study the spectral properties of an accretion disk as a function of the shock strength, compression ratio, flow accretion rate and flow geometry. In the absence of a satisfactory description of magnetic fields inside the advective disk, we consider the presence of only stochastic fields and use the ratio of the field energy density to the gravitational energy density to be a parameter. Not surprisingly, stronger fields produce stronger humps due to synchrotron radiation. We not only include `conventional' synchrotron emission and Comptonization due to Maxwell-Bolzmann electrons in the gas, we also com...
Correlation networks from flows. The case of forced and time-dependent advection-diffusion dynamics
Tupikina, Liubov; López, Cristóbal; Hernández-García, Emilio; Marwan, Norbert; Kurths, Jürgen
2016-01-01
Complex network theory provides an elegant and powerful framework to statistically investigate different types of systems such as society, brain or the structure of local and long-range dynamical interrelationships in the climate system. Network links in climate networks typically imply information, mass or energy exchange. However, the specific connection between oceanic or atmospheric flows and the climate network's structure is still unclear. We propose a theoretical approach for verifying relations between the correlation matrix and the climate network measures, generalizing previous studies and overcoming the restriction to stationary flows. Our methods are developed for correlations of a scalar quantity (temperature, for example) which satisfies an advection-diffusion dynamics in the presence of forcing and dissipation. Our approach reveals that correlation networks are not sensitive to steady sources and sinks and the profound impact of the signal decay rate on the network topology. We illustrate our r...
Dynamics of Magnetic Flux Tubes in an Advective Flow around a Black Hole
Deb, Arnab; Chakrabarti, Sandip Kumar; Giri, Kinsuk
2016-07-01
Magnetic fields cannibalized by an accretion flow would very soon have a dominant toroidal component. Without changing the topology, we study the movements of these flux tubes inside a geometrically thick advective disk which undergo centrifugal pressure supported shocks. We also consider the effects of the flux tubes on the flow. We use a finite element method (Total Variation Diminishing) for this purpose and specifically focussed whether the flux tubes contribute to changes in outflow properties in terms of its collimation and outflow rates. It is seen that depending upon the cross sectional radius of the flux tubes (which control the drag force), these field lines may move towards the central object or oscillate vertically before eventually escaping out of the funnel wall (pressure zero surface). These interesting results obtained with and without flux tubes point to the role the flux tubes play in collimation of jets and outflows.
Measurements on, and modelling of diffusive and advective radon transport in soil
DEFF Research Database (Denmark)
Graff, E.R. van der; Witteman, G.A.A.; Spoel, W.H. van der;
1994-01-01
Results are presented of measurements on radon transport in soil under controlled conditions with a laboratory facility consisting of a stainless steel vessel (height and diameter 2 m) filled with a uniform column of sand. At several depths under the sand surface, probes are radially inserted...... into the vessel to measure the radon concentration in the soil gas. To study advective radon transport a perforated circular box is placed in the sand close to the bottom of the vessel. By pressurising this box, an air flow through the sand column is induced. Radon concentration profiles were measured without...... an air flow as a function of time, and for several values of the air flow, equilibrium radon concentration profiles were measured....
International Nuclear Information System (INIS)
Effect of change in wasted water from nuclear or fossil fuel power plants discharging direction from horizontal one to depression angle one on an advective diffusion process of hot wasted water was investigated. As a result, it could be confirmed that an effect of depression angle jet discharge on water temperature reduction and so forth could be applied present experimental equation on horizontal discharging by a coordinate transformation of various factors with discharging water angle. And, a judgement equation to obtain a limiting area of hot wasted water affecting with bed surface was obtained by using distance from the lowest point of jet to the sea bed, inner diameter of discharging pipe, and field number for parameters, to elucidate its effectiveness. Furthermore, a diagram to estimate an effect of depression angle discharging water in the area on water temperature reduction and so forth was also proposed. (G.K.)
Kordilla, Jannes; Pan, Wenxiao; Tartakovsky, Alexandre
2014-12-01
We propose a novel smoothed particle hydrodynamics (SPH) discretization of the fully coupled Landau-Lifshitz-Navier-Stokes (LLNS) and stochastic advection-diffusion equations. The accuracy of the SPH solution of the LLNS equations is demonstrated by comparing the scaling of velocity variance and the self-diffusion coefficient with kinetic temperature and particle mass obtained from the SPH simulations and analytical solutions. The spatial covariance of pressure and velocity fluctuations is found to be in a good agreement with theoretical models. To validate the accuracy of the SPH method for coupled LLNS and advection-diffusion equations, we simulate the interface between two miscible fluids. We study formation of the so-called "giant fluctuations" of the front between light and heavy fluids with and without gravity, where the light fluid lies on the top of the heavy fluid. We find that the power spectra of the simulated concentration field are in good agreement with the experiments and analytical solutions. In the absence of gravity, the power spectra decay as the power -4 of the wavenumber—except for small wavenumbers that diverge from this power law behavior due to the effect of finite domain size. Gravity suppresses the fluctuations, resulting in much weaker dependence of the power spectra on the wavenumber. Finally, the model is used to study the effect of thermal fluctuation on the Rayleigh-Taylor instability, an unstable dynamics of the front between a heavy fluid overlaying a light fluid. The front dynamics is shown to agree well with the analytical solutions.
Institute of Scientific and Technical Information of China (English)
HUANG Guanhua; HUANG Quanzhong; ZHAN Hongbin; CHEN Jing; XIONG Yunwu; FENG Shaoyuan
2005-01-01
The newly developed Fractional Advection-Dispersion Equation (FADE), which is FADE was extended and used in this paper for modelling adsorbing contaminant transport by adding an adsorbing term. A parameter estimation method and its corresponding FORTRAN based program named FADEMain were developed on the basis of Nonlinear Least Square Algorithm and the analytical solution for one-dimensional FADE under the conditions of step input and steady state flow. Data sets of adsorbing contaminants Cd and NH4+-N transport in short homogeneous soil columns and conservative solute NaCI transport in a long homogeneous soil column, respectively were used to estimate the transport parameters both by FADEMain and the advection-dispersion equation (ADE) based program CXTFIT2.1. Results indicated that the concentration simulated by FADE agreed well with the measured data. Compared to the ADE model, FADE can provide better simulation for the concentration in the initial lower concentration part and the late higher concentration part of the breakthrough curves for both adsorbing contaminants. The dispersion coefficients for ADE were from 0.13 to 7.06 cm2/min, while the dispersion coefficients for FADE ranged from 0.119 to 3.05 cm1.856/min for NaCI transport in the long homogeneous soil column. We found that the dispersion coefficient of FADE increased with the transport distance, and the relationship between them can be quantified with an exponential function. Less scale-dependent was also found for the dispersion coefficient of FADE with respect to ADE.
Gillibrand, P. A.; Herzfeld, M.
2016-05-01
We present a flux-form semi-Lagrangian (FFSL) advection scheme designed for offline scalar transport simulation with coastal ocean models using curvilinear horizontal coordinates. The scheme conserves mass, overcoming problems of mass conservation typically experienced with offline transport models, and permits long time steps (relative to the Courant number) to be used by the offline model. These attributes make the method attractive for offline simulation of tracers in biogeochemical or sediment transport models using archived flow fields from hydrodynamic models. We describe the FFSL scheme, and test it on two idealised domains and one real domain, the Great Barrier Reef in Australia. For comparison, we also include simulations using a traditional semi-Lagrangian advection scheme for the offline simulations. We compare tracer distributions predicted by the offline FFSL transport scheme with those predicted by the original hydrodynamic model, assess the conservation of mass in all cases and contrast the computational efficiency of the schemes. We find that the FFSL scheme produced very good agreement with the distributions of tracer predicted by the hydrodynamic model, and conserved mass with an error of a fraction of one percent. In terms of computational speed, the FFSL scheme was comparable with the semi-Lagrangian method and an order of magnitude faster than the full hydrodynamic model, even when the latter ran in parallel on multiple cores. The FFSL scheme presented here therefore offers a viable mass-conserving and computationally-efficient alternative to traditional semi-Lagrangian schemes for offline scalar transport simulation in coastal models.
Influences of tidal energy advection on the surface energy balance in a mangrove forest
Directory of Open Access Journals (Sweden)
J. G. Barr
2012-08-01
Full Text Available Mangrove forests are ecosystems susceptible to changing water levels and temperatures due to climate change as well as perturbations resulting from tropical storms. Numerical models can be used to project mangrove forest responses to regional and global environmental changes, and the reliability of these models depends on surface energy balance closure. However, for tidal ecosystems, the surface energy balance is complex because the energy transport associated with tidal activity remains poorly understood. This study aimed to quantify impacts of tidal flows on energy dynamics within a mangrove ecosystem. To address the research objective, an intensive study was conducted in a mangrove forest located along the Shark River in the Everglades National Park, FL. Forest-atmosphere energy exchanges were quantified with an eddy covariance system deployed on a flux tower. The lateral energy transport associated with tidal activity was calculated based on a coupled mass and energy balance approach. The mass balance included tidal flows and accumulation of water on the forest floor. The energy balance included temporal changes in enthalpy, resulting from tidal flows and temperature changes in the water column. By serving as a net sink or a source of available energy, tidal flows reduced the impact of high radiational loads on the mangrove forest. Including tidal energy advection in the surface energy balance improved the 30-min daytime energy closure from 73% to 82% over the study period. Also, the cumulative sum of energy output improved from 79% to 91% of energy input during the study period. Results indicated that tidal inundation provides an important mechanism for heat removal and that tidal exchange should be considered in surface energy budgets of coastal ecosystems. Results also demonstrated the importance of including tidal energy advection in mangrove biophysical models that are used for predicting ecosystem response to changing climate and
Self-Similar Solutions for Viscous and Resistive Advection Dominated Accretion Flows
Indian Academy of Sciences (India)
Kazem Faghei
2012-03-01
In this paper, self-similar solutions of resistive advection dominated accretion flows (ADAF) in the presence of a pure azimuthal magnetic field are investigated. The mechanism of energy dissipation is assumed to be the viscosity and the magnetic diffusivity due to turbulence in the accretion flow. It is assumed that the magnetic diffusivity and the kinematic viscosity are not constant and vary by position and -prescription is used for them. In order to solve the integrated equations that govern the behavior of the accretion flow, a self-similar method is used. The solutions show that the structure of accretion flow depends on the magnetic field and the magnetic diffusivity. As the radial infall velocity and the temperature of the flow increase by magnetic diffusivity, the rotational velocity decreases. Also, the rotational velocity for all selected values of magnetic diffusivity and magnetic field is sub-Keplerian. The solutions show that there is a certain amount of magnetic field for which rotational velocity of the flow becomes zero. This amount of the magnetic field depends upon the gas properties of the disc, such as adiabatic index and viscosity, magnetic diffusivity, and advection parameters. The mass accretion rate increases by adding the magnetic diffusivity and the solutions show that in high magnetic pressure, the ratio of the mass accretion rate to the Bondi accretion rate is reduced with an increase in magnetic pressure. Also, the study of Lundquist and magnetic Reynolds numbers based on resistivity indicates that the linear growth of magnetorotational instability (MRI) of the flow reduces by resistivity. This property is qualitatively consistent with resistive magnetohydrodynamics (MHD) simulations.
Transport dissipative particle dynamics model for mesoscopic advection-diffusion-reaction problems
Li, Zhen; Yazdani, Alireza; Tartakovsky, Alexandre; Karniadakis, George Em
2015-07-01
We present a transport dissipative particle dynamics (tDPD) model for simulating mesoscopic problems involving advection-diffusion-reaction (ADR) processes, along with a methodology for implementation of the correct Dirichlet and Neumann boundary conditions in tDPD simulations. tDPD is an extension of the classic dissipative particle dynamics (DPD) framework with extra variables for describing the evolution of concentration fields. The transport of concentration is modeled by a Fickian flux and a random flux between tDPD particles, and the advection is implicitly considered by the movements of these Lagrangian particles. An analytical formula is proposed to relate the tDPD parameters to the effective diffusion coefficient. To validate the present tDPD model and the boundary conditions, we perform three tDPD simulations of one-dimensional diffusion with different boundary conditions, and the results show excellent agreement with the theoretical solutions. We also performed two-dimensional simulations of ADR systems and the tDPD simulations agree well with the results obtained by the spectral element method. Finally, we present an application of the tDPD model to the dynamic process of blood coagulation involving 25 reacting species in order to demonstrate the potential of tDPD in simulating biological dynamics at the mesoscale. We find that the tDPD solution of this comprehensive 25-species coagulation model is only twice as computationally expensive as the conventional DPD simulation of the hydrodynamics only, which is a significant advantage over available continuum solvers.
Ojha, Richa; Prakash, A.; Govindaraju, Rao S.
2014-08-01
Description of field-scale solute transport in unsaturated soils is essential for assessing the degree of contamination, estimating fluxes past a control plane and for designing remedial measures. The flow field is usually described by numerical solution of the Richards equation followed by numerical solution of the advection-dispersion equation to describe contaminant movement. These numerical solutions are highly complex, and do not provide the insights that are possible from simpler analytical representations. In this study, analytical solutions at the local scale are developed to describe purely advective vertical transport of a conservative solute along the principle characteristic of the flow field. Local-scale model development is simplified by using a sharp-front approximation for water movement. These local solutions are then upscaled to field-scale solute transport by adopting a lognormally distributed horizontal hydraulic conductivity field to represent the natural heterogeneity observed in field soils. Analytical expressions are developed for the mean behavior of solute transport at the field scale. Comparisons with experimental observations find that trends of field-scale solute behavior are reasonably reproduced by the model. The accuracy of the proposed solution improves with increasing spatial variability in the hydraulic conductivity as revealed by further comparisons with numerical results of the Richards equation-based field-scale solute movement. In some cases, the sharp-front approximation may lead to anomalous field-scale behavior depending on the role of pre and postponded conditions in the field, and this limitation is discussed. The proposed method shows promise for describing field-scale solute movement in loamy sand and sandy loam soils.
Interpretation of Isopycnal Layer Thickness Advection in Terms of Eddy-Topography Interaction
Liu, Chuanyu; Koehl, Armin; Stammer, Detlef
2013-04-01
Spatially varying amplitude of the eddy isopycnal layer thickness diffusivity Kgm and the layer thickness advection Kgmskew of the modified Gent and McWilliams parameterization are estimated using two different approaches: the adjoint estimation from a global data assimilation system and the inversion calculation according to divergent buoyancy eddy flux-mean buoyancy gradient relation using results from idealized eddy resolving numerical models with various bottom topographies. This work focuses on the properties of Kgmskew. From the adjoint estimation, large Kgmskew values are found along meandering currents and predominantly positive (negative) over the deep ocean and negative (positive) over seamounts in the southern (northern) hemisphere, implying close relation to the 'Neptune effect" parameterization by Holloway in which the eddy induced mean velocity stream function is represented by -fHL, where H is the bottom depth, f the Coriolis parameter and L a length scale. In the inversion calculation, divergent buoyancy eddy fluxes are obtained by removing the rotational components from the total buoyancy eddy fluxes through Helmholtz-Hodge decomposition. Though subject to topographic length scale, the inversed Kgmskew reveals characteristics of both f and H, and interactions with the mean current, inter-confirming the adjoint estimation results. Applying this parameterization for Kgmskew in the general circulation model produces cold domes and anti-cyclonic circulations over seamounts, which reduces common model biases there. By construction, the original thickness advection Kgmskew redistributes potential energy and the original "Neptune effect" parameterization improves potential vorticity conservation, applying the latter into the former as suggested in the present study thus more correctly reproduces the potential vorticity structure over a sloping topography while conserving the total potential energy.
International Nuclear Information System (INIS)
When transport in porous media is advection-dominated, the classical convection-dispersion equation behaves like an hyperbolic partial differential equation. Special numerical methods are then necessary to reduce numerical dispersion and/or spurious oscillations. Discontinuous Galerkin finite element methods are good candidates to solve this problem. At the discontinuities between two adjacent elements, numerical advective fluxes are calculated using one-dimensional approximate Riemann solvers. The method is stabilized with a multidimensional slope limiter which introduces small amounts of numerical diffusion when sharp concentration fronts occur. For a 2-dimensional domain and quadrangular elements, two space approximations are compared: a linear approximation (P1) based on average concentration value and average gradients (i.e. 3 degrees of freedom) and a bilinear approximation (Q1) based on nodal values of the concentration (i.e. 4 degrees of freedom). Numerical experiments based on structured or unstructured meshes and unidirectional or rotating flow have been run. For the same number of unknowns we show that: 1) the P1 approximation provides more accurate results than the Q1 approximation in simple configuration (structured meshes and unidirectional flow); 2) both approximations provide the same results for not too complicated configurations like structured meshes and rotating flow; 3) Q1 approximation provides more accurate results in complex situations like rotating flow on a unstructured mesh. However, because the required CPU time for the P1 approximation is much less than for the Q1 approximation, the P1 approximation was always found to be more efficient (in terms of CPU time for a given error) compared to the Q1 approximation. (authors)
Huang, Y.H.; Saiers, J.E.; Harvey, J.W.; Noe, G.B.; Mylon, S.
2008-01-01
The movement of particulate matter within wetland surface waters affects nutrient cycling, contaminant mobility, and the evolution of the wetland landscape. Despite the importance of particle transport in influencing wetland form and function, there are few data sets that illuminate, in a quantitative way, the transport behavior of particulate matter within surface waters containing emergent vegetation. We report observations from experiments on the transport of 1 ??m latex microspheres at a wetland field site located in Water Conservation Area 3A of the Florida Everglades. The experiments involved line source injections of particles inside two 4.8-m-long surface water flumes constructed within a transition zone between an Eleocharis slough and Cladium jamaicense ridge and within a Cladium jamaicense ridge. We compared the measurements of particle transport to calculations of two-dimensional advection-dispersion model that accounted for a linear increase in water velocities with elevation above the ground surface. The results of this analysis revealed that particle spreading by longitudinal and vertical dispersion was substantially greater in the ridge than within the transition zone and that particle capture by aquatic vegetation lowered surface water particle concentrations and, at least for the timescale of our experiments, could be represented as an irreversible, first-order kinetics process. We found generally good agreement between our field-based estimates of particle dispersion and water velocity and estimates determined from published theory, suggesting that the advective-dispersive transport of particulate matter within complex wetland environments can be approximated on the basis of measurable properties of the flow and aquatic vegetation. Copyright 2008 by the American Geophysical Union.
DEFF Research Database (Denmark)
Machefaux, Ewan; Larsen, Gunner Chr.; Troldborg, Niels;
2015-01-01
In the present paper, single-wake dynamics have been studied both experimentally and numerically. The use of pulsed lidar measurements allows for validation of basic dynamic wake meandering modeling assumptions. Wake center tracking is used to estimate the wake advection velocity experimentally and...... expansion fairly well in the far wake but lacks accuracy in the outer region of the near wake. An empirical relationship, relating maximum wake induction and wake advection velocity, is derived and linked to the characteristics of a spherical vortex structure. Furthermore, a new empirical model for single...
Moiseev, N. Ya.; Silant'eva, I. Yu.
2008-07-01
An approach to the construction of second-and higher order accurate difference schemes in time and space is described for solving the linear one-and multidimensional advection equations with constant coefficients by the Godunov method with antidiffusion. The differential approximations for schemes of up to the fifth order are constructed and written. For multidimensional advection equations with constant coefficients, it is shown that Godunov schemes with splitting over spatial variables are preferable, since they have a smaller truncation error than schemes without splitting. The high resolution and efficiency of the difference schemes are demonstrated using test computations.
DEFF Research Database (Denmark)
Cook, Perran L. M.; Wenzhofer, Frank; Glud, Ronnie N.;
2007-01-01
proceeded predominantly through sulfate reduction when benthic mineralization rates were high and advective pore-water flow low as a result of poorly developed topography. Previous studies of benthic mineralization in shallow sandy sediments have generally ignored these dynamics and, hence, have overlooked...
Evapotranspiration was continuously measured by an array of eddy covariance systems and large weighting lysimeter in a cotton field in Bushland, Texas. The advective divergence from both horizontal and vertical directions were measured through profile measurements above canopy. All storage terms wer...
Wind-driven gas networks and star formation in galaxies: reaction-advection hydrodynamic simulations
Chappell, David; Scalo, John
2001-07-01
The effects of wind-driven star formation feedback on the spatio-temporal organization of stars and gas in galaxies is studied using two-dimensional intermediate-representational quasi-hydrodynamical simulations. The model retains only a reduced subset of the physics, including mass and momentum conservation, fully non-linear fluid advection, inelastic macroscopic interactions, threshold star formation, and momentum forcing by winds from young star clusters on the surrounding gas. Expanding shells of swept-up gas evolve through the action of fluid advection to form a `turbulent' network of interacting shell fragments which have the overall appearance of a web of filaments (in two dimensions). A new star cluster is formed whenever the column density through a filament exceeds a critical threshold based on the gravitational instability criterion for an expanding shell, which then generates a new expanding shell after some time delay. A filament-finding algorithm is developed to locate the potential sites of new star formation. The major result is the dominance of multiple interactions between advectively distorted shells in controlling the gas and star morphology, gas velocity distribution and mass spectrum of high mass density peaks, and the global star formation history. The gas morphology strongly resembles the model envisioned by Norman & Silk, and observations of gas in the Large Magellanic Cloud (LMC)Q1 and local molecular clouds. The dependence of the frequency distribution of present-to-past average global star formation rate on a number of parameters is investigated. Bursts of star formation only occur when the time-averaged star formation rate per unit area is low, or the system is small. Percolation does not play a role. The broad distribution observed in late-type galaxies can be understood as a result of either small size or small metallicity, resulting in larger shell column densities required for gravitational instability. The star formation rate
Jurčišinová, E.; Jurčišin, M.
2013-03-01
Using the field theoretic renormalization group technique the model of passively advected weak magnetic field by an incompressible isotropic helical turbulent flow is investigated up to the second order of the perturbation theory (two-loop approximation) in the framework of an extended Kazantsev-Kraichnan model of kinematic magnetohydrodynamics. Statistical fluctuations of the velocity field are taken in the form of a Gaussian distribution with zero mean and defined noise with finite correlations in time. The two-loop analysis of all possible scaling regimes is done and the influence of helicity on the stability of scaling regimes is discussed and shown in the plane of exponents ɛ - η, where ɛ characterizes the energy spectrum of the velocity field in the inertial range E ∞ k 1 - 2ɛ, and η is related to the correlation time at the wave number k which is scaled as k -2 + η. It is shown that in non-helical case the scaling regimes of the present vector model are completely identical and have also the same properties as those obtained in the corresponding model of passively advected scalar field. Besides, it is also shown that when the turbulent environment under consideration is helical then the properties of the scaling regimes in models of passively advected scalar and vector (magnetic) fields are essentially different. The results demonstrate the importance of the presence of a symmetry breaking in a given turbulent environment for investigation of the influence of an internal tensor structure of the advected field on the inertial range scaling properties of the model under consideration and will be used in the analysis of the influence of helicity on the anomalous scaling of correlation functions of passively advected magnetic field.
Liu, G.; Knobbe, S.; Butler, J. J., Jr.
2015-12-01
Direct measurement of groundwater flux is difficult to obtain in the field so hydrogeologists often use easily-detectable environmental tracers, such as heat or chemicals, as an indirect way to characterize flux. Previously, we developed a groundwater flux characterization (GFC) probe by using distributed temperature sensing (DTS) to monitor the temperature responses to active heating in a well. The temperature responses were consistent with the hydraulic conductivity profiles determined at the same location, and provided high-resolution information (approx. 1.5 cm) about vertical variations in horizontal flux through the screen. One of the key assumptions in the previous GFC approach was that the vertical variations in the thermal conductivity of the aquifer materials near the well are negligible, so that the temperature differences with depth are primarily a result of groundwater flux instead of thermal conduction. Although this assumption is likely valid for wells constructed with an artificial filter pack, it might become questionable for wells with natural filter packs (such as the wells constructed by direct push where the sediments are allowed to directly collapse onto the well screen). In this work, we develop a new procedure for separating advection from thermal conduction during GFC measurement. In addition to the normal open-screen GFC profiling, an impermeable sleeve was used so that heating tests could be performed without advective flow entering the well. The heating tests under sleeved conditions were primarily controlled by the thermal conduction around the well, and therefore could be used to remove the impact of thermal conduction from the normal GFC results obtained under open-screen conditions. This new procedure was tested in a laboratory sandbox, where a series of open-screen and sleeved GFC tests were performed under different flow rates. Results indicated that for the tested range of rates (Darcy velocity 0 - 0.78 m/d), the relation between
The role of a delay time on the spatial structure of chaotically advected reactive scalars
Tzella, Alexandra
2009-01-01
The stationary-state spatial structure of reacting scalar fields, chaotically advected by a two-dimensional large-scale flow, is examined for the case for which the reaction equations contain delay terms. Previous theoretical investigations have shown that, in the absence of delay terms and in a regime where diffusion can be neglected (large P\\'eclet number), the emergent spatial structures are filamental and characterized by a single scaling regime with a H\\"older exponent that depends on the rate of convergence of the reactive processes and the strength of the stirring measured by the average stretching rate. In the presence of delay terms, we show that for sufficiently small scales all interacting fields should share the same spatial structure, as found in the absence of delay terms. Depending on the strength of the stirring and the magnitude of the delay time, two further scaling regimes that are unique to the delay system may appear at intermediate length scales. An expression for the transition length s...
Evaluating the advective Brewer-Dobson circulation in three reanalyses for the period 1979-2012
Abalos, Marta; Legras, Bernard; Ploeger, Felix; Randel, William J.
2015-08-01
Most chemistry-climate models show an intensification of the Brewer-Dobson circulation (BDC) in the stratosphere associated with increasing greenhouse gas emissions and ozone depletion in the last decades, but this trend remains to be confirmed in observational data. In this work the evolution of the advective BDC for the period 1979-2012 is evaluated and compared in three modern reanalyses (ERA-Interim, MERRA, and JRA-55). Three different estimates of the BDC are computed for each reanalysis, one based on the definition of the residual circulation and two indirect estimates derived from momentum and thermodynamic balances. The comparison among the nine estimates shows substantial uncertainty in the mean magnitude (˜40%) but significant common variability. The tropical upwelling series show variability linked to the stratospheric quasi-biennial oscillation and to El Niño-Southern Oscillation (ENSO) and also reflect extreme events such as major sudden stratospheric warmings and volcanic eruptions. The trend analysis suggests a strengthening of tropical upwelling of around 2-5%/decade throughout the layer 100-10 hPa. The global spatial structure of the BDC trends provides evidence of an overall acceleration of the circulation in both hemispheres, with qualitative agreement among the estimates. The global BDC trends are mainly linked to changes in the boreal winter season and can be tracked to long-term increases in the resolved wave drag in both hemispheres.
The advective Brewer-Dobson circulation in three reanalyses (1979-2012)
Abalos, Marta; Legras, Bernard; Ploeger, Felix; Randel, William
2015-04-01
Most chemistry-climate models predict an intensification of the Brewer-Dobson circulation in the stratosphere in the last decades, but this trend remains to be confirmed in observational data. In this work the evolution of the advective BDC for the period 1979-2012 is evaluated and compared in three modern reanalyses (ERA-Interim, MERRA and JRA-55). Three different estimates of the BDC are computed for each reanalysis, one based on the definition of the residual circulation and two indirect estimates derived from momentum and thermodynamic balance. The comparison among the nine estimates shows substantial uncertainty in the mean magnitude but significant common variability. The trend analysis suggests an intensification in tropical upwelling throughout the layer 100-10 hPa. Globally, an acceleration of the circulation is observed in both hemispheres, with qualitative agreement among the estimates. The global BDC trends are mainly due to changes in the DJF circulation and can be tracked to changes in the resolved wave drag in both hemispheres, which are highly consistent in the three reanalyses.
Correlation Networks from Flows. The Case of Forced and Time-Dependent Advection-Diffusion Dynamics.
Directory of Open Access Journals (Sweden)
Liubov Tupikina
Full Text Available Complex network theory provides an elegant and powerful framework to statistically investigate different types of systems such as society, brain or the structure of local and long-range dynamical interrelationships in the climate system. Network links in climate networks typically imply information, mass or energy exchange. However, the specific connection between oceanic or atmospheric flows and the climate network's structure is still unclear. We propose a theoretical approach for verifying relations between the correlation matrix and the climate network measures, generalizing previous studies and overcoming the restriction to stationary flows. Our methods are developed for correlations of a scalar quantity (temperature, for example which satisfies an advection-diffusion dynamics in the presence of forcing and dissipation. Our approach reveals that correlation networks are not sensitive to steady sources and sinks and the profound impact of the signal decay rate on the network topology. We illustrate our results with calculations of degree and clustering for a meandering flow resembling a geophysical ocean jet.
Correlation Networks from Flows. The Case of Forced and Time-Dependent Advection-Diffusion Dynamics.
Tupikina, Liubov; Molkenthin, Nora; López, Cristóbal; Hernández-García, Emilio; Marwan, Norbert; Kurths, Jürgen
2016-01-01
Complex network theory provides an elegant and powerful framework to statistically investigate different types of systems such as society, brain or the structure of local and long-range dynamical interrelationships in the climate system. Network links in climate networks typically imply information, mass or energy exchange. However, the specific connection between oceanic or atmospheric flows and the climate network's structure is still unclear. We propose a theoretical approach for verifying relations between the correlation matrix and the climate network measures, generalizing previous studies and overcoming the restriction to stationary flows. Our methods are developed for correlations of a scalar quantity (temperature, for example) which satisfies an advection-diffusion dynamics in the presence of forcing and dissipation. Our approach reveals that correlation networks are not sensitive to steady sources and sinks and the profound impact of the signal decay rate on the network topology. We illustrate our results with calculations of degree and clustering for a meandering flow resembling a geophysical ocean jet. PMID:27128846
Volume of Fluid (VOF) type advection methods in two-phase flow: a comparative study
Aniszewski, Wojciech; Marek, Maciej
2014-01-01
In this paper, four distinct approaches to Volume of Fluid (VOF) computational method are compared. Two of the methods are the 'simplified' VOF formulations, in that they do not require geometrical interface reconstruction. The assessment is made possible by implementing all four approaches into the same code as a switchable options. This allows to rule out possible influence of other parts of numerical scheme, be it the discretisation of Navier-Stokes equations or chosen approximation of curvature, so that we are left with conclusive arguments because only one factor differs the compared methods. The comparison is done in the framework of CLSVOF (Coupled Level Set Volume of Fluid), so that all four methods are coupled with Level Set interface, which is used to compute pressure jump via the GFM (Ghost-Fluid Method). Results presented include static advections, full N-S solutions in laminar and turbulent flows. The paper is aimed at research groups who are implementing VOF methods in their computations or inte...
Effect of Ionic Advection on Electroosmosis over Charge Surfaces: Beyond the Weak Field Limit
Ghosh, Uddipta
2015-01-01
The present study deals with the effect of ionic advection on electroosmotic flow over charge modulated surfaces in a generalized paradigm when the classically restrictive "weak field" limit may be relaxed. Going beyond the commonly portrayed weak field limit (i.e, the externally applied electric field is over-weighed by the surface-induced electrical potential, towards charge distribution in an electrified wall-adhering layer) for electroosmotic transport, we numerically solve the coupled full set of Poisson-Nernst-Planck (PNP) and Navier-Stokes equations, in a semi-infinite domain, bounded at the bottom by a charged wall. Further, in an effort to obtain deeper physical insight, we solve the simplified forms of the relevant governing equations for low surface potential in two separate asymptotic limits: (i) a regular perturbation solution for Low Ionic Peclet number (Pe), where Pe is employed as the gauge function and (ii) a matched asymptotic solution for O(1) Pe in the Thin Electric Double Layer (EDL) limi...
Endeve, Eirik; Xing, Yulong; Mezzacappa, Anthony
2014-01-01
We extend the positivity-preserving method of Zhang & Shu (2010, JCP, 229, 3091-3120) to simulate the advection of neutral particles in phase space using curvilinear coordinates. The ability to utilize these coordinates is important for non-equilibrium transport problems in general relativity and also in science and engineering applications with specific geometries. The method achieves high-order accuracy using Discontinuous Galerkin (DG) discretization of phase space and strong stability-preserving, Runge-Kutta (SSP-RK) time integration. Special care in taken to ensure that the method preserves strict bounds for the phase space distribution function $f$; i.e., $f\\in[0,1]$. The combination of suitable CFL conditions and the use of the high-order limiter proposed in Zhang & Shu (2010) is sufficient to ensure positivity of the distribution function. However, to ensure that the distribution function satisfies the upper bound, the discretization must, in addition, preserve the divergence-free property of ...
Johnson, Joel P. L.; Delbecq, Katie; Kim, Wonsuck; Mohrig, David
2016-01-01
A goal of paleotsunami research is to quantitatively reconstruct wave hydraulics from sediment deposits in order to better understand coastal hazards. Simple models have been proposed to predict wave heights and velocities, based largely on deposit grain size distributions (GSDs). Although seemingly consistent with some recent tsunamis, little independent data exist to test these equations. We conducted laboratory experiments to evaluate inversion assumptions and uncertainties. A computer-controlled lift gate instantaneously released ~ 6.5 m3 of water into a 32 m flume with shallow ponded water, creating a hydraulic bore that transported sand from an upstream source dune. Differences in initial GSDs and ponded water depths influenced entrainment, transport, and deposition. While the source dune sand was fully suspendable based on size alone, experimental tsunamis produced deposits dominated by bed load sand transport in the upstream ~ 1/3 of the flume and suspension-dominated transport downstream. The suspension deposits exhibited downstream fining and thinning. At 95% confidence, a published advection-settling model predicts time-averaged flow depths to approximately a factor of two, and time-averaged downstream flow velocities to within a factor of 1.5. Finally, reasonable scaling is found between flume and field cases by comparing flow depths, inundation distances, Froude numbers, Rouse numbers and grain size trends in suspension-dominated tsunami deposits, justifying laboratory study of sediment transport and deposition by tsunamis.
Lin, Neil Y. C.
2013-12-01
Using high-speed confocal microscopy, we measure the particle positions in a colloidal suspension under large-amplitude oscillatory shear. Using the particle positions, we quantify the in situ anisotropy of the pair-correlation function, a measure of the Brownian stress. From these data we find two distinct types of responses as the system crosses over from equilibrium to far-from-equilibrium states. The first is a nonlinear amplitude saturation that arises from shear-induced advection, while the second is a linear frequency saturation due to competition between suspension relaxation and shear rate. In spite of their different underlying mechanisms, we show that all the data can be scaled onto a master curve that spans the equilibrium and far-from-equilibrium regimes, linking small-amplitude oscillatory to continuous shear. This observation illustrates a colloidal analog of the Cox-Merz rule and its microscopic underpinning. Brownian dynamics simulations show that interparticle interactions are sufficient for generating both experimentally observed saturations. © 2013 American Physical Society.
Helical turbulent Prandtl number in the $A$ model of passive advection: Two loop approximation
Hnatič, Michal
2016-01-01
Using the field theoretic renormalization group technique in the two-loop approximation, turbulent Prandtl numbers are obtained in the general $A$ model of passive vector advected by fully developed turbulent velocity field with violation of spatial parity introduced via continuous parameter $\\rho$ ranging from $\\rho=0$ (no violation of spatial parity) to $|\\rho|=1$ (maximum violation of spatial parity). In non-helical environments, we demonstrate that $A$ is restricted to $-1.723 \\leq A \\leq 2.800$ (rounded on the last presented digit) due to the constraints of two-loop calculations. When $\\rho >0.749$ restrictions may be removed. Furthermore, three physically important cases $A \\in \\{-1, 0, 1\\}$ are shown to lie deep within the allowed interval of $A$ for all values of $\\rho$. For the model of linearized Navier-Stokes equations ($A = -1$) up to date unknown helical values of turbulent Prandtl number have been shown to equal $1$ regardless of parity violation. Furthermore, we have shown that interaction para...
A New Evapotranspiration Model Accounting for Advection and Its Validation during SMEX02
Directory of Open Access Journals (Sweden)
Yongmin Yang
2013-01-01
Full Text Available Based on the crop water stress index (CWSI concept, a new model was proposed to account for advection to estimate evapotranspiration. Both local scale evaluation with sites observations and regional scale evaluation with a remote dataset from Landsat 7 ETM+ were carried out to assess the performance of this model. Local scale evaluation indicates that this newly developed model can effectively characterize the daily variations of evapotranspiration and the predicted results show good agreement with the site observations. For all the 6 corn sites, the coefficient of determination (R2 is 0.90 and the root mean square difference (RMSD is 58.52W/m2. For all the 6 soybean sites, the R2 and RMSD are 0.85 and 49.46W/m2, respectively. Regional scale evaluation shows that the model can capture the spatial variations of evapotranspiration at the Landsat-based scale. Clear spatial patterns were observed at the Landsat-based scale and are closely related to the dominant land covers, corn and soybean. Furthermore, the surface resistance derived from instantaneous CWSI was applied to the Penman-Monteith equation to estimate daily evapotranspiration. Overall, results indicate that this newly developed model is capable of estimating reliable surface heat fluxes using remotely sensed data.
Transport dissipative particle dynamics model for mesoscopic advection- diffusion-reaction problems
Energy Technology Data Exchange (ETDEWEB)
Zhen, Li; Yazdani, Alireza; Tartakovsky, Alexandre M.; Karniadakis, George E.
2015-07-07
We present a transport dissipative particle dynamics (tDPD) model for simulating mesoscopic problems involving advection-diffusion-reaction (ADR) processes, along with a methodology for implementation of the correct Dirichlet and Neumann boundary conditions in tDPD simulations. tDPD is an extension of the classic DPD framework with extra variables for describing the evolution of concentration fields. The transport of concentration is modeled by a Fickian flux and a random flux between particles, and an analytical formula is proposed to relate the mesoscopic concentration friction to the effective diffusion coefficient. To validate the present tDPD model and the boundary conditions, we perform three tDPD simulations of one-dimensional diffusion with different boundary conditions, and the results show excellent agreement with the theoretical solutions. We also performed two-dimensional simulations of ADR systems and the tDPD simulations agree well with the results obtained by the spectral element method. Finally, we present an application of the tDPD model to the dynamic process of blood coagulation involving 25 reacting species in order to demonstrate the potential of tDPD in simulating biological dynamics at the mesoscale. We find that the tDPD solution of this comprehensive 25-species coagulation model is only twice as computationally expensive as the DPD simulation of the hydrodynamics only, which is a significant advantage over available continuum solvers.
Directory of Open Access Journals (Sweden)
Lingju Kong
2013-04-01
Full Text Available We study the existence of multiple solutions to the boundary value problem $$displaylines{ frac{d}{dt}Big(frac12{}_0D_t^{-eta}(u'(t+frac12{}_tD_T^{-eta}(u'(t Big+lambda abla F(t,u(t=0,quad tin [0,T],cr u(0=u(T=0, }$$ where $T>0$, $lambda>0$ is a parameter, $0leqeta<1$, ${}_0D_t^{-eta}$ and ${}_tD_T^{-eta}$ are, respectively, the left and right Riemann-Liouville fractional integrals of order $eta$, $F: [0,T]imesmathbb{R}^Nomathbb{R}$ is a given function. Our interest in the above system arises from studying the steady fractional advection dispersion equation. By applying variational methods, we obtain sufficient conditions under which the above equation has at least three solutions. Our results are new even for the special case when $eta=0$. Examples are provided to illustrate the applicability of our results.
The role of phase dynamics in a stochastic model of a passively advected scalar
Moradi, Sara
2016-01-01
Collective synchronous motion of the phases is introduced in a model for the stochastic passive advection-diffusion of a scalar with external forcing. The model for the phase coupling dynamics follows the well known Kuramoto model paradigm of limit-cycle oscillators. The natural frequencies in the Kuramoto model are assumed to obey a given scale dependence through a dispersion relation of the drift-wave form $-\\beta\\frac{k}{1+k^2}$, where $\\beta$ is a constant representing the typical strength of the gradient. The present aim is to study the importance of collective phase dynamics on the characteristic time evolution of the fluctuation energy and the formation of coherent structures. Our results show that the assumption of a fully stochastic phase state of turbulence is more relevant for high values of $\\beta$, where we find that the energy spectrum follows a $k^{-7/2}$ scaling. Whereas for lower $\\beta$ there is a significant difference between a-synchronised and synchronised phase states, and one could expe...
The role of phase dynamics in a stochastic model of a passively advected scalar
Moradi, Sara; Anderson, Johan
2016-05-01
Collective synchronous motion of the phases is introduced in a model for the stochastic passive advection-diffusion of a scalar with external forcing. The model for the phase coupling dynamics follows the well known Kuramoto model paradigm of limit-cycle oscillators. The natural frequencies in the Kuramoto model are assumed to obey a given scale dependence through a dispersion relation of the drift-wave form -βk/1 +k2 , where β is a constant representing the typical strength of the gradient. The present aim is to study the importance of collective phase dynamics on the characteristic time evolution of the fluctuation energy and the formation of coherent structures. Our results show that the assumption of a fully stochastic phase state of turbulence is more relevant for high values of β, where we find that the energy spectrum follows a k-7 /2 scaling. Whereas for lower β there is a significant difference between a-synchronised and synchronised phase states, one could expect the formation of coherent modulations in the latter case.
On the advection of tracer by eddies on the beta-plane: A numerical study
Directory of Open Access Journals (Sweden)
E. S. Benilov
1999-01-01
Full Text Available The evolution of tracer "injected" into an equivalent barotropic eddy on the beta-plane is examined numerically. The eddy is governed by the standard quasigeostrophic equation, and the concentration of tracer is governed by the advection equation with diffusion. At the initial moment of time, the streamfunction and distribution of tracer are both radially or elliptically symmetric. After the first 10-30 days, a spirallike strip, where the gradient of concentration is large, develops in the tracer field, whereas the eddy remains smooth for a relatively long time. To put this conclusion in quantitative terms, a "tracer variability indicator" is introduced and shown to grow much faster than a similar characteristic of the potential vorticity field (notwithstanding the fact that the tracer concentration and PV satisfy the same governing equation. A simple explanation as to why the tracer is more affected by filamentation than PV is provided for eddies with small Burger number. It is demonstrated that the high-gradient strip develops, unless stopped by turbulent diffusion, into an inversion (non-monotonicity of the tracer concentration field. Finally, the results of simulations are compared to the spiral patterns in the real-life eddies observed in the East Australian Current.
Central Arctic Ocean freshwater during a period of anomalous melt and advection in 2015
Rabe, Benjamin; Korhonen, Meri; Hoppmann, Mario; Ricker, Robert; Hendricks, Stefan; Krumpen, Thomas; Beckers, Justin; Schauer, Ursula
2016-04-01
During the recent decade the Arctic Ocean has shown several years of very low sea-ice extent and an increase in liquid freshwater. Yet, the processes underlying the interannual variability are still not fully understood. Hydrographic observations by ship campaigns and autonomous platforms reveal that summer 2015 showed above average liquid freshwater in the upper ocean of the central Arctic. Surface temperatures and sea level pressure were also higher than the average of the preceeding two decades. From hydrographic observations and atmospheric reanalysis data we show that this liquid freshwater anomaly is associated with above average sea-ice melt and intensified northward Ekman transport. We, further, found significant amounts of Pacific Water in the upper water column, from the mixed-layer to the upper halocline. Our results suggest that the freshening was due to both advection of low-salinity water from the direction of the Siberian shelves, the Beaufort Gyre and the Bering Strait, and enhance sea-ice melt.
Bad behavior of Godunov mixed methods for strongly anisotropic advection-dispersion equations
Mazzia, Annamaria; Manzini, Gianmarco; Putti, Mario
2011-09-01
We study the performance of Godunov mixed methods, which combine a mixed-hybrid finite element solver and a Godunov-like shock-capturing solver, for the numerical treatment of the advection-dispersion equation with strong anisotropic tensor coefficients. It turns out that a mesh locking phenomenon may cause ill-conditioning and reduce the accuracy of the numerical approximation especially on coarse meshes. This problem may be partially alleviated by substituting the mixed-hybrid finite element solver used in the discretization of the dispersive (diffusive) term with a linear Galerkin finite element solver, which does not display such a strong ill conditioning. To illustrate the different mechanisms that come into play, we investigate the spectral properties of such numerical discretizations when applied to a strongly anisotropic diffusive term on a small regular mesh. A thorough comparison of the stiffness matrix eigenvalues reveals that the accuracy loss of the Godunov mixed method is a structural feature of the mixed-hybrid method. In fact, the varied response of the two methods is due to the different way the smallest and largest eigenvalues of the dispersion (diffusion) tensor influence the diagonal and off-diagonal terms of the final stiffness matrix. One and two dimensional test cases support our findings.
Phase mixing vs. nonlinear advection in drift-kinetic plasma turbulence
Schekochihin, A A; Highcock, E G; Dellar, P J; Dorland, W; Hammett, G W
2015-01-01
A scaling theory of long-wavelength electrostatic turbulence in a magnetised, weakly collisional plasma (e.g., drift-wave turbulence driven by temperature gradients) is proposed, with account taken both of the nonlinear advection of the perturbed particle distribution by fluctuating ExB flows and of its phase mixing, which is caused by the streaming of the particles along the mean magnetic field and, in a linear problem, would lead to Landau damping. A consistent theory is constructed in which very little free energy leaks into high velocity moments of the distribution, rendering the turbulent cascade in the energetically relevant part of the wave-number space essentially fluid-like. The velocity-space spectra of free energy expressed in terms of Hermite-moment orders are steep power laws and so the free-energy content of the phase space does not diverge at infinitesimal collisionality (while it does for a linear problem); collisional heating due to long-wavelength perturbations vanishes in this limit (also i...
Energy Technology Data Exchange (ETDEWEB)
McGraw R.
2012-03-01
Moment methods are finding increasing usage for simulations of particle population balance in box models and in more complex flows including two-phase flows. These highly efficient methods have nevertheless had little impact to date for multi-moment representation of aerosols and clouds in atmospheric models. There are evidently two reasons for this: First, atmospheric models, especially if the goal is to simulate climate, tend to be extremely complex and take many man-years to develop. Thus there is considerable inertia to the implementation of novel approaches. Second, and more fundamental, the nonlinear transport algorithms designed to reduce numerical diffusion during advection of various species (tracers) from cell to cell, in the typically coarse grid arrays of these models, can and occasionally do fail to preserve correlations between the moments. Other correlated tracers such as isotopic abundances, composition of aerosol mixtures, hydrometeor phase, etc., are subject to this same fate. In the case of moments, this loss of correlation can and occasionally does give rise to unphysical moment sets. When this happens the simulation can come to a halt. Following a brief description and review of moment methods, the goal of this paper is to present two new approaches that both test moment sequences for validity and correct them when they fail. The new approaches work on individual grid cells without requiring stored information from previous time-steps or neighboring cells.
Effect of organic compounds for the advection of actinide elements in the environments
Energy Technology Data Exchange (ETDEWEB)
Muraoka, Susumu; Nagao, Seiya; Tanaka, Tadao [Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan). Tokai Research Establishment; Hiraki, Keizo; Nakaguchi, Yuzuru; Suzuki, Yasuhiro
1998-01-01
The aim of this studies is understood the effects of humic substances for the advection of actinide elements in the environments. These substances are a major role of dissolved organic matter in natural waters. In order to obtain the informations on the structure of metal-humic substances complexes, these substances were studied by fluorescence spectroscopy. Observation the spectrum forms, peak positions of maximum intensity are related to these informations on the chemical structures and functional groups in organic compounds. Using three-dimensional excitation emission matrix (3-D EEM) spectroscopy, the characteristics of metal-humic substances complexes were studied. Observation the wavelengths and fluorescence intensity of the peaks were varied between humic substances before the complex to the metal and these substances after ones. Understanding the fluorescence properties of metal-humic substances complexes, working program of the 3-D EEM spectroscopy was studied to obtaining detailed data collection. New program was applied to copper-humic acid complex, the peak positions which different with before the complex and after ones were recorded. This program is supported by the interpreation of fluorescence properties in the metal-humic substances by the 3-D EEM spectroscopy. (author)
The influence of advection on the short term CO2-budget in and above a forest canopy
Feigenwinter, C.; Vogt, R.; Bernhofer, C.
2003-04-01
The investigation of advective effects in complex terrain requires an experimental setup, which is capable to precisely measure the horizontal concentration gradients of a property (i.e. CO2). For this purpose, the CARBOEUROFLUX site in Tharandt (Germany) was completed with additional measurements to account for the entire mass balance of CO2 in a soil-vegetation-atmosphere volume during the AFO 2000 VERTIKO MORE 1 campaign (Sep/Oct 2001) in close cooperation with IHM TU Dresden. Net Ecosystem Exchange is calculated by the conservation equation, in which the horizontal advection term is undoubtedly the less known and less investigated term. The large scatter of horizontal and vertical advection during 13 consecutive days of available 30-min values is supposed to be mainly natural and not due to measurement errors. The latter were minimized by measuring the horizontal CO2 concentration differences at the three edges of a prism volume at two heights (2 m and 26 m a.g.l.) with the same IRGA gas analyser additionally to the single profile measurements at 7 levels at each edge point. Wind vectors were simultaneously measured at two levels (0.5 m and 2.5 m) in the trunk space with carefully calibrated sonics. From these measurements profiles of the horizontal CO2 gradient (amount and direction) and of the mean horizontal wind vector are constructed. These profiles are supposed to be representative for the closer surroundings of the site. The horizontal advection in a certain layer depends essentially on the horizontal wind vector and CO2 gradient (amount and direction). It is very sensitive to smallest changes in input variables and thus, their derivation from profile measurements is actually the crucial task. It is shown that the direction of the horizontal concentration gradient as well as the horizontal wind vector is often height dependent. A minimum and a maximum scenario for the horizontal advection term gives gain of 10..30 g CO2 m-2 d-1 compared to a mean loss of
Spielhagen, Robert F.; Bauch, Henning A.; Maudrich, Martin; Not, Christelle; Telesinski, Maciej M.; Werner, Kirstin
2015-04-01
The Arctic Gateway between Greenland and Svalbard is the main passage for the advection of Atlantic Water to the Arctic Ocean. Water temperature and intensity of this advection largely determine the degree of ice coverage which is fed by sea ice export from the north. Supported by a maximum in insolation, the Early Holocene was a period of extraordinarily strong advection and relatively high near-surface water temperatures in the eastern Nordic Seas (cf. Risebrobakken et al., 2011, Paleoceanography v. 26). Here we present a synthesis of radiocarbon-dated records from the northern and western part of this area, reaching from the SW Greenland Sea (73°N) to the Yermak Plateau (81°N) and revealing temporal and spatial differences in the development of the so-called Holocene Thermal Maximum (HTM). In the northern part of this region, the HTM started ca. 11-10.5 ka as indicated by rapidly increasing amounts of subpolar planktic foraminifers in the sediments. In the eastern Fram Strait and on the Yermak Plateau, our records of (sub)millennial scale resolution show that the maximum influx terminated already 2,000 years later (9-8 ka). Most likely, this development went along with a N-S relocation of the sea ice margin. According to the current stratigraphic model for a core with submillennial-scale resolution from Vesterisbanken seamount (73°N) in the Greenland Sea, the timing was different there. Increasing total amounts of planktic foraminifers in the sediment indicate an early (11-10 ka) reduction in sea ice coverage also in this region. However, evidence from subpolar planktic foraminifers for maximum Atlantic Water advection is younger (9-6 ka) than in the north. Apparently, the site in the SW Greenland Sea was affected by Atlantic Water in the Greenland Gyre that decoupled from the northward flowing Norwegian Atlantic Current/Westspitsbergen Current south of the Fram Strait. Thus, in a suite of events, strong Atlantic Water advection first affected the
Guihéneuf, N.; Boisson, A.; Bour, O.; Le Borgne, T.; Marechal, J.; Nigon, B.; Wajiddudin, M.; Ahmed, S.
2013-12-01
The prediction of transport in weathered and fractured rocks is critical as it represents the primary control of contaminant transfer from the subsurface in many parts of the world. This is the case in Southern India, where the subsurface is composed mainly of weathered and fractured granite and where the overexploitation of the groundwater resource since the 70's has led to high water table depletion and strong groundwater quality deterioration. One key issue for modelling transport in such systems is to quantify the respective role of advective heterogeneities and matrix diffusion, which can both lead to strongly non Fickian transport properties. We investigate this question by analysing tracer test experiments performed under different flow configurations at a fractured granite experimental site located in Andhra Pradesh (India). We performed both convergent and push-pull tracer tests within the same fracture and at different scales. Three convergent tracer tests were performed with a solution of fluorescein for different pumping rate and for different distances between injection and pumping boreholes: 6, 30 and 41 meters. To evaluate diffusive process, we performed two long-duration push-pull tests (push time of 3 hours) with a solution of two conservative tracers of different diffusion coefficient (fluorescein and sodium chloride). We performed also six others push-pull tests with only fluorescein but for a variable push times of 14 min and 55 min with or without resting time of about 60 min. The late-time behaviour on the breakthrough curves (BTCs) obtained for all convergent tracer tests showed a power-law slope of -2. Two of them showed an inflexion in the BTCs suggesting the existence of two independent flow paths and thus a highly channelized flow. The long-duration push-pull tests showed similar late-time behaviour with a power-law slope of -2.2 for both tracers. The six others push-pull tests showed a variation of power-law exponent from -3 to -2
Advective transport observations with MODPATH-OBS--documentation of the MODPATH observation process
Hanson, R.T.; Kauffman, L.K.; Hill, M.C.; Dickinson, J.E.; Mehl, S.W.
2013-01-01
The MODPATH-OBS computer program described in this report is designed to calculate simulated equivalents for observations related to advective groundwater transport that can be represented in a quantitative way by using simulated particle-tracking data. The simulated equivalents supported by MODPATH-OBS are (1) distance from a source location at a defined time, or proximity to an observed location; (2) time of travel from an initial location to defined locations, areas, or volumes of the simulated system; (3) concentrations used to simulate groundwater age; and (4) percentages of water derived from contributing source areas. Although particle tracking only simulates the advective component of conservative transport, effects of non-conservative processes such as retardation can be approximated through manipulation of the effective-porosity value used to calculate velocity based on the properties of selected conservative tracers. This program can also account for simple decay or production, but it cannot account for diffusion. Dispersion can be represented through direct simulation of subsurface heterogeneity and the use of many particles. MODPATH-OBS acts as a postprocessor to MODPATH, so that the sequence of model runs generally required is MODFLOW, MODPATH, and MODPATH-OBS. The version of MODFLOW and MODPATH that support the version of MODPATH-OBS presented in this report are MODFLOW-2005 or MODFLOW-LGR, and MODPATH-LGR. MODFLOW-LGR is derived from MODFLOW-2005, MODPATH 5, and MODPATH 6 and supports local grid refinement. MODPATH-LGR is derived from MODPATH 5. It supports the forward and backward tracking of particles through locally refined grids and provides the output needed for MODPATH_OBS. For a single grid and no observations, MODPATH-LGR results are equivalent to MODPATH 5. MODPATH-LGR and MODPATH-OBS simulations can use nearly all of the capabilities of MODFLOW-2005 and MODFLOW-LGR; for example, simulations may be steady-state, transient, or a combination
Horizontal Advection and Mixing of Pollutants in the Urban Atmospheric Environment
Magnusson, S. P.; Entekhabi, D.; Britter, R.; Norford, L.; Fernando, H. J.
2013-12-01
Although urban air quality and its impacts on the public health have long been studied, the increasing urbanization is raising concerns on how to better control and mitigate these health impacts. A necessary element in predicting exposure levels is fundamental understanding of flow and dispersion in urban canyons. The complex topology of building structures and roads requires the resolution of turbulence phenomena within urban canyons. The use of dense and low porosity construction material can lead to rapid heating in response to direct solar exposure due to large thermal mass. Hence thermal and buoyancy effects may be as important as mechanically-forced or shear-induced flows. In this study, the transport of pollutants within the urban environment, as well as the thermal and advection effects, are investigated. The focus is on the horizontal transport or the advection effects within the urban environment. With increased urbanization and larger and more spread cities, concern about how the upstream air quality situation can affect downstream areas. The study also examines the release and the dispersion of hazardous material. Due to the variety and complexity of urban areas around the world, the urban environment is simplified into adjacent two-dimensional urban street canyons. Pollutants are released inside each canyon. Computational Fluid Dynamics (CFD) simulations are applied to evaluate and quantify the flow rate out of each canyon and also the exchange of pollutants between the canyons. Imagine a row of ten adjacent urban street canyons of aspect ratio 1 with horizontal flow perpendicular to it as shown in the attached figure. C is the concentration of pollutants. The first digit indicates in what canyon the pollutant is released and the second digit indicates the location of that pollutant. For example, C3,4 is the concentration of pollutant released inside canyon 3 measured in canyon 4. The same amount of pollution is released inside the ten street canyons
A modified TVD scheme for the advection of two or more variables with consideration for their sum
Mercier, Christophe Y. M.; Delhez, Eric J. M.
2010-10-01
Total variation diminishing (TVD) advection schemes are known to produce results that are free from some of the numerical artifacts (no overshooting, no spurious oscillation, small diffusion) that can spoil the physical significance of the results. When two or more tracers are advected separately using a TVD scheme, the sum of these variables can however exhibit some inappropriate behaviors. The total variation of the sum will not necessarily be non- increasing and local artificial oscillations and extrema can appear. We show that these can be avoided with only minor perturbations of the original solution by adjusting the slope limiters used for the different variables. If the sum of these variables has some physical significance, for instance as refinement of a larger model compartment, the correction procedure introduced in this paper should be used to ensure a physically meaningful solution.
Kalise, Dante
2011-01-01
We present a WENO-TVD scheme for the simulation of atmospheric phenomena. The scheme considers a spatial discretization via a second-order TVD flux based upon a flux-centered limiter approach, which makes use of high-order accurate extrapolated values arising from a WENO reconstruction procedure. Time discretization is performed with a third order RK-TVD scheme, and splitting is used for the inclusion of source terms. We present a comprehensive performance study of the method in atmospheric applications involving advective and convective motion. We present a set of tests for space-dependent linear advection, where we assess convergence and robustness with respect to the parameters of the scheme. We apply the method to approximate the 2D Euler equations in a series of tests for atmospheric convection.
Cornaton, F; 10.1016/j.advwatres.2005.10.009
2011-01-01
We present a methodology for determining reservoir groundwater age and transit time probability distributions in a deterministic manner, considering advective-dispersive transport in steady velocity fields. In a first step, we propose to model the statistical distribution of groundwater age at aquifer scale by means of the classical advection-dispersion equation for a conservative and nonreactive tracer, associated to proper boundary conditions. The evaluated function corresponds to the density of probability of the random variable age, age being defined as the time elapsed since the water particles entered the aquifer. An adjoint backward model is introduced to characterize the life expectancy distribution, life expectancy being the time remaining before leaving the aquifer. By convolution of these two distributions, groundwater transit time distributions, from inlet to outlet, are fully defined for the entire aquifer domain. In a second step, an accurate and efficient method is introduced to simulate the tr...
Kemner, K. M.; Boyanov, M.; Flynn, T. M.; O'Loughlin, E. J.; Antonopoulos, D. A.; Kelly, S.; Skinner, K.; Mishra, B.; Brooks, S. C.; Watson, D. B.; Wu, W. M.
2015-12-01
FeIII- and SO42--reducing microorganisms and the mineral phases they produce have profound implications for many processes in aquatic and terrestrial systems. In addition, many of these microbially-catalysed geochemical transformations are highly dependent upon introduction of reactants via advective and diffusive hydrological transport. We have characterized microbial communities from a set of static microcosms to test the effect of ethanol diffusion and sulfate concentration on UVI-contaminated sediment. The spatial distribution, valence states, and speciation of both U and Fe were monitored in situ throughout the experiment by synchrotron x-ray absorption spectroscopy, in parallel with solution measurements of pH and the concentrations of sulfate, ethanol, and organic acids. After reaction initiation, a ~1-cm thick layer of sediment near the sediment-water (S-W) interface became visibly dark. Fe XANES spectra of the layer were consistent with the formation of FeS. Over the 4 year duration of the experiment, U LIII-edge XANES indicated reduction of U, first in the dark layer and then throughout the sediment. Next, the microcosms were disassembled and samples were taken from the overlying water and different sediment regions. We extracted DNA and characterized the microbial community by sequencing 16S rRNA gene amplicons with the Illumina MiSeq platform and found that the community evolved from its originally homogeneous composition, becoming significantly spatially heterogeneous. We have also developed an x-ray accessible column to probe elemental transformations as they occur along the flow path in a porous medium with the purpose of refining reactive transport models (RTMs) that describe coupled physical and biogeochemical processes in environmental systems. The elemental distribution dynamics and the RTMs of the redox driven processes within them will be presented.
Gamma irradiation test report of simulated grout specimens for gas generation/liquid advection
International Nuclear Information System (INIS)
This report presents the results from an irradiation test performed on four specimens of grout that were fabricated from synthetic Double Shell Slurry Feed (DSSF) liquid waste. The objective was to investigate the radiolytic generation of gases and the potential for advective rejection of waste liquids from the grout matrix and to provide experimental information for the validation of the C-Cubed calculated model. It has been demonstrated that a number of gases can be formed within the grout due to radiolytic decomposition of various chemical components that make up the grout. This observation leads to the conjecture that the potential exists for the rejection of a portion of the 60 vol% free liquid from the grout matrix driven by pressurization by these gases. It was found that, for the specimen geometries used in this test series, and for peak radiation dose accumulation rates on the order of 4 to 60 times of the initial rate expected in the grout vaults (300 Rads/hr), no liquid rejection was observed from 2% to 35% of the target exposure expected in the grout vaults (1E+08 Rads). When the irradiation rate exceeded the projected grout vault dose rate by a factor of 200 a small amount of liquid rejection was observed from one of two specimens that had received 20% more than the goal exposure. Because of the differences in the magnitudes of the relative radiation field strengths between this study and an actual grout vault, it is concluded that the potential for liquid rejection by internal gas pressurization from presently configured grout waste forms is very low for the expected conditions
Advective heat transport in the upper carbonate aquifer beneath Winnipeg, Manitoba
Energy Technology Data Exchange (ETDEWEB)
Ferguson, G.A.G.; Woodbury, A.D. [Manitoba Univ., Winnipeg, MB (Canada). Dept. of Civil Engineering
2003-07-01
Air conditioning and industrial cooling in Winnipeg, Manitoba requires large volumes of groundwater, with the bulk of this water pumped from the Upper Carbonate Aquifer. Pumping takes place at the erosional surface of several dipping Paleozoic carbonate units beneath the city. To prevent excessive drawdown, wastewater from these processes is reinjected into the aquifer. Heat loading from the surface, combined with this practice, leads to the creation of areas of elevated temperature within the Upper Carbonate Aquifer. An industrial area located in eastern Winnipeg is the site of the largest of these anomalies, where the aquifer's permeability is enhanced by the presence of conduits and discrete fractures. The use of numerical modeling showed that the greatest temperature anomalies occur where there are very high permeabilities, especially in the form of conduits and discrete fractures. Groundwater velocities are increased by these factors, and could result in the creation of plumes of heated water. Plumes of heated water are less likely to occur where the aquifer is thicker and conduits are absent, due to advective heat transport becoming focused between the injection well and the production well in lower permeability situations. These areas also correspond to the areas of decreased transmissivity in several parts of the Upper Carbonate Aquifer, and may not be capable of producing the required volumes of groundwater for thermal applications. Taking into account these permeability features in planning and design of non-consumptive groundwater systems in the Upper Carbonate Aquifer helps to minimize both drawdown and changes in aquifer temperature. 8 refs., 2 figs.
Abrupt cooling associated with the oceanic Rossby wave and lateral advection during CINDY2011
Seiki, Ayako; Katsumata, Masaki; Horii, Takanori; Hasegawa, Takuya; Richards, Kelvin J.; Yoneyama, Kunio; Shirooka, Ryuichi
2013-10-01
The cooperative Indian Ocean experiment on intraseasonal variability in the Year 2011 (CINDY2011) was conducted to capture atmospheric and oceanic characteristics of the Madden-Julian Oscillation (MJO) in the central Indian Ocean from late 2011 to early 2012. During CINDY2011, the research vessel (R/V) MIRAI stayed at 8°S, 80.5°E for two months during the special observing period (SOP). Intraseasonal convection associated with the MJO was organized in the central Indian Ocean in late October and late November during the SOP. In the middle of November, both sea surface temperature (SST) and mixed layer temperature decreased suddenly when cold low salinity water intruded into the upper layer around the R/V MIRAI. This intrusion was accompanied by a surface current change from southwestward to westward/west-northwestward associated with the passage of the annual oceanic downwelling Rossby wave. The mixed layer heat budget analysis shows that horizontal advection plays an important role in the abrupt cooling whereas the net surface heat flux cannot account for the cooling. This is an interesting result because the associated downwelling Rossby wave is usually considered to increase SST through a reduction of entrainment cooling. In addition, for the second MJO event convection was activated around 20 November over the central north and equatorial Indian Ocean but not in the south. It is suggested that the cooler surface waters (as seen at the location of the R/V MIRAI) tended to suppress the initial atmospheric convection, resulting in the lagged convective onset in the end of November over the central south Indian Ocean.
Summertime influences of tidal energy advection on the surface energy balance in a mangrove forest
Directory of Open Access Journals (Sweden)
J. G. Barr
2013-01-01
Full Text Available Mangrove forests are ecosystems susceptible to changing water levels and temperatures due to climate change as well as perturbations resulting from tropical storms. Numerical models can be used to project mangrove forest responses to regional and global environmental changes, and the reliability of these models depends on surface energy balance closure. However, for tidal ecosystems, the surface energy balance is complex because the energy transport associated with tidal activity remains poorly understood. This study aimed to quantify impacts of tidal flows on energy dynamics within a mangrove ecosystem. To address the research objective, an intensive 10-day study was conducted in a mangrove forest located along the Shark River in the Everglades National Park, FL, USA. Forest–atmosphere turbulent exchanges of energy were quantified with an eddy covariance system installed on a 30-m-tall flux tower. Energy transport associated with tidal activity was calculated based on a coupled mass and energy balance approach. The mass balance included tidal flows and accumulation of water on the forest floor. The energy balance included temporal changes in enthalpy, resulting from tidal flows and temperature changes in the water column. By serving as a net sink or a source of available energy, flood waters reduced the impact of high radiational loads on the mangrove forest. Also, the regression slope of available energy versus sink terms increased from 0.730 to 0.754 and from 0.798 to 0.857, including total enthalpy change in the water column in the surface energy balance for 30-min periods and daily daytime sums, respectively. Results indicated that tidal inundation provides an important mechanism for heat removal and that tidal exchange should be considered in surface energy budgets of coastal ecosystems. Results also demonstrated the importance of including tidal energy advection in mangrove biophysical models that are used for predicting ecosystem
Temporal Variability from the Two-Component Advective Flow Solution and Its Observational Evidence
Dutta, Broja G.; Chakrabarti, Sandip K.
2016-09-01
In the propagating oscillatory shock model, the oscillation of the post-shock region, i.e., the Compton cloud, causes the observed low-frequency quasi-periodic oscillations (QPOs). The evolution of QPO frequency is explained by the systematic variation of the Compton cloud size, i.e., the steady radial movement of the shock front, which is triggered by the cooling of the post-shock region. Thus, analysis of the energy-dependent temporal properties in different variability timescales can diagnose the dynamics and geometry of accretion flows around black holes. We study these properties for the high-inclination black hole source XTE J1550-564 during its 1998 outburst and the low-inclination black hole source GX 339-4 during its 2006-07 outburst using RXTE/PCA data, and we find that they can satisfactorily explain the time lags associated with the QPOs from these systems. We find a smooth decrease of the time lag as a function of time in the rising phase of both sources. In the declining phase, the time lag increases with time. We find a systematic evolution of QPO frequency and hard lags in these outbursts. In XTE J1550-564, the lag changes from hard to soft (i.e., from a positive to a negative value) at a crossing frequency (ν c) of ˜3.4 Hz. We present possible mechanisms to explain the lag behavior of high and low-inclination sources within the framework of a single two-component advective flow model.
Chaotic Advection in Multi-component Melts for the Manufacture of Composite Materials
Zumbrunnen, David
2011-10-01
Several forces arise when different liquids are placed into contact. The relative importance of these forces depends on the sizes and shapes of liquid domains and also on molecular characteristics of the liquids. When the liquids are agitated and in the absence of interdiffusion, a composite structure results that is defined by the spatial extent and size of each liquid domain in the presence of the other. Shaking a bottle with about equal parts of water and oil gives a structure that resembles a household sponge, for example. If the oil volume is much smaller than the water volume, oil droplets result instead. In polymer blends and composites, the structure can have feature sizes at the micron scale or smaller. Little has been known about the variety of structural types that can be formed because current information is based on mixing machinery that intrinsically restricts structural outcomes. This shortcoming has important consequences because physical properties of composite materials obtained by solidifying the structured liquids depend appreciably on structure characteristics. A recent approach to overcome this shortcoming makes use of chaotic advection to establish conditions that organize liquid domains into numerous thin layers. A multi-layer construction undergoes morphological changes in situ. Progressive structure development arises, whereby a specific structure leads in sequence to a morphologically different structure. A new manufacturing technology has resulted which allows control of the internal structure in extruded plastic materials. Micro- and nanostructured materials have been obtained. On-line process control allows rapid optimization of physical properties. In this presentation, the underlying physics will be described, examples of novel materials and their applications will be shown, and research opportunities will be highlighted.
Site use of advective flux probes for soil gas and soil analysis
International Nuclear Information System (INIS)
The success of soil vapor as a means of assessing subsurface conditions depends upon the volatility of the compounds and the ability of the vapor to migrate through soil pores. Normally, soil gas techniques are not considered valid for poorly volatile compounds or tight soils. Both of these factors can be overcome by a simultaneous application of heat and vacuum with heated gas streams or use of a liquid solution, combined with a means of creating an artificially porous substrate out of compacted poorly permeable soils. Special points and bits have been devised to fit on a miniature hollow stem shaft. The point receives a continuous flow of heated air or liquid which volatilises or dissolves organics from porous or pulverized soil as the point penetrates. The re-circulation of gas or fluid then transports the adsorbed organics to the surface for chromatographic analysis. A comparison of vapor pressures of different organics versus absolute temperatures can be used to extrapolate the extension of soil gas detection. Heavy oils, creosotes, naphthalenes, turpenes, and quinolines, all compounds whose boiling points exist in excess of 200 degrees C, can be analyzed by soil vapor techniques. Samples of the organic were obtained by either direct injection on to a heated GC column or by liquid chromatographic processing. The paper compares current vacuum procedures with those obtained from the advective flux procedure. The compounds are plotted on a grid of boiling point, vapor pressure, and aqueous solubility. A site containing soil contaminated with a mixture of light to heavy petroleum products was analyzed with enhanced hot gas and liquid flow. A comparison between the compounds analyzed is presented for both techniques
Lenhard, R. J.; Oostrom, M.; Simmons, C. S.; White, M. D.
1995-07-01
An experiment was conducted to evaluate whether vapor-density effects are significant in transporting volatile organic compounds (VOC's) with high vapor pressure and molecular mass through the subsurface. Trichloroethylene (TCE) was chosen for the investigation because it is a common VOC contaminant with high vapor pressure and molecular mass. For the investigation, a 2-m-long by 1-m-high by 7.5-cm-thick flow cell was constructed with a network of sampling ports. The flow cell was packed with sand, and a water table was established near the lower boundary. Liquid TCE was placed near the upper boundary of the flow cell in a chamber from which vapors could enter and migrate through the sand. TCE concentrations in the gas phase were measured by extracting 25-μl gas samples with an air-tight syringe and analyzing them with a gas chromatograph. The evolution of the TCE gas plume in the sand was investigated by examining plots of TCE concentrations over the domain for specific times and for particular locations as a function of time. To help in this analysis, a numerical model was developed that can predict the simultaneous movements of a gas, a nonaqueous liquid and water in porous media. The model also considers interphase mass transfer by employing the phase equilibrium assumption. The model was tested with one- and two-dimensional analytical solutions of fluid flow before it was used to simulate the experiment. Comparisons between experimental data and simulation results when vapor-density effects are considered were very good. When vapor-density effects were ignored, agreement was poor. These analyses suggest that vapor-density effects should be considered and that density-driven vapor advection may be an important mechanism for moving VOC's with high vapor pressures and molecular mass through the subsurface.
Characteristics of the surface layer above a row crop in the presence of local advection
Energy Technology Data Exchange (ETDEWEB)
Figuerola, P.I. [Universidad de Buenos Aires, Buenos Aires (Argentina)]. E-mail: figuerol@at.fcen.uba.ar; Berliner, P.R. [Blaustein Institute for Desert Research, Ben-Gurion University of the Negev (Israel)
2006-04-15
In some arid land, the irrigated fields are not contiguous and are surrounded by large patches of bare land. During the summer time and rainless season, the solar radiation flux is high and the surface temperature during daylight in the dry bare areas, is much higher than that of the air. The sensible heat generated over these areas may be advected to the irrigated fields. The crops are usually planted in rows and the irrigation systems used (trickle) do not wet the whole surface, the dry bare soil between the rows may develop high soil surface temperatures and lead to convective activity inside the canopy above the bare soil. Advection from the surrounding fields and convective activity inside the canopy affect the layer above the crop. We studied the surface layer above an irrigated tomato field planted in Israel's Negev desert. The crop was planted in rows, trickle irrigated and the distance between the outer edges of two adjacent rows was 0.36 m at the time of measurement. The gradients in temperature and water vapor pressure were obtained at various heights above the canopy using a Bowen ratio machine. The residual in the energy balance equation was used as a criterion to determine the equilibrium layer. During the morning, unstable conditions prevail, and the equilibrium layer was between Z/h {approx} 1.9 and 2.4. In some particular circumstances, in the late morning, the bare soil between the rows reached extremely high temperatures and during conditions with low wind speeds free convection was identified. During these hours the residuals of the energy budget to the heights Z/h = 1.5 and 2.4 were significantly different from zero and an extremely large variability was evident for the Z/h = 3.2 layer. Local advection took place during the afternoon resulting in an increase in the stability of the uppermost measured layer and propagated slowly downwards. The equilibrium layer was between Z/h {approx} 1.5 to 2.4. The residuals were significantly different
Sørensen, Steffen Aagaard
2011-01-01
The overall objective for this PhD-study was to further advance the understanding of the oceanographic variability and development in the Nordic Seas during the Late Glacial and the Holocene and towards the present. The focus is specifically on the poleward Atlantic Water advection along the continental margins of Norway, into the SW Barents Sea and along the West Spitsbergen slope. Four high resolution sediment cores retrieved from northern continental shelve allowed examination of spatial a...
Directory of Open Access Journals (Sweden)
R. L. Gattinger
2013-08-01
Full Text Available Observations of the mesospheric semi-annual oscillation (MSAO in the equatorial region have been reported dating back several decades. Seasonal variations in both species densities and airglow emissions are well documented. The extensive observations available offer an excellent case study for comparison with model simulations. A broad range of MSAO measurements is summarised with emphasis on the 80–100 km region. The objective here is not to address directly the complicated driving forces of the MSAO, but rather to employ a combination of observations and model simulations to estimate the limits of some of the underlying dynamical processes. Photochemical model simulations are included for near-equinox and near-solstice conditions, the two times with notable differences in the observed MSAO parameters. Diurnal tides are incorporated in the model to facilitate comparisons of observations made at different local times. The roles of water vapour as the "driver" species and ozone as the "response" species are examined to test for consistency between the model results and observations. The simulations suggest the interactions between vertical eddy diffusion and background vertical advection play a significant role in the MSAO phenomenon. Further, the simulations imply there are rigid limits on vertical advection rates and eddy diffusion rates. For August at the Equator, 90 km altitude, the derived eddy diffusion rate is approximately 1 × 106 cm2 s−1 and the vertical advection is upwards at 0.8 cm s−1. For April the corresponding values are 4 × 105 cm2 s−1 and 0.1 cm s−1. These results from the current 1-D model simulations will need to be verified by a full 3-D simulation. Exactly how vertical advection and eddy diffusion are related to gravity wave momentum as discussed by Dunkerton (1982 three decades ago remains to be addressed.
DEFF Research Database (Denmark)
Machefaux, Ewan; Larsen, Gunner Chr.; Troldborg, Niels;
2013-01-01
In this paper, single wake characteristics have been studied both experimentally and numerically. Firstly, the wake is studied experimentally using full-scale measurements from an adapted focused pulsed lidar system, which potentially gives more insight into the wake dynamics as compared to class...... using the EllipSys3D flow solver using Large Eddy Simulation (LES) and Actuator Line Technique (ACL) to model the rotor. Discrepancies due to the uncertainties on the wake advection velocity are observed and discussed....
DEFF Research Database (Denmark)
In this paper, single wake characteristics have been studied both experimentally and numerically. Firstly, the wake is studied experimentally using full-scale measurements from an adapted focused pulsed lidar system, which potentially gives more insight into the wake dynamics as compared to class...... using the EllipSys3D flow solver using Large Eddy Simulation (LES) and Actuator Line Technique (ACL) to model the rotor. Discrepancies due to the uncertainties on the wake advection velocity are observed and discussed....
Stefano L. Russo; Glenda Taddia
2010-01-01
Problem statement: The increasing diffusion of low-enthalpy geothermal open-loop Groundwater Heat Pumps (GWHP) providing buildings air conditioning requires a careful assessment of the overall effects on groundwater system, especially in the urban areas. The impact on the groundwater temperature in the surrounding area of the re-injection well is directly linked to the aquifer properties. Physical processes affecting heat transport within an aquifer include advection (or convection) and hydro...
Vinsard, G.; Dufour, S.; Saatdjian, E.; Mota, J. P. B.
2016-03-01
Chaotic advection can effectively enhance the heat transfer rate between a boundary and fluids with high Prandtl number. These fluids are usually highly viscous and thus turbulent agitation is not a viable solution since the energy required to mix the fluid would be prohibitive. Here, we analyze previously obtained results on chaotic advection and heat transfer in two similar 2-D periodic flows and on their corresponding 3-D periodic flows when an axial velocity component is superposed. The two flows studied are the flow between eccentric rotating cylinders and the flow between confocal ellipses. For both of these flows the analysis is simplified because the Stokes equations can be solved analytically to obtain a closed form solution. For both 2-D periodic flows, we show that chaotic heat transfer is enhanced by the displacement of the saddle point location during one period. Furthermore, the enhancement by chaotic advection in the elliptical geometry is approximately double that obtained in the cylindrical geometry because there are two saddle points instead of one. We also explain why, for high eccentricity ratios, there is no heat transfer enhancement in the cylindrical geometry. When an axial velocity component is added to both of these flows so that they become 3-D, previous work has shown that there is an optimum modulation frequency for which chaotic advection and heat transfer enhancement is a maximum. Here we show that the optimum modulation frequency can be derived from results without an axial flow. We also explain by physical arguments other previously unanswered questions in the published data.
Degond, Pierre; Lozinski, Alexei; Muljadi, Bagus Putra; Narski, Jacek
2013-01-01
The adaptation of Crouzeix - Raviart finite element in the context of multiscale finite element method (MsFEM) is studied and implemented on diffusion and advection-diffusion problems in perforated media. It is known that the approximation of boundary condition on coarse element edges when computing the multiscale basis functions critically influences the eventual accuracy of any MsFEM approaches. The weakly enforced continuity of Crouzeix - Raviart function space across element edges leads t...
Berenstein, Igal; Bullara, Domenico; De Decker, Yannick
2014-09-01
This paper studies the spatiotemporal dynamics of a reaction-diffusion-advection system corresponding to an extension of the Oregonator model, which includes two inhibitors instead of one. We show that when the reaction-diffusion, two-dimensional problem displays stationary patterns the addition of a plug flow can induce the emergence of new types of stationary structures. These patterns take the form of spots or arcs, the size and the spacing of which can be controlled by the flow.
Implementation of the Semi-Lagrangian Advection Scheme on a Quasi-Uniform Overset Grid on a Sphere
Institute of Scientific and Technical Information of China (English)
无
2006-01-01
The semi-Lagrangian advection scheme is implemented on a new quasi-uniform overset (Yin-Yang) grid on the sphere. The Yin-Yang grid is a newly developed grid system in spherical geometry with two perpendicularly-oriented latitude-longitude grid components (called Yin and Yang respectively) that overlapp each other, and this effectively avoids the coordinate singularity and the grid convergence near the poles. In this overset grid, the way of transferring data between the Yin and Yang components is the key to maintaining the accuracy and robustness in numerical solutions. A numerical interpolation for boundary data exchange, which maintains the accuracy of the original advection scheme and is computationally efficient, is given in this paper. A standard test of the solid-body advection proposed by Williamson is carried out on the Yin-Yang grid. Numerical results show that the quasi-uniform Yin-Yang grid can get around the problems near the poles, and the numerical accuracy in the original semi-Lagrangian scheme is effectively maintained in the Yin-Yang grid.
Directory of Open Access Journals (Sweden)
F. Hasebe
2007-01-01
Full Text Available Water vapor observations by chilled-mirror hygrometers were conducted at Bandung, Indonesia (6.90° S, 107.60° E and Tarawa, Kiribati (1.35° N, 172.91° E in December 2003 to examine the efficiency of dehydration during horizontal advection in the tropical tropopause layer (TTL. Trajectory analyses based on bundles of isentropic trajectories suggest that the modification of air parcels' identity due to irreversible mixing by the branching-out and merging-in of nearby trajectories is found to be an important factor, in addition to the routes air parcels follow, for interpreting the water vapor concentrations observed by chilled-mirror frostpoint hygrometers in the TTL. Clear correspondence between the observed water vapor concentration and the estimated temperature history of air parcels is found showing that drier air parcels were exposed to lower temperatures than were more humid ones during advection. Although the number of observations is quite limited, the water content in the observed air parcels on many occasions was more than that expected from the minimum saturation mixing ratio during horizontal advection prior to sonde observations.
Dorman, Jeffrey G.; Powell, Thomas M.; Sydeman, William J.; Bograd, Steven J.
2011-02-01
A decrease in krill abundance during 2005 in regions of the California Current has been hypothesized to have had immediate (seabird) and long-term (salmon) negative impacts on upper trophic level predators. We use a suite of coupled models to examine the population biology and spatial and temporal distribution of the krill species Euphausia pacifica during the winter/spring of 2001, a “normal” year, and 2005, an “anomalous” year, to determine if this hypothesis is supported mechanistically. Ocean conditions were simulated using the Regional Ocean Modeling System (ROMS), which forced an individual-based model parameterized to simulate the population biology of E. pacifica. Poleward transport during winter 2005 advected particles north of Cape Mendocino, away from seabirds and salmon feeding in the Gulf of the Farallons region. Few of the particles that were advected north in 2005 returned to their region of release throughout the model run time (200 days). Moreover, the “condition” of those particles remaining within the domain was poor in 2005, with greater mortality from starvation and a decreased mean particle weight. Our results indicate that both physical processes (anomalous northern advection) and biological processes (greater starvation and less weight per individual) contributed to reduced krill availability to predators in the northern California region during 2005, and that the productivity and survival of seabirds and salmonids is dependent on krill during critical life history stages.
Rubbab, Qammar; Mirza, Itrat Abbas; Qureshi, M. Zubair Akbar
2016-07-01
The time-fractional advection-diffusion equation with Caputo-Fabrizio fractional derivatives (fractional derivatives without singular kernel) is considered under the time-dependent emissions on the boundary and the first order chemical reaction. The non-dimensional problem is formulated by using suitable dimensionless variables and the fundamental solutions to the Dirichlet problem for the fractional advection-diffusion equation are determined using the integral transforms technique. The fundamental solutions for the ordinary advection-diffusion equation, fractional and ordinary diffusion equation are obtained as limiting cases of the previous model. Using Duhamel's principle, the analytical solutions to the Dirichlet problem with time-dependent boundary pulses have been obtained. The influence of the fractional parameter and of the drift parameter on the solute concentration in various spatial positions was analyzed by numerical calculations. It is found that the variation of the fractional parameter has a significant effect on the solute concentration, namely, the memory effects lead to the retardation of the mass transport.
Schelenz, Sophie; Dietrich, Peter; Vienken, Thomas
2016-04-01
A sustainable thermal exploitation of the shallow subsurface requires a precise understanding of all relevant heat transport processes. Currently, planning practice of shallow geothermal systems (especially for systems neglected or strongly simplified. The presented study proves that those simplifications of complex geological and hydrogeological subsurface characteristics are insufficient for a precise evaluation of site-specific energy extraction rates. Based on synthetic model scenarios with varying subsurface conditions (groundwater flow velocity and aquifer thickness) the impact of advection on induced long term temperature changes in 5 and 10 m distance of the borehole heat exchanger is presented. Extending known investigations, this study enhances the evaluation of shallow geothermal energy extraction rates by considering conductive and advective heat transport under varying aquifer thicknesses. Further, it evaluates the impact of advection on installation lengths of the borehole heat exchanger to optimize the initial financial investment. Finally, an evaluation approach is presented that classifies relevant heat transport processes according to their Péclet number to enable a first quantitative assessment of the subsurface energy regime and recommend further investigation and planning procedures.
Methods and Algorithms for Solving Inverse Problems for Fractional Advection-Dispersion Equations
Aldoghaither, Abeer
2015-11-12
Fractional calculus has been introduced as an e cient tool for modeling physical phenomena, thanks to its memory and hereditary properties. For example, fractional models have been successfully used to describe anomalous di↵usion processes such as contaminant transport in soil, oil flow in porous media, and groundwater flow. These models capture important features of particle transport such as particles with velocity variations and long-rest periods. Mathematical modeling of physical phenomena requires the identification of pa- rameters and variables from available measurements. This is referred to as an inverse problem. In this work, we are interested in studying theoretically and numerically inverse problems for space Fractional Advection-Dispersion Equation (FADE), which is used to model solute transport in porous media. Identifying parameters for such an equa- tion is important to understand how chemical or biological contaminants are trans- ported throughout surface aquifer systems. For instance, an estimate of the di↵eren- tiation order in groundwater contaminant transport model can provide information about soil properties, such as the heterogeneity of the medium. Our main contribution is to propose a novel e cient algorithm based on modulat-ing functions to estimate the coe cients and the di↵erentiation order for space FADE, which can be extended to general fractional Partial Di↵erential Equation (PDE). We also show how the method can be applied to the source inverse problem. This work is divided into two parts: In part I, the proposed method is described and studied through an extensive numerical analysis. The local convergence of the proposed two-stage algorithm is proven for 1D space FADE. The properties of this method are studied along with its limitations. Then, the algorithm is generalized to the 2D FADE. In part II, we analyze direct and inverse source problems for a space FADE. The problem consists of recovering the source term using final
Is the Coastal Ocean a Source of Mercury to Marine Advective Fog
Heim, W. A.; Weiss-Penzias, P. S.; Fernandez, D.; Byington, A.; Bonnema, A.; Beebe, C.; Chiswell, H.; Olson, A.; Coale, K. H.
2014-12-01
Marine advective fog is a common feature along the California coast during the summer season. This fog provides an important water source to many endemic fauna and flora. Studies are underway to better understand the chemical makeup of Pacific marine fog as it is an important input to the hydrologic cycle. We report results from our study focused on investigating the potential for coastal ocean upwelling to contribute volatile organic mercury to the overlying atmosphere where it could be incorporated into cloud droplets as monomethyl mercury (MMHg). Preliminary research by this group has indicated that fog water inputs to certain coastal locations may contribute up to 99% of the MMHg flux to land compared to the MMHg flux in rain. Mercury measurements, including total mercury (Hgt), MMHg, elemental mercury (Hg0), and dimethyl mercury (DMHg), were made to unfiltered water collected from depth profiles at 12 stations from Big Sur to Trinidad Head over the California shelf during summer 2014. Profiles of Hgt ranged from 0.3-2.4 pM and were similar to other reported measurements of Hgt for the North Pacific. A large range in concentration was observed for MMHg (10-540 fM) with elevated values generally occurring below the oxycline (>50m). Concentrations of Hg0 were 0.06 to 0.57 pM with elevated concentrations at depth relative to surface values. Depth profiles of DMHg were similar to MMHg and concentrations were measured from 10-295 fM with highest concentrations observed below the oxycline. Surface concentrations of DMHg averaged 40 ± 22 fM. Given the observed profiles for DMHg and the fact that it is sparingly soluble in water, a net flux of DMHg to the atmosphere is likely occurring. Based on these findings and the fact that MMHg and DMHg concentrations in the coastal ocean were highest in the low oxygen zone, we speculate that mercury is methylated in the water column and/or sediments as DMHg and that this water is upwelled seasonally in the coastal zones and
Evaporative loss from irrigated interrows in a highly advective semi-arid agricultural area
Agam, Nurit; Evett, Steven R.; Tolk, Judy A.; Kustas, William P.; Colaizzi, Paul D.; Alfieri, Joseph G.; McKee, Lynn G.; Copeland, Karen S.; Howell, Terry A.; Chávez, Jose L.
2012-12-01
Agricultural productivity has increased in the Texas High Plains at the cost of declining water tables, putting at risk the sustainability of the Ogallala Aquifer as a principal source of water for irrigated agriculture. This has led area producers to seek alternative practices that can increase water use efficiency (WUE) through more careful management of water. One potential way of improving WUE is by reducing soil evaporation (E), thus reducing overall evapotranspiration (ET). Before searching for ways to reduce E, it is first important to quantify E and understand the factors that determine its magnitude. The objectives of this study were (1) to quantify E throughout part of the growing season for irrigated cotton in a strongly advective semi-arid region; (2) to study the effects of LAI, days after irrigation, and measurement location within the row on the E/ET fraction; and (3) to study the ability of microlysimeter (ML) measures of E combined with sap flow gage measures of transpiration (T) to accurately estimate ET when compared with weighing lysimeter ET data and to assess the E/T ratio. The research was conducted in an irrigated cotton field at the Conservation & Production Research Laboratory of the USDA-ARS, Bushland, TX. ET was measured by a large weighing lysimeter, and E was measured by 10 microlysimeters that were deployed in two sets of 5 across the interrow. In addition, 10 heat balance sap flow gages were used to determine T. A moderately good agreement was found between the sum E + T and ET (SE = 1 mm or ˜10% of ET). It was found that E may account for >50% of ET during early stages of the growing season (LAI < 0.2), significantly decreasing with increase in LAI to values near 20% at peak LAI of three. Measurement location within the north-south interrows had a distinct effect on the diurnal pattern of E, with a shift in time of peak E from west to east, a pattern that was governed by the solar radiation reaching the soil surface. However, total
Mahesha, Chaitra
A unique processing technique based on chaotic advection developed at Clemson University and shown to controllably produce structured materials in the past was employed to produce structured nanocomposites with a high degree of clay orientation as well as localization of platelets within layers of nanoscale thicknesses. Continuous lengths of nanocomposites with different clay contents were extruded in the form of films by feeding separately melts of virgin polyamide-6 polymer and polyamide 6-clay masterbatch into a continuous chaotic advection blender. A variety of composite structures were producible at fixed clay compositions. The internal structure was characterized by transmission electron microscopy (TEM), x-ray diffraction (XRD) and differential scanning calorimetry (DSC). Nanocomposites with novel in-situ multi-layered structures and a high degree of platelet orientation were formed by the recursive stretching and folding of the melt domains due to chaotic advection. Clay platelets were localized within discrete regions to form alternating virgin and platelet-rich layers leading to a hierarchical structure with multiple nano-scales. The thicknesses of the layers reduced with prolonged chaotic advection, eventually leading to nanocomposites in which the multi-layering was no longer discernible. The oriented platelets appeared to be homogenously dispersed through the bulk of the nanocomposite. Investigation of the morphology of the matrix by XRD showed that the homogeneity of the crystalline phase and the orientation of polymer chains parallel to the film surface increased with increased chaotic advection. Also, as the layer thickness reduced, the number of polymer chains restricted by clay platelets increased causing the gamma-crystalline fraction to increase. While XRD results suggested a change in total crystallinity with chaotic advection and clay content but without a specific trend, no change in crystallinity was measured by DSC. Such contradictions are
Bachand, P.A.M.; S. Bachand,; Fleck, Jacob A.; Anderson, Frank E.; Windham-Myers, Lisamarie
2014-01-01
The current state of science and engineering related to analyzing wetlands overlooks the importance of transpiration and risks data misinterpretation. In response, we developed hydrologic and mass budgets for agricultural wetlands using electrical conductivity (EC) as a natural conservative tracer. We developed simple differential equations that quantify evaporation and transpiration rates using flowrates and tracer concentrations atwetland inflows and outflows. We used two ideal reactormodel solutions, a continuous flowstirred tank reactor (CFSTR) and a plug flow reactor (PFR), to bracket real non-ideal systems. From those models, estimated transpiration ranged from 55% (CFSTR) to 74% (PFR) of total evapotranspiration (ET) rates, consistent with published values using standard methods and direct measurements. The PFR model more appropriately represents these nonideal agricultural wetlands in which check ponds are in series. Using a fluxmodel, we also developed an equation delineating the root zone depth at which diffusive dominated fluxes transition to advective dominated fluxes. This relationship is similar to the Peclet number that identifies the dominance of advective or diffusive fluxes in surface and groundwater transport. Using diffusion coefficients for inorganic mercury (Hg) and methylmercury (MeHg) we calculated that during high ET periods typical of summer, advective fluxes dominate root zone transport except in the top millimeters below the sediment–water interface. The transition depth has diel and seasonal trends, tracking those of ET. Neglecting this pathway has profound implications: misallocating loads along different hydrologic pathways; misinterpreting seasonal and diel water quality trends; confounding Fick's First Law calculations when determining diffusion fluxes using pore water concentration data; and misinterpreting biogeochemicalmechanisms affecting dissolved constituent cycling in the root zone. In addition,our understanding of internal
Ballester, Joan; Bordoni, Simona; Petrova, Desislava; Rodó, Xavier
2016-06-01
The oscillatory nature of El Niño-Southern Oscillation results from an intricate superposition of near-equilibrium balances and out-of-phase disequilibrium processes between the ocean and the atmosphere. The main objective of the present work is to perform an exhaustive spatiotemporal analysis of the upper ocean heat budget in an ensemble of state-of-the-art ocean assimilation products. We put specific emphasis on the ocean heat advection mechanisms, and their representation in individual ensemble members and in the different stages of the ENSO oscillation leading to EN events. Our analyses consistently show that the initial subsurface warming in the western equatorial Pacific is advected to the central Pacific by the equatorial undercurrent, which, together with the equatorward advection associated with anomalies in both the meridional temperature gradient and circulation at the level of the thermocline, explains the heat buildup in the central Pacific during the recharge phase. We also find that the recharge phase is characterized by an increase of meridional tilting of the thermocline, as well as a southward upper-ocean cross-equatorial mass transport resulting from Ekman-induced anomalous vertical motion in the off-equatorial regions. Although differences between data sets are generally small, and anomalies tend to have the same sign, the differences in the magnitude of the meridional term are seen to be key for explaining the different propagation speed of the subsurface warming tendency along the thermocline. The only exception is GECCO, which does not produce the patterns of meridional surface Ekman divergence (subsurface Sverdrup convergence) in the western and central equatorial Pacific.
Institute of Scientific and Technical Information of China (English)
Alexandre Ern; Annette F.Stephansen
2008-01-01
We propose and analyze a posteriori energy-norm error estimates for weighted interior penalty discontinuous Galerkin approximations of advection-diffusion-reaction equations with heterogeneous and anisotropic diffusion.The weights,which play a key role in the analysis.depend on the diffusion tensor and are used to formulate the consistency terms in the discontinuous Galerkin method.The error upper bounds,in which all the constants are specified.consist of three terms:a residual estimator which depends only on the elementwise fluctuation of the discrete solution residual,a diffusive flux estimator where the weights used in the method enter explicitly,and a non-conforming estimator which is nonzero because of the use of discontinuous finite element spaces.The three estimators can be bounded locally by the approximation error.A particular attention is given to the dependency on problem parameters of the constants in the local lower error bounds,For moderate advection.it.is shown that full robustness with respect to diffusion heterogeneities is achieved owing to the specific design of the weights in the discontinuous Galerkin method,while diffusion anisotropies remain purely local and impact the constants through the square root of the condition number of the diffusion tensor.For dominant advection,the local lower error bounds can be written with constants involving a cut-off for the ratio of local mesh size to the reciprocal of the square root of the lowest local eignevalue of the diffusion tensor.
Digital Repository Service at National Institute of Oceanography (India)
Jyothi, D.; Murty, T.V.R.; Sarma, V.V.; Rao, D.P.
of Marine Sciences Vol. 29, June 2000, pp. 185-187 Short Communication Computation of diffusion coefficients for waters of Gauthami Godavari estuary using one-dimensional advection-diffusion model D Jyothi, T V Ramana Murty, V V Sarma & D P Rao National.... - Jan.) Y2(x) = 8.55283 x + 17.5469 (Jan. - April) These equations would be more useful to get diffusion coefficients for any point along the channel axis, which in turn, helps to compute the concentration of pollutant along the axis of estuary. Thus...
Directory of Open Access Journals (Sweden)
Stefano L. Russo
2010-01-01
Full Text Available Problem statement: The increasing diffusion of low-enthalpy geothermal open-loop Groundwater Heat Pumps (GWHP providing buildings air conditioning requires a careful assessment of the overall effects on groundwater system, especially in the urban areas. The impact on the groundwater temperature in the surrounding area of the re-injection well is directly linked to the aquifer properties. Physical processes affecting heat transport within an aquifer include advection (or convection and hydrodynamic thermodispersion (diffusion and mechanical dispersion. If the groundwater flows, the advective components tend to dominate the heat transfer process within the aquifer and the diffusion can be considered negligible. This study illustrates the experimental results derived from the groundwater monitoring in the surrounding area of an injection well connected to an open-loop GWHP plant which has been installed in the "Politecnico di Torino" (NW Italy for cooling some of the university buildings. Groundwater pumping and injection interfere only with the upper unconfined aquifer. Approach: After the description of the hydrogeological setting the authors examined the data deriving from multiparameter probes installed inside the pumping well (P2, the injection well (P4 and a downgradient piezometer (S2. Data refers to the summer 2009. To control the aquifer thermal stratification some multi-temporal temperature logs have been performed in the S2. Results: After the injection of warm water in P4 the plume arrived after 30 days in the S2. That delay is compatible with the calculated plume migration velocity (1.27 m d-1 and their respective distance (35 m. The natural temperature in the aquifer due to the switching-off of the GWHP plant has been reached after two month. The Electrical Conductivity (EC values tend to vary out of phase with the temperature. The temperature logs in the S2 highlighted a thermal stratification in the aquifer due to a low vertical
Directory of Open Access Journals (Sweden)
C M SURESHA
2012-01-01
Full Text Available A two dimensional advection-diffusion numerical model of air pollutant emitted from an area source of primary pollutant with wet deposition is presented. We study the effect of removal mechanism i.e. wet deposition on primary pollutant with respect to distance and height for stable and neutral cases. The numerical model has been solved by using Crank-Nicolson implicit finite difference technique. Concentration contours are plotted and results are analysed for primary pollutant in stable and neutral atmospheric situations for various meteorological parameters.
Energy Technology Data Exchange (ETDEWEB)
Bachand, P.A.M., E-mail: Philip.Bachand@Tetratech.com [Tetra Tech, Davis, CA (United States); Bachand, S. [Tetra Tech, Davis, CA (United States); Fleck, J.; Anderson, F. [U.S. Geological Survey, California Water Science Center, Sacramento, CA (United States); Windham-Myers, L. [U.S. Geological Survey, National Research Program, Menlo Park, CA (United States)
2014-06-01
The current state of science and engineering related to analyzing wetlands overlooks the importance of transpiration and risks data misinterpretation. In response, we developed hydrologic and mass budgets for agricultural wetlands using electrical conductivity (EC) as a natural conservative tracer. We developed simple differential equations that quantify evaporation and transpiration rates using flow rates and tracer concentrations at wetland inflows and outflows. We used two ideal reactor model solutions, a continuous flow stirred tank reactor (CFSTR) and a plug flow reactor (PFR), to bracket real non-ideal systems. From those models, estimated transpiration ranged from 55% (CFSTR) to 74% (PFR) of total evapotranspiration (ET) rates, consistent with published values using standard methods and direct measurements. The PFR model more appropriately represents these non-ideal agricultural wetlands in which check ponds are in series. Using a flux model, we also developed an equation delineating the root zone depth at which diffusive dominated fluxes transition to advective dominated fluxes. This relationship is similar to the Peclet number that identifies the dominance of advective or diffusive fluxes in surface and groundwater transport. Using diffusion coefficients for inorganic mercury (Hg) and methylmercury (MeHg) we calculated that during high ET periods typical of summer, advective fluxes dominate root zone transport except in the top millimeters below the sediment–water interface. The transition depth has diel and seasonal trends, tracking those of ET. Neglecting this pathway has profound implications: misallocating loads along different hydrologic pathways; misinterpreting seasonal and diel water quality trends; confounding Fick's First Law calculations when determining diffusion fluxes using pore water concentration data; and misinterpreting biogeochemical mechanisms affecting dissolved constituent cycling in the root zone. In addition, our
Healy, R.W.; Russell, T.F.
1992-01-01
A finite-volume Eulerian-Lagrangian local adjoint method for solution of the advection-dispersion equation is developed and discussed. The method is mass conservative and can solve advection-dominated ground-water solute-transport problems accurately and efficiently. An integrated finite-difference approach is used in the method. A key component of the method is that the integral representing the mass-storage term is evaluated numerically at the current time level. Integration points, and the mass associated with these points, are then forward tracked up to the next time level. The number of integration points required to reach a specified level of accuracy is problem dependent and increases as the sharpness of the simulated solute front increases. Integration points are generally equally spaced within each grid cell. For problems involving variable coefficients it has been found to be advantageous to include additional integration points at strategic locations in each well. These locations are determined by backtracking. Forward tracking of boundary fluxes by the method alleviates problems that are encountered in the backtracking approaches of most characteristic methods. A test problem is used to illustrate that the new method offers substantial advantages over other numerical methods for a wide range of problems.
Antonov, N V; Gulitskiy, N M
2015-10-01
In this work we study the generalization of the problem considered in [Phys. Rev. E 91, 013002 (2015)] to the case of finite correlation time of the environment (velocity) field. The model describes a vector (e.g., magnetic) field, passively advected by a strongly anisotropic turbulent flow. Inertial-range asymptotic behavior is studied by means of the field theoretic renormalization group and the operator product expansion. The advecting velocity field is Gaussian, with finite correlation time and preassigned pair correlation function. Due to the presence of distinguished direction n, all the multiloop diagrams in this model vanish, so that the results obtained are exact. The inertial-range behavior of the model is described by two regimes (the limits of vanishing or infinite correlation time) that correspond to the two nontrivial fixed points of the RG equations. Their stability depends on the relation between the exponents in the energy spectrum E∝k(⊥)(1-ξ) and the dispersion law ω∝k(⊥)(2-η). In contrast to the well-known isotropic Kraichnan's model, where various correlation functions exhibit anomalous scaling behavior with infinite sets of anomalous exponents, here the corrections to ordinary scaling are polynomials of logarithms of the integral turbulence scale L. PMID:26565343
Raghib, M; Levin, S A; Kevrekidis, I G
2010-06-01
We propose a (time) multiscale method for the coarse-grained analysis of collective motion and decision-making in self-propelled particle models of swarms comprising a mixture of 'naïve' and 'informed' individuals. The method is based on projecting the particle configuration onto a single 'meta-particle' that consists of the elongation of the flock together with the mean group velocity and position. We find that the collective states can be associated with the transient and asymptotic transport properties of the random walk followed by the meta-particle, which we assume follows a continuous time random walk (CTRW). These properties can be accurately predicted at the macroscopic level by an advection-diffusion equation with memory (ADEM) whose parameters are obtained from a mean group velocity time series obtained from a single simulation run of the individual-based model.
Energy Technology Data Exchange (ETDEWEB)
Zubov, V.A.; Rozanov, E.V. [Main Geophysical Observatory, St.Petersburg (Russian Federation); Schlesinger, M.E.; Andronova, N.G. [Illinois Univ., Urbana-Champaign, IL (United States). Dept. of Atmospheric Sciences
1997-12-31
The problems of ozone depletion, climate change and atmospheric pollution strongly depend on the processes of production, destruction and transport of chemical species. A hybrid transport scheme was developed, consisting of the semi-Lagrangian scheme for horizontal advection and the Prather scheme for vertical transport, which have been used for the Atmospheric Chemical Transport model to calculate the distributions of different chemical species. The performance of the new hybrid scheme has been evaluated in comparison with other transport schemes on the basis of specially designed tests. The seasonal cycle of the distribution of N{sub 2}O simulated by the model, as well as the dispersion of NO{sub x} exhausted from subsonic aircraft, are in a good agreement with published data. (author) 8 refs.
Fuller, Nathaniel J
2016-01-01
Obtaining a detailed understanding of the physical interactions between a cell and its environment often requires information about the flow of fluid surrounding the cell. Cells must be able to effectively absorb and discard material in order to survive. Strategies for nutrient acquisition and toxin disposal, which have been evolutionarily selected for their efficacy, should reflect knowledge of the physics underlying this mass transport problem. Motivated by these considerations, in this paper we consider a two-dimensional advection-diffusion problem at small Reynolds number and large P\\'eclet number. We discuss the problem of mass transport for a circular cell in a uniform far-field flow. We approach the problem numerically, and also analytically through a rescaling of the concentration boundary layer. A biophysically motivated first-passage problem for the absorption of material by the cell demonstrates quantitative agreement between the numerical and analytical approaches.
Energy Technology Data Exchange (ETDEWEB)
Sherwood, S.C. [Univ. of California, La Jolla, CA (United States)
1996-11-01
Analyzed wind fields are used to perform a simple advection of moisture by the large-scale circulation in three dimensions at 2.5{degrees} resolution. The unresolved moisture sink Q{sub 2} due to convection is neglected, except in regions of strong ascent where it is used to enforce a 90% relative humidity ceiling, as determined from sounding and geostationary satellite observations. The result is a simulation of water vapor that agrees quantitatively with satellite (Special Sensor Microwave Water Vapor) and sounding observations over the tropical oceans, in both and moist regions, to within 10% relative humidity or better from 700 to 300 mb inclusively. Horizontal transport into and regions from convective regions is accomplished by large coherent structures. Implications of the results for the role of convection in maintaining the observed humidity distribution, and for the interpretation of observed correlations between cloud cover and vapor, are discussed. 38 refs., 14 figs., 1 tab.
Healy, R.W.; Russell, T.F.
1993-01-01
Test results demonstrate that the finite-volume Eulerian-Lagrangian localized adjoint method (FVELLAM) outperforms standard finite-difference methods for solute transport problems that are dominated by advection. FVELLAM systematically conserves mass globally with all types of boundary conditions. Integrated finite differences, instead of finite elements, are used to approximate the governing equation. This approach, in conjunction with a forward tracking scheme, greatly facilitates mass conservation. The mass storage integral is numerically evaluated at the current time level, and quadrature points are then tracked forward in time to the next level. Forward tracking permits straightforward treatment of inflow boundaries, thus avoiding the inherent problem in backtracking of characteristic lines intersecting inflow boundaries. FVELLAM extends previous results by obtaining mass conservation locally on Lagrangian space-time elements. -from Authors
Directory of Open Access Journals (Sweden)
L. Dong
2015-01-01
Full Text Available The interparcel mixing algorithm in the Lagrangian advection scheme with shape matrix (LASM is updated to make the scheme more robust. The linear degeneration criterion is replaced by the maximum deviation of the skeleton points so that the new algorithm is more effective in controlling the shape of parcels, which is vital for long time simulation. LASM is inherently shape-preserving without any complicated filter or limiter, so it is linear. This fact contributes to the ability of LASM of preserving the sum of multiple tracers exactly. A newly proposed terminator "toy"-chemistry test is also used to test LASM, which shows that LASM can preserve the weighted sum of two reactive chlorine-like species precisely.
Biamonte, Mason; Idarraga, John
2013-04-01
A classical hybrid alternating-direction implicit difference scheme is used to simulate two-dimensional charge carrier advection-diffusion induced by alpha particles incident upon silicon pixel detectors at room temperature in vacuum. A mapping between the results of the simulation and a projection of the cluster size for each incident alpha is constructed. The error between the simulation and the experimental data diminishes with the increase in the applied voltage for the pixels in the central region of the cluster. Simulated peripheral pixel TOT values do not match the data for any value of applied voltage, suggesting possible modifications to the current algorithm from first principles. Coulomb repulsion between charge carriers is built into the algorithm using the Barnes-Hut tree algorithm. The plasma effect arising from the initial presence of holes in the silicon is incorporated into the simulation. The error between the simulation and the data helps identify physics not accounted for in standard literature simulation techniques.
DEFF Research Database (Denmark)
Rolle, Massimo
2015-01-01
Diffusion and compound-specific mixing significantly affect conservative and reactive transport in groundwater. The variability of diffusion coefficients for different solutes has a relevant impact on their displacement at different scales, not only under diffusion-dominated regimes but also under...... to multicomponent ionic dispersion: the dispersive fluxes of the different ions are cross-coupled due to the effects of Coulombic interactions. Such effects are illustrated in flow-through experiments in saturated porous media. Simple strong electrolytes were selected as tracers and their transport was studied...... under different advection-dominated conditions and in homogeneous and heterogeneous porous media. The interpretation of the experimental results requires a multicomponent modeling approach with an accurate description of local hydrodynamic dispersion and explicitly accounting for the cross...
Scheck, L; Foglizzo, T; Kifonidis, K
2007-01-01
By 2D hydrodynamic simulations including a detailed equation of state and neutrino transport, we investigate the interplay between different non-radial hydrodynamic instabilities that play a role during the postbounce accretion phase of collapsing stellar cores. The convective mode of instability, which is driven by negative entropy gradients caused by neutrino heating or by time variations of the shock strength, can be identified clearly by the development of typical Rayleigh-Taylor mushrooms. However, in cases where the gas in the postshock region is rapidly advected towards the gain radius, the growth of such a buoyancy instability can be suppressed. In such a situation the shocked flow nevertheless can develop non-radial asymmetry with an oscillatory growth of the amplitude. This phenomenon was previously termed ``standing accretion shock instability'' (SASI) by Blondin et al. (2003). It is shown here that the oscillation period of the SASI observed in our simulations agrees well with the one estimated fo...
Directory of Open Access Journals (Sweden)
Mcebisi Mkhwanazi
2015-11-01
Full Text Available Because the Surface Energy Balance Algorithm for Land (SEBAL tends to underestimate ET when there is advection, the model was modified by incorporating an advection component as part of the energy usable for crop evapotranspiration (ET. The modification involved the estimation of advected energy, which required the development of a wind function. In Part I, the modified SEBAL model (SEBAL-A was developed and validated on well-watered alfalfa of a standard height of 40–60 cm. In this Part II, SEBAL-A was tested on different crops and irrigation treatments in order to determine its performance under varying conditions. The crops used for the transferability test were beans (Phaseolus vulgaris L., wheat (Triticum aestivum L. and corn (Zea mays L.. The estimated ET using SEBAL-A was compared to actual ET measured using a Bowen Ratio Energy Balance (BREB system. Results indicated that SEBAL-A estimated ET fairly well for beans and wheat, only showing some slight underestimation of a Mean Bias Error (MBE of −0.7 mm·d−1 (−11.3%, a Root Mean Square Error (RMSE of 0.82 mm·d−1 (13.9% and a Nash Sutcliffe Coefficient of Efficiency (NSCE of 0.64. On corn, SEBAL-A resulted in an ET estimation error MBE of −0.7 mm·d−1 (−9.9%, a RMSE of 1.59 mm·d−1 (23.1% and NSCE = 0.24. This result shows an improvement on the original SEBAL model, which for the same data resulted in an ET MBE of −1.4 mm·d−1 (−20.4%, a RMSE of 1.97 mm·d−1 (28.8% and a NSCE of −0.18. When SEBAL-A was tested on only fully irrigated corn, it performed well, resulting in no bias, i.e., MBE of 0.0 mm·d−1; RMSE of 0.78 mm·d−1 (10.7% and NSCE of 0.82. The SEBAL-A model showed less or no improvement on corn that was either water-stressed or at early stages of growth. The errors incurred under these conditions were not due to advection not accounted for but rather were due to the nature of SEBAL and SEBAL-A being single-source energy balance models and
Pavese, G; Lettino, A; Calvello, M; Esposito, F; Fiore, S
2016-04-01
Aerosol composition and properties variation under the advection of different air masses were investigated, as case studies, by contemporary measurements over the atmospheric column and at the ground in a semi-rural site in South Italy. The absence of local strong sources in this area allowed to characterize background aerosol and to compare particle mixing effects under various atmospheric circulation conditions. Aerosol optical depth (AOD) and Ǻngström parameters from radiometric measurements allowed the detection and identification of polluted, dust, and volcanic atmospheric conditions. AODs were the input for a suitable model to evaluate the columnar aerosol composition, according to six main atmospheric components (water-soluble, soot, sea salt accumulation, sea salt coarse, mineral dus,t and biological). Scanning electron microscope (SEM) analysis of particulate sampled with a 13-stage impactor at the ground showed not only fingerprints typical of the different air masses but also the effects of transport and aging on atmospheric particles, suggesting processes that changed their chemical and optical properties. Background columnar aerosol was characterized by 72% of water-soluble and soot, in agreement with ground-based findings that highlighted 60% of contribution from anthropogenic carbonate particles and soot. In general, a good agreement between ground-based and columnar results was observed. Under the advection of trans-boundary air masses, water-soluble and soot were always present in columnar aerosol, whereas, in variable percentages, sea salt and mineral particles characterized both dust and volcanic conditions. At the ground, sulfates characterized the amorphous matrix produced in finer stages by the evaporation of solutions of organic and inorganic aerosols. Sulfates were also one of the key players involved in heterogeneous chemical reactions, producing complex secondary aerosol, as such clay-sulfate internally mixed particle externally mixed
International Nuclear Information System (INIS)
To assess the effectiveness of mitigative measures against radon (222Rn) entry into houses, experiments were conducted in a crawl-space house where the dirt floor of the crawl space was covered with sheets of 0.23 mm polyethylene foil fixed to the walls. The radon concentration was measured below the foil and in the crawl space together with environmental variables such as indoor-outdoor pressure differences. The experimental data was analyzed using various types of models including a simplistic mass-balance model, a regression model, and a two-dimensional numerical model based on Darcy flow or soil gas and combined diffusive and advective transport of radon. The main outcome of the work was that: (i) The soil-gas entry rate per pascal depressurization was at the order of 1 m3 h-1, (ii) the stack-related part of the depressurization of the crawl space (approx. 0.1 Pa deg. C-1) was controlled by the temperature difference between the living room of the house and the outdoors (not by the difference between the crawl space and the outdoors), (iii) that part of the wind-related depressurization that was measured by the pressure transducers seemed to force radon into the crawl space in the same proportion as the stack-related part of the depressurization, (iv) the ratio of advective and diffusive entry was approx. 0.7, when the crawl space was depressurized 1.5 Pa, (v) the effective diffusivity of the foil was found to be three orders of magnitude larger than that measured in the laboratory (the enhanced diffusivity was most likely caused by leaks in the foil and by mixing fans located in the crawl space), and (vi) there was no measurable mitigative impact of having the sheets of foil on the crawl-space floor even if the crawl space was artificially pressurized or depressurized. (au) 28 tabs., 36 ills., 61 refs
Energy Technology Data Exchange (ETDEWEB)
Zhou, Quanlin; Birkholzer, Jens T.; Javandel, Iraj; Jordan, Preston D.
2004-01-14
A calibrated groundwater flow model for a contaminated site can provide substantial information for assessing and improving hydraulic measures implemented for remediation. A three-dimensional transient groundwater flow model was developed for a contaminated mountainous site, at which interim corrective measures were initiated to limit further spreading of contaminants. This flow model accounts for complex geologic units that vary considerably in thickness, slope, and hydrogeologic properties, as well as large seasonal fluctuations of the groundwater table and flow rates. Other significant factors are local recharge from leaking underground storm drains and recharge from steep uphill areas. The zonation method was employed to account for the clustering of high and low hydraulic conductivities measured in a geologic unit. A composite model was used to represent the bulk effect of thin layers of relatively high hydraulic conductivity found within bedrock of otherwise low conductivity. The inverse simulator ITOUGH2 was used to calibrate the model for the distribution of rock properties. The model was initially calibrated using data collected between 1994 and 1996. To check the validity of the model, it was subsequently applied to predicting groundwater level fluctuation and groundwater flux between 1996 and 1998. Comparison of simulated and measured data demonstrated that the model is capable of predicting the complex flow reasonably well. Advective transport was approximated using pathways of particles originating from source areas of the plumes. The advective transport approximation was in good agreement with the trend of contaminant plumes observed over the years. The validated model was then refined to focus on a subsection of the large system. The refined model was subsequently used to assess the efficiency of hydraulic measures implemented for remediation.
Directory of Open Access Journals (Sweden)
J. Ungermann
2011-11-01
Full Text Available Infrared limb sounding from aircraft can provide 2-D curtains of multiple trace gas species. However, conventional limb sounders view perpendicular to the aircraft axis and are unable to resolve the observed airmass along their line-of-sight. GLORIA (Gimballed Limb Observer for Radiance Imaging of the Atmosphere is a new remote sensing instrument that is able to adjust its horizontal view angle with respect to the aircraft flight direction from 45° to 135°. This will allow for tomographic measurements of mesoscale structures for a wide variety of atmospheric constituents.
Many flights of the GLORIA instrument will not follow closed curves that allow measuring an airmass from all directions. Consequently, it is examined by means of simulations, what spatial resolution can be expected under ideal conditions from tomographic evaluation of measurements made during a straight flight. It is demonstrated that the achievable horizontal resolution in the line-of-sight direction could be reduced from over 200 km to around 70 km compared to conventional retrievals and that the tomographic retrieval is also more robust against horizontal gradients in retrieved quantities in this direction. In a second step, it is shown that the incorporation of channels exhibiting different optical depth can further enhance the spatial resolution of 3-D retrievals enabling the exploitation of spectral samples usually not used for limb sounding due to their opacity.
A second problem for tomographic retrievals is that advection, which can be neglected for conventional retrievals, plays an important role for the time-scales involved in a tomographic measurement flight. This paper presents a method to diagnose the effect of a time-varying atmosphere on a 3-D retrieval and demonstrates an effective way to compensate for effects of advection by incorporating wind-fields from meteorological datasets as a priori information.
International Nuclear Information System (INIS)
Mean duration of heat balance components during autumn nights with advection-radiation and radiation weather in years 1994-99 were stated on the basis of data observed in meteorological station Ursynów-WAU. Mean fluxes of heat balance components and values of components ratios are presented in tables
Institute of Scientific and Technical Information of China (English)
Yang Yang; Theodore A Endreny; David J Nowak
2016-01-01
Flood wave propagation modeling is of critical importance to advancing water re-sources management and protecting human life and property. In this study, we investigated how the advection-diffusion routing model performed in flood wave propagation on a 16 km long down-stream section of the Big Piney River, MO. Model performance was based on gaging station data at the upstream and downstream cross sections. We demonstrated with advection-diffusion theory that for small differences in watershed drainage area between the two river cross sections, inflow along the reach mainly contributes to the downstream hydrograph’s rising limb and not to the falling limb. The downstream hydrograph’s falling limb is primarily determined by the propagated flood wave originating at the upstream cross section. This research suggests the parameter for the advection-diffusion routing model can be calibrated by fitting the hydrograph falling limb. Application of the advection diffusion model to the flood wave of January 29, 2013 supports our theoretical finding that the propagated flood wave determines the downstream cross section falling limb, and the model has good performance in our test examples.
Bullen, T.; Izbicki, J.
2007-12-01
representative of regional groundwater, and the contaminated water do not pass through the remainder of the data, discounting a simple advective mixing scenario. We hypothesize a more likely scenario that involves both Cr(VI) reduction and advective mixing. As the plume initially expands downgradient, Cr(VI) in water at the leading edge encounters reductant in the aquifer resulting in limited Cr(VI) reduction. As a result of reduction, δ53Cr of Cr(VI) remaining in solution at the leading edge increases along the "reduction" trend from 0 to ~+2‰. Inevitable mixing of this water at the leading edge with regional groundwater results in a suitable mixing end-member to combine with Cr(VI) within the plume in order to explain the bulk of the remaining data. Neither Cr(VI) reduction nor advective mixing of plume and regional groundwaters can explain the data on their own, implying an interplay of at least these two processes during plume evolution. Ellis, A.S., Johnson, T.M. and Bullen, T.D. 2002, Science, 295, 2060-2062.
Energy Technology Data Exchange (ETDEWEB)
Andersen, C. [Risoe National Lab., Dept. of Nucl. Safety Res. and Nucl. Facilities, Roskilde (Denmark); Koopmanns, M.; Meijer, R.J. de [Kernfysische Versneller Inst., Environmental Radioactivity Res., Groningen (Netherlands)
1996-04-01
To assess the effectiveness of mitigative measures against radon ({sup 222}Rn) entry into houses, experiments were conducted in a crawl-space house where the dirt floor of the crawl space was covered with sheets of 0.23 mm polyethylene foil fixed to the walls. The radon concentration was measured below the foil and in the crawl space together with environmental variables such as indoor-outdoor pressure differences. The experimental data was analyzed using various types of models including a simplistic mass-balance model, a regression model, and a two-dimensional numerical model based on Darcy flow or soil gas and combined diffusive and advective transport of radon. The main outcome of the work was that: (i) The soil-gas entry rate per pascal depressurization was at the order of 1 m{sup 3} h{sup -1}, (ii) the stack-related part of the depressurization of the crawl space (approx. 0.1 Pa deg. C{sup -1}) was controlled by the temperature difference between the living room of the house and the outdoors (not by the difference between the crawl space and the outdoors), (iii) that part of the wind-related depressurization that was measured by the pressure transducers seemed to force radon into the crawl space in the same proportion as the stack-related part of the depressurization, (iv) the ratio of advective and diffusive entry was approx. 0.7, when the crawl space was depressurized 1.5 Pa, (v) the effective diffusivity of the foil was found to be three orders of magnitude larger than that measured in the laboratory (the enhanced diffusivity was most likely caused by leaks in the foil and by mixing fans located in the crawl space), and (vi) there was no measurable mitigative impact of having the sheets of foil on the crawl-space floor even if the crawl space was artificially pressurized or depressurized. (au) 28 tabs., 36 ills., 61 refs.
Belucz, Bernadett; Forgacs-Dajka, Emese
2015-01-01
Babcock-Leighton type solar dynamo models with single-celled meridional circulation are successful in reproducing many solar cycle features. Recent observations and theoretical models of meridional circulation do not indicate a single-celled flow pattern. We examine the role of complex multi-cellular circulation patterns in a Babcock-Leighton solar dynamo in advection- and diffusion-dominated regimes. We show from simulations that presence of a weak, second, high-latitude reverse cell speeds up the cycle and slightly enhances the poleward branch in butterfly diagram, whereas the presence of a second cell in depth reverses the tilt of butterfly wing to an anti-solar type. A butterfly diagram constructed from middle of convection zone yields a solar-like pattern, but this may be difficult to realize in the Sun because of magnetic buoyancy effects. Each of the above cases behaves similarly in higher and lower magnetic diffusivity regimes. However, our dynamo with a meridional circulation containing four cells in...
Debnath, Dipak; Mondal, Santanu; Chakrabarti, Sandip K.
2015-02-01
We study spectral properties of GX 339-4 during its 2010-11 outburst with two component advective flow (TCAF) model after its inclusion in XSPEC as a table model. We compare results fitted by TCAF model with combined disc blackbody and power-law model. For a spectral fit, we use 2.5-25 keV spectral data of the Proportional Counter Array instrument onboard RXTE satellite. From our fit, accretion flow parameters such as Keplerian (disc) rate, sub-Keplerian (halo) rate, location and strength of shock are extracted. We quantify how the disc and the halo rates vary during the entire outburst. We study how the halo to disc accretion rate ratio (ARR), quasi-periodic oscillations (QPOs), shock locations and its strength vary when the system passes through hard, hard-intermediate, soft-intermediate and soft states. We find pieces of evidence of monotonically increasing and decreasing nature of QPO frequencies depending on the variation of ARR during rising and declining phases. Interestingly, on days of transition from hard state to hard-intermediate spectral state (during the rising phase) or vice-versa (during decline phase), ARR is observed to be locally maximum. Non-constancy of ARR while obtaining reasonable fits points to the presence of two independent components in the flow.
Debnath, Dipak; Chakrabarti, Sandip K
2013-01-01
We study the spectral properties of the Galactic transient black hole candidate (BHC) GX 339-4 during its 2010-11 outburst with Two Component (Keplerian and sub-Keplerian) Advective Flow (TCAF) model after its inclusion in XSPEC as a local model. We also compare our TCAF model fitted results with combined disk black body (DBB) and power-law (PL) model fitted spectral results and find similar types of smooth variation in thermal (Keplerian or disk black body) as well as non-thermal (power-law or sub-Keplerian) fluxes. For spectral fit, we use 2.5-25 keV spectral data of PCA instrument onboard RXTE satellite. From the TCAF model fit, accretion flow parameters, such as the Keplerian (disk) rate, sub-Keplerian (halo) rate, location of the shock and strength of the shock are extracted. Our study provides a comprehensive understanding of the mass accretion processes and properties of the accretion disk around the BHC during the outburst phases. Based on the comparison of the halo to disk accretion rate ratio (ARR) ...
Directory of Open Access Journals (Sweden)
J.-S. Chen
2011-04-01
Full Text Available This study presents a generalized analytical solution for one-dimensional solute transport in finite spatial domain subject to arbitrary time-dependent inlet boundary condition. The governing equation includes terms accounting for advection, hydrodynamic dispersion, linear equilibrium sorption and first order decay processes. The generalized analytical solution is derived by using the Laplace transform with respect to time and the generalized integral transform technique with respect to the spatial coordinate. Several special cases are presented and compared to illustrate the robustness of the derived generalized analytical solution. Result shows an excellent agreement. The analytical solutions of the special cases derived in this study have practical applications. Moreover, the derived generalized solution which consists an integral representation is evaluated by the numerical integration to extend its usage. The developed generalized solution offers a convenient tool for further development of analytical solution of specified time-dependent inlet boundary conditions or numerical evaluation of the concentration field for arbitrary time-dependent inlet boundary problem.
Energy Technology Data Exchange (ETDEWEB)
Yamazawa, Hiromi [Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan). Tokai Research Establishment
1996-01-01
A numerical solution method, HIFI, for advection terms was developed. The method is a hybrid of the newly developed FI method, the first- and second-order upwind schemes. The excursion of the solution caused by the FI method is suppressed by applying the first- and second-order upwind schemes only at the grid points where the excursion of the solution is predicted. This limited use of the high-numerical-diffusion schemes can suppress the numerical diffusion to a reasonably low level. The FI method was designed so as to maximize on accuracy without loosing any stability due to the linear analysis. The accuracy and stability of the FI method vary according to the Courant number and other parameters. HIFI was adopted based on the meteorological sub-model of the numerical atmospheric dispersion model, PHYSIC. Predictability of wind speed in the lower atmosphere could be improved. It is considered that the HIFI method can be applied not only to the meteorological sub-mode in PHYSIC but also to the diffusion calculation of atmospheric radioactive materials. (author).
Möller, Johannes; Narayanan, Theyencheri
In colloidal suspensions internal or external fields can induce directed motions of particles in addition to Brownian diffusion. Here, gradients in temperature or chemical potential, shear flow as well as gravity can act as an external field. Examples for internal motions can be found in synthetic self-propelling particles and microorganisms, generally coined as active matter. We present multi-speckle X-ray photon correlation spectroscopy measurements in the Ultra-Small-Angle scattering range which probes an expanded length scale comparable to DLS and optical microscopy. To demonstrate the advanced capabilities, we show measurements probing the motions within a settling suspension of sub-micron sized silica particles. A global fitting procedure has been applied to separate the diffusive and advective contributions to the particle dynamics. With this, macroscopic parameters such as the sedimentation velocity can be probed on a microscopic level in highly opaque and concentrated systems, which are in general difficult to access for optical investigations. This procedure may prove its value for investigating various kinds of non-equilibrium systems.
Narayan, Ramesh; Penna, Robert F; Kulkarni, Akshay K
2012-01-01
We present results from two long-duration GRMHD simulations of an advection-dominated accretion flow around a non-spinning black hole. The first simulation was designed to avoid significant accumulation of magnetic flux around the black hole. This simulation was run for a time of 200,000GM/c^3 and achieved inflow equilibrium out to a radius \\sim 100GM/c^2. Up to this radius, we do not see significant mass outflow. We estimate that, if at all, only at radii \\gsim 300GM/c^2 does the mass outflow rate (\\dot{M}_{\\rm out}) exceed the net mass inflow rate into the black hole (\\dot{M}_{\\rm BH}). The second simulation was designed to achieve substantial magnetic flux accumulation around the black hole in a magnetically arrested disc. This simulation was run for a time of only 100,000GM/c^3. Nevertheless, because the mean radial velocity was several times larger than in the first simulation, it reached inflow equilibrium out to a radius \\sim 200GM/c^2. The mass outflow rate is larger, though even in this case, $\\dot{M...
X-ray Variability as a Probe of Advection-Dominated Accretion in Low-Luminosity AGN
Ptak, A; Mushotzky, R F; Serlemitsos, P J; Griffiths, R
1998-01-01
As a class, LINERs and Low-Luminosity AGN tend to show little or no significant short-term variability (i.e., with time-scales less than a day). This is a marked break for the trend of increased variability in Seyfert 1 galaxies with decreased luminosity. We propose that this difference is due to the lower accretion rate in LINERs and LLAGN which is probably causing the accretion flow to be advection-dominated. This results in a larger characteristic size for the X-ray producing region than is the case in ``normal'' AGN. Short-term variability may be caused by a localized instability or occultation events, but we note that such events would likely be accompanied by broad-band spectral changes. Since the ADAF is more compact in a Kerr metric, it is possible that the X-ray emission from ADAFs around rotating blackholes would be more variable than X-ray emission from ADAFs in a Schwarzchild metric. Similar variability arguments also apply to other wavelengths, and accordingly multiwavelength monitoring of LLAGN ...
Directory of Open Access Journals (Sweden)
Vincenzo Comegna
2012-06-01
Full Text Available We measured adsorption and transport of cadmium (Cd in the presence of Ca2+ and Na+ salts of varying ionic strengths and pH by using batch and miscible displacement experiments, carried out on undisturbed and homogenized soil columns. A fluvent-vertic soil was used in this study. In the column experiment a clear effect of ionic strength on breakthrough curves (BTCs of Cd2+ was observed when the Na+ concentration was increased from 0.02 to 0.2 M. The effect of increasing the Ca2+ concentration on Cd2+ absorption and transport was relatively less pronounced than that recorded for the Na+ solution. At low pH values, H+ ions competed strongly with Cd2+ ions and, at a high pH, precipitation was the main process taking place for Cd2+ sorption. The reliability of the advection- dispersion equation (ADE was tested. When implemented within the least-squares method, the model produced a sufficiently precise space-time distribution of Cd2+ ion concentrations. The results of this study demonstrated also, that laboratory leaching experiments, when performed on homogenized soil columns, can greatly underestimate Cd2+ ions transport in the field and that preferential flow can increase the mobility and velocity of cadmium movement to the groundwater.
Mazaheri, Alireza; Nishikawa, Hiroaki
2016-09-01
We propose arbitrary high-order discontinuous Galerkin (DG) schemes that are designed based on a first-order hyperbolic advection-diffusion formulation of the target governing equations. We present, in details, the efficient construction of the proposed high-order schemes (called DG-H), and show that these schemes have the same number of global degrees-of-freedom as comparable conventional high-order DG schemes, produce the same or higher order of accuracy solutions and solution gradients, are exact for exact polynomial functions, and do not need a second-derivative diffusion operator. We demonstrate that the constructed high-order schemes give excellent quality solution and solution gradients on irregular triangular elements. We also construct a Weighted Essentially Non-Oscillatory (WENO) limiter for the proposed DG-H schemes and apply it to discontinuous problems. We also make some accuracy comparisons with conventional DG and interior penalty schemes. A relative qualitative cost analysis is also reported, which indicates that the high-order schemes produce orders of magnitude more accurate results than the low-order schemes for a given CPU time. Furthermore, we show that the proposed DG-H schemes are nearly as efficient as the DG and Interior-Penalty (IP) schemes as these schemes produce results that are relatively at the same error level for approximately a similar CPU time.
Ningombam, Shantikumar S.; Bagare, S. P.; Khatri, P.; Sohn, B. J.; Song, H.-J.
2015-10-01
Estimation of aerosol radiative forcing (ARF) was performed using a radiative transfer model (Rstar6b) along with physical and optical parameters of aerosols obtained from sky radiometer observation over Indian Astronomical Observatory (IAO), Hanle, Ladakh, during 2008-2010 from dust, anthropogenic, and aged background observing conditions. ARF was estimated at the top of the atmosphere (TOA), in the atmosphere, and at the surface during the three observing conditions. During dust and anthropogenic events, average aerosol optical depth (AOD at 500 nm) went up to 0.24 from the aged background observing condition 0.04. Such enhancement of AOD is associated by the combination of desert-dust and anthropogenic aerosols transported from distant sources as noticed from Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO). Such three types of aerosols are also identified from the observed properties of single scattering albedo (SSA), aerosol asymmetry (AS) parameter, and aerosol size distribution. The estimated ARFs at TOA, at the surface, and in atmosphere are - 3.73, - 6.82, and 3.40 Wm- 2, respectively during the dust advection period. On the contrary, the respective ARFs during the aged background observing condition are - 1.50, - 2.22, and 0.70 Wm- 2, respectively. A significant difference of spectral AOD is observed during dust, anthropogenic, and aged background observing conditions. Ångström exponent (AE) decreases from 1.05 in the aged background observing condition to 0.40 in the dust event. A significant difference of coarse-fine mode volume distribution is also observed between the dust and the anthropogenic cases. Further, the study reveals high aerosols induced during the dust and the anthropogenic episodes caused warming at atmosphere and cooling at surface which collectively may affect the local atmospheric circulation.
Kurylyk, Barret L.; McKenzie, Jeffrey M; MacQuarrie, Kerry T. B.; Voss, Clifford I.
2014-01-01
Numerous cold regions water flow and energy transport models have emerged in recent years. Dissimilarities often exist in their mathematical formulations and/or numerical solution techniques, but few analytical solutions exist for benchmarking flow and energy transport models that include pore water phase change. This paper presents a detailed derivation of the Lunardini solution, an approximate analytical solution for predicting soil thawing subject to conduction, advection, and phase change. Fifteen thawing scenarios are examined by considering differences in porosity, surface temperature, Darcy velocity, and initial temperature. The accuracy of the Lunardini solution is shown to be proportional to the Stefan number. The analytical solution results obtained for soil thawing scenarios with water flow and advection are compared to those obtained from the finite element model SUTRA. Three problems, two involving the Lunardini solution and one involving the classic Neumann solution, are recommended as standard benchmarks for future model development and testing.
Energy Technology Data Exchange (ETDEWEB)
McCaulou, D.R. [Arizona Univ., Tucson, AZ (United States)
1993-10-01
Replicate column experiments were done to quantify the effects of temperature and bacterial motility on advective transport through repacked, but otherwise unaltered, natural aquifer sediment. The bacteria used in this study, A0500, was a flagellated, spore-forming rod isolated from the deep subsurface at DOE`s Savannah River Laboratory. Motility was controlled by turning on flagellar metabolism at 18{degrees}C but off at 40{degrees}C. Microspheres were used to independently quantify the effects of temperature on the sticking efficiency ({alpha}), estimated using a steady-state filtration model. The observed greater microsphere removal at the higher temperature agreed with the physical-chemical model, but bacteria removal at 18{degrees}C was only half that at 4{degrees}C. The sticking efficiency for non-motile A0500 (4{degrees}C) was over three times that of the motile A0500 (18{degrees}C), 0.073 versus 0.022 respectively. Analysis of complete breakthrough curves using a non-steady, kinetically limited, transport model to estimate the time scales of attachment and detachment suggested that motile A 0500 bacteria traveled twice as far as non-motile A 0500 bacteria before becoming attached. Once attached, non-motile colloids detached on the time scale of 9 to 17 days. The time scale for detachment of motile A0500 bacteria was shorter, 4 to 5 days. Results indicate that bacterial attachment was reversible and detachment was enhanced by bacterial motifity. The kinetic energy of bacterial motility changed the attachment-detachment kinetics in favor of the detached state. The chemical factors responsible for the enhanced transport are not known. However, motility may have caused weakly held bacteria to detach from the secondary minimum, and possibly from the primary minimum, as described by DLVO theory.
Alcaraz, Mar; García-Gil, Alejandro; Vázquez-Suñé, Enric; Velasco, Violeta
2016-02-01
Borehole Heat Exchangers (BHEs) are increasingly being used to exploit shallow geothermal energy. This paper presents a new methodology to provide a response to the need for a regional quantification of the geothermal potential that can be extracted by BHEs and the associated environmental impacts. A set of analytical solutions facilitates accurate calculation of the heat exchange of BHEs with the ground and its environmental impacts. For the first time, advection and dispersion heat transport mechanisms and the temporal evolution from the start of operation of the BHE are taken into account in the regional estimation of shallow geothermal resources. This methodology is integrated in a GIS environment, which facilitates the management of input and output data at a regional scale. An example of the methodology's application is presented for Barcelona, in Spain. As a result of the application, it is possible to show the strengths and improvements of this methodology in the development of potential maps of low temperature geothermal energy as well as maps of environmental impacts. The minimum and maximum energy potential values for the study site are 50 and 1800 W/m(2) for a drilled depth of 100 m, proportionally to Darcy velocity. Regarding to thermal impacts, the higher the groundwater velocity and the energy potential, the higher the size of the thermal plume after 6 months of exploitation, whose length ranges from 10 to 27 m long. A sensitivity analysis was carried out in the calculation of heat exchange rate and its impacts for different scenarios and for a wide range of Darcy velocities. The results of this analysis lead to the conclusion that the consideration of dispersion effects and temporal evolution of the exploitation prevent significant differences up to a factor 2.5 in the heat exchange rate accuracy and up to several orders of magnitude in the impacts generated.
Two-dimensional circulation and mixing in the far field of a surface-advected river plume
Mazzini, Piero L. F.; Chant, Robert J.
2016-06-01
Field observations of the Hudson River plume are presented to discuss circulation and mixing in the far field of this coastally trapped buoyant flow. The plume was surface advected and propagated downshelf near the internal wave speed. The plume outflow was characterized by a two-layer bulge-like feature but became continuously stratified and vertically sheared in the far field, where Richardson numbers are generally below 0.5. High-frequency velocity and backscatter data from a moored ADCP revealed strong vertical and horizontal oscillatory motions at the front with a wavelength approximately 7-8 times the plume thickness, consistent with Kelvin-Helmholtz instabilities. These motions quickly died out after 2-3 cycles. The combination of vertical shear and stratification in the plume leads to a buoyancy flux toward the nose of the plume, which competes with mixing. However, the continued salinity increase of the plume as it propagated downshelf indicates that mixing overcomes this delivery of freshwater to the plume front. A simple 2-D model is developed, which relates the time rate-of-change of the plume salinity to: (1) salt entrainment due to vertical mixing, and (2) freshwater flux and salt removal due to the vertical shear of the stratified plume. Estimates of an entrainment coefficient from this model are consistent with previous estimates from the near field of a river outflow. A scaling of the plume width is obtained by assuming that vertical shears are controlled by both thermal wind and a critical Richardson number. This scaling yields plume widths that are consistent with previous laboratory studies.
Alcaraz, Mar; García-Gil, Alejandro; Vázquez-Suñé, Enric; Velasco, Violeta
2016-02-01
Borehole Heat Exchangers (BHEs) are increasingly being used to exploit shallow geothermal energy. This paper presents a new methodology to provide a response to the need for a regional quantification of the geothermal potential that can be extracted by BHEs and the associated environmental impacts. A set of analytical solutions facilitates accurate calculation of the heat exchange of BHEs with the ground and its environmental impacts. For the first time, advection and dispersion heat transport mechanisms and the temporal evolution from the start of operation of the BHE are taken into account in the regional estimation of shallow geothermal resources. This methodology is integrated in a GIS environment, which facilitates the management of input and output data at a regional scale. An example of the methodology's application is presented for Barcelona, in Spain. As a result of the application, it is possible to show the strengths and improvements of this methodology in the development of potential maps of low temperature geothermal energy as well as maps of environmental impacts. The minimum and maximum energy potential values for the study site are 50 and 1800 W/m(2) for a drilled depth of 100 m, proportionally to Darcy velocity. Regarding to thermal impacts, the higher the groundwater velocity and the energy potential, the higher the size of the thermal plume after 6 months of exploitation, whose length ranges from 10 to 27 m long. A sensitivity analysis was carried out in the calculation of heat exchange rate and its impacts for different scenarios and for a wide range of Darcy velocities. The results of this analysis lead to the conclusion that the consideration of dispersion effects and temporal evolution of the exploitation prevent significant differences up to a factor 2.5 in the heat exchange rate accuracy and up to several orders of magnitude in the impacts generated. PMID:26605833
Energy Technology Data Exchange (ETDEWEB)
Karniadakis, George Em [Brown University
2014-03-11
The main objective of this project is to develop new computational tools for uncertainty quantifica- tion (UQ) of systems governed by stochastic partial differential equations (SPDEs) with applications to advection-diffusion-reaction systems. We pursue two complementary approaches: (1) generalized polynomial chaos and its extensions and (2) a new theory on deriving PDF equations for systems subject to color noise. The focus of the current work is on high-dimensional systems involving tens or hundreds of uncertain parameters.
Parisot, Martin; Vila, Jean-Paul
2015-01-01
The current paper is devoted to the numerical resolution in multi-dimensional framework of a large class of models satisfying a conservation of energy. The proposed strategy is based on a regularized model where the advection velocity is modified by the gradient of the potential of the conservative forces in both mass and momentum equations. The numerical scheme is consistent with the asymptotic model when the ratio of the potential waves celerities are much larger than the material waves cel...
Smith, Robert K.
2009-01-01
This thesis is aimed at extending the spherical barotropic contour-advective semi-Lagrangian (CASL) Algorithm, written in 1996 by David Dritschel and Maarten Ambaum, to more complex test cases within the shallow-water context. This is an integral part for development of any numerical model and the accuracy obtained depends on many factors, including knowledge of the initial state of the atmosphere or ocean, the numerical methods applied, and the resolutions used. The work undertaken throug...
Diémoz, Henri; Magri, Tiziana; Pession, Giordano; Zublena, Manuela; Campanelli, Monica; Gobbi, Gian Paolo; Barnaba, Francesca; Di Liberto, Luca; Dionisi, Davide
2016-04-01
A CHM-15k laser radar (lidar) was installed in April 2015 at the solar observatory of the Environmental Protection Agency (ARPA) of the Aosta Valley (Northern Italy, 45.74N, 7.36E, 560 m a.s.l.). The instrument operates at 1064 nm, is capable of mapping the vertical profile of aerosols and clouds up to the tropopause and is part of the Alice-net ceilometers network (www.alice-net.eu). The site is in a large Alpine valley floor, in a semi-rural context. Among the most interesting cases observed in the first months of operation, several days characterised by weak synoptic circulation and well-developed, thermally-driven up-valley winds are accompanied by the appearance of a thick aerosol layer in the afternoon. The phenomenon is frequent in Spring and Summer and is likely to be related to easterly airmass advections from polluted sites (e.g., the Po basin) rather than to local emissions. To test this hypothesis, the following method was adopted. First, some case studies were selected and the respective meteorological fields were analysed based on both observations at ground and the high-resolution output of the nonhydrostatic limited-area atmospheric prediction model maintained by the COnsortium for Small-scale MOdelling (COSMO) over the complex orography of the domain. Then, to evaluate the dynamics of the aerosol diffusion in the valley, the chemical transport 2D/3D eulerian Flexible Air quality Regional Model (FARM) was run. Finally, the three-dimensional output of the model was compared to the vertically-resolved aerosol field derived from the lidar-ceilometer soundings. The effects of up-slope winds, and the resulting subsidence along the main axis of the valley, is hypothesised to break up the aerosol layer close to the ground in the middle of the day and to drag the residual layer down into the mixing layer. The measurements by a co-located sun/sky photometer operating in the framework of the EuroSkyRad (ESR) network were additionally analysed to detect any
International Nuclear Information System (INIS)
In this paper, the variable-coefficient diffusion—advection (DA) equation, which arises in modeling various physical phenomena, is studied by the Lie symmetry approach. The similarity reductions are derived by determining the complete sets of point symmetries of this equation, and then exact and numerical solutions are reported for the reduced second-order nonlinear ordinary differential equations. Further, an extended (G'/G)-expansion method is applied to the DA equation to construct some new non-traveling wave solutions
Institute of Scientific and Technical Information of China (English)
Xin Wen; Shi Jin
2008-01-01
We study the L1-error estimates for the upwind scheme to the linear advection equations with a piecewise constant coefficients modeling linear waves crossing interfaces.Here the interface condition is immersed into the upwind scheme.We prove that,for initial data with a bounded variation,the numerical solution of the immersed interface upwind scheme converges in L1-norm to the differential equation with the corresponding interface condition.We derive the one-halfth order L1-error bounds with explicit coefficients following a technique used in [25].We also use some inequalities on binomial coefficients proved in a consecutive paper[32].
Directory of Open Access Journals (Sweden)
SUDHEER PAI K L
2012-01-01
Full Text Available A time dependent two dimensional advection-diffusion numerical model for primary pollutant with chemical reaction and dry deposition for an urban area is presented. The proposed numerical model takes into account of realistic form of variable wind velocity and eddy diffusivity profiles. The partial differential equation of primarypollutant is solved by using Crank-Nicolson implicit finite difference technique. The results are plotted for concentration of primary pollutant and the effect of chemical reaction and dry deposition on the dispersion of pollutant are analysed extensively.
Institute of Scientific and Technical Information of China (English)
HUANG Rui Xin
2014-01-01
Study of oceanic circulation and climate requires models which can simulate tracer eddy diffusion and ad-vection accurately. It is shown that the traditional Eulerian coordinates can introduce large artificial hori-zontal diffusivity/viscosity due to the incorrect alignment of the axis. Therefore, such models can smear sharp fronts and introduce other numerical artifacts. For simulation with relatively low resolution, large lateral diffusion was explicitly used in models;therefore, such numerical diffusion may not be a problem. However, with the increase of horizontal resolution, the artificial diffusivity/viscosity associated with hori-zontal advection in the commonly used Eulerian coordinates may become one of the most challenging ob-stacles for modeling the ocean circulation accurately. Isopycnal eddy diffusion (mixing) has been widely used in numerical models. The common wisdom is that mixing along isopycnal is energy free. However, a careful examination reveals that this is not the case. In fact, eddy diffusion can be conceptually separated into two steps:stirring and subscale diffusion. Due to the thermobaric effect, stirring, or exchanging water masses, along isopycnal surface is associated with the change of GPE in the mean state. This is a new type of instability, called the thermobaric instability. In addition, due to cabbeling subscale diffusion of water parcels always leads to the release of GPE. The release of GPE due to isopycnal stirring and subscale diffusion may lead to the thermobaric instability.
Healy, R.W.; Russell, T.F.
1998-01-01
We extend the finite-volume Eulerian-Lagrangian localized adjoint method (FVELLAM) for solution of the advection-dispersion equation to two dimensions. The method can conserve mass globally and is not limited by restrictions on the size of the grid Peclet or Courant number. Therefore, it is well suited for solution of advection-dominated ground-water solute transport problems. In test problem comparisons with standard finite differences, FVELLAM is able to attain accurate solutions on much coarser space and time grids. On fine grids, the accuracy of the two methods is comparable. A critical aspect of FVELLAM (and all other ELLAMs) is evaluation of the mass storage integral from the preceding time level. In FVELLAM this may be accomplished with either a forward or backtracking approach. The forward tracking approach conserves mass globally and is the preferred approach. The backtracking approach is less computationally intensive, but not globally mass conservative. Boundary terms are systematically represented as integrals in space and time which are evaluated by a common integration scheme in conjunction with forward tracking through time. Unlike the one-dimensional case, local mass conservation cannot be guaranteed, so slight oscillations in concentration can develop, particularly in the vicinity of inflow or outflow boundaries. Published by Elsevier Science Ltd.
Rogers, M. A.; Miller, S. D.; Haynes, J. M.; Heidinger, A. K.; Haupt, S. E.; Sengupta, M.
2014-12-01
Using satellite observations from GOES-E and GOES-W platforms in concert with GFS-derived cloud-level winds and a standalone radiative transfer model, an advection-derived forecast for surface GHI over the continental United States is described. In particular, comparisons from the satellite-derived forecast are shown against several SURFRAD sites, with particular attention to developing meaningful error metrics to better demonstrate forecast skill and identify sources of error. Challenges in advection-based forecast techniques, such as forecasting near regions of non-wind-driven cloud systems such as coastal marine stratocumulus, are described, as are methods integrated into the forecast algorithm to identify and address these challenges. Improvements in the particular algorithm with respect to comparison against surface observations, integration of the forecast technique into blended forecast products such as those described by the 'Public-Private-Academic Partnership to Advance Solar Power Forecasting' project spearheaded by the National Center for Atmospheric Research, and other observations germane to satellite-derived solar forecasting are covered using nearly two years of operational forecasts as background.
Analysis of Field Synergy on Heat Transfer Enhancement in Chaotic Advection%混沌对流强化传热的场协同分析
Institute of Scientific and Technical Information of China (English)
王永庆; 董其伍; 刘敏珊; 王丹
2011-01-01
Based on the numerical results of fluid flow and heat transfer in a chaotic advection channel by a-dopting periodic model, heat transfer enhancement in chaotic advection is analysed by using the field synergy principle. The synergy between velocity and temperature fields on the cross section in the duct was analyzed, and the relationship in the chaotic duct between the Nusselt number and the average vector product of velocity and temperature gradient, and average synergy angle in different Reynolds numbers were studied, which were compared with that in the regular straight channel. It is found that the chaotic channel resulted in the different distribution of velocity field, which changed temperature fields. The synergy of velocity and temperature fields is improved, which enhances heat transfer in chaotic channel. The Nusselt number changes monotonously with the vector product of velocity and temperature gradient, and the fundamental mechanism of heat transfer enhancement in chaotic advection is the improvement of synergy between velocity and temperature fields.%基于采用周期性计算模型得到的混沌对流流道内的流体流动与传热数值计算结果，应用场协同原理，对混沌对流内强化传热进行分析.分析了混沌流道截面上流场与温度场的协同关系，讨论了流道内不同雷诺数下Nusselt数与平均流速与温度梯度矢量积和平均协同角的对应变化趋势，并与普通直流道内层流下的流动与传热场协同情况进行了对比.结果表明，混沌流道改变了流体在流道内速度场的分布，流场的变化影响了温度场的分布，使得两场的协同效果得到明显的改善，从而强化传热.在整个流道内,混沌对流的Nusselt数与速度和温度梯度两矢量的点积具有相同变化关系，混沌对流强化传热的根本机理是改善了两场的协同关系.
Directory of Open Access Journals (Sweden)
Mourad Fadl Alla Dimian
2013-09-01
Full Text Available Analytical solutions are obtained, by using Laplace transformation method , for one dimensional advection –diffusion equation with variable coefficients in a longitudinal finite initially pollutant concentration free domain . Two cases for the boundary conditions, are studied . The first is the case of uniform continuous input condition and the second is the case of input condition of increasing nature .By writing the equations in the dimensionless form , the five physical parameters controlling the pollutant concentration is reduced to only two dimensionless parameters the dimensionless added pollutant concentration R1 and the dimensionless dispersion R2 .It is found that some physical parameters in the dimensional form have the same effect on the concentration of the pollutant, while other physical parameters have opposite effect. It is shown that the dimensionless concentration pollutant increases, as the dimensionless added pollutant increases along the river. But the concentration decreases , as the dimensionless dispersion increases. The details are demonstrated in graphs.
Romero-González, J; Walton, J C; Peralta-Videa, J R; Rodríguez, E; Romero, J; Gardea-Torresdey, J L
2009-01-15
The biosorption of Cr(III) onto packed columns of Agave lechuguilla was analyzed using an advective-dispersive (AD) model and its analytical solution. Characteristic parameters such as axial dispersion coefficients, retardation factors, and distribution coefficients were predicted as functions of inlet ion metal concentration, time, flow rate, bed density, cross-sectional column area, and bed length. The root-mean-square-error (RMSE) values 0.122, 0.232, and 0.285 corresponding to the flow rates of 1, 2, and 3 (10(-3))dm3min(-1), respectively, indicated that the AD model provides an excellent approximation of the simulation of lumped breakthrough curves for the adsorption of Cr(III) by lechuguilla biomass. Therefore, the model can be used for design purposes to predict the effect of varying operational conditions. PMID:18462882
Aldoghaither, Abeer
2015-12-01
In this paper, a new method, based on the so-called modulating functions, is proposed to estimate average velocity, dispersion coefficient, and differentiation order in a space-fractional advection-dispersion equation, where the average velocity and the dispersion coefficient are space-varying. First, the average velocity and the dispersion coefficient are estimated by applying the modulating functions method, where the problem is transformed into a linear system of algebraic equations. Then, the modulating functions method combined with a Newton\\'s iteration algorithm is applied to estimate the coefficients and the differentiation order simultaneously. The local convergence of the proposed method is proved. Numerical results are presented with noisy measurements to show the effectiveness and robustness of the proposed method. It is worth mentioning that this method can be extended to general fractional partial differential equations.
DEFF Research Database (Denmark)
Guyonvarch, Estelle; Ramin, Elham; Kulahci, Murat;
2015-01-01
The present study aims at using statistically designed computational fluid dynamics (CFD) simulations as numerical experiments for the identification of one-dimensional (1-D) advection-dispersion models – computationally light tools, used e.g., as sub-models in systems analysis. The objective...... is to develop a new 1-D framework, referred to as interpreted CFD (iCFD) models, in which statistical meta-models are used to calculate the pseudo-dispersion coefficient (D) as a function of design and flow boundary conditions. The method – presented in a straightforward and transparent way – is illustrated...... using the example of a circular secondary settling tank (SST). First, the significant design and flow factors are screened out by applying the statistical method of two-level fractional factorial design of experiments. Second, based on the number of significant factors identified through the factor...
Song, Lisheng; Kustas, William P.; Liu, Shaomin; Colaizzi, Paul D.; Nieto, Hector; Xu, Ziwei; Ma, Yanfei; Li, Mingsong; Xu, Tongren; Agam, Nurit; Tolk, Judy A.; Evett, Steven R.
2016-09-01
In this study ground measured soil and vegetation component temperatures and composite temperature from a high spatial resolution thermal camera and a network of thermal-IR sensors collected in an irrigated maize field and in an irrigated cotton field are used to assess and refine the component temperature partitioning approach in the Two-Source Energy Balance (TSEB) model. A refinement to TSEB using a non-iterative approach based on the application of the Priestley-Taylor formulation for surface temperature partitioning and estimating soil evaporation from soil moisture observations under advective conditions (TSEB-A) was developed. This modified TSEB formulation improved the agreement between observed and modeled soil and vegetation temperatures. In addition, the TSEB-A model output of evapotranspiration (ET) and the components evaporation (E), transpiration (T) when compared to ground observations using the stable isotopic method and eddy covariance (EC) technique from the HiWATER experiment and with microlysimeters and a large monolithic weighing lysimeter from the BEAREX08 experiment showed good agreement. Difference between the modeled and measured ET measurements were less than 10% and 20% on a daytime basis for HiWATER and BEAREX08 data sets, respectively. The TSEB-A model was found to accurately reproduce the temporal dynamics of E, T and ET over a full growing season under the advective conditions existing for these irrigated crops located in arid/semi-arid climates. With satellite data this TSEB-A modeling framework could potentially be used as a tool for improving water use efficiency and conservation practices in water limited regions. However, TSEB-A requires soil moisture information which is not currently available routinely from satellite at the field scale.
Indian Academy of Sciences (India)
Dilip Saha; Sukanya Chakraborti
2007-10-01
Syntectonic plutons emplaced in shallow crust often contain intermediate-to low-temperature deformation microstructures but lack a high-temperature, subsolidus deformation fabric,although the relict magmatic fabric is preserved. The Proterozoic Vellaturu granite emplaced at the eastern margin of the northern Nallamalai fold belt,south India during the late phase of regional deformation has a common occurrence of intermediate-to low-temperature deformation fabric, superimposed over magmatic fabric with an internally complex pattern. But high-T subsolidus deformation microstructure and fabric are absent in this pluton.The main crystal plastic deformation and ﬂuid enhanced reaction softening was concentrated along the margin of the granite body. Resulting granite mylonites show Y-maximum c axis fabric in completely recrystallized quartz ribbons,dynamic recrystallization of perthites,and myrmekite indicative of fabric development under intermediate temperature (∼500-400° C). The weakly-deformed interior shows myrmekite,feldspar microfracturing and limited bulging recrystallization of quartz.The abundance of prism subgrain boundaries is indicative of continuing deformation through low-temperature(∼300° C).The relative rates of cooling in ﬂuenced by advective heat transfer and deformation of the pluton seem to control the overall subsolidus fabric development.The rapid advective heat transfer from the interior in the early stages of subsolidus cooling was followed by slow cooling through intermediate temperature window as a well-developed phyllosilicate rich mylonitic skin around the granite body slowed down conductive heat loss.Low-T crystal plastic deformation of quartz was effected at a late stage of cooling and deformation of the shallow crustal granite body emplaced within the greenschist facies Nallamalai rocks.
Switzer, A.; Goodkin, N.; Bolton, A.; Chen, M.; Druffel, E. R. M.; Boyle, E. A.
2015-12-01
Two independent studies were undertaken to use anthropogenic emissions to investigate natural systems using a massive Porites coral taken from off the coast of Vietnam (12ο12'49.90"N, 109 ο18'17.51"E). Annual uptake of bomb radiocarbon (14CO2) was measured to investigate the impact of coastal upwelling; while Pb/Ca levels and Pb isotopes were measured to investigate oceanic infiltration of anthropogenic Pb. Both records reveal a signal of sub-surface seawater advection from the tropical North Pacific to the South China Sea (SCS) providing independent evidence for the source and delivery time of the upwelled water off the coast of Vietnam. The radiocarbon record, extending from 1900-1986 at ~annual resolution, shows a post-bomb peak lower and broader than those found from other corals in the SCS and Japan, but higher than those found in the Makassar Strait in Indonesia. The Makassar coral experiences three water masses: the South Equatorial Current (SEC), upwelled and SCS water. The SEC has a relatively low radiocarbon content. However, water in the SCS does not mix with SEC water that enters the Indonesia Seas via the Halmahera as the main throughflow is from north to south. Hence, the upwelling signature must be from the North Equatorial Current that enters from the Luzon strait at depth. Leaded gasoline was phased-out between 1997 and 2000 in most Asian countries, however unlike other regional records, the Pb/Ca of the coral continued to increase until 2004 indicating a non-atmospheric source of Pb to the region. Both records indicate the source of upwelled water from the tropical North Pacific at roughly ~100-200 meters with a transport time of >2-5 years. This water is carried westward, via the Luzon Strait and into the South China Sea, where is it upwelled during the summer months. A higher resolution study of this coral combined with other coral records from the region could further narrow the location and timing of the advection and upwelling.
Liu; Yuan; Meyer; Meyer-Hofmeister; Xie
1999-12-10
We apply the disk-corona evaporation model (Meyer & Meyer-Hofmeister) originally derived for dwarf novae to black hole systems. This model describes the transition of a thin cool outer disk to a hot coronal flow. The mass accretion rate determines the location of this transition. For a number of well-studied black hole binaries, we take the mass flow rates derived from a fit of the advection-dominated accretion flow (ADAF) model to the observed spectra (for a review, see Narayan, Mahadevan, & Quataert) and determine where the transition of accretion via a cool disk to a coronal flow/ADAF would be located for these rates. We compare this with the observed location of the inner disk edge, as estimated from the maximum velocity of the Halpha emission line. We find that the transition caused by evaporation agrees with this determination in stellar disks. We also show that the ADAF and the "thin outer disk + corona" are compatible in terms of the physics in the transition region. PMID:10566989
Allen, S. E.; Dinniman, M. S.; Klinck, J. M.; Gorby, D. D.; Hewett, A. J.; Hickey, B. M.
2003-01-01
Submarine canyons which indent the continental shelf are frequently regions of steep (up to 45°), three-dimensional topography. Recent observations have delineated the flow over several submarine canyons during 2-4 day long upwelling episodes. Thus upwelling episodes over submarine canyons provide an excellent flow regime for evaluating numerical and physical models. Here we compare a physical and numerical model simulation of an upwelling event over a simplified submarine canyon. The numerical model being evaluated is a version of the S-Coordinate Rutgers University Model (SCRUM). Careful matching between the models is necessary for a stringent comparison. Results show a poor comparison for the homogeneous case due to nonhydrostatic effects in the laboratory model. Results for the stratified case are better but show a systematic difference between the numerical results and laboratory results. This difference is shown not to be due to nonhydrostatic effects. Rather, the difference is due to truncation errors in the calculation of the vertical advection of density in the numerical model. The calculation is inaccurate due to the terrain-following coordinates combined with a strong vertical gradient in density, vertical shear in the horizontal velocity and topography with strong curvature.
Merritt, M.L.
1993-01-01
The simulation of the transport of injected freshwater in a thin brackish aquifer, overlain and underlain by confining layers containing more saline water, is shown to be influenced by the choice of the finite-difference approximation method, the algorithm for representing vertical advective and dispersive fluxes, and the values assigned to parametric coefficients that specify the degree of vertical dispersion and molecular diffusion that occurs. Computed potable water recovery efficiencies will differ depending upon the choice of algorithm and approximation method, as will dispersion coefficients estimated based on the calibration of simulations to match measured data. A comparison of centered and backward finite-difference approximation methods shows that substantially different transition zones between injected and native waters are depicted by the different methods, and computed recovery efficiencies vary greatly. Standard and experimental algorithms and a variety of values for molecular diffusivity, transverse dispersivity, and vertical scaling factor were compared in simulations of freshwater storage in a thin brackish aquifer. Computed recovery efficiencies vary considerably, and appreciable differences are observed in the distribution of injected freshwater in the various cases tested. The results demonstrate both a qualitatively different description of transport using the experimental algorithms and the interrelated influences of molecular diffusion and transverse dispersion on simulated recovery efficiency. When simulating natural aquifer flow in cross-section, flushing of the aquifer occurred for all tested coefficient choices using both standard and experimental algorithms. ?? 1993.
Cao, Xinwu
2010-01-01
The broad-line region (BLR) disappears in many low-luminosity AGNs, the reason of which is still controversial. The BLRs in AGNs are believed to be associated with the outflows from the accretion disks. Most of the low-luminosity AGNs (LLAGNs) contain advection dominated accretion flows (ADAFs), which are very hot and have a positive Bernoulli parameter. ADAFs are therefore associated with strong outflows. We estimate the cooling of the outflows from the ADAFs, and find that the gases in such hot outflows always cannot be cooled efficiently by bremsstrahlung radiation. The ADAF may co-exist with the standard disk, i.e., the inner ADAF connects to the outer thin accretion disk at radius R_tr, in the sources accreting at slightly lower than the critical rate. For the ADAFs with >0.001 L_edd, a secondary small inner cold disk is suggested to co-exist with the ADAF due to the condensation process. We estimate the Compton cooling of the outflow, of which the soft seed photons either come from the outer cold disk o...
Preheated Advection Dominated Accretion Flow
Park, M G; Park, Myeong-Gu; Ostriker, Jeremiah P.
2001-01-01
All high temperature accretion solutions including ADAF are physically thick, so outgoing radiation interacts with the incoming flow, sharing as much or more resemblance with classical spherical accretion flows as with disk flows. We examine this interaction for the popular ADAF case. We find that without allowance for Compton preheating, a very restricted domain of ADAF solution is permitted and with Compton preheating included a new high temperature PADAF branch appears in the solution space. In the absence of preheating, high temperature flows do not exist when the mass accretion rate mdot == Mdot c^2 / L_E >~ 10^-1.5. Below this mass accretion rate, a roughly conical region around the hole cannot sustain high temperature ions and electrons for all flows having mdot >~ 10^-4, which may lead to a funnel possibly filled with a tenuous hot outgoing wind. If the flow starts at large radii with the usual equilibrium temperature ~10^4 K, the critical mass accretion rate is much lower, mdot exist. However, above ...
Witherden, F. D.; Farrington, A. M.; Vincent, P. E.
2014-11-01
High-order numerical methods for unstructured grids combine the superior accuracy of high-order spectral or finite difference methods with the geometric flexibility of low-order finite volume or finite element schemes. The Flux Reconstruction (FR) approach unifies various high-order schemes for unstructured grids within a single framework. Additionally, the FR approach exhibits a significant degree of element locality, and is thus able to run efficiently on modern streaming architectures, such as Graphical Processing Units (GPUs). The aforementioned properties of FR mean it offers a promising route to performing affordable, and hence industrially relevant, scale-resolving simulations of hitherto intractable unsteady flows within the vicinity of real-world engineering geometries. In this paper we present PyFR, an open-source Python based framework for solving advection-diffusion type problems on streaming architectures using the FR approach. The framework is designed to solve a range of governing systems on mixed unstructured grids containing various element types. It is also designed to target a range of hardware platforms via use of an in-built domain specific language based on the Mako templating engine. The current release of PyFR is able to solve the compressible Euler and Navier-Stokes equations on grids of quadrilateral and triangular elements in two dimensions, and hexahedral elements in three dimensions, targeting clusters of CPUs, and NVIDIA GPUs. Results are presented for various benchmark flow problems, single-node performance is discussed, and scalability of the code is demonstrated on up to 104 NVIDIA M2090 GPUs. The software is freely available under a 3-Clause New Style BSD license (see www.pyfr.org). Catalogue identifier: AETY_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AETY_v1_0.html Program obtainable from: CPC Program Library, Queen’s University, Belfast, N. Ireland Licensing provisions: New style BSD license No. of lines in
Directory of Open Access Journals (Sweden)
E. Dellwik
2009-08-01
Full Text Available An analysis of flow angles from a fetch-limited beech forest site with clearings is presented. Flow angles and vertical velocities from two types of sonic anemometers as well as a ground based remote sensing lidar were analysed. Instead of using rotations, where zero-flow angles were assumed for neutral flow, the data from the instruments were interpreted in relation to the terrain.
Uncertainties regarding flow distortion and limited sampling time (statistical uncertainty were evaluated and found to be significant. Especially for one of the sonic anemometers, relatively small changes in the flow distortion correction could change the sign of mean vertical velocities taken during stable atmospheric stratification relative to the neutral flow. Despite the uncertainties, it was possible to some extent to relate both positive and negative mean flow angles to features in the terrain.
Conical and linear scans with a remote sensing lidar were evaluated for estimation of vertical velocities and flow angles. The results of the vertical conical scans were promising, and yielded negative flow angles for a sector where the forest is fetch-limited. However, more data and analysis is needed for a complete evaluation of the technique. The horizontal linear scans showed the variability of the mean wind speed field. A vertical velocity was calculated from different focusing distances, but this estimate yielded unrealistically high vertical velocities, due to neglect of the transversal wind component.
The vertical advection term was calculated using the measured mean flow angles at the mast and profile measurements of carbon dioxide, but it is not recommended to use in relation with the flux measurement as the vertical velocity measured at the mast is most likely not representative for the whole forest.
Mohanram, A.; Ray, C.; Harvey, R.W.; Metge, D.W.; Ryan, J.N.; Chorover, J.; Eberl, D.D.
2010-01-01
In order to gain more information about the fate of Cryptosporidium parvum oocysts in tropical volcanic soils, the transport and attachment behaviors of oocysts and oocyst-sized polystyrene microspheres were studied in the presence of two soils. These soils were chosen because of their differing chemical and physical properties, i.e., an organic-rich (43-46% by mass) volcanic ash-derived soil from the island of Hawaii, and a red, iron (22-29% by mass), aluminum (29-45% by mass), and clay-rich (68-76% by mass) volcanic soil from the island of Oahu. A third agricultural soil, an organic- (13% by mass) and quartz-rich (40% by mass) soil from Illinois, was included for reference. In 10-cm long flow-through columns, oocysts and microspheres advecting through the red volcanic soil were almost completely (98% and 99%) immobilized. The modest breakthrough resulted from preferential flow-path structure inadvertently created by soil-particle aggregation during the re-wetting process. Although a high (99%) removal of oocysts and microsphere within the volcanic ash soil occurred initially, further examination revealed that transport was merely retarded because of highly reversible interactions with grain surfaces. Judging from the slope of the substantive and protracted tail of the breakthrough curve for the 1.8-??m microspheres, almost all (>99%) predictably would be recovered within ~4000 pore volumes. This suggests that once contaminated, the volcanic ash soil could serve as a reservoir for subsequent contamination of groundwater, at least for pathogens of similar size or smaller. Because of the highly reversible nature of organic colloid immobilization in this soil type, C. parvum could contaminate surface water should overland flow during heavy precipitation events pick up near-surface grains to which they are attached. Surprisingly, oocyst and microsphere attachment to the reference soil from Illinois appeared to be at least as sensitive to changes in pH as was observed
Guyonvarch, Estelle; Ramin, Elham; Kulahci, Murat; Plósz, Benedek Gy
2015-10-15
The present study aims at using statistically designed computational fluid dynamics (CFD) simulations as numerical experiments for the identification of one-dimensional (1-D) advection-dispersion models - computationally light tools, used e.g., as sub-models in systems analysis. The objective is to develop a new 1-D framework, referred to as interpreted CFD (iCFD) models, in which statistical meta-models are used to calculate the pseudo-dispersion coefficient (D) as a function of design and flow boundary conditions. The method - presented in a straightforward and transparent way - is illustrated using the example of a circular secondary settling tank (SST). First, the significant design and flow factors are screened out by applying the statistical method of two-level fractional factorial design of experiments. Second, based on the number of significant factors identified through the factor screening study and system understanding, 50 different sets of design and flow conditions are selected using Latin Hypercube Sampling (LHS). The boundary condition sets are imposed on a 2-D axi-symmetrical CFD simulation model of the SST. In the framework, to degenerate the 2-D model structure, CFD model outputs are approximated by the 1-D model through the calibration of three different model structures for D. Correlation equations for the D parameter then are identified as a function of the selected design and flow boundary conditions (meta-models), and their accuracy is evaluated against D values estimated in each numerical experiment. The evaluation and validation of the iCFD model structure is carried out using scenario simulation results obtained with parameters sampled from the corners of the LHS experimental region. For the studied SST, additional iCFD model development was carried out in terms of (i) assessing different density current sub-models; (ii) implementation of a combined flocculation, hindered, transient and compression settling velocity function; and (iii
Makedonska, N.; Karra, S.; Painter, S. L.; Viswanathan, H.; Gable, C. W.
2014-12-01
's Manual: A Massively Parallel Reactive Flow andTransport Model for describing Surface and Subsurface Processes, 2014. [3] Makedonska N., Painter S.L., Karra S., and Gable C.W., NumericalExperiments on Advective Transport in Large Three-Dimensional DFNs,Abstract H53A-1398 ,2013, AGU, San-Francisco, CA, 9-13 Dec.
Mohanram, Arvind; Ray, Chittaranjan; Harvey, Ronald W; Metge, David W; Ryan, Joseph N; Chorover, Jon; Eberl, D D
2010-10-01
In order to gain more information about the fate of Cryptosporidium parvum oocysts in tropical volcanic soils, the transport and attachment behaviors of oocysts and oocyst-sized polystyrene microspheres were studied in the presence of two soils. These soils were chosen because of their differing chemical and physical properties, i.e., an organic-rich (43-46% by mass) volcanic ash-derived soil from the island of Hawaii, and a red, iron (22-29% by mass), aluminum (29-45% by mass), and clay-rich (68-76% by mass) volcanic soil from the island of Oahu. A third agricultural soil, an organic- (13% by mass) and quartz-rich (40% by mass) soil from Illinois, was included for reference. In 10-cm long flow-through columns, oocysts and microspheres advecting through the red volcanic soil were almost completely (98% and 99%) immobilized. The modest breakthrough resulted from preferential flow-path structure inadvertently created by soil-particle aggregation during the re-wetting process. Although a high (99%) removal of oocysts and microsphere within the volcanic ash soil occurred initially, further examination revealed that transport was merely retarded because of highly reversible interactions with grain surfaces. Judging from the slope of the substantive and protracted tail of the breakthrough curve for the 1.8-μm microspheres, almost all (>99%) predictably would be recovered within ∼4000 pore volumes. This suggests that once contaminated, the volcanic ash soil could serve as a reservoir for subsequent contamination of groundwater, at least for pathogens of similar size or smaller. Because of the highly reversible nature of organic colloid immobilization in this soil type, C. parvum could contaminate surface water should overland flow during heavy precipitation events pick up near-surface grains to which they are attached. Surprisingly, oocyst and microsphere attachment to the reference soil from Illinois appeared to be at least as sensitive to changes in pH as was
Guyonvarch, Estelle; Ramin, Elham; Kulahci, Murat; Plósz, Benedek Gy
2015-10-15
The present study aims at using statistically designed computational fluid dynamics (CFD) simulations as numerical experiments for the identification of one-dimensional (1-D) advection-dispersion models - computationally light tools, used e.g., as sub-models in systems analysis. The objective is to develop a new 1-D framework, referred to as interpreted CFD (iCFD) models, in which statistical meta-models are used to calculate the pseudo-dispersion coefficient (D) as a function of design and flow boundary conditions. The method - presented in a straightforward and transparent way - is illustrated using the example of a circular secondary settling tank (SST). First, the significant design and flow factors are screened out by applying the statistical method of two-level fractional factorial design of experiments. Second, based on the number of significant factors identified through the factor screening study and system understanding, 50 different sets of design and flow conditions are selected using Latin Hypercube Sampling (LHS). The boundary condition sets are imposed on a 2-D axi-symmetrical CFD simulation model of the SST. In the framework, to degenerate the 2-D model structure, CFD model outputs are approximated by the 1-D model through the calibration of three different model structures for D. Correlation equations for the D parameter then are identified as a function of the selected design and flow boundary conditions (meta-models), and their accuracy is evaluated against D values estimated in each numerical experiment. The evaluation and validation of the iCFD model structure is carried out using scenario simulation results obtained with parameters sampled from the corners of the LHS experimental region. For the studied SST, additional iCFD model development was carried out in terms of (i) assessing different density current sub-models; (ii) implementation of a combined flocculation, hindered, transient and compression settling velocity function; and (iii
Energy Technology Data Exchange (ETDEWEB)
Savage, Kaye S. [Wofford College; Zhu, Wenyi [Wofford College; Barnett, Mark O. [Auburn University
2013-05-13
Experimental approach Column experiments were devised to investigate the role of changing fluid composition on mobility of uranium through a sequence of geologic media. Fluids and media were chosen to be relevant to the ground water plume emanating from the former S-3 ponds at the Oak Ridge Integrated Field Research Challenge (ORIFC) site. Synthetic ground waters were pumped upwards at 0.05 mL/minute for 21 days through layers of quartz sand alternating with layers of uncontaminated soil, quartz sand mixed with illite, quartz sand coated with iron oxides, and another soil layer. Increases in pH or concentration of phosphate, bicarbonate, or acetate were imposed on the influent solutions after each 7 pore volumes while uranium (as uranyl) remained constant at 0.1mM. A control column maintained the original synthetic groundwater composition with 0.1mM U. Pore water solutions were extracted to assess U retention and release in relation to the advective ligand or pH gradients. Following the column experiments, subsamples from each layer were characterized using microbeam X-ray absorption spectroscopy (XANES) in conjunction with X-ray fluorescence mapping and compared to sediment core samples from the ORIFC, at SSRL Beam Line 2-3. Results U retention of 55-67mg occurred in phosphate >pH >control >acetate >carbonate columns. The mass of U retained in the first-encountered quartz layer in all columns was highest and increased throughout the experiment. The rate of increase in acetate- and bicarbonate-bearing columns declined after ligand concentrations were raised. U also accumulated in the first soil layer; the pH-varied column retained most, followed by the increasing-bicarbonate column. The mass of U retained in the upper layers was far lower. Speciation of U, interpreted from microbeam XANES spectra and XRF maps, varied within and among the columns. Evidence of minor reduction to U(IV) was observed in the first-encountered quartz layer in the phosphate, bicarbonate
Parker, Jack C; Kim, Ungtae
2015-11-01
The mono-continuum advection-dispersion equation (mADE) is commonly regarded as unsuitable for application to media that exhibit rapid breakthrough and extended tailing associated with diffusion between high and low permeability regions. This paper demonstrates that the mADE can be successfully used to model such conditions if certain issues are addressed. First, since hydrodynamic dispersion, unlike molecular diffusion, cannot occur upstream of the contaminant source, models must be formulated to prevent "back-dispersion." Second, large variations in aquifer permeability will result in differences between volume-weighted average concentration (resident concentration) and flow-weighted average concentration (flux concentration). Water samples taken from wells may be regarded as flux concentrations, while soil samples may be analyzed to determine resident concentrations. While the mADE is usually derived in terms of resident concentration, it is known that a mADE of the same mathematical form may be written in terms of flux concentration. However, when solving the latter, the mathematical transformation of a flux boundary condition applied to the resident mADE becomes a concentration type boundary condition for the flux mADE. Initial conditions must also be consistent with the form of the mADE that is to be solved. Thus, careful attention must be given to the type of concentration data that is available, whether resident or flux concentrations are to be simulated, and to boundary and initial conditions. We present 3-D analytical solutions for resident and flux concentrations, discuss methods of solving numerical models to obtain resident and flux concentrations, and compare results for hypothetical problems. We also present an upscaling method for computing "effective" dispersivities and other mADE model parameters in terms of physically meaningful parameters in a diffusion-limited mobile-immobile model. Application of the latter to previously published studies of
Institute of Scientific and Technical Information of China (English)
Ya-Di Xu; Xin-Wu Cao
2009-01-01
It was found that advection-dominated accretion flow (ADAF)+thin disk model calculations can reproduce the observed spectral energy distributions (SEDs) of two low- luminosity active galactic nuclei (AGNs), provided they are accreting at ～ 0.01 - 0.03 Eddington rates and the thin disks are truncated to ADAFs at～ 100Rs (Rs is the Schwarzschild radius) for M81 and NGC 4579 (Quataert et al. 1999). However, the black hole masses adopted in their work are about one order of magnitude lower than recent measurements on these two sources. Adopting the well estimated black hole masses, our ADAF+thin disk model calculations can reproduce the observed SEDs of these two low- luminosity AGNs, if the black hole is accreting at 2.5 × 10-4 Eddington rates with the thin disk truncated at Rtr = 120Rs for M81 ((m) = 3.3 × 10-3 and Rtr = 80Rs are required for NGC 4579). The transition zones with temperature from the thin disk with 104 - 105 to～109 - 1010 K in the ADAF will inevitably emit thermal X-ray lines, which provides a useful diagnosis of their physical properties. The observed widths of the thermal X-ray iron lines at(～)6.8 keV are consistent with Doppler broadening by Keplerian motion of the gases in the transition zones at～100Rs. We use the structure of the transition zone between the ADAF and the thin disk derived by assuming the turbulent diffusive heat mechanism to calculate their thermal X-ray line emission with the standard software package Astrophysical Plasma Emission Code (APEC). Comparing them with the equivalent widths of the observed thermal X-ray iron lines in these two sources, we find that the turbulent diffusive heat mechanism seems to be unable to reproduce the ob- served thermal X-ray line emission. The test of the evaporation model for the accretion mode transition with the observed thermal X-ray line emission is briefly discussed.
Raghib, Michael; Levin, Simon; Kevrekidis, Ioannis
2010-05-01
2. The long-time behavior of the msd of the centroid walk scales linearly with time for naïve groups (diffusion), but shows a sharp transition to quadratic scaling (advection) for informed ones. These observations suggest that the mesoscopic variables of interest are the magnitude of the drift, the diffusion coefficient and the time-scales at which the anomalous and the asymptotic behavior respectively dominate transport, the latter being linked to the time scale at which the group reaches a decision. In order to estimate these summary statistics from the msd, we assumed that the configuration centroid follows an uncoupled Continuous Time Random Walk (CTRW) with smooth jump and waiting time pdf's. The mesoscopic transport equation for this type of random walk corresponds to an Advection-Diffusion Equation with Memory (ADEM). The introduction of the memory, and thus non-Markovian effects, is necessary in order to correctly account for the two time scales present. Although we were not able to calculate the memory directly from the individual-level rules, we show that it can estimated from a single, relatively short, simulation run using a Mittag-Leffler function as template. With this function it is possible to predict accurately the behavior of the msd, as well as the full pdf for the position of the centroid. The resulting ADEM is self-consistent in the sense that transport parameters estimated from the memory via a Kubo relationship coincide with those estimated from the moments of the jump size pdf of the associated CTRW for a large number of group sizes, proportions of informed individuals, and degrees of bias along the preferred direction. We also discuss the phase diagrams for the transport coefficients estimated from this method, where we notice velocity-precision trade-offs, where precision is a measure of the deviation of realized group orientations with respect to the informed direction. We also note that the time scale to collective decision is invariant
Ackerman, Daniel J.; Rousseau, Joseph P.; Rattray, Gordon W.; Fisher, Jason C.
2010-01-01
Three-dimensional steady-state and transient models of groundwater flow and advective transport in the eastern Snake River Plain aquifer were developed by the U.S. Geological Survey in cooperation with the U.S. Department of Energy. The steady-state and transient flow models cover an area of 1,940 square miles that includes most of the 890 square miles of the Idaho National Laboratory (INL). A 50-year history of waste disposal at the INL has resulted in measurable concentrations of waste contaminants in the eastern Snake River Plain aquifer. Model results can be used in numerical simulations to evaluate the movement of contaminants in the aquifer. Saturated flow in the eastern Snake River Plain aquifer was simulated using the MODFLOW-2000 groundwater flow model. Steady-state flow was simulated to represent conditions in 1980 with average streamflow infiltration from 1966-80 for the Big Lost River, the major variable inflow to the system. The transient flow model simulates groundwater flow between 1980 and 1995, a period that included a 5-year wet cycle (1982-86) followed by an 8-year dry cycle (1987-94). Specified flows into or out of the active model grid define the conditions on all boundaries except the southwest (outflow) boundary, which is simulated with head-dependent flow. In the transient flow model, streamflow infiltration was the major stress, and was variable in time and location. The models were calibrated by adjusting aquifer hydraulic properties to match simulated and observed heads or head differences using the parameter-estimation program incorporated in MODFLOW-2000. Various summary, regression, and inferential statistics, in addition to comparisons of model properties and simulated head to measured properties and head, were used to evaluate the model calibration. Model parameters estimated for the steady-state calibration included hydraulic conductivity for seven of nine hydrogeologic zones and a global value of vertical anisotropy. Parameters
Kwasniewski, Slawomir; Gluchowska, Marta; Trudnowska, Emilia; Ormanczyk, Mateusz; Walczowski, Waldemar; Beszczynska-Moeller, Agnieszka
2016-04-01
The Arctic is among the regions where the climate change effects on ecosystem will be the most rapid and consequential, with Arctic amplification recognized as an integral part of the process. Great part of the changes are forced by advection of warm waters from the North Atlantic and the expected modifications of Arctic marine ecosystem will be induced not only by changing environmental conditions but also as a result of introducing Atlantic biota. Thus, the knowledge of physical and biological heterogeneity of Atlantic inflow is requisite for understanding the effects of climate change on biological diversity and ecosystem functioning in the Arctic. The complex and variable two-branched structure of the Atlantic Water flow via Fram Strait and the Barents Sea most likely has a strong influence on the ocean biology in these regions, especially in the pelagic realm. Zooplankton are key components of marine ecosystems which form essential links between primary producers and grazer/predator consumers, thus they are important for functioning of the biological carbon pump. Changes in zooplankton distribution and abundance may have cascading effects on ecosystem functioning, with regulatory effects on climate. Based on data collected in summers of 2012-2014, within the scope of the Polish-Norwegian PAVE research project, we investigate zooplankton distribution, abundance and selected structural characteristics of communities, in relation to water mass properties in the Atlantic Water complex flow to the Arctic Ocean. The main questions addressed here are: what are the differences in zooplankton patterns between the Fram Strait and Barents Sea branches, and how does the inter-annual variability of Atlantic Water advection relate to changes in zooplankton? The results of the investigation are precondition for foreseeing changes in the pelagic realm in the Arctic Ocean and are necessary for constructing and tuning plankton components of ecosystem models.
Institute of Scientific and Technical Information of China (English)
麦艳红; 韦联琦
2013-01-01
在糖厂生产过程中，从压榨机出来的混合汁含有大量的蔗渣、泥等杂质，因此在澄清工段时通过中和汁快沉把蔗渣和泥汁从蔗汁里分离出来。为提高产糖质量、降低生产能耗物耗，设计了基于iFix和PLC的糖厂平流沉降器配套自动控制系统，稳定沉降器的来汁流量，防止滤汁箱冒箱或抽空，实现絮凝剂、澄清剂、清净剂自动按比例添加，泥汁自动按比例排放。实际运行结果表明，平流沉降器控制系统设计合理，有效，且安全可靠。%In the sugar mill production process, from the press out of the mixed juice contains a lot of bagasse, mud and impurities, so in clarification section by neutralization juice quickly sink the bagasse and mud juice from sugarcane juice separated. In order to improve the sugar quality, reduce production energy consumption material consumptions, designed based on iFix and PLC sugar-refinery advection settler supporting the automatic control system, the stable settler to juice flow, prevent filter juice box take box or depression, realize flocculating agent, clarifying agent, clearing agent to be automatic scale to add, mud juice automatic scale emissions.The actual operation shows that the advection settler control system design is reasonable, effective, safe and reliable.
Institute of Scientific and Technical Information of China (English)
许爱华; 陈翔翔; 肖安; 许彬
2016-01-01
利用江西省2000—2012年常规地面观测资料及探空资料，采用合成和统计方法，分析了54次区域性平流雾的天气形势及气象要素，得到了平流雾逆温层、温湿条件、低层风场及影响系统等统计特征。结果表明：（1）江西省区域性平流雾主要发生于2—3月，北部多于南部。（2）其形势特征为：江南地区低层有较明显的暖湿平流。850 hPa 上的切变线或辐合区位于长江流域到江淮一带，925和850 hPa西南风速分别达3～8和7～15 m·s－1。地面形势多为弱低压倒槽和锋面前部的低压，其次为高压底部。（3）850 hPa以下低层有相对湿度≥80％的湿层，500 hPa中层多数有相对湿度≤50％的干层。地面气温和露点多在10～16℃，且达到近饱和。（4）平流雾的逆温结构以单层逆温为主，多数比辐射雾逆温层高、厚度大。逆温强度主要在1～3℃。最后给出了江西平流雾（我国南方）的预报着眼点或预报思路。%Based on the 2000-2012 conventional surface observations and sounding data in Jiangxi Prov-ince,this paper analyzed 54 regional advection fog weather events and meteorological factors by using the synthetic and statistical method,obtaining the statistical characteristics of the advection fog temperature inversion layer,temperature and humidity conditions,low-level wind field and the impact system.The re-sults showed that:(1 )The Jiangxi regional advection fog mainly occurs in February and March,seen more in the north than in the south.(2)The situation features are as follows:The low-level of Jiangnan Region has obvious warm and humidity advection,the shear line or convergence zone at 850 hPa is located in the region from Yangtze River to Jianghuai,the southwest wind speed at 925 hPa and 850 hPa is up to 3-8 m ·s-1 and 7-15 m·s-1 respectively.Surface situation is mostly inverted trough and low pressure in the forepart of cold front,followed by the
Adjoint Error Estimation for Linear Advection
Energy Technology Data Exchange (ETDEWEB)
Connors, J M; Banks, J W; Hittinger, J A; Woodward, C S
2011-03-30
An a posteriori error formula is described when a statistical measurement of the solution to a hyperbolic conservation law in 1D is estimated by finite volume approximations. This is accomplished using adjoint error estimation. In contrast to previously studied methods, the adjoint problem is divorced from the finite volume method used to approximate the forward solution variables. An exact error formula and computable error estimate are derived based on an abstractly defined approximation of the adjoint solution. This framework allows the error to be computed to an arbitrary accuracy given a sufficiently well resolved approximation of the adjoint solution. The accuracy of the computable error estimate provably satisfies an a priori error bound for sufficiently smooth solutions of the forward and adjoint problems. The theory does not currently account for discontinuities. Computational examples are provided that show support of the theory for smooth solutions. The application to problems with discontinuities is also investigated computationally.
Monarch butterfly spatially discrete advection model.
Yakubu, Abdul-Aziz; Sáenz, Roberto; Stein, Julie; Jones, Laura E
2004-08-01
We study the population cycles of the Monarch butterfly using one of the simplest systems incorporating both migration and local dynamics. The annual migration of the Monarch involves four generations. Members of Generations 1-3 (occasionally 4) migrate from the over-wintering site in Central Mexico to breeding grounds that extend as far north as the Northern United States and Southern Canada. A portion of the Generation 3 and all members of the Generation 4 butterflies begin their return to the over-wintering grounds in August through October where they enter reproductive diapause for several months. We developed a simple discrete-time island chain model in which different fecundity functions are used to model the reproductive strategies of each generation. The fecundity functions are selected from broad classes of functions that capture the effects of either contest or scramble intraspecific competition in the Monarch population. The objectives of our research are multiple and include the study of the generationally dependent intraspecific competition and its effect on the pool size of migrants as well as the persistence of the overall butterfly populations. The stage structure used in modeling the Monarch butterfly dynamics and their generationally dependent reproductive strategies naturally support fluctuating patterns and multiple attractors. The implications of these fluctuations and attractors on the long-term survival of the Monarch butterfly population are explored. PMID:15234616
Institute of Scientific and Technical Information of China (English)
王洋; 张可霓; 范蕊; 王小清
2015-01-01
为确保地源热泵系统能够得到合理利用，本文在TOUGH2平台基础上建立了垂直U形地埋管三维精细热渗耦合数值模型，对系统的全年运行特性进行分析，针对冬夏负荷不平衡特点，利用TOUGH2-MP/EOS3数值代码，分析讨论系统运行过程中不同单位井深换热量对土壤温度及土壤温度恢复的影响。模拟结果表明利用TOUGH2数值模拟方法研究地埋管热渗耦合问题具有一定的优势和可行性。%To ensure that a ground source heat pump can be used effectively, basic methods for conducting numerical simulations of vertical U-shape buried pipe are described based on TOUGH2 code. The operating characteristics of the system are analyzed throughout the year according to the characteristics of heat load imbalance in winter and summer. Heat exchange quantities per unit wel depth that affect soil temperature and recovery are discussed. This study also shows that numerical simulation methods can be used to study geothermal heat exchange under coupled thermal conduction and groundwater advection.
Institute of Scientific and Technical Information of China (English)
王明欢; 沈学顺; 肖锋
2011-01-01
针对半隐式半拉格朗日数值预报模式GRAPES,研究发展了与之相适合的高精度正定保形的物质平流方案--分段有理函数法(PRM,Piecewise Rational Method).文中在进行理想试验验证该方案简单、实用、易于编程对于空间变化幅度大的物理量具有较高的平流计算能力且在GRAPES模式中具有可行性的基础上,对2005年7月连续1个月的24小时降水进行实际预报试验.通过细致的个例分析、月平均比较以及TS评分计算,PRM方案实际预报结果与GRAPES模式中原来采用的水物质平流方案预报的主要雨带的分布、走向相一致,但对大雨以上量级的降水预报具有明显优势,对网格尺度的降水的影响比较敏感,进一步验证了高精度正定保形方案对实际降水预报的改进效果,表明该方案对于改进GRAPES模式大到暴雨预报能力具有较大的潜力.PRM平流方案较GRAPES原来采用的准单调正定保形的平流方案能够更加合理地计算水物质场的输送,尤其是能够很好地反映出梅雨季东亚大气下层水汽水平梯度大以及沿梅雨锋水汽的小尺度变率较大的特点描写.%In a series of papers, for the semi-implicit semi-Lagrangian GRAPES model, the high-accuracy and positive-definite advection scheme called the piecewise rational function methed (PRM) is developed. First, in Part I of the papers, it was found that this scheme is simple, practical and easy to code and has great ability in treating the variables of large spatial variation. Its feasibility in the GRAPES can also be confirmed by ideal experiments. In Part Ⅱ , the 24 hour rainfall forecast has been made continuously for one month: July in 2005. Through detailed case analyses based on a comparison of the monthly mean 24 hour rainfall and the calculation of TS (Threat Score), it is found that the spatial distribution of forecasted rainbelts by the PRM is similar to that by the original water substances
Institute of Scientific and Technical Information of China (English)
张磊; 金莲姬; 朱彬; 银燕
2013-01-01
基于单条后向轨迹的滞留时间场和污染物排放强度场,设计了一种可以评估该轨迹对污染物的平流输送强度参数.利用2011年6～8月光明顶CO和O3浓度资料对该参数进行了验证,进而分析了该观测时段平流输送对光明顶污染物的影响；此外将O3浓度分成3档,利用改进的PSCF(Potential source contribution function)方法分析了各档浓度对应的源区分布.结果表明:(1)平流输送评估参数与污染物浓度的变化具有很好的一致性,表明平流输送对光明顶污染物浓度的变化具有重要作用.其中,安徽、湖北和江西三省交界区域的城市群向光明顶输送的污染物占到输送总量的一半以上；(2)光明项O3浓度＞55×10-9、(30～55)×10-9、＜30×10-9时所对应的主要源区分别为华北及长三角发达工业区、黄山西南方向的工业区、较远的南部沿海地区；(3)影响光明顶污染物浓度变化的输送类型可以分为秸秆燃烧输送、发达工业区气团输送、西南方向气团输送和海洋性气团输送4种类型,对应的污染物浓度(CO/O3)(×10-9)依次为474.47/72.50、221.16/57.71、86.31/30.41、51.67/27.45.%A parameter aimed to evaluate pollutants advective transport intensity was designed based on the residence time field of backword trajectory and pollutants emission intensity field.The parameter was evaluated by using the data of CO (carbon monoxide) and O3 (ozone) from June to August 2011 in Bright Summit of Mt Huang,and then the contributions of pollutants advective transport to this site were calculated.The potential source distributions of O3,which was assorted into three bins of O3 levels were investigated by a modified potential source contribution function (PSCF).Results showed that the advective transport parameters well reproduced the variation of CO and O3 concentrations respectively,indicating that advective transport played great impact on the change of CO and O3 at the
Directory of Open Access Journals (Sweden)
Gertrudes Macario de Oliveira
2000-12-01
Full Text Available Objetivou-se com esse estudo, analisar as conseqüências nas estimativas da evapotranspiração (ET durante o ciclo de desenvolvimento de uma cultura de amendoim, devido aos erros cometidos na determinação do saldo de radiação (Rn e àqueles causados pelos efeitos advectivos. Esta pesquisa foi conduzida no perímetro irrigado da Estação Experimental da CODEVASF, na cidade de Rodelas, BA, no período de setembro a dezembro de 1996. Os resultados mostraram que erros no cálculo de Rn de até 2,2 MJ m-2 d-1 e, conseqüentemente, na estimativa da ET, podem ser cometidos dependendo do tempo considerado na totalização diária de Rn. Verificou-se, ainda, que tanto as áreas circunvizinhas próximas ao campo experimental, como as áreas de solos expostos entre fileiras dentro do próprio campo, contribuíram de forma significativa para a geração de advecção local de calor sensível e, portanto, para o aumento da evapotranspiração.The objective of this study was to analyze the consequences in the evapotranspiration estimates (ET during the growing cycle of a peanut crop due to the errors commited in the determination of the radiation balance (Rn, as well as those caused by the advective effects. This research was conducted at the Experimental Station of CODEVASF in an irrigated perimeter located in the city of Rodelas, BA, during the period of September to December of 1996. The results showed that errors of the order of 2.2 MJ m-2 d-1 in the calculation of Rn, and consequently in the estimate of ET, can occur depending on the time considered for the daily total of Rn. It was verified that the surrounding areas of the experimental field, as well as the areas of exposed soil within the field, contributed significantly to the generation of local advection of sensible heat, which resulted in the increase of the evapotranspiration.
Simulating cyclic voltammetry under advection for electrochemical cantilevers
DEFF Research Database (Denmark)
Adesokan, Bolaji James; Evgrafov, Anton; Sørensen, Mads Peter
2015-01-01
We present a mathematical model describing an electrochemical system involving electrode–electrolyte interaction. The model is governed by a system of advection–diffusion equations with a nonlinear reaction term at the boundary. Our calculations based on such model demonstrate the dynamics of ion...
Advection and diffusion of shore-attached sand nourishments
Huisman, B.J.A.; Van Thiel De Vries, J.S.M.; Walstra, D.J.R.; Roelvink, J.A.; Ranasinghe, R.W.M.R.J.B.; Stive, M.J.F.
2013-01-01
Understanding of the behaviour of coastline perturbations at soft-coastlines is essential for modelling coastal evolution at decadal time scales. Many coastline models do, for example, implicitly assume dominant diffusive behaviour of coastline features. The validity of this assumption is investigat
Advection of magnetic flux by accretion disks around neutron stars
Flores-Tulian, S.; Reisenegger, A.
The aim of our research is to address why millisecond pulsars have relatively weak surface magnetic fields, of about 10^8 G, with a narrow spread. We propose that the accretion of plasma from the companion star fully screens the original neutron star field, but the accretion disk carries additional magnetic flux from the companion star, or itself can generate field by means of dynamo processes. For a strongly magnetized star, the field prevents the disk from approaching the star. The accretion is along the field lines and deposits the matter on the polar cap. Then, the accreted plasma flows, dragging with itself the magnetic field lines, from the pole to the equator (Payne & Melatos 2004). In a following stage, when the star becomes non-magnetic, because the field has been buried, the disk touches the star. We suggest that some effective mechanism of magnetic flux transport such as that proposed by Spruit & Uzdensky 2005 (or Bisnovatyi-Kogan & Lovelace 2007), operates and necessarily leads to a "strongly magnetized disk''. It becomes laminar because the magneto-rotational instability saturates (it is considered to be responsible for turbulence in the disk), and the magnetic difussivity is negligible. Then, the loss of angular momentum allowing the accretion is only caused by the magneto-centrifugal disk-wind (Blandford & Payne 1982). Meanwhile, the wind-driven transport of the magnetic flux by the disk re-magnetizes the star. This process continues until the Lorentz force due to the star's magnetic field forbids any further accretion of matter and magnetic flux, in the Ideal Magneto-Hydro-Dynamics approach. Additional of material can fall onto the star (but at lower rate) if some instability process sets in, allowing the diffusion of mass through the magnetic field lines (e.g the Interchange Instability, Spruit & Taam 1990). All these processes might lead to an asymptotic magnetic field of 10^8 G,as is inferred from observations. We are developing a self-consistent theoretical model to describe the above dynamical processes taking into account the interaction among the star, the strongly magnetized disk, and the disk-wind, justifying our hypothesis.
Development of TVD numerical models: I. Linear advection equation
Energy Technology Data Exchange (ETDEWEB)
Lee, Jong-Wook; Cho, Yong-Sik; Yoon, Tae-Hoon [Hanyang University, Seoul(Korea); Yoon, Kwang-Seok [Korea Institute of Construction Technology, Koyang(Korea)
2001-04-30
By using the total variation diminishing (TVD) condition, accurate and upwind based schemes are firstly introduced to develop numerical models free from nonphysical oscillations in the vicinity of large gradients. These models are then applied to both abruptly and smoothly varying initial conditions. By comparing computed predictions to analytical solutions, it is clearly shown that the first-order upwind scheme produces the numerical viscosity and the second-order Lax-Wendroff scheme produces the spurious oscillations. However, the TVD scheme gives the most reasonable results. (author). 22 refs., 6 figs.
Planktonic interactions and chaotic advection in Langmuir circulation
DEFF Research Database (Denmark)
Bees, Martin Alan; Mezic, I.; McGlade, J.
1998-01-01
The role of unsteady laminar flows for planktonic communities is investigated. Langmuir circulation is used, as a typical medium-scale structure, to illustrate mechanisms for the generation of plankton patches. Two behaviours are evident: chaotic regions that help to spread plankton and locally...
Accretion discs around black holes two dimensional, advection cooled flows
Igumenshchev, I V; Abramowicz, M A; Igumenshchev, Igor V; Chen, Xingming; Abramowicz, Marek Artur
1995-01-01
Two-dimensional accretion flows near black holes have been investigated by time-dependent hydrodynamical calculations. We assume that the flow is axisymmetric and that radiative losses of internal energy are negligible, so that the disc is geometrically thick and hot. Accretion occurs due to the overflow of the effective potential barrier near the black hole, similar to the case of the Roche lobe overflowing star in a binary system. We make no pre-assumptions on the properties of the flow, instead our models evolve self-consistently from an initially non-accreting state. The viscosity is due to the the small-scale turbulence and it is described by the \\alpha-viscosity prescription. We confirm earlier suggestions that viscous accretion flows are convectively unstable. We found that the instability produces transient eddies of various length-scales. The eddies contribute to the strength of the viscosity in the flow by redistributing the angular momentum. They also introduce low amplitude oscillatory variations ...
Three dimensional chaotic advection by mixed layer baroclinic instabilities
Mukiibi, Daniel; Serra, Nuno
2015-01-01
Three dimensional (3D) Finite Time Lyapunov Exponents (FTLEs) are computed from numerical simulations of a freely evolving mixed layer (ML) front in a zonal channel undergoing baroclinic instability. The 3D FTLEs show a complex structure, with features that are less defined than the two-dimensional (2D) FTLEs, suggesting that stirring is not confined to the edges of vortices and along filaments and posing significant consequences on mixing. The magnitude of the FTLEs is observed to be strongly determined by the vertical shear. A scaling law relating the local FTLEs and the nonlocal density contrast used to initialize the ML front is derived assuming thermal wind balance. The scaling law only converges to the values found from the simulations within the pycnocline, while it displays differences within the ML, where the instabilities show a large ageostrophic component. The probability distribution functions of 2D and 3D FTLEs are found to be non Gaussian at all depths. In the ML, the FTLEs wavenumber spectra d...
Homogenization for advection-diffusion in a perforated domain
Haynes, P H; Norris, J R; Zygalakis, K C
2010-01-01
The volume of a Wiener sausage constructed from a diffusion process with periodic, mean-zero, divergence-free velocity field, in dimension 3 or more, is shown to have a non-random and positive asymptotic rate of growth. This is used to establish the existence of a homogenized limit for such a diffusion when subject to Dirichlet conditions on the boundaries of a sparse and independent array of obstacles. There is a constant effective long-time loss rate at the obstacles. The dependence of this rate on the form and intensity of the obstacles and on the velocity field is investigated. A Monte Carlo algorithm for the computation of the volume growth rate of the sausage is introduced and some numerical results are presented for the Taylor--Green velocity field.
Concentration polarization, surface currents, and bulk advection in a microchannel
DEFF Research Database (Denmark)
Nielsen, Christoffer Peder; Bruus, Henrik
2014-01-01
We present a comprehensive analysis of salt transport and overlimiting currents in a microchannel during concentration polarization. We have carried out full numerical simulations of the coupled Poisson-Nernst-Planck-Stokes problem governing the transport and rationalized the behavior of the system...
Advectional enhancement of eddy diffusivity under parametric disorder
Goldobin, Denis S.
2009-01-01
Frozen parametric disorder can lead to appearance of sets of localized convective currents in an otherwise stable (quiescent) fluid layer heated from below. These currents significantly influence the transport of an admixture (or any other passive scalar) along the layer. When the molecular diffusivity of the admixture is small in comparison to the thermal one, which is quite typical in nature, disorder can enhance the effective (eddy) diffusivity by several orders of magnitude in comparison ...
Regional Advection Perturbations in an Irrigated Desert (RAPID) Experiment
Debruin, H.A.R.; Hartogensis, O.K.; Allen, R.G.; Kramer, J.W.J.L.
2005-01-01
The RAPID field experiment took place in August - September 1999 at a site 25km south of Twin Falls, Idaho, USA. The experiment concerned micrometeorological observations over extensive, well-irrigated fields covered with the fast-growing crop alfalfa. During daytime, on a number of days the sensibl
A two-dimensional, finite-difference model simulating a highway has been developed which is able to handle linear and nonlinear chemical reactions. Transport of the pollutants is accomplished by use of an upstream-flux-corrected algorithm developed at the Naval Research Laborator...
Comparison of precipitation nowcasting by extrapolation and statistical-advection methods
Sokol, Zbynek; Kitzmiller, David; Pesice, Petr; Mejsnar, Jan
2013-04-01
Two models for nowcasting of 1-h, 2-h and 3-h precipitation in the warm part of the year were evaluated. The first model was based on the extrapolation of observed radar reflectivity (COTREC-IPA) and the second one combined the extrapolation with the application of a statistical model (SAMR). The accuracy of the model forecasts was evaluated on independent data using the standard measures of root-mean-squared-error, absolute error, bias and correlation coefficient as well as by spatial verification methods Fractions Skill Score and SAL technique. The results show that SAMR yields slightly better forecasts during the afternoon period. On the other hand very small or no improvement is realized at night and in the very early morning. COTREC-IPA and SAMR forecast a very similar horizontal structure of precipitation patterns but the model forecasts differ in values. SAMR, similarly as COTREC-IPA, is not able to develop new storms or significantly intensify already existing storms. This is caused by a large uncertainty regarding future development. On the other hand, the SAMR model can reliably predict decreases in precipitation intensity.
Advection/diffusion of large scale magnetic field in accretion disks
Directory of Open Access Journals (Sweden)
R. V. E. Lovelace
2009-02-01
Full Text Available Activity of the nuclei of galaxies and stellar mass systems involving disk accretion to black holes is thought to be due to (1 a small-scale turbulent magnetic field in the disk (due to the magneto-rotational instability or MRI which gives a large viscosity enhancing accretion, and (2 a large-scale magnetic field which gives rise to matter outflows and/or electromagnetic jets from the disk which also enhances accretion. An important problem with this picture is that the enhanced viscosity is accompanied by an enhanced magnetic diffusivity which acts to prevent the build up of a significant large-scale field. Recent work has pointed out that the disk's surface layers are non-turbulent and thus highly conducting (or non-diffusive because the MRI is suppressed high in the disk where the magnetic and radiation pressures are larger than the thermal pressure. Here, we calculate the vertical (z profiles of the stationary accretion flows (with radial and azimuthal components, and the profiles of the large-scale, magnetic field taking into account the turbulent viscosity and diffusivity due to the MRI and the fact that the turbulence vanishes at the surface of the disk. We derive a sixth-order differential equation for the radial flow velocity v_{r}(z which depends mainly on the midplane thermal to magnetic pressure ratio β>1 and the Prandtl number of the turbulence P=viscosity/diffusivity. Boundary conditions at the disk surface take into account a possible magnetic wind or jet and allow for a surface current in the highly conducting surface layer. The stationary solutions we find indicate that a weak (β>1 large-scale field does not diffuse away as suggested by earlier work.
Experimental studies of coherent structures in an advection-reaction-diffusion system
Gowen, Savannah; Solomon, Tom
2015-08-01
We present experimental studies of reaction front propagation in a single vortex flow with an imposed external wind. The fronts are produced by the excitable, ferroin-catalyzed Belousov-Zhabotinsky chemical reaction. The flow is generated using an electromagnetic forcing technique: an almost-radial electrical current interacts with a magnetic field from a magnet below the fluid layer to produce the vortex. The magnet is mounted on crossed translation stages allowing for movement of the vortex through the flow. Reaction fronts triggered in or in front of the moving vortex form persistent structures that are seen experimentally for time-independent (constant motion), time-periodic, and time-aperiodic flows. These results are examined with the use of burning invariant manifolds that act as one-way barriers to front motion in the flows. We also explore the usefulness of finite-time Lyapunov exponent fields as an instrument for analyzing front propagation behavior in a fluid flow.
Solutes and cells - aspects of advection-diffusion-reaction phenomena in biochips
DEFF Research Database (Denmark)
Vedel, Søren
2012-01-01
The results in this thesis are part of the work carried out during the author’s doctoral studies. Funding for the project has been provided by the Programme Commission on Strategic Growth Technologies, the Danish Agency for Science, Technology and Innovation (grant no. 2106-08-0018 ‘Pro....... Presented in this thesis is selected parts of the results obtained, which in some cases have also been published in peer-reviewed journals or presented at conferences and meetings, as listed in Sec. 1.2. The studies of the distributions of solutes are motivated by microbiological phenomena in which cells...... subproject, we study the influence of neighboring cells in shaping the iii Abstract migration of the individual cell by a combined experimental and theoretical approach. Using highly controlled microfluidic cell to obtain culture high-resolution image data with subcellular resolution of migrating cells...
Phase dependent advection-diffusion in drift wave - zonal flow turbulence
Moradi, Sara
2016-01-01
In plasma turbulence theory, due to the complexity of the system with many non-linearly interacting waves, the dynamics of the phases is often disregarded and the so-called random-phase approximation (RPA) is used assuming the existence of a Chirikov-like criterion for the onset of wave stochasticity. The dynamical amplitudes are represented as complex numbers, $\\psi = \\psi_r + i\\psi_i = ae^{i\\theta}$, with the amplitudes slowly varying whereas the phases are rapidly varying and, in particular, distributed uniformly over the interval $[0;2\\pi)$. However, one could expect that the phase dynamics can play a role in the self-organisation and the formation of coherent structures. In the same manner it is also expected that the RPA falls short to take coherent interaction between phases into account. In this work therefore, we studied the role of phase dynamics and the coupling of phases between different modes on the characteristic time evolution of the turbulent. We assume a simple turbulent system where the so-...
Spectral decomposition in advection-diffusion analysis by finite element methods
Energy Technology Data Exchange (ETDEWEB)
Nickell, R.E.; Gartling, D.K.; Strang, G.
1978-08-11
In a recent study of the convergence properties of finite element methods in nonlinear fluid mechanics, an indirect approach was taken. A two-dimensional example with a known exact solution was chosen as the vehicle for the study, and various mesh refinements were tested in an attempt to extract information on the effect of the local Reynolds number. However, more direct approaches are usually preferred. In this study one such direct approach is followed, based upon the spectral decomposition of the solution operator. Spectral decomposition is widely employed as a solution technique for linear structural dynamics problems and can be applied readily to linear, transient heat transfer analysis; in this case, the extension to nonlinear problems is of interest. It was shown previously that spectral techniques were applicable to stiff systems of rate equations, while recent studies of geometrically and materially nonlinear structural dynamics have demonstrated the increased information content of the numerical results. The use of spectral decomposition in nonlinear problems of heat and mass transfer would be expected to yield equally increased flow of information to the analyst, and this information could include a quantitative comparison of various solution strategies, meshes, and element hierarchies.
Spectral decomposition in advection-diffusion analysis by finite element methods
Energy Technology Data Exchange (ETDEWEB)
Nickell, R.E.; Gartling, D.K.
1979-03-01
A spectral decomposition method based upon finite element modeling is compared to a Crank-Nicolson direct integration solution scheme and the exact solution for the one-dimensional, nonlinear system defined by Burger's equation. Results from this study are applicable to both fluid mechanics and combined conduction-convection heat transfer. The parameter ..cap alpha.., which governs the importance of diffusive transport, was varied over a sufficiently wide range such that comments on the comparisons are general. The mode superposition method proved to be very attractive in comparison to the second-order accurate Crank-Nicolson approach, generally allowing an order of magnitude larger time step for equivalent convergence to the exact solution. The modal shapes themselves tend to provide useful information about the ability of a given mesh to produce accurate results, much in the same way that modal information is used in nonlinear structural dynamics. For this class of problems, in contrast to structural dynamics, system nonlinearities did not manifest themselves in dramatic changes in the eigenspectrum.
Energy Technology Data Exchange (ETDEWEB)
Shadid, John Nicolas; Bochev, Pavel Blagoveston; Gunzburger, Max Donald (Florida State University, Tallahasse, FL)
2003-09-01
Implicit time integration coupled with SUPG discretization in space leads to additional terms that provide consistency and improve the phase accuracy for convection dominated flows. Recently, it has been suggested that for small Courant numbers these terms may dominate the streamline diffusion term, ostensibly causing destabilization of the SUPG method. While consistent with a straightforward finite element stability analysis, this contention is not supported by computational experiments and contradicts earlier Von-Neumann stability analyses of the semidiscrete SUPG equations. This prompts us to re-examine finite element stability of the fully discrete SUPG equations. A careful analysis of the additional terms reveals that, regardless of the time step size, they are always dominated by the consistent mass matrix. Consequently, SUPG cannot be destabilized for small Courant numbers. Numerical results that illustrate our conclusions are reported.
Engelbrektson, A. L.; Hubbard, C. G.; Piceno, Y.; Boussina, A.; Jin, Y.; Dubinsky, E. A.; Tom, L.; Hu, P.; Conrad, M. E.; Anderson, G. L.; Coates, J. D.
2013-12-01
Hydrogen sulfide (H2S) biogenesis in oil reservoirs is a primary cause of souring and of associated costs in reservoir and pipeline maintenance. In addition to the corrosive effects of the H2S itself, abiotic and biological oxidation also generates sulfuric acid, further degrading metallic surfaces. Amending these environments with perchlorate (ClO4-) resolves these problems by inhibition of biological sulfate reduction and re-oxidation of H2S to elemental sulfur by dissimilatory (per)chlorate reducing bacteria (DPRB). Triplicate flow through columns packed with San Francisco bay sediment were flushed with bay water ([SO4=] = 25-30 mM) containing yeast extract with 50 mM inhibitor concentrations (NO3-or ClO4-) decreasing to 25 mM and finally 12.5 mM. Influent and effluent geochemistry was monitored and DNA was prepared from the sediment bed for microbial community analysis. Souring was reversed by both treatments (at 50 mM) compared to the control columns that had no ion addition. Nitrate began to re-sour when treatment concentration was decreased to 25 mM but treatment had to be decreased to 12.5 mM before the perchlorate treated columns began to re-sour. However, the treated columns re-soured to a lesser extent than the control columns. Phylochip microbial community analyses indicated microbial community shifts and phylogenetic clustering by treatment. Isotopic analysis of sulfate showed trends that broadly agreed with the geochemistry but also suggested further sulfur cycling was occurring. This study indicates that perchlorate shows great promise as an inhibitor of sulfidogenesis in natural communities and provides insight into which organisms are involved in this process.
Brine-induced advection of dissolved aromatic hydrocarbons to arctic bottom waters
International Nuclear Information System (INIS)
Extruded brine, generated during sea ice formation in nearshore arctic waters, will sink to the bottom and can form a stable bottom boundary layer. This layer can persist for periods of up to 4-6 months. Limited quantities of dissolved aromatic hydrocarbons resulting from a spill of crude oil or refined petroleum distillate products during periods of ice growth can be transported as conservative components to the benthos with sinking brine. Once incorporated into the stable bottom boundary layer, these aromatic components are no longer subject to loss by evaporative processes, and they only can be diluted by ultimately mixing with uncontaminated water masses, a process that proceeds slowly throughout the ice-covered period. This mechanism for the transport of dissolved hydrocarbons has been demonstrated through a laboratory test-tank simulation and a chemical/physical oceanographic field program conducted in the Chukchi Sea near Pt. Frankline, AK (March 1985). The results are pertinent to shallow nearshore oil and gas exploration, development, production, and transportation activities in high latitude marine systems
Energy Technology Data Exchange (ETDEWEB)
Wang, Wei [Deprartment of Mathematics. Florida Intl Univ., Miami, FL (United States); Shu, Chi-Wang [Division of Applied Mathematics. Brown Univ., Providence, RI (United States); Yee, H.C. [NASA Ames Research Center (ARC), Moffett Field, Mountain View, CA (United States); Sjögreen, Björn [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
2012-01-01
A new high order finite-difference method utilizing the idea of Harten ENO subcell resolution method is proposed for chemical reactive flows and combustion. In reaction problems, when the reaction time scale is very small, e.g., orders of magnitude smaller than the fluid dynamics time scales, the governing equations will become very stiff. Wrong propagation speed of discontinuity may occur due to the underresolved numerical solution in both space and time. The present proposed method is a modified fractional step method which solves the convection step and reaction step separately. In the convection step, any high order shock-capturing method can be used. In the reaction step, an ODE solver is applied but with the computed flow variables in the shock region modified by the Harten subcell resolution idea. For numerical experiments, a fifth-order finite-difference WENO scheme and its anti-diffusion WENO variant are considered. A wide range of 1D and 2D scalar and Euler system test cases are investigated. Studies indicate that for the considered test cases, the new method maintains high order accuracy in space for smooth flows, and for stiff source terms with discontinuities, it can capture the correct propagation speed of discontinuities in very coarse meshes with reasonable CFL numbers.
Quantifying advective and nonstationary effects on eddy fluxes in the AmeriFlux network
Energy Technology Data Exchange (ETDEWEB)
Fitzjarrald, David R
2012-12-19
Our goal was to study the flows within and above of a forested area and assess the degree to which horizontal subcanopy motions transport significant amounts of CO2. This process can explain why ecosystem respiration appears to be underestimated on calm nights. It is essential to understand the physical and biological mechanisms that determine relevant processes that occur on these suspect nights.
Corrected mean-field models for spatially dependent advection-diffusion-reaction phenomena
Simpson, Matthew J.; Baker, Ruth E.
2011-05-01
In the exclusion-process literature, mean-field models are often derived by assuming that the occupancy status of lattice sites is independent. Although this assumption is questionable, it is the foundation of many mean-field models. In this work we develop methods to relax the independence assumption for a range of discrete exclusion-process-based mechanisms motivated by applications from cell biology. Previous investigations that focused on relaxing the independence assumption have been limited to studying initially uniform populations and ignored any spatial variations. By ignoring spatial variations these previous studies were greatly simplified due to translational invariance of the lattice. These previous corrected mean-field models could not be applied to many important problems in cell biology such as invasion waves of cells that are characterized by moving fronts. Here we propose generalized methods that relax the independence assumption for spatially inhomogeneous problems, leading to corrected mean-field descriptions of a range of exclusion-process-based models that incorporate (i) unbiased motility, (ii) biased motility, and (iii) unbiased motility with agent birth and death processes. The corrected mean-field models derived here are applicable to spatially variable processes including invasion wave-type problems. We show that there can be large deviations between simulation data and traditional mean-field models based on invoking the independence assumption. Furthermore, we show that the corrected mean-field models give an improved match to the simulation data in all cases considered.
El Gharamti, Mohamad
2012-04-01
Accurate knowledge of the movement of contaminants in porous media is essential to track their trajectory and later extract them from the aquifer. A two-dimensional flow model is implemented and then applied on a linear contaminant transport model in the same porous medium. Because of different sources of uncertainties, this coupled model might not be able to accurately track the contaminant state. Incorporating observations through the process of data assimilation can guide the model toward the true trajectory of the system. The Kalman filter (KF), or its nonlinear invariants, can be used to tackle this problem. To overcome the prohibitive computational cost of the KF, the singular evolutive Kalman filter (SEKF) and the singular fixed Kalman filter (SFKF) are used, which are variants of the KF operating with low-rank covariance matrices. Experimental results suggest that under perfect and imperfect model setups, the low-rank filters can provide estimates as accurate as the full KF but at much lower computational effort. Low-rank filters are demonstrated to significantly reduce the computational effort of the KF to almost 3%. © 2012 American Society of Civil Engineers.
In aquatic systems, time series of dissolved oxygen (DO) have been used to compute estimates of ecosystem metabolism. Central to this open-water method is the assumption that the DO time series is a Lagrangian specification of the flow field. However, most DO time series are coll...
The distribution of "time of flight" in 3D stationary chaotic advection
Raynal, Florence
2014-01-01
The distributions of "time of flight" (time spent by a single fluid particle between two crossings of the Poincar\\'e section) are investigated for five different 3D stationary chaotic mixers. Above all, we study the large tails of those distributions, and show that mainly two types of behaviors are encountered. In the case of slipping walls, as expected, we obtain an exponential decay, which, however, does not scale with the Lyapunov exponent. Using a simple model, we suggest that this decay is related to the negative eigenvalues of the fixed points of the flow. When no-slip walls are considered, as predicted by the model, the behavior is radically dfferent, with a very large tail following a power law with an exponent close to -3.
DEFF Research Database (Denmark)
Santos, Isaac R.; Glud, Ronnie N.; Maher, Damien;
2011-01-01
Little is known about how biogeochemical processes in permeable sediments affect the pH of coastal waters. We demonstrate that seawater recirculation in permeable sands can play a major role in proton (H+) cycling in a coral reef lagoon. The diel pH range (up to 0.75 units) in the Heron Island la...... that the metabolism of advection‐dominated carbonate sands may provide a currently unknown feedback to ocean acidification....
Temporal variability from the two-component advective flow solution and its observational evidence
Dutta, Broja G
2016-01-01
In the propagating oscillatory shock model, the oscillation of the post-shock region, i.e., the Compton cloud, causes the observed low-frequency quasi-periodic oscillations (QPOs). The evolution of QPO frequency is explained by the systematic variation of the Compton cloud size, i.e., the steady radial movement of the shock front, which is triggered by the cooling of the post-shock region. Thus, analysis of energy-dependent temporal properties in different variability time scales can diagnose the dynamics and geometry of accretion flows around black holes. We study these properties for the high inclination black hole source XTE J1550-564 during its 1998 outburst and the low-inclination black hole source GX 339-4 during its 2006-07 outburst using RXTE/PCA data, and we find that they can satisfactorily explain the time lags associated with the QPOs from these systems. We find a smooth decrease of the time lag as a function of time in the rising phase of both sources. In the declining phase the time lag increase...
Parity properties of an advection-dominated solar $\\alpha^2\\Om$-dynamo
Bonanno, A; Rüdiger, G; Belvedere, G
2002-01-01
We have developed a high-precision code which solves the kinematic dynamo problem both for given rotation law and meridional flow in the case of a low eddy diffusivity of the order of $10^{11}$ cm$^2$/s known from the sunspot decay. All our models work with an \\alf-effect which is positive (negative) in the northern (southern) hemisphere. It is concentrated in radial layers located either at the top or at the bottom of the convection zone. We have also considered an \\alf-effect uniformly distributed in all the convection zone. In the present paper the main attention is focused on i) the parity of the solution, ii) the form of the butterfly diagram and iii) the phase relation of the resulting field components. If the helioseismologically derived internal solar rotation law is considered, a model without meridional flow of high magnetic Reynolds number (corresponding to low eddy diffusivity) fails in all the three issues in comparison with the observations. However, a meridional flow with equatorial drift at th...
Parity properties of an advection dominated solar alpha 2Omega -dynamo
Bonanno, A.; Elstner, D.; Rüdiger, G.; Belvedere, G.
We present the results of numerical simulations of the solar dynamo both for given rotation law and meridional flow in the case of a low eddy diffusivity of the order of 1011 cm2/s known from the sunspot decay. If the helioseismologically derived internal solar rotation law is considered, a model without meridional flow of high magnetic Reynolds number (corresponding to low eddy diffusivity) fails in all the three issues in comparison with the observations. However, a meridional flow with equatorial drift at the bottom of the convection zone of few meters by second can indeed enforce the equatorward migration of the toroidal magnetic field belts similar to the observed butterfly diagram but, the solution has only a dipolar parity if the (positive) alpha -effect is located at the base of the convection zone rather than at the top.
Parity properties of an advection-dominated solar $\\alpha^2\\Om$-dynamo
Bonanno, A.; Elstner, D.; Ruediger, G.; G. Belvedere
2002-01-01
We have developed a high-precision code which solves the kinematic dynamo problem both for given rotation law and meridional flow in the case of a low eddy diffusivity of the order of $10^{11}$ cm$^2$/s known from the sunspot decay. All our models work with an \\alf-effect which is positive (negative) in the northern (southern) hemisphere. It is concentrated in radial layers located either at the top or at the bottom of the convection zone. We have also considered an \\alf-effect uniformly dist...
Parity properties of an advection-dominated solar alpha 2 Omega-dynamo
Bonanno, A.; Elstner, D.; Rüdiger, G.; Belvedere, G.
2002-08-01
We have developed a high-precision code which solves the kinematic dynamo problem both for given rotation law and meridional flow in the case of a low eddy diffusivity of the order of 1011 cm2 s-1 known from the sunspot decay. All our models work with an alpha -effect which is positive (negative) in the northern (southern) hemisphere. It is concentrated in radial layers located either at the top or at the bottom of the convection zone. We have also considered an alpha -effect uniformly distributed in all the convection zone. In the present paper the main attention is focused on i) the parity of the solution, ii) the form of the butterfly diagram and iii) the phase relation of the resulting field components. If the helioseismologically derived internal solar rotation law is considered, a model without meridional flow of high magnetic Reynolds number (corresponding to low eddy diffusivity) fails in all the three issues in comparison with the observations. However, a meridional flow with equatorial drift at the bottom of the convection zone of few meters by second can indeed enforce the equatorward migration of the toroidal magnetic field belts similar to the observed butterfly diagram but, the solution has only a dipolar parity if the (positive) alpha -effect is located at the base of the convection zone rather than at the top. We can, therefore, confirm the main results of a similar study by Dikpati & Gilman (\\cite{Dikpati01}).
Advective heat transport associated with regional Earth degassing in central Apennine (Italy)
Chiodini, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia; Cardellini, C.; Dipartimento di Scienze della Terra, Universita` di Perugia,Italy; Caliro, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia; Chiarabba, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Frondini, F.; Dipartimento di Scienze della Terra, Universita` di Perugia, Piazza dell’Universita`, Perugia, Italy
2013-01-01
In this work we show that the main springs of the central Apennine transport a total amount of heat of ∼2.2 109 J s−1. Most of this heat (57%) is the result of geothermal warming while the remaining 43% is due to gravitational potential energy dissipation. This result indicates that a large area of the central Apennines is very hot with heat flux values 4300 mWm−2. These values are higher than those measured in the magmatic and famously geothermal provinces of Tuscany and Latium a...
Impact of vertical and horizontal advection on nutrient distribution in the southeast Pacific
Barceló-Llull, Bàrbara; Mason, Evan; Capet, Arthur; Pascual, Ananda
2016-08-01
An innovative approach is used to analyze the impact of vertical velocities associated with quasi-geostrophic (QG) dynamics on the redistribution and uptake of nitrate in the southeast Pacific (SEP). A total of 12 years of vertical and horizontal currents are derived from an observation-based estimate of the ocean state. Horizontal velocities are obtained through the application of thermal wind balance to weekly temperature and salinity fields. Vertical velocities are estimated by integration of the QG omega equation. Seasonal variability of the synthetic vertical velocity and kinetic energy associated with the horizontal currents is coincident, with peaks in austral summer (November-December) in accord with published observations. The impact of vertical velocity on SEP nitrate uptake rates is assessed by using two Lagrangian particle tracking experiments that differ according to vertical forcing (ω = ωQG vs. ω = 0). From identical initial distributions of nitrate-tagged particles, the Lagrangian results show that vertical motions induce local increases in nitrate uptake reaching up to 30 %. Such increases occur in low uptake regions with high mesoscale activity. Despite being weaker than horizontal currents by a factor of up to 10-4, vertical velocity associated with mesoscale activity is demonstrated to make an important contribution to nitrate uptake, hence productivity, in low uptake regions.
Advection of an alkaline fluid through boom clay cores: geochemical modelling of experimental data
International Nuclear Information System (INIS)
As part of the ECOCLAY II project, with the financial support of NIRAS-ONDRAF and the European Commission, SCK-CEN has carried out experiments on the percolation of alkaline cement waters through Boom Clay cores. The effluent from these percolation experiments has been analysed as a function of time to provide information about the fluid-rock interactions occurring in the samples. However, the changes in the effluent composition with time are quite complex and require interpretation if insight is to be gained into the mechanisms of the interactions occurring in the samples between the invading alkaline fluid and the Boom Clay. Two cementitious waters were used in the experiments: a high pH (∼ 13,5) young cement water (YCW ) representing the initial eluate from a cement, and a lower pH (∼ 12) evolved cement water (ECW) representing the fluids that would emerge from the cements after long times. These fluids were passed through Boom Clay cores over several years and the composition of the effluent fluid monitored. The primary purpose of the modelling work was to provide an explanation of the processes controlling the interactions between the alkaline fluids and the Boom Clay. Four mechanisms were considered: the maintenance of the dissolution-precipitation thermodynamic equilibrium between the minerals and the pore fluids, ion exchange, kinetically controlled dissolution of primary minerals, and the functional group capacity of organic matter as a function of pH. The modelling was carried out using three essentially independent geochemical modelling packages: PHREEQC [Parkhurst and Apello, 1999] (Serco Assurance), PRECIP [Noy, 1990] (British Geological Survey) and CRUNCH [Steefel, 2001] (SCK-CEN). However, the general approach was similar in the three cases. Overall, this work has shown that it is possible to model the experiments to reproduce the main features seen on the correct time scales using simple models of plausible mechanisms. Similar conclusions have been reached from work using three different geochemical modelling programs, although the approaches differ in the detail of the assumptions examined. It is likely that the mechanisms are more complicated than the ones considered here and that some assumptions made may require modification. (authors)
The effect of advection at luminosities close to Eddington: The ULX in M 31
O. Straub; C. Done; M. Middleton
2013-01-01
The transient, ultra-luminous X-ray source CXOM31 J004253.1+411422 in the Andromeda galaxy is most likely a 10 solar mass black hole, with super-Eddington luminosity at its peak. The XMM-Newton spectra taken during the decline then trace luminosities of 0.86−0.27 LEdd. These spectra are all dominate
Directory of Open Access Journals (Sweden)
Libor Kukačka
2012-01-01
The quadrant analysis is applied to the synchronized signals of velocity and concentration fluctuation to determine events with the dominant contribution to the momentum flux and turbulent scalar flux.
Advection/Diffusion of Large-Scale B-Field in Accretion Disks
Lovelace, R V E; Bisnovatyi-Kogan, G S
2009-01-01
Activity of the nuclei of galaxies and stellar mass systems involving disk accretion to black holes is thought to be due to (1) a small-scale turbulent magnetic field in the disk (due to the magneto-rotational instability or MRI) which gives a large viscosity enhancing accretion, and (2) a large-scale magnetic field which gives rise to matter outflows and/or electromagnetic jets from the disk which also enhances accretion. An important problem with this picture is that the enhanced viscosity is accompanied by an enhanced magnetic diffusivity which acts to prevent the build up of a significant large-scale field. Recent work has pointed out that the disk's surface layers are non-turbulent and thus highly conducting (or non-diffusive) because the MRI is suppressed high in the disk where the magnetic and radiation pressures are larger than the thermal pressure. Here, we calculate the vertical ($z$) profiles of the stationary accretion flows (with radial and azimuthal components), and the profiles of the large-sca...
Global warming in a coupled climate model including oceanic eddy-induced advection
Hirst, Anthony C.; Gordon, Hal B.; O'Farrell, Siobhan P.
The Gent and McWilliams (GM) parameterization for large-scale water transport caused by mesoscale oceanic eddies is introduced into the oceanic component of a global coupled ocean-atmosphere model. Parallel simulations with and without the GM scheme are performed to examine the effect of this parameterization on model behavior under constant atmospheric CO2 and on the model response to increasing CO2. The control (constant CO2) runs show substantial differences in the oceanic stratification and extent of convection, similar to differences found previously using uncoupled ocean models. The transient (increasing CO2) runs show moderate differences in the rate of oceanic heat sequestration (less in the GM case), as expected based on passive tracer uptake studies. However, the surface warming is weaker in the GM case, especially over the Southern Ocean, which is contrary to some recent supposition. Reasons for the reduced warming in the GM case are discussed.
Mass transfer through clay by diffusion and advection: description of INTRAVAL Test Case 1a
International Nuclear Information System (INIS)
UK Nirex Ltd is planning the development of a deep geological repository for the disposal of solid low-level and intermediate-level radioactive waste. The rock surrounding such a waste repository is an important barrier restricting the return of radionuclides in the waste to Man's environment. It is important to validate the models used in Safety assessments of such a repository. The international INTRAVAL project is specifically concerned with the validation of models used to describe the transport of radionuclides through the geosphere. INTRAVAL was initiated by the Swedilsh Nuclear Power Inspectorate (SKI) in 1987. The format of the INTRAVAL project is that there are a number of test cases based on well characterized experiments. There is a mixture of laboratory and field experiments and natural analogues. In the first phase of the project there are 14 test cases. This report describes Test Case 1a, which is concerned with laboratory experiments on clay. The experimental techniques and the results of the experiments on which the INTRAVAL analysis is carried out are described. (author)
Spectral Properties of a Two Component and Two Temperature Advective Flow
Mandal, S; Mandal, Samir; Chakrabarti, Sandip K.
2005-01-01
Low angular momentum accretion flows very often have centrifugal pressure supported standing shock waves which can accelerate flow particles. The accelerated particles in turn emit synchrotron radiation in presence of magnetic fields. Efficient cooling of the electrons reduces its temperature in comparison to the protons. In this paper, we assume two temperature flows to explore this property of shocks and present an example of the emitted radiation spectrum.
Signatures of Accretion Shocks in Broadband Spectrum of Advective Flows Around Black Holes
Mandal, S; Mandal, Samir; Chakrabarti, Sandip K.
2005-01-01
We compute the effects of the centrifugal pressure supported shock waves on the emitted spectrum from an accretion disk primarily consisting of low angular momentum matter. Electrons are very efficiently accelerated by the accretion shock and acquire power-law distribution. The accelerated particles in turn emit synchrotron radiation in presence of a stochastic magnetic field in equipartition with the gas. Efficient cooling of the electrons by these soft photons reduces its temperature in comparison to the protons. We explore the nature of the broadband spectra by using Comptonization, bremsstrahlung and synchrotron emission. We then show that there could be two crossing points in a broadband spectrum, one near $\\sim 10 keV$ and the other $\\sim 300-400$KeV.
Advection of the salt wedge and evolution of the internal flow structure in the Rotterdam Waterway
De Nijs, M.A.J.; Pietrzak, J.D.; Winterwerp, J.C.
2011-01-01
An analysis of field measurements recorded over a tidal cycle in the Rotterdam Waterway is presented. These measurements are the first to elucidate the processes influencing the along-channel current structure and the excursion of the salt wedge in this estuary. The salt wedge structure remained sta
Zaramella, M.; Marion, A.; Lewandowski, J.; Nützmann, G.
2016-07-01
Solute transport in rivers is controlled by surface flow hydrodynamics and by transient storage in dead zones, pockets of vegetation and hyporheic sediments where mass exchange and retention are governed by complex mechanisms. The physics of these processes are generally investigated by optimization of transient storage models (TSMs) to experimental data often yielding inconsistent and equifinal parameter sets. Uncertainty on parameters estimation is found to depend not only on the rates of exchange between the stream and storage zones, the stream-water velocity and the stream reach length according to the experimental Damkohler number (DaI), but also on the relative significance between transient storage and longitudinal dispersion on breakthrough curves (BTCs). An optimization strategy was developed and applied to an experimental dataset obtained from tracer tests in a small lowland river, analyzing BTCs generated through tracer injections under different conditions. The method supplies a tool to estimate model parameters from observed data through the analysis of the relative parameter significance. To analyze model performance a double compartment TSM was optimized by a regular fit procedure based on simple root mean square error minimization and by a fit based on a relative significance analysis of mechanism signatures. As a result consistent longitudinal dispersion and transient storage parameters were obtained when the signature targeted optimization was used.
Song, Helen; Bringer, Michelle R; Tice, Joshua D; Gerdts, Cory J; Ismagilov, Rustem F
2003-12-01
This letter describes an experimental test of a simple argument that predicts the scaling of chaotic mixing in a droplet moving through a winding microfluidic channel. Previously, scaling arguments for chaotic mixing have been described for a flow that reduces striation length by stretching, folding, and reorienting the fluid in a manner similar to that of the baker's transformation. The experimentally observed flow patterns within droplets (or plugs) resembled the baker's transformation. Therefore, the ideas described in the literature could be applied to mixing in droplets to obtain the scaling argument for the dependence of the mixing time, t~(aw/U)log(Pe), where w [m] is the cross-sectional dimension of the microchannel, a is the dimensionless length of the plug measured relative to w, U [m s(-1)] is the flow velocity, Pe is the Péclet number (Pe=wU/D), and D [m(2)s(-1)] is the diffusion coefficient of the reagent being mixed. Experiments were performed to confirm the scaling argument by varying the parameters w, U, and D. Under favorable conditions, submillisecond mixing has been demonstrated in this system.
Uncertainties in the CO2 buget associated to boundary layer dynamics and CO2-advection
Kaikkonen, J.P.; Pino, D.; Vilà-Guerau de Arellano, J.
2012-01-01
The relationship between boundary layer dynamics and carbon dioxide (CO2) budget in the convective boundary layer (CBL) is investigated by using mixed-layer theory. We derive a new set of analytical relations to quantify the uncertainties on the estimation of the bulk CO2 mixing ratio and the inferr
Digital Repository Service at National Institute of Oceanography (India)
PrasannaKumar, S.; Madhupratap, M.; DileepKumar, M.; Muraleedharan, P.M.; DeSouza, S.N.; Gauns, M.; Sarma, V.V.S.S.
COMMUNICATIONS CURRENT SCIENCE, VOL. 81, NO. 12, 25 DECEMBER 2001 1633 *For correspondence. (e - mail: prasanna@csnio.ren.nic.in) or the style 26 . The stochasticity in such a process can also bring out variations in petal - drop r e sponse...
International Nuclear Information System (INIS)
Document available in extended abstract form only. Fine-grained saturated porous materials can act as a semi-permeable osmotic membrane when exposed to a solute concentration gradient. The ions diffusion is hindered while water movement towards higher concentrations takes place in the semi-permeable membrane. The capacity of the fine-grained porous material to act as a semi permeable osmotic membrane is referred to as the osmotic efficiency (its value is 1 when the membranes is ideal, less than 1 when the membrane is leaky, allowing diffusion). The efficiency to retain ions in solution is dependent on the thickness of the diffuse double layer which itself depends on the solution concentration in the membrane. Clay rich formations have been shown to act as non-ideal semi-permeable membrane. Andra is investigating the Callovo-Oxfordian clay as a host rock for intermediate-level to high-level radioactive waste. In this context, it has been feared that osmotic water flows generated by the release of sodium nitrate salt in high concentrations, out of intermediate radioactive bituminous waste, could induce important over-pressures. The latest would eventually lead to fracturing of the host rock around the waste disposal drifts. The purpose of the present study was to develop a simulation code with the capacity to assess the potential impact of osmosis on: the re-saturation of the waste disposal drifts, the pressure evolution and the solute transport in and around a waste disposal drift. A chemo-osmotic coupled flow and transport model was implemented using the FlexPDE-finite element library. Our model is based on the chemo-osmotic formulation developed by Bader and Kooi, 2005. The model has been extended to highly concentrated solutions based on Pitzer's equation. In order to assess the impact of osmotic flow on the re-saturation time, the model was also designed to allow unsaturated flow modelling. The model configuration consists of an initially unsaturated 2D cylindrical radioactive waste disposal drift surrounded by a saturated Callovo-Oxfordian host rock at its undisturbed hydraulic state. Evolution of saturation of the disposal drift, pressure, osmotic efficiency and concentration were investigated through the analyses of 9 simulation runs with ranges of physical parameters and different release scenarios. The following conclusions could be drawn: - The impact of the variation of the activity coefficient (high concentrated solutions) showed to be negligible in comparison to the impact of Bresler's relationship (= dependency of the efficiency coefficient on the concentration). - Simulated pressure and overpressure are mainly influenced by Bresler's relationship. The assumption of an osmotic efficiency coefficient following Bresler's relationship induces a strong limitation of the over-pressures and limits the impact of salt concentrations above 1 M. - The maximal overpressure expected in the disposal drift is of 98 m (0.96 MPa). Therefore no fracturing of the rock should be feared due to osmotic flow. - Mass limitation of the source is also a factor strongly limiting the osmotic overpressure. The release scenario has therefore a strong impact on the results. - Further experimental studies are needed to assess Bresler's relationship in the Callovo-Oxfordian clay. (authors)
Tesi, Tommaso; Goñi, Miguel A.; Langone, Leonardo; Puig, Pere; Canals, Miquel; Nittrouer, Charles A.; Durrieu De Madron, Xavier; Calafat, Antoni; Palanques, Albert; Heussner, Serge; Davies, Maureen H.; Drexler, Tina M.; Fabres, Joan; Miserocchi, Stefano
2010-01-01
Outcrops of old strata at the shelf edge resulting from erosive gravity-driven flows have been globally described on continental margins. The reexposure of old strata allows for the reintroduction of aged organic carbon (OC), sequestered in marine sediments for thousands of years, into the modern carbon cycle. This pool of reworked material represents an additional source of C-14-depleted organic carbon supplied to the ocean, in parallel with the weathering of fossil organic carbon delivered ...
Rao, A.M.F.; Polerecky, L.; Ionescu, D.; Meysman, F.J.R.; de-Beer, D.
2012-01-01
To investigate diel calcium carbonate (CaCO_{3}) dynamics in permeable coral reef sands, we measured pore-water profiles and fluxes of oxygen (O_{2}), nutrients, pH, calcium (Ca^{2+}), and alkalinity (TA) across the sediment-water interface in sands of different permeability
The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Concl...
Lund-hansen, Lc; Vang, T
2003-01-01
Upwelling of cold. saline, and nutrient rich water was observed in late September 1999 along an east-west transect in the SW Kattegat. The Kattegat forms part of the transitional zone between the high saline North Sea and the low saline Baltic Sea. The upwelling occurred after an extended period of northward flow and eastern winds in the Kattegat, that changed into a southward flow as wind ceased. The upwelling was the result of a combination of high current speeds and bottom topography where...
Wilson, Alicia M.; Woodward, Gwendolyn L.; Savidge, William B.
2016-07-01
Rapid exchange of surface waters and porewaters in shallow sediments has important biogeochemical implications for streams and marine systems alike, but mapping these important reaction zones has been difficult. As a means of bridging the gap between the stream and submarine groundwater discharge communities we suggest that the rapid, transient mixing in this zone be called "hydrodynamic exchange". We then present a new model, MATTSI, which was developed to estimate the timing, depth and magnitude of hydrodynamic exchange below the sediment-water interface by inverting thermal time-series observations. The model uses an effective thermal dispersion term to emulate 3-D hydrodynamic exchange in a 1-D model. The effective dispersion is assumed to decline exponentially below the sediment water interface. Application of the model to a synthetic dataset and two field datasets from 50 km offshore in the South Atlantic Bight shows that exchange events can be clearly identified from thermal data. The model is relatively insensitive to realistic errors in sensor depth and thermal conductivity. Although the datasets tested here were too shallow to fully span the depth of flushing, we were able to estimate the depth of hydrodynamic exchange via sensitivity studies.
International Nuclear Information System (INIS)
Conservation laws in ideal gas dynamics and magnetohydrodynamics (MHD) associated with fluid relabeling symmetries are derived using Noether's first and second theorems. Lie dragged invariants are discussed in terms of the MHD Casimirs. A nonlocal conservation law for fluid helicity applicable for a non-barotropic fluid involving Clebsch variables is derived using Noether's theorem, in conjunction with a fluid relabeling symmetry and a gauge transformation. A nonlocal cross helicity conservation law involving Clebsch potentials, and the MHD energy conservation law are derived by the same method. An Euler–Poincaré variational approach is also used to derive conservation laws associated with fluid relabeling symmetries using Noether's second theorem. (paper)
Digital Repository Service at National Institute of Oceanography (India)
Mandal, R.; Dewangan, P.; Ramprasad, T.; Kumar, B.J.P.; Vishwanath, K.
of ~7° which is about half of the observed decrease in GTG. In addition, the Lachenbruch’s approximate solution was obtained at the seafloor and is applicable only for shallow heat flow probe measurements where the average height of the relief... history of the Indian ocean between India and Australia. Earth and Planetary Science Letters, 47, 131–143. Kaul, N., Rosenberger, A., Villinger, H., 2000. Comparison of measured and BSR-derived heat flow values, Makran accretionary prism, Pakistan...
由海面蒸发波导预报平流海雾的方法%THE WAY TO FORECAST SEA ADVECTION FOG FROM EVAPORATION DUCT
Institute of Scientific and Technical Information of China (English)
郭铁宝
2004-01-01
在实际工作中发现:当雷达探测到海面存在蒸发波导现象时,该区域傍晚或次日出现平流海雾的概率很大,反之,当海面出现平流雾时,海面存在蒸发波导的概率也很大.本文试图阐明二者之间的关系,进而提出一种预报平流海雾的新方法.
International Nuclear Information System (INIS)
This paper deals with the identification of a point source (localization of its position and recovering the history of its time-varying intensity function) that constitutes the right-hand side of the first equation in a system of two coupled 1D linear transport equations. Assuming that the source intensity function vanishes before reaching the final control time, we prove the identifiability of the sought point source from recording the state relative to the second coupled transport equation at two observation points framing the source region. Note that at least one of the two observation points should be strategic. We establish an identification method that uses these records to identify the source position as the root of a continuous and strictly monotonic function. Whereas the source intensity function is recovered using a recursive formula without any need of an iterative process. Some numerical experiments on a variant of the surface water pollution BOD–OD coupled model are presented
Latorre Hidalgo, C.; García, J. L.; Gonzalez, A. L.; Marquet, P. A.
2015-12-01
The coastal Atacama Desert is home to a complex geo-ecosystem supported by fog with multiple atmospheric and oceanic drivers. Fog collectors in place for the last 17 years reveal that monthly fog intensity and amount are significantly linked to the El Niño-Southern Oscillation (ENSO 1+2) with cold (warm) anomalies correlated to increased (decreased) fog (R2 = 0.41). Rainfall, however, can occur during extreme positive ENSO anomalies. Tillandsia landbeckii is an epiarenitic plant common to the coastal Atacama where fog is intercepted by the coastal escarpment between 950-1250 m.a.s.l. These plants possess multiple adaptations to survive exclusively on fog, including the construction of "dune" ecosystems known as "tillandsiales". Buried T. landbeckii layers in such dunes contain a record of past variations of fog over time (dunes can top 3 m in height) and alternating plant and sand layers are readily visible in dune stratigraphy. Stable N isotopes on modern plants and fog indicate that these plants reflect δ15N values of total N dissolved in fog. We measured δ15N values from buried T. landbeckii layers from five different tillandsiales found across c. 50 km the coastal escarpment. The isotope values in these buried plants indicate a prominent c. 8.0 ‰ shift towards more negative δ15N values on average over the last 3,200 years. Based on differences in δ15N between modern and more extensive "paleo" tillandsiales at one of our lowest elevation study sites, we interpret this shift as an increase in available moisture due to increased fog input during the late Holocene. Increased variability in ENSO as well as increased upwelling and southerly winds along the coastal Atacama would explain in part this increase. Clearly, the Atacama tillandsiales have considerable potential for monitoring past and present change of these large-scale ocean-atmosphere systems.
Ohta, Yusaku; Iguchi, Masato
2015-09-01
Data from a dense GNSS network were used to investigate the temporal and spatial development of a volcanic plume during the eruptive event at Sakurajima volcano in Japan on July 24, 2012. We extracted the post-fit phase residuals (PPR) of ionosphere-free linear combinations for each satellite based on the precise point positioning (PPP) approach. Temporal and spatial PPR anomalies clearly detected the movement of the volcanic plume. The maximum height of the crossing points of anomalous PPR paths was determined to be approximately 4000 m. We also compared the estimated wet zenith tropospheric delay with the estimated PPR anomalies, which suggested that we might successfully extract the PPR anomalies caused by the eruptive event. We then compared the PPR with the signal-to-noise ratio (SNR) anomalies. Only the path passing just above the crater showed significant change in the SNR value, suggesting that the volcanic ash and the water vapor within the volcanic plume became separated after reaching a high altitude because of ash fall during the plume's lateral movement. Each of the two observables might reflect different characteristics of the water vapor and volcanic ash.
Directory of Open Access Journals (Sweden)
C. V. Dylmer
2013-03-01
Full Text Available Three marine sediment cores distributed along the Norwegian (MD95-2011, Barents Sea (JM09-KA11-GC, and Svalbard (HH11-134-BC continental margins have been investigated in order to reconstruct changes in the poleward flow of Atlantic Waters (AW and in the nature of upper surface water masses within the eastern Nordic Seas over the last 3000 yr. These reconstructions are based on a limited set of coccolith proxies: the abundance ratio between Emiliania huxleyi and Coccolithus pelagicus, an index of Atlantic vs. Polar-Arctic surface water masses; and Gephyrocapsa muellerae, a drifted coccolith species from the temperate North Atlantic, whose abundance changes are related to variations in the volume transport of the North Atlantic Current and its northernmost extension (the West Spitsbergen Current – WSC off western Svalbard. The entire investigated area, from 66 to 77° N, was affected by an overall increase in volume flow of AW from 3000 cal yr BP to Present. The long-term modulation of westerlies strength and location which are essentially driven by the dominant mode of the North Atlantic Oscillation (NAO, is thought to explain the observed dynamics of poleward AW flow. The same mechanism also reconciles the recorded opposite zonal shifts in the location of the Arctic Front between the area off western Norway and the Barents Sea-eastern Fram Strait region. The Little Ice Age was governed by deteriorating conditions, with Arctic/Polar waters dominating in the surface off western Svalbard and western Barents Sea, possibly associated with both severe sea-ice conditions and a strongly reduced AW volume flow. A sudden short pulse of resumed high WSC flow interrupted this cold spell in eastern Fram Strait from 330 to 410 cal yr BP, with a a magnitude only surpassed by the one which characterizes the Modern Period. Our dataset not only confirms the high amplitude warming of surface waters at the turn of the 19th century off western Svalbard, it also shows that such a warming was primarily induced by an excess volume flow of AW which stands as unprecedented over the last 3000 yr.
1972-01-01
A user's manual is provided for the environmental computer model proposed for the Richmond-Cape Henry Environmental Laboratory (RICHEL) application project for coastal zone land use investigations and marine resources management. The model was developed around the hydrologic cycle and includes two data bases consisting of climate and land use variables. The main program is described, along with control parameters to be set and pertinent subroutines.
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Otto Klemm
2015-11-01
Full Text Available Fog and rain was collected during an 18-day period in January 2011 at Mt. Bamboo, northern Taiwan. Almost 300 hourly fog samples and 16 daily rain samples were taken. One single fog sample (pH 3.17 was influenced by local volcanic activity, otherwise the pH ranged from 3.23 to 6.41 in fog and from 3.59 to 6.31 in rain. All the respective air masses arrived from the northeast, but exhibited two distinct groups: Group_1 had high concentrations of all ions (median interquartile range of total ion concentrations 3200–6200 µeq.·L−1 and low pHs (median 3.52, the respective air masses had travelled over densely populated and industrialized regions of mainland China. Group_2 was from air masses with long travel times over the ocean and relatively low total ion concentrations (80–570 µeq.·L−1 and higher pHs (median 4.80. The cleanest samples are among the cleanest reported in the literature of worldwide fog and rain. In both groups, the pH was governed by the balance of sulfate, nitrate, ammonium, and, in some cases, calcium. The variability of these ions was higher than the variability of 10−pH, which shows that the pH is a rather robust parameter in contrast to its drivers such as non-sea-salt sulfate.
Chacón Rebollo, Tomás
2015-03-01
This paper introduces a variational multi-scale method where the sub-grid scales are computed by spectral approximations. It is based upon an extension of the spectral theorem to non necessarily self-adjoint elliptic operators that have an associated base of eigenfunctions which are orthonormal in weighted L2 spaces. This allows to element-wise calculate the sub-grid scales by means of the associated spectral expansion. We propose a feasible VMS-spectral method by truncation of this spectral expansion to a finite number of modes. We apply this general framework to the convection-diffusion equation, by analytically computing the family of eigenfunctions. We perform a convergence and error analysis. We also present some numerical tests that show the stability of the method for an odd number of spectral modes, and an improvement of accuracy in the large resolved scales, due to the adding of the sub-grid spectral scales.
Monger, Gregg R.; Duncan, Candice Morrison; Brusseau, Mark L.
2014-01-01
A gas-phase tracer test (GTT) was conducted at a landfill in Tucson, AZ, to help elucidate the impact of landfill gas generation on the transport and fate of chlorinated aliphatic volatile organic contaminants (VOCs). Sulfur hexafluoride (SF6) was used as the non-reactive gas tracer. Gas samples were collected from a multiport monitoring well located 15.2 m from the injection well, and analyzed for SF6, CH4, CO2, and VOCs. The travel times determined for SF6 from the tracer test are approxima...
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S. K. Kharol
2011-08-01
Full Text Available The transport of aerosols and pollutants from continental India to the adjoining oceanic areas is a major topic of concern and several experimental campaigns have been conducted over the region focusing on aerosol characteristics and their climate implications. The present study analyzes the spectral aerosol optical depth (AOD variations over Bay of Bengal (BoB during Winter-Integrated Campaign for Aerosols, gases and Radiation Budget (W-ICARB from 27 December 2008 to 30 January 2009 and investigates the influence of the adjoining landmass to the marine aerosol field. High AOD_{500} values (>0.7 occurred over northern BoB due to outflow of aerosols and pollutants from the densely populated Indo-Gangetic Plains (IGP; low AOD_{500} (0.1–0.2 was observed in central and southern BoB, far away from the mainland. The Angstrom exponent "α" was observed to be high (>1.2 near coastal waters, indicating relative abundance of accumulation-mode continental aerosols. On the other hand, over southern BoB its values dropped below ~0.7. National Center for Environmental Prediction (NCEP reanalysis data on winds at 850 and 700 hPa, along with air-mass trajectories calculated using Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT model, suggested transport of continental aerosols from central and northern India over the BoB. On the other hand, when the ship was crossing the eastern BoB, the aerosol loading was strongly affected by air-masses originating from Southeast Asia, causing an increase in AOD and α. Biomass-burning episodes over the region played an important role in the observed aerosol properties. Terra/Aqua Moderate Resolution Imaging Spectroradiometer (MODIS AOD_{550} and cruise measured AOD_{550} showed good agreement (R^{2} = 0.86 and 0.77, respectively over BoB, exhibiting similar AOD and α spatio-temporal variation.
Energy Technology Data Exchange (ETDEWEB)
Kharol, S.K. [Dept. of Space-Govt. of India, Balanagar, Hyderabad (India). Atmospheric Science Section; Dalhousie Univ., Halifax (Canada). Dept. of Physics and Atmospheric Science; Badarinath, K.V.S.; Sharma, A.R.; Gharai, B. [Dept. of Space-Govt. of India, Balanagar, Hyderabad (India). Atmospheric Science Section; Kaskaoutis, D.G. [Sharda Univ., Greater Noida (India). Research and Technology Development Centre
2011-07-01
The transport of aerosols and pollutants from continental India to the adjoining oceanic areas is a major topic of concern and several experimental campaigns have been conducted over the region focusing on aerosol characteristics and their climate implications. The present study analyzes the spectral aerosol optical depth (AOD) variations over Bay of Bengal (BoB) during Winter-Integrated Campaign for Aerosols, gases and Radiation Budget (W-ICARB) from 27 December 2008 to 30 January 2009 and investigates the influence of the adjoining landmass to the marine aerosol field. High AOD{sub 500} values (>0.7) occurred over northern BoB due to outflow of aerosols and pollutants from the densely populated Indo-Gangetic Plains (IGP); low AOD500 (0.1-0.2) was observed in central and southern BoB, far away from the mainland. The Angstrom exponent ''{alpha}'' was observed to be high (>1.2) near coastal waters, indicating relative abundance of accumulation-mode continental aerosols. On the other hand, over southern BoB its values dropped below {proportional_to}0.7. National Center for Environmental Prediction (NCEP) reanalysis data on winds at 850 and 700 hPa, along with airmass trajectories calculated using Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model, suggested transport of continental aerosols from central and northern India over the BoB. On the other hand, when the ship was crossing the eastern BoB, the aerosol loading was strongly affected by air-masses originating from Southeast Asia, causing an increase in AOD and {alpha}. Biomass-burning episodes over the region played an important role in the observed aerosol properties. Terra/Aqua Moderate Resolution Imaging Spectroradiometer (MODIS) AOD550 and cruise measured AOD550 showed good agreement (R{sup 2} =0.86 and 0.77, respectively) over BoB, exhibiting similar AOD and spatiotemporal variation. (orig.)
Energy Technology Data Exchange (ETDEWEB)
Smith, Sharon L.
1999-03-26
Evaluation of the role of continental margins in planetary carbon cycles can be approached in various ways, with the extremes being knowledge generated either by large-scale studies of a few basic characteristics of the carbon cycle of shelves worldwide (comparative approach) or by temporally intensive studies of a few sites selected to typify contrasting processes. Mechanisms of cross-shelf transfer, for example, are presently of great interest and within the US there are at least four differing continental shelf environments in which cross-shelf processes are driven by storms (southern Bering Sea, northeastern US), by jets and eddies (northern California coast), by freshwater runoff (Bering Sea, Gulf of Mexico), and by frontal meanders and filaments of the Gulf Stream (southeastern US). Because the type and magnitude of the physical forcing, and its variability on an annual scale, are fundamental to the response of the carbon cycle, investigation of each of these shelves would offer insight useful to predictive global understanding of the carbon cycle on continental shelves.
Energy Technology Data Exchange (ETDEWEB)
Akamatsu, M. [Kawasaki Heavy Industries, Ltd., Kobe (Japan)
1995-06-25
Time marching methods coupled with a third order upwind TVD scheme are compared from the viewpoints of accuracy, memory requirement and computational cost. The methods examined are the second and the third order Runge-Kutta presented by Shu and Osher, the explicit Euler, the second order Adams-Bashforth, the implicit Euler and the Crank-Nicolson methods. Benchmark problems on time-dependent linear adjective transport are solved using these methods. As a result, the Shu and Osher`s Runge-Kutta methods of the second and the third order are recommended. The explicit Euler method suffers from oversteppning of the gradient due to numerical diffusion with a negative coefficient. The Adams-Bashforth method is inferior to the Runge-Kutta method in accuracy and memory requirement. The Crank-Nicolson method produces solutions as accurate as the Runge-Kutta method, but requires much CPU time due to the nonlinear feature of the TVD flux limiter. 9 refs., 5 figs., 1 tab.
Indian Academy of Sciences (India)
Marina Aloysius; S Sijikumar; S S Prijith; Mannil Mohan; K Parameswaran
2011-04-01
The circulation dynamics of an event marked by the formation of an aerosol cluster off the coast of Maharashtra on April 22, 2006, its southward migration along the Indian west coast with a mean speed of ∼200 km/day and its final dissipation after reaching the end of the peninsula by April 28, 2006 as revealed by MODIS (Moderate Resolution Imaging Spectroradiometer) against the pre-monsoon conditions of April 2006 are examined in this study. The maximum aerosol concentration in the cluster was found getting confined to lower and lower altitudes during its southward movement. The NCEP/NCAR (National Centers for Environmental Prediction/National Center for Atmospheric Research) reanalysis wind field indicates that the atmospheric circulation, especially the horizontal wind convergence is the major factor that guides the formation and the dynamics of the cluster. Fine mode fraction from MODIS suggests that the cluster mainly consists of coarse dust particles. The regional climate model, RegCM3 with an efficient dust generation module simulates the formation and movement of the cluster appreciably well. The simulations which also exhibit the altitudinally descending nature of the cluster during its southward movement confirm the mechanism which governs the cluster dynamics suggested based on MODIS and NCEP/NCAR reanalysis data.
Institute of Scientific and Technical Information of China (English)
黄素珍
2009-01-01
通过指数变换将方程变形,消去方程中的"对流项",再利用反指数变换和待定系数法,构造了求解一维对流扩散方程的一种三层差分格式.采用Von Neumann方法分析了差分格式的稳定性,得到了格式稳定的充分必要条件.
Accretion Disks Around Black Holes Twenty Five Years Later
Chakrabarti, S K
1998-01-01
We study the progress of the theory of accretion disks around black holes in last twenty five years and explain why advective disks are the best bet in explaining varied stationary and non-stationary observations from black hole candidates. We show also that the recently proposed advection dominated flows are incorrect.
Evaluation of a stratiform cloud parameterization for general circulation models
Energy Technology Data Exchange (ETDEWEB)
Ghan, S.J.; Leung, L.R. [Pacific Northwest National Lab., Richland, WA (United States); McCaa, J. [Univ. of Washington, Seattle, WA (United States)
1996-04-01
To evaluate the relative importance of horizontal advection of cloud versus cloud formation within the grid cell of a single column model (SCM), we have performed a series of simulations with our SCM driven by a fixed vertical velocity and various rates of horizontal advection.
The physical statistics analysis of the contributing factors of the low level clouds development
Huseynov, N. Sh.; Malikov, B. M.
2009-04-01
In this article studying of conditions of low level clouds development and applicability of individual predictive factors in prognostic models are considered. In this purposes advective variations of temperature (A), radius of isobars (R), ground pressure Laplasian (P ), horizontal gradient of air pressure (grad P) are calculated. It is shown, that the consideration of advective variations of temperature and humidity, radius of curvature of isobars, ground pressure Laplasian and a vertical movements allows to survey conditions of low clouds development comprehensively. At presence of clouds main values of advective variations of temperature during cold and warm air advections were -0.630Ch and 0.530Ch appropriately. At the above stated conditions main values of advective variation of a dew-point was -0.500Ch and 0.620Ch. At the absence of low clouds main advective variations of temperature and dew-point were -0.150Ch for cold air advection, and -0.030Ch for warm air advection. References: Bruks K., Karuzers N.: Application of statistics in meteorology. Hydrometizdat, 416 pp., Leningrad, 1963. Gruza G.V., Rankova E.Y.: The structural changes of up to date climate // Meteorology and Hydrology, vol. #7, 14-18, Moscow, 1990. Panofsky G.A., Brayer G.V.: Statistical methods in meteorology. Hydrometizdat, 209 pp., Leningrad, 1977.
Uffink, G.J.M.; Elfeki, A.; Dekking, M.; Bruining, J.; Kraaikamp, C.
2011-01-01
In the present study, we examine non-Gaussian spreading of solutes subject to advection, dispersion and kinetic sorption (adsorption/desorption). We start considering the behavior of a single particle and apply a random walk to describe advection/dispersion plus a Markov chain to describe kinetic so
Impact of river discharge on phytoplankton bloom dynamics in eutrophic estuaries: A model study
Liu, B.; de Swart, H.E.
2015-01-01
Field observations in estuaries reveal that phytoplankton blooms are strongly affected by advection processes related to river flow. To gain quantitative insight into this dependence, experiments were performed with a new idealised model that couples physical and biological processes. Advection of p
A systematic method to enforce conservativity on semi-Lagrangian schemes
Cameron, Alexandre
2016-01-01
Semi-Lagrangian schemes have proven to be very efficient to model advection problems. However most semi-Lagrangian schemes are not conservative. Here, a systematic method is introduced in order to enforce the conservative property on a semi-Lagrangian advection scheme. This method is shown to generate conservative schemes with the same linear stability range and the same order of accuracy as the initial advection scheme from which they are derived. We used a criterion based on the column-balance property of the schemes to assess their conservativity property. We show that this approach can be used with large CFL numbers and third order schemes.
Diurnal variability of Synechococcus abundance in Sagami Bay, Japan
Digital Repository Service at National Institute of Oceanography (India)
Mitbavkar, S.; Saino, T.
region (Sagami Bay, Japan) by sampling at fixed intervals vertically across the euphotic zone. Day-to-day variations in physical processes such as mixing, induced by wind, and advective events played an important role in structuring Synechococcus...
Picophytoplankton as tracers of environmental forcing in a tropical monsoonal Bay
Digital Repository Service at National Institute of Oceanography (India)
Mitbavkar, S.; Patil, J.S.; Rajaneesh, K.M.
-PEI (phycoerythrin) throughout the year suggested its ability to tolerate salinity and temperature variations and low light conditions. Synechococcus-PEII appearance toward monsoon end and non-monsoon during high water transparency suggests its tidal advection from...
On the stability of Godunov-projection methods for incompressible flow
Energy Technology Data Exchange (ETDEWEB)
Minion, M.L. [New York Univ., NY (United States)
1996-02-01
An analysis of the stability of certain numerical methods for the linear advection-diffusion equation in two dimensions is performed. The advection-diffusion equation is studied because it is a linearized version of the Navier-Stokes equations, the evolution equation for density in Boussinesq flows, and a simplified form of the equations for bulk thermodynamic temperature and mass fraction in reacting flows. It is found that various methods currently in use which are based on a Crank-Nicholson type temporal discretization utilizing second-order Godunov methods for explicitly calculating advective terms suffer from a time-step restriction which depends on the coefficients of diffusive terms. A simple modification in the computation of the advective derivatives results in a method with a stability condition that is independent of the magnitude of the coefficients of the diffusive terms. 19 refs., 9 figs., 1 tab.
Digital Repository Service at National Institute of Oceanography (India)
Gopalakrishna, V.V.; Johnson, Z.; Salgaonkar, G.; Nisha, K.; Rajan, C.K.; Rao, R.R.
The sea surface salinity (SSS) of the Lakshadweep Sea (LS) shows large seasonal variability due to horizontal advection of low (high) salinity waters from south (north) during winter (summer) monsoon. The measurements made in the LS during...
Digital Repository Service at National Institute of Oceanography (India)
Ramaswamy, V.
. Tropical cyclones and storms, located further away from dust source areas, significantly alter the dispersal pathways of dust plumes raised by other mechanisms. The Northern Bay of Bengal cyclone events are shown to aid advection of dust plumes from...
Seasonal Sea Surface Temperature Asymmetry in the Northwestern Pacific Marginal Seas
Directory of Open Access Journals (Sweden)
Hyeonyeong Kwak
2015-01-01
Full Text Available Sea surface temperature (SST is an important component of climate and weather systems at various time scales. Asymmetric seasonal SST variations in the Northwestern Pacific Marginal Seas (NWPMS are investigated in this study using observation data and numerical model results. The asymmetry in SST seasonal variation is estimated quantitatively and compared with heat advection and surface net heat flux using SST data and atmospheric variables from the European Centre for Medium-Range Weather Forecast (ECMWF. The SST increases faster than it decreases, whereas air temperature increases slowly. Heat advection and surface heat flux were estimated using numerically modeled SST and ocean currents, which contribute to the asymmetry of seasonal SST variations. Heat advection shows good correlation with the SST seasonal variation asymmetry. Model results without currents along the boundary show more symmetrical SST variations. This suggests that heat advection is a prominent cause of asymmetry in the seasonal variation.
Gorsel, van E.; Delpierre, N.; Leuning, R.; Black, A.; Munger, J.W.; Wofsy, S.; Aubinet, M.; Feigenwinter, C.; Beringer, J.; Bonal, D.; Chen, B.; Chen, J.; Clement, R.; Davis, K.J.; Desai, A.R.; Dragoni, D.; Etzold, S.; Grünwald, T.; Gu, L.; Heinesch, B.; Hutyra, L.R.; Jans, W.W.P.; Kutsch, W.; Law, B.E.; Leclerc, Y.; Mammarella, I.; Montagnani, L.; Noormets, A.; Rebmann, C.; Wharton, S.
2009-01-01
Micrometeorological measurements of nighttime ecosystem respiration can be systematically biased when stable atmospheric conditions lead to drainage flows associated with decoupling of air flow above and within plant canopies. The associated horizontal and vertical advective fluxes cannot be measure
Technology and human purpose: the problem of solids transport on the Earth's surface
Directory of Open Access Journals (Sweden)
P. K. Haff
2012-11-01
Full Text Available Displacement of mass of limited deformability ("solids" on the Earth's surface is opposed by friction and (the analog of form resistance – impediments relaxed by rotational motion, self-powering of mass units, and transport infrastructure. These features of solids transport first evolved in the biosphere prior to the emergence of technology, allowing slope-independent, diffusion-like motion of discrete objects as massive as several tons, as illustrated by animal foraging and movement along game trails. However, high-energy-consumption technology powered by fossil fuels required a mechanism that could support fast advective transport of solids, i.e., long-distance, high-volume, high-speed, unidirectional, slope-independent transport across the land surface of materials like coal, containerized fluids, minerals, and economic goods. Pre-technology nature was able to sustain regional- and global-scale advection only in the limited form of piggybacking on geophysical flows of water (river sediment and air (dust. The appearance of a mechanism for sustained advection of solids independent of fluid flows and gravity appeared only upon the emergence of human purpose. Purpose enables solids advection by, in effect, simulating a continuous potential gradient, otherwise lacking, between discrete and widely separated fossil-fuel energy sources and sinks. Invoking purpose as a mechanism in solids advection is an example of the need to import anthropic principles and concepts into the language and methodology of modern Earth system dynamics. As part of the emergence of a generalized solids advection mechanism, several additional transport requirements necessary to the function of modern large-scale technological systems were also satisfied. These include spatially accurate delivery of advected payload, targetability to essentially arbitrarily located destinations (such as cities, and independence of structure of advected payload from transport mechanism. The
Technology and human purpose: the problem of solids transport on the earth's surface
Directory of Open Access Journals (Sweden)
P. K. Haff
2012-05-01
Full Text Available Displacement of mass of limited deformability ("solids" on the Earth's surface is opposed by friction and (the analog of form resistance – impediments relaxed by rotational motion, self-powering of mass units, and transport infrastructure. These features of solids transport first evolved in the biosphere prior to the emergence of technology, allowing slope-independent, diffusion-like motion of discrete objects as massive as several tons, as illustrated by animal foraging and movement along game trails. However, high-energy-consumption technology powered by fossil fuels required a mechanism that could support advective transport of solids, i.e., long-distance, high-volume, high-speed, unidirectional, slope independent transport across the land surface of materials like coal, containerized fluids, and minerals. Pre-technology nature was able to sustain large-scale, long-distance solids advection only in the limited form of piggybacking on geophysical flows of water (river sediment and air (dust. The appearance of a generalized mechanism for advection of solids independent of fluid flows and gravity appeared only upon the emergence of human purpose. Purpose enables solids advection by, in effect, enabling a simulated continuous potential gradient, otherwise lacking, between discrete and widely separated fossil-fuel energy sources and sinks. Invoking purpose as a mechanism in solids advection is an example of the need to import anthropic principles and concepts into the language and methodology of modern Earth system dynamics. As part of the emergence of a generalized solids advection mechanism, several additional transport requirements necessary to the function of modern large-scale technological systems were also satisfied. These include spatially accurate delivery of advected payload, targetability to essentially arbitrarily located destinations (such as cities, and independence of structure of advected payload from transport mechanism. The
Remote sensing of contrails and aircraft altered cirrus clouds
Energy Technology Data Exchange (ETDEWEB)
Palikonda, R.; Nguyen, L.; Garber, D.P.; Smith, W.L. Jr [Analytical Services and Materials, Inc., Hampton, VA (United States); Minnis, P.; Young, D.F. [National Aeronautics and Space Administration, Hampton, VA (United States). Langley Research Center
1997-12-31
Analyses of satellite imagery are used to show that contrails can develop into fully extended cirrus cloud systems. Contrails can be advective on great distances, but would appear to observers as natural cirrus clouds. The conversion of simple contrails into cirrus may help explain the apparent increase of cloudiness over populated areas since the beginning of commercial jet air travel. Statistics describing the typical growth, advection, and lifetime of contrail cirrus is needed to evaluate their effects on climate. (author) 4 refs.
Magnetic method for stimulating transport in fluids
Energy Technology Data Exchange (ETDEWEB)
Martin, James E.; Solis, Kyle J.
2016-10-18
A method for producing mass and heat transport in fluids, wherein the method does not rely on conventional convection, that is, it does not require gravity, a thermal gradient, or a magnetic field gradient. This method gives rise to a unique class of vigorous, field-controllable flow patterns termed advection lattices. The advection lattices can be used to transport heat and/or mass in any desired direction using only magnetic fields.
Numerical study of rotating interstellar clouds: equilibrium and collapse
International Nuclear Information System (INIS)
Equilibrium and collapse of rotating, axisymmetric, idealized interstellar gas clouds is calculated with a 2D hydrodynamics code. The hydrodynamics features an improved angular momentum advection algorithm. Angular momentum is advected consistently with mass by deriving angular momentum fluxes from mass fluxes and the local distribution of specific angular momentum. Local conservation is checked by a graph of mass versus specific angular momentum for the cloud as a whole
Ensslin, Torsten A.; Pfrommer, Christoph; Miniati, Francesco; Subramanian, Kandaswamy
2010-01-01
We investigate the interplay of cosmic ray (CR) propagation and advection in galaxy clusters. Propagation in form of CR diffusion and streaming tends to drive the CR radial profiles towards being flat, with equal CR number density everywhere. Advection of CR by the turbulent gas motions tends to produce centrally enhanced profiles. We assume that the CR streaming velocity is of the order of the sound velocity. This is motivated by plasma physical arguments. The CR streaming is then usually la...
Moiseev, N. Ya.
2011-04-01
An approach to the construction of high-order accurate monotone difference schemes for solving gasdynamic problems by Godunov's method with antidiffusion is proposed. Godunov's theorem on monotone schemes is used to construct a new antidiffusion flux limiter in high-order accurate difference schemes as applied to linear advection equations with constant coefficients. The efficiency of the approach is demonstrated by solving linear advection equations with constant coefficients and one-dimensional gasdynamic equations.
Numerical study of rotating interstellar clouds: equilibrium and collapse
Energy Technology Data Exchange (ETDEWEB)
Norman, M.L.
1980-06-01
Equilibrium and collapse of rotating, axisymmetric, idealized interstellar gas clouds is calculated with a 2D hydrodynamics code. The hydrodynamics features an improved angular momentum advection algorithm. Angular momentum is advected consistently with mass by deriving angular momentum fluxes from mass fluxes and the local distribution of specific angular momentum. Local conservation is checked by a graph of mass versus specific angular momentum for the cloud as a whole.
Design and Validation of Medical Devices for Photothermally Augmented Treatments
Andriani, Rudy Thomas
2014-01-01
*1-Dimensional Advective-Diffusion Model in Porous Media Infusion of therapeutic agents into tissue is makes use of two mass transport modes: advective transport, and molecular diffusion. Bulk infusion into a 0.6% wt agarose phantom was modeled as an infinite, homogenous, and isotropic porous medium saturated with the same solvent used in the infused dye tracer. The source is assumed to be spherical and isotropic with constant flow rate and concentration. The Peclet numberdecreases wit...
James, Andrew I.; Jawitz, James W.; Munoz-Carpena, Rafael
2009-01-01
A model to simulate transport of materials in surface water and ground water has been developed to numerically approximate solutions to the advection-dispersion equation. This model, known as the Transport and Reaction Simulation Engine (TaRSE), uses an algorithm that incorporates a time-splitting technique where the advective part of the equation is solved separately from the dispersive part. An explicit finite-volume Godunov method is used to approximate the advective part, while a mixed-finite element technique is used to approximate the dispersive part. The dispersive part uses an implicit discretization, which allows it to run stably with a larger time step than the explicit advective step. The potential exists to develop algorithms that run several advective steps, and then one dispersive step that encompasses the time interval of the advective steps. Because the dispersive step is computationally most expensive, schemes can be implemented that are more computationally efficient than non-time-split algorithms. This technique enables scientists to solve problems with high grid Peclet numbers, such as transport problems with sharp solute fronts, without spurious oscillations in the numerical approximation to the solution and with virtually no artificial diffusion.
Molins, S.; Mayer, K.
2007-05-01
The unsaturated zone acts as a buffer zone for contaminants on their way to the water table but can also attenuate the emission of contaminants leaving the subsurface environment through the gas phase. A reactive transport model that includes multicomponent gas transport has been developed to investigate the processes that contribute to the generation and attenuation of contaminants in the unsaturated zone. In particular, the model is suitable to study the feedback processes between advective-diffusive gas transport and geochemical reactions. The model is also able to estimate diffusive and advective contributions to gas transport in multicomponent systems. Two model applications are presented that investigate gas transport and reactions in mine tailings and at a site with organic contamination. In mine tailings, atmospheric oxygen transported into the sediment column is consumed in the oxidation of sulfide minerals. Gas volume loss caused by the consumption of atmospheric oxygen drives advective fluxes. In the absence of carbonate minerals, the advective component accounts for 16 % of the net oxygen flux into the column, while, in a carbonate-rich system, advection accounts for 10 % of the net oxygen flux. Dissolution of carbonate minerals has a moderating effect on advective gas transport since carbon dioxide can partially compensate for the depletion of oxygen. At an oil spill site, volatilization and degradation of organic contaminants cause advective and diffusive fluxes of organic vapors away from the source zone. At early stages, volatilization dominates and oxidation of these organic vapors attenuates the emission of contaminants to the atmosphere. The contribution of advection to organic vapor fluxes is significant initially but decreases with time. At later stages, the oil source becomes depleted of its most volatile fraction, and anaerobic degradation of aromatic compounds and heavier n-alkanes results in the production of methane. Up to 15 % of methane
Kim, Seung-Bum; Lee, Tong; Fukumori, Ichiro
2007-01-01
The present study examines processes governing the interannual variation of MLT in the eastern equatorial Pacific.Processes controlling the interannual variation of mixed layer temperature (MLT) averaged over the Nino-3 domain (5 deg N-5 deg S, 150 deg-90 deg W) are studied using an ocean data assimilation product that covers the period of 1993-2003. The overall balance is such that surface heat flux opposes the MLT change but horizontal advection and subsurface processes assist the change. Advective tendencies are estimated here as the temperature fluxes through the domain's boundaries, with the boundary temperature referenced to the domain-averaged temperature to remove the dependence on temperature scale. This allows the authors to characterize external advective processes that warm or cool the water within the domain as a whole. The zonal advective tendency is caused primarily by large-scale advection of warm-pool water through the western boundary of the domain. The meridional advective tendency is contributed to mostly by Ekman current advecting large-scale temperature anomalies through the southern boundary of the domain. Unlike many previous studies, the subsurface processes that consist of vertical mixing and entrainment are explicitly evaluated. In particular, a rigorous method to estimate entrainment allows an exact budget closure. The vertical mixing across the mixed layer (ML) base has a contribution in phase with the MLT change. The entrainment tendency due to the temporal change in ML depth is negligible compared to other subsurface processes. The entrainment tendency by vertical advection across the ML base is dominated by large-scale changes in upwelling and the temperature of upwelling water. Tropical instability waves (TIWs) result in smaller-scale vertical advection that warms the domain during La Nina cooling events. However, such a warming tendency is overwhelmed by the cooling tendency associated with the large-scale upwelling by a factor of
Local quantification of numerically-induced mixing and dissipation
Klingbeil, Knut; Mohammadi-Aragh, Mahdi; Gräwe, Ulf; Burchard, Hans
2016-04-01
The discretisation of the advection terms in transport equations introduces truncation errors in numerical models. These errors are usually associated with spurious diffusion, i.e. numerically-induced mixing of the advected quantities or dissipation of kinetic energy associated with the advection of momentum. Especially the numerically-induced diapycnal mixing part is very problematic for realistic model simulations. Since any diapycnal mixing of temperature and salinity increases the reference potential energy (RPE), numerically-induced mixing is often quantified in terms of RPE. However, this global bulk measure does not provide any information about the local amount of numerically-induced mixing of a single advected quantity. In this talk we will present a recently developed analysis method that quantifies the numerically-induced mixing of a single advected quantity locally (Klingbeil et al., 2014***). The method is based on the local tracer variance decay in terms of variance fluxes associated with the corresponding advective tracer fluxes. Because of its physically sound definition, this analysis method provides a reliable diagnostic tool, e.g., to assess the performance of advection schemes and to identify hotspots of numerically-induced mixing. At these identified positions the model could be adapted in terms of resolution or the applied numerical schemes. In this context we will demonstrate how numerically-induced mixing of temperature and salinity can be substantially reduced by vertical meshes adapting towards stratification. *** Klingbeil, K., M. Mohammadi-Aragh, U. Gräwe, H. Burchard (2014) . Quantification of spurious dissipation and mixing -- Discrete Variance Decay in a Finite-Volume framework. Ocean Modelling. doi:10.1016/j.ocemod.2014.06.001.
Diffusive Barrier and Getter Under Waste Packages VA Reference Design Feature Evaluations
Energy Technology Data Exchange (ETDEWEB)
MacNeil, K.
1999-05-24
This technical document evaluates those aspects of the diffusive barrier and getter features which have the potential for enhancing the performance of the Viability Assessment Reference Design and are also directly related to the key attributes for the repository safety strategy of that design. The effects of advection, hydrodynamic dispersion, and diffusion on the radionuclide migration rates through the diffusive barrier were determined through the application of the one-dimensional, advection/dispersion/diffusion equation. The results showed that because advective flow described by the advection-dispersion equation dominates, the diffusive barrier feature alone would not be effective in retarding migration of radiocuclides. However, if the diffusive barrier were combined with one or more features that reduced the potential for advection, then transport of radionuclides would be dominated by diffusion and their migration from the EBS would be impeded. Apatite was chosen as the getter material used for this report. Two getter configurations were developed, Case 1 and Case 2. As in the evaluation of the diffusive barrier, the effects of advection, hydrodynamic dispersion, and diffusion on the migration of radionuclides through the getter are evaluated. However, in addition to these mechanisms, the one-dimensional advection/dispersion/diffusion model is modified to include the effect of sorption on radionuclide migration rates through the sorptive medium (getter). As a result of sorption, the longitudinal dispersion coefficient, and the average linear velocity are effectively reduced by the retardation factor. The retardation factor is a function of the getter material's dry bulk density, sorption coefficient and moisture content. The results of the evaluation showed that a significant delay in breakthrough through the getter can be achieved if the thickness of the getter barrier is increased.
Large-Scale Mid- and Upper-Tropospheric Vertical Motions and MJO Convective Onset
Powell, Scott; Houze, Robert
2015-04-01
Reanalysis (ERA-Interim) is used to demonstrate that anomalies of large-scale vertical motion with ~30 day variability at Addu City, Maldives, exist to the west of the Indian Ocean prior to the occurrence of widespread, organized convection associated with convectively active Madden-Julian Oscillation (MJO) events during DYNAMO/AMIE. The upward motions are associated with large negative anomalies of 150 hPa velocity potential, extend as low as 700 hPa, and apparently circumnavigate the globe several times. Sustained, widespread, organized convection does not initially develop until 0-2 days after large-scale upper-tropospheric upward motion anomalies arrive over the Indian Ocean. Over low-precipitation regions where they are not reinforced by latent heating, the magnitude of the equatorial anomalies is as large as 0.03 Pa s-1. Using large-scale forcing data derived from a sounding array in conjunction with ground-based radar, typical profiles of environmental heating, vertical motion, and moisture advection are computed for periods prior to those during which deep convection is prevalent and those during which moderately deep cumulonimbi do not form into deep clouds. In both environmental regimes, convection with tops between 3 and 7 km are present. Drying by horizontal advection is also ubiquitous. During periods when moderately deep cumulonimbus do not tend to grow into deep convection, vertical moisture advection is insufficient on the large-scale to overcome drying by horizontal advection. Prior to sustenance of deep convection,vertical advection of moisture in the mid- to upper-troposphere overcomes drying by horizontal advection such that the total (horizontal + vertical) moisture advection throughout the troposphere is positive. In order to do so, upward motion in the middle- and upper-troposphere, in excess of the median by as much as 0.03 Pa s-1, is necessary. The large-scale upward motions connected to equatorially trapped, eastward propagating divergent
Sarhadi Zadeh, Ehsan; Hejazi, Kourosh
2009-11-01
Having two water frontiers, namely (everlasting) Persian Gulf and Oman Sea in the south and Caspian Sea in the north, intense dependence on extracting and exporting oil, especially via marine fleets and ever-increasing development of petrochemical industry, Iran is exposed to severe environmental damages caused by oil and petrochemical industries. This essay investigates how oil spill is diffused and its environmental pollution is spread. The movement of oil spill, and its diffusion in water and its effects on water and the environment has been simulated by developing a Depth-Averaged numerical model and using the Finite Volume method. The existing models are not efficient enough to fulfill current modeling needs. The developed model uses the parameters useful in the advection and diffusion of oil pollutions in a model appropriate for predicting the transport of oil spill. Since the Navier-Stokes Equations play an important role in the advection and diffusion of oil pollutions, it is highly important to choose an appropriate numerical method in the advection and diffusion section. In this essay, choosing the methods used in the advection and diffusion have been emphasized and highly-accurate algorithms has been used in the advection terms. These algorithms are not present in similar models. The resulting equations have been solved using the ADI method. This method solves the unknown parameters with solving a Penta-Diagonal matrix in each time step. It does so without sacrificing the desired precision.
Correlated signals and causal transport in ocean circulation
Jeffress, Stephen
2014-05-01
This paper presents a framework for interpreting the time-lagged correlation of oceanographic data in terms of physical transport mechanisms. Previous studies have inferred aspects of ocean circulation by correlating fluctuations in temperature and salinity measurements at distant stations. Typically, the time-lag of greatest correlation is interpreted as an advective transit time and hence the advective speed of the current. In this paper we relate correlation functions directly to the underlying equations of fluid transport. This is accomplished by expressing the correlation functions in terms of the Green's function of the transport equation. Two types of correlation functions are distinguished: field-forcing correlation and field-field correlation. Their unique relationships to the Green's function are illustrated in two idealized models of geophysical transport: a leaky pipe model and an advective-diffusive model. Both models show that the field-forcing correlation function converges to the Green's function as the characteristic (time or length) scale of forcing autocorrelation decreases. The leaky pipe model provides an explanation for why advective speeds inferred from time-lagged correlations are often less than the speed of the main current. The advective-diffusive model reveals a structural bias in the field-field correlation function when used to estimate transit times.
Institute of Scientific and Technical Information of China (English)
ZHANG Yuhong; DU Yan
2012-01-01
Based on HYbrid Coordinate Ocean Model (HYCOM) assimilation and observations,we analyzed seasonal variability of the salinity budget in the southeastern Arabian Sea (AS) and the southern part of the Bay of Bengal (BOB),as well as water exchange between the two basins.Results show that fresh water flux cannot explain salinity changes in salinity budget of both regions.Oceanic advection decreases salinity in the southeastern AS during the winter monsoon season and increases salinity in the southern BOB during the summer monsoon season.In winter,the Northeast Monsoon Current (NMC) carries fresher water from the BOB westward into the southern AS; this westward advection is confined to 4°-6°N and the upper 180 m south of the Indian peninsula.Part of the less saline water then turns northward,decreasing salinity in the southeastern AS.In summer,the Southwest Monsoon Current (SMC) advects high-salinity water from the AS eastward into the BOB,increasing salinity along its path.This eastward advection of high-salinity water south of the India Peninsula extends southward to 2°N,and the layer becomes shallower than in winter.In addition to the monsoon current,the salinity difference between the two basins is important for salinity advection.
Conceptual model for transport processes in the Culebra Dolomite Member, Rustler Formation
International Nuclear Information System (INIS)
The Culebra Dolomite Member of the Rustler Formation represents a possible pathway for contaminants from the Waste Isolation Pilot Plant underground repository to the accessible environment. The geologic character of the Culebra is consistent with a double-porosity, multiple-rate model for transport in which the medium is conceptualized as consisting of advective porosity, where solutes are carried by the groundwater flow, and fracture-bounded zones of diffusive porosity, where solutes move through slow advection or diffusion. As the advective travel length or travel time increases, the nature of transport within a double-porosity medium changes. This behavior is important for chemical sorption, because the specific surface area per unit mass of the diffusive porosity is much greater than in the advective porosity. Culebra transport experiments conducted at two different length scales show behavior consistent with a multiple-rate, double-porosity conceptual model for Culebra transport. Tracer tests conducted on intact core samples from the Culebra show no evidence of significant diffusion, suggesting that at the core scale the Culebra can be modeled as a single-porosity medium where only the advective porosity participates in transport. Field tracer tests conducted in the Culebra show strong double-porosity behavior that is best explained using a multiple-rate model
Anomalous scaling in a non-Gaussian random shell model for passive scalars
Institute of Scientific and Technical Information of China (English)
2007-01-01
In this paper, we have introduced a shell-model of Kraichnan's passive scalar problem. Different from the original problem, the prescribed random velocity field is non-Gaussian and δ correlated in time, and its introduction is inspired by She and Lév(e)que (Phys. Rev. Lett. 72,336 (1994)). For comparison, we also give the passive scalar advected by the Gaussian random velocity field. The anomalous scaling exponents H(p) of passive scalar advected by these two kinds of random velocities above are determined for structure function with values of p up to 15 by Monte Carlo simulations of the random shell model, with Gear methods used to solve the stochastic differential equations. We find that the H(p) advected by the non-Gaussian random velocity is not more anomalous than that advected by the Gaussian random velocity. Whether the advecting velocity is non-Gaussian or Gaussian, similar scaling exponents of passive scalar are obtained with the same molecular diffusivity.
Institute of Scientific and Technical Information of China (English)
WU; Jiabing; GUAN; Dexin; SUN; Xiaomin; YU; Guirui; ZHAO; X
2005-01-01
Based on analysis of mechanisms causing energy no-closure and nocturnal low fluxes issues for CO2 exchange studies by eddy covariance method, corrections were done with the raw data sets obtained from Changbai Mountains forest flux site, to evaluate the impacts of sonic anemometer tilt, frequency response limitations and advection on estimation of CO2 exchange, respectively. The results show that the planar fit coordinate transforming method is superior to the streamline coordinate transforming method in tilt correction. The latter could cause a systematical underestimation of eddy fluxes relating with the angle of sensor and terrain tilt. The underestimation of CO2 and energy fluxes for frequency response limitations average 3.0% and 2.0% during daytime, respectively, which increase by 9.0% and 5.5% during nighttime, respectively. The corrections of frequency response limitations are closely related to atmospheric stability. The advection loss of CO2 fluxes is dominated by nocturnal vertical advection, which is at least 18% when the horizontal advection is neglected. It is suggested that more work be done to understand the characteristics of horizontal advection and turbulent eddies under a complexcircumstance.
DEFF Research Database (Denmark)
Nielsen, Jesper Ellerbæk; Thorndahl, Søren Liedtke; Rasmussen, Michael R.
2014-01-01
for vector field estimation already known from short-term weather radar nowcasting. However, instead of forecasting the weather radar rainfall, the proposed interpolation method exploits the advection of the rainfall in the interpolation. The interpolated rainfall fields are validated by measurements......The topic of this paper is temporal interpolation of precipitation observed by weather radars. Precipitation measurements with high spatial and temporal resolution are, in general, desired for urban drainage applications. An advection-based interpolation method is developed which uses methods...... at ground level from laser disdrometers. The proposed interpolation method performs better when compared to traditional interpolation of weather radar rainfall where the radar observation is considered constant in time between measurements. It is demonstrated that the advection-based interpolation method...
Mechanism and scaling for convection of isolated structures in nonuniformly magnetized plasmas
DEFF Research Database (Denmark)
Garcia, O.E.; Bian, N.H.; Naulin, V.;
2005-01-01
Large-scale radial advection of isolated structures in nonuniformly magnetized plasmas is investigated. The underlying mechanism considered is due to the nonlinear evolution of interchange motions, without any presumption of plasma sheaths. Theoretical arguments supported by numerical simulations...... structures, compares favorably with recent experimental measurements of radially propagating blob structures in the scrape-off layer of magnetically confined plasmas. (C) 2005 American Institute of Physics.......Large-scale radial advection of isolated structures in nonuniformly magnetized plasmas is investigated. The underlying mechanism considered is due to the nonlinear evolution of interchange motions, without any presumption of plasma sheaths. Theoretical arguments supported by numerical simulations...... reveal an inertial scaling for the radial velocity of isolated structures in the ideal limit. This velocity increases as the square root of the structure size relative to the length scale of the magnetic field. The magnitude of the radial advection velocity, as well as the dynamical evolution of the...
Institute of Scientific and Technical Information of China (English)
SUO LingLing; TAN BenKui; HUANG JiaYou
2009-01-01
This article concerns the temperature anomalies during the high index phase of the northern annual mode for the wintertime from January to March. The response of the zonal and meridional winds and the temperature advection caused by the anomalous horizontal wind are investigated. The results show that both the zonal and meridional winds experience strong anomalies and the temperature advecUon induced by both the anomalous zonal and meridional winds is responsible for the temperature anomalies associated with the high index northern annual mode. The temperature advection induced by the anomalous zonal wind contributes dominantly to the cooling in the Atlantic and the Bering Sea while the temperature advection induced by the anomalous merional wind contributes dominantly the warming in the United States of America and the cooling in southern Europe and Canada. The superposed influences caused the obvious warming in north Eurasia.
Dynamics of three anomalous SST events in the Coral Sea
Schiller, A.; Ridgway, K. R.; Steinberg, C. R.; Oke, P. R.
2009-03-01
Variability of the circulation in the Coral Sea, accompanied by large heat transport anomalies, has the potential to have detrimental impacts on underlying ecosystems, including the Great Barrier Reef. In this study we analyze the dynamics of three events, characterized by extremes in sea-surface temperature, as simulated in an eddy-resolving ocean reanalysis. We show that a cooling in April 1997 results from strong wind anomalies and is supported by vertical and horizontal advective heat losses. A warm event in October 1998 is attributable to a heat gain by horizontal advection. A heat budget of the mixed-layer within a closed box shows that warm anomalies in January 2002 involve a quasi-balance between horizontal advection and vertical entrainment with a large local heat gain through the ocean surface near-shore that apparently caused a coral bleaching event. The dynamics of these extreme events are all quite different, with both local and remote influences.
ANALYSIS OF EXTRATROPICAL TRANSITION OF TROPICAL CYCLONE OVER MAINLAND CHINA
Institute of Scientific and Technical Information of China (English)
朱佩君; 郑永光; 陶祖钰
2003-01-01
Typhoon Winnie (1997) experienced three stages after landfall on China: weakening, transition, and re-intensification. The transition is similar to the "complex transition" model proposed by Matano and Sekioka. During the re-intensification stage, the transformed cyclone developed into a pattern of Shapiro-Keyser Cyclone model. From the diagnosis we can find that the cause of Winnie's transition is the intrusion of cold air from the mid- and upper- troposphere and the warm temperature advection in the lower. Winnie redeveloped after transition,which is the result of three vital factors: the warm temperature advection in the lower troposphere, the divergence on the right side of the upper jet entry and the cyclonic vorticity advection in the upper.
The saturation of SASI by parasitic instabilities
Guilet, Jerome; Foglizzo, Thierry
2009-01-01
The Standing Accretion Shock Instability (SASI) is commonly believed to be responsible for large amplitude dipolar oscillations of the stalled shock during core collapse, potentially leading to an asymmetric supernovae explosion. The degree of asymmetry depends on the amplitude of SASI, which nonlinear saturation mechanism has never been elucidated. We investigate the role of parasitic instabilities as a possible cause of nonlinear SASI saturation. As the shock oscillations create both vorticity and entropy gradients, we show that both Kelvin-Helmholtz and Rayleigh-Taylor types of instabilities are able to grow on a SASI mode if its amplitude is large enough. We obtain simple estimates of their growth rates, taking into account the effects of advection and entropy stratification. In the context of the advective-acoustic cycle, we use numerical simulations to demonstrate how the acoustic feedback can be decreased if a parasitic instability distorts the advected structure. The amplitude of the shock deformation...
Chaotic mixing and fractals in a geophysical jet current
Budyansky, M V; 10.1016/j.cnsns.2006.05.004
2012-01-01
We model Lagrangian lateral mixing and transport of passive scalars in meandering oceanic jet currents by two-dimensional advection equations with a kinematic stream function with a time-dependent amplitude of a meander imposed. The advection in such a model is known to be chaotic in a wide range of the meander's characteristics. We study chaotic transport in a stochastic layer and show that it is anomalous. The geometry of mixing is examined and shown to be fractal-like. The scattering characteristics (trapping time of advected particles and the number of their rotations around elliptical points) are found to have a hierarchical fractal structure as functions of initial particle's positions. A correspondence between the evolution of material lines in the flow and elements of the fractal is established.
International Nuclear Information System (INIS)
This report describes the methods which were used to measure sediment temperatures, conductivity and heat flow at ten stations in the northeast Atlantic. These have yielded data from a total of 53 individual penetrations. Surface heat fluxes are compared to the values predicted by crustal cooling models while sediment temperature profiles are examined for evidence of vertical pore water advection. No thermal evidence was found for advection through sediments in the Great Meteor East study area. However, non-linear temperature profiles may be evidence for rapid pore water advection at several locations within the King's Trough Flank study region. These results are critically assessed in terms of other factors which may give rise to the observed non-linear temperature profiles. (author)
Kinetic modeling of Nernst effect in magnetized hohlraums
Joglekar, A. S.; Ridgers, C. P.; Kingham, R. J.; Thomas, A. G. R.
2016-04-01
We present nanosecond time-scale Vlasov-Fokker-Planck-Maxwell modeling of magnetized plasma transport and dynamics in a hohlraum with an applied external magnetic field, under conditions similar to recent experiments. Self-consistent modeling of the kinetic electron momentum equation allows for a complete treatment of the heat flow equation and Ohm's law, including Nernst advection of magnetic fields. In addition to showing the prevalence of nonlocal behavior, we demonstrate that effects such as anomalous heat flow are induced by inverse bremsstrahlung heating. We show magnetic field amplification up to a factor of 3 from Nernst compression into the hohlraum wall. The magnetic field is also expelled towards the hohlraum axis due to Nernst advection faster than frozen-in flux would suggest. Nonlocality contributes to the heat flow towards the hohlraum axis and results in an augmented Nernst advection mechanism that is included self-consistently through kinetic modeling.
Speed and structure of turbulent fronts in pipe flow
Song, Baofang; Hof, Björn; Avila, Marc
2016-01-01
The dynamics of laminar-turbulent fronts in pipe flow is investigated for Reynolds numbers between Re=1900 and Re=5500 using extensive direct numerical simulations. In this range the flow undergoes a continuous transition from localised puffs to weakly expanding and ultimately to strongly expanding turbulent slugs (Barkley et al. 2015). We here investigate the physical distinction between these two types of slug by analysing time-resolved statistics of their downstream fronts in the frame moving at the bulk turbulent advection speed. While weak fronts travel slower than the bulk turbulent advection speed, implying local relaminarisation, strong fronts travel faster and so feed on the laminar flow ahead. At Re$\\approx$2900 the downstream front speed becomes faster than the advection speed, marking the onset of strong fronts. We argue that large temporal fluctuations of production and dissipation at the laminar-turbulent interface drive the dynamical switches between the two types of front observed up to Re$\\si...
Cvetkovic, V.; Molin, S.
2012-02-01
We present a methodology that combines numerical simulations of groundwater flow and advective transport in heterogeneous porous media with analytical retention models for computing the infection risk probability from pathogens in aquifers. The methodology is based on the analytical results presented in [1,2] for utilising the colloid filtration theory in a time-domain random walk framework. It is shown that in uniform flow, the results from the numerical simulations of advection yield comparable results as the analytical TDRW model for generating advection segments. It is shown that spatial variability of the attachment rate may be significant, however, it appears to affect risk in a different manner depending on if the flow is uniform or radially converging. In spite of the fact that numerous issues remain open regarding pathogen transport in aquifers on the field scale, the methodology presented here may be useful for screening purposes, and may also serve as a basis for future studies that would include greater complexity.
Application of remote sensing in estimating evapotranspiration in the Platte river basin
Blad, B. L.; Rosenberg, N. J.
1976-01-01
A 'resistance model' and a mass transport model for estimating evapotranspiration (ET) were tested on large fields of naturally subirrigated alfalfa. Both models make use of crop canopy temperature data. Temperature data were obtained with an IR thermometer and with leaf thermocouples. A Bowen ratio-energy balance (BREB) model, adjusted to account for underestimation of ET during periods of strong sensible heat advection, was used as the standard against which the resistance and mass transport models were compared. Daily estimates by the resistance model were within 10% of estimates made by the BREB model. Daily estimates by the mass transport model did not agree quite as well. Performance was good on clear and cloudy days and also during periods of non-advection and strong advection of sensible heat. The performance of the mass transport and resistance models was less satisfactory for estimation of fluxes of latent heat for short term periods. Both models tended to overestimate at low LE fluxes.
Puff models for simulation of fugitive radioactive emissions in atmosphere
Energy Technology Data Exchange (ETDEWEB)
Costa, Camila P. da, E-mail: camila.costa@ufpel.edu.b [Universidade Federal de Pelotas (UFPel), RS (Brazil). Inst. de Fisica e Matematica. Dept. de Matematica e Estatistica; Pereira, Ledina L., E-mail: ledinalentz@yahoo.com.b [Universidade do Extremo Sul Catarinense (UNESC), Criciuma, SC (Brazil); Vilhena, Marco T., E-mail: vilhena@pq.cnpq.b [Universidade Federal do Rio Grande do Sul (UFRGS), Porto Alegre, RS (Brazil). Programa de Pos-Graduacao em Engenharia Mecanica; Tirabassi, Tiziano, E-mail: t.tirabassi@isac.cnr.i [Institute of Atmospheric Sciences and Climate (CNR/ISAC), Bologna (Italy)
2009-07-01
A puff model for the dispersion of material from fugitive radioactive emissions is presented. For vertical diffusion the model is based on general techniques for solving time dependent advection-diffusion equation: the ADMM (Advection Diffusion Multilayer Method) and GILTT (Generalized Integral Laplace Transform Technique) techniques. The first one is an analytical solution based on a discretization of the Atmospheric Boundary Layer (ABL) in sub-layers where the advection-diffusion equation is solved by the Laplace transform technique. The solution is given in integral form. The second one is a well-known hybrid method that had solved a wide class of direct and inverse problems mainly in the area of Heat Transfer and Fluid Mechanics and the solution is given in series form. Comparisons between values predicted by the models against experimental ground-level concentrations are shown. (author)
Institute of Scientific and Technical Information of China (English)
WANG Caixia; Paola Malanotte-Rizzoli
2014-01-01
The linkage between physical and biological processes, particularly the effect of the circulation field on the distribution of phytoplankton, is studied by applying a two-dimensional model and an adjoint data assimilation approach to the Gulf of Maine-Georges Bank region. The model results, comparing well with observation data, reveal seasonal and geographic variations of phytoplankton concentration and verify that the seasonal cycles of phytoplankton are controlled by both biological sources and ad-vection processes which are functions of space and time and counterbalance each other. Although advective flux divergences have greater magnitudes on Georges Bank than in the coastal region of the western Gulf of Maine, advection control over phytoplankton concentration is more significant in the coastal region of the western Gulf of Maine. The model results also suggest that the two separated populations in the coastal regions of the western Gulf of Maine and on Georges Bank are self-sustaining.
The Cosmic Battery in Astrophysical Accretion Disks
Contopoulos, Ioannis; Katsanikas, Matthaios
2015-01-01
The aberrated radiation pressure at the inner edge of the accretion disk around an astrophysical black hole imparts a relative azimuthal velocity on the electrons with respect to the ions which gives rise to a ring electric current that generates large scale poloidal magnetic field loops. This is the Cosmic Battery established by Contopoulos and Kazanas in 1998. In the present work we perform realistic numerical simulations of this important astrophysical mechanism in advection-dominated accretion flows-ADAF. We confirm the original prediction that the inner parts of the loops are continuously advected toward the central black hole and contribute to the growth of the large scale magnetic field, whereas the outer parts of the loops are continuously diffusing outward through the turbulent accretion flow. This process of inward advection of the axial field and outward diffusion of the return field proceeds all the way to equipartition, thus generating astrophysically significant magnetic fields on astrophysicall...
Contaminant transport in soils and its significance in the design of waste management facilities
International Nuclear Information System (INIS)
Transport of contaminants in soils is governed by advection, dispersion, geochemical mass transfer and decay in the case of radioactive materials. Advection is the process whereby the contaminant is being carried along by moving water. Dispersion arises from mechanical mixing due to velocity distributions between soil particles and molecular diffusion. Geochemical mass transfer retards the migration because of adsorption and/or precipitation. Decay results in a decrease of contaminant concentrations for radioactive materials. Studies on the effectiveness of a cutoff wall in granular soils beneath a tailings dyke show that the most important parameter is the groundwater flow velocity. It not only controls the advective transport but also directly affects the dispersive component and the attenuation that may be obtained through adsorption and decay
Loubet, Benjamin; Milford, Celia; Sutton, Mark A.; Cellier, Pierre
2001-10-01
Exchange of atmospheric ammonia (NH3) with vegetation is characterized by the juxtaposition of sources and sinks at a landscape level. Such situations lead to a large fraction of the landscape being exposed to local advection effects that if not accounted for, introduce errors in standard micrometeorological measurements of NH3 exchange with the surface. In this study, a simplified dispersion - exchange model for NH3 (Flux Interpretation by Dispersion and Exchange over Short Range, FIDES) is evaluated and used to assess the advection fluxes at 260 m downwind of an isolated pasture, grazed with sheep, using the measurements of a classical three-point NH3 gradient system located on adjacent moorland. The method consists of fitting the measured and modeled concentration profile by adjusting at the same time the emission strength of the local source and the exchange rate of NH3 to the moorland area downwind. A local dispersion and surface exchange model such as FIDES has proved to be a valuable tool to estimate advection corrections, given sound estimates of background NH3 concentrations, source location, and standard meteorological parameters. According to the model results the advection fluxes at the moorland measurement site, at 1.0 m height and 260 m downwind of the grazed pasture, were positive. For 80% of the situations they ranged between 30% and 60% of the vertical flaxes. In stable conditions the advection fluxes were large and more sensitive to the surface exchange parameters. These results demonstrate that if not accounted for, advection fluxes may lead to a severe underestimate of the NH3 deposition to seminatural ecosystems, such as moorland, in the vicinity of ground level agricultural sources.
Modeling two-dimensional reactive transport using a Godunov-mixed finite element method
James, Andrew I.; Jawitz, James W.
2007-05-01
SummaryThe development of a model to simulate transport of materials in variable-depth flows is discussed. The model numerically approximates solutions to the advection-dispersion-reaction equation using a time-splitting technique where the advective, dispersive, and reactive parts of the equation are solved separately. An explicit finite-volume Godunov method is used to approximate the advective part while a hybridized mixed finite element method is used to solve for the dispersive step. A backward Euler method is used to solve the reactive component. Rather than solving each component once at each time step, the advective and reactive steps are fractionally and symmetrically split around the dispersive step, so that half of a reactive and advective step are solved before and after each dispersive step. Since the dispersive step is implicit, but computationally expensive, while the advective step is explicit but has time step constraints, this allows stable and more efficient schemes to be implemented in contrast to non-split or simple time-split algorithms. This technique allows problems with high grid Peclet numbers, such as transport problems with sharp solute fronts, to be solved without oscillations in the solution and with virtually no artificial diffusion. By applying the technique to variable depth flows, a variety of applications to transport and reaction problems in surface water and unconfined aquifers can be undertaken. Numerical results for several non-reactive and reactive transport problems in one- and two-dimensions are presented. Observed convergence rates are up to second-order for these simulations.
A reduced thermodynamic model on the formation of the Nansha warm water
Institute of Scientific and Technical Information of China (English)
CAI Shuqun; GAN Zijun; LI Chiwai; LONG Xiaomin; DONG Danpeng
2004-01-01
A reduced vertically integrated upper mixed layer model is set up to numerically study the thermodynamic process of the formation of the "Nansha warm water"(NWW) in the Nansha Islands sea areas in spring. According to the numerical experiments, it is shown that, in spring, the formation of the NWW is mainly due to the sea surface net heat flux and the local weak current strength; the contribution from temperature advection transport and warm water exchange with the outer seas (Sulu Sea or south of Sunda shelf) is very little. In the sea areas where the current is strong, the advection may also play an important role in the temperature field.
Yoon, Min; Ahn, Junsun; Hwang, Jinyul; Sung, Hyung Jin
2016-08-01
The relationship between the frictional drag and the velocity-vorticity correlations in wall-bounded turbulent flows is derived from the mean vorticity equation. A formula for the skin friction coefficient is proposed and evaluated with regards to three canonical wall-bounded flows: turbulent boundary layer, turbulent channel flow, and turbulent pipe flow. The frictional drag encompasses four terms: advective vorticity transport, vortex stretching, viscous, and inhomogeneous terms. Drag-reduced channel flow with the slip condition is used to test the reliability of the formula. The advective vorticity transport and vortex stretching terms are found to dominate the contributions to the frictional drag.
Solute transport via alternating-direction collocation using the modified method of characteristics
Allen, Myron B.; Khosravani, Azar
We present a finite-element collocation method for modeling underground solute transport in two space dimensions when advection is dominant. The scheme uses a modified method of characteristics to approximate advective terms, thereby reducing the temporal truncation error and allowing accurate transport of solute by the velocity field. In conjunction with this approach, we employ an alternating-direction algorithm to yield a highly parallelizable algorithm for solving two-dimensional problems as sequences of simpler problems having one-dimensional matrix structure.
Teaching Thermal Hydraulics and Numerical Methods: An Introductory Control Volume Primer
International Nuclear Information System (INIS)
This paper covers the basics of the implementation of the control volume method in the context of the Homogeneous Equilibrium Model (HEM)(T/H) code using the conservation equations of mass, momentum, and energy. This primer uses the advection equation as a template. The discussion will cover the basic equations of the control volume portion of the course in the primer, which includes the advection equation, numerical methods, along with the implementation of the various equations via FORTRAN into computer programs and the final result for a three equation HEM code and its validation
A Fully Discrete Galerkin Method for a Nonlinear Space-Fractional Diffusion Equation
Directory of Open Access Journals (Sweden)
Yunying Zheng
2011-01-01
Full Text Available The spatial transport process in fractal media is generally anomalous. The space-fractional advection-diffusion equation can be used to characterize such a process. In this paper, a fully discrete scheme is given for a type of nonlinear space-fractional anomalous advection-diffusion equation. In the spatial direction, we use the finite element method, and in the temporal direction, we use the modified Crank-Nicolson approximation. Here the fractional derivative indicates the Caputo derivative. The error estimate for the fully discrete scheme is derived. And the numerical examples are also included which are in line with the theoretical analysis.
Attraction-Based Computation of Hyperbolic Lagrangian Coherent Structures
Karrasch, Daniel; Haller, George
2014-01-01
Recent advances enable the simultaneous computation of both attracting and repelling families of Lagrangian Coherent Structures (LCS) at the same initial or final time of interest. Obtaining LCS positions at intermediate times, however, has been problematic, because either the repelling or the attracting family is unstable with respect to numerical advection in a given time direction. Here we develop a new approach to compute arbitrary positions of hyperbolic LCS in a numerically robust fashion. Our approach only involves the advection of attracting material surfaces, thereby providing accurate LCS tracking at low computational cost. We illustrate the advantages of this approach on a simple model and on a turbulent velocity data set.
Energy Technology Data Exchange (ETDEWEB)
Bartels, J.; Peters, D. [Rostock Univ. (Germany). Inst. fuer Atmosphaerenphysik
1997-12-31
The poleward advection of upper-tropospheric air is investigated for poleward Rossby wave breaking events. During boreal winter months the isentropic deformations of the tropopause are examined using maps of Ertel`s potential vorticity (EPV) and contour advection (CA) calculations. The role of ambient baro-tropic flow is further examined by idealized numerical models. In the vicinity of the tropopause the characteristic Lagrangian transport of air masses for ECMWF-analysis data are compared with high resolution (T106) ECHAM4 experiments. (author) 3 refs.
Transport of subsurface bacteria in porous media
Energy Technology Data Exchange (ETDEWEB)
Bales, R.C.; Arnold, R.G.; Gerba, C.P.
1995-02-01
The primary objective of this study was to develop tools with which to measure the advective transport of microorganisms through porous media. These tools were then applied to investigate the sorptive properties of representative microorganisms that were selected at random from the DOE`s deep subsurface collection of bacterial, maintained at Florida State University. The transport screening procedure that arose from this study was also used to investigate biological factors that affect the transport/sorption of biocolloids during their movement through porous media with the bulk advective flow.
Gas diffusion, non-darcy air permeability and CT-scans for a traffic-affected clay subsoil
DEFF Research Database (Denmark)
Lamandé, Mathieu; Schjønning, Per; Berisso, Feto Esimo;
2013-01-01
, to what extent the compaction affected the air flow pattern in the macropores. The combination of diffusive and advective gas transport characteristics was expected to enhance the ability to deduce how the soil pore system was affected. This included advective air flow measurements at a range of pneumatic...... pressure drops. Compaction at 50 cm depth was persistent 29 years after the compaction event. Compaction diminished the size of vertical macropores that served as arterial pores, while the volume and role of marginal pores branching from the arterial pores were diminished. Compacted soil had...
DEFF Research Database (Denmark)
Jacobsen, M.W.; Pujolar, J.M.; Gilbert, M.T.P.;
2014-01-01
Processes leading to speciation in oceanic environments without obvious physical barriers remain poorly known. European and American eel (Anguilla anguilla and A. rostrata) spawn in partial sympatry in the Sargasso Sea. Larvae are advected by the Gulf Stream and other currents towards the European......, coinciding with the closure of the Panama Gateway that led to reinforcement of the Gulf Stream. This could have advected larvae towards European/North African coasts, in which case American eel would be expected to be the ancestral species. This scenario could, however, not be unequivocally confirmed...
DEFF Research Database (Denmark)
Riemann, L.; Alfredsson, H.; Hansen, Michael Møller;
2010-01-01
European eels (Anguilla anguilla) undertake spawning migrations of more than 5000 km from continental Europe and North Africa to frontal zones in the Sargasso Sea. Subsequently, the larval offspring are advected by large-scale eastward ocean currents towards continental waters. However, the Sarga......European eels (Anguilla anguilla) undertake spawning migrations of more than 5000 km from continental Europe and North Africa to frontal zones in the Sargasso Sea. Subsequently, the larval offspring are advected by large-scale eastward ocean currents towards continental waters. However...
Excess surface area in bioelectrochemical systems causes ion transport limitations
Harrington, Timothy D.; Babauta, Jerome T.; Davenport, Emily K.; Ryan S Renslow; Beyenal, Haluk
2015-01-01
We investigated ion transport limitations on 3D graphite felt electrodes by growing Geobacter sulfurreducens biofilms with advection to eliminate external mass transfer limitations. We characterized ion transport limitations by: 1) showing that serially increasing NaCl concentration up to 200 mM increased current linearly up to a total of +273% vs. 0 mM NaCl under advective conditions, 2) growing the biofilm with a starting concentration of 200 mM NaCl, which led to a maximum current increase...
Convection-Dominated Accretion Flows with Radiative Cooling
Institute of Scientific and Technical Information of China (English)
LI Shuang-Liang; XUE Li; LU Ju-Fu
2007-01-01
@@ By numerically solving the set of basic equations describing black hole accretion flows with low accretion rates,we show that although the dynamical structure of these flows is essentially unaffected by radiative processes in comparison with the case in which the radiation is not considered, the radiative cooling can be more important than the advective cooling in the flow's convection-dominated zone, and this result may have implications to distinguish observationally convection-dominated accretion flows from advection-dominated accretion flows.
Three-dimensional generalization for W modification of a Godunov method
Vasil'Ev, E. I.; Demin, A. S.
2008-09-01
A high-accuracy modification of Godunov’s method for three-dimensional unsteady ideal gas flows is proposed. For the linear advection equation, a fully three-dimensional second-order accurate monotone scheme is designed with corrections computed on a variable stencil whose orientation depends on the signs of the equation coefficients. For the linear scalar advection equation, the scheme is proved to possess the positive approximation property. The method is tested by computing the flow in a three-dimensional Ludwieg tube with a square cross section.
Piecewise-parabolic methods for astrophysical fluid dynamics
Energy Technology Data Exchange (ETDEWEB)
Woodward, P.R.
1983-11-01
A general description of some modern numerical techniques for the simulation of astrophysical fluid flow is presented. The methods are introduced with a thorough discussion of the especially simple case of advection. Attention is focused on the piecewise-parabolic method (PPM). A description of the SLIC method for treating multifluid problems is also given. The discussion is illustrated by a number of advection and hydrodynamics test problems. Finally, a study of Kelvin-Helmholtz instability of supersonic jets using PPM with SLIC fluid interfaces is presented.
A wavenumber-frequency spectral model for atmospheric boundary layers
International Nuclear Information System (INIS)
Motivated by the need to characterize power fluctuations in wind farms, we study spatio-temporal correlations of a neutral atmospheric boundary layer in terms of the joint wavenumber-frequency spectrum of the streamwise velocity fluctuations. To this end, we perform a theoretical analysis of a simple advection model featuring the advection of small- scale velocity fluctuations by the mean flow and large-scale velocity fluctuations. The model is compared to data from large-eddy simulations (LES). We find that the model captures the trends observed in LES, specifically a Doppler shift of frequencies due to the mean flow as well as a Doppler broadening due to random sweeping effects
Estimating local atmosphere-surface fluxes using eddy covariance and numerical Ogive optimization
Sievers, J.; Papakyriakou, T.; Larsen, S.; Jammet, M. M.; Rysgaard, S.; Sejr, M. K.; Sørensen, L. L.
2014-08-01
Regardless of study type, site topography, homogeneity and large-scale meteorological flows, estimating ecosystem-scale surface-fluxes using the micrometeorological eddy covariance method inevitably leads to questions concerning inclusion or exclusion of advective flux contributions, in providing representative results. For process-oriented studies in which fluxes are linked to local physical parameters and up-scaled through numerical modeling efforts, advection represents a site-specific component which interferes with our ability to isolate local biochemical processes of interest, as represented by turbulent fluxes. Yet, outside of discarding data reflecting excessive advective interference, no method currently exists to disentangle these contributions on flux estimates. Here, we present a novel comprehensive numerical scheme to identify and separate out advective contributions to exchanges in the surface layer. Comparison between the presented method and conventional methodology on observations of sensible heat, latent heat and CO2-fluxes from a number of sites suggests the presence of absolute flux thresholds at |QSENS|=30 Wm-2, |QLAT|=16 Wm-2 and |FCO2|=2.0 μmol m-2 s-1 marking clear shifts in the influence of advection. Above the thresholds, the relative difference of flux estimates δ remained fixed at δ =5-25% suggesting arguably negligible advection influence. Below the thresholds, however, relative difference rises to δSENS=⟨ 51%|88%|225%⟩, δLAT=⟨14%|28%|99%⟩ and δCO2=⟨ 41%|83%|521%⟩, where bracketed values are the 13.6th percentile, 50th percentile (the median) and the 86.4th percentile respectively, suggesting non-negligible relative influence of advection on low flux estimates. The thresholds thus serve as lower limits to local-scale flux resolvability by conventional methodology. The presented method is shown to allow for flux estimation during severe signal disruption and to yield fewer estimates for an enclosed gas analyzer during
DEFF Research Database (Denmark)
Kessler, Adam J.; Glud, Ronnie N.; Cardenas, M. Bayani;
2012-01-01
insight into the coupled hydrodynamic and biogeochemical processes. There was broad agreement between the model results and experimental data. The model showed that the coupling between nitrification and denitrification was relatively weak in comparison to that in cohesive sediments. This was due...... to the direct advective transport between anoxic pore water and the overlying water column, and little interaction between the mostly oxic advective region and the underlying anoxic region. Denitrification was therefore mainly fueled by nitrate supplied from the water column. This suggests that the capacity...
Dynamics of Finite-Size Particles in Chaotic Fluid Flows
Cartwright, Julyan H. E.; Feudel, Ulrike; Károlyi, György; de Moura, Alessandro; Piro, Oreste; Tél, Tamás
We review recent advances on the dynamics of finite-size particles advected by chaotic fluid flows, focusing on the phenomena caused by the inertia of finite-size particles which have no counterpart in traditionally studied passive tracers. Particle inertia enlarges the phase space and makes the advection dynamics much richer than the passive tracer dynamics, because particles' trajectories can diverge from the trajectories of fluid parcels. We cover both confined and open flow regimes, and we also discuss the dynamics of interacting particles, which can undergo fragmentation and coagulation.
Piecewise-parabolic methods for astrophysical fluid dynamics
International Nuclear Information System (INIS)
A general description of some modern numerical techniques for the simulation of astrophysical fluid flow is presented. The methods are introduced with a thorough discussion of the especially simple case of advection. Attention is focused on the piecewise-parabolic method (PPM). A description of the SLIC method for treating multifluid problems is also given. The discussion is illustrated by a number of advection and hydrodynamics test problems. Finally, a study of Kelvin-Helmholtz instability of supersonic jets using PPM with SLIC fluid interfaces is presented
Operator splitting for well-posed active scalar equations
Holden, Helge; Karper, Trygve K
2012-01-01
We analyze operator splitting methods applied to scalar equations with a nonlinear advection operator, and a linear (local or nonlocal) diffusion operator or a linear dispersion operator. The advection velocity is determined from the scalar unknown itself and hence the equations are so-called active scalar equations. Examples are provided by the surface quasi-geostrophic and aggregation equations. In addition, Burgers-type equations with fractional diffusion as well as the KdV and Kawahara equations are covered. Our main result is that the Godunov and Strang splitting methods converge with the expected rates provided the initial data is sufficiently regular.
Targeted mixing in an array of alternating vortices.
Bachelard, R; Benzekri, T; Chandre, C; Leoncini, X; Vittot, M
2007-10-01
Transport and mixing properties of passive particles advected by an array of vortices are investigated. Starting from the integrable case, it is shown that a special class of perturbations allows one to preserve separatrices which act as effective transport barriers, while triggering chaotic advection. In this setting, mixing within the two dynamical barriers is enhanced while long range transport is prevented. A numerical analysis of mixing properties depending on parameter values is performed; regions for which optimal mixing is achieved are proposed. Robustness of the targeted mixing properties regarding errors in the applied perturbation are considered, as well as slip/no-slip and/or boundary conditions for the flow.
Digital Repository Service at National Institute of Oceanography (India)
Mohan, R.; Guptha, M.V.S.
, it is postulated that these corroded specimens of Gr.menardii tests could have been supplied by lateral advection and mixed up with the settling particles at SBBT, thus this assemblage is a resultant of two different sources, during this particular period....
Digital Repository Service at National Institute of Oceanography (India)
Nayak, R.K.
over the one-year period of the JGOFS time-series starting from mid-October 1994 in the central Arabian Sea at (61.5°E & 15.5°N). Atmospheric forcing data are available from the moored array observations (Weller et al. [2]). The horizontal advective...
Time-series of turbulent flow in a pipe measured with PIV
DEFF Research Database (Denmark)
Meyer, Knud Erik; Westerweel, Jerry
1999-01-01
Measurements with particle image velocimetry of the fully developed flow of water in a pipe with a Reynolds number of 5370 are presented. The measurements are taken with a frame rate high enough to capture the same flow structure on 2 or 3 frames. This makes it possible to estimate advection...
Hydrography and water masses in the southeastern Arabian Sea during March-June 2003
Digital Repository Service at National Institute of Oceanography (India)
Shenoi, S.S.C.; Shankar, D.; Michael, G.S.; Kurian, J.; Varma, K.K.; RameshKumar, M.R.; Almeida, A.M.; Unnikrishnan, A.S.; Fernandes, W.A.; Barreto, N; Gnanaseelan, C.; Mathew, R.; Praju, K.V.; Mahale, V.
that the intermittency of the RSW in the eastern Arabian Sea may be due to the occurrence of the RSW even in the northwestern Arabian Sea in the form of patches or lenses (Shapiro et al 1994; Beal et al 2000), which are advected to the northern end of the Indian west...
Diffusive transport in Stokeslet flow and its application to plankton ecology
DEFF Research Database (Denmark)
Thygesen, Uffe Høgsbro; Kiørboe, Thomas
2006-01-01
In this paper we consider the advective/diffusive transport of a solute near a hovering zooplankter. We approximate the fluid flow with that of a Stokeslet, corresponding to the plankter exerting a point force on the water, and assume that the plankter acts as a point source for the transported...
DEFF Research Database (Denmark)
Rosenbrand, Esther; Fabricius, Ida Lykke; Yuan, Hao
2012-01-01
The seasonal imbalance in supply and demand of renewable energy requires seasonal storage, which potentially may be achieved by hot water injection in geothermal aquifers to minimize heat loss by advection. A reduction of porosity and permeability is a risk of heating the rock above the in...
CO2 transport over complex terrain
Sun, Jielun; Burns, Sean P.; Delany, A.C.; Oncley, S.P.; Turnipseed, A.A.; Stephens, B.B.; Lenschow, D.H.; LeMone, M.A.; Monson, Russell K.; Anderson, D.E.
2007-01-01
CO2 transport processes relevant for estimating net ecosystem exchange (NEE) at the Niwot Ridge AmeriFlux site in the front range of the Rocky Mountains, Colorado, USA, were investigated during a pilot experiment. We found that cold, moist, and CO2-rich air was transported downslope at night and upslope in the early morning at this forest site situated on a ???5% east-facing slope. We found that CO2 advection dominated the total CO2 transport in the NEE estimate at night although there are large uncertainties because of partial cancellation of horizontal and vertical advection. The horizontal CO2 advection captured not only the CO2 loss at night, but also the CO2 uptake during daytime. We found that horizontal CO2 advection was significant even during daytime especially when turbulent mixing was not significant, such as in early morning and evening transition periods and within the canopy. Similar processes can occur anywhere regardless of whether flow is generated by orography, synoptic pressure gradients, or surface heterogeneity as long as CO2 concentration is not well mixed by turbulence. The long-term net effect of all the CO2 budget terms on estimates of NEE needs to be investigated. ?? 2007 Elsevier B.V. All rights reserved.
DEFF Research Database (Denmark)
The, Hai Le; Ta, Bao Quoc; Lê Thanh, Hoà;
2015-01-01
advection. The effects of geometric parameters of the TZM on mixing performance are systematically investigated by the Taguchi method and numerical simulations in COMSOL Multiphysics. The number of mixing units, the slope angle of the trapezoidal channel, the height of the constriction element...
Chloride Transport in Undersea Concrete Tunnel
Directory of Open Access Journals (Sweden)
Yuanzhu Zhang
2016-01-01
Full Text Available Based on water penetration in unsaturated concrete of underwater tunnel, a diffusion-advection theoretical model of chloride in undersea concrete tunnel was proposed. The basic parameters including porosity, saturated hydraulic conductivity, chloride diffusion coefficient, initial water saturation, and moisture retention function of concrete specimens with two water-binder ratios were determined through lab-scale experiments. The variation of chloride concentration with pressuring time, location, solution concentration, initial saturation, hydraulic pressure, and water-binder ratio was investigated through chloride transport tests under external water pressure. In addition, the change and distribution of chloride concentration of isothermal horizontal flow were numerically analyzed using TOUGH2 software. The results show that chloride transport in unsaturated concrete under external water pressure is a combined effect of diffusion and advection instead of diffusion. Chloride concentration increased with increasing solution concentration for diffusion and increased with an increase in water pressure and a decrease in initial saturation for advection. The dominant driving force converted with time and saturation. When predicting the service life of undersea concrete tunnel, it is suggested that advection is taken into consideration; otherwise the durability tends to be unsafe.
Spatial Moment Equations for a Groundwater Plume with Degradation and Rate-Limited Sorption
In this note, we analytically derive the solution for the spatial moments of groundwater solute concentration distributions simulated by a one-dimensional model that assumes advective-dispersive transport with first-order degradation and rate-limited sorption. Sorption kinetics...
Directory of Open Access Journals (Sweden)
J. Thuburn
2014-05-01
Full Text Available A new algorithm is presented for the solution of the shallow water equations on quasi-uniform spherical grids. It combines a mimetic finite volume spatial discretization with a Crank–Nicolson time discretization of fast waves and an accurate and conservative forward-in-time advection scheme for mass and potential vorticity (PV. The algorithm is implemented and tested on two families of grids: hexagonal–icosahedral Voronoi grids, and modified equiangular cubed-sphere grids. Results of a variety of tests are presented, including convergence of the discrete scalar Laplacian and Coriolis operators, advection, solid body rotation, flow over an isolated mountain, and a barotropically unstable jet. The results confirm a number of desirable properties for which the scheme was designed: exact mass conservation, very good available energy and potential enstrophy conservation, consistent mass, PV and tracer transport, and good preservation of balance including vanishing ∇ × ∇, steady geostrophic modes, and accurate PV advection. The scheme is stable for large wave Courant numbers and advective Courant numbers up to about 1. In the most idealized tests the overall accuracy of the scheme appears to be limited by the accuracy of the Coriolis and other mimetic spatial operators, particularly on the cubed-sphere grid. On the hexagonal grid there is no evidence for damaging effects of computational Rossby modes, despite attempts to force them explicitly.
Geomagnetic Secular Variation and Its Applications to the Core
DEFF Research Database (Denmark)
Jackson, Andrew; Finlay, Chris
2015-01-01
of physical core processes. These divide themselves into processes associatedwith movement of core fluid, which is capable of advecting the field, and processes associated withthe finite resistivity of the core, commonly termed diffusive processes. We lay the foundations for some of the more theoretical...
Cifani, P.; Michalek, W.R.; Priems, G.J.M.; Kuerten, J.G.M.; Geld, van der C.W.M.; Geurts, B.J.
2016-01-01
In direct numerical simulations of multiphase flows, based on the Volume of Fluid (VOF) approach, the advection of the volume fraction field is a crucial point. The choice of the discretisation scheme for the transport of the volume fraction is decisive for an accurate description of surface dynamic
Phase separation dynamics under stirring
Lacasta Palacio, Ana María; Sancho, Jose Maria; Sagués Mestre, Francesc
1995-01-01
Phase separation dynamics in the presence of externally imposed stirring is stuidied. The stirring is assumed independent of the concentration and it is generated with a well-defined energy spectrum. The domain growth process is either favored or frozen depending on the intensity and correlation length of this advective flow. This behavior is explained by analytical arguments.
Front Speed Enhancement by Incompressible Flows in Three or Higher Dimensions
El Smaily, Mohammad; Kirsch, Stéphane
2014-07-01
We study, in dimensions N ≥ 3, the family of first integrals of an incompressible flow: these are functions whose level surfaces are tangential to the streamlines of the advective incompressible field. One main motivation for this study comes from earlier results proving that the existence of nontrivial first integrals of an incompressible flow q is the main key that leads to a "linear speed up" by a large advection of pulsating traveling fronts solving a reaction-advection-diffusion equation in a periodic heterogeneous framework. The family of first integrals is not well understood in dimensions N ≥ 3 due to the randomness of the trajectories of q and this is in contrast with the case N = 2. By looking at the domain of propagation as a union of different components produced by the advective field, we provide more information about first integrals and we give a class of incompressible flows which exhibit "ergodic components" of positive Lebesgue measure (and hence are not shear flows) and which, under certain sharp geometric conditions, speed up the KPP fronts linearly with respect to the large amplitude. In the proofs, we establish a link between incompressibility, ergodicity, first integrals and the dimension to give a sharp condition about the asymptotic behavior of the minimal KPP speed in terms of the configuration of ergodic components.
Tillman, Fred D.; Smith, James A.
2004-11-01
To determine if an aquifer contaminated with volatile organic compounds (VOCs) has potential for natural remediation, all natural processes affecting the fate and transport of VOCs in the subsurface must be identified and quantified. This research addresses the quantification of air-phase volatile organic compounds (VOCs) leaving the unsaturated zone soil gas and entering the atmosphere—including the additional flux provided by advective soil-gas movement induced by barometric pumping. A simple and easy-to-use device for measuring VOC flux under natural conditions is presented. The vertical flux chamber (VFC) was designed using numerical simulations and evaluated in the laboratory. Mass-balance numerical simulations based on continuously stirred tank reactor equations (CSTR) provided information on flux measurement performance of several sampling configurations with the final chamber configuration measuring greater than 96% of model-simulated fluxes. A laboratory device was constructed to evaluate the flux chamber under both diffusion-only and advection-plus-diffusion transport conditions. The flux chamber measured an average of 82% of 15 diffusion-only fluxes and an average of 95% of 15 additional advection-plus-diffusion flux experiments. The vertical flux chamber has the capability of providing reliable measurement of VOC flux from the unsaturated zone under both diffusion and advection transport conditions.
Aluminium in an ocean general circulation model compared with the West Atlantic Geotraces cruises
van Hulten, M. M. P.; Sterl, A.; Tagliabue, A.; Dutay, J. -C.; Gehlen, M.; de Baar, H. J. W.; Middag, R.
2013-01-01
A model of aluminium has been developed and implemented in an Ocean General Circulation Model (NEMO-PISCES). In the model, aluminium enters the ocean by means of dust deposition. The internal oceanic processes are described by advection, mixing and reversible scavenging. The model has been evaluated
Statistical Properties of Turbulence: An Overview
Pandit, Rahul; Ray, Samriddhi Sankar
2009-01-01
We present an introductory overview of several challenging problems in the statistical characterisation of turbulence. We provide examples from fluid turbulence in three and two dimensions, from the turbulent advection of passive scalars, turbulence in the one-dimensional Burgers equation, and fluid turbulence in the presence of polymer additives.
Implicit and semi-implicit schemes: algorithms
Keppens, R.; Toth, G.; Botchev, M.A.; Ploeg, van der A.
1999-01-01
This study formulates general guidelines to extend an explicit code with a great variety of implicit and semi-implicit time integration schemes. The discussion is based on their specific implementation in the Versatile Advection Code, which is a general purpose software package for solving systems o
Generalized formulation of TVD Lax-Wendroff schemes
Roe, P. L.
1984-01-01
The work of Davis which imports the concept of total variation diminution (TVD) into non-upwinded, Lax-Wendroff type schemes is reformulated in a way which is easier to analyze. The analysis reveals a class of TVD schemes not observed by Davis. Only the case of one dimensional linear advection is treated.
Implicit and semi-implicit schemes: Algorithms
Keppens, R.; Toth, G.; Botchev, M. A.; van der Ploeg, A.
1999-01-01
This study formulates general guidelines to extend an explicit code with a great variety of implicit and semi-implicit time integration schemes. The discussion is based on their specific implementation in the Versatile Advection Code, which is a general purpose software package for solving systems o
Halpern, Laurence; Japhet, Caroline
2010-01-01
We design and analyze a Schwarz waveform relaxation algorithm for domain decomposition of advection-diffusion-reaction problems with strong heterogeneities. The interfaces are curved, and we use optimized Robin or Ventcell transmission conditions. We analyze the semi-discretization in time with Discontinuous Galerkin as well. We also show two-dimensional numerical results using generalized mortar finite elements in space.
Clay membrane made of natural high plasticity clay:
DEFF Research Database (Denmark)
Foged, Niels; Baumann, Jens
1999-01-01
into account advective ion transport as well as diffusion. Clay prospecting for clays rich in smectite has revealed large deposits of Tertiary clay of very high plasticity in the area around Rødbyhavn on the Danish island of Lolland. The natural clay contains 60-75% smectite, dominantly as a sodium...
A modeling study of the processes of surface salinity seasonal cycle in the Bay of Bengal.
Digital Repository Service at National Institute of Oceanography (India)
Akhil, V.P.; Durand, F.; Lengaigne, M.; Vialard, J.; Keerthi, M.G.; Gopalakrishna, V.V.; Deltel, C.; Papa, F.; Montegut, C.deB.
, but by vertical processes that eventually overcome the freshening by southward advection and restore SSS to its premonsoon values. The salinity-stratified barrier layer hence only acts as a “barrier” for vertical heat fluxes, but is associated with intense...
Mixed layer heat budget of Kuroshio-Tango Triangle using satellite and ship observations
Digital Repository Service at National Institute of Oceanography (India)
Pankajakshan, T.; Akiyama, M.; Sugimori, Y.; Wuwa, J.; Okada, Y.; Siripong, A.
heat flux across the air-sea boundary both satellite (NIMBUS-7 SMMR) and ship observations are used. The advective fluxes across the lateral boundaries of the system are derived from sequential images of AVHRR. The net heat divergence of the triangular...