Vertical Structure of Advection-dominated Accretion Flows
NASA Astrophysics Data System (ADS)
Zahra Zeraatgari, Fateme; Abbassi, Shahram
2015-08-01
We solve the set of hydrodynamic equations for optically thin advection-dominated accretion flows by assuming a radially self-similar spherical coordinate system (r,θ ,φ ). The disk is considered to be in steady state and axisymmetric. 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 {τ }rφ component of the viscous stress tensor is assumed, and we have set {v}θ =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 θ direction and reaches its maximum near the rotation axis. Our results also show that, in terms of the no-outflow solution, thermal equilibrium still exists and consequently advection cooling can balance viscous heating.
NASA Astrophysics Data System (ADS)
Wang, Jian-Min; Cheng, Cheng; Li, Yan-Rong
2012-04-01
We investigate the dynamics of clumps embedded in and confined by the advection-dominated accretion flows (ADAFs), in which collisions among the clumps are neglected. We start from the collisionless Boltzmann equation and assume that interaction between the clumps and the ADAF is responsible for transporting the angular momentum of clumps outward. The inner edge of the clumpy-ADAF is set to be the tidal radius of the clumps. We consider strong- and weak-coupling cases, in which the averaged properties of clumps follow the ADAF dynamics and are mainly determined by the black hole potential, respectively. We propose the analytical solution of the dynamics of clumps for the two cases. The velocity dispersion of clumps is one magnitude higher than the ADAF for the strong-coupling case. For the weak-coupling case, we find that the mean radial velocity of clumps is linearly proportional to the coefficient of the drag force. We show that the tidally disrupted clumps would lead to an accumulation of the debris to form a debris disk in the Shakura-Sunyaev regime. The entire hot ADAF will be efficiently cooled down by photons from the debris disk, giving rise to a collapse of the ADAF, and quench the clumpy accretion. Subsequently, evaporation of the collapsed ADAF drives resuscitate of a new clumpy-ADAF, resulting in an oscillation of the global clumpy-ADAF. Applications of the present model are briefly discussed to X-ray binaries, low ionization nuclear emission regions, and BL Lac objects.
Wang Jianmin; Cheng Cheng; Li Yanrong
2012-04-01
We investigate the dynamics of clumps embedded in and confined by the advection-dominated accretion flows (ADAFs), in which collisions among the clumps are neglected. We start from the collisionless Boltzmann equation and assume that interaction between the clumps and the ADAF is responsible for transporting the angular momentum of clumps outward. The inner edge of the clumpy-ADAF is set to be the tidal radius of the clumps. We consider strong- and weak-coupling cases, in which the averaged properties of clumps follow the ADAF dynamics and are mainly determined by the black hole potential, respectively. We propose the analytical solution of the dynamics of clumps for the two cases. The velocity dispersion of clumps is one magnitude higher than the ADAF for the strong-coupling case. For the weak-coupling case, we find that the mean radial velocity of clumps is linearly proportional to the coefficient of the drag force. We show that the tidally disrupted clumps would lead to an accumulation of the debris to form a debris disk in the Shakura-Sunyaev regime. The entire hot ADAF will be efficiently cooled down by photons from the debris disk, giving rise to a collapse of the ADAF, and quench the clumpy accretion. Subsequently, evaporation of the collapsed ADAF drives resuscitate of a new clumpy-ADAF, resulting in an oscillation of the global clumpy-ADAF. Applications of the present model are briefly discussed to X-ray binaries, low ionization nuclear emission regions, and BL Lac objects.
High-speed compressible flow and other advection-dominated problems of fluid dynamics
NASA Technical Reports Server (NTRS)
Zienkiewicz, O. C.; Lohner, R.; Morgan, K.; Peraire, J.
1985-01-01
Finite element methods are described for modeling high speed compressible flows with strong advection, problems important to aerodynamics. The situations are characterized by high pressure and temperature gradients, transients and the appearance of discontinuities, factors which require mesh refinement during computations. Techniques are developed for temporal and spatial discretization of a model problem. Several observations are made regarding the explicit and implicit features of the calculations, the use of the Lax-Wendroff scheme to produce a mass-matrix for obtaining accurate results for transients, methods of performing stability analyses, and simplification techniques. Examples are provided of solving the nonlinear shallow-water equations and describing compressible flows, particularly transonic flows. Domain splitting is defined for improving the calculations at each time step and in different parts of the flow regime while simultaneously advancing the calculations towards a solution.
NASA Astrophysics Data System (ADS)
Le, Truong V.; Wood, Kent S.; Wolff, Michael Thomas; Becker, Peter A.; Putney, Joy; Edge, Elizabeth
2016-01-01
Previously, we have demonstrated that particle acceleration in the vicinity of a shock in an advection-dominated accretion disk can extract enough energy to power a relativistic jet from a supermassive black hole at the center of a radio-loud active galaxy. However, to maintain a steady jet, a stable shock location is required. By employing the Chevalier & Imamura linearization method and the Nakayama instability boundary conditions, we have also shown that there is a region of the energy and angular momentum parameter space in which disk/shocks with outflows can be either stable or unstable. In a region of instability, the velocity profiles that exhibit pre-shock deceleration and pre-shock acceleration are always unstable to the zeroth mode with zero frequency of oscillation. However, in a region of stability, the zeroth mode, the fundamental, and the overtones are all stable for both pre-shock deceleration as well as pre-shock acceleration. Building on this new insight, in this paper, we explore new parameter values in the regions of stability and instability to explain the production of the observed continuous and episodic relativistic outflows (jets) in M87 and Sgr A*, respectively.
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
Cao Xinwu
2010-12-01
The broad-line region (BLR) disappears in many low-luminosity active galactic nuclei (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 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 cannot always 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{sub d,tr} in the sources accreting at slightly lower than the critical rate m-dot{sub crit} (m-dot = M-dot / M-dot{sub Edd}). For the ADAFs with L{sub bol}/L{sub Edd} {approx}> 0.001, 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 or the secondary inner cold disk. It is found that the gas in the outflow far from the ADAF may be efficiently cooled to form BLR clouds due to the soft seed photons emitted from the cold disks, provided the transition radius of the ADAF to the outer cold disk is small [r{sub d,tr} = R{sub d,tr}/(2GM/c {sup 2}) {approx}< 20] or/and the secondary small cold disk has a luminosity L{sub sd} {approx}> 0.003 L{sub Edd}. The BLR clouds can still be formed in the outflows from the outer cold thin disks, if the transition radius r{sub tr} is not very large. For the sources with L{sub bol}/L{sub Edd} {approx}< 0.001, the inner small cold disk is evaporated completely in the ADAF and the outer thin accretion disk may be suppressed by the ADAF, which leads to the disappearance of the BLR. The physical implications of this scenario on the double-peaked broad-line emitters are also
3D Flow Visualization Using Texture Advection
NASA Technical Reports Server (NTRS)
Kao, David; Zhang, Bing; Kim, Kwansik; Pang, Alex; Moran, Pat (Technical Monitor)
2001-01-01
Texture advection is an effective tool for animating and investigating 2D flows. In this paper, we discuss how this technique can be extended to 3D flows. In particular, we examine the use of 3D and 4D textures on 3D synthetic and computational fluid dynamics flow fields.
Chaotic advection in blood flow.
Schelin, A B; Károlyi, Gy; de Moura, A P S; Booth, N A; Grebogi, C
2009-07-01
In this paper we argue that the effects of irregular chaotic motion of particles transported by blood can play a major role in the development of serious circulatory diseases. Vessel wall irregularities modify the flow field, changing in a nontrivial way the transport and activation of biochemically active particles. We argue that blood particle transport is often chaotic in realistic physiological conditions. We also argue that this chaotic behavior of the flow has crucial consequences for the dynamics of important processes in the blood, such as the activation of platelets which are involved in the thrombus formation. PMID:19658798
Clay with Desiccation Cracks is an Advection Dominated Environment
NASA Astrophysics Data System (ADS)
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.
Black Hole Event Horizons and Advection-Dominated Accretion
NASA Technical Reports Server (NTRS)
McClintock, Jeffrey; Mushotzky, Richard F. (Technical Monitor)
2001-01-01
The XMM data on black-hole X-ray novae are only now becoming available and they have so far not been included in any publications. This work is part of a larger project that makes use of both XMM and Chandra data. Our first publication on the Chandra results is the following: "New Evidence for Black Hole Event Horizons from Chandra" by M.R. Garcia, J.E. McClintock, R. Narayan, P. Callanan, D. Barret and S. Murray (2001, ApJ, 553, L47). Therein we present the luminosities of the two black-hole X-ray novae, GRO J0422+22 and 4U1 543-47, which were observed by Chandra. These results are combined with the luminosities of four additional black-hole X-ray novae, which were observed as part of a Chandra GTO program (PI: S. Murray). The very low, but nonzero, quiescent X-ray luminosities of these black hole binaries is very difficult to understand in the context of standard viscous accretion disk theory. The principal result of this work is that X-ray novae that contain black hole primaries are about 100 times fainter that X-ray novae that contain neutron star primaries. This result had been suggested in earlier work, but the present work very firmly establishes this large luminosity difference. The result is remarkable because the black-hole and the neutron-star systems are believed to be similar in many respects. Most importantly, the mass transfer rate from the secondary star is believed to be very comparable for the two kinds of systems for similar orbital periods. The advection-dominated accretion flow (ADAF) model provides a natural framework for understanding the extraordinarily low luminosities of the black hole systems and the hundred-fold greater luminosities of the neutron star systems. The chief feature of an ADAF is that the heat energy in the accreting gas is trapped in the gas and travels with it, rather than being radiated promptly. Thus the accreting gas reaches the central object with a huge amount of thermal energy. If the accretor is a black hole, the
Coupled ensemble flow line advection and analysis.
Guo, Hanqi; Yuan, Xiaoru; Huang, Jian; Zhu, Xiaomin
2013-12-01
Ensemble run simulations are becoming increasingly widespread. In this work, we couple particle advection with pathline analysis to visualize and reveal the differences among the flow fields of ensemble runs. Our method first constructs a variation field using a Lagrangian-based distance metric. The variation field characterizes the variation between vector fields of the ensemble runs, by extracting and visualizing the variation of pathlines within ensemble. Parallelism in a MapReduce style is leveraged to handle data processing and computing at scale. Using our prototype system, we demonstrate how scientists can effectively explore and investigate differences within ensemble simulations. PMID:24051840
Relativistic Outflows from Advection-dominated Accretion Disks around Black Holes
NASA Astrophysics Data System (ADS)
Subramanian, P.; Becker, P. A.
1999-05-01
Advection dominated accretion flows have been recently proposed as attractive models for explaining low luminosity black hole systems. However, the so-called ADAF models suffer from a serious drawback; namely, the accretion flow has a postive Bernoulli parameter, and is therefore gravitationally unbound. Blandford & Begelman (1999, MNRAS) recently proposed advection-dominated flows that incorporate an outflow that carries away an appreciable amount of mass, energy and angular momentum (ADIOS), thereby alleviating this problem. However, their solutions merely assume the existence of such outflows, and do not elaborate on the mechanisms that could drive them. Subramanian, Becker & Kazanas (1999, ApJ, astro-ph/9805044) have described a mechanism whereby particles are accelerated via collisions with magnetic scattering centers (kinks in the tangled magnetic field) embedded in the accreting plasma and form relativistic outflows. We examine the role of this mechanism in the context of Blandford & Begelman's ADIOS solutions with a view to elucidating the physical processes that drive the outflows, which in turn are a crucial component of the overall solution.
Chaotic advection, diffusion, and reactions in open flows
Tel, Tamas; Karolyi, Gyoergy; Pentek, Aron; Scheuring, Istvan; Toroczkai, Zoltan; Grebogi, Celso; Kadtke, James
2000-03-01
We review and generalize recent results on advection of particles in open time-periodic hydrodynamical flows. First, the problem of passive advection is considered, and its fractal and chaotic nature is pointed out. Next, we study the effect of weak molecular diffusion or randomness of the flow. Finally, we investigate the influence of passive advection on chemical or biological activity superimposed on open flows. The nondiffusive approach is shown to carry some features of a weak diffusion, due to the finiteness of the reaction range or reaction velocity. (c) 2000 American Institute of Physics.
Advecting Procedural Textures for 2D Flow Animation
NASA Technical Reports Server (NTRS)
Kao, David; Pang, Alex; Moran, Pat (Technical Monitor)
2001-01-01
This paper proposes the use of specially generated 3D procedural textures for visualizing steady state 2D flow fields. We use the flow field to advect and animate the texture over time. However, using standard texture advection techniques and arbitrary textures will introduce some undesirable effects such as: (a) expanding texture from a critical source point, (b) streaking pattern from the boundary of the flowfield, (c) crowding of advected textures near an attracting spiral or sink, and (d) absent or lack of textures in some regions of the flow. This paper proposes a number of strategies to solve these problems. We demonstrate how the technique works using both synthetic data and computational fluid dynamics data.
MAST solution of advection problems in irrotational flow fields
NASA Astrophysics Data System (ADS)
Aricò, Costanza; Tucciarelli, Tullio
2007-03-01
A new numerical-analytical Eulerian procedure is proposed for the solution of convection-dominated problems in the case of existing scalar potential of the flow field. The methodology is based on the conservation inside each computational elements of the 0th and 1st order effective spatial moments of the advected variable. This leads to a set of small ODE systems solved sequentially, one element after the other over all the computational domain, according to a MArching in Space and Time technique. The proposed procedure shows the following advantages: (1) it guarantees the local and global mass balance; (2) it is unconditionally stable with respect to the Courant number, (3) the solution in each cell needs information only from the upstream cells and does not require wider and wider stencils as in most of the recently proposed higher-order methods; (4) it provides a monotone solution. Several 1D and 2D numerical test have been performed and results have been compared with analytical solutions, as well as with results provided by other recent numerical methods.
THE ADVECTION OF SUPERGRANULES BY THE SUN'S AXISYMMETRIC FLOWS
Hathaway, David H.; Williams, Peter E.; Rosa, Kevin Dela; Cuntz, Manfred E-mail: peter.williams@nasa.go
2010-12-10
We show that the motions of supergranules are consistent with a model in which they are simply advected by the axisymmetric flows in the Sun's surface shear layer. We produce a 10 day series of simulated Doppler images at a 15 minute cadence that reproduces most spatial and temporal characteristics seen in the SOHO/MDI Doppler data. Our simulated data have a spectrum of cellular flows with just two components-a granule component that peaks at spherical wavenumbers of about 4000 and a supergranule component that peaks at wavenumbers of about 110. We include the advection of these cellular components by the axisymmetric flows-differential rotation and meridional flow-whose variations with latitude and depth (wavenumber) are consistent with observations. We mimic the evolution of the cellular pattern by introducing random variations to the phases of the spectral components at rates that reproduce the levels of cross-correlation as functions of time and latitude. Our simulated data do not include any wave-like characteristics for the supergranules yet can reproduce the rotation characteristics previously attributed to wave-like behavior. We find rotation rates which appear faster than the actual rotation rates and attribute this to projection effects. We find that the measured meridional flow does accurately represent the actual flow and that the observations indicate poleward flow to 65{sup 0}-70{sup 0} latitude with equatorward countercells in the polar regions.
Advection-Based Sparse Data Management for Visualizing Unsteady Flow.
Guo, Hanqi; Zhang, Jiang; Liu, Richen; Liu, Lu; Yuan, Xiaoru; Huang, Jian; Meng, Xiangfei; Pan, Jingshan
2014-12-01
When computing integral curves and integral surfaces for large-scale unsteady flow fields, a major bottleneck is the widening gap between data access demands and the available bandwidth (both I/O and in-memory). In this work, we explore a novel advection-based scheme to manage flow field data for both efficiency and scalability. The key is to first partition flow field into blocklets (e.g. cells or very fine-grained blocks of cells), and then (pre)fetch and manage blocklets on-demand using a parallel key-value store. The benefits are (1) greatly increasing the scale of local-range analysis (e.g. source-destination queries, streak surface generation) that can fit within any given limit of hardware resources; (2) improving memory and I/O bandwidth-efficiencies as well as the scalability of naive task-parallel particle advection. We demonstrate our method using a prototype system that works on workstation and also in supercomputing environments. Results show significantly reduced I/O overhead compared to accessing raw flow data, and also high scalability on a supercomputer for a variety of applications. PMID:26356969
Deconvolved spectra of Two Component Advective Flow including jet
NASA Astrophysics Data System (ADS)
Mondal, Santanu; Debnath, Dipak; Chakrabarti, Sandip Kumar
2016-07-01
Outflows and winds are produced when the accretion flows have positive specific energy. Two Component Advective Flow (TCAF) model suggests that the centrifugal pressure supported region of the flow outside the black hole horizon, acts as the base of this outflow. We study the spectral properties of the TCAF which includes a jet component. We consider the jet as a conical in shape which also up-scatters the soft photons from the Keplerian disc. We see that due to the presence of jet component, spectrum become harder as the jet itself behaves like an another Compton cloud above the inner hot corona. We also see how the jet spectra depends on the flow rates. This gives the direct link in timing properties of the X-rays in CENBOL component and the radiation emitted in the jet component.
Implementation of two-component advective flow solution in XSPEC
NASA Astrophysics Data System (ADS)
Debnath, Dipak; Chakrabarti, Sandip K.; Mondal, Santanu
2014-05-01
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 disc 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 disc 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 Goddard Space Flight Center (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 using this model. Most importantly, unlike any other model, we show that TCAF is capable of predicting timing properties from the spectral fits, since in TCAF, a shock is responsible for deciding spectral slopes as well as quasi-periodic oscillation frequencies. L86
Variability of Sub-Canopy Flow, Temperature, and Horizontal Advection in Moderately Complex Terrain
NASA Astrophysics Data System (ADS)
Thomas, Christoph K.
2011-04-01
We examine the space-time structure of the wind and temperature fields, as well as that of the resulting spatial temperature gradients and horizontal advection of sensible heat, in the sub-canopy of a forest with a dense overstorey in moderately complex terrain. Data were collected from a sensor network consisting of ten stations and subject to orthogonal decomposition using the multiresolution basis set and stochastic analyses including two-point correlations, dimensional structure functions, and various other bulk measures for space and time variability. Despite some similarities, fundamental differences were found in the space-time structure of the motions dominating the variability of the sub-canopy wind and temperature fields. The dominating motions occupy similar spatial, but different temporal, scales. A conceptual space-time diagram was constructed based on the stochastic analysis that includes the important end members of the spatial and temporal scales of the observed motions of both variables. Short-lived and small-scale motions govern the variability of the wind, while the diurnal temperature oscillation driven by the surface radiative transfer is the main determinant of the variability in the temperature signal, which occupies much larger time scales. This scale mismatch renders Taylor's hypothesis for sub-canopy flow invalid and aggravates the computation of meaningful estimates of horizontal advective fluxes without dense spatial information. It may further explain the ambiguous and inconclusive results reported in numerous energy and mass balance and advection studies evaluating the hypothesis that accounting for budget components other than the change in storage term and the vertical turbulent flux improves the budget closure when turbulent diffusion is suppressed in plant canopies. Estimates of spatial temperature gradients and advective fluxes were sensitive to the network geometry and the spatial interpolation method. The assumption of linear
The predictability of advection-dominated flux-transport solar dynamo models
Sanchez, Sabrina; Fournier, Alexandre; Aubert, Julien
2014-01-20
Space weather is a matter of practical importance in our modern society. Predictions of forecoming solar cycles mean amplitude and duration are currently being made based on flux-transport numerical models of the solar dynamo. Interested in the forecast horizon of such studies, we quantify the predictability window of a representative, advection-dominated, flux-transport dynamo model by investigating its sensitivity to initial conditions and control parameters through a perturbation analysis. We measure the rate associated with the exponential growth of an initial perturbation of the model trajectory, which yields a characteristic timescale known as the e-folding time τ {sub e}. The e-folding time is shown to decrease with the strength of the α-effect, and to increase with the magnitude of the imposed meridional circulation. Comparing the e-folding time with the solar cycle periodicity, we obtain an average estimate for τ {sub e} equal to 2.76 solar cycle durations. From a practical point of view, the perturbations analyzed in this work can be interpreted as uncertainties affecting either the observations or the physical model itself. After reviewing these, we discuss their implications for solar cycle prediction.
Dynamics of Magnetic Flux Tubes in an Advective Flow around a Black Hole
NASA Astrophysics Data System (ADS)
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.
Fast Coherent Particle Advection through Time-Varying Unstructured Flow Datasets.
Chen, Mingcheng; Shadden, Shawn C; Hart, John C
2016-08-01
Tracing the paths of collections of particles through a flow field is a key step for many flow visualization and analysis methods. When a flow field is interpolated from the nodes of an unstructured mesh, the process of advecting a particle must first find which cell in the unstructured mesh contains the particle. Since the paths of nearby particles often diverge, the parallelization of particle advection quickly leads to incoherent memory accesses of the unstructured mesh. We have developed a new block advection GPU approach that reorganizes particles into spatially coherent bundles as they follow their advection paths, which greatly improves memory coherence and thus shared-memory GPU performance. This approach works best for flows that meet the CFL criterion on unstructured meshes of uniformly sized elements, small enough to fit at least two timesteps in GPU memory. PMID:26353375
Update on Advection-Diffusion Purge Flow Model
NASA Technical Reports Server (NTRS)
Brieda, Lubos
2015-01-01
Gaseous purge is commonly used in sensitive spacecraft optical or electronic instruments to prevent infiltration of contaminants and/or water vapor. Typically, purge is sized using simplistic zero-dimensional models that do not take into account instrument geometry, surface effects, and the dependence of diffusive flux on the concentration gradient. For this reason, an axisymmetric computational fluid dynamics (CFD) simulation was recently developed to model contaminant infiltration and removal by purge. The solver uses a combined Navier-Stokes and Advection-Diffusion approach. In this talk, we report on updates in the model, namely inclusion of a particulate transport model.
Subsurface barrier design alternatives for confinement and controlled advection flow
Phillips, S.J.; Stewart, W.E.; Alexander, R.G.; Cantrell, K.J.; McLaughlin, T.J.
1994-02-01
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.
Carbon dioxide degassing by advective flow from Usu volcano, Japan.
Hernández, P A; Notsu, K; Salazar, J M; Mori, T; Natale, G; Okada, H; Virgili, G; Shimoike, Y; Sato, M; Pérez, N M
2001-04-01
Magmatic carbon dioxide (CO2) degassing has been documented before the 31 March 2000 eruption of Usu volcano, Hokkaido, Japan. Six months before the eruption, an increase in CO2 flux was detected on the summit caldera, from 120 (September 1998) to 340 metric tons per day (September 1999), followed by a sudden decrease to 39 metric tons per day in June 2000, 3 months after the eruption. The change in CO2 flux and seismic observations suggests that before the eruption, advective processes controlled gas migration toward the surface. The decrease in flux after the eruption at the summit caldera could be due to a rapid release of CO2 during the eruption from ascending dacitic dikes spreading away from the magma chamber beneath the caldera. PMID:11292867
A global spectral element model for poisson equations and advective flow over a sphere
NASA Astrophysics Data System (ADS)
Mei, Huan; Wang, Faming; Zeng, Zhong; Qiu, Zhouhua; Yin, Linmao; Li, Liang
2016-03-01
A global spherical Fourier-Legendre spectral element method is proposed to solve Poisson equations and advective flow over a sphere. In the meridional direction, Legendre polynomials are used and the region is divided into several elements. In order to avoid coordinate singularities at the north and south poles in the meridional direction, Legendre-Gauss-Radau points are chosen at the elements involving the two poles. Fourier polynomials are applied in the zonal direction for its periodicity, with only one element. Then, the partial differential equations are solved on the longitude-latitude meshes without coordinate transformation between spherical and Cartesian coordinates. For verification of the proposed method, a few Poisson equations and advective flows are tested. Firstly, the method is found to be valid for test cases with smooth solution. The results of the Poisson equations demonstrate that the present method exhibits high accuracy and exponential convergence. Highprecision solutions are also obtained with near negligible numerical diffusion during the time evolution for advective flow with smooth shape. Secondly, the results of advective flow with non-smooth shape and deformational flow are also shown to be reasonable and effective. As a result, the present method is proved to be capable of solving flow through different types of elements, and thereby a desirable method with reliability and high accuracy for solving partial differential equations over a sphere.
Accretion shock signatures in the spectrum of two-temperature advective flows around black holes
NASA Astrophysics Data System (ADS)
Mandal, S.; Chakrabarti, S. K.
2005-05-01
The 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 caused by standing or oscillating shock waves that accelerate electrons very efficiently and produce a power-law distribution. The accelerated particles in turn emit synchrotron radiation in the presence of the magnetic field. We study the spectral properties of an accretion disk as a function of 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 only consider the stochastic fields and use the ratio of field energy density to gravitational energy density as a parameter. Not surprisingly, stronger fields produce larger humps due to synchrotron radiation. We not only include “conventional” synchrotron emission and Comptonization due to Maxwell-Boltzmann electrons in the gas, but also compute the effects of power-law electrons. For strong shocks, a bump is produced just above the synchrotron self-absorption frequency at ν_bump ˜ ν_inj [1+4/3 {R-1}/{R} {1}/{x_s1/2}]x_s^{1/2}, where, ν_inj is the frequency of the dominant photons from the pre-shock flow, and R the compression ratio of the shock located at x_s. For strong shocks, a bump at a higher frequency appears predominantly due to the power-law electrons formed at the shock front.
NASA Astrophysics Data System (ADS)
Jaunet, V.; Collin, E.; Delville, J.
2016-05-01
This article describes a model obtained by applying proper orthogonal decomposition to the advection equation. The resulting set of equations links the POD modes, their temporal and spatial derivatives and the flow convection velocity. It provides a technique to calculate the convection velocity of coherent structures. It follows, from the model, that a priori knowledge of the convection velocity suffices to construct a dynamical model of the flow. This is demonstrated using experimental data.
Koch, M.
1995-12-31
A new mesh-adaptive 1D collocation technique has been developed to efficiently solve transient advection-dominated transport problems in porous media that are governed by a hyperbolic/parabolic (singularly perturbed) PDE. After spatial discretization a singularly perturbed ODE is obtained which is solved by a modification of the COLNEW ODE-collocation code. The latter also contains an adaptive mesh procedure that has been enhanced here to resolve linear and nonlinear transport flow problems with steep fronts where regular FD and FE methods often fail. An implicit first-order backward Euler and a third-order Taylor-Donea technique are employed for the time integration. Numerical simulations on a variety of high Peclet-number transport phenomena as they occur in realistic porous media flow situations are presented. Examples include classical linear advection-diffusion, nonlinear adsorption, two-phase Buckley-Leverett flow without and with capillary forces (Rapoport-Leas equation) and Burgers` equation for inviscid fluid flow. In most of these examples sharp fronts and/or shocks develop which are resolved in an oscillation-free manner by the present adaptive collocation method. The backward Euler method has some amount of numerical dissipation is observed when the time-steps are too large. The third-order Taylor-Donea technique is less dissipative but is more prone to numerical oscillations. The simulations show that for the efficient solution of nonlinear singularly perturbed PDE`s governing flow transport a careful balance must be struck between the optimal mesh adaptation, the nonlinear iteration method and the time-stepping procedure. More theoretical research is needed with this regard.
Parity properties of an advection dominated solar alpha 2Omega -dynamo
NASA Astrophysics Data System (ADS)
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.
Downes, Barbara J; Lancaster, Jill
2010-01-01
1. In advection-dominated systems (both freshwater and marine), population dynamics are usually presumed to be dominated by the effects of migrants dispersing by advection, especially over the small spatial scales at which populations can be studied, but few studies have tested this presumption. We tested the hypothesis that benthic densities are controlled by densities of dispersers for two aquatic insects in upland streams. 2. Our study animals were two species of caddisflies (Hydropsychidae), which become sedentary filter-feeders following settlement onto substrata. Densities of dispersers in the drift (advective dispersal) were quantified using nets placed along the upstream edges of riffles, where the latter abruptly abutted a slower, upstream run. Settlement was estimated at each site using brick pavers, half of which had been fenced to prevent colonization of their top surfaces by walking hydropsychids, thus allowing us to distinguish also the mode of movement during settlement. 3. First through fifth instars of two species, Smicrophylax sp. AV2 and Asmicridea sp. AV1, were abundant and showed disparate results. Drift and settlement were relatively strongly related for Smicrophylax. The best fit lines were shown by second and third instars settling on plain bricks, suggesting that drift played a strong role in settlement, but that some drifters dropped to the bottom and located substrata by walking. Quantile regression suggested that drift sets limits to settlement in this species and that settlement success was highly variable. In contrast, settlement by Asmicridea was poorly related to drift; settlers were mainly individuals re-dispersing within sites. 4. Smicrophylax densities appear to be controlled by dispersal from upstream, but benthic density of Asmicridea is more likely linked to local demography. Our data demonstrate the dangers of assuming that supposedly drift-prone species can all be modelled in the same way. Alternative models emphasizing
Parity properties of an advection-dominated solar alpha 2 Omega-dynamo
NASA Astrophysics Data System (ADS)
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}).
NASA Astrophysics Data System (ADS)
Maiti, Soumyabrata; Chaudhury, Kaustav; DasGupta, Debabrata; Chakraborty, Suman
2013-01-01
Spatial distributions of particles carried by blood exhibit complex filamentary pattern under the combined effects of geometrical irregularities of the blood vessels and pulsating pumping by the heart. This signifies the existence of so called chaotic advection. In the present article, we argue that the understanding of such pathologically triggered chaotic advection is incomplete without giving due consideration to a major constituent of blood: abundant presence of red blood cells quantified by the hematocrit (HCT) concentration. We show that the hematocrit concentration in blood cells can alter the filamentary structures of the spatial distribution of advected particles in an intriguing manner. Our results reveal that there primarily are two major impacts of HCT concentrations towards dictating the chaotic dynamics of blood flow: changing the zone of influence of chaotic mixing and determining the enhancement of residence time of the advected particles away from the wall. This, in turn, may alter the extent of activation of platelets or other reactive biological entities, bearing immense consequence towards dictating the biophysical mechanisms behind possible life-threatening diseases originating in the circulatory system.
Advective and Conductive Heat Flow Budget Across the Wagner Basin, Northern Gulf of California
NASA Astrophysics Data System (ADS)
Neumann, F.; Negrete-Aranda, R.; Contreras, J.; Müller, C.; Hutnak, M.; Gonzalez-Fernandez, A.; Harris, R. N.; Sclater, J. G.
2015-12-01
In May 2015, we conducted a cruise across the northern Gulf of California, an area of continental rift basin formation and rapid deposition of sediments. The cruise was undertaken aboard the R/V Alpha Helix; our goal was to study variation in superficial conductive heat flow, lateral changes in the shallow thermal conductivity structure, and advective transport of heat across the Wagner basin. We used a Fielax heat flow probe with 22 thermistors that can penetrate up to 6 m into the sediment cover. The resulting data set includes 53 new heat flow measurements collected along three profiles. The longest profile (42 km) contains 30 measurements spaced 1-2 km apart. The western part of the Wagner basin (hanging wall block) exhibit low to normal conductive heat flow whereas the eastern part of the basin (foot wall block) heat flow is high to very high (up to 2500 mWm-2). Two other short profiles (12 km long each) focused on resolving an extremely high heat flow anomaly up to 15 Wm-2 located near the intersection between the Wagner bounding fault system and the Cerro Prieto fault. We hypothesize that the contrasting heat flow values observed across the Wagner basin are due to horizontal water circulation through sand layers and fault pathways of high permeability. Circulation appears to be from west (recharge zone) to east (discharge zone). Additionally, our results reveal strong vertical advection of heat due to dehydration reactions and compaction of fine grained sediments.
Walter, Donald A.; Masterson, John P.
2003-01-01
The U.S. Geological Survey has developed several ground-water models in support of an investigation of ground-water contamination being conducted by the Army National Guard Bureau at Camp Edwards, Massachusetts Military Reservation on western Cape Cod, Massachusetts. Regional and subregional steady-state models and regional transient models were used to (1) improve understanding of the hydrologic system, (2) simulate advective transport of contaminants, (3) delineate recharge areas to municipal wells, and (4) evaluate how model discretization and time-varying recharge affect simulation results. A water-table mound dominates ground-water-flow patterns. Near the top of the mound, which is within Camp Edwards, hydraulic gradients are nearly vertically downward and horizontal gradients are small. In downgradient areas that are further from the top of the water-table mound, the ratio of horizontal to vertical gradients is larger and horizontal flow predominates. The steady-state regional model adequately simulates advective transport in some areas of the aquifer; however, simulation of ground-water flow in areas with local hydrologic boundaries, such as ponds, requires more finely discretized subregional models. Subregional models also are needed to delineate recharge areas to municipal wells that are inadequately represented in the regional model or are near other pumped wells. Long-term changes in recharge rates affect hydraulic heads in the aquifer and shift the position of the top of the water-table mound. Hydraulic-gradient directions do not change over time in downgradient areas, whereas they do change substantially with temporal changes in recharge near the top of the water-table mound. The assumption of steady-state hydraulic conditions is valid in downgradient area, where advective transport paths change little over time. In areas closer to the top of the water-table mound, advective transport paths change as a function of time, transient and steady-state paths
NASA Astrophysics Data System (ADS)
Fulton, P. M.; Brodsky, E. E.; Kano, Y.; Mori, J. J.; Chester, F. M.; Eguchi, N.; Toczko, S.
2013-12-01
In July 2012, the JFAST project (IODP Expedition 343/343T) installed a temperature observatory across the fault that generated the March 2011 Mw9.0 Tohoku earthquake. The observatory consisted of 55 temperature-sensing dataloggers with <0.001°C resolution attached to a rope extending 820 m beneath the seafloor in a fully cased 3.5' inner diameter borehole. Sensor spacing varied from 1.3 to 9 m over the lowermost ~150 m. Most measurements were taken every 10 seconds - 10 minutes depending on the instrument. Ten of the instruments also recorded pressure at <1000 Pa resolution to provide control on sensor depths. The sensor string and data were recovered after a 9-month deployment in April 2013. In addition to monitoring a frictional heat signal across the plate boundary fault from slip during the 11 March 2011 Tohoku Earthquake, signatures of advective fluid flow are observed within a damage zone at shallower depths. These advective signals appear as transient temperature anomalies above the background geotherm and have large spatially-correlative variability suggestive of fluctuations in fluid flow rate. The advective signals also correspond with locations inferred to have high permeability on the basis of prolonged decay time of drilling disturbances. The locations are also consistent with a zone of steeply-dipping open faults or fractures identified by logging data in an adjacent borehole ~30 m away along strike. The plate boundary fault at 818 mbsf inferred to have slipped during the Tohoku Earthquake shows no indication of advective fluid flow or high permeability. On December 7, 2012, in the middle of the experiment, a Mw7.4 earthquake occurred very close to the observatory. While this earthquake occurred at a depth below the plate boundary fault, it had a clear effect on the hydrogeology and temperatures monitored by the observatory. An advective signal observed at 784 mbsf immediately begins to decay following the earthquake and reappears at 763 mbsf with a
Convective dominated flows in open capillary channels
NASA Astrophysics Data System (ADS)
Rosendahl, Uwe; Grah, Aleksander; Dreyer, Michael E.
2010-05-01
This paper is concerned with convective dominated liquid flows in open capillary channels. The channels consist of two parallel plates bounded by free liquid surfaces along the open sides. In the case of steady flow the capillary pressure of the free surface balances the differential pressure between the liquid and the surrounding constant pressure gas phase. A maximum flow rate is achieved when the adjusted volumetric flow rate exceeds a certain limit leading to a collapse of the free surfaces. The convective dominated flow regime is a special case of open capillary flow, since the viscous forces are negligibly small compared with the convective forces. Flows of this type are of peculiar interest since the free surfaces possess a quasisymmetry in the flow direction. This quasisymmetry enables the application of a new effective method for evaluation of the flow limit. The flow limit is caused by a choking effect. This effect is indicated by the speed index, S, which is defined by the ratio of the flow velocity and the longitudinal capillary wave speed. The speed index is defined analogously to Mach number and tends toward unity in the case of flow limitation, i.e., when the maximum flow rate is reached. Utilizing the quasisymmetry, a new approach for a very precise determination of the speed index is presented. This approach uses a new approximation for the curvature of the surfaces by means of the empirical surface profiles. On the basis of empirical and theoretical data, the paper discusses the typical features of the stable flow. The experiments were performed under microgravity aboard the sounding rockets TEXUS 41 and TEXUS 42. The experiment setup enables the approach to the flow limit through either increase in flow rate or channel length. The theoretical data have been gained from numerical solutions of a one-dimensional flow model. The empirical and theoretical results are in good agreement and both confirm the choking effect as cause of the flow limitation
NASA Astrophysics Data System (ADS)
Cartwright, Ian
Advection-dispersion fluid flow models implicitly assume that the infiltrating fluid flows through an already fluid-saturated medium. However, whether rocks contain a fluid depends on their reaction history, and whether any initial fluid escapes. The behaviour of different rocks may be illustrated using hypothetical marble compositions. Marbles with diverse chemistries (e.g. calcite + dolomite + quartz) are relatively reactive, and will generally produce a fluid during heating. By contrast, marbles with more restricted chemistries (e.g. calcite + quartz or calcite-only) may not. If the rock is not fluid bearing when fluid infiltration commences, mineralogical reactions may produce a reaction-enhanced permeability in calcite + dolomite + quartz or calcite + quartz, but not in calcite-only marbles. The permeability production controls the pattern of mineralogical, isotopic, and geochemical resetting during fluid flow. Tracers retarded behind the mineralogical fronts will probably be reset as predicted by the advection-dispersion models; however, tracers that are expected to be reset ahead of the mineralogical fronts cannot progress beyond the permeability generating reaction. In the case of very unreactive lithologies (e.g. pure calcite marbles, cherts, and quartzites), the first reaction to affect the rocks may be a metasomatic one ahead of which there is little pervasive resetting of any tracer. Centimetre-scale layering may lead to the formation of self-perpetuating fluid channels in rocks that are not fluid saturated due to the juxtaposition of reactants. Such layered rocks may show patterns of mineralogical resetting that are not predicted by advection-dispersion models. Patterns of mineralogical and isotopic resetting in marbles from a number of terrains, for example: Chillagoe, Marulan South, Reynolds Range (Australia); Adirondack Mountains, Old Woman Mountains, Notch Peak (USA); and Stephen Cross Quarry (Canada) vary as predicted by these models.
Inverse Comptonization in a Two Component Advective Flow: Results of a Monte Carlo simulation
Ghosh, Himadri; Chakrabarti, S. K.; Laurent, Philippe
2008-10-08
We compute the resultant spectrum due to multiple scattering of soft photons emitted from a Keplerian disk by thermal electrons inside a torus axisymmetrically placed around a black hole. In a two component advective flow model, the post-shock region is similar to a thick accretion disk and the pre-shock sub-keplerian flow is highly optically thin. As a preliminary run of the Monte Carlo simulation of the system, we assume the CENBOL to be a small (2-14r{sub g}) thick accretion disk without a cusp to allow bulk motion of the flow. Bulk Motion Comptonization (BMC) has also been added. We show that the spectral behaviour is very similar to what is predicted in Chakrabarti and Titarchuk (1995)
Dark energy domination in the Virgocentric flow
NASA Astrophysics Data System (ADS)
Chernin, A. D.; Karachentsev, I. D.; Nasonova, O. G.; Teerikorpi, P.; Valtonen, M. J.; Dolgachev, V. P.; Domozhilova, L. M.; Byrd, G. G.
2010-09-01
Context. The standard ΛCDM cosmological model implies that all celestial bodies are embedded in a perfectly uniform dark energy background, represented by Einstein's cosmological constant, and experience its repulsive antigravity action. Aims: Can dark energy have strong dynamical effects on small cosmic scales as well as globally? Continuing our efforts to clarify this question, we now focus on the Virgo Cluster and the flow of expansion around it. Methods: We interpret the Hubble diagram from a new database of velocities and distances of galaxies in the cluster and its environment, using a nonlinear analytical model, which incorporates the antigravity force in terms of Newtonian mechanics. The key parameter is the zero-gravity radius, the distance at which gravity and antigravity are in balance. Results: 1. The interplay between the gravity of the cluster and the antigravity of the dark energy background determines the kinematical structure of the system and controls its evolution. 2. The gravity dominates the quasi-stationary bound cluster, while the antigravity controls the Virgocentric flow, bringing order and regularity to the flow, which reaches linearity and the global Hubble rate at distances ⪆15 Mpc. 3. The cluster and the flow form a system similar to the Local Group and its outflow. In the velocity-distance diagram, the cluster-flow structure reproduces the group-flow structure with a scaling factor of about 10; the zero-gravity radius for the cluster system is also 10 times larger. Conclusions: The phase and dynamical similarity of the systems on the scales of 1-30 Mpc suggests that a two-component pattern may be universal for groups and clusters: a quasi-stationary bound central component and an expanding outflow around it, caused by the nonlinear gravity-antigravity interplay with the dark energy dominating in the flow component.
Anaerobic, Nitrate-Dependent Fe(II) Oxidation Under Advective Flow
NASA Astrophysics Data System (ADS)
Weber, K. A.; Coates, J. D.
2005-12-01
Microbially-catalyzed nitrate-dependent Fe(II) oxidation has been identified as a ubiquitous biogeochemical process contributing to anaerobic iron redox cycling in sedimentary environments. Most probable number enumeration revealed nitrate-dependent Fe(II) oxidizing microbial communities in groundwater and subsurface sediments in the order of 0 - 2.04 x 103 cells mL-1 and 2.39 x 102 - 1.17 x 103 cells (g wet sediment)-1, respectively. The efficacy of nitrate-dependent Fe(II) oxidation under advective flow was evaluated in a meso-scale column reactor packed with sterile low iron sand amended with subsurface sediments collected from the NABIR FRC background field site (10% mass/mass). Continuous flow of minimal medium mimicked the natural groundwater. Periodic FeCl2 and nitrate injections over a period of 49 days resulted in the retention of 95% of the iron (290 mmol). Extraction of solid-phase Fe revealed a net increase in Fe(III) of 160 mmol above background Fe(III) content indicating that 55% of the injected Fe(II) was oxidized. Differential solubility analysis of 0.5M HCl-extractable Fe and 3M HCl-extractable Fe indicated that the oxidation product was crystalline in nature as only 20% was soluble in 0.5M HCl. This formation of crystalline biogenic Fe(III) oxides is consistent with previous studies. Periodic injections of nitrate and acetate did not result in significant changes in Fe(II) or Fe(III) throughout a control column. Together these results demonstrate that native subsurface sediments harbor microbial communities capable of nitrate-dependent Fe(II) oxidation under advective flow. The biogenic formation of reactive Fe(III) oxide minerals capable of immobilizing heavy metals and radionuclides presents a plausible bioremediative strategy for contaminated subsurface environments.
Chaotic advection of finite-size bodies in a cavity flow
NASA Astrophysics Data System (ADS)
Vikhansky, A.
2003-07-01
We considered advection of neutrally buoyant discs in two-dimensional chaotic Stokes flow. The goal of the study is to explore a possibility to enhance laminar mixing in batch-flow mixers. Addition of freely moving bodies to periodically driven chaotic flow renders the flowfield nonperiodic [D. F. Zhang and D. A. Zumbrunnen, AIChE J. 42, 3301 (1996)], i.e., the Lagrangian chaos of the bodies motion induces Eulerian chaos of the flow that makes mixing more intensive. The presence of three bodies creates new topological features that do not exist in "pure" fluid. The trajectories of the discs in the augmented phase space tangle and form a braid that leads to so-called topological chaos [P. L. Boyland, H. Aref, and M. A. Stremler, J. Fluid Mech. 403, 277 (2000)]. Simulations were performed using a new variant of the immersed boundaries method that allows the direct numerical simulation of fluid-solid flows on a regular rectangular grid without explicit calculation of the forces that the particles exert on the fluid.
Multiscale numerical methods for passive advection-diffusion in incompressible turbulent flow fields
NASA Astrophysics Data System (ADS)
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.
Lump Solitons in Surface Tension Dominated Flows
NASA Astrophysics Data System (ADS)
Milewski, Paul; Berger, Kurt
1999-11-01
The Kadomtsev-Petviashvilli I equation (KPI) which models small-amplitude, weakly three-dimensional surface-tension dominated long waves is integrable and allows for algebraically decaying lump solitary waves. It is not known (theoretically or numerically) whether the full free-surface Euler equations support such solutions. We consider an intermediate model, the generalised Benney-Luke equation (gBL) which is isotropic (not weakly three-dimensional) and contains KPI as a limit. We show numerically that: 1. gBL supports lump solitary waves; 2. These waves collide elastically and are stable; 3. They are generated by resonant flow over an obstacle.
Effect of advective flow in fractures and matrix diffusion on natural gas production
Karra, Satish; Makedonska, Nataliia; Viswanathan, Hari S.; Painter, Scott L.; Hyman, Jeffrey D.
2015-10-12
Although hydraulic fracturing has been used for natural gas production for the past couple of decades, there are significant uncertainties about the underlying mechanisms behind the production curves that are seen in the field. A discrete fracture network based reservoir-scale work flow is used to identify the relative effect of flow of gas in fractures and matrix diffusion on the production curve. With realistic three dimensional representations of fracture network geometry and aperture variability, simulated production decline curves qualitatively resemble observed production decline curves. The high initial peak of the production curve is controlled by advective fracture flow of free gas within the network and is sensitive to the fracture aperture variability. Matrix diffusion does not significantly affect the production decline curve in the first few years, but contributes to production after approximately 10 years. These results suggest that the initial flushing of gas-filled background fractures combined with highly heterogeneous flow paths to the production well are sufficient to explain observed initial production decline. Lastly, these results also suggest that matrix diffusion may support reduced production over longer time frames.
Effect of advective flow in fractures and matrix diffusion on natural gas production
Karra, Satish; Makedonska, Nataliia; Viswanathan, Hari S.; Painter, Scott L.; Hyman, Jeffrey D.
2015-10-12
Although hydraulic fracturing has been used for natural gas production for the past couple of decades, there are significant uncertainties about the underlying mechanisms behind the production curves that are seen in the field. A discrete fracture network based reservoir-scale work flow is used to identify the relative effect of flow of gas in fractures and matrix diffusion on the production curve. With realistic three dimensional representations of fracture network geometry and aperture variability, simulated production decline curves qualitatively resemble observed production decline curves. The high initial peak of the production curve is controlled by advective fracture flow of freemore » gas within the network and is sensitive to the fracture aperture variability. Matrix diffusion does not significantly affect the production decline curve in the first few years, but contributes to production after approximately 10 years. These results suggest that the initial flushing of gas-filled background fractures combined with highly heterogeneous flow paths to the production well are sufficient to explain observed initial production decline. Lastly, these results also suggest that matrix diffusion may support reduced production over longer time frames.« less
NASA Astrophysics Data System (ADS)
Eslami, Parastou; Seo, Jung-Hee; Rahsepar, Amirali; George, Richard; Lardo, Albert; Mittal, Rajat
2014-11-01
Coronary computed tomography angiography (CTA) is a promising tool for assessment of coronary stenosis and plaque burden. Recent studies have shown the presence of axial contrast concentration gradients in obstructed arteries, but the mechanism responsible for this phenomenon is not well understood. We use computational fluid dynamics to study intracoronary contrast dispersion and the correlation of concentration gradients with intracoronary blood flow and stenotic severity. Data from our CFD patient-specific simulations reveals that contrast dispersions are generated by intracoronary advection effects, and therefore, encode the coronary flow velocity. This novel method- Transluminal Attenuation Flow Encoding (TAFE) - is used to estimate the flowrate in phantom studies as well as preclinical experiments. Our results indicate a strong correlation between the values estimated from TAFE and the values measured in these experiments. The flow physics of contrast dispersion associated with TAFE will be discussed. This work is funded by grants from Coulter Foundation and Maryland Innovation Initiative. The authors have pending patents in this technology and RM and ACL have other financial interests associated with TAFE.
Effect of advective flow in fractures and matrix diffusion on natural gas production
Karra, Satish; Makedonska, Nataliia; Viswanathan, Hari S.; Painter, Scott L.; Hyman, Jeffrey D.
2015-06-26
Although hydraulic fracturing has been used for natural gas production for the past couple of decades, there are significant uncertainties about the underlying mechanisms behind the production curves that are seen in the field. A discrete fracture network based reservoir-scale work flow is used to identify the relative effect of flow of gas in fractures and matrix diffusion on the production curve. With realistic three dimensional representations of fracture network geometry and aperture variability, simulated production decline curves qualitatively resemble observed production decline curves. The high initial peak of the production curve is controlled by advective fracture flow of free gas within the network and is sensitive to the fracture aperture variability. Matrix diffusion does not significantly affect the production decline curve in the first few years, but contributes to production after approximately 10 years. These results suggest that the initial flushing of gas-filled background fractures combined with highly heterogeneous flow paths to the production well are sufficient to explain observed initial production decline. Lastly, these results also suggest that matrix diffusion may support reduced production over longer time frames.
Effect of advective flow in fractures and matrix diffusion on natural gas production
NASA Astrophysics Data System (ADS)
Karra, Satish; Makedonska, Nataliia; Viswanathan, Hari S.; Painter, Scott L.; Hyman, Jeffrey D.
2015-10-01
Although hydraulic fracturing has been used for natural gas production for the past couple of decades, there are significant uncertainties about the underlying mechanisms behind the production curves that are seen in the field. A discrete fracture network-based reservoir-scale work flow is used to identify the relative effect of flow of gas in fractures and matrix diffusion on the production curve. With realistic three-dimensional representations of fracture network geometry and aperture variability, simulated production decline curves qualitatively resemble observed production decline curves. The high initial peak of the production curve is controlled by advective fracture flow of free gas within the network and is sensitive to the fracture aperture variability. Matrix diffusion does not significantly affect the production decline curve in the first few years, but contributes to production after approximately 10 years. These results suggest that the initial flushing of gas-filled background fractures combined with highly heterogeneous flow paths to the production well are sufficient to explain observed initial production decline. These results also suggest that matrix diffusion may support reduced production over longer time frames.
Chaotic advection and nonlinear resonances in an oceanic flow above submerged obstacle
NASA Astrophysics Data System (ADS)
Koshel, K. V.; Sokolovskiy, M. A.; Davies, P. A.
2008-10-01
The effect of an isolated submarine obstacle on the motion of fluid particles in a periodic external flow is studied within the framework of the barotropic, quasi-geostrophic approximation on f-plane. The concept of background currents advanced by Kozlov [1995. Background currents in geophysical hydrodynamics. Izvestia, Atmos. Oceanic Phys. 31 (2), 245-250] is used to construct a dynamically consistent stream function satisfying the potential vorticity conservation law. It is shown that a system of two topographic vortices revolving about a rotation center can form in a circular external flow. Unsteady periodic perturbations, associated with either variations in the background current or deviations of the external flow from circulation, are analyzed. Unsteadiness in the external flow essentially complicates the pattern of the motion of fluid particles. Vortex-type quasi-periodic structures, identified with nonlinear resonances that form in Lagrangian equations of fluid particle advection, are examined. They either surround the stationary configuration by a vortex chain—a ringlet-like structure [ Kennelly, M.A., Evans, R.H., Joyce, T.M., 1985. Small-scale cyclones on the periphery of Gulf Stream warm-core rings. J. Geophys. Res. 90(5), 8845-8857], or they form a complex-structure multivortex domain. Asymptotic estimates and numerical modeling are used to study the distribution and widths of the nonlinear resonance domains that appear under unsteady perturbations of different types. The onset of chaotic regimes owing to the overlapping of nonlinear resonance domains is analyzed. Transport fluxes determined by chaotic advection and barriers for transport (KAM-tori) and the conditions of their existence are studied. The relation of the rotation frequency of fluid particles on their initial position (when the dependence is calculated in the undisturbed system) is shown to completely determine the main features of the pattern of Lagrangian trajectories and chaotization
Orbital Advection by Interpolation: A Fast and Accurate Numerical Scheme for Super-Fast MHD Flows
Johnson, B M; Guan, X; Gammie, F
2008-04-11
In numerical models of thin astrophysical disks that use an Eulerian scheme, gas orbits supersonically through a fixed grid. As a result the timestep is sharply limited by the Courant condition. Also, because the mean flow speed with respect to the grid varies with position, the truncation error varies systematically with position. For hydrodynamic (unmagnetized) disks an algorithm called FARGO has been developed that advects the gas along its mean orbit using a separate interpolation substep. This relaxes the constraint imposed by the Courant condition, which now depends only on the peculiar velocity of the gas, and results in a truncation error that is more nearly independent of position. This paper describes a FARGO-like algorithm suitable for evolving magnetized disks. Our method is second order accurate on a smooth flow and preserves {del} {center_dot} B = 0 to machine precision. The main restriction is that B must be discretized on a staggered mesh. We give a detailed description of an implementation of the code and demonstrate that it produces the expected results on linear and nonlinear problems. We also point out how the scheme might be generalized to make the integration of other supersonic/super-fast flows more efficient. Although our scheme reduces the variation of truncation error with position, it does not eliminate it. We show that the residual position dependence leads to characteristic radial variations in the density over long integrations.
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
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
Truncated disks - advective tori; new solutions of accretion flows around black holes
NASA Astrophysics Data System (ADS)
Hujeirat, A.; Camenzind, M.
2000-09-01
Our quasi-steady 2D numerical radiative hydrodynamical investigations of two-temperature accretion flows around black holes indicate that standard disks are thermally and hydrodynamically stable against transition to optically thin disks at large radii. Optically thin disks cool sufficiently rapid at large radii inducing a vertical collapse and forming thereby a standard disk which truncates close to the last stable orbit. In the absence of soft photons from the adjusting standard disk, we confirm the runaway cooling of the inner optically thin disk. This runaway however terminates if the radial flux of soft photons from the outer standard disk is taken into account. Instead, a cooling-driven front starts to propagates from outside-to-inside continuously extending the thick disk down to the very inner region where it terminates via an oppositely-oriented heating front that forms a hot advective and sub-keplerian torus. The transition between the two configuration occurs where the ratio of the cooling to the heating time attains a minimum value. The transition is found to be rather sharp and gives rise to outwards-oriented motions of very hot plasma that enlarges the combined Compton-Synchrotron cooling regions considerably. While the disk-torus configuration obtained depends weakly on whether the flow is a one or two-temperature plasma, one-temperature tori are hotter and fill larger volumes than their two-temperature counterparts.
On the potential importance of transient air flow in advective radon entry into buildings
Narasimhan, T.N.; Tsang, Y.W.; Holman, H.Y. )
1990-05-01
The authors have investigated, using a mathematical model, the temporal variations of air flux within the soil mass surrounding a basement in the presence of time dependent periodic variations of barometric pressure and a persistent under-pressure at the basement. The results of transient air flow show that for a homogeneous soil medium, the effects of barometric fluctuations are most significant in the cases where soil permeability to air is low and the fluctuation frequency is high. In these cases, the barometric fluctuation can greatly enhance the magnitude of fluxes as well as introduce flow direction reversals from surrounding soil into the basement. These large fluxes with direction reversals have strong implications in regard to advective transport of radon. The results suggest that the transient oscillations have to be accounted for in quantifying radon entry into buildings. In the actual field set up, the transient behavior will be further influenced by soil permeability heterogeneity, by soil moisture variations, and by the effects of multiple periodic components in the barometric pressure fluctuations.
Dark Energy Domination In The Virgocentric Flow
NASA Astrophysics Data System (ADS)
Byrd, Gene; Chernin, A. D.; Karachentsev, I. D.; Teerikorpi, P.; Valtonen, M.; Dolgachev, V. P.; Domozhilova, L. M.
2011-04-01
Dark energy (DE) was first observationally detected at large Gpc distances. If it is a vacuum energy formulated as Einstein's cosmological constant, Λ, DE should also have dynamical effects at much smaller scales. Previously, we found its effects on much smaller Mpc scales in our Local Group (LG) as well as in other nearby groups. We used new HST observations of member 3D distances from the group centers and Doppler shifts. We find each group's gravity dominates a bound central system of galaxies but DE antigravity results in a radial recession increasing with distance from the group center of the outer members. Here we focus on the much larger (but still cosmologically local) Virgo Cluster and systems around it using new observations of velocities and distances. We propose an analytic model whose key parameter is the zero-gravity radius (ZGR) from the cluster center where gravity and DE antigravity balance. DE brings regularity to the Virgocentric flow. Beyond Virgo's 10 Mpc ZGR, the flow curves to approach a linear global Hubble law at larger distances. The Virgo cluster and its outer flow are similar to the Local Group and its local outflow with a scaling factor of about 10; the ZGR for Virgo is 10 times larger than that of the LG. The similarity of the two systems on the scales of 1 to 30 Mpc suggests that a quasi-stationary bound central component and an expanding outflow applies to a wide range of groups and clusters due to small scale action of DE as well as gravity. Chernin, et al 2009 Astronomy and Astrophysics 507, 1271 http://arxiv.org/abs/1006.0066 http://arxiv.org/abs/1006.0555
Coherent and incoherent scattering by a plume of particles advected by turbulent velocity flow.
Palmer, David R
2009-08-01
Studies of acoustic remote sensing of the plumes that result from the injection of particulate matter in the ocean, either naturally or by dumping or dredging activities, have assumed the scattering is incoherent. These plumes are always turbulent, however. The particle density is a passive scalar that is advected by the turbulent velocity flow. The possibility exists, therefore, that the scattered waves from a significant number of particles add coherently as a result of Bragg scattering. In this paper, we investigate this possibility. We derive an expression for the ratio of the coherent intensity to the incoherent one in terms of the turbulent spectrum and the properties of the particles that make up the plume. The sonar is modeled as a high-Q, monostatic, pulsed sonar with arbitrary pulse envelope and arbitrary, but narrow, beam pattern. We apply the formalism to acoustic remote sensing of black smoker hydrothermal plumes. We find that, at most, the coherent intensity is less than 1% of the incoherent one. The implications are that Bragg scattering does not lead to a significant coherent component and in analyses of scattering from this type of plume, one can ignore the complications of turbulence altogether. PMID:19640023
Temporal Variability from the Two-Component Advective Flow Solution and Its Observational Evidence
NASA Astrophysics Data System (ADS)
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.
NASA Astrophysics Data System (ADS)
Hansel, Colleen M.; Benner, Shawn G.; Neiss, Jim; Dohnalkova, Alice; Kukkadapu, Ravi K.; Fendorf, Scott
2003-08-01
Iron (hydr)oxides not only serve as potent sorbents and repositories for nutrients and contaminants but also provide a terminal electron acceptor for microbial respiration. The microbial reduction of Fe (hydr)oxides and the subsequent secondary solid-phase transformations will, therefore, have a profound influence on the biogeochemical cycling of Fe as well as associated metals. Here we elucidate the pathways and mechanisms of secondary mineralization during dissimilatory iron reduction by a common iron-reducing bacterium, Shewanella putrefaciens (strain CN32), of 2-line ferrihydrite under advective flow conditions. Secondary mineralization of ferrihydrite occurs via a coupled, biotic-abiotic pathway primarily resulting in the production of magnetite and goethite with minor amounts of green rust. Operating mineralization pathways are driven by competing abiotic reactions of bacterially generated ferrous iron with the ferrihydrite surface. Subsequent to the initial sorption of ferrous iron on ferrihydrite, goethite (via dissolution/reprecipitation) and/or magnetite (via solid-state conversion) precipitation ensues resulting in the spatial coupling of both goethite and magnetite with the ferrihydrite surface. The distribution of goethite and magnetite within the column is dictated, in large part, by flow-induced ferrous Fe profiles. While goethite precipitation occurs over a large Fe(II) concentration range, magnetite accumulation is only observed at concentrations exceeding 0.3 mmol/L (equivalent to 0.5 mmol Fe[II]/g ferrihydrite) following 16 d of reaction. Consequently, transport-regulated ferrous Fe profiles result in a progression of magnetite levels downgradient within the column. Declining microbial reduction over time results in lower Fe(II) concentrations and a subsequent shift in magnetite precipitation mechanisms from nucleation to crystal growth. While the initial precipitation rate of goethite exceeds that of magnetite, continued growth is inhibited by
Brine heterogeneity and dispersed interstitial advective flow underneath the sea of galilee, Israel
NASA Astrophysics Data System (ADS)
Weinstein, Y.; Katz, A.; Kastner, M.; Nishri, A.; Jannasch, H.
2003-04-01
Saline groundwater from submerged sources is today the main source of salts to the Sea of Galilee, supplying annually 72,000 tons chloride to the lake. MOSQUITO flux-meters were deployed during April to September 2001 at seven shallow Kinneret sites in order to study the dispersed interstitial flow. Each instrument carried 3-5 Osmo-Samplers that continuously sampled pore fluids at various depths in the sediment (0-45 cm). Samples were analyzed for their chemistry and for concentration of Na-fluorescein that was previously injected into the sediment. In general, oncentrations of conservative elements (e.g. Cl, Na, B) increase with depth into the sediment at all sites. However, concentrations vary significantly from one site to another. For instance, in sub-lacustrine brines next to the Tiberias Hot Springs Cl concentration reaches more than 14,500 mg/l at 35 cm below lake floor (not much less than the 18,000 mg/l in the nearby on-shore springs), while at other stations, brines are diluted by meteoric water to less than 1,500 mg/l Cl. Ion ratios in pore water indicate that the shallow parts of Lake Kinneret are underlain by several, separate, brine pockets, that are sometimes located very close to each other and discharge to the same area. Pore water at the east and northwest of the lake have Na/Cl ionic ratios between 0.7 and 0.8, similar to that of the overlying lake water, while at the west and south, ratios are significantly lower (<0.6 and <0.5, respectively), indicating larger degree of evaporation of the original brine end-member. Brines next to Tiberias Hot Springs have significantly higher Br/Cl and lower Mg/Cl ratios than pore water from other sites. Eastern shore sub-lacusrine brines (next to Gofra) are distinguished by their very high Sr/Cl and B/Cl ratios. Advective flow rates were derived from temporal patterns of Na-fluorescein concentration in pore water. Flow rates were between 0 and 80 cm/yr. Annual fluxes through the shallow part of the lake are
NASA Astrophysics Data System (ADS)
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.
Heat Flow, Climate Change and Advective Heat Transfer Beneath Winnipeg, Canada
NASA Astrophysics Data System (ADS)
Ferguson, G. A.; Woodbury, A. D.
2002-12-01
appear to have the greatest impacts in an industrial area in eastern Winnipeg and in an area with several large apartment buildings in western Winnipeg where the largest volumes of warm water are injected. Temperature profiles in areas where anomalous advective heat flow is prevalent are characterized by elevated temperatures occurring over discrete intervals, indicating transport through fractures and paleokarst features in the Upper Carbonate Aquifer. The presence of elevated temperatures beneath Winnipeg indicate that the current practices of using groundwater for cooling may not be sustainable due to the current injections of warm water and basement construction. However, the increases in heat flow beneath Winnipeg make the use of geothermal energy by heat pumps an attractive alternative for space heating.
Yao, Yijun; Wu, Yun; Wang, Yue; Verginelli, Iason; Zeng, Tian; Suuberg, Eric M; Jiang, Lin; Wen, Yuezhong; Ma, Jie
2015-10-01
At petroleum vapor intrusion (PVI) sites at which there is significant methane generation, upward advective soil gas transport may be observed. To evaluate the health and explosion risks that may exist under such scenarios, a one-dimensional analytical model describing these processes is introduced in this study. This new model accounts for both advective and diffusive transport in soil gas and couples this with a piecewise first-order aerobic biodegradation model, limited by oxygen availability. The predicted results from the new model are shown to be in good agreement with the simulation results obtained from a three-dimensional numerical model. These results suggest that this analytical model is suitable for describing cases involving open ground surface beyond the foundation edge, serving as the primary oxygen source. This new analytical model indicates that the major contribution of upward advection to indoor air concentration could be limited to the increase of soil gas entry rate, since the oxygen in soil might already be depleted owing to the associated high methane source vapor concentration. PMID:26322369
Computational methods for vortex dominated compressible flows
NASA Technical Reports Server (NTRS)
Murman, Earll M.
1987-01-01
The principal objectives were to: understand the mechanisms by which Euler equation computations model leading edge vortex flows; understand the vortical and shock wave structures that may exist for different wing shapes, angles of incidence, and Mach numbers; and compare calculations with experiments in order to ascertain the limitations and advantages of Euler equation models. The initial approach utilized the cell centered finite volume Jameson scheme. The final calculation utilized a cell vertex finite volume method on an unstructured grid. Both methods used Runge-Kutta four stage schemes for integrating the equations. The principal findings are briefly summarized.
A field study of air flow and turbulent features of advection fog
NASA Technical Reports Server (NTRS)
Connell, J. D.
1979-01-01
The setup and initial operation of a set of specialized meteorological data collection hardware are described. To study the life cycle of advection fogs at a lake test site, turbulence levels in the fog are identified, and correlated with the temperature gradients and mean wind profiles. A meteorological tower was instrumented to allow multiple-level measurements of wind and temperature on a continuous basis. Additional instrumentation was: (1)hydrothermograph, (2)microbarograph, (3)transmissometers, and (4)a boundary layer profiler. Two types of fogs were identified, and important differences in the turbulence scales were noted.
Inertia dominated thin-film flows over microdecorated surfaces
NASA Astrophysics Data System (ADS)
Dressaire, Emilie; Courbin, Laurent; Crest, Jérome; Stone, Howard A.
2010-07-01
We analyze the inertia dominated flow of thin liquid films on microtextured substrates, which here are assemblies of micron-size posts arranged on regular lattices. We focus on situations for which the thin-film thickness and the roughness characteristic length scale are of the same order of magnitude, i.e., a few hundred microns. We assume that the liquid flows isotropically through the roughness at a flow rate that depends on the geometrical features of the porous layer; above the texture, the flow is characterized by a larger Reynolds number and modeled using a boundary layer approach. The influence of the microtexture on the thin-film flow above the microposts is captured by a reduction of the flow rate due to the leakage flow through the texture and a slip boundary condition, which depends on the flow direction as well as on the lattice properties. In this way, the velocity field in the free surface flow adopts the symmetry of the microtexture underneath. The results of this model are in good agreement with experimental observations obtained for thin-film flows formed upon jet impact on microtextures. The characteristics of the polygonal hydraulic jumps that we obtain depend on both the jet parameters and the topographical features of the surface roughness. We use the measurements and the numerical predictions to estimate the flow rate through the shallow porous layer and the effective slip length for this inertia dominated flow regime. We also discuss the limitations of the model.
Efficient mass transport by optical advection
NASA Astrophysics Data System (ADS)
Kajorndejnukul, Veerachart; Sukhov, Sergey; Dogariu, Aristide
2015-10-01
Advection is critical for efficient mass transport. For instance, bare diffusion cannot explain the spatial and temporal scales of some of the cellular processes. The regulation of intracellular functions is strongly influenced by the transport of mass at low Reynolds numbers where viscous drag dominates inertia. Mimicking the efficacy and specificity of the cellular machinery has been a long time pursuit and, due to inherent flexibility, optical manipulation is of particular interest. However, optical forces are relatively small and cannot significantly modify diffusion properties. Here we show that the effectiveness of microparticle transport can be dramatically enhanced by recycling the optical energy through an effective optical advection process. We demonstrate theoretically and experimentally that this new advection mechanism permits an efficient control of collective and directional mass transport in colloidal systems. The cooperative long-range interaction between large numbers of particles can be optically manipulated to create complex flow patterns, enabling efficient and tunable transport in microfluidic lab-on-chip platforms.
NASA Astrophysics Data System (ADS)
Debnath, Dipak; Chakrabarti, Sandip K.; Mondal, Santanu
We study the spectral properties of Galactic transient black hole candidate H~1743-322 during its early phase of 2010 outburst with Two Component Advective Flow (TCAF) model, after its inclusion in spectral analysis software package XSPEC as a local model. For the analysis, spectral data from RXTE/PCA instrument in 2.5-25 keV energy band are used. From the spectral fit, accretion flow parameters such as Keplerian (disk) rate, sub-Keplerian (halo) rate, location of the shock and strength of the shock are directly extracted. QPO frequencies are predicted from the TCAF model spectral fitted shock parameters, `closely' matches with the observed frequencies.
Ackerman, D.J.
1995-01-01
Quantitative estimates of ground-water flow directions and traveltimes for advective flow were developed for the regional aquifer system of the eastern Snake River Plain, Idaho. The work included: (1) descriptions of compartments in the aquifer that function as intermediate and regional flow systems, (2) descriptions of pathlines for flow originating at or near the water table, and (3) quantitative estimates of traveltimes for advective transport originating at or near the water table. A particle-tracking postprocessing program was used to compute pathlines on the basis of output from an existing three-dimensional steady-state flow model. The flow model uses 1980 conditions to approximate average annual conditions for 1950-80. The advective transport model required additional information about the nature of flow across model boundaries, aquifer thickness, and porosity. Porosity of two types of basalt strata has been reported for more than 1,500 individual cores from test holes, wells, and outcrops near the south side of the Idaho National Engineering Laboratory. The central 80 percent of samples had porosities of 0.08 to 0.25, the central 50 percent of samples, O. 11 to 0.21. Calibration of the model involved choosing a value for porosity that yielded the best solution. Two radiologic contaminants, iodine-129 and tritium, both introduced to the flow system about 40 years ago, are relatively conservative tracers. Iodine- 129 was considered to be more useful because of a lower analytical detection limit, longer half-life, and longer flow path. The calibration value for porosity was 0.21. Most flow in the aquifer is contained within a regional-scale compartment and follows paths that discharge to the Snake River downstream from Milner Dam. Two intermediate-scale compartments exist along the southeast side of the aquifer and near Mud Lake.One intermediate-scale compartment along the southeast side of the aquifer discharges to the Snake River near American Fails
Dark energy domination in the local flow of giant galaxies
NASA Astrophysics Data System (ADS)
Chernin, A. D.; Emelyanov, N. V.; Karachentsev, I. D.
2015-05-01
A dozen of the most luminous galaxies, at distances of up to 10 Mpc from the Local Group, move away from the group, forming the local expansion flow of giants. We use recent Hubble Space Telescope data on local giants and their numerous fainter companions to study the dynamical structure and evolutionary trends of the flow. An N-body computer model, which reproduces the observed kinematics of the flow, is constructed under the assumption that the flow is embedded in the universal dark energy background. In the model, the motions of the flow members are controlled by their mutual attraction force and the repulsion force produced by the dark energy. It is found that the dark energy repulsion dominates the force field of the flow. Because of this, the flow expands with acceleration. The dark energy domination is enhanced by the environment effect of the low mean matter density on the spatial scale of 50 Mpc in the local Universe. The dark energy domination increases with time and introduces to the flow an asymptotically linear velocity-distance relation with the universal time-rate that depends on the dark energy density only.
NASA Astrophysics Data System (ADS)
Hornby, P. G.
2005-12-01
Understanding chemical and thermal processes taking place in hydrothermal mineral deposition systems could well be a key to unlocking new mineral reserves through improved targeting of exploration efforts. To aid in this understanding it is very helpful to be able to model such processes with sufficient fidelity to test process hypotheses. To gain understanding, it is often sufficient to obtain semi-quantitative results that model the broad aspects of the complex set of thermal and chemical effects taking place in hydrothermal systems. For example, it is often sufficient to gain an understanding of where thermal, geometric and chemical factors converge to precipitate gold (say) without being perfectly precise about how much gold is precipitated. The traditional approach is to use incompressible Darcy flow together with the Boussinesq approximation. From the flow field, the heat equation is used to advect-conduct the heat. The flow field is also used to transport solutes by solving an advection-dispersion-diffusion equation. The reactions in the fluid and between fluid and rock act as source terms for these advection-dispersion equations. Many existing modelling systems that are used for simulating such systems use explicit time marching schemes and finite differences. The disadvantage of this approach is the need to work on rectilinear grids and the number of time steps required by the Courant condition in the solute transport step. The second factor can be particularly significant if the chemical system is complex, requiring (at a minimum) an equilibrium calculation at each grid point at each time step. In the approach we describe, we use finite elements rather than finite differences, and the pressure, heat and advection-dispersion equations are solved implicitly. The general idea is to put unconditional numerical stability of the time integration first, and let accuracy assume a secondary role. It is in this sense that the method is semi-quantiative. However
A partially open porous media flow with chaotic advection: towards a model of coupled fields.
Metcalfe, Guy; Lester, Daniel; Ord, Alison; Kulkarni, Pandurang; Trefry, Mike; Hobbs, Bruce E; Regenaur-Lieb, Klaus; Morris, Jeffery
2010-01-13
In nature, dissipative fluxes of fluid, heat and/or reacting species couple to each other and may also couple to deformation of a surrounding porous matrix. We use the well-known analogy of Hele-Shaw flow to Darcy flow to make a model porous medium with porosity proportional to local cell height. Time- and space-varying fluid injection from multiple source/sink wells lets us create many different kinds of chaotic flows and chemical concentration patterns. Results of an initial time-dependent potential flow model illustrate that this is a partially open flow, in which parts of the material transported by the flow remain in the cell forever and parts pass through with residence time and exit time distributions that have self-similar features in the control parameter space of the stirring. We derive analytically the existence boundary in stirring control parameter space between where isolated fluid regions can and cannot remain forever in the open flow. Experiments confirm the predictions. PMID:19948552
NASA Astrophysics Data System (ADS)
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.
Advection Scheme for Phase-changing Porous Media Flow of Fluids with Large Density Ratio
NASA Astrophysics Data System (ADS)
Zhang, Duan; Padrino, Juan
2015-11-01
Many flows in a porous media involve phase changes between fluids with a large density ratio. For instance, in the water-steam phase change the density ratio is about 1000. These phase changes can be results of physical changes, or chemical reactions, such as fuel combustion in a porous media. Based on the mass conservation, the velocity ratio between the fluids is of the same order of the density ratio. As the result the controlling Courant number for the time step in a numerical simulation is determined by the high velocity and low density phase, leading to small time steps. In this work we introduce a numerical approximation to increase the time step by taking advantage of the large density ratio. We provide analytical error estimation for this approximate numerical scheme. Numerical examples show that using this approximation about 40-fold speedup can be achieved at the cost of a few percent error. Work partially supported by LDRD project of LANL.
NASA Astrophysics Data System (ADS)
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.
Embry, Irucka; Roland, Victor; Agbaje, Oluropo; Watson, Valetta; Martin, Marquan; Painter, Roger; Byl, Tom; Sharpe, Lonnie
2013-01-01
A new residence-time distribution (RTD) function has been developed and applied to quantitative dye studies as an alternative to the traditional advection-dispersion equation (AdDE). The new method is based on a jointly combined four-parameter gamma probability density function (PDF). The gamma residence-time distribution (RTD) function and its first and second moments are derived from the individual two-parameter gamma distributions of randomly distributed variables, tracer travel distance, and linear velocity, which are based on their relationship with time. The gamma RTD function was used on a steady-state, nonideal system modeled as a plug-flow reactor (PFR) in the laboratory to validate themore » effectiveness of the model. The normalized forms of the gamma RTD and the advection-dispersion equation RTD were compared with the normalized tracer RTD. The normalized gamma RTD had a lower mean-absolute deviation (MAD) (0.16) than the normalized form of the advection-dispersion equation (0.26) when compared to the normalized tracer RTD. The gamma RTD function is tied back to the actual physical site due to its randomly distributed variables. The results validate using the gamma RTD as a suitable alternative to the advection-dispersion equation for quantitative tracer studies of non-ideal flow systems.« less
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.
Scaling properties in the production range of shear dominated flows.
Casciola, C M; Gualtieri, P; Jacob, B; Piva, R
2005-07-01
In large Reynolds number turbulence, isotropy is recovered as the scale is reduced and homogeneous-isotropic scalings are eventually observed. This picture is violated in many cases, e.g., wall bounded flows, where, due to the shear, different scaling laws emerge. This effect has been ascribed to the contamination of the inertial range by the larger anisotropic scales. The issue is addressed here by analyzing both numerical and experimental data for a homogeneous shear flow. In fact, under strong shear, the alteration of the scaling exponents is not induced by the contamination from the anisotropic sectors. Actually, the exponents are universal properties of the isotropic component of the structure functions of shear dominated flows. The implications are discussed in the context of turbulence near solid walls, where improved closure models would be advisable. PMID:16090687
NASA Astrophysics Data System (ADS)
Watts, D.; Cohen, M. J.; Kaplan, D. A.; Mclaughlin, D. L.; Osborne, T.
2013-12-01
Groundwater movement within wetlands can have substantial implications for solute transport even where surface water is the dominant flowpath. For example, water table head gradients driven by evapotranspiration have been used to explain elevated nutrient levels in higher-elevation patches. However, where lateral transport occurs via nearly instantaneous water table equilibration of the water table between adjacent patches, no sustained hydraulic gradient will be observed even though water and solute movement is occurring. Here we present evidence for this effect in the ridge-slough patterned landscape of the Everglades (Florida, USA). Ridges and sloughs occupy different elevation modes, with ridges between 5 and 30 cm higher than sloughs in the present-day system. In the absence of water level equilibration between ridges and sloughs, we would expect distinct divergence in water levels when the water table drops below the ridge soil surface but sloughs remain inundated due to differences in specific yield (Sy) between ridges (Sy~0.2) and sloughs (Sy~1.0). On the contrary, we observed a 'lock-step' response in the diurnal signature of the water table, suggesting a mixing of open-water and ground-water signatures due to equilibration (i.e., advection) of water from sloughs to ridges. This mechanism may help explain the observation of higher soil phosphorus with higher soil elevation, a relationship that breaks down as ridge-slough elevation differences degrade. We place this mechanism in the context of vertical and horizontal conductivites of the Everglades peats and discuss the implications for solute transport.
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
Gravity-flow processes and deposits in a tidally dominated coastal environment
NASA Astrophysics Data System (ADS)
Eidam, E.; Ogston, A. S.; Nittrouer, C. A.
2014-12-01
Small mountainous rivers (SMRs) are characterized by episodic sediment delivery to marine environments, and have been recognized as a source of sediment gravity flows along storm-dominated coasts. These important modes of cross-shelf sediment transport are largely dependent on suspended-sediment concentration (SSC), bottom slope, and energy supplied by waves and currents. The mechanics and deposits of gravity flows are relatively unstudied on tidally dominated coasts receiving episodic SMR sediment discharge. Data collected during and after a March 2014 sediment delivery event from the small mountainous Elwha River (WA, USA) demonstrates the challenges of forming and preserving gravity-flow deposits in a persistently energetic tidal system. The river discharges to a narrow strait; near the river mouth, maximum boundary-layer tidal currents (50 cm above bed) reach 80-100 cm/s during spring tides and 30-60 cm/s during neap tides. Since 2011, the deconstruction of two dams has generated fluvial SSCs from 3 g/L to >9 g/L (max. monitoring value) during rainstorms and freshets. Instruments stationed near the river mouth since 2011 have shown that tidal currents advect this fine-grained sediment for days to weeks after delivery, and ultimately disperse it away from the river mouth. In March 2014, fluvial SSC reached ≥9 g/L during the largest river discharge since dam removal began. One day later, boundary-layer SSCs reached 2 g/L and 1 g/L at 23 and 102 cmab, respectively, and 5-8 days later, the bed under the instrument system aggraded by ~30 cm. Currents subsequently eroded the deposit, and within 3 weeks the bed elevation returned to its pre-event level. This is consistent with evidence of little to no grain-size change of the sand/gravel seabed in 10-60 m water depth up to 5 km from the river mouth since the dam removal began. To date, the only measurable accumulation of new sediment is in an embayment adjacent to the river mouth where currents weaken. These
Fast multigrid solution of the advection problem with closed characteristics
Yavneh, I.; Venner, C.H.; Brandt, A.
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.
Detection of dominant flow and abnormal events in surveillance video
NASA Astrophysics Data System (ADS)
Kwak, Sooyeong; Byun, Hyeran
2011-02-01
We propose an algorithm for abnormal event detection in surveillance video. The proposed algorithm is based on a semi-unsupervised learning method, a kind of feature-based approach so that it does not detect the moving object individually. The proposed algorithm identifies dominant flow without individual object tracking using a latent Dirichlet allocation model in crowded environments. It can also automatically detect and localize an abnormally moving object in real-life video. The performance tests are taken with several real-life databases, and their results show that the proposed algorithm can efficiently detect abnormally moving objects in real time. The proposed algorithm can be applied to any situation in which abnormal directions or abnormal speeds are detected regardless of direction.
RELATIVISTIC GLOBAL SOLUTIONS OF NEUTRINO-DOMINATED ACCRETION FLOWS
Xue Li; Liu Tong; Gu Weimin; Lu Jufu
2013-08-15
Neutrino-dominated accretion flows (NDAFs) around rotating stellar-mass black holes are plausible candidates for the central engines of gamma-ray bursts (GRBs). We investigate one-dimensional global solutions of NDAFs, taking into account general relativity in the Kerr metric, neutrino physics, and nucleosynthesis more precisely than previous works. We calculate 16 solutions with different characterized accretion rates and black hole spins to exhibit the radial distributions of various physical properties in NDAFs. We confirm that the electron degeneracy has important effects in NDAFs and we find that the electron fraction is about 0.46 in the outer region for all 16 solutions. From the perspective of the mass fraction, free nucleons, {sup 4}He, and {sup 5}6Fe dominate in the inner, middle, and outer regions, respectively. The influence of neutrino trapping on the annihilation is of importance for the superhigh accretion ( M-dot =10 M{sub sun} s{sup -1}) and most of the 16 solutions have an adequate annihilation luminosity for GRBs.
Spectral approximation to advection-diffusion problems by the fictitious interface method
NASA Astrophysics Data System (ADS)
Frati, A.; Pasquarelli, F.; Quarteroni, A.
1993-08-01
The algorithmic aspects of the 'fictitious interface' method used in numerical approximations of convection-dominated flows are discussed. The solution algorithm presented alternates the advection-equation solution with that of the advection-diffusion equation within complementary subdomains. For the problems presently considered, spatial discretization is obtained by the spectral collocation method via Legendre-Gaussian modes. Attention is given to the the fictitious interface method's application to the Burgers equation.
NASA Astrophysics Data System (ADS)
Rosenberg, R.; Harris, R. N.; Hurwitz, S.; Fulton, P. M.; Davis, M. G.; Werner, C. A.
2009-12-01
Any attempt to characterize the vigor of magmatic activity and forecast future volcanism in Yellowstone caldera requires knowledge regarding the thermal state of its magmatic system, one of the largest and most focused heat sources on Earth. Current knowledge of heat transport between magma and the ground surface is limited. Advective heat transport from the caldera has been quantified by measuring chloride flux from the major rivers draining the caldera, based on the assumptions of the chloride inventory method (Fournier, JVGR1979). We have quantified the total (conductive, advective, and evaporative) heat flux from one of the most active thermal areas in Yellowstone caldera, the Obsidian Pool thermal area (OPTA) which includes 0.1 km2 of thermal ground within the Mud Volcano thermal area. The OPTA is characterized by vapor dominated conditions. Rising steam and other gases (mainly CO2) fill open fractures beneath a low-permeability cap consisting of clay minerals (Bargar and Muffler, 1982). Conduction-dominated heat transfer through the clay cap is associated with a high temperature gradient. We made at least 4 soil-temperature measurements at 0-1 m depth at 251 locations in the OPTA and measured soil thermal conductivity in the laboratory. Evaporative heat from several thermal pools was quantified based on pool temperatures and meteorological data. Our preliminary analysis indicates that surface heat loss from OPTA is dominantly conductive. Extrapolation of the OPTA results to approximately 35 km2 of vapor-dominated area in Yellowstone caldera and surroundings would yield a total heat flow that constitutes a major fraction of the total heat power from Yellowstone’s magmatic system.
Zonal flow modes in a tokamak plasma with dominantly poloidal mean flows
Zhou Deng
2010-10-15
The zonal flow eigenmodes in a tokamak plasma with dominantly poloidal mean flows are theoretically investigated. It is found that the frequencies of both the geodesic acoustic mode and the sound wave increase with respect to the poloidal Mach number. In contrast to the pure standing wave form in static plasmas, the density perturbations consist of a standing wave superimposed with a small amplitude traveling wave in the poloidally rotating plasma.
NASA Astrophysics Data System (ADS)
Zhang, L. Q.; Dai, L.; Baumjohann, W.; Rème, H.; Dunlop, M. W.; Wei, X. H.
2015-11-01
Utilizing multipoint observations by the Cluster satellites, we investigated the ion distributions of the fast bulk flows (FBFs) in the plasma sheet. Simultaneous observation by C1 and C3 revealed that parallel-dominant and perpendicular-dominant components of the flows coexist and correspond to Bx-dominant and Bz-dominant magnetic field regions within the FBFs, respectively. In both cases, the ions distributions are characterized by a single-beam/crescent shape. In particular, no reflected ions are found within the FBFs. Statistical analysis showed that within the FBFs, the strength of the Bx component is typically less than 5 nT for Bz-dominant regions and above 10 nT for Bx-dominant regions. To distinguish between the parallel-dominant component of the FBFs and the field-aligned beams in the plasma sheet boundary layer (PSBL), we further statistically analyzed the tailward parallel flows (TPF) with positive Bz in the plasma sheet. The results indicated that the FBFs tend to have higher velocity, weaker B, and higher magnetic tilt angle (θMTA) than the TPFs/PSBL beams. Statistically, in the region of B > 30 nT (θMTA > 10°), only PSBL beams can be observed, while in the region of B < 10 nT (θMTA > 30°), the FBFs are dominant. In the intermediate region (10° < θMTA < 30°) of the plasma sheet, the FBFs and the PSBL beams cooccur. These Cluster observations suggest that the X line can produce both perpendicular flow in central plasma sheet and parallel flow in the PSBL. In addition, the parallel-dominant component of the FBFs could be an important origin for the PSBL beams.
Efficient mass transport by optical advection
Kajorndejnukul, Veerachart; Sukhov, Sergey; Dogariu, Aristide
2015-01-01
Advection is critical for efficient mass transport. For instance, bare diffusion cannot explain the spatial and temporal scales of some of the cellular processes. The regulation of intracellular functions is strongly influenced by the transport of mass at low Reynolds numbers where viscous drag dominates inertia. Mimicking the efficacy and specificity of the cellular machinery has been a long time pursuit and, due to inherent flexibility, optical manipulation is of particular interest. However, optical forces are relatively small and cannot significantly modify diffusion properties. Here we show that the effectiveness of microparticle transport can be dramatically enhanced by recycling the optical energy through an effective optical advection process. We demonstrate theoretically and experimentally that this new advection mechanism permits an efficient control of collective and directional mass transport in colloidal systems. The cooperative long-range interaction between large numbers of particles can be optically manipulated to create complex flow patterns, enabling efficient and tunable transport in microfluidic lab-on-chip platforms. PMID:26440069
Flow structure in canopy models dominated by progressive waves
NASA Astrophysics Data System (ADS)
Pujol, Dolors; Serra, Teresa; Colomer, Jordi; Casamitjana, Xavier
2013-04-01
SummaryLaboratory experiments were carried out to study the flow structure both inside and above different canopy models which were dominated by progressive waves. A set of experimental conditions were considered in a laboratory flume: three vegetation models (submerged rigid, submerged flexible and emergent rigid), three plant densities (128, 640 and 1280 stems m-2) and three wave frequencies (f = 0.8, 1 and 1.4 Hz). The progressive waves followed the second-order Stokes theory in the intermediate depth range. The observations revealed that submerged and emergent rigid vegetation models modified the wave-induced velocities i.e., both mean current and wave velocity. The submerged rigid vegetation model for plant densities higher than 640 plants m-2 and wave frequency higher than 1 Hz acted akin to a false floor, confining the mean current to above the plant bed. A penetration depth around 2 cm below the top of submerged rigid vegetation was found. For the other runs, the vertical profile of mean current did not present changes with respect to runs without plants. The emergent rigid vegetation model reversed the direction of the induced mean current, with the highest velocity corresponding to the highest plant density. In contrast, the submerged flexible vegetation model had a weak effect on the mean current, with the vertical velocity profile similar to that found in experiments without vegetation. The wave velocities inside the vegetation for the densest submerged rigid vegetation were found to be reduced by 20%, when compared to the wave velocities without vegetation, while in emergent rigid vegetation this reduction was of 45%.
BUOYANT ADVECTION OF GASES IN UNSATURATED SOIL
Seely, Gregory E.; Falta, Ronald W.; Hunt, James R.
2010-01-01
In unsaturated soil, methane and volatile organic compounds can significantly alter the density of soil gas and induce buoyant gas flow. A series of laboratory experiments was conducted in a two-dimensional, homogeneous sand pack with gas permeabilities ranging from 110 to 3,000 darcy. Pure methane gas was injected horizontally into the sand and steady-state methane profiles were measured. Experimental results are in close agreement with a numerical model that represents the advective and diffusive components of methane transport. Comparison of simulations with and without gravitational acceleration permits identification of conditions where buoyancy dominates methane transport. Significant buoyant flow requires a Rayleigh number greater than 10 and an injected gas velocity sufficient to overcome dilution by molecular diffusion near the source. These criteria allow the extension of laboratory results to idealized field conditions for methane as well as denser-than-air vapors produced by volatilizing nonaqueous phase liquids trapped in unsaturated soil. PMID:20396624
Hill, M.C.; Ely, D.M.; Tiedeman, C.R.; O'Brien, G.M.; D'Agnese, F.A.; Faunt, C.C.
2001-08-01
When a model is calibrated by nonlinear regression, calculated diagnostic statistics and measures of uncertainty provide a wealth of information about many aspects of the system. This report presents a method of ranking the likely importance of existing observation locations using measures of prediction uncertainty. It is suggested that continued monitoring is warranted at more important locations, and unwarranted or less warranted at less important locations. The report develops the methodology and then demonstrates it using the hydraulic-head observation locations of a three-layer model of the Death Valley regional flow system (DVRFS). The predictions of interest are subsurface transport from beneath Yucca Mountain and 14 underground Test Area (UGTA) sites. The advective component of transport is considered because it is the component most affected by the system dynamics represented by the regional-scale model being used. The problem is addressed using the capabilities of the U.S. Geological Survey computer program MODFLOW-2000, with its ADVective-Travel Observation (ADV) Package, and an additional computer program developed for this work.
NASA Astrophysics Data System (ADS)
Adam, A.; Pavlidis, D.; Percival, J. R.; Salinas, P.; Xie, Z.; Fang, F.; Pain, C. C.; Muggeridge, A. H.; Jackson, M. D.
2016-09-01
A general, higher-order, conservative and bounded interpolation for the dynamic and adaptive meshing of control-volume fields dual to continuous and discontinuous finite element representations is presented. Existing techniques such as node-wise interpolation are not conservative and do not readily generalise to discontinuous fields, whilst conservative methods such as Grandy interpolation are often too diffusive. The new method uses control-volume Galerkin projection to interpolate between control-volume fields. Bounded solutions are ensured by using a post-interpolation diffusive correction. Example applications of the method to interface capturing during advection and also to the modelling of multiphase porous media flow are presented to demonstrate the generality and robustness of the approach.
Cao, Xinwu; Liang, En-Wei; Yuan, Ye-Fei E-mail: lew@gxu.edu.cn
2014-07-10
It was suggested that the relativistic jets in gamma-ray bursts (GRBs) are powered via the Blandford-Znajek (BZ) mechanism or the annihilation of neutrinos and anti-neutrinos from a neutrino cooling-dominated accretion flow (NDAF). The advection and diffusion of the large-scale magnetic field of an NDAF is calculated, and the external magnetic field is found to be dragged inward efficiently by the accretion flow for a typical magnetic Prandtl number P{sub m}=η/ν∼1. The maximal BZ jet power can be ∼10{sup 53}-10{sup 54} erg s{sup –1} for an extreme Kerr black hole, if an external magnetic field with 10{sup 14} Gauss is advected by the NDAF. This is roughly consistent with the field strength of the disk formed after a tidal disrupted magnetar. The accretion flow near the black hole horizon is arrested by the magnetic field if the accretion rate is below than a critical value for a given external field. The arrested accretion flow fails to drag the field inward and the field strength decays, and then the accretion re-starts, which leads to oscillating accretion. The typical timescale of such episodic accretion is of an order of one second. This can qualitatively explain the observed oscillation in the soft extended emission of short-type GRBs.
NASA Astrophysics Data System (ADS)
Cao, Xinwu; Liang, En-Wei; Yuan, Ye-Fei
2014-07-01
It was suggested that the relativistic jets in gamma-ray bursts (GRBs) are powered via the Blandford-Znajek (BZ) mechanism or the annihilation of neutrinos and anti-neutrinos from a neutrino cooling-dominated accretion flow (NDAF). The advection and diffusion of the large-scale magnetic field of an NDAF is calculated, and the external magnetic field is found to be dragged inward efficiently by the accretion flow for a typical magnetic Prandtl number \\mathscr{P}_m=η /ν ˜ 1. The maximal BZ jet power can be ~1053-1054 erg s-1 for an extreme Kerr black hole, if an external magnetic field with 1014 Gauss is advected by the NDAF. This is roughly consistent with the field strength of the disk formed after a tidal disrupted magnetar. The accretion flow near the black hole horizon is arrested by the magnetic field if the accretion rate is below than a critical value for a given external field. The arrested accretion flow fails to drag the field inward and the field strength decays, and then the accretion re-starts, which leads to oscillating accretion. The typical timescale of such episodic accretion is of an order of one second. This can qualitatively explain the observed oscillation in the soft extended emission of short-type GRBs.
Experiments in Advective and Turbulent Hyporheic Pumping
NASA Astrophysics Data System (ADS)
Mccluskey, A. H.; Grant, S.; Stewardson, M. J.
2014-12-01
Hyporheic exchange (HE) is the mixing of stream and subsurface waters beneath the sediment-water interface (SWI). At the patch and reach scales, HE is dominated by periodic upwelling and downwelling zones, induced by pressure variation and processes within the turbulent boundary layer (TBL). This can be caused by (1) the geometry of the stream, imposing a stationary wave at the SWI or (2) by a travelling wave associated with the propagation of turbulent pressure waves generated from the TBL. Case (1) has generally been the favoured model of hyporheic exchange and has been referred to as hyporheic 'pumping' by Elliott and Brooks, and subsequently others. Case (2) can be termed turbulent pumping, and has been proposed as a mechanism to model the combined effects of turbulent dispersion alongside steady-state advection. While this has been represented numerically and analytically, conjecture remains about the physical representation of these combined processes. We present initial results from experiments undertaken to classify the spatial and temporal characteristics of pressure variation at and beneath the SWI, with a periodic sinusoidal geometry of wavelength 0.28m and height 0.02m. As an initial characterisation, the advective flow profile has been examined using time-lapse photography of dyes released across the span of a periodic downwelling zone. These tracer tests confirmed delineation of isolated upwelling and downwelling cells as noted by previous authors in modelling studies. However, their distribution deviates from the typical pumping pattern with increased discharge and stream gradient. Empirical orthogonal function (EOF) analysis of high frequency (250Hz) pressure measurements, sampled at an array along the centroid of the flume underneath one wavelength gave further insight into the spatial distribution of turbulent signatures arising from roughness-generated turbulence. A turbulent frequency of 6-10Hz dominates, however the penetration depth appears to
Convective flow dominates aerosol delivery to the lung segments
van Ertbruggen, C.; Prisk, G. K.
2011-01-01
Most previous computational studies on aerosol transport in models of the central airways of the human lung have focused on deposition, rather than transport of particles through these airways to the subtended lung regions. Using a model of the bronchial tree extending from the trachea to the segmental bronchi (J Appl Physiol 98: 970–980, 2005), we predicted aerosol delivery to the lung segments. Transport of 0.5- to 10-μm-diameter particles was computed at various gravity levels (0–1.6 G) during steady inspiration (100–500 ml/s). For each condition, the normalized aerosol distribution among the lung segments was compared with the normalized flow distribution by calculating the ratio (Ri) of the number of particles exiting each segmental bronchus i to the flow. When Ri = 1, particle transport was directly proportional to segmental flow. Flow and particle characteristics were represented by the Stokes number (Stk) in the trachea. For Stk < 0.01, Ri values were close to 1 and were unaffected by gravity. For Stk > 0.01, Ri varied greatly among the different outlets (Ri = 0.30–1.93 in normal gravity for 10-μm particles at 500 ml/s) and was affected by gravity and inertia. These data suggest that, for Stk < 0.01, ventilation defines the delivery of aerosol to lung segments and that the use of aerosol tracers is a valid technique to visualize ventilation in different parts of the lung. At higher Stokes numbers, inertia, but not gravitational sedimentation, is the second major factor affecting the transport of large particles in the lung. PMID:21474695
Effects of seagrass structure on a wave dominated flow
NASA Astrophysics Data System (ADS)
Pujol, D.; Serra, T.; Colomer, J.; Casamitjana, X.
2012-04-01
Shallow coastal areas are characterized by the presence of seagrass which occupy ~ 10% of the zone. In natural systems flows are a combination of steady, oscillatory and turbulent flows. Turbulence significantly affects the bottom boundary, therefore the interaction between turbulence and plant canopies is particularly important. In an effort to understand the dynamics of these complex flows we isolated each physical process in a laboratory study. We studied the progressive waves generated by a wavemaker situated at the beginning of the tank impinging on a simulated seagrass meadow. Our experiment is aimed at studying the relationship between flow structure and canopies in terms of a wide variety of parameters. We quantified the vertical distribution of mean current (uc), oscillatory velocity (uw), turbulent kinetic energy (TKE) and shear stress () above and within different types of vegetation, measured by an Acoustic Doppler Velocimeter (Sontek Instruments). Different experimental conditions were considered: two vegetation models (rigid and flexible), vegetation heights (14 and 30 cm, corresponding to submerged and emergent vegetation), plants densities (SPF = 1, 5, 10%) and three oscillatory frequencies (f = 0.8, 1 and 1.4Hz). Our observations suggest that the presence of submerged vegetation alter the flow structure within and above the canopy when the ratio of orbital excursion above the canopy to stem center-center spacing is higher than 1, corresponding to SPF = 5 and 10%. Above the vegetation, the mean current is always higher than without vegetation, whereas within the canopy the mean current is damped by submerged vegetation. The TKE decreases with depth and above the canopy it is higher with vegetation until 2 cm below the top of the canopy, compared to what it is found without vegetation. The presence of vegetation produces a peak of shear stress at the top of the canopy. High levels of shear stress together with fast mean current near the top of the
Prediction and Control of Vortex Dominated and Vortex-wake Flows
NASA Technical Reports Server (NTRS)
Kandil, Osama
1996-01-01
This report describes the activities and accomplishments under this research grant, including a list of publications and dissertations, produced in the field of prediction and control of vortex dominated and vortex wake flows.
Surfzone alongshore advective accelerations: observations and modeling
NASA Astrophysics Data System (ADS)
Hansen, J.; Raubenheimer, B.; Elgar, S.
2014-12-01
The sources, magnitudes, and impacts of non-linear advective accelerations on alongshore surfzone currents are investigated with observations and a numerical model. Previous numerical modeling results have indicated that advective accelerations are an important contribution to the alongshore force balance, and are required to understand spatial variations in alongshore currents (which may result in spatially variable morphological change). However, most prior observational studies have neglected advective accelerations in the alongshore force balance. Using a numerical model (Delft3D) to predict optimal sensor locations, a dense array of 26 colocated current meters and pressure sensors was deployed between the shoreline and 3-m water depth over a 200 by 115 m region near Duck, NC in fall 2013. The array included 7 cross- and 3 alongshore transects. Here, observational and numerical estimates of the dominant forcing terms in the alongshore balance (pressure and radiation-stress gradients) and the advective acceleration terms will be compared with each other. In addition, the numerical model will be used to examine the force balance, including sources of velocity gradients, at a higher spatial resolution than possible with the instrument array. Preliminary numerical results indicate that at O(10-100 m) alongshore scales, bathymetric variations and the ensuing alongshore variations in the wave field and subsequent forcing are the dominant sources of the modeled velocity gradients and advective accelerations. Additional simulations and analysis of the observations will be presented. Funded by NSF and ASDR&E.
Kukačka, Libor; Nosek, Štĕpán; Kellnerová, Radka; Jurčáková, Klára; Jaňour, Zbyněk
2012-01-01
The objective of this study is to determine processes of pollution ventilation in the X-shaped street intersection in an idealized symmetric urban area for the changing approach flow direction. A unique experimental setup for simultaneous wind tunnel measurement of the flow velocity and the tracer gas concentration in a high temporal resolution is assembled. Advective horizontal and vertical scalar fluxes are computed from averaged measured velocity and concentration data within the street intersection. Vertical advective and turbulent scalar fluxes are computed from synchronized velocity and concentration signals measured in the plane above the intersection. All the results are obtained for five approach flow directions. The influence of the approach flow on the advective and turbulent fluxes is determined. The contribution of the advective and turbulent flux to the ventilation is discussed. Wind direction with the best dispersive conditions in the area is found. 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. PMID:22649290
Vortex-dominated conical-flow computations using unstructured adaptively-refined meshes
NASA Technical Reports Server (NTRS)
Batina, John T.
1989-01-01
A conical Euler/Navier-Stokes algorithm is presented for the computation of vortex-dominated flows. The flow solver involves a multistage Runge-Kutta time stepping scheme which uses a finite-volume spatial discretization on an unstructured grid made up of triangles. The algorithm also employs an adaptive mesh refinement procedure which enriches the mesh locally to more accurately resolve the vortical flow features. Results are presented for several highly-swept delta wing and circular cone cases at high angles of attack and at supersonic freestream flow conditions. Accurate solutions were obtained more efficiently when adaptive mesh refinement was used in contrast with refining the grid globally. The paper presents descriptions of the conical Euler/Navier-Stokes flow solver and adaptive mesh refinement procedures along with results which demonstrate the capability.
NASA Astrophysics Data System (ADS)
Tóth, Gábor; Keppens, Rony
2012-07-01
The Versatile Advection Code (VAC) is a freely available general hydrodynamic and magnetohydrodynamic simulation software that works in 1, 2 or 3 dimensions on Cartesian and logically Cartesian grids. VAC runs on any Unix/Linux system with a Fortran 90 (or 77) compiler and Perl interpreter. VAC can run on parallel machines using either the Message Passing Interface (MPI) library or a High Performance Fortran (HPF) compiler.
NASA Astrophysics Data System (ADS)
Yang, Jun; Chu, Xuefeng
2015-04-01
Realistic modeling of discontinuous overland flow on irregular topographic surfaces has been proven to be a challenge. This study is aimed to develop a new modeling framework to simulate the discontinuous puddle-to-puddle (P2P) overland flow dynamics for infiltrating surfaces with various microtopographic characteristics. In the P2P model, puddles were integrated in a well-delineated, cascaded drainage system to facilitate explicit simulation of their dynamic behaviors and interactions. Overland flow and infiltration were respectively simulated by using the diffusion wave model and a modified Green-Ampt model for the DEM-derived flow drainage network that consisted of a series of puddle-based units (PBUs). The P2P model was tested by using a series of data from laboratory overland flow experiments for various microtopography, soil, and rainfall conditions. The modeling results indicated that the hierarchical relationships and microtopographic properties of puddles significantly affected their connectivity, filling-spilling dynamics, and the associated threshold flow. Surface microtopography and rainfall characteristics also exhibited strong influences on the spatio-temporal distributions of infiltration rates, runoff fluxes, and unsaturated flow. The model tests demonstrated its applicability in simulating microtopography-dominated overland flow on infiltrating surfaces.
Unsteady vortex-dominated flow around wings with oscillating leading-edge flaps
NASA Technical Reports Server (NTRS)
Kandil, Osama A.; Salman, Ahmed A.
1991-01-01
Unsteady vortex-dominated flow around delta wings with oscillating leading-edge flaps represents an important classs of problems for supermaneuverability and flow control of advanced aircraft. The problem is solved using time accurate integration of the unsteady, compressible, thin-layer Navier-Stokes equations in conjunction with the unsteady, linearized, Navier-displacement equations. Starting with an initial configuration of the wing and its flaps, the Navier-Stokes equations are solved on an initial structured grid for the steady flow. The forced oscillation of the flaps is then applied, and the problem is solved accurately in time. The Navier-displacement equations are solved for the grid deformation and the Navier-Stokes equations are solved for the flowfield. Symmetric and anti-symmetric flaps oscillations are presented to study the effect of the flaps oscillation on the leading-edge vortical flow.
Estimating flow concentration and sediment redistribution in shrub-dominated rangeland communities
NASA Astrophysics Data System (ADS)
Nouwakpo, S. K.; Weltz, M.; McGwire, K. C.; Rossi, C.
2014-12-01
In arid and semi-arid rangelands where vegetation is typically sparse, a synergistic relationship is assumed to exist between spatial distribution of plants and hydrologic and erosion processes. It is believed that areas underneath plant canopy have been conditioned to act as sediment, nutrients and water sinks whereas interspaces evolve into flow concentration pathways acting as source areas. This vegetation - hydrology feedback mechanism is part of a broader Vegetation Driven Spatial Heterogeneity (VDSH) concept that has been traditionally studied from a theoretical stand point but with little support from experimental data. In shrub-dominated rangeland communities, this VDSH concept implies that spatial distribution of vegetation can be used to model: (1) the level of hillslope dissection into concentrated flow and sheet flow areas and (2) the magnitude of sediment entrapment (deposition) expected from a given vegetation spatial arrangement. In this study, we developed a methodology to test these two hypotheses and derive practical equations for modeling purposes. From a series of rainfall / runoff experiments on naturally vegetated shrubland erosion plots, flow concentration and erosion / deposition processes were quantified using a combination of sediment yield data and high resolution microtopographic changes detected with advance 3D reconstruction technologies (lidar and photogrammetry). This study is expected to produce for the first time (1) predictive equations for spatial frequency of flow concentration pathways in shrub-dominated rangeland communities and (2) equations for sediment delivery ratio, a measure of the portion of eroded sediment that reaches the hillslope outlet as a function of vegetation spatial arrangement.
MAGNETIC ADVECTION DUE TO DIFFUSIVITY GRADIENTS
NASA Astrophysics Data System (ADS)
Zita, E. J.
2009-12-01
We derive and discuss an important source of advection of magnetic fields in plasmas, for a completely general case. Magnetic diffusivity is proportional to electrical resistivity: where the value this parameter is high, it is well known that magnetic fields can leak (or diffuse) rapidly into (or out) of the plasma. Magnetohydrodynamic lore has it that where gradients, or changes in space, of the value of the diffusivity are high, magnetic fields can have enhanced flow (or advection). We derive this phenomenon rigorously, compare our results to other work in the literature, and discuss its implications, especially for kinematic dynamos. As an extra mathematical bonus, we find that the magnetic advection due to diffusivity gradients can be expressed in terms of a diffusion equation within the induction equation, making its computational implementation especially simple.
Siyahhan, Bercan; Knobloch, Verena; de Zélicourt, Diane; Asgari, Mahdi; Schmid Daners, Marianne; Poulikakos, Dimos; Kurtcuoglu, Vartan
2014-01-01
While there is growing experimental evidence that cerebrospinal fluid (CSF) flow induced by the beating of ependymal cilia is an important factor for neuronal guidance, the respective contribution of vascular pulsation-driven macroscale oscillatory CSF flow remains unclear. This work uses computational fluid dynamics to elucidate the interplay between macroscale and cilia-induced CSF flows and their relative impact on near-wall dynamics. Physiological macroscale CSF dynamics are simulated in the ventricular space using subject-specific anatomy, wall motion and choroid plexus pulsations derived from magnetic resonance imaging. Near-wall flow is quantified in two subdomains selected from the right lateral ventricle, for which dynamic boundary conditions are extracted from the macroscale simulations. When cilia are neglected, CSF pulsation leads to periodic flow reversals along the ventricular surface, resulting in close to zero time-averaged force on the ventricle wall. The cilia promote more aligned wall shear stresses that are on average two orders of magnitude larger compared with those produced by macroscopic pulsatile flow. These findings indicate that CSF flow-mediated neuronal guidance is likely to be dominated by the action of the ependymal cilia in the lateral ventricles, whereas CSF dynamics in the centre regions of the ventricles is driven predominantly by wall motion and choroid plexus pulsation. PMID:24621815
Concentration through large advection
NASA Astrophysics Data System (ADS)
Aleja, D.; López-Gómez, J.
2014-11-01
In this paper we extend the elegant results of Chen, Lam and Lou [6, Section 2], where a concentration phenomenon was established as the advection blows up, to a general class of adventive-diffusive generalized logistic equations of degenerate type. Our improvements are really sharp as we allow the carrying capacity of the species to vanish in some subdomain with non-empty interior. The main technical devices used in the derivation of the concentration phenomenon are Proposition 3.2 of Cano-Casanova and López-Gómez [5], Theorem 2.4 of Amann and López-Gómez [1] and the classical Harnack inequality. By the relevance of these results in spatial ecology, complete technical details seem imperative, because the proof of Theorem 2.2 of [6] contains some gaps originated by an “optimistic” use of Proposition 3.2 of [5]. Some of the general assumptions of [6] are substantially relaxed.
A network flow model for short-term hydro-dominated hydrothermal scheduling problems
Franco, P.E.C. ); Carvalho, M.F. ); Soares, S. )
1994-05-01
This paper is concerned with the Short-Term Hydrothermal Scheduling (STHS) of hydro-dominated power systems. The problem's formulation includes the representation of operational constraints such as the hydraulic coupling between hydro plants in cascade and the transmission limits in the electric network. In order to allow the problem's decomposition into hydraulic and electric subproblems, a linear-quadratic penalty approach is applied to enforce the coupling between hydro and electric variables. As a result, the problem's natural network flow structure is fully exploited through special-purposed network flow algorithms. The technique has been implemented in FORTRAN in a SUN SPARCstation IPX and tested in a 440 KV subsystem of the main interconnected Brazilian power system.
Influence of numerical dissipation in computing supersonic vortex-dominated flows
NASA Technical Reports Server (NTRS)
Kandil, O. A.; Chuang, A.
1986-01-01
Steady supersonic vortex-dominated flows are solved using the unsteady Euler equations for conical and three-dimensional flows around sharp- and round-edged delta wings. The computational method is a finite-volume scheme which uses a four-stage Runge-Kutta time stepping with explicit second- and fourth-order dissipation terms. The grid is generated by a modified Joukowski transformation. The steady flow solution is obtained through time-stepping with initial conditions corresponding to the freestream conditions, and the bow shock is captured as a part of the solution. The scheme is applied to flat-plate and elliptic-section wings with a leading edge sweep of 70 deg at an angle of attack of 10 deg and a freestream Mach number of 2.0. Three grid sizes of 29 x 39, 65 x 65 and 100 x 100 have been used. The results for sharp-edged wings show that they are consistent with all grid sizes and variation of the artificial viscosity coefficients. The results for round-edged wings show that separated and attached flow solutions can be obtained by varying the artificial viscosity coefficients. They also show that the solutions are independent of the way time stepping is done. Local time-stepping and global minimum time-steeping produce same solutions.
Effect of advanced and delayed rotation on the dominant flow pattern and its temporal evolution
NASA Astrophysics Data System (ADS)
Uksul, Esra; Krishna, Swathi; Mulleners, Karen
2015-11-01
During a flapping cycle of an insect, complex time dependent flows are produced as the wing reciprocates, producing a maximum lift at the stroke reversals. By flipping the wing rapidly at the end of each stroke, the insect modulates the flow around the wing and hence the aerodynamic forces necessary to hover. The duration and starting point of the flip play an important role in determining the amount of lift produced. To understand and tailor the effect of wing kinematics on the aerodynamic performance we focussed on the vortex dynamics of the flow field. Phase-averaged data from particle image velocimetry was used to evaluate the flow features inherent to changes in rotation during a stroke of a flat plate, which is modelled based on hoverfly characteristics. The period of rotation is one-third of the total time period. A +10% phase shift is used for delayed rotation, a -10% phase shift for advanced rotation. Vortex detection methods like the λ2 and Γ2 criteria are used to determine the effect of a delay or early rotation on the trajectories, size, shape and location of the prominent vortical structures. Proper orthogonal decomposition is used to study the influence of the phase-shifts on the dominant mode structure and the related time-scales.
LAYER DEPENDENT ADVECTION IN CMAQ
The advection methods used in CMAQ require that the Courant-Friedrichs-Lewy (CFL) condition be satisfied for numerical stability and accuracy. In CMAQ prior to version 4.3, the ADVSTEP algorithm established CFL-safe synchronization and advection timesteps that were uniform throu...
Adaptive domain decomposition methods for advection-diffusion problems
Carlenzoli, C.; Quarteroni, A.
1995-12-31
Domain decomposition methods can perform poorly on advection-diffusion equations if diffusion is dominated by advection. Indeed, the hyperpolic part of the equations could affect the behavior of iterative schemes among subdomains slowing down dramatically their rate of convergence. Taking into account the direction of the characteristic lines we introduce suitable adaptive algorithms which are stable with respect to the magnitude of the convective field in the equations and very effective on bear boundary value problems.
NASA Astrophysics Data System (ADS)
Levinson, A.; Globus, N.
2016-05-01
The dynamics of a dissipative Poynting-dominated flow subject to a radiation drag due to Compton scattering of ambient photons by relativistic electrons accelerated in reconnecting current sheets is studied. It is found that the efficiency at which magnetic energy is converted to radiation is limited to a maximum value of ɛc = 3ldis σ0/4(σ0 + 1), where σ0 is the initial magnetization of the flow and ldis ≤ 1 the fraction of initial Poynting flux that can dissipate. The asymptotic Lorentz factor satisfies Γ∞ ≥ Γ0(1 + ldis σ0/4), where Γ0 is the initial Lorentz factor. This limit is approached in cases where the cooling time is shorter than the local dissipation time. A somewhat smaller radiative efficiency is expected if radiative losses are dominated by synchrotron and Synchrotron Self-Compton emissions. It is suggested that under certain conditions magnetic field dissipation may occur in two distinct phases: On small scales, asymmetric magnetic fields that are advected into the polar region and dragged out by the outflow dissipate to a more stable configuration. The dissipated energy is released predominantly as gamma rays. On much larger scales, the outflow encounters a flat density profile medium and re-collimates. This leads to further dissipation and wobbling of the jet head by the kink instability, as found recently in 3D magnetohydrodynamic simulations. Within the framework of a model proposed recently to explain the dichotomy of radio loud active galactic nuclei (AGN), this scenario can account for the unification of gamma-ray blazars with Fanaroff-Riley type I and Fanaroff-Riley type II radio sources.
Advection around ventilated U-shaped burrows: A model study
NASA Astrophysics Data System (ADS)
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.
NASA Astrophysics Data System (ADS)
Lyons, N. J.; Mitasova, H.; Wegmann, K. W.
2011-12-01
Landslide inventories, frequently created by aerial photograph interpretation (API), are often used in the production of hillslope hazard maps to characterize past landslides or to evaluate a hazard model. In the former application of inventories, potential landslides in hazard maps are delineated as areas that have similar morphometrics as past landslides at locations of modeled hillslope instability. Therefore, the accuracy of the inventory has a strong influence upon hazard extent. In the latter application, the partial inventories that sometimes result from API, due to the subjectivity of interpretation and revegetation of landslides, likely results in incorrect evaluations. A more complete, less subjective technique is needed to not only better characterize past landslides and improve evaluation of hazard models, but also to assess the extent of areas prone to significant mass wasting in mountainous regions due to the evolution of landscapes. Inventory accuracy continues to improve with new technology and automated techniques, though rarely is the form of a channel's topography incorporated into the inventory process despite the growing evidence of a topographic signature of debris flows. This signature demarcates the transition between the dominant channel erosional process: fluvial or debris flow. These process transitions are often observed at scaling breaks in log-log plots of a channel's drainage area versus slope (DS plot). The scaling breaks, above which the effects of fluvial power laws upon channel topography are not observed and below which debris flow scars are not found, may signify the lowest point in the watershed where debris flows occur. We present an inventory technique that limits a land classification algorithm to areas that are upstream from this scaling break determined from DS plots of five streams in the Great Smoky Mountains National Park (GSMNP) region of the southern Appalachians. Topographic data for the DS plots and the
Water movement through blanket peat is dominated by a complicated pattern of near-surface flows
NASA Astrophysics Data System (ADS)
Turner, Ed; Baird, Andy; Billett, Mike; Chapman, Pippa; Dinsmore, Kerry; Holden, Joseph
2015-04-01
Blanket peatland formation and functioning depend strongly on hydrology. Omitting the potential for pipe flow, the acrotelm-catotelm model is still widely held to apply to blanket peatlands. In the model, water flow through the peat profile is dominated by near-surface flow in the acrotelm, whereas water movement below the level of (near) permanent saturation (the catotelm) is characterised by very low hydraulic conductivity (K). Whilst some work has been done on characterising Kat different depths in blanket peatlands, very little is known about near-surface K, particularly with respect to how it varies between microforms and over fine spatial scales. We undertook a detailed investigation of near-surface (0 - 12 cm) and deeper (30 and 50 cm) K at a blanket peatland site in the Flow Country in Scotland (UK). Near-surface Kof peat samples taken across a range of microforms was measured vertically (Kv) and horizontally (Kh) in the laboratory using a new 'split cylinder' method (n = 48 excluding repeat tests). K30 (n = 20) andK50 (n = 20) were estimated in situ using the piezometer or seepage-tube method. To help our interpretation of the near-surface K measurements we recorded the vegetation cover from where the peat samples were taken and characterised each peat sample in terms of its plant macrofossil assemblage and dry bulk density. We found that Kvand Khwere highly variable between microforms in the near-surface samples, ranging over two orders of magnitude (0.489 - 0.003 cm s-1). Kernel density plots show that Kvwas most commonly in the region of ~0.03 cm s-1 at 0 - 6 cm, and ~0.015 cm s-1 at 6 - 12 cm, whereas Kh was ~0.05 and ~0.001 cm s-1 respectively. These data reveal a high degree of absolute variability and anisotropy in K over small scales. The deeper K30and K50 values were typically an order of magnitude or more lower than the near-surface K, and were less variable between test locations with the exception of poorly humified Sphagnum-dominated peat
Improving Godunov-type reconstructions for simulation of vortex-dominated flows
NASA Astrophysics Data System (ADS)
Tang, Lei; Baeder, James D.
2006-04-01
A systematic Fourier accuracy analysis is performed to examine the numerical diffusion inherent in a Godunov-type reconstruction, including both the reconstruction of the solution within each cell and the computation of the derivative terms of the reconstruction. It is found that compared with the more popular fifth-order polynomial fit of the interface values, a piecewise quadratic reconstruction of the solution with more accurate slope and curvature, especially those computed by compact difference schemes, is much less dissipative. Therefore, further given in the paper is a general framework to make a piecewise quadratic reconstruction free of numerical oscillations around the shocks. The improved accuracy and robustness of the resulting Godunov-type schemes for simulation of vortex-dominated flows are demonstrated with the numerical results of several carefully selected cases, including vortex convection and shock-vortex interaction.
Nandi, Anjan K.; Sumana, Annagiri; Bhattacharya, Kunal
2014-01-01
Social insects provide an excellent platform to investigate flow of information in regulatory systems since their successful social organization is essentially achieved by effective information transfer through complex connectivity patterns among the colony members. Network representation of such behavioural interactions offers a powerful tool for structural as well as dynamical analysis of the underlying regulatory systems. In this paper, we focus on the dominance interaction networks in the tropical social wasp Ropalidia marginata—a species where behavioural observations indicate that such interactions are principally responsible for the transfer of information between individuals about their colony needs, resulting in a regulation of their own activities. Our research reveals that the dominance networks of R. marginata are structurally similar to a class of naturally evolved information processing networks, a fact confirmed also by the predominance of a specific substructure—the ‘feed-forward loop’—a key functional component in many other information transfer networks. The dynamical analysis through Boolean modelling confirms that the networks are sufficiently stable under small fluctuations and yet capable of more efficient information transfer compared to their randomized counterparts. Our results suggest the involvement of a common structural design principle in different biological regulatory systems and a possible similarity with respect to the effect of selection on the organization levels of such systems. The findings are also consistent with the hypothesis that dominance behaviour has been shaped by natural selection to co-opt the information transfer process in such social insect species, in addition to its primal function of mediation of reproductive competition in the colony. PMID:25320069
Effect of random errors in planar PIV data on pressure estimation in vortex dominated flows
NASA Astrophysics Data System (ADS)
McClure, Jeffrey; Yarusevych, Serhiy
2015-11-01
The sensitivity of pressure estimation techniques from Particle Image Velocimetry (PIV) measurements to random errors in measured velocity data is investigated using the flow over a circular cylinder as a test case. Direct numerical simulations are performed for ReD = 100, 300 and 1575, spanning laminar, transitional, and turbulent wake regimes, respectively. A range of random errors typical for PIV measurements is applied to synthetic PIV data extracted from numerical results. A parametric study is then performed using a number of common pressure estimation techniques. Optimal temporal and spatial resolutions are derived based on the sensitivity of the estimated pressure fields to the simulated random error in velocity measurements, and the results are compared to an optimization model derived from error propagation theory. It is shown that the reductions in spatial and temporal scales at higher Reynolds numbers leads to notable changes in the optimal pressure evaluation parameters. The effect of smaller scale wake structures is also quantified. The errors in the estimated pressure fields are shown to depend significantly on the pressure estimation technique employed. The results are used to provide recommendations for the use of pressure and force estimation techniques from experimental PIV measurements in vortex dominated laminar and turbulent wake flows.
NASA Astrophysics Data System (ADS)
Tchelepi, H. A.; Wang, X.
2011-12-01
We describe a Newton-based nonlinear solver for immiscible two-phase Darcy flow and transport in the presence of significant viscous, buoyancy, and capillary forces. The evolution of CO2 plumes in heterogeneous saline aquifers, especially during the post-injection period, is an important example of this class of problem. The total flux (fractional flow) function is split into two parts: one part accounts for the viscous and buoyancy forces, and the other part accounts for capillarity. These flux functions, which are strongly nonlinear functions of saturation, are divided into trust regions. The delineation of the regions is dictated by the inflection, sonic, and end points present in the two flux functions. Within each trust region, the standard Newton iterative scheme is guaranteed to converge. For problems where the dynamics are dominated by buoyancy and capillary forces, the proposed scheme allows for taking much larger time steps than existing Newton based solvers. The nonlinear solver is demonstrated using challenging CO2-brine problems in heterogeneous domains with emphasis on the post-injection period.
Exploring a deep meridional flow hypothesis for a circulation dominated solar dynamo model
NASA Astrophysics Data System (ADS)
Guerrero, G. A.; Muñoz, J. D.; de Gouveia dal Pino, E. M.
2005-09-01
Circulation-dominated solar dynamo models, which employ a helioseismic rotation profile and a fixed meridional flow, give a good approximation to the large scale solar magnetic phenomena, such as the 11-year cycle or the so called Hale's law of polarities. Nevertheless, the larger amplitude of the radial shear ∂Ω/∂r at the high latitudes makes the dynamo to produce a strong toroidal magnetic field at high latitudes, in contradiction with the observations of the sunspots (Sporer's Law). A possible solution was proposed by Nandy and Choudhuri in which a deep meridional flow can conduct the magnetic field inside of a stable layer (the radiative core) and then allow that it erupts just at lower latitudes. Although they obtain good results, this hypothesis generates new problems like the mixture of elements in the radiative core (that alters the abundance of the elements) and the transfer of angular momentum. We have recently explored this hypothesis in a different approximation, using the magnetic buoyancy mechanism proposed by Dikpati and Charbonneau (1999) and found that a deep meridional flow pushes the maximum of the toroidal magnetic field towards the solar equator, but, in contrast to Nandy and Choudhuri (2002 ), a second zone of maximum fields remains at the poles. In that work, we have also introduced a bipolytropic density profile in order to better reproduce the stratification in the radiative zone. We here review these results and also discuss a new possible scenario where the tachocline has an ellipsoidal shape, following early helioseismologic observations, and find that the modification of the geometry of the tachocline can lead to results which are in good agreement with observations and opens the possibility to explore in more detail, through the dynamo model, the place where the magnetic field could be really stored.
Hurwitz, Shaul; Harris, Robert; Werner, Cynthia Anne; Murphy, Fred
2012-01-01
Characterizing the vigor of magmatic activity in Yellowstone requires knowledge of the mechanisms and rates of heat transport between magma and the ground surface. We present results from a heat flow study in two vapor dominated, acid-sulfate thermal areas in the Yellowstone Caldera, the 0.11 km2 Obsidian Pool Thermal Area (OPTA) and the 0.25 km2 Solfatara Plateau Thermal Area (SPTA). Conductive heat flux through a low permeability layer capping large vapor reservoirs is calculated from soil temperature measurements at >600 locations and from laboratory measurements of soil properties. The conductive heat output is 3.6 ± 0.4 MW and 7.5 ± 0.4 MW from the OPTA and the SPTA, respectively. The advective heat output from soils is 1.3 ± 0.3 MW and 1.2 ± 0.3 MW from the OPTA and the SPTA, respectively and the heat output from thermal pools in the OPTA is 6.8 ± 1.4 MW. These estimates result in a total heat output of 11.8 ± 1.4 MW and 8.8 ± 0.4 MW from OPTA and SPTA, respectively. Focused zones of high heat flux in both thermal areas are roughly aligned with regional faults suggesting that faults in both areas serve as conduits for the rising acid vapor. Extrapolation of the average heat flux from the OPTA (103 ± 2 W·m−2) and SPTA (35 ± 3 W·m−2) to the ~35 km2 of vapor dominated areas in Yellowstone yields 3.6 and 1.2 GW, respectively, which is less than the total heat output transported by steam from the Yellowstone Caldera as estimated by the chloride inventory method (4.0 to 8.0 GW).
NASA Astrophysics Data System (ADS)
Hurwitz, Shaul; Harris, Robert N.; Werner, Cynthia A.; Murphy, Fred
2012-10-01
Characterizing the vigor of magmatic activity in Yellowstone requires knowledge of the mechanisms and rates of heat transport between magma and the ground surface. We present results from a heat flow study in two vapor dominated, acid-sulfate thermal areas in the Yellowstone Caldera, the 0.11 km2 Obsidian Pool Thermal Area (OPTA) and the 0.25 km2 Solfatara Plateau Thermal Area (SPTA). Conductive heat flux through a low permeability layer capping large vapor reservoirs is calculated from soil temperature measurements at >600 locations and from laboratory measurements of soil properties. The conductive heat output is 3.6 ± 0.4 MW and 7.5 ± 0.4 MW from the OPTA and the SPTA, respectively. The advective heat output from soils is 1.3 ± 0.3 MW and 1.2 ± 0.3 MW from the OPTA and the SPTA, respectively and the heat output from thermal pools in the OPTA is 6.8 ± 1.4 MW. These estimates result in a total heat output of 11.8 ± 1.4 MW and 8.8 ± 0.4 MW from OPTA and SPTA, respectively. Focused zones of high heat flux in both thermal areas are roughly aligned with regional faults suggesting that faults in both areas serve as conduits for the rising acid vapor. Extrapolation of the average heat flux from the OPTA (103 ± 2 W·m-2) and SPTA (35 ± 3 W·m-2) to the ˜35 km2 of vapor dominated areas in Yellowstone yields 3.6 and 1.2 GW, respectively, which is less than the total heat output transported by steam from the Yellowstone Caldera as estimated by the chloride inventory method (4.0 to 8.0 GW).
High Order Semi-Lagrangian Advection Scheme
NASA Astrophysics Data System (ADS)
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).
Advective turbulent transport in the fluid plasma
NASA Astrophysics Data System (ADS)
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).
Two-dimensional flux-corrected transport solver for convectively dominated flows
Baer, M.R.; Gross, R.J.
1986-01-01
A numerical technique designed to solve a wide class of convectively dominated flow problems is presented. An attractive feature of the technique is its ability to resolve the behavior of field quantities possessing large gradients and/or shocks. The method is a finite-difference technique known as flux-corrected transport (FCT) that maintains four important numerical considerations - stability, accuracy, monotonicity, and conservation. The theory and methodology of two-dimensional FCT is presented. The method is applied in demonstrative example calculations of a 2-D Riemann problem with known exact solutions and to the Euler equations in a study of classical Rayleigh-Taylor and Kelvin-Helmholtz instability problems. The FCT solver has been vectorized for execution on the Cray 1S - a typical call with a 50 by 50 mesh requires about 0.00428 cpu seconds of execution time per call to the routine. Additionally, we have maintained a modular structure for the solver that eases its implementation. Fortran listings of two versions of the 2-D FCT solvers are appended with a driver main program illustrating the call sequence for the modules. 59 refs., 49 figs.
Detectable MeV neutrinos from black hole neutrino-dominated accretion flows
NASA Astrophysics Data System (ADS)
Liu, Tong; Zhang, Bing; Li, Ye; Ma, Ren-Yi; Xue, Li
2016-06-01
Neutrino-dominated accretion flows (NDAFs) around rotating stellar-mass black holes (BHs) have been theorized as the central engine of relativistic jets launched in massive star core collapse events or compact star mergers. In this work, we calculate the electron neutrino/antineutrino spectra of NDAFs by fully taking into account the general relativistic effects, and investigate the effects of viewing angle, BH spin, and mass accretion rate on the results. We show that even though a typical NDAF has a neutrino luminosity lower than that of a typical supernova (SN), it can reach 1050- 1051 erg s-1 peaking at ˜10 MeV , making NDAFs potentially detectable with the upcoming sensitive MeV neutrino detectors if they are close enough to Earth. Based on the observed gamma-ray burst (GRB) event rate in the local universe and requiring that at least three neutrinos are detected to claim a detection, we estimate a detection rate up to ˜(0.10 - 0.25 ) per century for GRB-related NDAFs by the Hyper-Kamiokande (Hyper-K) detector if one neglects neutrino oscillation. If one assumes that all type Ib/c SNe have an engine-driven NDAF, the Hyper-K detection rate would be ˜(1 - 3 ) per century. By considering neutrino oscillations, the detection rate may decrease by a factor of 2-3. Detecting one such event would establish the observational evidence of NDAFs in the Universe.
NASA Astrophysics Data System (ADS)
Kampf, S. K.; Lefsky, M. A.
2015-12-01
For a given quantity of precipitation, its form (snow or rain) will affect the magnitude and timing of streamflow, with consequences for both water resource and flood management. Using 20 streamflow gaging stations along a gradient of snow persistence and elevation, we identify annual peak flow sources (snowmelt, rainfall, mixed) from a gridded snow accumulation and melt model. We then relate these peak flow sources to annual average January-June snow persistence (SP), evaluate whether peak flow sources have changed over time, and examine how peak flow magnitude and timing differ with flow source. Results show that watersheds with SP<0.3 (low snow, mean elevation <2000 m) have experienced only rainfall-runoff annual peak flows in the period of record, and watersheds with SP>0.7 (persistent snow, mean elevation >3100 m) have mostly snowmelt-runoff peak flows, with mixed sources between these thresholds. At all elevations, rainfall may produce the annual peak flow, but the likelihood of rainfall-runoff peaks declines with increasing SP. Regional Kendall trend tests show that the contributions of snowmelt to peak flows and total annual inputs have declined in the mixed zone but not in the snowmelt-dominated zone, where SP is still high enough for peak flows to remain snowmelt-dominated. While rainfall runoff has produced some of the highest unit area peak flows in the region, on average snowmelt runoff produces higher unit discharge and more attenuated hydrographs than rainfall runoff. This example illustrates how peak flow sources are most sensitive to loss of snow in elevations where snow transitions from persistent to intermittent, whereas high elevations still have long enough snow persistence that they have remained snowmelt-dominated.
Cechovic, M.T.; Schmitt, J.G. . Dept. of Earth Sciences)
1993-04-01
Facies models for debris flow-dominated alluvial fans are based exclusively upon studies of relatively few fans in the arid American southwest. Detailed geomorphic, stratigraphic, and sedimentologic analyses of several highly-active, debris flow-dominated alluvial fans in northern Yellowstone National Park, WY (temperature, semi-arid) serve to diversify and increase the usefulness of alluvial fan facies models. These fans display an intricate distributary pattern of incised active (0--6 m deep; 700--900 m long) and abandoned channels (1--4 m deep; 400 m long) with levees/levee complexes (<3 m high; <20 m wide; <750 m long) and lobes constructed by pseudoplastic to plastic debris flows. The complex pattern of debris flow deposits is due to repeated channel back filling and overtopping by debris flows behind in-channel obstructions which subsequently lead to channel abandonment. Debris-flow deposition is dominant due to: (1) small, steep (up to 35 degrees) source area catchments, (2) extensive mud rock outcrops in the source area, and (3) episodic summer rainfall events. Proximal to distal fan surfaces exhibit sheetflood deposits several cm thick and up to 70 m in lateral extent. Vertical lithofacies profiles reveal: (1) massive, matrix- and clast-supported gravel units (1--2 m thick) deposited by clast-poor and clast-rich debris flows respectively, with reworked; scoured tops overlain by thin (<0.25 m) trough cross-bedded gravel and ripple cross-laminated sand intervals, and (2) volumetrically less significant 1--2 m thick intervals comprising fining-upward sequences of interbedded cm-scale trough cross-bedded pebbly gravel, massive sand, horizontally stratified sand, and mud rock deposited by hyperconcentrated flow and stream flow during decelerating sheetflood events. Organic rich layers record periods of non-deposition. Channelized stream flow is restricted to minor reworking of in-channel debris flow and hyperconcentrated flow deposits.
NUCLEAR DOMINATED ACCRETION FLOWS IN TWO DIMENSIONS. I. TORUS EVOLUTION WITH PARAMETRIC MICROPHYSICS
Fernandez, Rodrigo; Metzger, Brian D.
2013-02-15
We explore the evolution of radiatively inefficient accretion disks in which nuclear reactions are dynamically important ('Nuclear Dominated Accretion Flows' or NuDAFs). Examples of such disks are those generated by the merger of a white dwarf with a neutron star or black hole, or by the collapse of a rotating star. Here, we present two-dimensional hydrodynamic simulations that systematically explore the effect of adding a single nuclear reaction to a viscous torus. The equation of state, anomalous shear stress, and nuclear reactions are given parametric forms. Our results point to the existence of two qualitatively different regimes of NuDAF evolution: (1) steady accretion with quiescent burning or (2) detonation of the disk. These outcomes are controlled primarily by the ratio {Psi} of the nuclear energy released to the enthalpy at the burning radius. Disks detonate if {Psi} exceeds a critical value {Psi}{sub crit} {approx} 1, and if burning occurs in regions where neutrino cooling is unimportant. Thermonuclear runaways are seeded by the turbulent mixing of hot ash with cold fuel at the burning front. Disks with {Psi} < {Psi}{sub crit} do not explode, but instead power a persistent collimated outflow of unbound material composed primarily of ash, with a mass-loss rate that increases with {Psi}. We discuss the implications of our results for supernova-like counterparts from astrophysical events in the NuDAF regime. In particular, detonations following a white dwarf-neutron star merger could account for some subluminous Type Ia supernovae, such as the class defined by SN 2002cx.
Kaffenberger, W.; Gruber, D.F.; MacVittie, T.J.
1988-05-01
Thymuses of rats that had been: a) gamma-irradiated (500 cGy whole-body radiation (R)), or b) thermally injured (20% BSA dorsal, scald burn (TI)), or c) combined injured (irradiation followed by burn (CI)) were studied for involution and recovery processes after sublethal treatments. The expression of surface antigens on thymic cells before and after injuries was evaluated using the monoclonal antibodies (mcAB) MRC OX4, MRC OX7, MRC OX8, W3/13 HLK, and W3/25 and flow cytometric analysis. Thymic cellularity decreased to less than 1% of normal (N), age-matched rats by 4 days after R or CI. Recovery reached 60% to 70% of N by 28 days post treatments. TI caused a biphasic thymic recovery pattern with nadirs of 40% of N on days 7 and 21. Recovery at day 28 was similar to that after R and CI. Expression of OX7, OX8, W3/13, and W3/25 antigens all reached nadirs of 40% of N by day 4 after R and CI. Recovery of antigen expression, except for W3/25, was near completion by day 7 after R and CI. Changes in antigen expression after TI were less pronounced for all mcAB tested. Decreases in labeling of thymocytes with the helper T-cell marker, W3/25, observed after TI, could not be correlated with elevated expressions of the suppressor/cytotoxic T-lymphocyte antigen, OX8. Variations in relative labeling of nonlymphoid thymic cells with OX4 (Ia-antigen) reflected the disappearance and recovery of radiosensitive lymphoid thymocytes. The similarity of results after R and CI demonstrate that the model of CI is radiation-dominated. The addition of burn injury to radiation trauma had no synergistically damaging effect on the parameters studied.
Plan curvature and landslide probability in regions dominated by earth flows and earth slides
Ohlmacher, G.C.
2007-01-01
Damaging landslides in the Appalachian Plateau and scattered regions within the Midcontinent of North America highlight the need for landslide-hazard mapping and a better understanding of the geomorphic development of landslide terrains. The Plateau and Midcontinent have the necessary ingredients for landslides including sufficient relief, steep slope gradients, Pennsylvanian and Permian cyclothems that weather into fine-grained soils containing considerable clay, and adequate precipitation. One commonly used parameter in landslide-hazard analysis that is in need of further investigation is plan curvature. Plan curvature is the curvature of the hillside in a horizontal plane or the curvature of the contours on a topographic map. Hillsides can be subdivided into regions of concave outward plan curvature called hollows, convex outward plan curvature called noses, and straight contours called planar regions. Statistical analysis of plan-curvature and landslide datasets indicate that hillsides with planar plan curvature have the highest probability for landslides in regions dominated by earth flows and earth slides in clayey soils (CH and CL). The probability of landslides decreases as the hillsides become more concave or convex. Hollows have a slightly higher probability for landslides than noses. In hollows landslide material converges into the narrow region at the base of the slope. The convergence combined with the cohesive nature of fine-grained soils creates a buttressing effect that slows soil movement and increases the stability of the hillside within the hollow. Statistical approaches that attempt to determine landslide hazard need to account for the complex relationship between plan curvature, type of landslide, and landslide susceptibility. ?? 2007 Elsevier B.V. All rights reserved.
Submarine slumps, slides, and flows dominate sculpting of Beringian Margin, Alaska
Carlson, P.R.; Karl, H.A.; Edwards, B.D.; Gardner, J.V.; Hall, R. )
1990-06-01
The 1,400 km long Beringian margin is characterized by several very large submarine canyons and by a large oceanic plateau at the southern end. GLORIA sidescan-sonar imagery provides a perspective of this margin that is unattainable with conventional acoustic profiles. The broad coverage of GLORIA images emphasizes that, of all the sedimentary processes affecting this vast margin, mass movement is clearly the dominant shaping process. Styles of failure include mud and debris flows, slumps, and massive block slides, some covering areas greater than 1,500 km{sup 2}. GLORIA imagery and seismic-reflection profiles show evidence for a wide variety of slides and slumps in the canyons of the northern margin, Navarin and Pervenets. The 100 km long shelf edge between these two canyons is characterized by a series of scalloped slide scars and incipient scars associated with blocks of sedimentary material, 1 to 2 km across. One of the largest single slide masses is a huge block tens of kilometers wide that occurs on the rise in the central part of the margin beyond the mouth of Zhemchug Canyon. Sliding of this block may have initiated the incision of the world's largest submarine canyon. The removal of this block accelerated headward erosion by retrograde failure until Zhemchug Canyon was cut back to a fault parallel to the shelf edge. Mass movement along the southern margin is widespread at the edges of Umnak Plateau. One mass failure, well-defined by GLORIA, is about 30 km wide and 55 km long. This and other slides along the plateau are associated with diapiric-like structures, suggesting relatively recent tectonism.
Dynamic typology of hydrothermal systems: competing effects of advection, dispersion and reactivity
NASA Astrophysics Data System (ADS)
Dolejs, David
2016-04-01
Genetic interpretation hydrothermal systems relies on recognition of (i) hydrothermal fluid source, (ii) fluid migration pathways, and (iii) deposition site identified by hydrothermal alteration and/or mineralization. Frequently, only the last object is of interest or accessible to direct observation, but constraints on the fluid source (volume) and pathways can be obtained from evaluation of the time-integrated fluid flux during hydrothermal event. Successful interpretation of the petrological record, that is, progress of alteration reactions, relies on identification of individual contributions arising from solute advection (to the deposition site), its lateral dispersion, and reaction efficiency. Although these terms are all applicable in a mass-conservation relationship within the framework of the transport theory, they are rarely considered simultaneously and their relative magnitudes evaluated. These phenomena operate on variable length and time scales, and may in turn provide insight into the system dynamics such as flow, diffusion and reaction rates, or continuous vs. episodic behavior of hydrothermal events. In addition, here we demonstrate that they also affect estimate of the net fluid flux, frequently by several orders of magnitude. The extent of alteration and mineralization reactions between the hydrothermal fluid and the host environment is determined by: (i) temperature, pressure or any other gradients across the mineralization site, (ii) magnitude of disequilibrium at inflow to the mineralization site, which is related to physico-chemical gradient between the fluid source and the mineralization site, and (iii) chemical redistribution (dispersion) within the mineralization site. We introduce quantitative mass-transport descriptors - Péclet and Damköhler II numbers - to introduce division into dispersion-dominated, advection-dominated and reaction-constrained systems. Dispersive systems are characterized by lateral solute redistribution, driven by
Effect of advection on variations in zooplankton at a single location near Cabo Nazca, Peru
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.
Honig, Hen; Ofer, Lior; Kaim, Moshe; Jacobi, Shamay; Shinder, Dima; Gershon, Eran
2016-07-15
The use of ultrasound imaging for the examination of reproductive organs has contributed substantially to the fertility management of dairy cows around the world. This method has many advantages such as noninvasiveness and immediate availability of information. Adding Doppler index to the ultrasound imaging examination, improved the estimation of blood volume and flow rate to the ovaries in general and to the dominant follicle in particular. The aim of this study was to examine changes in the blood flow to the dominant follicle and compare them to the follicular development throughout the cycle. We further set out to examine the effects of different types of cooling management during the summer on the changes in blood flow to the dominant follicle. For this purpose, 24 Israeli-Holstein dairy cows, under heat stress, were randomly assigned one of two groups: one was exposed to five cooling sessions per day (5CS) and the other to eight cooling sessions per day (8CS). Blood flow to the dominant follicle was measured daily using Doppler index throughout the estrous cycle. No differences in the preovulatory dominant follicle diameter were detected between the two cooling management regimens during the cycle. However, the length of the first follicular wave was significantly longer, whereas the second follicular wave was nonsignificantly shorter in the 5CS group as compared to the 8CS group. In addition, no difference in blood flow was found during the first 18 days of the cycle between the two groups. However, from Day 20 until ovulation a higher rate of blood flow was measured in the ovaries of cows cooled 8 times per day as compared to the 5CS group. No differences in progesterone levels were noted. Finally, the estrous cycle length was shorter in the 8CS group as compared to the 5CS group. Our data suggest that blood flow to the dominant follicle and estrous cycle length is affected by heat stress. Using the appropriate cooling management during heat stress can
Waves, advection, and cloud patterns on Venus
NASA Technical Reports Server (NTRS)
Schinder, Paul J.; Gierasch, Peter J.; Leroy, Stephen S.; Smith, Michael D.
1990-01-01
The stable layers adjacent to the nearly neutral layer within the Venus clouds are found to be capable of supporting vertically trapped, horizontally propagating waves with horizontal wavelengths of about 10 km and speeds of a few meters per second relative to the mean wind in the neutral layer. These waves may possibly be excited by turbulence within the neutral layer. Here, the properties of the waves, and the patterns which they might produce within the visible clouds if excited near the subsolar point are examined. The patterns can be in agreement with many features in images. The waves are capable of transferring momentum latitudinally to help maintain the general atmospheric spin, but at present we are not able to evaluate wave amplitudes. We also examine an alternative possibility that the cloud patterns are produced by advection and shearing by the mean zonal and meridional flow of blobs formed near the equator. It is concluded that advection and shearing by the mean flow is the most likely explanation for the general pattern of small scale striations.
Numerical simulation of fluid/structure interaction phenomena in viscous dominated flows
NASA Astrophysics Data System (ADS)
Tran, Hai Duong
2001-12-01
The accurate prediction of buffet boundaries is essential in modern military aircraft and suspension bridge design in order to avoid the potentially disastrous consequences of unsteady loads. The design of lightweight structures and thermal protection systems for supersonic and hypersonic vehicles depends on the accurate prediction of the aerothermal loads, the structural temperatures and their gradients, and the structural deformations and stresses. Despite their bounded nature, limit-cycle oscillations can exhibit important amplitudes which affect the fatigue life of aircraft structures. Therefore, the main objective of this thesis is to develop and design an integrated multidisciplinary computational methodology for the analyses of the coupled responses exhibited by these phenomena. To simulate fluid/structure interaction problems in turbulent flows, we formulate the k--epsilon turbulence model and Reichardt's wall law in ALE form for dynamic meshes. This law is used with the generalized boundary conditions on k and epsilon of Jaeger and Dhatt and allows a closer integration to the wall compared to standard logarithmic laws and boundary conditions on k and epsilon. In order to apply the methodology to buffeting problems dominated by vortex shedding, we validate our solution approach on the square cylinder benchmark problem. There, we stress the minimization of numerical dissipation induced by an upwinding scheme, and apply our methodology to the aeroelastic stability analysis of a sectional dynamic model of the Tacoma Narrows Bridge. Then, we extend the three field formulation of aeroelasticity to a four-field formulation of aerothermoelasticity for the analysis of aerodynamic heating on structures. With a k--epsilon model, the time-averaged Navier-Stokes equations are integrated up to a distance delta from the real wall. This gap creates a problem for the transmission of the structural temperature to the fluid system. To resolve this problem, we exchange the
Ispolatov, Iaroslav; Maslov, Sergei
2008-01-01
Background Finding the dominant direction of flow of information in densely interconnected regulatory or signaling networks is required in many applications in computational biology and neuroscience. This is achieved by first identifying and removing links which close up feedback loops in the original network and hierarchically arranging nodes in the remaining network. In mathematical language this corresponds to a problem of making a graph acyclic by removing as few links as possible and thus altering the original graph in the least possible way. The exact solution of this problem requires enumeration of all cycles and combinations of removed links, which, as an NP-hard problem, is computationally prohibitive even for modest-size networks. Results We introduce and compare two approximate numerical algorithms for solving this problem: the probabilistic one based on a simulated annealing of the hierarchical layout of the network which minimizes the number of "backward" links going from lower to higher hierarchical levels, and the deterministic, "greedy" algorithm that sequentially cuts the links that participate in the largest number of feedback cycles. We find that the annealing algorithm outperforms the deterministic one in terms of speed, memory requirement, and the actual number of removed links. To further improve a visual perception of the layout produced by the annealing algorithm, we perform an additional minimization of the length of hierarchical links while keeping the number of anti-hierarchical links at their minimum. The annealing algorithm is then tested on several examples of regulatory and signaling networks/pathways operating in human cells. Conclusion The proposed annealing algorithm is powerful enough to performs often optimal layouts of protein networks in whole organisms, consisting of around ~104 nodes and ~105 links, while the applicability of the greedy algorithm is limited to individual pathways with ~100 vertices. The considered examples
Merritt, David M; Poff, N LeRoy
2010-01-01
Tamarix ramosissima is a naturalized, nonnative plant species which has become widespread along riparian corridors throughout the western United States. We test the hypothesis that the distribution and success of Tamarix result from human modification of river-flow regimes. We conducted a natural experiment in eight ecoregions in arid and semiarid portions of the western United States, measuring Tamarix and native Populus recruitment and abundance at 64 sites along 13 perennial rivers spanning a range of altered flow regimes. We quantified biologically relevant attributes of flow alteration as an integrated measure (the index of flow modification, IFM), which was then used to explain between-site variation in abundance and recruitment of native and nonnative riparian plant species. We found the likelihood of successful recruitment of Tamarix to be highest along unregulated river reaches and to remain high across a gradient of regulated flows. Recruitment probability for Populus, in contrast, was highest under free-flowing conditions and declined abruptly under even slight flow modification (IFM > 0.1). Adult Tamarix was most abundant at intermediate levels of IFM. Populus abundance declined sharply with modest flow regulation (IFM > 0.2) and was not present at the most flow-regulated sites. Dominance of Tamarix was highest along rivers with the most altered flow regimes. At the 16 least regulated sites, Tamarix and Populus were equally abundant. Given observed patterns of Tamarix recruitment and abundance, we infer that Tamarix would likely have naturalized, spread, and established widely in riparian communities in the absence of dam construction, diversions, and flow regulation in western North America. However, Tamarix dominance over native species would likely be less extensive in the absence of human alteration of river-flow regimes. Restoration that combines active mechanical removal of established stands of Tamarix with a program of flow releases conducive to
Bachand, P A M; Bachand, S; Fleck, J; Anderson, F; Windham-Myers, L
2014-06-15
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 understanding of
Advective transport and decomposition of chain-forming planktonic diatoms in permeable sediments
NASA Astrophysics Data System (ADS)
Ehrenhauss, Sandra; Huettel, Markus
2004-09-01
In laboratory chamber experiments we demonstrate that permeable sediments (>7×10 -12 m 2) exposed to boundary flows filter chain-forming coastal bloom diatoms ( Skeletonema costatum and Thalassiosira rotula) from the water column, causing rapid transfer of fresh organic particulate matter into sediment layers as deep as 5 cm within 72 h. The penetration depth of the diatoms depends on the permeability of the bed and the length of the chains. Long chains were not transported as deep into the sediment as short chains or single cells. The fast advective transfer of phytoplankton cells into sandy sediments may be an important process facilitating organic matter uptake and preventing resuspension of deposited organic material in high-energy coastal environments. High advective flushing rates in medium- and coarse-grained sandy sediments enhanced the mineralisation of the trapped diatoms (2300 to 3200 μmol C m -2 d -1), stimulated benthic oxygen consumption (2300 to 3000 μmol O 2 m -2 d -1), as well as nitrification (up to 20 μmol NO 3- m -2 d -1), relative to sediment where diffusion dominated the solute exchange. Advective solute exchange rates that increase with increasing permeability prevent the accumulation of Si(OH) 4 near the dissolving frustules and in the pore water, leading to an effective recycling of dissolved silica to the production process in the water column (95 to 101 μmol Si(OH) 4 m -2 d -1). This process may also enhance dissolution rates of the deposited opal in coarse-grained sands by maintaining higher degrees of undersaturation than in fine-grained sediments. Our results suggest that advective filtration of planktonic diatoms into permeable sediments increases mineralisation and recycling of Si(OH) 4 and organic matter in high energetic shelf areas.
NASA Astrophysics Data System (ADS)
Olins, H. C.; Rogers, D.; Scholin, C. A.; Preston, C. J.; Vidoudez, C.; Ussler, W.; Pargett, D.; Jensen, S.; Roman, B.; Birch, J. M.; Girguis, P. R.
2014-12-01
Hydrothermal vents are hotspots of microbial primary productivity often described as "windows into the subsurface biosphere." High temperature vents have received the majority of research attention, but cooler diffuse flows are as, if not more, important a source of heat and chemicals to the overlying ocean. We studied patterns of in situ gene expression and co-registered geochemistry in order to 1) describe the diversity and physiological poise of active microbial communities that span thermal and geochemical gradients from active diffuse flow to background vent field seawater, and 2) determine to what extent seawater or subsurface microbes were active throughout this environment. Analyses of multiple metatranscriptomes from 5 geochemically distinct sites (some from samples preserved in situ) show that proximate diffuse flows showed strikingly different transcription profiles. Specifically, caldera background and some diffuse flows were similar, both dominated by seawater-derived Gammaproteobacteria despite having distinct geochemistries. Intra-field community shows evidence of increased primary productivity throughout the entire vent field and not just at individual diffuse flows. In contrast, a more spatially limited, Epsilonproteobacteria-dominated transcription profile from the most hydrothermally-influenced diffuse flow appeared to be driven by the activity of vent-endemic microbes, likely reflecting subsurface microbial activity. We suggest that the microbial activity within many diffuse flow vents is primarily attributable to seawater derived Gammaproteobacterial sulfur oxidizers, while in certain other flows vent-endemic Epsilonproteobactiera are most active. These data reveal a diversity in microbial activity at diffuse flows that has not previously been recognized, and reshapes our thinking about the relative influence that different microbial communities may have on local processes (such as primary production) and potentially global biogeochemical
Prediction and control of vortex-dominated and vortex-wake flows
NASA Technical Reports Server (NTRS)
Kandil, Osama
1993-01-01
This progress report documents the accomplishments achieved in the period from December 1, 1992 until November 30, 1993. These accomplishments include publications, national and international presentations, NASA presentations, and the research group supported under this grant. Topics covered by documents incorporated into this progress report include: active control of asymmetric conical flow using spinning and rotary oscillation; supersonic vortex breakdown over a delta wing in transonic flow; shock-vortex interaction over a 65-degree delta wing in transonic flow; three dimensional supersonic vortex breakdown; numerical simulation and physical aspects of supersonic vortex breakdown; and prediction of asymmetric vortical flows around slender bodies using Navier-Stokes equations.
Silliman, Brian R; McCoy, Michael W; Trussell, Geoffrey C; Crain, Caitlin M; Ewanchuk, Patrick J; Bertness, Mark D
2013-01-01
Although consumers can strongly influence community recovery from disturbance, few studies have explored the effects of consumer identity and density and how they may vary across abiotic gradients. On rocky shores in Maine, recent experiments suggest that recovery of plant- or animal- dominated community states is governed by rates of water movement and consumer pressure. To further elucidate the mechanisms of consumer control, we examined the species-specific and density-dependent effects of rocky shore consumers (crabs and snails) on community recovery under both high (mussel dominated) and low flow (plant dominated) conditions. By partitioning the direct impacts of predators (crabs) and grazers (snails) on community recovery across a flow gradient, we found that grazers, but not predators, are likely the primary agent of consumer control and that their impact is highly non-linear. Manipulating snail densities revealed that herbivorous and bull-dozing snails (Littorina littorea) alone can control recovery of high and low flow communities. After ∼1.5 years of recovery, snail density explained a significant amount of the variation in macroalgal coverage at low flow sites and also mussel recovery at high flow sites. These density-dependent grazer effects were were both non-linear and flow-dependent, with low abundance thresholds needed to suppress plant community recovery, and much higher levels needed to control mussel bed development. Our study suggests that consumer density and identity are key in regulating both plant and animal community recovery and that physical conditions can determine the functional forms of these consumer effects. PMID:23940510
Silliman, Brian R.; McCoy, Michael W.; Trussell, Geoffrey C.; Crain, Caitlin M.; Ewanchuk, Patrick J.; Bertness, Mark D.
2013-01-01
Although consumers can strongly influence community recovery from disturbance, few studies have explored the effects of consumer identity and density and how they may vary across abiotic gradients. On rocky shores in Maine, recent experiments suggest that recovery of plant- or animal- dominated community states is governed by rates of water movement and consumer pressure. To further elucidate the mechanisms of consumer control, we examined the species-specific and density-dependent effects of rocky shore consumers (crabs and snails) on community recovery under both high (mussel dominated) and low flow (plant dominated) conditions. By partitioning the direct impacts of predators (crabs) and grazers (snails) on community recovery across a flow gradient, we found that grazers, but not predators, are likely the primary agent of consumer control and that their impact is highly non-linear. Manipulating snail densities revealed that herbivorous and bull-dozing snails (Littorina littorea) alone can control recovery of high and low flow communities. After ∼1.5 years of recovery, snail density explained a significant amount of the variation in macroalgal coverage at low flow sites and also mussel recovery at high flow sites. These density-dependent grazer effects were were both non-linear and flow-dependent, with low abundance thresholds needed to suppress plant community recovery, and much higher levels needed to control mussel bed development. Our study suggests that consumer density and identity are key in regulating both plant and animal community recovery and that physical conditions can determine the functional forms of these consumer effects. PMID:23940510
NASA Technical Reports Server (NTRS)
Kandil, Osama A.
1990-01-01
The conservative unsteady Euler equations for the flow relative motion in the moving frame of reference are used to solve for the steady and unsteady flows around sharp-edged delta wings. The resulting equations are solved by using an implicit approximately-factored finite volume scheme. Implicit second-order and explicit second- and fourth-order dissipations are added to the scheme. The boundary conditions are explicitly satisfied. The grid is generated by locally using a modified Joukowski transformation in cross flow planes at the grid chord stations. The computational applications cover a steady flow around a delta wing whose results serve as the initial conditions for the unsteady flow around a pitching delta wing about a large angle of attack. The steady results are compared with the experimental data and the periodic solution is achieved within the third cycle of oscillation.
Theory of advection-driven long range biotic transport
Technology Transfer Automated Retrieval System (TEKTRAN)
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...
NASA Astrophysics Data System (ADS)
Mudunuru, M. K.; Nakshatrala, K.
2012-12-01
Advection-Diffusion-Reaction (ADR) equations naturally arises in many physical phenomena, which include seepage of contaminants in heterogeneous porous media, transport of injected tracers due to the flow of oil in a petroleum reservoir, and degradation of a deformable solid due to diffusing chemical species. Vast literature exists on how to solve this equation in the cases when the medium is isotropic, velocity field being divergence free, and for advection-dominated problems. However, it is well know that many popular finite element formulations (e.g., the standard Galerkin formulation, stabilized methods, variational multi-scale methods, subgrid-scale methods, and primitive least-squares formulations) do not satisfy element-by-element mass/species balance and do not produce non-negative solutions on general computational grids. Various post-processing based methods were developed in order to recover some properties of computed numerical solutions. Most of these post-processing techniques are ad hoc, and are not variationally consistent. In this poster, we shall present a novel numerical methodology for ADR equations that satisfy discrete maximum principles, the non-negative constraint, and element-by-element mass/species balance. The methodology can handle general computational grids, no additional restrictions on time-step, and for heterogeneous anisotropic media. Several numerical results pertinent to advection-dominated ADR problems will be presented to illustrate the performance of the proposed numerical formulation.
Computation of vortex-dominated flow for a delta wing undergoing pitching oscillation
NASA Technical Reports Server (NTRS)
Kandil, Osama A.; Chuang, H. Andrew
1990-01-01
The conservative, unsteady Euler equations for the flow relative to a moving frame of reference are used to solve for the three-dimensional steady and unsteady flows around a sharp-edged delta wing. The resulting equations are solved by using an implicit, approximately factored, finite-volume scheme. Implicit second-order and explicit second- and fourth-order dissipations are added to the scheme. The boundary conditions are explicitly satisfied. The grid is generated by locally using a modified Joukowski transformation in crossflow planes at the grid-chord stations. The computational applications cover a steady flow around a delta wing, whose results serve as the initial conditions for the unsteady flow around a pitching delta wing at a large mean angle of attack. The steady results are compared with the experimental data, and the unsteady results are compared with results of a flux-difference splitting scheme.
NASA Astrophysics Data System (ADS)
Gomez, Francisco; Blackburn, Hugh M.; Rudman, Murray; McKeon, Beverley J.; Luhar, Mitul; Moarref, Rashad; Sharma, Ati S.
2014-11-01
The idea of constructing reduced-order models for canonical wall-bounded turbulent flows based on exploiting the sparse energetically dominant frequencies observed in direct numerical simulation of pipe flow by Bourguignon et al. (2013, Phys. Fluids) is examined. The resolvent analysis of a pipe flow is extended in order to consider the influence of finite domain length on the flow dynamics, which restricts the possible wavespeeds in the flow. This analysis shows that large sparse amplifications take place when one of the allowable wavespeeds is equal to the local wavespeed via the critical layer mechanism. A connection between amplification and energy is presented through the similar features displayed by the most energetically relevant flow structures, emerging from a dynamic mode decomposition of direct numerical simulation data, and the resolvent modes associated with the most amplified sparse frequencies. These findings support the viability of reduced-order models based on the selection of the most amplified modes arising from the resolvent model, with the potential to drastically decrease the computational costs required to represent turbulent flows. This work was supported by ARC Grant DP130103103 and AFOSR Grant FA9550- 09-1-0701 (ML, RM, BJM).
Chekmarev, Sergei F
2013-03-01
The transition from laminar to turbulent fluid motion occurring at large Reynolds numbers is generally associated with the instability of the laminar flow. On the other hand, since the turbulent flow characteristically appears in the form of spatially localized structures (e.g., eddies) filling the flow field, a tendency to occupy such a structured state of the flow cannot be ruled out as a driving force for turbulent transition. To examine this possibility, we propose a simple analytical model that treats the flow as a collection of localized spatial structures, each of which consists of elementary cells in which the behavior of the particles (atoms or molecules) is uncorrelated. This allows us to introduce the Reynolds number, associating it with the ratio between the total phase volume for the system and that for the elementary cell. Using the principle of maximum entropy to calculate the most probable size distribution of the localized structures, we show that as the Reynolds number increases, the elementary cells group into the localized structures, which successfully explains turbulent transition and some other general properties of turbulent flows. An important feature of the present model is that a bridge between the spatial-statistical description of the flow and hydrodynamic equations is established. We show that the basic assumptions underlying the model, i.e., that the particles are indistinguishable and elementary volumes of phase space exist in which the state of the particles is uncertain, are involved in the derivation of the Navier-Stokes equation. Taking into account that the model captures essential features of turbulent flows, this suggests that the driving force for the turbulent transition is basically the same as in the present model, i.e., the tendency of the system to occupy a statistically dominant state plays a key role. The instability of the flow at high Reynolds numbers can then be a mechanism to initiate structural rearrangement of
NASA Astrophysics Data System (ADS)
Deardorff, N.; Cashman, K.
2014-12-01
The crust of lava flows (of all compositions) is commonly folded into arcuate ridges, bent such that the convex ridges point down flow. In theory, the geometry of flow surface folds can be used to constrain the thickness and viscosity of the folding layer (from the fold wavelength) and the compressional stress (from the fold amplitude). Crustal thickness is controlled primarily by lava composition and extent of cooling. Therefore, lavas of more evolved compositions (higher silica content) have thicker crusts, which should generate surface folds with larger wavelengths. We have determined the characteristic scale of surface folds using 1000m along-channel segments from Lidar-derived 3D Digital Terrain Models over a range of lava compositions (53-72 wt% SiO2). All profiles were analyzed by discrete Fourier transform (DFT) analysis in Matlab, used to determine the spatial scale of periodic surface features. The DFT periodograms produce 1D arrays of spectral density over a range of spatial frequencies, which describe the amplitude and spatial scale (wavelength) of lava surface topography. The DFT analysis allows for unbiased measurements of dominant surface fold wavelengths as well as identification of primary and secondary folds (i.e. folds within folds). Measurements of multiple fold generations are not possible from satellite images or in the field on intermediate to high silica blocky lavas. In our analyses, strong signals of surface periodicities were found at multiple frequencies for all lava flows, indicating multiple generations of surface folds. Additionally, mafic to intermediate lavas (<60 wt% SiO2) show a positive correlation between dominant fold wavelengths and wt% silica. This correlation breaks down with high silica lavas (>65 wt% SiO2) which have a much larger range in dominant wavelength (10 - >100m). The deviation in expected dominant wavelengths for high silica flows is likely explained by effective viscosity, which is strongly influenced by lava
Tidal variability of lateral advection in a coastal plain estuary
NASA Astrophysics Data System (ADS)
Basdurak, N. B.; Valle-Levinson, A.
2013-07-01
Tidal variability of lateral advection of momentum (vuy, where u and v are along-estuary and lateral flows, respectively, and the subindex indicates differentiation with respect to the cross-estuary direction) was investigated in a coastal plain estuary with observations at Hampton Roads, which is the transition between the James River and Chesapeake Bay. Towed current velocity profiles and hydrographic profiles were captured during 9 expeditions in 2004 and 2005, to determine the intratidal and spatial changes in lateral advection of momentum and its contribution to along-channel flow. Curvature effects and lateral density gradients were important in driving lateral circulation and in modifying intratidal lateral advection of momentum. Lateral advection had the same order of magnitude as the baroclinic pressure gradient. Its contribution to the along-channel momentum balance was greatest during or just after peak flood and weakest at the end of ebb. During peak flood and peak ebb, the spatial distribution of vuy was seaward at the southern (left) side near surface and at the northern side (right) near bed (looking up-estuary), and landward in the rest of the channel. During slack periods the vuy structures were mostly landward. Observations were in good agreement with analytical model results during peak ebb and flood, but inconsistent during slack periods. The discrepancies between model results and field measurements can be attributed to bathymetry-density gradient interactions, which enhanced ebb-to-flood asymmetries in the along-channel and lateral flow.
Technical Note: Variability of flow discharge in lateral inflow-dominated stream channels
NASA Astrophysics Data System (ADS)
Chang, C.-M.; Yeh, H.-D.
2015-02-01
The influence of the temporal changes in lateral inflow rate on the discharge variability in stream channels is explored through the analysis of diffusion wave equation (the linearized St. Venant equations). To account for variability and uncertainty, the lateral inflow rate is regarded as a temporal random function. Based on the spectral representation theory, analytical expressions for the covariance function and evolutionary power spectral density of the random discharge perturbation process are derived to quantify variability in stream flow discharge induced by the temporal changes in lateral inflow rate. Upon evaluating the closed-form expressions, it is found that the variability in stream flow discharge increases with distance from the upstream boundary of the channel and time as well. The temporal correlation scale of inflow rate fluctuations plays a positive role in enhancing the variability of the flow discharge in channels. The treatment of the discharge variance gives us a quantitative estimate of uncertainty from the use of the deterministic model.
NASA Astrophysics Data System (ADS)
Ludar, Lotan; Yariv, Ehud
2015-11-01
As surface conduction has no effect on electro-osmosis in uniform channel flows, where the tangential Debye-layer currents are longitudinally uniform, it may appear as it would only result in a small modifying correction in lubrication analyses of slowly varying channels. This misconception is refuted here by analyzing flows through periodic channels of slowly varying but otherwise arbitrary geometry. Assuming that the channel width is still large compared with the Debye thickness we employ the simplest thin-double-layer model which incorporates surface conduction. We find that surface conduction affects the leading-order flow and the consequent net volumetric flux, introducing a nonlinear dependence upon the zeta potential. Remarkably, as the channel becomes more and more narrow, the scaled flux approaches a limit which is independent of the Dukhin number yet different from that calculated for zero Dukhin number.
NASA Technical Reports Server (NTRS)
Erickson, Gary E.
2008-01-01
Laser vapor screen (LVS) flow visualization and pressure sensitive paint (PSP) techniques were applied in a unified approach to wind tunnel testing of slender wing and missile configurations dominated by vortex flows and shock waves at subsonic, transonic, and supersonic speeds. The off-surface cross-flow patterns using the LVS technique were combined with global PSP surface static pressure mappings to characterize the leading-edge vortices and shock waves that coexist and interact at high angles of attack (alpha). The synthesis of LVS and PSP techniques was also effective in identifying the significant effects of passive surface porosity and the presence of vertical tail surfaces on the flow topologies. An overview is given of LVS and PSP applications in selected experiments on small-scale models of generic slender wing and missile configurations in the NASA Langley Research Center (NASA LaRC) Unitary Plan Wind Tunnel (UPWT) and 8-Foot Transonic Pressure Tunnel (8-Foot TPT).
NASA Technical Reports Server (NTRS)
Erickson, Gary E.
2010-01-01
Laser vapor screen (LVS) flow visualization and pressure sensitive paint (PSP) techniques were applied in a unified approach to wind tunnel testing of slender wing and missile configurations dominated by vortex flows and shock waves at subsonic, transonic, and supersonic speeds. The off-surface cross-flow patterns using the LVS technique were combined with global PSP surface static pressure mappings to characterize the leading-edge vortices and shock waves that coexist and interact at high angles of attack. The synthesis of LVS and PSP techniques was also effective in identifying the significant effects of passive surface porosity and the presence of vertical tail surfaces on the flow topologies. An overview is given of LVS and PSP applications in selected experiments on small-scale models of generic slender wing and missile configurations in the NASA Langley Research Center (NASA LaRC) Unitary Plan Wind Tunnel (UPWT) and 8-Foot Transonic Pressure Tunnel (8-Foot TPT).
Advective Mechanisms in Tree Island Formation
NASA Astrophysics Data System (ADS)
Stothoff, S.
2002-05-01
Tree islands are important landscape features in the Florida Everglades. Tres islands are formed of peat deposited on the shallow limestone bedrock, and have been stressed as the system has changed in response to anthropogenic activities due to the sensitivity of organic soils to hydrologic cycles. The plume shape aligned with flow direction for typical tree islands is characteristic of advective transport, despite the rather low flow velocities in the system. Hypothesized mechanisms for the plume shape include sediment transport downstream from the head of the island (often anchored by a bedrock rise), or nutrient transport downstream allowing plants to produce more sediments in situ. Understanding mechanisms controlling tree island shape will aid in understanding the response of tree islands to hydrologic management. An integrated system of field, laboratory, and modeling studies is underway, with the first effort aimed at bounding the importance of the simpler sediment transport processes before tackling more-complex nutrient transport processes. The numerical model integrating the field and laboratory efforts is a 3D finite volume model considering water flow in the shallow groundwater/surface-water system together with sediment transport. The model can account for variable vegetative resistance through the flow column, including the important case where a dense mat forms at the surface. Model components specific for this system and associated data requirements are presented.
Optic Flow Dominates Visual Scene Polarity in Causing Adaptive Modification of Locomotor Trajectory
NASA Technical Reports Server (NTRS)
Nomura, Y.; Mulavara, A. P.; Richards, J. T.; Brady, R.; Bloomberg, Jacob J.
2005-01-01
Locomotion and posture are influenced and controlled by vestibular, visual and somatosensory information. Optic flow and scene polarity are two characteristics of a visual scene that have been identified as being critical in how they affect perceived body orientation and self-motion. The goal of this study was to determine the role of optic flow and visual scene polarity on adaptive modification in locomotor trajectory. Two computer-generated virtual reality scenes were shown to subjects during 20 minutes of treadmill walking. One scene was a highly polarized scene while the other was composed of objects displayed in a non-polarized fashion. Both virtual scenes depicted constant rate self-motion equivalent to walking counterclockwise around the perimeter of a room. Subjects performed Stepping Tests blindfolded before and after scene exposure to assess adaptive changes in locomotor trajectory. Subjects showed a significant difference in heading direction, between pre and post adaptation stepping tests, when exposed to either scene during treadmill walking. However, there was no significant difference in the subjects heading direction between the two visual scene polarity conditions. Therefore, it was inferred from these data that optic flow has a greater role than visual polarity in influencing adaptive locomotor function.
NASA Astrophysics Data System (ADS)
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.
Transonic and supersonic Euler computations of vortex-dominated flow fields about a generic fighter
NASA Technical Reports Server (NTRS)
Goodsell, Aga M.; Melton, John E.
1991-01-01
Flow fields about a generic flighter model were computed using FL057, a 3-D, finite volume Euler code. Computed pressure coefficients, forces, and moments at several Mach numbers (0.6, 0.8, 1.2, 1.4, and 1.6) are compared with wind tunnel data over a wide range of angles of attack in order to determine the applicability of the code for the analysis of fighter configurations. Two configurations were studied, a wing-body and a wing-body-chine. FL057 predicted pressure distributions, forces, and moments well at low angles of attack, at which the flow was fully attached. The FL057 predictions were also accurate for some test conditions once the leading edge vortex became well established. At the subsonic speeds, FL057 predicted vortex breakdown earlier than that seen in the experimental results. Placing the chine on the forebody delayed the onset of bursting and improved the correlation between numerical and experimental data at the subsonic conditions.
Advective hydrogel membrane chromatography for monoclonal antibody purification in bioprocessing.
Hou, Ying; Brower, Mark; Pollard, David; Kanani, Dharmesh; Jacquemart, Renaud; Kachuik, Bradley; Stout, James
2015-01-01
Protein A chromatography is widely employed for the capture and purification of monoclonal antibodies (mAbs). Because of the high cost of protein A resins, there is a significant economic driving force to seek new downstream processing strategies. Membrane chromatography has emerged as a promising alternative to conventional resin based column chromatography. However, to date, the application has been limited to mostly ion exchange flow through (FT) mode. Recently, significant advances in Natrix hydrogel membrane has resulted in increased dynamic binding capacities for proteins, which makes membrane chromatography much more attractive for bind/elute operations. The dominantly advective mass transport property of the hydrogel membrane has also enabled Natrix membrane to be run at faster volumetric flow rates with high dynamic binding capacities. In this work, the potential of using Natrix weak cation exchange membrane as a mAb capture step is assessed. A series of cycle studies was also performed in the pilot scale device (> 30 cycles) with good reproducibility in terms of yield and product purities, suggesting potential for improved manufacturing flexibility and productivity. In addition, anion exchange (AEX) hydrogel membranes were also evaluated with multiple mAb programs in FT mode. Significantly higher binding capacity for impurities (support mAb loads up to 10Kg/L) and 40X faster processing speed were observed compared with traditional AEX column chromatography. A proposed protein A free mAb purification process platform could meet the demand of a downstream purification process with high purity, yield, and throughput. PMID:26018631
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
Dynamo dominated accretion and energy flow: The mechanism of active galactic nuclei
Colgate, S.A.; Li, H.
1998-12-31
An explanation of the magnetic fields of the universe, the central mass concentration of galaxies, the massive black hole of every galaxy, and the AGN phenomena has been an elusive goal. The authors suggest here the outlines of such a theoretical understanding and point out where the physical understanding is missing. They believe there is an imperative to the sequence of mass flow and hence energy flow in the collapse of a galactic mass starting from the first non-linearity appearing in structure formation following decoupling. This first non-linearity of a two to one density fluctuation, the Lyman-{alpha} clouds, ultimately leads to the emission spectra of the phenomenon of AGN, quasars, blazars, etc. The over-arching physical principle is the various mechanisms for the transport of angular momentum. They believe they have now understood the new physics of two of these mechanisms that have previously been illusive and as a consequence they impose strong constraints on the initial conditions of the mechanisms for the subsequent emission of the gravitational binding energy. The new phenomena described are: (1) the Rossby vortex mechanism of the accretion disk {alpha}-viscosity, and (2) the mechanism of the {alpha}-{Omega} dynamo in the accretion disk. The Rossby vortex mechanism leads to a prediction of the black hole mass and rate of energy release and the {alpha}-{Omega} dynamo leads to the generation of the magnetic flux of the galaxy (and the far greater magnetic flux of clusters) and separately explains the primary flux of energy emission as force-free magnetic energy density. This magnetic flux and magnetic energy density separately are the necessary consequence of the saturation of a dynamo created by the accretion disk with a gain greater than unity.
Gene flow and population structure of a solitary top carnivore in a human-dominated landscape
McManus, Jeannine S; Dalton, Desiré L; Kotzé, Antoinette; Smuts, Bool; Dickman, Amy; Marshal, Jason P; Keith, Mark
2015-01-01
While African leopard populations are considered to be continuous as demonstrated by their high genetic variation, the southernmost leopard population exists in the Eastern and Western Cape, South Africa, where anthropogenic activities may be affecting this population's structure. Little is known about the elusive, last free-roaming top predator in the region and this study is the first to report on leopard population structuring using nuclear DNA. By analyzing 14 microsatellite markers from 40 leopard tissue samples, we aimed to understand the populations' structure, genetic distance, and gene flow (Nm). Our results, based on spatially explicit analysis with Bayesian methods, indicate that leopards in the region exist in a fragmented population structure with lower than expected genetic diversity. Three population groups were identified, between which low to moderate levels of gene flow were observed (Nm 0.5 to 3.6). One subpopulation exhibited low genetic differentiation, suggesting a continuous population structure, while the remaining two appear to be less connected, with low emigration and immigration between these populations. Therefore, genetic barriers are present between the subpopulations, and while leopards in the study region may function as a metapopulation, anthropogenic activities threaten to decrease habitat and movement further. Our results indicate that the leopard population may become isolated within a few generations and suggest that management actions should aim to increase habitat connectivity and reduce human–carnivore conflict. Understanding genetic diversity and connectivity of populations has important conservation implications that can highlight management of priority populations to reverse the effects of human-caused extinctions. PMID:25691961
Accuracy of a pulse-coherent acoustic Doppler profiler in a wave-dominated flow
Lacy, J.R.; Sherwood, C.R.
2004-01-01
The accuracy of velocities measured by a pulse-coherent acoustic Doppler profiler (PCADP) in the bottom boundary layer of a wave-dominated inner-shelf environment is evaluated. The downward-looking PCADP measured velocities in eight 10-cm cells at 1 Hz. Velocities measured by the PCADP are compared to those measured by an acoustic Doppler velocimeter for wave orbital velocities up to 95 cm s-1 and currents up to 40 cm s-1. An algorithm for correcting ambiguity errors using the resolution velocities was developed. Instrument bias, measured as the average error in burst mean speed, is -0.4 cm s-1 (standard deviation = 0.8). The accuracy (root-mean-square error) of instantaneous velocities has a mean of 8.6 cm s-1 (standard deviation = 6.5) for eastward velocities (the predominant direction of waves), 6.5 cm s-1 (standard deviation = 4.4) for northward velocities, and 2.4 cm s-1 (standard deviation = 1.6) for vertical velocities. Both burst mean and root-mean-square errors are greater for bursts with ub ??? 50 cm s-1. Profiles of burst mean speeds from the bottom five cells were fit to logarithmic curves: 92% of bursts with mean speed ??? 5 cm s-1 have a correlation coefficient R2 > 0.96. In cells close to the transducer, instantaneous velocities are noisy, burst mean velocities are biased low, and bottom orbital velocities are biased high. With adequate blanking distances for both the profile and resolution velocities, the PCADP provides sufficient accuracy to measure velocities in the bottom boundary layer under moderately energetic inner-shelf conditions.
NASA Astrophysics Data System (ADS)
Ebner, Pirmin Philipp; Andreoli, Christian; Schneebeli, Martin; Steinfeld, Aldo
2015-12-01
Snow at or close to the surface commonly undergoes temperature gradient metamorphism under advective flow, which alters its microstructure and physical properties. A functional understanding of this process is essential for many disciplines, from modeling the effects of snow on regional and global climate to assessing avalanche formation. Time-lapse X-ray microtomography was applied to investigate the structural dynamics of temperature gradient snow metamorphism exposed to an advective airflow in controlled laboratory conditions. Experiments specifically analyzed sublimation and deposition of water vapor on the ice structure. In addition, an analysis of the ice-air interface dynamics was carried out using a macroscopic equivalent model of heat and water vapor transport through a snow layer. The results indicate that sublimation of the ice matrix dominated for flow rates < 10-6 m3 s-1 while during increased mass flow rates the water vapor deposition supplied by the advective flow counteracted sublimation. A flow rate dependence of water vapor deposition at the ice interface was observed, asymptotically approaching an average estimated maximum deposition rate on the whole sample of 1.05 · 10-4 kg m-3 s-1. The growth of microsized whisker-like crystals on larger ice crystals was detected on microscope photographs, leading to an increase of the specific surface area and thus suggest a change of the physical and optical properties of the snow. The estimated values of the curvature effect of the ice crystals and the interface kinetic coefficient are in good agreement with previously published values.
Logan, W.S.; Auge, M.P.; Panarello, H.O.
1999-03-01
Most of the cities southeast of Buenos Aires, Argentina, depend heavily on ground water for water supply. Whereas ground water quality is generally good in the region, economic development along the coastal plain has been constrained by high salinities. Fifty-four wells were sampled for major ions in zones of recharge, transport and discharge in an area near La Plata, 50 km southeast of Buenos Aires. The shallow, southwest to northeast coastal flow system is >30 km long but is only 50 to 80 m thick. It consists of Plio-Pleistocene fluvial sand overlain by Pleistocene eolian and fluvial silt and Holocene estuarine silty clay. Hydrochemical endmembers include HCO{sub 3}, SO{sub 4}, and Cl water. Bicarbonate-type water includes high plain recharge water that evolves through cation exchange and calcite dissolution to a high pH, pure Na-HCO{sub 3} endmember at the southwest edge of the coastal plain. Similar Na-HCO{sub 3} water is also found underlying recharge areas of the central coastal plain, and a lens of Ca-HCO{sub 3} water is associated with a ridge of shell debris parallel to the coast. Mixed cation-Cl water near the coastline represents intruded sea water that has undergone cation exchange. Chemically similar water underlying the southwest coastal plain, however, can be shown isotopically to have formed from fairly dilute solutions concentrated many times by evapotranspiration.
Continuous flow dielectrophoretic particle concentrator
Cummings, Eric B.
2007-04-17
A continuous-flow filter/concentrator for separating and/or concentrating particles in a fluid is disclosed. The filter is a three-port device an inlet port, an filter port and a concentrate port. The filter separates particles into two streams by the ratio of their dielectrophoretic mobility to their electrokinetic, advective, or diffusive mobility if the dominant transport mechanism is electrokinesis, advection, or diffusion, respectively.Also disclosed is a device for separating and/or concentrating particles by dielectrophoretic trapping of the particles.
Phase mixing versus nonlinear advection in drift-kinetic plasma turbulence
NASA Astrophysics Data System (ADS)
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).
Topology preserving advection of implicit interfaces on Cartesian grids
NASA Astrophysics Data System (ADS)
Qin, Zhipeng; Delaney, Keegan; Riaz, Amir; Balaras, Elias
2015-06-01
Accurate representation of implicit interface topology is important for the numerical computation of two phase flow on Cartesian grids. A new method is proposed for the construction of signed distance function by geometrically projecting interface topology onto the Cartesian grid using a multi-level projection framework. The method involves a stepwise improvement in the approximation to the signed distance function based on pointwise, piecewise and locally smooth reconstructions of the interface. We show that this approach provides accurate representation of the projected interface and its topology on the Cartesian grid, including the distance from the interface and the interface normal and curvature. The projected interface can be in the form of either a connected set of marker particles that evolve with Lagrangian advection, or a discrete set of points associated with an implicit interface that evolves with the advection of a scalar function. The signed distance function obtained with geometric projection is independent of the details of the scaler field, in contrast to the conventional approach where advection and reinitialization cannot be decoupled. As a result, errors introduced by reinitialization do not amplify advection errors, which leads to substantial improvement in both volume conservation and topology representation.
NASA Technical Reports Server (NTRS)
Waugh, Darryn W.; Plumb, R. Alan
1994-01-01
We present a trajectory technique, contour advection with surgery (CAS), for tracing the evolution of material contours in a specified (including observed) evolving flow. CAS uses the algorithms developed by Dritschel for contour dynamics/surgery to trace the evolution of specified contours. The contours are represented by a series of particles, which are advected by a specified, gridded, wind distribution. The resolution of the contours is preserved by continually adjusting the number of particles, and finescale features are produced that are not present in the input data (and cannot easily be generated using standard trajectory techniques). The reliability, and dependence on the spatial and temporal resolution of the wind field, of the CAS procedure is examined by comparisons with high-resolution numerical data (from contour dynamics calculations and from a general circulation model), and with routine stratospheric analyses. These comparisons show that the large-scale motions dominate the deformation field and that CAS can accurately reproduce small scales from low-resolution wind fields. The CAS technique therefore enables examination of atmospheric tracer transport at previously unattainable resolution.
Duncan, C J; Worth, J R P; Jordan, G J; Jones, R C; Vaillancourt, R E
2016-01-01
Nothofagus cunninghamii is a long-lived, wind-pollinated tree species that dominates the cool temperate rainforests of southeastern Australia. The species' distribution is more or less continuous in western Tasmania but is fragmented elsewhere. However, it is unknown whether this fragmentation has affected the species' genetic architecture. Thus, we examined N. cunninghamii using 12 nuclear microsatellites and 633 individuals from 18 populations spanning the species' natural range. Typical of wind-pollinated trees, there was low range-wide genetic structure (FST=0.04) consistent with significant gene flow across most of the species' range. However, gene flow was not high enough to overcome the effects of drift across some disjunctions. Victorian populations (separated from Tasmania by the 240 km wide Bass Strait) formed a genetic group distinct from Tasmanian populations, had lower diversity (mean allelic richness (Ar)=5.4 in Victoria versus 6.9 in Tasmania) and were significantly more differentiated from one another than those in Tasmania (FST=0.045 in Victoria versus 0.012 in Tasmania). Evidence for bottlenecking was found in small populations that were at least 20 km from other populations. Interestingly, we found little divergence in microsatellite markers between the extremes of genetically based morphological and physiological altitudinal clines suggesting adaptive differentiation is strongly driven by selection because it is likely to be occurring in the presence of gene flow. Even though the cool temperate rainforests of Australia are highly relictual, the species is relatively robust to population fragmentation due to high levels of genetic diversity and gene flow, especially in Tasmania. PMID:26350630
Lévy-taxis: a novel search strategy for finding odor plumes in turbulent flow-dominated environments
NASA Astrophysics Data System (ADS)
Pasternak, Zohar; Bartumeus, Frederic; Grasso, Frank W.
2009-10-01
Locating chemical plumes in aquatic or terrestrial environments is important for many economic, conservation, security and health related human activities. The localization process is composed mainly of two phases: finding the chemical plume and then tracking it to its source. Plume tracking has been the subject of considerable study whereas plume finding has received little attention. We address here the latter issue, where the searching agent must find the plume in a region often many times larger than the plume and devoid of the relevant chemical cues. The probability of detecting the plume not only depends on the movements of the searching agent but also on the fluid mechanical regime, shaping plume intermittency in space and time; this is a basic, general problem when exploring for ephemeral resources (e.g. moving and/or concealing targets). Here we present a bio-inspired search strategy named Lévy-taxis that, under certain conditions, located odor plumes significantly faster and with a better success rate than other search strategies such as Lévy walks (LW), correlated random walks (CRW) and systematic zig-zag. These results are based on computer simulations which contain, for the first time ever, digitalized real-world water flow and chemical plume instead of their theoretical model approximations. Combining elements of LW and CRW, Lévy-taxis is particularly efficient for searching in flow-dominated environments: it adaptively controls the stochastic search pattern using environmental information (i.e. flow) that is available throughout the course of the search and shows correlation with the source providing the cues. This strategy finds natural application in real-world search missions, both by humans and autonomous robots, since it accomodates the stochastic nature of chemical mixing in turbulent flows. In addition, it may prove useful in the field of behavioral ecology, explaining and predicting the movement patterns of various animals searching for
Advective and diffusive cosmic ray transport in galactic haloes
NASA Astrophysics Data System (ADS)
Heesen, Volker; Dettmar, Ralf-Jürgen; Krause, Marita; Beck, Rainer; Stein, Yelena
2016-05-01
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 Australia Telescope Compact Array observations of two edge-on galaxies, NGC 7090 and 7462, at λλ 22 and 6 cm. Our result is that the cosmic ray transport in NGC 7090 is advection dominated with V=150^{+80}_{-30} km s^{-1}, and that the one in NGC 7462 is diffusion dominated with D=3.0± 1.0 × 10^{28}E_GeV^{0.5} cm^2 s^{-1}. NGC 7090 has both a thin and thick radio disc with respective magnetic field scale heights of hB1 = 0.8 ± 0.1 kpc and hB2 = 4.7 ± 1.0 kpc. NGC 7462 has only a thick radio disc with hB2 = 3.8 ± 1.0 kpc. In both galaxies, the magnetic field scale heights are significantly smaller than what estimates from energy equipartition would suggest. A non-negligible fraction of cosmic ray electrons can escape from NGC 7090, so that this galaxy is not an electron calorimeter.
Thullen, J.S.; Nelson, S.M.; Cade, B.S.; Sartoris, J.J.
2008-01-01
Decomposition of senesced culm material of two bulrush species was studied in a surface-flow ammonia-dominated treatment wetland in southern California. Decomposition of the submerged culm material during summer months was relatively rapid (k = 0.037 day-1), but slowed under extended submergence (up to 245 days) and during fall and spring sampling periods (k = 0.009-0.014 day-1). Stepwise regression of seasonal data indicated that final water temperature and abundance of the culm-mining midge, Glyptotendipes, were significantly associated with culm decomposition. Glyptotendipes abundance, in turn, was correlated with water quality parameters such as conductivity and dissolved oxygen and ammonia concentrations. No differences were detected in decomposition rates between the bulrush species, Schoenoplectus californicus and Schoenoplectus acutus.
Cellwise conservative unsplit advection for the volume of fluid method
NASA Astrophysics Data System (ADS)
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.
Verification of Advective Bar Elements Implemented in the Aria Thermal Response Code.
Mills, Brantley
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.
Advection, diffusion, and delivery over a network
NASA Astrophysics Data System (ADS)
Heaton, Luke L. M.; López, Eduardo; Maini, Philip K.; Fricker, Mark D.; Jones, Nick S.
2012-08-01
Many biological, geophysical, and technological systems involve the transport of a resource over a network. In this paper, we present an efficient method for calculating the exact quantity of the resource in each part of an arbitrary network, where the resource is lost or delivered out of the network at a given rate, while being subject to advection and diffusion. The key conceptual step is to partition the resource into material that does or does not reach a node over a given time step. As an example application, we consider resource allocation within fungal networks, and analyze the spatial distribution of the resource that emerges as such networks grow over time. Fungal growth involves the expansion of fluid filled vessels, and such growth necessarily involves the movement of fluid. We develop a model of delivery in growing fungal networks, and find good empirical agreement between our model and experimental data gathered using radio-labeled tracers. Our results lead us to suggest that in foraging fungi, growth-induced mass flow is sufficient to account for long-distance transport, if the system is well insulated. We conclude that active transport mechanisms may only be required at the very end of the transport pathway, near the growing tips.
NASA Astrophysics Data System (ADS)
hrachowitz, M.; Savenije, H.; Bogaard, T.; Soulsby, C.; Tetzlaff, D.
2011-12-01
Flow generation processes on catchment scale are not yet quite understood. This commonly leads to substantial structural deficiencies and subsequent prediction uncertainties of particularly conceptual hydrological models when calibrated against runoff alone. Additional orthogonal information, such as observations of groundwater fluctuations or tracer response in streams, can help to gain crucial insights into the internal processes of catchments and thus help to reduce misrepresentations of these processes in model structures. However, such orthogonal data are frequently not available or where available, trade-offs have to be made between spatial and temporal coverage as well as temporal resolution. In this study we use long term (< 16 years) tracer data sets at relatively high resolution (1 week) for three contrasting catchments (~ 2 - 10 km2) in the Scottish Highlands together with parsimonious conceptual models to get a better understanding of catchment internal processes and of how changes in these processes are directly related to variations in external forcings. Furthermore the individual processes and their temporally changing importance are compared for the three catchments in order identify catchment characteristic dependent patterns of change in dominant flow generation and tracer translation processes. As a first step, owing to the contrasting appearance of the individual catchments, the most suitable out of 250 possible model structures for each catchment was identified in a FLEX-type modeling approach (Fenicia et al., 2008), based on the entire individual observation periods (NSE = 0.85, 0.78 and 0.65 for flow as well as 0.78, 0.65 and 0.51 for the tracer signal). Subsequently, these three model structures were calibrated individually for all n hydrological years of the observation period as well as for n one year periods classified according to the catchment wetness of these periods, i.e. from the wettest to the driest period. This then allowed
DEVELOPMENT AND DEMONSTRATION OF A BIDIRECTIONAL ADVECTIVE FLUX METER FOR SEDIMENT-WATER INTERFACE
A bidirectional advective flux meter for measuring water transport across the sediment-water interface has been successfully developed and field tested. The flow sensor employs a heat-pulse technique combined with a flow collection funnel for the flow measurement. Because the dir...
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. PMID:21600670
Super-diffusion versus competitive advection: a simulation
NASA Astrophysics Data System (ADS)
Del Moro, D.; Giannattasio, F.; Berrilli, F.; Consolini, G.; Lepreti, F.; Gošić, M.
2015-04-01
Context. Magnetic element tracking is often used to study the transport and diffusion of the magnetic field on the solar photosphere. From the analysis of the displacement spectrum of these tracers, it has recently been agreed that a regime of super-diffusivity dominates the solar surface. Quite habitually this result is discussed in the framework of fully developed turbulence. Aims: However, the debate whether the super-diffusivity is generated by a turbulent dispersion process, by the advection due to the convective pattern, or even by another process is still open, as is the question of the amount of diffusivity at the scales relevant to the local dynamo process. Methods: To understand how such peculiar diffusion in the solar atmosphere takes place, we compared the results from two different data sets (ground-based and space-borne) and developed a simulation of passive tracers advection by the deformation of a Voronoi network. Results: The displacement spectra of the magnetic elements obtained by the data sets are consistent in retrieving a super-diffusive regime for the solar photosphere, but the simulation also shows a super-diffusive displacement spectrum: its competitive advection process can reproduce the signature of super-diffusion. Conclusions: Therefore, it is not necessary to hypothesize a totally developed turbulence regime to explain the motion of the magnetic elements on the solar surface.
NASA Astrophysics Data System (ADS)
Mwelwa, Elenestina; Crosato, Alessandra; Wright, Nigel; Beevers, Lindsay
2013-04-01
The research work in the Middle Zambezi sub-catchment has the key objective to investigate the state of the river and its flood plain in terms of flow variation, river and flood plain morphological variation for both the pre and post hydropower schemes. From the rich biodiversity that this area supports, both Zambia and Zimbabwe has established National Parks with Mana Pools National Park, Sapi and Chewore safari areas being designated as UNESCO World Heritage Site in 1984. The habitat sustenance depend on the river channels and the associated morphological features with the flood and recession interaction whose modification can lead to negative environmental consequences. The research findings on the state of the sub-catchment flows and morphology will be outlined. Highlights will be given on the following findings: dominance of hydropower regulation in the water balance of the river reach, historical map analysis and related rates of river channel morphology changes associated to dam operating events and, bed load sediment characterisation and distribution. With the use of SOBEK-Rural (1D/2D) model, analysis of future state of the sub-catchment will be outlined, taking into account the following scenarios: no dam state of the river reach; continue with current water regulation and operations; modification in water regulation to take into account favorable changes and; climate related variation of droughts. The research deductions and implications for maintaining the current dam operation practices will be outline as relates to the sustainability of the hydro-morphology and ecosystem of the catchment which support a rich wildlife habitat. The research observed critical water needs form the basis for environmental flows prescription and recommendation. Whereas the restoration of regular flooding has been identified to be important, the most critical need however is the timing of flood gate regulation which has been observed as a trigger to loss of islands and bars
NASA Astrophysics Data System (ADS)
Marren, Philip; Nyman, Petter; Kermode, Stephanie
2016-04-01
Bushfires play a major role in shaping landscapes across the globe. Whilst the role of fire in shaping and changing vegetation assemblages is relatively well understood, there is still debate about the significance of fire in driving landscape denudation, relative to other processes, such as major rainfall and flood events and questions remain about the frequency of extreme fire events over longer timescales in response to climate forcing. Studies of post-fire landscape impact of recent bushfires in southeast Australia indicate that where storm events occur shortly after a major bushfire, hillslope erosion is enhanced, due to debris flows and erosion of both primary hillslope sediment and sediment stored in hillslope channel networks. In Australia, knowledge of long-term bushfire frequency is largely derived from pollen and micro-charcoal records in lake-sediment archives and is not directly relevant to resolving questions regarding fire impacts on landscape denudation and sediment transfer. We excavated trenches in four alluvial fans at the base of hillslopes in the high country of northeast Victoria, Australia. This area was burnt by bushfires in 1939 and 2003, and regional climate and hydrology are strongly controlled by El Niño. The trenches were up to 3.5m deep, and in most cases intersected underlying floodplain sediment at the base of the trench, indicating that they provide a full record of sedimentation for that sector of the fan. Fan stratigraphy consisted of sub-horizontal (parallel to the fan surface) units 0.3-0.5m thick, with occasional units 1-1.2m thick, and cross-cutting channelized units. Debris flow deposits accounted for 70-80% of the observed sediments, with water-laid gravels and soil units forming the remainder. Most soil layers were burnt, and most (but not all) debris flow units contained charcoal. A typical stratigraphy consisted of 6-8 debris flow units per fan, with four units containing a fire signature or overlying a burnt soil layer
A Quasi-Conservative Adaptive Semi-Lagrangian Advection-Diffusion Scheme
NASA Astrophysics Data System (ADS)
Behrens, Joern
2014-05-01
Many processes in atmospheric or oceanic tracer transport are conveniently represented by advection-diffusion type equations. Depending on the magnitudes of both components, the mathematical representation and consequently the discretization is a non-trivial problem. We will focus on advection-dominated situations and will introduce a semi-Lagrangian scheme with adaptive mesh refinement for high local resolution. This scheme is well suited for pollutant transport from point sources, or transport processes featuring fine filamentation with corresponding local concentration maxima. In order to achieve stability, accuracy and conservation, we combine an adaptive mesh refinement quasi-conservative semi-Lagrangian scheme, based on an integral formulation of the underlying advective conservation law (Behrens, 2006), with an advection diffusion scheme as described by Spiegelman and Katz (2006). The resulting scheme proves to be conservative and stable, while maintaining high computational efficiency and accuracy.
Distinguishing resuspension and advection signals in a hypertidal estuary
NASA Astrophysics Data System (ADS)
Todd, David; Souza, Alex; Jago, Colin
2015-04-01
Terrestrial material is supplied to an estuary system by the river, while marine material is supplied by the sea. Whether the estuary acts as a trap or a bypass zone for SPM (suspended particulate matter) depends upon the properties and dynamics of both the estuary, including the tidal and residual behaviour of the currents, and the SPM, including particle sizes and settling velocities and concentration gradients, which together control the dynamics, such as the trapping efficiency, of the estuary. Whether an SPM signal is regarded as being one of resuspension or advection depends upon the area of interest, and therefore distinguishing between resuspension and advection can be complex. Material that is resuspended within the area of study is regarded as resuspension, while that which is resuspended outside, but passes through, the area of interest, is regarded as advection. The results of a measurement campaign undertaken in a hypertidal UK estuary during the pre-spring bloom February-March and post-spring bloom May-June are presented utilising a combination of acoustic and optical instruments, moorings, and CTD stations. A characteristic asymmetric "twin peak" signal is present during both time periods, implying the presence of both resuspension and advection. This is confirmed through the use of harmonic analysis. A seasonal variation in the relative importance of the resuspension and advection components is seen between the two observation periods, with the small (<122µm) and large (>122µm) particles displaying different behaviours and providing a strong indication of the presence of flocculation. Approximate point flux calculations showed a reduction in the horizontal gradient of concentration, and subsequently the flood dominance of sediment transport, between May-June and February-March. This has been attributed to changes in biological activity and atmospheric forcing between the two observational periods. Ebb-dominant concentrations brought about by the
NASA Astrophysics Data System (ADS)
Li, Q.; Wu, D. J.
2013-09-01
The use of concrete bridges in urban rail transit systems has raised many concerns regarding low-frequency (20-200 Hz) structure-borne noise due to the vibration of bridges when subjected to moving trains. Understanding the mechanism that determines the dominant frequencies of bridge vibrations is essential for both vibration and noise reduction. This paper presents a general procedure based on the force method to obtain the power flows within a coupled vehicle-track-bridge system, the point mobility of the system and the dynamic interaction forces connecting various components. The general coupling system consists of multi-rigid-bodies for the vehicles, infinite Euler beams representing the rails, two-dimensional or three-dimensional elements of the concrete bridges, and spring-dashpot pairs to model the wheel-rail contacts, the vehicle suspensions, the rail pads and the bridge bearings. The dynamic interaction of the coupled system is solved in the frequency domain by assuming the combined wheel-rail roughness moves forward relative to the stationary vehicles. The proposed procedure is first applied to a rail on discrete supports and then to a real urban rail transit U-shaped concrete bridge. The computed results show that the wheel-rail contact forces, the power flows to the rail/bridge subsystem and the accelerations of the bridge are primarily dominated by the contents around the natural frequency of a single wheel adhered to the elastically supported rail. If the ath node of the mth spring-dashpot pair and the bth node of the nth spring-dashpot pair are connected to the same rigid body, then δmnab(ω) can be expressed as δmnab(ω)=-{(}/{Mlω}, where Ml is the mass of the lth rigid body. If the ath node of the mth spring-dashpot pair and the bth node of the nth spring-dashpot pair are connected to the same infinite rail, δmnab(ω) can be expressed as [8] δmnab(ω)=-j{((e-je)}/{4EIk}, where xm and xn are the x-coordinates of the mth and nth spring
Kaffenberger, K.; Gruber, D.F.; MacVittie, T.J.
1988-01-01
Thymuses of rats that had been: (a) gamma-irradiated 500 cGy whole-body radiation (R), or (b) thermally injured 20% BSA dorsal, scald burn (TI), or c) combined injured irradiation followed by burn (CI) were studied for involution and recovery processes after sublethal treatments. The expression of surface antigens on thymic cells before and after injuries was evaluated using the monoclonal antibodies and flow cytometric analysis. Thymic cellularity decreased to less than 1% of normal (N), age-matched rats by 4 days after R or CI. Recovery reached 60% to 70% of N by 28 days post treatments. Expression of OX7, OX8, W3/13, and W3/25 antigens all reached nadirs of 40% of N by day 4 after R and CI. Recovery of antigen expression, except for W3/25, was near completion by day 7 after R and CI. Changes in antigen expression after TI were less pronounced for all mcAB tested. Variations in relative labeling of nonlymphoid thymic cells with OX4 (Ia-antigen) reflected the disappearance and recovery of radiosensitive lymphoid thymocytes. The similarity of results after R and CI demonstrate that the model of CI is radiation-dominated. The addition of burn injury to radiation trauma had no synergistically damaging effect on the parameters studied.
Gerrity, S; Kennelly, C; Clifford, E; Collins, G
2016-09-01
Hydrogen Sulfide (H2S) is an odourous, highly toxic gas commonly encountered in various commercial and municipal sectors. Three novel, laboratory-scale, Horizontal-Flow Biofilm Reactors (HFBRs) were tested for the removal of H2S gas from air streams over a 178-day trial at 10°C. Removal rates of up to 15.1 g [H2S] m(-3) h(-1) were achieved, demonstrating the HFBRs as a feasible technology for the treatment of H2S-contaminated airstreams at low temperatures. Bio-oxidation of H2S in the reactors led to the production of H(+) and sulfate (SO(2-)4) ions, resulting in the acidification of the liquid phase. Reduced removal efficiency was observed at loading rates of 15.1 g [H2S] m(-3) h(-1). NaHCO3 addition to the liquid nutrient feed (synthetic wastewater (SWW)) resulted in improved H2S removal. Bacterial diversity, which was investigated by sequencing and fingerprinting 16S rRNA genes, was low, likely due to the harsh conditions prevailing in the systems. The HFBRs were dominated by two species from the genus Acidithiobacillus and Thiobacillus. Nonetheless, there were significant differences in microbial community structure between distinct HFBR zones due to the influence of alkalinity, pH and SO4 concentrations. Despite the low temperature, this study indicates HFBRs have an excellent potential to biologically treat H2S-contaminated airstreams. PMID:26829048
Cox, T.J.; Runkel, R.L.
2008-01-01
Past applications of one-dimensional advection, dispersion, and transient storage zone models have almost exclusively relied on a central differencing, Eulerian numerical approximation to the nonconservative form of the fundamental equation. However, there are scenarios where this approach generates unacceptable error. A new numerical scheme for this type of modeling is presented here that is based on tracking Lagrangian control volumes across a fixed (Eulerian) grid. Numerical tests are used to provide a direct comparison of the new scheme versus nonconservative Eulerian numerical methods, in terms of both accuracy and mass conservation. Key characteristics of systems for which the Lagrangian scheme performs better than the Eulerian scheme include: nonuniform flow fields, steep gradient plume fronts, and pulse and steady point source loadings in advection-dominated systems. A new analytical derivation is presented that provides insight into the loss of mass conservation in the nonconservative Eulerian scheme. This derivation shows that loss of mass conservation in the vicinity of spatial flow changes is directly proportional to the lateral inflow rate and the change in stream concentration due to the inflow. While the nonconservative Eulerian scheme has clearly worked well for past published applications, it is important for users to be aware of the scheme's limitations. ?? 2008 ASCE.
Laser speckle contrast imaging is sensitive to advective flux
NASA Astrophysics Data System (ADS)
Khaksari, Kosar; Kirkpatrick, Sean J.
2016-07-01
Unlike laser Doppler flowmetry, there has yet to be presented a clear description of the physical variables that laser speckle contrast imaging (LSCI) is sensitive to. Herein, we present a theoretical basis for demonstrating that LSCI is sensitive to total flux and, in particular, the summation of diffusive flux and advective flux. We view LSCI from the perspective of mass transport and briefly derive the diffusion with drift equation in terms of an LSCI experiment. This equation reveals the relative sensitivity of LSCI to both diffusive flux and advective flux and, thereby, to both concentration and the ordered velocity of the scattering particles. We demonstrate this dependence through a short series of flow experiments that yield relationships between the calculated speckle contrast and the concentration of the scatterers (manifesting as changes in scattering coefficient), between speckle contrast and the velocity of the scattering fluid, and ultimately between speckle contrast and advective flux. Finally, we argue that the diffusion with drift equation can be used to support both Lorentzian and Gaussian correlation models that relate observed contrast to the movement of the scattering particles and that a weighted linear combination of these two models is likely the most appropriate model for relating speckle contrast to particle motion.
Advection fog formation in a polluted atmosphere
Hung, R.J.; Liaw, G.S.
1981-01-01
Large quantities of atmospheric aerosols with composition SO/sub 4//sup 2 -/, NO/sub 3//sup -/ and NH/sub 4//sup +/ have been detected in highly industrialized areas. The major portions of aerosol products are the results of energy related fuel combustion. Both microphysical and macrophysical processes are considered in investigating the time dependent evolution of the saturation spectra of condensation nuclei associated with both polluted and clean atmospheres during the time periods of advection fog formation. The results show that the condensation nuclei associated with a polluted atmosphere provide more favorable conditions than condensation nuclei associated with a clean atmosphere to produce dense advection fog, and that attaining a certain degree of supersaturation is not necessarily required for the formation of advection fog with condensation nuclei associated with a polluted atmosphere for monodisperse distribution.
Antidiffusive velocities for multipass donor cell advection
Margolin, L.; Smolarkiewicz, P.K.
1999-01-01
Multidimensional positive definite advection transport algorithm (MPDATA) is an iterative process for approximating the advection equation, which uses a donor cell approximation to compensate for the truncation error of the originally specified donor cell scheme. This step may be repeated an arbitrary number of times, leading to successfully more accurate solutions to the advection equation. In this paper, the authors show how to sum the successive approximations analytically to find a single antidiffusive velocity that represents the effects of an arbitrary number of passes. The analysis is first done in one dimension to illustrate the method and then is repeated in two dimensions. The existence of cross terms in the truncation analysis of the two-dimensional equations introduces an extra complication into the calculation. The authors discuss the implementation of the antidiffusive velocities and provide some examples of applications, including a third-order accurate scheme.
Visualizing Vector Fields Using Line Integral Convolution and Dye Advection
NASA Technical Reports Server (NTRS)
Shen, Han-Wei; Johnson, Christopher R.; Ma, Kwan-Liu
1996-01-01
We present local and global techniques to visualize three-dimensional vector field data. Using the Line Integral Convolution (LIC) method to image the global vector field, our new algorithm allows the user to introduce colored 'dye' into the vector field to highlight local flow features. A fast algorithm is proposed that quickly recomputes the dyed LIC images. In addition, we introduce volume rendering methods that can map the LIC texture on any contour surface and/or translucent region defined by additional scalar quantities, and can follow the advection of colored dye throughout the volume.
Chaotic Advection, Fluid Spreading, and Groundwater Contaminant Plumes
NASA Astrophysics Data System (ADS)
Neupauer, R. M.; Mays, D. C.
2011-12-01
In situ remediation of contaminated groundwater requires degradation reactions at the interface between the contaminant plume and an injected treatment solution containing chemical or biological amendments. Therefore a promising approach to accelerate in situ remediation is to elongate the interface between the contaminant plume and treatment solution through fluid spreading. The literature on chaotic advection describes how to accomplish spreading in laminar flows, which lack the turbulent eddies that provide spreading in streams or engineered reactors. A key result from the literature on chaotic advection is that spreading is inherent in the vicinity of certain periodic points, which are points to which fluid particles return in successive iterations of chaotic flows. Specifically, spreading is enhanced near the stable and unstable manifolds associated with hyperbolic periodic points. We investigate the transient flow created with a four-well system in which wells are operated sequentially as either injection wells or extraction wells. In particular, we identify the periodic points and demonstrate that fluid spreading occurs nearby. For appropriately designed injection and extraction sequences, the periodic points are located near the interface between the contaminant plume and treatment solution, leading to elongation of the interface, with expected benefits of enhanced reaction and accelerated remediation.
Advection of surface-derived organic carbon fuels microbial reduction in Bangladesh groundwater
Mailloux, Brian J.; Trembath-Reichert, Elizabeth; Cheung, Jennifer; Watson, Marlena; Stute, Martin; Freyer, Greg A.; Ferguson, Andrew S.; Ahmed, Kazi Matin; Alam, Md. Jahangir; Buchholz, Bruce A.; Thomas, James; Layton, Alice C.; Zheng, Yan; Bostick, Benjamin C.; van Geen, Alexander
2013-01-01
Chronic exposure to arsenic (As) by drinking shallow groundwater causes widespread disease in Bangladesh and neighboring countries. The release of As naturally present in sediment to groundwater has been linked to the reductive dissolution of iron oxides coupled to the microbial respiration of organic carbon (OC). The source of OC driving this microbial reduction—carbon deposited with the sediments or exogenous carbon transported by groundwater—is still debated despite its importance in regulating aquifer redox status and groundwater As levels. Here, we used the radiocarbon (14C) signature of microbial DNA isolated from groundwater samples to determine the relative importance of surface and sediment-derived OC. Three DNA samples collected from the shallow, high-As aquifer and one sample from the underlying, low-As aquifer were consistently younger than the total sediment carbon, by as much as several thousand years. This difference and the dominance of heterotrophic microorganisms implies that younger, surface-derived OC is advected within the aquifer, albeit more slowly than groundwater, and represents a critical pool of OC for aquifer microbial communities. The vertical profile shows that downward transport of dissolved OC is occurring on anthropogenic timescales, but bomb 14C-labeled dissolved OC has not yet accumulated in DNA and is not fueling reduction. These results indicate that advected OC controls aquifer redox status and confirm that As release is a natural process that predates human perturbations to groundwater flow. Anthropogenic perturbations, however, could affect groundwater redox conditions and As levels in the future. PMID:23487743
NASA Astrophysics Data System (ADS)
Petrelli, Maurizio; El Omari, Kamal; Le Guer, Yves; Perugini, Diego
2016-02-01
We numerically define the thermochemical evolution of a subduction-related crystal-bearing magmatic mass at mid crustal levels (0.7 GPa, 20-25 km). Two main dynamic mechanisms are considered: (1) a pure buoyancy-driven system where the convective flow is induced by density changes during magma cooling; (2) a buoyancy-driven convective system governed by chaotic advection. The non-Newtonian rheology of natural magmas is taken into account linking the Herschel-Bulkley formulation with the results of fractional crystallization experiments of magmas with the same composition and at the same conditions of temperature and pressure of the studied system. The latent heat of crystallization is also considered in order to address the thermal release in the system induced by the crystallization. Results indicate that the development of chaotic advection generates a complex thermochemical evolution of the system speeding up the crystallization process and the timing required to reach the jamming condition relative to the pure buoyancy-driven convective system (nearly 2 times faster). Our results have important implications for both the rheological history of the magmatic body and the refilling of shallower magmatic systems. In particular, (1) a time-dependent composition ranging from basalt to andesite can be extracted from an initial basaltic magmatic batch; (2) at the attainment of the maximum packing fraction (i.e., just before the jamming condition), homogeneous andesitic melts can be potentially extracted from the system; and (3) the development of chaotic advection within the system allows for the extraction of andesitic melt in shorter times compared to a buoyancy-dominated system.
Positivity-preserving numerical schemes for multidimensional advection
NASA Technical Reports Server (NTRS)
Leonard, B. P.; Macvean, M. K.; Lock, A. P.
1993-01-01
This report describes the construction of an explicit, single time-step, conservative, finite-volume method for multidimensional advective flow, based on a uniformly third-order polynomial interpolation algorithm (UTOPIA). Particular attention is paid to the problem of flow-to-grid angle-dependent, anisotropic distortion typical of one-dimensional schemes used component-wise. The third-order multidimensional scheme automatically includes certain cross-difference terms that guarantee good isotropy (and stability). However, above first-order, polynomial-based advection schemes do not preserve positivity (the multidimensional analogue of monotonicity). For this reason, a multidimensional generalization of the first author's universal flux-limiter is sought. This is a very challenging problem. A simple flux-limiter can be found; but this introduces strong anisotropic distortion. A more sophisticated technique, limiting part of the flux and then restoring the isotropy-maintaining cross-terms afterwards, gives more satisfactory results. Test cases are confined to two dimensions; three-dimensional extensions are briefly discussed.
Metamorphism during temperature gradient with undersaturated advective airflow in a snow sample
NASA Astrophysics Data System (ADS)
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.
Horizontal advection, diffusion and plankton spectra at the sea surface.
NASA Astrophysics Data System (ADS)
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.
Multiple anisotropic collisions for advection-diffusion Lattice Boltzmann schemes
NASA Astrophysics Data System (ADS)
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.
NASA Astrophysics Data System (ADS)
Santos, Isaac R.; Eyre, Bradley D.; Glud, Ronnie N.
2012-11-01
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). Experimental conditions (flow path length, advection rate, and temperature) were manipulated to represent conditions similar to near shore tropical environments. HgCl2-poisoned controls were used to assess whether reactions were microbially mediated. Overall, significant correlations were found between oxygen consumption and N2 production. The N:O2 slope of 0.114 implied that about 75% of all the nitrogen mineralized was denitrified. A 4-fold increase in sediment column length (from 10 to 40 cm) resulted in an overall increase in oxygen consumption (1.6-fold), TCO2 production (1.8-fold), and denitrification (1.9-fold). Oxic respiration increased quickly until advection reached 80 L m-2 h-1 and then plateaued at higher advection rates. Interestingly, denitrification peaked (up to 336 μmol N2 m-2 h-1) at intermediate advection rates (30-80 L m-2 h-1). We speculate that intermediate advection rates enhance the development of microniches (i.e., steep oxygen gradients) within porous carbonate sands, perhaps providing optimum conditions for denitrification. The denitrification peak fell within the broad range of advection rates (often on scales of 1-100 L m-2 h-1) typically found on continental shelves implying that carbonate sands may play a major, but as yet unquantified, role in oceanic nitrogen budgets.
NASA Astrophysics Data System (ADS)
Kampf, Stephanie K.; Lefsky, Michael A.
2016-01-01
The Colorado Front Range has a large elevation gradient with deep seasonal snowpack in the mountains and limited snow accumulation in the foothills and plains. This study examines how the sources of annual peak flows (snowmelt, rainfall, mixed) change with the fraction of time snow persists on the ground, snow persistence (SP), and whether these sources have changed over time. Sources of peak flows for 20 gaging stations are estimated using a gridded rain and snow model forced with PRISM daily precipitation and both PRISM and TopoWx temperature. The mean snowmelt contribution to peak flow is highly correlated with SP (r2 = 0.86-0.90). Watersheds with SP < 0.3 (low snow, elevation <2000 m) are rainfall-dominated, and watersheds with SP > 0.7 (persistent snow, elevation >3100 m) are mostly snowmelt-dominated, with mixed sources between these thresholds. Rainfall runoff peak flows are possible at all elevations, but their likelihood declines with increasing SP. Rainfall runoff from an extreme storm in September 2013 produced the highest annual peaks at many stations, including some snowmelt-dominated watersheds. Regional Kendall trend tests indicate that the contributions of snowmelt to peak flows and total annual inputs have declined in the mixed source zone. These changes may affect hydrographs, as analyses confirm that snowmelt runoff generally produces more attenuated peaks than rainfall runoff. Discrimination of peak flow source is sensitive to input data and model structure for mixed rain and snowmelt events, and both observation and modeling research are needed to help understand potential runoff changes in these conditions.
Frictional drag reduction by wavy advection of deformable bubbles
NASA Astrophysics Data System (ADS)
Oishi, Yoshihiko; Murai, Yuichi; Tasaka, Yuji; Yasushi, Takeda
2009-02-01
Bubbles can reduce frictional drag in wall turbulence, and its effect is expected to use for ships and pipelines to save their power consumptions. A number of basic experiments have been carried out to date for finding out the best condition for enhancing the drag reduction. One issue that remains at present is the difference of the performance between steady and unsteady status in terms of bubble concentration. All the experiments in the past deal with the steady effect, i.e., the drag reduction is evaluated as a function of mean void fraction or given gas flow rate of continuous injection. Despite to this, the actual phenomena highly depend on local interaction between two phases upon unsteady manner. We focus on this point and elucidate the influence of time-fluctuating void fraction on the total response to the drag reduction. This view is in fact important to estimate the persistency of the bubble-based drag reduction in the flow direction since bubbles formulate wavy advection during their migration. Our experiments are designed to measure the above-mentioned effect from laminar, transitional, and turbulent flows in a horizontal channel. For avoiding the contamination effect that worsens the reproducibility of the experiment, Silicone oil is used as carrier fluid. The oil also simulates the high Weber number bubble condition because of low surface tension. The unsteady interaction between the wavy advection of bubbles and the local skin friction, a synchronized system is constructed to connect the high-speed camera with the shear transducer, which can evaluate the interaction at 1000 fps. From the results, we confirm that the drag reduction is provided at Re>3000 in the turbulent flow regime, and also the total drag reduction is enhanced by the presence of the waves.
Evolution of Advection Upstream Splitting Method Schemes
NASA Technical Reports Server (NTRS)
Liou, Meng-Sing
2010-01-01
This paper focuses on the evolution of advection upstream splitting method(AUSM) schemes. The main ingredients that have led to the development of modern computational fluid dynamics (CFD) methods have been reviewed, thus the ideas behind AUSM. First and foremost is the concept of upwinding. Second, the use of Riemann problem in constructing the numerical flux in the finite-volume setting. Third, the necessity of including all physical processes, as characterised by the linear (convection) and nonlinear (acoustic) fields. Fourth, the realisation of separating the flux into convection and pressure fluxes. The rest of this review briefly outlines the technical evolution of AUSM and more details can be found in the cited references. Keywords: Computational fluid dynamics methods, hyperbolic systems, advection upstream splitting method, conservation laws, upwinding, CFD
Passive advection in a collisionless plasma
NASA Astrophysics Data System (ADS)
Kanekar, Anjor; Schekochihin, Alexander; Hammett, Greg; Dorland, William; Loureiro, Nuno
2014-10-01
We consider a simple kinetic model for the evolution of the particle distribution function in a magnetized turbulent plasma that includes both phase mixing (Landau damping) and advection by a stochastic velocity field: a ``kinetic passive scalar'' in the Batchelor regime. The advection due to stochastic velocity field allows for a stochastic version of the plasma echo by coupling the ``phase-mixing'' and the ``un-phase-mixing'' components of the free energy. We have developed a new analytical framework to diagnose the efficiency of such coupling. We have also developed a new GPU code named Gandalf that solves this kinetic model numerically. In this poster, we shall present numerical and analytical results related to this work.
Antidiffusive velocities for multipass donor cell advection
Margolin, L.G. ); Smolarkiewicz, P.K. )
1989-12-01
Smolarkiewicz describes an iterative process for approximating the advection equation. Basically, he uses a donor cell approximation to correct for the truncation error of the originally specified donor cell scheme. This step may be repeated an arbitrary number of times leading to successively more accurate solutions to the advection equation. In this report, we show how to sum the successive approximations analytically to find a single antidiffusive velocity that represents the effects of an arbitrary number of passes. The analysis is first done dimension to illustrate the method. The analysis is then repeated in two dimensions. The existence of cross terms in the truncation analysis of the two-dimensional equations introduces an extra complication into the calculation. We discuss the implementation of our new antidiffusive velocities and provide some examples of applications. 6 refs., 5 figs., 4 tabs.
Fanaian, Safa; Graas, Susan; Jiang, Yong; van der Zaag, Pieter
2015-02-01
The flow regime of rivers, being an integral part of aquatic ecosystems, provides many important services benefiting humans in catchments. Past water resource developments characterized by river embankments and dams, however, were often dominated by one (or few) economic use(s) of water. This results in a dramatically changed flow regime negatively affecting the provision of other ecosystem services sustained by the river flow. This study is intended to demonstrate the value of alternative flow regimes in a river that is highly modified by the presence of large hydropower dams and reservoirs, explicitly accounting for a broad range of flow-dependent ecosystem services. In this study, we propose a holistic approach for conducting an ecological economic assessment of a river's flow regime. This integrates recent advances in the conceptualization and classification of ecosystem services (UK NEA, 2011) with the flow regime evaluation technique developed by Korsgaard (2006). This integrated approach allows for a systematic comparison of the economic values of alternative flow regimes, including those that are considered beneficial for aquatic ecosystems. As an illustration, we applied this combined approach to the Lower Zambezi Basin, Mozambique. Empirical analysis shows that even though re-operating dams to create environmentally friendly flow regimes reduces hydropower benefits, the gains to goods derived from the aquatic ecosystem may offset the forgone hydropower benefits, thereby increasing the total economic value of river flow to society. The proposed integrated flow assessment approach can be a useful tool for welfare-improving decision-making in managing river basins. PMID:25461048
CONTAMINANT TRANSPORT IN SEDIMENT UNDER THE INFLUENCE OF ADVECTIVE FLUX
Chemical flux across the sediment/water interface is controlled by a combination of diffusive, dispersive and advective processes. The advective process is a function of submarine groundwater discharge and tidal effects. In areas where surface water interacts with groundwater, ...
Distributed Parallel Particle Advection using Work Requesting
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.
Mitchell, Sean C; Cunjak, Richard A
2007-11-01
The current paradigm of fish community distribution is one of a downstream increase in species richness by addition, but this concept is based on a small number of streams from the mid-west and southern United States, which are dominated by cyprinids. Further, the measure of species richness traditionally used, without including evenness, may not be providing an accurate reflection of the fish community. We hypothesize that in streams dominated by anadromous salmonids, fish community diversity will be affected by the presence of the anadromous species, and therefore be influenced by those factors affecting the salmonid population. Catamaran Brook, New Brunswick, Canada, provides a long-term data set to evaluate fish community diversity upstream and downstream of an obstruction (North American beaver Castor canadensis dam complex), which affects distribution of Atlantic salmon Salmo salar. The Shannon Weiner diversity index and community evenness were calculated for sample sites distributed throughout the brook and over 15 years. Fish community diversity was greatest upstream of the beaver dams and in the absence of Atlantic salmon. The salmon appear to depress the evenness of the community but do not affect species richness. The community upstream of the beaver dams changes due to replacement of slimy sculpin Cottus cognatus by salmon, rather than addition, when access is provided. Within Catamaran Brook, location of beaver dams and autumn streamflow interact to govern adult Atlantic salmon spawner distribution, which then dictates juvenile production and effects on fish community. These communities in an anadromous Atlantic salmon dominated stream do not follow the species richness gradient pattern shown in cyprinid-dominated streams and an alternative model for stream fish community distribution in streams dominated by anadromous salmonids is presented. This alternative model suggests that community distribution may be a function of semipermeable obstructions
A cryogenic circulating advective multi-pass absorption cell
NASA Astrophysics Data System (ADS)
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.
Chaotic advection in 2D anisotropic porous media
NASA Astrophysics Data System (ADS)
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.
A cryogenic circulating advective multi-pass absorption cell
Stockett, M. H.; Lawler, J. E.
2012-03-15
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 10{sup 7} cm{sup -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.
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 10(7) 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. PMID:22462957
OBSERVATION OF MAGNETIC RECONNECTION DRIVEN BY GRANULAR SCALE ADVECTION
Zeng Zhicheng; Cao Wenda; Ji Haisheng
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.
NASA Astrophysics Data System (ADS)
Tertre, E.; Hubert, F.; Bruzac, S.; Pacreau, M.; Ferrage, E.; Prêt, D.
2013-07-01
The present study aims at testing the validity of using an Na+/Ca2+ ion-exchange model, derived from batch data to interpret experimental Ca2+-for-Na+ exchange breakthrough curves obtained on vermiculite (a common swelling clay mineral in surface environments). The ion-exchange model was constructed considering the multi-site nature of the vermiculite surface as well as the exchange of all aqueous species (Mg2+ derived from the dissolution of the solid and H+). The proposed ion-exchange model was then coupled with a transport model, and the predicted breakthrough curves were compared with the experimental ones obtained using a well stirred flow-through reactor. For a given solute residence time in the reactor (typically 50 min), our thermodynamic model based on instantaneous equilibrium was found to accurately reproduce several of the experimental breakthrough curves, depending on the Na+ and Ca2+ concentrations of the influents pumped through the reactor. However the model failed to reproduce experimental breakthrough curves obtained at high flow rates and low chemical gradient between the exchanger phase and the solution. An alternative model based on a hybrid equilibrium/kinetic approach was thus used and allowed predicting experimental data. Based on these results, we show that a simple parameter can be used to differentiate between thermodynamic and kinetic control of the exchange reaction with water flow. The results of this study are relevant for natural systems where two aquatic environments having contrasted chemistries interact. Indeed, the question regarding the attainment of a full equilibrium in such a system during the contact time of the aqueous phase with the particle/colloid remains most often open. In this context, we show that when a river (a flow of fresh water) encounters marine colloids, a systematic full equilibrium can be assumed (i.e., the absence of kinetic effects) when the residence time of the solute in 1 m3 of the system is ⩾6200 h.
Advection and resulting CO2 exchange uncertainty in a tall forest in central Germany.
Kutsch, Werner L; Kolle, Olaf; Rebmann, Corinna; Knohl, Alexander; Ziegler, Waldemar; Schulze, Ernst-Detlef
2008-09-01
Potential losses by advection were estimated at Hainich Forest, Thuringia, Germany, where the tower is located at a gentle slope. Three approaches were used: (1) comparing nighttime eddy covariance fluxes to an independent value of total ecosystem respiration by bottom-up modeling of the underlying processes, (2) direct measurements of a horizontal CO2 gradient and horizontal wind speed at 2 m height in order to calculate horizontal advection, and (3) direct measurements of a vertical CO2 gradient and a three-dimensional wind profile in order to calculate vertical advection. In the first approach, nighttime eddy covariance measurements were compared to independent values of total ecosystem respiration by means of bottom-up modeling of the underlying biological processes. Turbulent fluxes and storage term were normalized to the fluxes calculated by the bottom-up model. Below a u(*) threshold of 0.6 m/s the normalized turbulent fluxes decreased with decreasing u(*), but the flux to the storage increased only up to values less than 20% of the modeled flux at low turbulence. Horizontal advection was measured by a horizontal CO2 gradient over a distance of 130 m combined with horizontal wind speed measurements. Horizontal advection occurred at most of the evenings independently of friction velocity above the canopy. Nevertheless, horizontal advection was higher when u(*) was low. The peaks of horizontal advection correlated with changes in temperature. A full mass balance including turbulent fluxes, storage, and horizontal and vertical advection resulted in an increase of spikes and scatter but seemed to generally improve the results from the flux measurements. The comparison of flux data with independent bottom-up modeling results as well as the direct measurements resulted in strong indications that katabatic flows along the hill slope during evening and night reduces the measured apparent ecosystem respiration rate. In addition, anabatic flows may occur during the
Sea breezes and advective effects in southwest James Bay
NASA Technical Reports Server (NTRS)
Mckendry, Ian; Roulet, Nigel
1994-01-01
Observations from a transect extending 100 km inland during the Northern Wetlands Study (NOWES) in 1990 show that the sea breeze develops on approximately 25% of days during summer and may penetrate up to 100 km inland on occasions. The sea breeze exhibits a marked diurnal clockwise rotation as a result of the Coriolis effect along the unobstructed coastline. The marine advective effect is shown to depend on gradient wind direction. With northwesterly upper level flow the sea breeze tends to be northeasterly in direction and is associated with decreased temperatures and vapor pressure deficits (VPD). With southwesterly upper level flow the sea breeze tends to have a southeasterly direction and less effect on temperatures and VPD. This is attributed to shorter residence times of air parcels over water. For two cases, Colorado State University mesoscale model simulations show good agreement with surface wind observations and suggest that under northwesterly gradient flow, Bowen ratios are increased in the onshore flow along western James Bay, while during southwesterly gradient flow these effects are negligible. These results have implications for the interpretation of local climate, ecology, and hydrology as well as land-based and airborne turbulent flux measurements made during NOWES.
ERIC Educational Resources Information Center
Selvaratnam, Viswanathan
1988-01-01
Third World adoption of the Western university and the accompanying Eurocentric system of information flow is criticized as sometimes being counterproductive and alien to developing nations. The potential for a self-reliant, interdependent higher education system among Third World countries is discussed. (MSE)
Power law breakthrough curve tailing in a fracture: The role of advection
NASA Astrophysics Data System (ADS)
Fiori, Aldo; Becker, Matthew W.
2015-06-01
We offer an explanation of the strongly tailed solute breakthrough curve typically observed when a tracer test is conducted in fractured bedrock. In this example, we limit the model to a single planar fracture of varying aperture. Flow heterogeneity derives from variable fracture aperture, which implies variable transmissivity (T). The analysis employs a physically based model well-suited to strong heterogeneity and relies only upon advective transport. The purely advective model is able to explain a power-law trend of magnitude -2 to -3 in the breakthrough curve tail; a range that has been found in field tracer experiments. The principle cause of this trend is the comparatively slow transport in zones of small transmissivity (tight aperture). Slow advection occurs when either heterogeneity (variance of lnT) is strong or when the assumed heterogeneity distribution is non-Gaussian. Thus, we link breakthrough tailing to the statistical parameters for the transmissivity field.
Garges, J.A.; Baehr, A.L.
1998-01-01
The relative importance of advection and dispersion for both solute and vapor transport can be determined from type curves or concentration, flux, or cumulative flux. The dimensionless form of the type curves provides a means to directly evaluate the importance of mass transport by advection relative to that of mass transport by diffusion and dispersion. Type curves based on an analytical solution to the advection-dispersion equation are plotted in terms of dimensionless time and Peclet number. Flux and cumulative flux type curves provide additional rationale for transport regime determination in addition to the traditional concentration type curves. The extension of type curves to include vapor transport with phase partitioning in the unsaturated zone is a new development. Type curves for negative Peclet numbers also are presented. A negative Peclet number characterizes a problem in which one direction of flow is toward the contamination source, and thereby diffusion and advection can act in opposite directions. Examples are the diffusion of solutes away from the downgradient edge of a pump-and-treat capture zone, the upward diffusion of vapors through the unsaturated zone with recharge, and the diffusion of solutes through a low hydraulic conductivity cutoff wall with an inward advective gradient.
A Novel Electrical Model for Advection-Diffusion-Based Molecular Communication in Nanonetworks.
Azadi, Mehdi; Abouei, Jamshid
2016-04-01
In this paper, we propose an end-to-end electrical model to characterize the communication between two nanomachines via advection-diffusion motion along the conventional pipe medium. For this modeling, we consider three modules consisting of transmitter, advection-diffusion propagation and receiver. The modulation scheme and releasing molecules through the conventional pipe medium from the transmitter nanomachine is represented in the transmitter module. The advection-diffusion propagation of molecules along the flow-induced path is shown in advection-diffusion propagation module, and the demodulation scheme of bounded particles at the receiver nanomachine is characterized in the receiver module. Our objective is to find an electrical model of each module under the zero initial condition which enables us to represent the electrical circuit related to each module. The transmitter and the signal propagation models are built on the basis of the molecular advection-diffusion physics, whereas the receiver model is interpreted by stemming from the theory of the ligand-receptor binding chemical process. In addition, we employ the transfer function of modules to derive the normalized gain and the delay of each module. Supported by numerical results, we analyze the effect of physical parameters of the pipe medium on the total normalized gain and delay of molecular communications. PMID:27046879
NASA Astrophysics Data System (ADS)
Sofiev, M.; Vira, J.; Kouznetsov, R.; Prank, M.; Soares, J.; Genikhovich, E.
2015-11-01
The paper presents the transport module of the System for Integrated modeLling of Atmospheric coMposition SILAM v.5 based on the advection algorithm of Michael Galperin. This advection routine, so far weakly presented in the international literature, is positively defined, stable at any Courant number, and efficient computationally. We present the rigorous description of its original version, along with several updates that improve its monotonicity and shape preservation, allowing for applications to long-living species in conditions of complex atmospheric flows. The scheme is connected with other parts of the model in a way that preserves the sub-grid mass distribution information that is a cornerstone of the advection algorithm. The other parts include the previously developed vertical diffusion algorithm combined with dry deposition, a meteorological pre-processor, and chemical transformation modules. The quality of the advection routine is evaluated using a large set of tests. The original approach has been previously compared with several classic algorithms widely used in operational dispersion models. The basic tests were repeated for the updated scheme and extended with real-wind simulations and demanding global 2-D tests recently suggested in the literature, which allowed one to position the scheme with regard to sophisticated state-of-the-art approaches. The advection scheme performance was fully comparable with other algorithms, with a modest computational cost. This work was the last project of Dr. Sci. Michael Galperin, who passed away on 18 March 2008.
Advection and diffusion in shoreline change prediction
NASA Astrophysics Data System (ADS)
Anderson, T. R.; Frazer, L. N.
2010-12-01
We added longshore advection and diffusion to the simple cross-shore rate calculation method, as used widely by the USGS and others, to model historic shorelines and to predict future shoreline positions; and applied this to Hawaiian Island beach data. Aerial photographs, sporadically taken throughout the past century, yield usable, albeit limited, historic shoreline data. These photographs provide excellent spatial coverage, but poor temporal resolution, of the shoreline. Due to the sparse historic shoreline data, and the many natural and anthropogenic events influencing coastlines, we constructed a simplistic shoreline change model that can identify long-term behavior of a beach. Our new, two-dimensional model combines the simple rate method to accommodate for cross-shore sediment transport with the classic Pelnard-Considère model for diffusion, as well as a longshore advection speed term. Inverse methods identify cross-shore rate, longshore advection speed, and longshore diffusivity down a sandy coastline. A spatial averaging technique then identifies shoreline segments where one parameter can reasonably account for the cross-shore and longshore transport rates in that area. This produces model results with spatial resolution more appropriate to the temporal spacing of the data. Because changes in historic data can be accounted for by varying degrees of cross-shore and longshore sediment transport - for example, beach erosion can equally be explained by sand moving either off-shore or laterally - we tested several different model scenarios on the data: allowing only cross-shore sediment movement, only longshore movement, and a combination of the two. We used statistical information criteria to determine both the optimal spatial resolution and best-fitting scenario. Finally, we employed a voting method predicting the relaxed shoreline position over time.
MECHANISM OF OUTFLOWS IN ACCRETION SYSTEM: ADVECTIVE COOLING CANNOT BALANCE VISCOUS HEATING?
Gu, Wei-Min
2015-01-20
Based on the no-outflow assumption, we investigate steady-state, axisymmetric, optically thin accretion flows in spherical coordinates. By comparing the vertically integrated advective cooling rate with the viscous heating rate, we find that the former is generally less than 30% of the latter, which indicates that the advective cooling itself cannot balance the viscous heating. As a consequence, for radiatively inefficient flows with low accretion rates such as M-dot ≲10{sup −3} M-dot {sub Edd}, where M-dot {sub Edd} is the Eddington accretion rate, the viscous heating rate will be larger than the sum of the advective cooling rate and the radiative cooling one. Thus, no thermal equilibrium can be established under the no-outflow assumption. We therefore argue that in such cases outflows ought to occur and take away more than 70% of the thermal energy generated by viscous dissipation. Similarly, for optically thick flows with extremely large accretion rates such as M-dot ≳10 M-dot {sub Edd}, outflows should also occur owing to the limited advection and the low efficiency of radiative cooling. Our results may help to understand the mechanism of outflows found in observations and numerical simulations.
How Hydrate Saturation Anomalies are Diffusively Constructed and Advectively Smoothed
NASA Astrophysics Data System (ADS)
Rempel, A. W.; Irizarry, J. T.; VanderBeek, B. P.; Handwerger, A. L.
2015-12-01
The physical processes that control the bulk characteristics of hydrate reservoirs are captured reasonably well by long-established model formulations that are rooted in laboratory-verified phase equilibrium parameterizations and field-based estimates of in situ conditions. More detailed assessments of hydrate distribution, especially involving the occurrence of high-saturation hydrate anomalies have been more difficult to obtain. Spatial variations in sediment properties are of central importance for modifying the phase behavior and promoting focussed fluid flow. However, quantitative predictions of hydrate anomaly development cannot be made rigorously without also addressing the changes in phase behavior and mechanical balances that accompany changes in hydrate saturation level. We demonstrate how pore-scale geometrical controls on hydrate phase stability can be parameterized for incorporation in simulations of hydrate anomaly development along dipping coarse-grained layers embedded in a more fine-grained background that is less amenable to fluid transport. Model simulations demonstrate how hydrate anomaly growth along coarse-layer boundaries is promoted by diffusive gas transport from the adjacent fine-grained matrix, while advective transport favors more distributed growth within the coarse-grained material and so effectively limits the difference between saturation peaks and background levels. Further analysis demonstrates how sediment contacts are unloaded once hydrate saturation reaches sufficient levels to form a load-bearing skeleton that can evolve to produce segregated nodules and lenses. Decomposition of such growth forms poses a significant geohazard that is expected to be particularly sensitive to perturbations induced by gas extraction. The figure illustrates the predicted evolution of hydrate saturation Sh in a coarse-grained dipping layer showing how prominent bounding hydrate anomalies (spikes) supplied by diffusive gas transport at early times
Advection, diffusion and delivery over a network
Heaton, Luke L.M.; López, Eduardo; Maini, Philip K.; Fricker, Mark D.; Jones, Nick S.
2014-01-01
Many biological, geophysical and technological systems involve the transport of resource over a network. In this paper we present an algorithm for calculating the exact concentration of resource at any point in space or time, given that the resource in the network is lost or delivered out of the network at a given rate, while being subject to advection and diffusion. We consider the implications of advection, diffusion and delivery for simple models of glucose delivery through a vascular network, and conclude that in certain circumstances, increasing the volume of blood and the number of glucose transporters can actually decrease the total rate of glucose delivery. We also consider the case of empirically determined fungal networks, and analyze the distribution of resource that emerges as such networks grow over time. Fungal growth involves the expansion of fluid filled vessels, which necessarily involves the movement of fluid. In three empirically determined fungal networks we found that the minimum currents consistent with the observed growth would effectively transport resource throughout the network over the time-scale of growth. This suggests that in foraging fungi, the active transport mechanisms observed in the growing tips may not be required for long range transport. PMID:23005783
NASA Astrophysics Data System (ADS)
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.
Perturbation of ground surface temperature reconstructions by groundwater flow?
NASA Astrophysics Data System (ADS)
Ferguson, Grant; Beltrami, Hugo; Woodbury, Allan D.
2006-07-01
Subsurface temperatures have been shown to be a robust source of information on past climates. Most analyses neglect groundwater flow (GWF) and assume purely conductive heat flow. However, in many situations GWF has not been fully considered and to date there are no general GWF criteria for either accepting or rejecting a temperature profile for paleoclimate analysis. Here we examine the transition from conduction dominated environments to environments where advection has a significant effect on the subsurface temperature regime and thus ground surface temperature (GST) histories. We provide guidelines indicating when advection is important and conclude that it is unlikely that groundwater flow is a significant source of error in the global data set maintained by the International Heat Flow Commission.
NASA Astrophysics Data System (ADS)
Lazzarini, Simone; Brardinoni, Francesco; Draganits, Erich; Cavalli, Marco
2015-04-01
combines zones with colluvial transport regimes with areas in which fluvial transport prevails, whereas Plaies is essentially dominated by mass-wasting processes strongly controlled by the dynamics of the overhanging Ortler Glacier. Further, Cengles is a supply-limited system, since there the occurrence of debris flows is strongly controlled by in-channel sediment evacuation and recharge cycles that interact with the overcoming of variable hydrometeorological thresholds. In contrast, Plaies is a transport-limited resulting from the almost unlimited availability of loose, mainly glacigenic material that can be mobilized. The debris-flow activity in Plaies is strongly controlled by a combination of hydrometeorological forcing and glacier dynamics. This work is part of SedAlp (www.sedalp.eu), a project funded through the Alpine Space Programme.
Kim, Hong; Benson, Craig H
2004-07-01
The relative contributions of four mechanisms of oxygen transport in multilayer composite (MLC) caps placed over oxygen-consuming mine waste were evaluated using numerical and analytical methods. MLC caps are defined here as caps consisting of earthen and geosynthetic (polymeric) components where a composite barrier layer consisting of a geomembrane (1-2 mm thick polymeric sheet) overlying a clay layer is the primary barrier to transport. The transport mechanisms that were considered are gas-phase advective transport, gas-phase diffusive transport, liquid-phase advective transport via infiltrating precipitation and liquid-phase diffusive transport. A numerical model was developed to simulate gas-phase advective-diffusive transport of oxygen through a multilayer cap containing seven layers. This model was also used to simulate oxygen diffusion in the liquid phase. An approximate analytical method was used to compute the advective flux of oxygen in the liquid phase. The numerical model was verified for limiting cases using an analytical solution. Comparisons were also made between model predictions and field data for earthen caps reported by others. Results of the analysis show that the dominant mechanism for oxygen transport through MLC caps is gas-phase diffusion. For the cases that were considered, the gas-phase diffusive flux typically comprises at least 99% of the total oxygen flux. Thus, designers of MLC caps should focus on design elements and features that will limit diffusion of gas-phase oxygen. PMID:15145567
NASA Astrophysics Data System (ADS)
Moura, R. C.; Sherwin, S. J.; Peiró, J.
2016-02-01
This study addresses linear dispersion-diffusion analysis for the spectral/hp continuous Galerkin (CG) formulation in one dimension. First, numerical dispersion and diffusion curves are obtained for the advection-diffusion problem and the role of multiple eigencurves peculiar to spectral/hp methods is discussed. From the eigencurves' behaviour, we observe that CG might feature potentially undesirable non-smooth dispersion/diffusion characteristics for under-resolved simulations of problems strongly dominated by either convection or diffusion. Subsequently, the linear advection equation augmented with spectral vanishing viscosity (SVV) is analysed. Dispersion and diffusion characteristics of CG with SVV-based stabilization are verified to display similar non-smooth features in flow regions where convection is much stronger than dissipation or vice-versa, owing to a dependency of the standard SVV operator on a local Péclet number. First a modification is proposed to the traditional SVV scaling that enforces a globally constant Péclet number so as to avoid the previous issues. In addition, a new SVV kernel function is suggested and shown to provide a more regular behaviour for the eigencurves along with a consistent increase in resolution power for higher-order discretizations, as measured by the extent of the wavenumber range where numerical errors are negligible. The dissipation characteristics of CG with the SVV modifications suggested are then verified to be broadly equivalent to those obtained through upwinding in the discontinuous Galerkin (DG) scheme. Nevertheless, for the kernel function proposed, the full upwind DG scheme is found to have a slightly higher resolution power for the same dissipation levels. These results show that improved CG-SVV characteristics can be pursued via different kernel functions with the aid of optimization algorithms.
Ovtchinnikov, Mikhail; Easter, Richard C.
2009-02-01
Monotonicity constraints and gradient preserving flux corrections employed by many advection algorithms used in atmospheric models make these algorithms non-linear. Consequently, any relations among model variables transported separately are not necessarily preserved in such models. These errors cannot be revealed by traditional algorithm testing based on advection of a single tracer. New type of tests are developed and conducted to evaluate the preservation of a sum of several number mixing ratios advected independently of each other, as is the case, for example, in models using bin or sectional representation of aerosol or cloud particle size distribution. The tests show that when three tracers are advected in 1D uniform constant velocity flow, local errors in the sum can be on the order of 10%. When cloud-like interactions are allowed among the tracers, errors in total sum of three mixing ratios can reach up to 30%. Several approaches to eliminate the error are suggested, all based on advecting the sum as a separate variable and then normalizing mixing ratios for individual tracers to match the total sum. A simple scalar normalization preserves the total number mixing ratio and positive definiteness of the variables but the monotonicity constraint for individual tracers is no longer maintained. More involved flux normalization procedures are developed for the flux based advection algorithms to maintain the monotonicity for individual scalars and their sum.
NASA Astrophysics Data System (ADS)
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.
Hourly and daily evapotranspiration of alfalfa under regional advection
Technology Transfer Automated Retrieval System (TEKTRAN)
Regional advection often affects the evapotranspiration rates of irrigated crops in the Southern High Plains. In 1998, during a 10-day period (13-22 June) of unusually strong advection, high evapotranspiration (ET) rates for unstressed, irrigated alfalfa (Medicago sativa) were measured with two prec...
NASA Astrophysics Data System (ADS)
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.
Shadowing and the role of small diffusivity in the chaotic advection of scalars
NASA Technical Reports Server (NTRS)
Klapper, I.
1992-01-01
Using techniques from shadowing theory, the solution of the scalar advection-diffusion equation is studied. It is shown that, under certain circumstances, the effect of small scalar diffusivity is to smooth the zero-diffusivity solution by averaging local fine-scaled structure against a Gaussian. The method of study depends on shadowing and thus fails for nonuniformly stretching systems, its failure suggesting the ways in which the effects of asymptotically small molecular diffusion can become nonlocal in chaotic fluid flows.
NASA Astrophysics Data System (ADS)
Darbandi, Masoud; Ghafourizadeh, Majid
2015-12-01
In this work, we derive a few new advective flux approximation expressions, apply them in a hybrid finite-volume-element (FVE) formulation, and solve the turbulent reacting flow governing equations in the cylindrical frame. To derive these advective-kinetic-based expressions, we benefit from the advantages of a physical influence scheme (PIS) basically, extend it to the cylindrical frame suitably, and approximate the required advective flux terms at the cell faces more accurately. The present numerical scheme not only respects the physics of flow correctly but also resolves the pressure-velocity coupling problem automatically. We also suggest a bi-implicit algorithm to solve the set of coupled turbulent reacting flow governing equations, in which the turbulence and chemistry governing equations are solved simultaneously. To evaluate the accuracy of new derived FVE-PIS expressions, we compare the current solutions with other available numerical solutions and experimental data. The comparisons show that the new derived expressions provide some more advantages over the past numerical approaches in solving turbulent diffusion flame in the cylindrical frame. Indeed, the current method and formulations can be used to solve and analyze the turbulent diffusion flames in the cylindrical coordinates very reliably.
Richon, Patrick; Perrier, Frédéric; Koirala, Bharat Prasad; Girault, Frédéric; Bhattarai, Mukunda; Sapkota, Soma Nath
2011-02-01
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 Barasol™ probes between January 2008 and November 2009 in two small natural cavities with high CO(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(-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(2) 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 S(1) and semi-diurnal S(2) periodic components. At the advection-dominated points, radon concentration did not exhibit S(1) or S(2) components. At the reference points, however, the S(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(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 possible temporal variations associated with the
NASA Technical Reports Server (NTRS)
Atlas, R. M.
1976-01-01
An advective mixed layer ocean model was developed by eliminating the assumption of horizontal homogeneity in an already existing mixed layer model, and then superimposing a mean and anomalous wind driven current field. This model is based on the principle of conservation of heat and mechanical energy and utilizes a box grid for the advective part of the calculation. Three phases of experiments were conducted: evaluation of the model's ability to account for climatological sea surface temperature (SST) variations in the cooling and heating seasons, sensitivity tests in which the effect of hypothetical anomalous winds was evaluated, and a thirty-day synoptic calculation using the model. For the case studied, the accuracy of the predictions was improved by the inclusion of advection, although nonadvective effects appear to have dominated.
Sediment transport in a surface-advected estuarine plume
NASA Astrophysics Data System (ADS)
Yao, H. Y.; Leonardi, N.; Li, J. F.; Fagherazzi, S.
2016-03-01
The interplay between suspended-sediment transport and plume hydrodynamics in a surface-advected estuarine plume is studied using a three-dimensional numerical model. Our analysis focuses on the formation of a sediment-rich alongshore current and on the effect of sediments on the structure of the recirculating freshwater bulge. We introduce the ratio Y between the traveling time of sediment along the bulge edge and the settling timescale. When Y <1, suspended sediments enter the alongshore coastal current. When Y >1 the sediments are deposited within the bulge. We find that a critical range of settling velocities exist above which no transport in the costal current is allowed. Critical settling-velocity values increase with river discharge. Therefore, low magnitude and long-lasting floods promote sediment sorting in the continental shelf. We further find that, for a given flood duration, intermediate flood magnitudes at the limit between subcritical and supercritical flow maximize the alongshore sediment transport. Similarly, for a fixed input of water and sediments, intermediate discharge durations maximize alongshore sediment transport.
An improved second moment method for solution of pure advection problems
NASA Astrophysics Data System (ADS)
Ghods, Abdolreza; Sobouti, Farhad; Arkani-Hamed, Jafar
2000-04-01
The second moment numerical method (SMM) of Egan and Mahoney [Numerical modeling of advection and diffusion of urban area source pollutant. Journal of Applied Meteorology 1972; 11: 312-322] is adapted to solve for the pure advection transport equation in a variety of flow fields. SMM eliminates numerical diffusion by employing a procedure that takes into account the first and second moments of mass distribution in each grid element. For pure translational flow fields, the method is conservative, positive definite and shape-preserving. In rotational and/or shear flows, the accuracy of SMM is significantly reduced. Two improvements are presented to make the SMM applicable to a wider range of flow problems. It is shown that the improved SMM (ISMM) is less diffusive and more shape-preserving than the SMM in rotational and/or deformational flows. The ISMM can also be used to solve for a color function in compressible flow fields. The computational efficiency of this method is compared with that of other methods and, for a given accuracy, it is shown that ISMM is a cost-effective, non-diffusive and shape-preserving method. Copyright
On Vortex Genesis. An Heuristic Model of Convection-Advection Linkages
NASA Astrophysics Data System (ADS)
Bouali, S.
2003-04-01
We connect to a model of convection roll an appropriate feedback loop (i.e., the advection retroaction) which unfolds a wide range of vorticity behavior. The 3D numerical computations display the conservative aerologic flows of waterspouts and tropical cyclones. Moreover, several simulations exhibit the singular topology of the structure of cyclones eventually trapped in period-2 orbit. On the other hand, additional advection linkages provide our dynamical system with an explicative proof of the tornadogenesis. These amendements modify the model. The airflows are now dissipatives and we investigate the kinematics of these short life span phenomena. The extended model leads the trajectories of air pockets to one or more vortices. The downbursts and microbursts described in the Fujita classification are also simulated. Our heuristic dynamical system lays the foundation of an unified modelisation of vortices. Theory and Direct Numerical Simulation of the vortex genesis are associated in a new perspective.
CDF Solutions of Advection-Reaction equations with uncertain parameters (Invited)
NASA Astrophysics Data System (ADS)
Boso, F.; Tartakovsky, D. M.
2013-12-01
Flow and transport models are affected by parametric uncertainty. Quantitative forecasting of such processes in natural porous media are especially prone to uncertainty because of the inaccessibility and multi-scale nature of the subsurface. We consider a reduced-complexity stochastic transport system which takes into account advection and nonlinear reactions in advection-reaction equations (AREs) with uncertain (random) velocity and reaction parameters. We derive a deterministic equation that governs the evolution of cumulative distribution function (CDF) of a solution of the underlying ARE. Although requiring closure, this differential equation benefits from uniquely defined boundary and initial conditions and can be solved with classic techniques. Here we analyze the accuracy and robustness of the large-eddy-diffusivity closure by comparison with Monte Carlo simulations for different correlation structures and parameters.
Burgers turbulence and passive random advection
NASA Astrophysics Data System (ADS)
Boldyrev, Stanislav Anatolievich
1999-10-01
, and the diffusivity is neglected. These considerations illustrate that even with simple statistics of the velocity field, the statistics of advected quantities are nontrivial due to nonlinear interactions of different spatial directions. The last Chapter 5 summarizes the results and discusses future directions of research.
Anomalous scaling of a scalar field advected by turbulence
Kraichnan, R.H.
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.
Magnetic helicity transport in the advective gauge family
Candelaresi, Simon; Brandenburg, Axel; Hubbard, Alexander; Mitra, Dhrubaditya
2011-01-15
Magnetic helicity fluxes are investigated in a family of gauges in which the contribution from ideal magnetohydrodynamics takes the form of a purely advective flux. Numerical simulations of magnetohydrodynamic turbulence in this advective gauge family exhibit instabilities triggered by the build-up of unphysical irrotational contributions to the magnetic vector potential. As a remedy, the vector potential is evolved in a numerically well behaved gauge, from which the advective vector potential is obtained by a gauge transformation. In the kinematic regime, the magnetic helicity density evolves similarly to a passive scalar when resistivity is small and turbulent mixing is mild, i.e., when the fluid Reynolds number is not too large. In the dynamical regime, resistive contributions to the magnetic helicity flux in the advective gauge are found to be significant owing to the development of small length scales in the irrotational part of the magnetic vector potential.
NASA Astrophysics Data System (ADS)
Pendergrass, D. R.; Arsuffi, T. L.
2005-05-01
The Blanco River is a relatively pristine karst stream in central Texas and designated a conservation target by The Nature Conservancy. It is fed primarily by groundwater in the upper reaches and dominated by runoff and intermittency downstream. The spatial and temporal structure of macroinvertebrates in the Blanco River was assessed with seasonal Hess and d-net samples during 2003-2004 and three diel drift samples from May to October 2004. Our downstream site showed a 47% drop in diversity, but comparable abundances to up- and mid-stream sites. Ephemeropteran and trichopteran taxa (e.g. Tricorythodes and Cheumatopsyche) comprised about 60% of drift and benthic samples alike, however, non-insect taxa were nearly absent from the drift. Some taxa not present in the benthic samples were present in the drift. Post-dusk and pre-dawn peaks in diel drift were discerned. No strong seasonal patterns were detected which may be attributable to an unusually wet year and asynchronous, multivoltinous life cycles associated with mild seasonality in subtropical regions. The Blanco River's historically variable hydrological regime may be further exacerbated by long-term flow alteration associated with increasing anthropogenic development and could alter the composition and distribution of macroinvertebrate assemblages.
A spatial SIS model in advective heterogeneous environments
NASA Astrophysics Data System (ADS)
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 < 1, the unique disease-free equilibrium (DFE) is 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.
NASA Astrophysics Data System (ADS)
Solis, Kyle J.; Martin, James E.
2012-11-01
Isothermal magnetic advection (IMA) is a recently discovered method of inducing highly organized, non-contact flow lattices in suspensions of magnetic particles, using only uniform ac magnetic fields of modest strength. The initiation of these vigorous flows requires neither a thermal gradient nor a gravitational field, and so can be used to transfer heat and mass in circumstances where natural convection does not occur. These advection lattices are comprised of a square lattice of antiparallel flow columns. If the column spacing is sufficiently large compared to the column length and the flow rate within the columns is sufficiently large, then one would expect efficient transfer of both heat and mass. Otherwise, the flow lattice could act as a countercurrent heat exchanger and only mass will be efficiently transferred. Although this latter case might be useful for feeding a reaction front without extracting heat, it is likely that most interest will be focused on using IMA for heat transfer. In this paper, we explore the various experimental parameters of IMA to determine which of these can be used to control the column spacing. These parameters include the field frequency, strength, and phase relation between the two field components, the liquid viscosity, and particle volume fraction. We find that the column spacing can easily be tuned over a wide range to enable the careful control of heat and mass transfer.
NASA Astrophysics Data System (ADS)
Windhorst, David; Timbe, Edison; Kraft, Philipp; Frede, Hans-Georg; Breuer, Lutz
2013-04-01
Knowing the dominant flow paths within a hydrological system is challenging and crucial to assess the relevant discharge generating processes and the fate of water and solutes in the system. However especially the interpretation of those path ways seems controversy within our study area of the Rio San Francisco in the outskirts of the Amazon basin in a tropical mountainous region of South Ecuador. E.g. the recorded flashiness of the hydrograph contravenes the long mean residence time and hydrogeochemical signature of the event water marking it as old water. Even though theories exist which could reveal these contradictions (e.g. the concept of transmissivity feedback which could be used to explain the rapid mobilization of old water) proof is currently missing to support those concepts. To further study the fate of the water and water pound solutes we installed along two hillslopes (length about 500m each and decline 230m under forest and 157m under pasture) three wick samplers collecting weekly bulk samples of soil water in 10, 25, 40 cm depths for 2 years. The isotopic signature (δ18O and δ2H) of the soil water as well as the incoming rainfall was analyzed using an isotope laser spectrometer (Picarro). We propose the usage of stable water isotopes as conservative tracers to validate a 2D setup of the Catchment Modeling Framework (CMF) simulating the water flow and fate of solutes along the hillslopes. The usage of conservative tracers, such as δ18O and δ2H, to validate hydrological models, bears the advantage that not only the amount of transported solute needs to be correctly simulated but also the concentration of the modeled tracer needs to be correctly accounted for. Model structures derived by such a tracer driven calibration procedure thereby are more likely to represent the actual nature of the hydrological system. Results proving the suitability of the model setup to reproduce the collected isotope data will be shown and the discharge generating
Modulated point-vortex pairs on a rotating sphere: Dynamics and chaotic advection
NASA Astrophysics Data System (ADS)
Drótos, Gábor; Tél, Tamás; Kovács, Gergely
2013-06-01
The dynamics of modulated point-vortex pairs is investigated on a rotating sphere, where modulation is chosen to reflect the conservation of angular momentum (potential vorticity). For sufficiently close vortices (dipoles) the trajectories of their center-of-mass are shown to correspond to those of a point particle moving freely on a rotating sphere. For finite size vortex pairs, a qualitative similarity to the geodesic dynamics is found. The advection dynamics generated by vortex pairs on a rotating sphere is found to be chaotic. In the short time dynamics we point out a transition from closed to open chaotic advection, which implies that the transport properties of the flow might drastically be altered by changing the initial conditions of the pair on the sphere. Due to spherical topology, for long times, even the open advection patterns are found to gradually cross over to that corresponding to a homogeneous closed mixing. This pattern extends along a zonal band, whereas short term closed mixing remains always bounded to the moving pair.
Modulated point-vortex pairs on a rotating sphere: dynamics and chaotic advection.
Drótos, Gábor; Tél, Tamás; Kovács, Gergely
2013-06-01
The dynamics of modulated point-vortex pairs is investigated on a rotating sphere, where modulation is chosen to reflect the conservation of angular momentum (potential vorticity). For sufficiently close vortices (dipoles) the trajectories of their center-of-mass are shown to correspond to those of a point particle moving freely on a rotating sphere. For finite size vortex pairs, a qualitative similarity to the geodesic dynamics is found. The advection dynamics generated by vortex pairs on a rotating sphere is found to be chaotic. In the short time dynamics we point out a transition from closed to open chaotic advection, which implies that the transport properties of the flow might drastically be altered by changing the initial conditions of the pair on the sphere. Due to spherical topology, for long times, even the open advection patterns are found to gradually cross over to that corresponding to a homogeneous closed mixing. This pattern extends along a zonal band, whereas short term closed mixing remains always bounded to the moving pair. PMID:23848782
Advection-condensation of water vapor with coherent stirring: a stochastic approach
NASA Astrophysics Data System (ADS)
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.
NASA Technical Reports Server (NTRS)
Leonard, B. P.
1988-01-01
A fresh approach is taken to the embarrassingly difficult problem of adequately modeling simple pure advection. An explicit conservative control-volume formation makes use of a universal limiter for transient interpolation modeling of the advective transport equations. This ULTIMATE conservative difference scheme is applied to unsteady, one-dimensional scalar pure advection at constant velocity, using three critical test profiles: an isolated sine-squared wave, a discontinuous step, and a semi-ellipse. The goal, of course, is to devise a single robust scheme which achieves sharp monotonic resolution of the step without corrupting the other profiles. The semi-ellipse is particularly challenging because of its combination of sudden and gradual changes in gradient. The ULTIMATE strategy can be applied to explicit conservation schemes of any order of accuracy. Second-order schemes are unsatisfactory, showing steepening and clipping typical of currently popular so-called high resolution shock-capturing of TVD schemes. The ULTIMATE third-order upwind scheme is highly satisfactory for most flows of practical importance. Higher order methods give predictably better step resolution, although even-order schemes generate a (monotonic) waviness in the difficult semi-ellipse simulation. Little is to be gained above ULTIMATE fifth-order upwinding which gives results close to the ultimate for which one might hope.
Anisotropic Turbulent Advection of a Passive Vector Field: Effects of the Finite Correlation Time
NASA Astrophysics Data System (ADS)
Antonov, N. V.; Gulitskiy, N. M.
2016-02-01
The turbulent passive advection under the environment (velocity) field with finite correlation time is studied. Inertial-range asymptotic behavior of a vector (e.g., magnetic) field, passively advected by a strongly anisotropic turbulent flow, is investigated by means of the field theoretic renormalization group and the operator product expansion. The advecting velocity field is Gaussian, with finite correlation time and prescribed pair correlation function. The inertial-range behavior of the model is described by two regimes (the limits of vanishing or infinite correlation time) that correspond to nontrivial fixed points of the RG equations and depend on the relation between the exponents in the energy energy spectrum ɛ ∝ k⊥1-ξ and the dispersion law ω ∝ k⊥2-η . The corresponding anomalous exponents are associated with the critical dimensions of tensor composite operators built solely of the passive vector field itself. In contrast to the well-known isotropic Kraichnan model, where various correlation functions exhibit anomalous scaling behavior with infinite sets of anomalous exponents, here the dependence on the integral turbulence scale L has a logarithmic behavior: instead of power-like corrections to ordinary scaling, determined by naive (canonical) dimensions, the anomalies manifest themselves as polynomials of logarithms of L. Due to the presence of the anisotropy in the model, all multiloop diagrams are equal to zero, thus this result is exact.
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
Round Window Membrane Intracochlear Drug Delivery Enhanced by Induced Advection
Borkholder, David A.; Zhu, Xiaoxia; Frisina, Robert D.
2014-01-01
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 1 week, 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 1 week 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
Advective Removal of Intraparticle Uranium from Contaminated Vadose Zone Sediments, Hanford, USA
Ilton, Eugene S.; Qafoku, Nikolla; Liu, Chongxuan; Moore, D. A.; Zachara, John M.
2008-03-01
A column study on U contaminated vadose zone sediments from the Hanford Site, WA, was performed in order to aid the development of a model for predicting U(VI) release rates under a dynamic flow regime and for variable geochemical conditions. The sediments of interest are adjacent to and below tank BX-102, part of the BX tank farm that contained high level liquid radioactive waste. Two sediments, with different U(VI) loadings and intraparticle large fracture vs. smaller fracture ratios, were reacted with three different solutions. The primary reservoir for U(VI) appears to be a micron-sized nanocrystalline Na-U-Si phase, possibly Na-boltwoodite, that nucleated and grew on plagioclase grains that line fractures within sand-sized granitic clasts. The solutions were all calcite saturated and in equilibrium with atmospheric CO2, where one solution was simply DI-water, the second was a synthetic ground water (SGW) with elevated Na, and the third was the same SGW but with both elevated Na and Si. The latter two solutions were employed, in part, to test the effect of saturation state on U(VI) release. For both sediments and all three electrolytes, there was an initial rapid release of U(VI) to the advecting solution followed by a plateau of low U(VI) concentration. U(VI) effluent concentration increased during subsequent stop flow (SF) events. The electrolytes with elevated Na and Si appreciably depressed U(VI) concentrations relative to DI water. The effluent data for both sediments and all three electrolytes was simulated reasonably well by a three domain model (the advecting fluid, fractures, and matrix) that coupled U(VI) dissolution rates, intraparticle U(VI) diffusion, and interparticle advective transport of U(VI); where key transport and dissolution processes had been parameterized in previous batch studies. For the calcite-saturated DI-water, U(VI) concentrations in the effluent remained far below saturation with respect to Na-boltwoodite and release of U(VI) to
NASA Astrophysics Data System (ADS)
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 < 30 kW) focuses on conductive heat transport as the main energy source while the impact of groundwater flow as the driver for advective heat transport is 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.
Permafrost thaw in a nested groundwater-flow system
McKenzie, Jeffery M.; Voss, Clifford I.
2013-01-01
Groundwater flow in cold regions containing permafrost accelerates climate-warming-driven thaw and changes thaw patterns. Simulation analyses of groundwater flow and heat transport with freeze/thaw in typical cold-regions terrain with nested flow indicate that early thaw rate is particularly enhanced by flow, the time when adverse environmental impacts of climate-warming-induced permafrost loss may be severest. For the slowest climate-warming rate predicted by the Intergovernmental Panel on Climate Change (IPCC), once significant groundwater flow begins, thick permafrost layers can vanish in several hundred years, but survive over 1,000 years where flow is minimal. Large-scale thaw depends mostly on the balance of heat advection and conduction in the supra-permafrost zone. Surface-water bodies underlain by open taliks allow slow sub-permafrost flow, with lesser influence on regional thaw. Advection dominance over conduction depends on permeability and topography. Groundwater flow around permafrost and flow through permafrost impact thaw differently; the latter enhances early thaw rate. Air-temperature seasonality also increases early thaw. Hydrogeologic heterogeneity and topography strongly affect thaw rates/patterns. Permafrost controls the groundwater/surface-water-geomorphology system; hence, prediction and mitigation of impacts of thaw on ecology, chemical exports and infrastructure require improved hydrogeology/permafrost characterization and understanding
Concentration polarization, surface currents, and bulk advection in a microchannel
NASA Astrophysics Data System (ADS)
Nielsen, Christoffer P.; Bruus, Henrik
2014-10-01
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. A remarkable outcome of the investigations is the discovery of strong couplings between bulk advection and the surface current; without a surface current, bulk advection is strongly suppressed. The numerical simulations are supplemented by analytical models valid in the long channel limit as well as in the limit of negligible surface charge. By including the effects of diffusion and advection in the diffuse part of the electric double layers, we extend a recently published analytical model of overlimiting current due to surface conduction.
The role of advection and diffusion in waste disposal by sea urchin embryos
NASA Astrophysics Data System (ADS)
Clark, Aaron; Licata, Nicholas
2014-03-01
We determine the first passage probability for the absorption of waste molecules released from the microvilli of sea urchin embryos. We calculate a perturbative solution of the advection-diffusion equation for a linear shear profile similar to the fluid environment which the embryos inhabit. Rapid rotation of the embryo results in a concentration boundary layer of comparable thickness to the length of the microvilli. A comparison of the results to the regime of diffusion limited transport indicates that fluid flow is advantageous for efficient waste disposal.
Application of a Particle Method to the Advection-Diffusion-Reaction Equation
NASA Astrophysics Data System (ADS)
Paster, A.; Bolster, D.; Benson, D. A.
2012-12-01
-known phenomena of incomplete mixing (Ovchinnikov-Zeldovich segregation). The numerical results of the particle-tracking simulations are compared to an approximate analytical solution and the late time discrepancy is explained. We also study, for a two dimensional system, how shear flow effects the reaction rate. We do so since shear flow is the simplest form of a spatially variable advection. For the shear flow system, we find that shear flow leads to better mixing of the system on one hand, and a surprising one dimensional segregation at late times, on the other hand. This is in contrast with zero-advection two-dimensional system, where the late time behavior is characterized by the formation of two-dimensional islands. References (Manuscripts in submission): Paster A., D. Bolster and D.A. Benson. Connecting the dots: application of a particle method to the diffusion-reaction equation. Submitted to Advances in Water Resources. Paster A., D. Bolster and D.A. Benson. Particle Tracking and the Diffusion-Reaction Equation. Submitted to Water Resources Research.
Inheritance - sex-linked dominant; Genetics - sex-linked dominant; X-linked dominant; Y-linked dominant ... one of the sex chromosomes, which are the X and Y chromosomes. Dominant inheritance occurs when an ...
Consistency problem with tracer advection in the Atmospheric Model GAMIL
NASA Astrophysics Data System (ADS)
Zhang, Kai; Wan, Hui; Wang, Bin; Zhang, Meigen
2008-03-01
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.
ADVECTION INFLUENCES ON EVAPOTRANSPIRATION OF ALFALFA IN A SEMIARID ENVIRONMENT
Technology Transfer Automated Retrieval System (TEKTRAN)
Advective enhancement of crop evapotranspiration (ET) occurs when drier, hotter air is transported into the crop by wind and can be an important factor in the water balance of irrigated crops in a semiarid climate. Thirteen days of moderate to extremely high ET rates of irrigated alfalfa (Medicago ...
The 'optimum' upwind advection on a triangular mesh
NASA Technical Reports Server (NTRS)
Roe, P. L.
1990-01-01
For advection schemes based on fluctuation splitting, a design criterion of optimizing the time step leads to linear schemes that coincide with those designed for least truncation error. A further stage of optimizing the time step using a nonlinear positivity criterion, leads to considerable further gains in resolution.
Pattern formation induced by a differential Poiseuille flow
NASA Astrophysics Data System (ADS)
Stucchi, L.; Vasquez, D. A.
2014-12-01
Differential advection, where a reactant is advected while another one is immobilized, leads to instabilities in reaction-advection-diffusion systems. In particular, a homogeneous steady state looses stability for strong enough flows, leading to chemical patterns moving in the direction of the flow. In this paper we study the effects of differential advection due to a two-dimensional Poiseuille flow. We carry out a linear stability analysis on a homogeneous state using an activator-inhibitor reaction. We find that shear dispersion induced by the Poiseuille flow may lead to instabilities at slower flow rates. We find that contrary to the one-dimensional system, the instability depends on which substance is advected. We find a critical average flow speed for instability depending on tube size. Numerical solutions of the nonlinear reaction-advection-diffusion result in patterns of constant shape propagating along the tube.
Webb, S.W.
1996-05-01
Two models for gas-phase diffusion and advection in porous media, the Advective-Dispersive Model (ADM) and the Dusty-Gas Model (DGM), are reviewed. The ADM, which is more widely used, is based on a linear addition of advection calculated by Darcy`s Law and ordinary diffusion using Fick`s Law. Knudsen diffusion is often included through the use of a Klinkenberg factor for advection, while the effect of a porous medium on the diffusion process is through a porosity-tortuosity-gas saturation multiplier. Another, more comprehensive approach for gas-phase transport in porous media has been formulated by Evans and Mason, and is referred to as the Dusty- Gas Model (DGM). This model applies the kinetic theory of gases to the gaseous components and the porous media (or ``dust``) to develop an approach for combined transport due to ordinary and Knudsen diffusion and advection including porous medium effects. While these two models both consider advection and diffusion, the formulations are considerably different, especially for ordinary diffusion. The various components of flow (advection and diffusion) are compared for both models. Results from these two models are compared to isothermal experimental data for He-Ar gas diffusion in a low-permeability graphite. Air-water vapor comparisons have also been performed, although data are not available, for the low-permeability graphite system used for the helium-argon data. Radial and linear air-water heat pipes involving heat, advection, capillary transport, and diffusion under nonisothermal conditions have also been considered.
Magnetic flux and heat losses by diffusive, advective, and Nernst effects in MagLIF-like plasma
Velikovich, A. L. Giuliani, J. L.; Zalesak, S. T.
2014-12-15
The MagLIF approach to inertial confinement fusion involves subsonic/isobaric compression and heating of a DT plasma with frozen-in magnetic flux by a heavy cylindrical liner. The losses of heat and magnetic flux from the plasma to the liner are thereby determined by plasma advection and gradient-driven transport processes, such as thermal conductivity, magnetic field diffusion and thermomagnetic effects. Theoretical analysis based on obtaining exact self-similar solutions of the classical collisional Braginskii's plasma transport equations in one dimension demonstrates that the heat loss from the hot plasma to the cold liner is dominated by the transverse heat conduction and advection, and the corresponding loss of magnetic flux is dominated by advection and the Nernst effect. For a large electron Hall parameter ω{sub e}τ{sub e} effective diffusion coefficients determining the losses of heat and magnetic flux are both shown to decrease with ω{sub e}τ{sub e} as does the Bohm diffusion coefficient, which is commonly associated with low collisionality and two-dimensional transport. This family of exact solutions can be used for verification of codes that model the MagLIF plasma dynamics.
NASA Astrophysics Data System (ADS)
Velikovich, A. L.; Giuliani, J. L.; Zalesak, S. T.
2015-04-01
The magnetized liner inertial fusion (MagLIF) approach to inertial confinement fusion [Slutz et al., Phys. Plasmas 17, 056303 (2010); Cuneo et al., IEEE Trans. Plasma Sci. 40, 3222 (2012)] involves subsonic/isobaric compression and heating of a deuterium-tritium plasma with frozen-in magnetic flux by a heavy cylindrical liner. The losses of heat and magnetic flux from the plasma to the liner are thereby determined by plasma advection and gradient-driven transport processes, such as thermal conductivity, magnetic field diffusion, and thermomagnetic effects. Theoretical analysis based on obtaining exact self-similar solutions of the classical collisional Braginskii's plasma transport equations in one dimension demonstrates that the heat loss from the hot compressed magnetized plasma to the cold liner is dominated by transverse heat conduction and advection, and the corresponding loss of magnetic flux is dominated by advection and the Nernst effect. For a large electron Hall parameter ( ωeτe≫1 ), the effective diffusion coefficients determining the losses of heat and magnetic flux to the liner wall are both shown to decrease with ωeτe as does the Bohm diffusion coefficient c T /(16 e B ) , which is commonly associated with low collisionality and two-dimensional transport. We demonstrate how this family of exact solutions can be used for verification of codes that model the MagLIF plasma dynamics.
Magnetic flux and heat losses by diffusive, advective, and Nernst effects in MagLIF-like plasma
NASA Astrophysics Data System (ADS)
Velikovich, A. L.; Giuliani, J. L.; Zalesak, S. T.
2014-12-01
The MagLIF approach to inertial confinement fusion involves subsonic/isobaric compression and heating of a DT plasma with frozen-in magnetic flux by a heavy cylindrical liner. The losses of heat and magnetic flux from the plasma to the liner are thereby determined by plasma advection and gradient-driven transport processes, such as thermal conductivity, magnetic field diffusion and thermomagnetic effects. Theoretical analysis based on obtaining exact self-similar solutions of the classical collisional Braginskii's plasma transport equations in one dimension demonstrates that the heat loss from the hot plasma to the cold liner is dominated by the transverse heat conduction and advection, and the corresponding loss of magnetic flux is dominated by advection and the Nernst effect. For a large electron Hall parameter ωeτe effective diffusion coefficients determining the losses of heat and magnetic flux are both shown to decrease with ωeτe as does the Bohm diffusion coefficient, which is commonly associated with low collisionality and two-dimensional transport. This family of exact solutions can be used for verification of codes that model the MagLIF plasma dynamics.
Velikovich, A. L.; Giuliani, J. L.; Zalesak, S. T.
2015-04-15
The magnetized liner inertial fusion (MagLIF) approach to inertial confinement fusion [Slutz et al., Phys. Plasmas 17, 056303 (2010); Cuneo et al., IEEE Trans. Plasma Sci. 40, 3222 (2012)] involves subsonic/isobaric compression and heating of a deuterium-tritium plasma with frozen-in magnetic flux by a heavy cylindrical liner. The losses of heat and magnetic flux from the plasma to the liner are thereby determined by plasma advection and gradient-driven transport processes, such as thermal conductivity, magnetic field diffusion, and thermomagnetic effects. Theoretical analysis based on obtaining exact self-similar solutions of the classical collisional Braginskii's plasma transport equations in one dimension demonstrates that the heat loss from the hot compressed magnetized plasma to the cold liner is dominated by transverse heat conduction and advection, and the corresponding loss of magnetic flux is dominated by advection and the Nernst effect. For a large electron Hall parameter (ω{sub e}τ{sub e}≫1), the effective diffusion coefficients determining the losses of heat and magnetic flux to the liner wall are both shown to decrease with ω{sub e}τ{sub e} as does the Bohm diffusion coefficient cT/(16eB), which is commonly associated with low collisionality and two-dimensional transport. We demonstrate how this family of exact solutions can be used for verification of codes that model the MagLIF plasma dynamics.
NASA Technical Reports Server (NTRS)
White, Jeffrey A.; Baurle, Robert A.; Fisher, Travis C.; Quinlan, Jesse R.; Black, William S.
2012-01-01
The 2nd-order upwind inviscid flux scheme implemented in the multi-block, structured grid, cell centered, finite volume, high-speed reacting flow code VULCAN has been modified to reduce numerical dissipation. This modification was motivated by the desire to improve the codes ability to perform large eddy simulations. The reduction in dissipation was accomplished through a hybridization of non-dissipative and dissipative discontinuity-capturing advection schemes that reduces numerical dissipation while maintaining the ability to capture shocks. A methodology for constructing hybrid-advection schemes that blends nondissipative fluxes consisting of linear combinations of divergence and product rule forms discretized using 4th-order symmetric operators, with dissipative, 3rd or 4th-order reconstruction based upwind flux schemes was developed and implemented. A series of benchmark problems with increasing spatial and fluid dynamical complexity were utilized to examine the ability of the candidate schemes to resolve and propagate structures typical of turbulent flow, their discontinuity capturing capability and their robustness. A realistic geometry typical of a high-speed propulsion system flowpath was computed using the most promising of the examined schemes and was compared with available experimental data to demonstrate simulation fidelity.
A Hybrid Advection Scheme for Conserving Angular Momentum on a Refined Cartesian Mesh
NASA Astrophysics Data System (ADS)
Byerly, Zachary D.; Adelstein-Lelbach, Bryce; Tohline, Joel E.; Marcello, Dominic C.
2014-06-01
We test a new "hybrid" scheme for simulating dynamical fluid flows in which cylindrical components of the momentum are advected across a rotating Cartesian coordinate mesh. This hybrid scheme allows us to conserve angular momentum to machine precision while capitalizing on the advantages offered by a Cartesian mesh, such as a straightforward implementation of mesh refinement. Our test focuses on measuring the real and imaginary parts of the eigenfrequency of unstable nonaxisymmetric modes that naturally arise in massless polytropic tori having a range of different aspect ratios and on quantifying the uncertainty in these measurements. Our measured eigenfrequencies show good agreement with the results obtained from the linear stability analysis of Kojima and from nonlinear hydrodynamic simulations performed on a cylindrical coordinate mesh by Woodward et al. When compared against results conducted with a traditional Cartesian advection scheme, the hybrid scheme achieves qualitative convergence at the same or, in some cases, much lower grid resolutions and conserves angular momentum to a much higher degree of precision. As a result, this hybrid scheme is much better suited for simulating astrophysical fluid flows such as accretion disks and mass-transferring binary systems.
Tidal Mixing and Buoyancy Advection: Joint Influences on Lobster Distribution in Coastal Maine
NASA Astrophysics Data System (ADS)
Brooks, D. A.
2004-12-01
The Eastern Maine Coastal Current (EMCC) flows southwestward from the mouth of the Bay of Fundy to Penobscot Bay on the central Maine coast. Maximum non-tidal surface speeds reach 20-30 cm/s about 20 km offshore during April-May when the outflow from the Saint John River is strongest. Vigorous tides cause strong vertical and horizontal mixing, so that dispersal of neutral particles is influenced both by advection and tidal mixing. To survive, planktonic lobsters carried southwestward in the surface flow must settle to a nearshore cobble substrate. Larvae hatched near the Bay of Fundy can be advected to the central coast in 2-3 weeks, roughly the time needed to reach settlement stage. Over the same period, transverse tidal mixing is sufficient to raise nearshore larval concentrations to about half that offshore in the axis of the EMCC. Both processes may be necessary to explain the observed lobster distribution, which exhibits a distinct maximum in the central coastal region. The seasonal development of the EMCC is also influenced by winds and the larger circulation of the Gulf of Maine. This work is part of a multidisciplinary synthesis study funded by the NOAA Coastal Ocean Program.
Circulation-dominated solar shell dynamo models with positive alpha-effect
NASA Astrophysics Data System (ADS)
Küker, M.; Rüdiger, G.; Schultz, M.
2001-07-01
We present shell dynamo models for the solar convection zone with positive alpha -effect in the northern hemisphere and a meridional circulation which is directed equatorward at the bottom and poleward at the top of the convection zone. Two different rotation patterns are used: a simple variation of the rotation rate with depth and the rotation law as derived by helioseismology. Depending on the Reynolds number associated with the meridional flow, the dynamo shows a whole ``zoo'' of solutions. For sufficiently small values of the eddy magnetic diffusivity (1011 cm2/s), field advection by the meridional flow becomes dominant and even changes the character of the butterfly diagram. Flow amplitudes of a few m/s are then sufficient to turn the originally ``wrong'' butterfly diagram into a ``solar-type'' butterfly diagram, i.e. with activity belts drifting equatorward. This effect can easily be demonstrated with a super-rotation law (partial \\Omegaega /partial r > 0) with $Omega ega$ independent of the latitude. The situation is much more complicated for the ``real'' rotation law with the observed strong negative shear at high latitudes. With zero meridional flow, oscillating solutions are found without any latitudinal migration of the toroidal field belts, neither poleward nor equatorward. Small but finite flow amplitudes cause the magnetic field belts to drift poleward while in case of fast flow they move equatorward.
Mass and Momentum Transport in Microcavities for Diffusion-Dominant Cell Culture Applications
NASA Technical Reports Server (NTRS)
Yew, Alvin G.; Pinero, Daniel; Hsieh, Adam H.; Atencia, Javier
2012-01-01
For the informed design of microfluidic devices, it is important to understand transport phenomena at the microscale. This letter outlines an analytically-driven approach to the design of rectangular microcavities extending perpendicular to a perfusion microchannel for microfluidic cell culture devices. We present equations to estimate the spatial transition from advection- to diffusion-dominant transport inside cavities as a function of the geometry and flow conditions. We also estimate the time required for molecules, such as nutrients or drugs to travel from the microchannel to a given depth into the cavity. These analytical predictions can facilitate the rational design of microfluidic devices to optimize and maintain long-term, physiologically-based culture conditions with low fluid shear stress.
Enhancement of microbial motility due to advection-dependent nutrient absorption
NASA Astrophysics Data System (ADS)
Condat, Carlos A.; di Salvo, Mario E.
2014-03-01
In their classical work, Berg and Purcell [Biophys. J. 20, 193 (1977)] concluded that the motion of a small microorganism would not significantly increase its nutrient uptake rate, if the nutrient consisted of high diffusivity particles. As a result, it has been generally assumed that nutrient transport to small microorganisms such as bacteria is dominated by molecular diffusion and that swimming and feeding currents play a negligible role. On the other hand, recent studies have found that flagellar motion may increase advection-mediated uptake. We formulate a model to investigate the hypothesis that fast-moving microbes may enhance their swimming speed by taking advantage of advection to increase nutrient absorption. Surprisingly, using realistic parameter values for bacteria and algae, we find that even modest increases in nutrient absorption may lead to a significant increase of the microbial speed. We also show that, optimally, the rate of effective energy transfer to the microbial propulsion system should be proportional to the speed for slow motion, while it should be proportional to a power of the speed close to two for fast motion. We are grateful to SECyT-UNC and CONICET, Argentina, for financial support.
Inheritance - sex-linked dominant; Genetics - sex-linked dominant; X-linked dominant; Y-linked dominant ... type of chromosome that is affected (autosomal or sex chromosome). It also depends on whether the trait ...
Exact PDF equations and closure approximations for advective-reactive transport
Venturi, D.; Tartakovsky, Daniel M.; Tartakovsky, Alexandre M.; Karniadakis, George E.
2013-06-01
Mathematical models of advection–reaction phenomena rely on advective flow velocity and (bio) chemical reaction rates that are notoriously random. By using functional integral methods, we derive exact evolution equations for the probability density function (PDF) of the state variables of the advection–reaction system in the presence of random transport velocity and random reaction rates with rather arbitrary distributions. These PDF equations are solved analytically for transport with deterministic flow velocity and a linear reaction rate represented mathematically by a heterog eneous and strongly-correlated random field. Our analytical solution is then used to investigate the accuracy and robustness of the recently proposed large-eddy diffusivity (LED) closure approximation [1]. We find that the solution to the LED-based PDF equation, which is exact for uncorrelated reaction rates, is accurate even in the presence of strong correlations and it provides an upper bound of predictive uncertainty.
Numerical Modeling of Deep Mantle Convection: Advection and Diffusion Schemes for Marker Methods
NASA Astrophysics Data System (ADS)
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
Aerosol particles and the formation of advection fog
NASA Technical Reports Server (NTRS)
Hung, R. J.; Liaw, G. S.; Vaughan, O. H., Jr.
1979-01-01
A study of numerical simulation of the effects of concentration, particle size, mass of nuclei, and chemical composition on the dynamics of warm fog formation, particularly the formation of advection fog, is presented. This formation is associated with the aerosol particle characteristics, and both macrophysical and microphysical processes are considered. In the macrophysical model, the evolution of wind components, water vapor content, liquid water content, and potential temperature under the influences of vertical turbulent diffusion, turbulent momentum, and turbulent energy transfers are taken into account. In the microphysical model, the supersaturation effect is incorporated with the surface tension and hygroscopic material solution. It is shown that the aerosol particles with the higher number density, larger size nuclei, the heavier nuclei mass, and the higher ratio of the Van't Hoff factor to the molecular weight favor the formation of the lower visibility advection fogs with stronger vertical energy transfer during the nucleation and condensation time period.
Spiral defect chaos in an advection-reaction-diffusion system
NASA Astrophysics Data System (ADS)
Affan, H.; Friedrich, R.
2014-06-01
This paper comprises numerical and theoretical studies of spatiotemporal patterns in advection-reaction-diffusion systems in which the chemical species interact with the hydrodynamic fluid. Due to the interplay between the two, we obtained the spiral defect chaos in the activator-inhibitor-type model. We formulated the generalized Swift-Hohenberg-type model for this system. Then the evolution of fractal boundaries due to the effect of the strong nonlinearity at the interface of the two chemical species is studied numerically. The purpose of the present paper is to point out that spiral defect chaos, observed in model equations of the extended Swift-Hohenberg equation for low Prandtl number convection, may actually be obtained also in certain advection-reaction-diffusion systems.
Phase Segregation of Passive Advective Particles in an Active Medium.
Das, Amit; Polley, Anirban; Rao, Madan
2016-02-12
Localized contractile configurations or asters spontaneously appear and disappear as emergent structures in the collective stochastic dynamics of active polar actomyosin filaments. Passive particles which (un)bind to the active filaments get advected into the asters, forming transient clusters. We study the phase segregation of such passive advective scalars in a medium of dynamic asters, as a function of the aster density and the ratio of the rates of aster remodeling to particle diffusion. The dynamics of coarsening shows a violation of Porod behavior; the growing domains have diffuse interfaces and low interfacial tension. The phase-segregated steady state shows strong macroscopic fluctuations characterized by multiscaling and intermittency, signifying rapid reorganization of macroscopic structures. We expect these unique nonequilibrium features to manifest in the actin-dependent molecular clustering at the cell surface. PMID:26919022
Phase Segregation of Passive Advective Particles in an Active Medium
NASA Astrophysics Data System (ADS)
Das, Amit; Polley, Anirban; Rao, Madan
2016-02-01
Localized contractile configurations or asters spontaneously appear and disappear as emergent structures in the collective stochastic dynamics of active polar actomyosin filaments. Passive particles which (un)bind to the active filaments get advected into the asters, forming transient clusters. We study the phase segregation of such passive advective scalars in a medium of dynamic asters, as a function of the aster density and the ratio of the rates of aster remodeling to particle diffusion. The dynamics of coarsening shows a violation of Porod behavior; the growing domains have diffuse interfaces and low interfacial tension. The phase-segregated steady state shows strong macroscopic fluctuations characterized by multiscaling and intermittency, signifying rapid reorganization of macroscopic structures. We expect these unique nonequilibrium features to manifest in the actin-dependent molecular clustering at the cell surface.
NASA Astrophysics Data System (ADS)
Dean, A. M.; Benson, D. A.; Major, E.
2010-12-01
By adding a fractional-in-time term to the traditional advection dispersion equation, a model is able to simulate a late-time heavy-tailed contaminant breakthrough curve. This heavy-tailed breakthrough curve is observed in data collected during a conservative tracer “push-pull” test at the Macrodispersion Experiment (MADE) site. A time fractional advection dispersion equation (fADE) is able to predict power law tailing of conservative solutes by accounting for solutes transferring between the mobile and relatively immobile phases. Solutes can become trapped in a low permeability zone where the transport is controlled by diffusion instead of advection. It has been observed that the late-time heavy-tailed breakthrough curve may follow a power law due to the movement into these low flow zones. By solving the time fADE in a particle tracking program (SLIM-FAST) the model accounts for mass transfer between various phases and produces the same power law tail as observed in field data. For the implementation of the time fADE, in SLIM-FAST, the particles move based on a random-walk motion but have the ability to transition into a relatively immobile phase after (exponentially) random mobile times. Following a period in the immobile phase, the particle re-enters the mobile phase to be moved by advection and Fickian dispersion. To test the fADE approach, a recent single-well push-pull tracer test at the MADE site is reproduced using a groundwater flow code (ParFlow) and a particle tracking code (SLIM-FAST) using various immobile residence-time distributions.
Lattice Boltzmann method for the fractional advection-diffusion equation
NASA Astrophysics Data System (ADS)
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.
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. PMID:27176431
Anomalous diffusion of a tracer advected by wave turbulence
NASA Astrophysics Data System (ADS)
Balk, Alexander M.
2001-02-01
We consider the advection of a passive tracer when the velocity field is a superposition of random waves. Green's function for the turbulent transport (turbulent diffusion and turbulent drift) is derived. This Green's function is shown to imply sub-diffusive or super-diffusive behavior of the tracer. For the analysis we introduce the statistical near-identity transformation. The results are confirmed by numerical simulations.
Modeling solute advection coupled with sorption kinetics in heterogeneous formations
NASA Astrophysics Data System (ADS)
Selroos, Jan-Olof; Cvetkovic, Vladimir
1992-05-01
A method for coupling sorption kinetics and solute advection in particle-tracking models is proposed; this method is efficient for the case where sorption rate coefficients can be assumed constant field scale parameters. A simulation example of reactive solute advection in two-dimensional heterogeneous porous media is presented. The effect of sorption kinetics on solute advection is investigated. Nonequilibrium effects are exhibited as enhanced tailing in the solute breakthrough. Because high variability in the hydraulic conductivity also yields enhanced tailing, the nonequilibrium effect is more pronounced for the case of low variability. Moreover, it may be difficult to distinguish cases of low variability with nonequilibrium sorption from cases of high variability with equilibrium sorption. A comparison of Monte Carlo ensemble results is made with an analytical model for the mass arrival of kinetically sorbing solute in heterogeneous porous media obtained using first-order perturbation. The comparison indicates that the analytical model provides reasonable approximations of the expected solute breakthrough if the variance of the natural logarithm of the hydraulic conductivity is smaller than 1.
Atmospheric Surface Layer Flow over Distributions of Cubes and Evaluation of Transient Dynamics
NASA Astrophysics Data System (ADS)
Anderson, W.; Li, Q.; Bou-Zeid, E.
2014-12-01
The vertical transition from roughness sublayer to inertial layer is a well-established concept in turbulent boundary layer flows over complex topographies. The transition occurs at approximately three times the canopy height, below which the turbulence statistics resemble a turbulent mixing layer. Turbulent momentum fluxes in `canopy turbulence' or `obstructed shear flows' (Ghisalberti, 2008 JFM 641, 51—61) are typically dominated by turbulent sweep events (downward excursions of high momentum fluid), owing to the presence of coherent motions that occupy the region of fluid above the canopy. We have used large-eddy simulation with an immersed boundary method to study turbulent flows over a distribution of uniform height, staggered cubes. The computational domain has been designed such that both the roughness sublayer and a region of the inertial layer are resolved. With this, we record vertical profiles of time series of fluctuations of streamwise velocity, , and vertical velocity, . Contour images of fluctuating velocity component (where fluctuation is computed as a quantity's deviation from its time-averaged value during a time period over which the simulation exhibits statistical stationarity) shown relative to vertical position and time reveals an advective-lag between the passage of a high- or low-momentum region in the aloft inertial layer and excitation or relaxation of cube-scale coherent vortices in the sublayer. We quantify this advective lag and demonstrate how these events precede elevated Reynolds stresses associated with turbulent sweeps at the cube height. We propose that coherent, low and high momentum regions in the inertial layer are responsible for the reported advective lag. Vortex identification techniques are used to illustrate the presence of hairpin packets encapsulating low momentum regions. A simple, semi-empirical model for prediction of advective lag with height is developed. In spite of its simplicity, the model manages to capture
Hernandez-Santana, V.; Asbjornsen, H.; Sauer, T.; Isenhart, T.; Schilling, K.; Schultz, Ronald
2011-01-01
Riparian buffers are designed as management practices to increase infiltration and reduce surface runoff and transport of sediment and nonpoint source pollutants from crop fields to adjacent streams. Achieving these ecosystem service goals depends, in part, on their ability to remove water from the soil via transpiration. In these systems, edges between crop fields and trees of the buffer systems can create advection processes, which could influence water use by trees. We conducted a field study in a riparian buffer system established in 1994 under a humid temperate climate, located in the Corn Belt region of the Midwestern U.S. (Iowa). The goals were to estimate stand level transpiration by the riparian buffer, quantify the controls on water use by the buffer system, and determine to what extent advective energy and tree position within the buffer system influence individual tree transpiration rates. We primarily focused on the water use response (determined with the Heat Ratio Method) of one of the dominant species (Acer saccharinum) and a subdominant (Juglans nigra). A few individuals of three additional species (Quercus bicolor, Betula nigra, Platanus occidentalis) were monitored over a shorter time period to assess the generality of responses. Meteorological stations were installed along a transect across the riparian buffer to determine the microclimate conditions. The differences found among individuals were attributed to differences in species sap velocities and sapwood depths, location relative to the forest edge and prevailing winds and canopy exposure and dominance. Sapflow rates for A. saccharinum trees growing at the SE edge (prevailing winds) were 39% greater than SE interior trees and 30% and 69% greater than NW interior and edge trees, respectively. No transpiration enhancement due to edge effect was detected in the subdominant J. nigra. The results were interpreted as indicative of advection effects from the surrounding crops. Further, significant
North Atlantic Surface Winds Examined as the Source of Warm Advection into Europe in Winter
NASA Technical Reports Server (NTRS)
Otterman, J.; Angell, J. K.; Ardizzone, J.; Atlas, Robert; Schubert, S.; Starr, D.; Wu, M.-L.
2002-01-01
When from the southwest, North Atlantic ocean surface winds are known to bring warm and moist airmasses into central Europe in winter. By tracing backward trajectories from western Europe, we establish that these airmasses originate in the southwestern North Atlantic, in the very warm regions of the Gulf Stream. Over the eastern North Atlantic, Lt the gateway to Europe, the ocean-surface winds changed directions in the second half of the XXth century, those from the northwest and from the southeast becoming so infrequent, that the direction from the southwest became even more dominant. For the January-to-March period, the strength of south-westerlies in this region, as well as in the source region, shows in the years 1948-1995 a significant increase, above 0.2 m/sec/ decade. Based on the sensitivity of the surface temperature in Europe, slightly more than 1 C for a 1m/sec increase in the southwesterly wind, found in the previous studies, the trend in the warm advection accounts for a large part of the warming in Europe established for this period in several reports. However, for the most recent years, 1996-2001, the positive trend in the southwesterly advection appears to be is broken, which is consistent with unseasonally cold events reported in Europe in those winters. This study had, some bearing on evaluating the respective roles of the North Atlantic Oscillation and the Greenhouse Gas Global warming, GGG, in the strong winter warming observed for about half a century over the northern-latitude continents. Changes in the ocean-surface temperatures induced by GGG may have produced the dominant southwesterly direction of the North Atlantic winds. However, this implies a monotonically (apart from inherent interannual variability) increasing advection, and if the break in the trend which we observe after 1995 persists, this mechanism is counter-indicated. The 1948-1995 trend in the south-westerlies could then be considered to a large degree attributable to the
Shapiro, A.M.; Renken, R.A.; Harvey, R.W.; Zygnerski, M.R.; Metge, D.W.
2008-01-01
A tracer experiment, using a nonreactive tracer, was conducted as part of an investigation of the potential for chemical and pathogen migration to public supply wells that draw groundwater from the highly transmissive karst limestone of the Biscayne aquifer in southeastern Florida. The tracer was injected into the formation over approximately 1 h, and its recovery was monitored at a pumping well approximately 100 m from the injection well. The first detection of the tracer occurred after approximately 5 h, and the peak concentration occurred at about 8 h after the injection. The tracer was still detected in the production well more than 6 days after injection, and only 42% of the tracer mass was recovered. It is hypothesized that a combination of chemical diffusion and slow advection resulted in significant retention of the tracer in the formation, despite the high transmissivity of the karst limestone. The tail of the breakthrough curve exhibited a straight-line behavior with a slope of -2 on a log-log plot of concentration versus time. The -2 slope is hypothesized to be a function of slow advection, where the velocities of flow paths are hypothesized to range over several orders of magnitude. The flow paths having the slowest velocities result in a response similar to chemical diffusion. Chemical diffusion, due to chemical gradients, is still ongoing during the declining limb of the breakthrough curve, but this process is dwarfed by the magnitude of the mass flux by slow advection.
Feasibility of Measuring Mean Vertical Motion for Estimating Advection. Chapter 6
NASA Technical Reports Server (NTRS)
Vickers, Dean; Mahrt, L.
2005-01-01
Numerous recent studies calculate horizontal and vertical advection terms for budget studies of net ecosystem exchange of carbon. One potential uncertainty in such studies is the estimate of mean vertical motion. This work addresses the reliability of vertical advection estimates by contrasting the vertical motion obtained from the standard practise of measuring the vertical velocity and applying a tilt correction, to the vertical motion calculated from measurements of the horizontal divergence of the flow using a network of towers. Results are compared for three different tilt correction methods. Estimates of mean vertical motion are sensitive to the choice of tilt correction method. The short-term mean (10 to 60 minutes) vertical motion based on the horizontal divergence is more realistic compared to the estimates derived from the standard practise. The divergence shows long-term mean (days to months) sinking motion at the site, apparently due to the surface roughness change. Because all the tilt correction methods rely on the assumption that the long-term mean vertical motion is zero for a given wind direction, they fail to reproduce the vertical motion based on the divergence.
Comparison of advection and steam fogs: From direct observation over the sea
NASA Astrophysics Data System (ADS)
Heo, Ki-Young; Ha, Kyung-Ja; Mahrt, Larry; Shim, Jae-Seol
2010-11-01
Sea fog occurs frequently over the Yellow Sea in spring and summer, which causes costly or even catastrophic events including property damage, marine accidents, public health and financial losses. Case studies of advection and steam fogs using direct observation over the sea are constructed to better understand their formation, evolution and dissipation. A southerly wind supplies moisture to initiate advection fog events (AFs). Approximately -100 to -200 W m-2 of latent heat flux and -70 W m-2 of sensible heat flux during mature AFs are characterized with stable stratification which maintains dense fog by limiting downward mixing of dryer air. Steam fogs (SFs) develop from flow of cold air over warmer water, but are normally of limited persistence. During the SFs, a northerly wind decreases the air temperature below the sea surface temperature, which increases the relative humidity through evaporation from the warmer ocean. During mature SF, 360 W m-2 of latent heat flux and 150 W m-2 of sensible heat flux are characterized with neutral and unstable atmospheric conditions. The increase in wind speed and wind shear mixes dry air downward to the surface and limits the duration of the SF.
On the Offshore Advection of Boundary-Layer Structures and the Influence on Offshore Wind Conditions
NASA Astrophysics Data System (ADS)
Dörenkämper, Martin; Optis, Michael; Monahan, Adam; Steinfeld, Gerald
2015-06-01
The coastal discontinuity imposes strong signals to the atmospheric conditions over the sea that are important for wind-energy potential. Here, we provide a comprehensive investigation of the influence of the land-sea transition on wind conditions in the Baltic Sea using data from an offshore meteorological tower, data from a wind farm, and mesoscale model simulations. Results show a strong induced stable stratification when warm inland air flows over a colder sea. This stratification demonstrates a strong diurnal pattern and is most pronounced in spring when the land-sea temperature difference is greatest. The strength of the induced stratification is proportional to this parameter and inversely proportional to fetch. Extended periods of stable stratification lead to increased influence of inertial oscillations and increased frequency of low-level jets. Furthermore, heterogeneity in land-surface roughness along the coastline is found to produce pronounced horizontal streaks of reduced wind speeds that under stable stratification are advected several tens of kilometres over the sea. The intensity and length of the streaks dampen as atmospheric stability decreases. Increasing sea surface roughness leads to a deformation of these streaks with increasing fetch. Slight changes in wind direction shift the path of these advective streaks, which when passing through an offshore wind farm are found to produce large fluctuations in wind power. Implications of these coastline effects on the accurate modelling and forecasting of offshore wind conditions, as well as damage risk to the turbine, are discussed.
NASA Astrophysics Data System (ADS)
Comolli, Alessandro; Moussey, Charlie; Dentz, Marco
2016-04-01
Transport processes in groundwater systems are strongly affected by the presence of heterogeneity. The heterogeneity leads to non-Fickian features, that manifest themselves in the heavy-tailed breakthrough curves, as well as in the non-linear growth of the mean squared displacement and in the non-Gaussian plumes of solute particles. The causes of non-Fickian transport can be the heterogeneity in the flow fields and the processes of mass exchange between mobile and immobile phases, such as sorption/desorption reactions and diffusive mass transfer. Here, we present a Continuous Time Random Walk (CTRW) model that describes the transport of solutes in d-dimensional systems by taking into account both heterogeneous advection and mobile-immobile mass transfer. In order to account for these processes in the CTRW, the heterogeneities are mapped onto a distribution of transition times, which can be decomposed into advective transition times and trapping times, the latter being treated as a compound Poisson process. While advective transition times are related to the Eulerian flow velocities and, thus, to the conductivity distribution, trapping times depend on the sorption/desorption time scale, in case of reactive problems, or on the distribution of diffusion times in the immobile zones. Since the trapping time scale is typically much larger than the advective time scale, we observe the existence of two temporal regimes. The pre-asymptotic regime is defined by a characteristic time scale at which the properties of transport are fully determined by the heterogeneity of the advective field. On the other hand, in the asymptotic regime both the heterogeneity and the mass exchange processes play a role in conditioning the behaviour of transport. We consider different scenarios to discuss the relative importance of the advective heterogeneity and the mass transfer for the occurrence of non-Fickian transport. For each case we calculate analytically the scalings of the breakthrough
NASA Astrophysics Data System (ADS)
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
NASA Astrophysics Data System (ADS)
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.
NASA Astrophysics Data System (ADS)
Bernabé, Y.; Wang, Y.; Qi, T.; Li, M.
2016-02-01
The main purpose of this work is to investigate the relationship between passive advection-dispersion and permeability in porous materials presumed to be statistically homogeneous at scales larger than the pore scale but smaller than the reservoir scale. We simulated fluid flow through pipe network realizations with different pipe radius distributions and different levels of connectivity. The flow simulations used periodic boundary conditions, allowing monitoring of the advective motion of solute particles in a large periodic array of identical network realizations. In order to simulate dispersion, we assumed that the solute particles obeyed Taylor dispersion in individual pipes. When a particle entered a pipe, a residence time consistent with local Taylor dispersion was randomly assigned to it. When exiting the pipe, the particle randomly proceeded into one of the pipes connected to the original one according to probabilities proportional to the outgoing volumetric flow in each pipe. For each simulation we tracked the motion of at least 6000 solute particles. The mean fluid velocity was 10-3 ms-1, and the distance traveled was on the order of 10 m. Macroscopic dispersion was quantified using the method of moments. Despite differences arising from using different types of lattices (simple cubic, body-centered cubic, and face-centered cubic), a number of general observations were made. Longitudinal dispersion was at least 1 order of magnitude greater than transverse dispersion, and both strongly increased with decreasing pore connectivity and/or pore size variability. In conditions of variable hydraulic radius and fixed pore connectivity and pore size variability, the simulated dispersivities increased as power laws of the hydraulic radius and, consequently, of permeability, in agreement with previously published experimental results. Based on these observations, we were able to resolve some of the complexity of the relationship between dispersivity and permeability.
NASA Astrophysics Data System (ADS)
Frassi, Chiara
2015-12-01
I conducted new vorticity and deformation temperatures studies to test competing models of the exhumation of the mid-crustal rocks exposed in the Dolpo region (West Nepal). My results indicate that the Main Central Thrust is located ∼5 km structurally below the previous mapped locations. Deformation temperature increasing up structural section from ∼450 °C to ∼650 °C and overlap with peak metamorphic temperature indicating that penetrative shearing was responsible for the exhumation of the GHS occurred at "close" to peak metamorphic conditions. I interpreted the telescoping and the inversion of the paleo-isotherms at the base of the GHS as produced mainly by a sub-simple shearing (Wm = 0.88-1) pervasively distributed through the lower portion of the GHS. My results are consistent with hybrid channel flow-type models where the boundary between lower and upper portions of the GHS, broadly corresponding to the tectonometamorphic discontinuity recently documented in west Nepal, represents the limit between buried material, affected by dominant simple shearing, and exhumed material affected by a general flow dominates by pure shearing. This interpretation is consistent with the recent models suggesting the simultaneous operation of channel flow- and critical wedge-type processes at different structural depth.
NASA Astrophysics Data System (ADS)
Yan, Yunjun; Li, Xiaoyu
2007-07-01
The production dynamics and trophic basis of 7 dominant species of chironomids were investigated in the area of a second-order river of the Hanjiang River basin, in central China from June 2003 to June 2004. The results showed that Tvetenia discoloripes was by far the most abundant chironomid, dominating the overall standing stock of the taxa. In terms of lif ecycle, Chaetocladius sp., Eukiefferiella potthasti and T. discoloripes developed 1 generation a year, whereas Microtendipes sp. and Pagastia sp. developed two, while Pentaneura sp. and Polypedilum sp. developed three. T. discoloripes was the most productive chironomid with 120.305 8 g/m2. a, Pentaneura sp. and E. potthasti had relatively high production values of >17 g/m2.a, and the rest were <10 g/m2.a. All the production temporal variation tended to follow biomass patterns. T. discoloripes, Chaetocladius sp. and Pagastia sp. concentrated most of their production in winter, whereas E. potthasti, Pentaneura sp. and Polypedilum sp. had relatively higher production throughout the year. Only Microtendipes sp. had a production that peaked in summer. The overlap in temporal distribution of production among the chironomid species was generally high (>0.5), especially for filter-collectors Microtendipes sp., Chaetocladius sp., Chaetocladius sp., T. discoloripes and Pagastia sp. All species except Pentaneura sp. consumed a large portion of amorphous detritus, constituting more than 90% of their diets, and contributing nearly 90% to their secondary production. All the 7 chironomids represent obvious adaptation to local highly variable climate in summer and autumn in life cycle pattern, production dynamics, and food type.
NASA Astrophysics Data System (ADS)
Kim, Hyojin; Bishop, James K. B.; Dietrich, William E.; Fung, Inez Y.
2014-09-01
Significant solute flux from the weathered bedrock zone - which underlies soils and saprolite - has been suggested by many studies. However, controlling processes for the hydrochemistry dynamics in this zone are poorly understood. This work reports the first results from a four-year (2009-2012) high-frequency (1-3 day) monitoring of major solutes (Ca, Mg, Na, K and Si) in the perched, dynamic groundwater in a 4000 m2 zero-order basin located at the Angelo Coast Range Reserve, Northern California. Groundwater samples were autonomously collected at three wells (downslope, mid-slope, and upslope) aligned with the axis of the drainage. Rain and throughfall samples, profiles of well headspace pCO2, vertical profiles and time series of groundwater temperature, and contemporaneous data from an extensive hydrologic and climate sensor network provided the framework for data analysis. All runoff at this soil-mantled site occurs by vertical unsaturated flow through a 5-25 m thick weathered argillite and then by lateral flows to the adjacent channel as groundwater perched over fresher bedrock. Driven by strongly seasonal rainfall, over each of the four years of observations, the hydrochemistry of the groundwater at each well repeats an annual cycle, which can be explained by two end-member processes. The first end-member process, which dominates during the winter high-flow season in mid- and upslope areas, is CO2 enhanced cation exchange reaction in the vadose zone in the more shallow conductive weathered bedrock. This process rapidly increases the cation concentrations of the infiltrated rainwater, which is responsible for the lowest cation concentration of groundwater. The second-end member process occurs in the deeper perched groundwater and either dominates year-round (at the downslope well) or becomes progressively dominant during low flow season at the two upper slope wells. This process is the equilibrium reaction with minerals such as calcite and clay minerals, but not
Report on Hydrologic Flow in Low-Permeability Media
Liu, Hui-Hai; Birkholzer, Jens
2013-11-13
We demonstrate that under normal conditions (under which there are no intersections between tunnels/drifts and conductive geological structures, such as faults), the water flow velocity in the damage zone, as a result of non-Darcian flow behavior, is extremely small such that solute transport is dominated by diffusion, rather than advection. We show that unless non-Darcian flow behavior is considered, significant errors can occur in the “measured” relative-permeability values. We propose a hypothesis to consider the temperature impact based on limited test results from the petroleum literature. To consider the bedding effects, we present an empirical relationship between water flux and hydraulic gradient for non-Darcian water flow in anisotropic cases.
The Current-driven Kink Instability of the Poynting Flux Dominated Jets
NASA Astrophysics Data System (ADS)
Nakamura, Masanori; Meier, David L.
2004-11-01
The spatial stability properties are one of the most important problem in astrophysical jets dynamics. The non-relativistic 3-D MHD simulations of Poynting flux dominated (PFD) jets are presented. Our study focuses on the propagation of strongly magnetized hypersonic, but sub-Alfvénic flow and on the subsequent development of a current-driven (CD) kink instability. This instability may be responsible for the ``wiggled'' structures seen in sub-parsec scale (VLBI) AGN jets and pulsar jets. Our numerical results show that the PFD jets can develop CD distortions in the trans-Alfvénic flow case. An internal non axisymmetric body mode grows on time scales of order of the Alfvén crossing time and distorts the structure and magnetic configuration of the jet. The kink (m=1) mode of the CD instability, driven by the asymmetrically distribution of hoop-stress, grows faster than other higher order modes (m>1). This could be caused by a sudden loss of kinetic angular momentum to the magnetic field via the reverse slow-mode MHD shock wave. In the jet frame the mode grows locally and expands radially at each axial position where the jet is unstable: the instability, therefore, does not propagate as a wave along the jet length. The wiggled structures saturate and advect with the bulk flow and then, the local plasma flow follows a helical path along the kinked magnetic field backbone. M.N. is supported by a NRC RRA award.
Numerical simulation of life cycles of advection warm fog
NASA Technical Reports Server (NTRS)
Hung, R. J.; Vaughan, O. H.
1977-01-01
The formation, development and dissipation of advection warm fog is investigated. The equations employed in the model include the equation of continuity, momentum and energy for the descriptions of density, wind component and potential temperature, respectively, together with two diffusion equations for the modification of water-vapor mixing ratio and liquid-water mixing ratios. A description of the vertical turbulent transfer of heat, moisture and momentum has been taken into consideration. The turbulent exchange coefficients adopted in the model are based on empirical flux-gradient relations.
Yi, Chuixiang; Anderson, Dean E; Turnipseed, Andrew A; Burns, Sean P; Sparks, Jed P; Stannard, David I; Monson, Russell K
2008-09-01
The eddy covariance technique, which is used in the determination of net ecosystem CO2 exchange (NEE), is subject to significant errors when advection that carries CO2 in the mean flow is ignored. We measured horizontal and vertical advective CO2 fluxes at the Niwot Ridge AmeriFlux site (Colorado, USA) using a measurement approach consisting of multiple towers. We observed relatively high rates of both horizontal (F(hadv)) and vertical (F(vadv)) advective fluxes at low surface friction velocities (u(*)) which were associated with downslope katabatic flows. We observed that F(hadv) was confined to a relatively thin layer (0-6 m thick) of subcanopy air that flowed beneath the eddy covariance sensors principally at night, carrying with it respired CO2 from the soil and lower parts of the canopy. The observed F(vadv) came from above the canopy and was presumably due to the convergence of drainage flows at the tower site. The magnitudes of both F(hadv) and F(vadv) were similar, of opposite sign, and increased with decreasing u(*), meaning that they most affected estimates of the total CO2 flux on calm nights with low wind speeds. The mathematical sign, temporal variation and dependence on u(*) of both F(hadv) and F(vadv) were determined by the unique terrain of the Niwot Ridge site. Therefore, the patterns we observed may not be broadly applicable to other sites. We evaluated the influence of advection on the cumulative annual and monthly estimates of the total CO2 flux (F(c)), which is often used as an estimate of NEE, over six years using the dependence of F(hadv) and F(vadv) on u(*). When the sum of F(hadv) and F(vadv) was used to correct monthly F(c), we observed values that were different from the monthly F(c) calculated using the traditional u(*)-filter correction by--16 to 20 g C x m(-2) x mo(-1); the mean percentage difference in monthly Fc for these two methods over the six-year period was 10%. When the sum of F(hadv) and F(vadv) was used to correct annual Fc
Self-advection of density perturbations on a sloping continental shelf
Ping-Tung Shaw; Csanady, G.T.
1983-05-01
Bottom water movement on the continental shelf is modeled by the nonlinear interaction between longshore bottom geostrophic flow and the density field. Bottom geostrophic velocity, subject to linear steady momentum equations with linear bottom friction, can be generated by along-isobath density variations over a sloping bottom. At the same time, the density field is slowly advected by the velocity field. Away from boundary layers, the interplay is governed by Burgers' equation, which shows the formation and self-propulsion of strong density gradients along an isobath. The direction of propagation of a dense water blob is to have shallow water on the right- (left-) hand side facing downstream in the Northern (Southern) Hemisphere. The propagation of a light water blob is opposite to that of a dense water blob.
NASA Astrophysics Data System (ADS)
Carrera-Hernández, J. J.; Carreón-Freyre, D.; Cerca-Martínez, M.; Levresse, G.
2016-03-01
The city of Querétaro, located near the political boundary of the Mexican states of Querétaro and Guanajuato, relies on groundwater as it sole water supply. Groundwater extraction in the city increased from 21 × 106 m3/yr in 1970 to 104 × 106 m3/yr in 2010, with an associated drawdown of 100 m in some parts of the aquifer. A three-dimensional numerical groundwater-flow model has been developed that represents the historical evolution of the aquifer's potentiometric levels and is used to simulate the effect of two scenarios: (1) a 40 % reduction in the extraction rate from public water supply wells in early 2011 (thus reducing the extraction to 62 × 106 m3/yr), and (2) a further reduction in 2021 to 1 × 106 m3/yr. The modeling results project a temporary recovery of the potentiometric levels after the 40 % reduction of early 2011, but a return to 2010 levels by 2020. If scenario 2 is implemented in 2021, the aquifer will take nearly 30 years to recover to the simulated levels of 1995. The model also shows that the wells located in the city of Querétaro started to extract water from part of the aquifer beneath the State of Guanajuato in the late 1970s, thus showing that the administrative boundaries used in Mexico to study and develop water resources are inappropriate, and consideration should be given to physical boundaries instead. A regional approach to studying aquifers is needed in order to adequately understand groundwater flow dynamics.
NASA Astrophysics Data System (ADS)
Chen, Ke; Gawarkiewicz, Glen; Kwon, Young-Oh; Zhang, Weifeng G.
2015-06-01
In the coastal ocean off the Northeast U.S., the sea surface temperature (SST) in the first half of 2012 was the highest on the record for the past roughly 150 years of recorded observations. The underlying dynamical processes responsible for this extreme event are examined using a numerical model, and the relative contributions of air-sea heat flux versus lateral ocean advective heat flux are quantified. The model accurately reproduces the observed vertical structure and the spatiotemporal characteristics of the thermohaline condition of the Gulf of Maine and the Middle Atlantic Bight waters during the anomalous warming period. Analysis of the model results show that the warming event was primarily driven by the anomalous air-sea heat flux, while the smaller contribution by the ocean advection worked against this flux by acting to cool the shelf. The anomalous air-sea heat flux exhibited a shelf-wide coherence, consistent with the shelf-wide warming pattern, while the ocean advective heat flux was dominated by localized, relatively smaller-scale processes. The anomalous cooling due to advection primarily resulted from the along-shelf heat flux divergence in the Gulf of Maine, while in the Middle Atlantic Bight the advective contribution from the along-shelf and cross-shelf heat flux divergences was comparable. The modeling results confirm the conclusion of the recent analysis of in situ data by Chen et al. (2014a) that the changes in the large-scale atmospheric circulation in the winter of 2011-2012 primarily caused the extreme warm anomaly in the spring of 2012. The effect of along-shelf or cross-shelf ocean advection on the warm anomalies from either the Scotian Shelf or adjacent continental slope was secondary.
Moisture advection to the Arctic : forecasted, analysed and observed
NASA Astrophysics Data System (ADS)
Dufour, Ambroise; Zolina, Olga
2015-04-01
Besides its contribution to the Arctic hydrological budget, moisture imports from mid-latitudes are also influential on shorter time scales since water vapour advection tends to occur together with extratropical cyclones. Influx of moisture to the Arctic cause the formation of clouds that have an immediate impact on the surface energy budget especially in winter. In the long run, inaccuracies in the description of cloud cover and phase lead to temperature biases in CMIP5 models. The ECMWF workshop on polar prediction has highlighted moisture advection as one of the problematic physical processes limiting the quality of forecasts. Verifying the accuracy of medium-term forecasts is of interest beyond weather prediction : it points to the ability of models to bring adequate quantities of moisture to the Arctic when they are less constrained by observations than in analyses. In this study, we have compared forecasted moisture flux fields with analyses and observations over the period 2000-2010. ECMWF's ERA-Interim provided the forecasts, extending to ten days. For the analyses, in addition to ERA-Interim, we used the Arctic System Reanalysis whose forecast model is optimized for the polar regions and runs at high resolution (30 km). Finally, the Integrated Global Radiosonde Archive data over the Arctic allowed a validation by observations.
Backward fractional advection dispersion model for contaminant source prediction
NASA Astrophysics Data System (ADS)
Zhang, Yong; Meerschaert, Mark M.; Neupauer, Roseanna M.
2016-04-01
The forward Fractional Advection Dispersion Equation (FADE) provides a useful model for non-Fickian transport in heterogeneous porous media. The space FADE captures the long leading tail, skewness, and fast spreading typically seen in concentration profiles from field data. This paper develops the corresponding backward FADE model, to identify source location and release time. The backward method is developed from the theory of inverse problems, and then explained from a stochastic point of view. The resultant backward FADE differs significantly from the traditional backward Advection Dispersion Equation (ADE) because the fractional derivative is not self-adjoint and the probability density function for backward locations is highly skewed. Finally, the method is validated using tracer data from a well-known field experiment, where the peak of the backward FADE curve predicts source release time, while the median or a range of percentiles can be used to determine the most likely source location for the observed plume. The backward ADE cannot reliably identify the source in this application, since the forward ADE does not provide an adequate fit to the concentration data.
SEPs Dropout Events Associated with Advected Interplanetary Magnetic Structures
NASA Astrophysics Data System (ADS)
Bruno, R.; Trenchi, L.; Telloni, D.; D'Amicis, R.; Marcucci, F.; Zurbuchen, T.; Weberg, M. J.
2013-05-01
The intensity profile of energetic particles from impulsive solar flares (SEP) often shows abrupt dropouts affecting all energies simultaneously, without time-dispersion. Part of the community thinks that these modulations are directly related to the presence of magnetic structures with a different magnetic topology advected by the wind, a sort of magnetic flux tubes. During the expansion, following the dynamical interaction between plasma regions travelling at different speed, these structures would be partially tangled up in a sort of spaghetti-like bundle. These flux tubes would be alternatively connected or not connected with the flare site and, consequently, they would be filled or devoid of SEPs. When the observer passes through them, he would observe clear particles dropout signatures. We will report about results from a detailed analysis of SEP events which showed several signatures in the local magnetic field and/or plasma parameters associated with SEP modulations. These findings corroborate the idea of a possible link between these particles events observed at the Earth's orbit and magnetic connection or disconnection of the ambient magnetic field with the flare region at the Sun. We will also discuss the advantages represented by future Solar Orbiter in-situ observations. As a matter of fact, Solar Orbiter, from its orbital vantage point during the quasi corotation phase, will be a priviledged observer of this kind of phenomenon since it will observe the advected structure of the solar wind not yet reprocessed by dynamical interaction due to wind expansion.
Purely Lagrangian Simulation of Advection, Dispersion, Precipitation, and Dissolution
NASA Astrophysics Data System (ADS)
Benson, D.; Zhang, Y.; Reeves, D. M.
2008-05-01
We extend the advantages of Lagrangian random walk particle tracking (RWPT) methods that have long been used to simulate advection and dispersion in highly heterogeneous media. By formulating dissolution as a random, independent decay process, the classical continuum rate law is recovered. Formulating the random precipitation process requires a consideration of the probability that two nearby particles will coincide in a given time period. This depends on local mixing (as by diffusion) and the total domain particle number density, which are fixed and therefore easy to calculate. The result is that the classical law of mass action for equilibrium reactions can be reproduced in an ensemble sense. The same number of parameters for A+B ⇌ C are needed in a probabilistic versus continuum reaction simulation-- —one each for forward and backward probabilities that correspond to rates. The random nature of the simulations allows for significant disequilibrium in any given region at any time that is independent of the numerical details such as time stepping or particle density. This is exemplified by nearby or intermingled groups of reactants and little or no product--—a result that is often noted in the field that is difficult to reconcile with continuum methods or coarse-grained Eulerian models. Our results support recent results of perturbed advection-dispersion-reaction continuum models (Luo et al., WRR 44, 2008), and suggest that many different kinds of reactions can be easily added to existing RWPT codes.
Advection, pelagic food webs and the biogeography of seabirds in Beringia
Piatt, J.F.; Springer, A.M.
2003-01-01
Despite its great distance from productive shelf-edge habitat, the inner shelf area of the Bering Sea, from St. Lawrence Island to the Bering Strait, supports a surprisingly large number (>5 million) of seabirds during summer, mostly small plantivorous auklets (65%) and large piscivorous murres (19%) and kittiwakes (5%). This paradox of seabird biogeography is explained by the Anadyr "Green Belt" - a current that advects nutrients and plankton over 1200 km from the outer Bering Sea shelf-edge to the central Chukchi Sea. Turbulent upwelling of this nutrient-rich water at Anadyr and Bering straits further enhances high levels of primary production:(360 gC m-2y-1) and helps sustain the enormous biomass of zooplankton entrained in the Anadyr Current. Primary production in adjacent waters of the Chukchi Sea (420 gC m-2y-1) exceeds that observed below Bering Strait, and zooplankton are equally abundant. Auklets account for 49% of total food consumption below Bering Strait (411 mt d-1), whereas piscivores dominate (88% of 179 mt d-1) in the Chukchi Sea. Of 2 million seabirds in the Chukchi region, auklets (6%) are supplanted by planktivorous phalaropes (25%), and piscivorous murres (38%) and kittiwakes (15%). Average carbon flux to seabirds (0.65 mgC m -2d-1) over the whole region is more typical of upwelling than shelf ecosystems. The pelagic distribution of seabirds in the region appears to be a function of advection, productivity and water column stability. Planktivores flourish in areas with high zooplankton concentrations on the edge of productive upwelling and frontal zones along the "Green Belt", whereas piscivores avoid turbulent, mixed waters and forage in stable, stratified waters along the coast and in the central Chukchi Sea.
Transport and Recruitment of Blue Crab Larvae:a Model with Advection and Mortality
NASA Astrophysics Data System (ADS)
Garvine, R. W.; Epifanio, C. E.; Epifanio, C. C.; Wong, K.-C.
1997-07-01
The present paper develops a mathematical model for the transport and recruitment of blue crab (Callinectes sapidus) larvae, and applies it to the inner continental shelf of the Middle Atlantic Bight near Delaware Bay, U.S.A. Blue crab larvae develop through seven or eight planktonic zoeal stages to a megalopa stage suitable for recruitment to adult populations of east coast estuaries. The larvae are concentrated near the surface, and the currents are primarily forced by alongshelf winds and river discharge through major estuaries. Model currents are prescribed based on a realistic synthesis of their observed relationship to wind and river discharge. Besides the resulting advection, particle diffusion and biological mortality are added to determine the fate of larvae released from their parent estuary. Groups of particles were released across the source region of the outflowing buoyancy-driven current in the model estuary mouth. Most larvae were swept alongshelf to the south with the buoyancy-driven coastal current, and thus were lost as recruits to the population of their parent estuary. However, some larvae released close to the seaward edge of the emerging coastal current were able to cross the coastal current front and move seaward into inner shelf water during upwelling-favorable (northward) wind events. Some of these, in turn, were suitably placed near the parent estuary mouth so that they could be advected landward as megalopae into the estuary during a subsequent downwelling-favorable (southward) wind event and thus join the adult population. The model results for megalopae returns were computed from consecutive daily release of 1000 particles, and were compared with 4 years of blue crab megalopa settlement data for Delaware Bay. The model results for 1989 and 1990 matched the observed data remarkably well, with both years showing dominance by a single return event of a few days duration. For 1991 and 1992, the observed results showed multiple return events
NASA Astrophysics Data System (ADS)
Ringgaard, Rasmus; Herbst, Mathias; Friborg, Thomas
2014-09-01
Spatial and temporal variation in interception evaporation, energy balance during rain and total water loss was explored in a structurally heterogeneous Norway spruce [Picea abies (L.) H. Karst.] plantation in western Denmark. The trees are arranged in a distinctive small scale mosaic (0.25 ha) of young open canopy stands interspaced with older mature closed canopy stands. The mature stands are bound by a single line of taller Grand Fir [Abies grandis] on their northern edge. Interception loss (I) was measured and modeled in the open and closed canopy stands and under a Grand Fir row using net precipitation gauges and the Gash rain interception model. Incorporating complementary data on individual stand transpiration, forest floor evaporation and total ET (Ringgaard et al., 2012) we show that (a) I is 3% points higher in the closed canopy than in the open canopy (34% and 31% of PG respectively) while the Grand Fir row promotes a zone of relative drought with I = 47%, (b) in terms of total water loss, the open canopy has an annual ET of about 7.5% higher than the closed canopy stand and (c) in months with little precipitation there is good agreement between the individual components of the evaporation balance and the gap-filled eddy-covariance evapotranspiration (EC-ET) estimate while in months with high precipitation the EC-ET data underestimate both the magnitude and variability of I. The Gash model had to be parameterized separately for summer and winter. In winter, the available energy for evaporation during rain was dominated by regional scale advection of heat from the North Sea, while in summer half the available energy came from local advection. The mean evaporation rate during rain was 0.09 mm h-1 in winter and 0.21 mm h-1 in summer.
NASA Astrophysics Data System (ADS)
Arnaud-Fassetta, Gilles; Lissak, Candide; Fort, Monique; Bétard, François; Carlier, Benoit; Cossart, Etienne; Madelin, Malika; Viel, Vincent; Charnay, Bérengère; Bletterie, Xavier
2014-05-01
In the upper, wider reaches of Alpine valleys, shaping of active channels is usually subject to rapid change. It mostly depends upon hydro-climatic variability, runoff concentration and sediment supply, and may result in alternating sequences of fluvial and debris-flow pulses, as recorded in alluvial fans and terraces. Our study, carried in the frame of SAMCO (ANR) project, focuses on the upper Guil River Valley (Queyras, Southern French Alps) cut into the slaty shale "schistes lustrés". Steep, lower order drains carry a contrasted solid discharge, including predominantly sandy-loam particles mixed with gravels and boulders (sandstone schists, ophiolites). Abundant sediment supply by frost shattering, snow avalanche and landslides is then reworked during snowmelt or summer storm runoff events, and may result in catastrophic, very destructive floods along the main channel, as shown by historical records. Following the RI-30 year 2000 flood, our investigations included sediment budgets, i.e. balance of erosion and deposition, and the mapping of the source, transport and storage of various sediments (talus, colluvium, torrential fans, terraces). To better assess sediment fluxes and sediment delivery into the main channel network, we implemented tracers (pit-tags) in selected sub-catchments, significantly contributing to the sediment yield of the valley bottoms during the floods and/or avalanches: Maloqueste, Combe Morel, Bouchouse and Peyronnelle catchments. The first three are direct tributaries of the Guil River whereas the Peyronnelle is a left bank tributary of the Peynin River, which joins the Guil River via an alluvial cone with high human and material stakes. The Maloqueste and the Combe Morel are two tributaries facing each other in the Guil valley, representing a double lateral constraint for the road during flood events of the Guil River. After pit-tag initialisation in laboratory, we set them up along the four tributaries: Maloqueste (20 pit-tags), Combe
NASA Astrophysics Data System (ADS)
Basilici, Giorgio; de Luca, Pedro Henrique Vieira; Poiré, Daniel G.
2012-08-01
Turbidity-current and storm-induced deposits may exhibit similarities, in particularly when the latter is laid down by a combination of oscillatory and unidirectional flows. Recent progress in facies analysis helps to discriminate the sedimentary effects of oscillatory from unidirectional components of the flow. On the basis of detailed analysis of sedimentary facies, strata geometry, and palaeocurrent data, the present study reinterprets the Punta Negra Formation (PNF) (Lower-Middle Devonian, Argentine Precordillera), previously considered as a depositional system of deep-water, as a storm-dominated prodeltaic shelf depositional system. In the sandstone beds of the PNF, planar, low-angle and undulating laminations with weakly asymmetric hummocky and swaley bedforms, combined-flow ripples, accretionary hummocky cross-stratification-like (HCS-like), and anisotropic HCS-like suggest the action of oscillatory currents combined with unidirectional currents in forming the deposits. Different hypotheses on the origin of the oscillatory currents have been examined. The most convincing interpretation is that the oscillatory component of the velocity is attributed to storm-induced waves. The palaeocurrent data indicate offshore current directions, suggesting that the unidirectional flow was a gravity-induced bottom current. Inverse grading at the base and overlying normally graded divisions of the sandstone beds testify to waxing-waning behaviour of the depositional flows; interbedding of sedimentary structures (undulating laminations, low-angle and parallel laminations, and combined-flow ripples) in the lower and intermediate divisions of the beds indicate fluctuations of flow velocity. This organisation of the sedimentary structures permits association of the unidirectional component with hyperpycnal bottom currents. The terrestrial origin of the hyperpycnal flows is suggested by the abundance of terrestrial plant remains, the mineralogical and textural immaturity of the
NASA Astrophysics Data System (ADS)
Crane, R. A.; Cuthbert, M. O.; Timms, W.
2015-09-01
We present an interrupted-flow centrifugation technique to characterise preferential flow in low permeability media. The method entails a minimum of three phases: centrifuge-induced flow, no flow and centrifuge-induced flow, which may be repeated several times in order to most effectively characterise multi-rate mass transfer behaviour. In addition, the method enables accurate simulation of relevant in situ total stress conditions during flow by selecting an appropriate centrifugal force. We demonstrate the utility of the technique for characterising the hydraulic properties of smectite-clay-dominated core samples. All core samples exhibited a non-Fickian tracer breakthrough (early tracer arrival), combined with a decrease in tracer concentration immediately after each period of interrupted flow. This is indicative of dual (or multi-)porosity behaviour, with solute migration predominately via advection during induced flow, and via molecular diffusion (between the preferential flow network(s) and the low hydraulic conductivity domain) during interrupted flow. Tracer breakthrough curves were simulated using a bespoke dual porosity model with excellent agreement between the data and model output (Nash-Sutcliffe model efficiency coefficient was > 0.97 for all samples). In combination, interrupted-flow centrifuge experiments and dual porosity transport modelling are shown to be a powerful method to characterise preferential flow in low permeability media.
NASA Astrophysics Data System (ADS)
Crane, R. A.; Cuthbert, M. O.; Timms, W.
2015-01-01
We present an interrupted-flow centrifugation technique to characterise preferential flow in low permeability media. The method entails a minimum of three phases: centrifuge induced flow, no flow and centrifuge induced flow, which may be repeated several times in order to most effectively characterise multi-rate mass transfer behaviour. In addition, the method enables accurate simulation of relevant in situ total stress conditions during flow by selecting an appropriate centrifugal force level. We demonstrate the utility of the technique for characterising the hydraulic properties of smectite clay dominated core samples. All samples exhibited a non-Fickian tracer breakthrough (early tracer arrival), combined with a decrease in tracer concentration immediately after each period of interrupted-flow. This is indicative of dual (or multi) porosity behaviour, with solute migration predominately via advection during induced flow, and via molecular diffusion (between the preferential flow network(s) and the low hydraulic conductivity domain) during interrupted-flow. Tracer breakthrough curves were simulated using a bespoke dual porosity model with excellent agreement between the data and model output (Nash-Sutcliffe model efficiency coefficient was >0.97 for all samples). In combination interrupted-flow centrifuge experiments and dual porosity transport modelling are shown to be a powerful method to characterise preferential flow in low permeability media.
NASA Astrophysics Data System (ADS)
Staley, Dennis M.; Wasklewicz, Thad A.; Kean, Jason W.
2014-06-01
Wildfire dramatically alters the hydrologic response of a watershed such that even modest rainstorms can produce hazardous debris flows. Relative to shallow landslides, the primary sources of material and dominant erosional processes that contribute to post-fire debris-flow initiation are poorly constrained. Improving our understanding of how and where material is eroded from a watershed during a post-fire debris-flow requires (1) precise measurements of topographic change to calculate volumetric measurements of erosion and deposition, and (2) the identification of relevant morphometrically defined process domains to spatially constrain these measurements of erosion and deposition. In this study, we combine the morphometric analysis of a steep, small (0.01 km2) headwater drainage basin with measurements of topographic change using high-resolution (2.5 cm) multi-temporal terrestrial laser scanning data made before and after a post-fire debris flow. The results of the morphometric analysis are used to define four process domains: hillslope-divergent, hillslope-convergent, transitional, and channelized incision. We determine that hillslope-divergent and hillslope-convergent process domains represent the primary sources of material over the period of analysis in the study basin. From these results we conclude that raindrop-impact induced erosion, ravel, surface wash, and rilling are the primary erosional processes contributing to post-fire debris-flow initiation in the small, steep headwater basin. Further work is needed to determine (1) how these results vary with increasing drainage basin size, (2) how these data might scale upward for use with coarser resolution measurements of topography, and (3) how these results change with evolving sediment supply conditions and vegetation recovery.
Staley, Dennis M.; Waslewicz, Thad A.; Kean, Jason W.
2014-01-01
Wildfire dramatically alters the hydrologic response of a watershed such that even modest rainstorms can produce hazardous debris flows. Relative to shallow landslides, the primary sources of material and dominant erosional processes that contribute to post-fire debris-flow initiation are poorly constrained. Improving our understanding of how and where material is eroded from a watershed during a post-fire debris-flow requires (1) precise measurements of topographic change to calculate volumetric measurements of erosion and deposition, and (2) the identification of relevant morphometrically defined process domains to spatially constrain these measurements of erosion and deposition. In this study, we combine the morphometric analysis of a steep, small (0.01 km2) headwater drainage basin with measurements of topographic change using high-resolution (2.5 cm) multi-temporal terrestrial laser scanning data made before and after a post-fire debris flow. The results of the morphometric analysis are used to define four process domains: hillslope-divergent, hillslope-convergent, transitional, and channelized incision. We determine that hillslope-divergent and hillslope-convergent process domains represent the primary sources of material over the period of analysis in the study basin. From these results we conclude that raindrop-impact induced erosion, ravel, surface wash, and rilling are the primary erosional processes contributing to post-fire debris-flow initiation in the small, steep headwater basin. Further work is needed to determine (1) how these results vary with increasing drainage basin size, (2) how these data might scale upward for use with coarser resolution measurements of topography, and (3) how these results change with evolving sediment supply conditions and vegetation recovery.
Dynamical structure of magnetized dissipative accretion flow around black holes
NASA Astrophysics Data System (ADS)
Sarkar, Biplob; Das, Santabrata
2016-06-01
We study the global structure of optically thin, advection dominated, magnetized accretion flow around black holes. We consider the magnetic field to be turbulent in nature and dominated by the toroidal component. With this, we obtain the complete set of accretion solutions for dissipative flows where bremsstrahlung process is regarded as the dominant cooling mechanism. We show that rotating magnetized accretion flow experiences virtual barrier around black hole due to centrifugal repulsion that can trigger the discontinuous transition of the flow variables in the form of shock waves. We examine the properties of the shock waves and find that the dynamics of the post-shock corona (PSC) is controlled by the flow parameters, namely viscosity, cooling rate and strength of the magnetic field, respectively. We separate the effective region of the parameter space for standing shock and observe that shock can form for wide range of flow parameters. We obtain the critical viscosity parameter that allows global accretion solutions including shocks. We estimate the energy dissipation at the PSC from where a part of the accreting matter can deflect as outflows and jets. We compare the maximum energy that could be extracted from the PSC and the observed radio luminosity values for several super-massive black hole sources and the observational implications of our present analysis are discussed.
Dynamical structure of magnetized dissipative accretion flow around black holes
NASA Astrophysics Data System (ADS)
Sarkar, Biplob; Das, Santabrata
2016-09-01
We study the global structure of optically thin, advection dominated, magnetized accretion flow around black holes. We consider the magnetic field to be turbulent in nature and dominated by the toroidal component. With this, we obtain the complete set of accretion solutions for dissipative flows where bremsstrahlung process is regarded as the dominant cooling mechanism. We show that rotating magnetized accretion flow experiences virtual barrier around black hole due to centrifugal repulsion that can trigger the discontinuous transition of the flow variables in the form of shock waves. We examine the properties of the shock waves and find that the dynamics of the post-shock corona (PSC) is controlled by the flow parameters, namely viscosity, cooling rate and strength of the magnetic field, respectively. We separate the effective region of the parameter space for standing shock and observe that shock can form for wide range of flow parameters. We obtain the critical viscosity parameter that allows global accretion solutions including shocks. We estimate the energy dissipation at the PSC from where a part of the accreting matter can deflect as outflows and jets. We compare the maximum energy that could be extracted from the PSC and the observed radio luminosity values for several supermassive black hole sources and the observational implications of our present analysis are discussed.
Thermally driven advection for radioxenon transport from an underground nuclear explosion
NASA Astrophysics Data System (ADS)
Sun, Yunwei; Carrigan, Charles R.
2016-05-01
Barometric pumping is a ubiquitous process resulting in migration of gases in the subsurface that has been studied as the primary mechanism for noble gas transport from an underground nuclear explosion (UNE). However, at early times following a UNE, advection driven by explosion residual heat is relevant to noble gas transport. A rigorous measure is needed for demonstrating how, when, and where advection is important. In this paper three physical processes of uncertain magnitude (oscillatory advection, matrix diffusion, and thermally driven advection) are parameterized by using boundary conditions, system properties, and source term strength. Sobol' sensitivity analysis is conducted to evaluate the importance of all physical processes influencing the xenon signals. This study indicates that thermally driven advection plays a more important role in producing xenon signals than oscillatory advection and matrix diffusion at early times following a UNE, and xenon isotopic ratios are observed to have both time and spatial dependence.
Advection and Diffusion of Substances in Biological Tissues With Complex Vascular Networks
Beard, Daniel A.; Bassingthwaighte, James B.
2010-01-01
For highly diffusive solutes the kinetics of blood–tissue exchange is only poorly represented by a model consisting of sets of independent parallel capillary–tissue units. We constructed a more realistic multicapillary network model conforming statistically to morphometric data. Flows through the tortuous paths in the network were calculated based on constant resistance per unit length throughout the network and the resulting advective intracapillary velocity field was used as a framework for describing the extravascular diffusion of a substance for which there is no barrier or permeability limitation. Simulated impulse responses from the system, analogous to tracer water outflow dilution curves, showed flow-limited behavior over a range of flows from about 2 to 5 ml min−1 g−1, as is observed for water in the heart in vivo. The present model serves as a reference standard against which to evaluate computationally simpler, less physically realistic models. The simulated outflow curves from the network model, like experimental water curves, were matched to outflow curves from the commonly used axially distributed models only by setting the capillary wall permeability–surface area (PS) to a value so artifactually low that it is incompatible with the experimental observations that transport is flow limited. However, simple axially distributed models with appropriately high PSs will fit water outflow dilution curves if axial diffusion coefficients are set at high enough values to account for enhanced dispersion due to the complex geometry of the capillary network. Without incorporating this enhanced dispersion, when applied to experimental curves over a range of flows, the simpler models give a false inference that there is recruitment of capillary surface area with increasing flow. Thus distributed models must account for diffusional as well as permeation processes to provide physiologically appropriate parameter estimates. PMID:10784090
NASA Astrophysics Data System (ADS)
Makedonska, N.; Karra, S.; Painter, S. L.; Viswanathan, H.; Gable, C. W.
2014-12-01
Natural gas from unconventional fossil energy sources such as shale and tight gasformations has a profound impact on US energy independence. The current state ofproduction of methane and other hydrocarbons from low permeability shale involvesprocesses such as hydraulic fracturing of rock, multiphase flow, and recovery of the gasvia these fractures. Although hydraulic fracturing has been used for the past couple ofdecades, little is known about the underlying mechanisms behind the production curvesthat are seen in the field, such as, reasons for 50-60% decline after the first year in typicalproduction curves.Numerical experiments on a realistic fractured shale system are presented toidentify the effect of complex flow of gas in fractures and matrix diffusion on theproduction curve. For characterizing flow, including the characteristics and geometriesfor the fracture networks, we use a methodology that incorporates a recently developeddiscrete fracture network meshing approach [1], which is combined with the highlyparallel PFLOTRAN subsurface flow and reactive transport code [2] and a new particletracking capability [3]. The results of this reservoir-scale methodology for analyzing thedecline in gas production rates indicate dominant flow in fractures in the initial highproduction rate. Increase in matrix diffusivity improves production recovery after theinitial production of gas from fractures. Moreover, it is observed that increasing aperturevariability within a single fracture has little effect on the production compared tovariations of the mean fracture aperture from fracture to fracture in a fracture network. [1] Hyman, J.D., Gable C.W., Painter S.L., and Makedonska N., ConformingDelaunay Triangulation of Stochastically Generated Three Dimensional DiscreteFracture Networks: a Feature Rejection Algorithm f or Meshing Strategy, SIAM J.Sci. Comput, 2014 (in press). [2] Lichtner, P.C., Hammond G.E., Lu C., Karra S., Bisht G., Mills R.T., and KumarJ., PFLOTRAN User
Advection from the North Atlantic as the Forcing of Winter Greenhouse Effect Over Europe
NASA Technical Reports Server (NTRS)
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.
NASA Astrophysics Data System (ADS)
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
NASA Astrophysics Data System (ADS)
Mudunuru, M. K.; Nakshatrala, K. B.
2016-01-01
We present a robust computational framework for advective-diffusive-reactive systems that satisfies maximum principles, the non-negative constraint, and element-wise species balance property. The proposed methodology is valid on general computational grids, can handle heterogeneous anisotropic media, and provides accurate numerical solutions even for very high Péclet numbers. The significant contribution of this paper is to incorporate advection (which makes the spatial part of the differential operator non-self-adjoint) into the non-negative computational framework, and overcome numerical challenges associated with advection. We employ low-order mixed finite element formulations based on least-squares formalism, and enforce explicit constraints on the discrete problem to meet the desired properties. The resulting constrained discrete problem belongs to convex quadratic programming for which a unique solution exists. Maximum principles and the non-negative constraint give rise to bound constraints while element-wise species balance gives rise to equality constraints. The resulting convex quadratic programming problems are solved using an interior-point algorithm. Several numerical results pertaining to advection-dominated problems are presented to illustrate the robustness, convergence, and the overall performance of the proposed computational framework.
Mobile scintillometry to study heat advection over heterogeneous surfaces
NASA Astrophysics Data System (ADS)
Kleissl, J.
2007-12-01
Large Aperture Scintillometer (LAS) receivers measure the structure parameter of the refractive index from intensity fluctuations of the transmitter beam. Due to the spatial averaging over 1-4 km employed by this emerging technique the constraints for long temporal averaging (15-30 min) and associated uncertainties that have to be met by other flux measurement techniques do not apply for LASs. In this paper the constraints for temporal averaging of LASs will be examined as a function of environmental conditions and transect geometry. Moreover, analysis of data from a mobile LAS measurement across a surface gradient from rough and dry to smoother and wet will be presented. In this experiment the LAS was mounted on a pickup truck, allowing for quick redeployment of the transect after meaurement. The potential for the use of LAS to study local advection of heat in riparian or irrigated areas in the semi-arid southwest will be evaluated.
Unification of some advection schemes in two dimensions
NASA Technical Reports Server (NTRS)
Sidilkover, D.; Roe, P. L.
1995-01-01
The relationship between two approaches towards construction of genuinely two-dimensional upwind advection schemes is established. One of these approaches is of the control volume type applicable on structured cartesian meshes. It resulted in the compact high resolution schemes capable of maintaining second order accuracy in both homogeneous and inhomogeneous cases. Another one is the fluctuation splitting approach, which is well suited for triangular (and possibly) unstructured meshes. Understanding the relationship between these two approaches allows us to formulate here a new fluctuation splitting high resolution (i.e. possible use of artificial compression, while maintaining positivity property) scheme. This scheme is shown to be linearity preserving in inhomogeneous as well as homogeneous cases.
Multirate Runge-Kutta schemes for advection equations
NASA Astrophysics Data System (ADS)
Schlegel, Martin; Knoth, Oswald; Arnold, Martin; Wolke, Ralf
2009-04-01
Explicit time integration methods can be employed to simulate a broad spectrum of physical phenomena. The wide range of scales encountered lead to the problem that the fastest cell of the simulation dictates the global time step. Multirate time integration methods can be employed to alter the time step locally so that slower components take longer and fewer time steps, resulting in a moderate to substantial reduction of the computational cost, depending on the scenario to simulate [S. Osher, R. Sanders, Numerical approximations to nonlinear conservation laws with locally varying time and space grids, Math. Comput. 41 (1983) 321-336; H. Tang, G. Warnecke, A class of high resolution schemes for hyperbolic conservation laws and convection-diffusion equations with varying time and pace grids, SIAM J. Sci. Comput. 26 (4) (2005) 1415-1431; E. Constantinescu, A. Sandu, Multirate timestepping methods for hyperbolic conservation laws, SIAM J. Sci. Comput. 33 (3) (2007) 239-278]. In air pollution modeling the advection part is usually integrated explicitly in time, where the time step is constrained by a locally varying Courant-Friedrichs-Lewy (CFL) number. Multirate schemes are a useful tool to decouple different physical regions so that this constraint becomes a local instead of a global restriction. Therefore it is of major interest to apply multirate schemes to the advection equation. We introduce a generic recursive multirate Runge-Kutta scheme that can be easily adapted to an arbitrary number of refinement levels. It preserves the linear invariants of the system and is of third order accuracy when applied to certain explicit Runge-Kutta methods as base method.
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.
Advection from the North Atlantic as the Forcing of Winter Greenhouse Effect Over Europe
NASA Technical Reports Server (NTRS)
Otterman, Jay; Angell, J.; Atlas, Robert; Bungato, D.; Schubert, S.; Starr, D.; Susskind, J.; Wu, M.-L. C.
2001-01-01
In winter, large interannual fluctuations in the surface skin temperature are observed over central Europe: we observe a difference of 9.8 K comparing warm February 1990 with cold February 1996 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 Ina for February 1990 was 10.6 in s(exp -1), but for February 1996 I(sub na) was only 2.4 m s(exp -1). A large value of I(sub na) means a strong southwesterly flow which brings warm and moist air into Europe at low level, producing a steeper tropospheric lapse rate. Strong ascending motions result, which we observe in February 1990 at 700 mb. The near-surface moisture rises to higher (and cooler) levels, producing clouds and precipitation. Total preciptable water and cloud-cover fraction have larger values in February 1990 than in 1996. The difference in the greenhouse effect between these two scenarios can be translated into a virtual irradiating source of 2.6 W m(exp -2) above the February 1990 atmosphere, which, as an order of magnitude estimate, contributes to the warming of the surface by 2.6 K. If we accept this estimate as numerically pertinent, the direct effect stands as 7.2 K (9.8 K - 2.6 K), and therefore its greenhouse-effect reinforcement is by 36%. This constitutes a substantial positive feedback to the direct effect, which is the inflow of warm air to the low troposphere over Europe.
NASA Astrophysics Data System (ADS)
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.
Examination of the evolution of radiation and advection fogs. Final report
Orgill, M.M.
1993-01-01
A literature study was done on radiation and advection fog evolution. For radiation fog, six stages of fog evolution have been identified -- (1) precursor, (2) sunset, (3) conditioning, (4) mature, (5) sunrise, and (6) dissipation. The evolution of advection fog models has been in parallel with radiation fog models, but no identified stages in the evolution of advection fog have been proposed: (1) precursor, (2) initiation, (3) mature, and (4) dissipation. Radiation and advection fog models will require greater sophistication in order to study fog spatial and temporal variability. Physical aspects that require further study are discussed.
NASA Astrophysics Data System (ADS)
He, Y.; Billen, M. I.; Puckett, E. G.
2015-12-01
Flow in the Earth's mantle is driven by thermo-chemical convection in which the properties and geochemical signatures of rocks vary depending on their origin and composition. For example, tectonic plates are composed of compositionally-distinct layers of crust, residual lithosphere and fertile mantle, while in the lower-most mantle there are large compositionally distinct "piles" with thinner lenses of different material. Therefore, tracking of active or passive fields with distinct compositional, geochemical or rheologic properties is important for incorporating physical realism into mantle convection simulations, and for investigating the long term mixing properties of the mantle. The difficulty in numerically advecting fields arises because they are non-diffusive and have sharp boundaries, and therefore require different methods than usually used for temperature. Previous methods for tracking fields include the marker-chain, tracer particle, and field-correction (e.g., the Lenardic Filter) methods: each of these has different advantages or disadvantages, trading off computational speed with accuracy in tracking feature boundaries. Here we present a method for modeling active fields in mantle dynamics simulations using a new solver implemented in the deal.II package that underlies the ASPECT software. The new solver for the advection-diffusion equation uses a Local Discontinuous Galerkin (LDG) algorithm, which combines features of both finite element and finite volume methods, and is particularly suitable for problems with a dominant first-order term and discontinuities. Furthermore, we have applied a post-processing technique to insure that the solution satisfies a global maximum/minimum. One potential drawback for the LDG method is that the total number of degrees of freedom is larger than the finite element method. To demonstrate the capabilities of this new method we present results for two benchmarks used previously: a falling cube with distinct buoyancy and
Rawy, M S; Derar, R I; El-Sherry, T M; Megahed, G A
2014-08-01
The objectives of this study were to investigate the ovarian follicular waves and their corresponding hormonal changes in she-camels and to elucidate blood perfusion of the ovarian structures. Three reproductively sound, non-pregnant female camels were examined daily using B-mode and color Doppler to detect changes in their ovarian structures and blood vasculature for 22 follicular waves. Blood area (BA) and percentage (BA%) were determined for the ovarian structures. Three phases of follicular development, those of growth, maturation, and regression, were observed during each follicular wave. Deviation occurred on Day 6.1±1.08. Estradiol increased from basal levels of 27.4±0.4pg/ml to peak concentrations of 134.4±47.5pg/ml as the follicle reached a diameter of 13.2mm. Peripheral progesterone concentrations remained low (<0.4ng/ml) throughout the follicular waves. The blood flow to the dominant follicles increased gradually with follicular growth. The BA and BA% reached the maximum values of 18.4±11.6mm(2) and 6.04±2.03%, respectively, when the diameter of the dominant follicle was 17.5±3.4mm. The blood flow to the corpus luteum rose markedly after ovulation to reach a maximum BA% and BA at Days 5 and 7, respectively, post ovulation. In conclusion, the follicular wave pattern in dromedaries consists of individually variable periods of growth, maturation and regression. Deviation occurs 6.1±1.08d from emergence. Transrectal color-Doppler sonography is a useful technique for noninvasive evaluation of follicular vascularity in camels during various stages of the follicular wave. It provides additional information to assess the developmental stage and activity of the ovarian structures. PMID:24957969
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.
NASA Astrophysics Data System (ADS)
Figueroa, Aldo; Meunier, Patrice; Cuevas, Sergio; Villermaux, Emmanuel; Ramos, Eduardo
2014-01-01
We present a combination of experiment, theory, and modelling on laminar mixing at large Péclet number. The flow is produced by oscillating electromagnetic forces in a thin electrolytic fluid layer, leading to oscillating dipoles, quadrupoles, octopoles, and disordered flows. The numerical simulations are based on the Diffusive Strip Method (DSM) which was recently introduced (P. Meunier and E. Villermaux, "The diffusive strip method for scalar mixing in two-dimensions," J. Fluid Mech. 662, 134-172 (2010)) to solve the advection-diffusion problem by combining Lagrangian techniques and theoretical modelling of the diffusion. Numerical simulations obtained with the DSM are in reasonable agreement with quantitative dye visualization experiments of the scalar fields. A theoretical model based on log-normal Probability Density Functions (PDFs) of stretching factors, characteristic of homogeneous turbulence in the Batchelor regime, allows to predict the PDFs of scalar in agreement with numerical and experimental results. This model also indicates that the PDFs of scalar are asymptotically close to log-normal at late stages, except for the large concentration levels which correspond to low stretching factors.
Figueroa, Aldo; Meunier, Patrice; Villermaux, Emmanuel; Cuevas, Sergio; Ramos, Eduardo
2014-01-15
We present a combination of experiment, theory, and modelling on laminar mixing at large Péclet number. The flow is produced by oscillating electromagnetic forces in a thin electrolytic fluid layer, leading to oscillating dipoles, quadrupoles, octopoles, and disordered flows. The numerical simulations are based on the Diffusive Strip Method (DSM) which was recently introduced (P. Meunier and E. Villermaux, “The diffusive strip method for scalar mixing in two-dimensions,” J. Fluid Mech. 662, 134–172 (2010)) to solve the advection-diffusion problem by combining Lagrangian techniques and theoretical modelling of the diffusion. Numerical simulations obtained with the DSM are in reasonable agreement with quantitative dye visualization experiments of the scalar fields. A theoretical model based on log-normal Probability Density Functions (PDFs) of stretching factors, characteristic of homogeneous turbulence in the Batchelor regime, allows to predict the PDFs of scalar in agreement with numerical and experimental results. This model also indicates that the PDFs of scalar are asymptotically close to log-normal at late stages, except for the large concentration levels which correspond to low stretching factors.
NASA Technical Reports Server (NTRS)
Otterman, J.; Ardizzone, J.; Atlas, R.; Hu, H.; Jusem, J. C.; Starr, D.
1999-01-01
As established in previous studies, and analyzed further herein for the years 1988-1998, warm advection from the North Atlantic is the predominant control of the surface-air temperature in northern-latitude Europe in late winter. This thesis is supported by the substantial correlation Cti between the speed of the southwesterly surface winds over the eastern North Atlantic, as quantified by a specific Index Ina, and the 2-meter level temperature Ts over central Europe (48-54 deg N; 5-25 deg E), for January, February and early March. In mid-March and subsequently, the correlation Cti drops drastically (quite often it is negative). The change in the relationship between Ts and Ina marks a transition in the control of the surface-air temperature. As (a) the sun rises higher in the sky, (b) the snows melt (the surface absorptivity can increase by a factor of 3.0), (c) the ocean-surface winds weaken, and (d) the temperature difference between land and ocean (which we analyze) becomes small, absorption of insolation replaces the warm advection as the dominant control of the continental temperature. We define the onset of spring by this transition, which evaluated for the period of our study occurs at pentad 16 (Julian Date 76, that is, March 16). The control by insolation means that the surface is cooler under cloudy conditions than under clear skies. This control produces a much smaller interannual variability of the surface temperature and of the lapse rate than prevailing in winter, when the control is by advection. Regional climatic data would be of greatest value for agriculture and forestry if compiled for well-defined seasons. For continental northern latitudes, analysis presented here of factors controlling the surface temperature appears an appropriate tool for this task.
Kile, D.E.; Eberl, D.D.
2003-01-01
Crystal growth experiments were conducted using potassium alum and calcite crystals in aqueous solution under both non-stirred and stirred conditions to elucidate the mechanism for size-dependent (proportionate) and size-independent (constant) crystal growth. Growth by these two laws can be distinguished from each other because the relative size difference among crystals is maintained during proportionate growth, leading to a constant crystal size variance (??2) for a crystal size distribution (CSD) as the mean size increases. The absolute size difference among crystals is maintained during constant growth, resulting in a decrease in size variance. Results of these experiments show that for centimeter-sized alum crystals, proportionate growth occurs in stirred systems, whereas constant growth occurs in non-stirred systems. Accordingly, the mechanism for proportionate growth is hypothesized to be related to the supply of reactants to the crystal surface by advection, whereas constant growth is related to supply by diffusion. Paradoxically, micrometer-sized calcite crystals showed proportionate growth both in stirred and in non-stirred systems. Such growth presumably results from the effects of convection and Brownian motion, which promote an advective environment and hence proportionate growth for minute crystals in non-stirred systems, thereby indicating the importance of solution velocity relative to crystal size. Calcite crystals grown in gels, where fluid motion was minimized, showed evidence for constant, diffusion-controlled growth. Additional investigations of CSDs of naturally occurring crystals indicate that proportionate growth is by far the most common growth law, thereby suggesting that advection, rather than diffusion, is the dominant process for supplying reactants to crystal surfaces.
Technology Transfer Automated Retrieval System (TEKTRAN)
Advective energy occurring in edge environments may increase tree water use (e.g., latent heat loss, LE > net radiation, Rn). In humid agricultural landscapes, advection-enhanced transpiration in riparian buffers may provide hydrologic regulation and flood control benefits; however, research in humi...
Fractional Advective-Dispersive Equation as a Model of Solute Transport in Porous Media
Technology Transfer Automated Retrieval System (TEKTRAN)
Understanding and modeling transport of solutes in porous media is a critical issue in the environmental protection. The common model is the advective-dispersive equation (ADE) describing the superposition of the advective transport and the Brownian motion in water-filled pore space. Deviations from...
Technology Transfer Automated Retrieval System (TEKTRAN)
Advective energy occurring in edge environments may increase tree water use. In humid agricultural landscapes, advection-enhanced transpiration in riparian buffers may provide hydrologic regulation; however, research in humid environments is lacking. The objectives of this study were to determine ho...
Analytical solution for the advection-dispersion transport equation in layered media
Technology Transfer Automated Retrieval System (TEKTRAN)
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...
NASA Astrophysics Data System (ADS)
Karimi, S.; Nakshatrala, K. B.
2014-12-01
Advection-Diffusion-Reaction (ADR) equations play a crucial role in simulating numerous geo- physical phenomena. It is well-known that the solution to these equations exhibit disparate spatial and temporal scales. These mathematical scales occur due to relative dominance of either advec- tion, diffusion, or reaction processes. Hence, in a careful simulation, one has to choose appropriate time-integrators, time-steps, and numerical formulations for spatial discretization. Multi-time-step coupling methods allow specific choice of integration methods (either temporal or spatial) in dif- ferent regions of the spatial domain. In recent years, most of the attempts to design monolithic multi-time-step frameworks favored second-order transient systems in structural dynamics. In this presentation, we will introduce monolithic multi-time-step computational frameworks for ADR equations. These methods are based on the theory of differential/algebraic equations. We shall also provide an overview of results from stability analysis, study of drift from compatibility con- straints, and analysis of influence of perturbations. Several benchmark problems will be utilized to demonstrate the theoretical findings and features of the proposed frameworks. Finally, application of the proposed methods to fast bimolecular reactive systems will be shown.
Revisiting the Rossby Haurwitz wave test case with contour advection
NASA Astrophysics Data System (ADS)
Smith, Robert K.; Dritschel, David G.
2006-09-01
This paper re-examines a basic test case used for spherical shallow-water numerical models, and underscores the need for accurate, high resolution models of atmospheric and ocean dynamics. The Rossby-Haurwitz test case, first proposed by Williamson et al. [D.L. Williamson, J.B. Drake, J.J. Hack, R. Jakob, P.N. Swarztrauber, A standard test set for numerical approximations to the shallow-water equations on the sphere, J. Comput. Phys. (1992) 221-224], has been examined using a wide variety of shallow-water models in previous papers. Here, two contour-advective semi-Lagrangian (CASL) models are considered, and results are compared with previous test results. We go further by modifying this test case in a simple way to initiate a rapid breakdown of the basic wave state. This breakdown is accompanied by the formation of sharp potential vorticity gradients (fronts), placing far greater demands on the numerics than the original test case does. We also go further by examining other dynamical fields besides the height and potential vorticity, to assess how well the models deal with gravity waves. Such waves are sensitive to the presence or not of sharp potential vorticity gradients, as well as to numerical parameter settings. In particular, large time steps (convenient for semi-Lagrangian schemes) can seriously affect gravity waves but can also have an adverse impact on the primary fields of height and velocity. These problems are exacerbated by a poor resolution of potential vorticity gradients.
The Granite Aqueduct and Advection of Water and Heat Through Plutonic Terranes
NASA Astrophysics Data System (ADS)
Glazner, A. F.; Bartley, J. M.; Law, B.; Coleman, D. S.
2011-12-01
Although water plays a critical role in the genesis and movement of magma, it is largely lost from rocks upon crystallization. Observation of active volcanoes, analysis of magmatic inclusions, and experimental petrology indicate that intermediate magmas in subduction zones are water-rich, containing 5 wt% or more H2O. Carmichael (2002) wrote of the "andesite aqueduct" that conveys copious amounts of water from magma source regions in subduction zones to the surface and atmosphere. We suggest that this water plays a significant role in the thermal and textural history of the plutonic rocks through which it passes. A dacite magma with 5 wt% H2O crystallizes to granodiorite with ~0.5 wt% H2O, releasing >100 kg of H2O per m3. Field and geochronological data indicate that many sheet-like plutons are constructed from the top down, typically over 1 m.y. or more, likely bathing earlier pulses in ascending water released from later pulses. For a 5 km thick pluton, this release amounts to a condensed-water equivalent depth of ~500 m per unit of horizontal area, a truly vast amount. Plutons preserve abundant evidence for late-stage fluid transfer via a "granite aqueduct." For example, the Tuolumne Intrusive Suite of California is cut by myriad hydrothermally altered pipes that are typically found within or near aplite-pegmatite dikes (Mustart & Horrigan, 2000). The pipes attest to focused fluid flow, and the dikes themselves are the crystallized remnants of late-stage magmatic liquids. Upward advection of heat through dikes and pipes transfers thermal energy from newly crystallizing magma increments to older ones above much more efficiently and rapidly than thermal conduction, and could account for the widespread and profound recrystallization that produces the large grain size and low-temperature mineral assemblages of many granitic rocks. Although the concept that plutons represent the frozen record of huge, highly liquid magma chambers is losing favor, some recent studies
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.
Lancaster, Jill; Downes, Barbara J
2014-12-01
Many communities comprise species that select resources that are patchily distributed in an environment that is otherwise unsuitable or suboptimal. Effects of this patchiness can depend on the characteristics of patch arrays and animal movements, and produce non-intuitive outcomes in which population densities are unrelated to resource abundance. Resource mosaics are predicted to have only weak effects, however, where patches are ephemeral or organisms are transported advectively. The running waters of streams and benthic invertebrates epitomize such systems, but empirical tests of resource mosaics are scarce. We sampled 15 common macroinvertebrates inhabiting distinct detritus patches at four sites within a sand-bed stream, where detritus formed a major resource of food and living space. At each site, environmental variables were measured for 100 leaf packs; invertebrates were counted in 50 leaf packs. Sites differed in total abundance of detritus, leaf pack sizes and invertebrate densities. Multivariate analysis indicated that patch size was the dominant environmental variable, but invertebrate densities differed significantly between sites even after accounting for patch size. Leaf specialists showed positive and strong density-area relationships, except where the patch size range was small and patches were aggregated. In contrast, generalist species had weaker and variable responses to patch sizes. Population densities were not associated with total resource abundance, with the highest densities of leaf specialists in sites with the least detritus. Our results demonstrate that patchy resources can affect species even in communities where species are mobile, have advective dispersal, and patches are relatively ephemeral. PMID:25190216
Xu, Bruce S; Lollar, Barbara Sherwood; Passeport, Elodie; Sleep, Brent E
2016-04-15
Aqueous phase diffusion-related isotope fractionation (DRIF) for carbon isotopes was investigated for common groundwater contaminants in systems in which transport could be considered to be one-dimensional. This paper focuses not only on theoretically observable DRIF effects in these systems but introduces the important concept of constraining "observable" DRIF based on constraints imposed by the scale of measurements in the field, and on standard limits of detection and analytical uncertainty. Specifically, constraints for the detection of DRIF were determined in terms of the diffusive fractionation factor, the initial concentration of contaminants (C0), the method detection limit (MDL) for isotopic analysis, the transport time, and the ratio of the longitudinal mechanical dispersion coefficient to effective molecular diffusion coefficient (Dmech/Deff). The results allow a determination of field conditions under which DRIF may be an important factor in the use of stable carbon isotope measurements for evaluation of contaminant transport and transformation for one-dimensional advective-dispersive transport. This study demonstrates that for diffusion-dominated transport of BTEX, MTBE, and chlorinated ethenes, DRIF effects are only detectable for the smaller molar mass compounds such as vinyl chloride for C0/MDL ratios of 50 or higher. Much larger C0/MDL ratios, corresponding to higher source concentrations or lower detection limits, are necessary for DRIF to be detectable for the higher molar mass compounds. The distance over which DRIF is observable for VC is small (less than 1m) for a relatively young diffusive plume (<100years), and DRIF will not easily be detected by using the conventional sampling approach with "typical" well spacing (at least several meters). With contaminant transport by advection, mechanical dispersion, and molecular diffusion this study suggests that in field sites where Dmech/Deff is larger than 10, DRIF effects will likely not be
Assessing Bilingual Dominance.
ERIC Educational Resources Information Center
Flege, James Emil; Mackay, Ian R. A.; Piske, Thorsten
2002-01-01
Used two methods to assess bilingual dominance in four groups of Italian-English bilinguals. Ratios were derived from bilinguals' self-rating of ability to speak and understand Italian compared to English. Dominance in Italian was associated with a relatively high level of performance in Italian (assessed in a translation task) and relatively poor…
Genetic Dominance & Cellular Processes
ERIC Educational Resources Information Center
Seager, Robert D.
2014-01-01
In learning genetics, many students misunderstand and misinterpret what "dominance" means. Understanding is easier if students realize that dominance is not a mechanism, but rather a consequence of underlying cellular processes. For example, metabolic pathways are often little affected by changes in enzyme concentration. This means that…
NASA Astrophysics Data System (ADS)
Sanay, Rosario; Yankovsky, Alexander; Voulgaris, George
2008-08-01
The role of a curved coastline and associated bathymetry in the development of downwelling circulation in a stratified inner shelf is examined through a number of numerical experiments. Different scenarios include constant versus variable wind-forcing and variations in bottom friction. The three-dimensional response of the shelf within the domain (embayment enclosed by capes) is associated with the generation of a velocity/pycnocline disturbance at the upstream cape and its subsequent downstream advection. This disturbance is more pronounced under variable wind conditions. Its downstream advection through the bay exhibits different patterns depending on the competition between inertia and bottom friction near the cape. When inertia dominates, the disturbance separates from the cape and travels downwind with an enhanced downstream flow offshore and a countercurrent inshore. The separation occurs at a low Rossby number (Ro ˜ 0.15), which is attributed to the positive curvature of the coastline forming the cape. When friction dominates, the advection path is constrained along the coastline, resulting in an alongshore temperature gradient and a transient thermal front running almost perpendicular to the coast/isobaths. Simulations with spatially variable bottom friction, with higher friction toward the coast, result in the generation of eddy-like features. The numerical results are in agreement with both observations and surface temperature imagery from Long Bay, South Carolina, an embayment enclosed by two capes, and emphasize the role that coastline and associated shelf morphology can play in enhancing cross-shelf transport and exchange.
Bourguet, D
1999-07-01
The evolution of dominance has been subject to intensive debate since Fisher first argued that modifiers would be selected for if they made wild-type alleles more dominant over mutant alleles. An alternative explanation, put forward by Wright, is that the commonly observed dominance of wild-type alleles is simply a physiological consequence of metabolic pathways. Wright's explanation has gained support over the years, largely ending the debate over the general recessivity of deleterious mutations. Nevertheless there is reason to believe that dominance relationships have been moulded by natural selection to some extent. First, the metabolic pathways are themselves products of evolutionary processes that may have led them to be more stable to perturbations, including mutations. Secondly, theoretical models and empirical experiments suggest that substantial selection for dominance modifiers exists during the spread of adaptive alleles or when a polymorphism is maintained either by overdominant selection or by migration-selection balance. PMID:10447697
Differences between tangential geostrophy and columnar flow
NASA Astrophysics Data System (ADS)
Amit, Hagay; Pais, M. Alexandra
2013-04-01
Core flows inverted from time-dependent geomagnetic field models image the geodynamo at the top of its generation region, the Earth's outer core. Physical assumptions incorporated in these inversions may affect the resulting flows. Based on rapid rotation dominance, two assumptions similar in form yet different in essence were proposed: Tangential geostrophy (TG, LeMouël, 1984) and columnar flow (CF, Amit and Olson, 2004). We show that CF is theoretically consistent with the quasi-geostrophy (QG) theory for an incompressible fluid with spherical solid boundaries, whereas TG is not. The areas of ambiguous patches at the core surface where invisible TG or CF flows reside are roughly comparable. The spatial distribution of ambiguous patches for both TG and CF is quite asymmetric about the equator, so assuming equatorial symmetry may hypothetically reduce the non-uniqueness significantly. TG flows exhibit a strong Atlantic/Pacific hemispheric dichotomy and a well-defined eccentric gyre, whereas in CF flows the dichotomy between these two hemispheres is weaker and the gyre is less clear, suggesting that the eccentric gyre might not conserve mass. Both TG and CF upwelling/downwelling patterns are strongly localized in the equatorial region. In addition, in both cases upwelling/downwelling is correlated with equatorward/poleward flow respectively, as expected for QG convection. CF upwelling is more intense than TG upwelling but the magnitude ratio is smaller than the factor 2 distinguishing the analytical expressions of the two assumptions due to the dominance of magnetic field advection by toroidal core flow in the geomagnetic secular variation.
Lichtner, P.C.; Helgeson, H.C.
1986-06-20
A general formulation of multi-phase fluid flow coupled to chemical reactions was developed based on a continuum description of porous media. A preliminary version of the computer code MCCTM was constructed which implemented the general equations for a single phase fluid. The computer code MCCTM incorporates mass transport by advection-diffusion/dispersion in a one-dimensional porous medium coupled to reversible and irreversible, homogeneous and heterogeneous chemical reactions. These reactions include aqueous complexing, oxidation/reduction reactions, ion exchange, and hydrolysis reactions of stoichiometric minerals. The code MCCTM uses a fully implicit finite difference algorithm. The code was tested against analytical calculations. Applications of the code included investigation of the propagation of sharp chemical reaction fronts, metasomatic alteration of microcline at elevated temperatures and pressures, and ion-exchange in a porous column. Finally numerical calculations describing fluid flow in crystalline rock in the presence of a temperature gradient were compared with experimental results for quartzite.
Influence of surface clinker on the crustal structures and dynamics of 'a'ā lava flows
NASA Astrophysics Data System (ADS)
Applegarth, L. J.; James, M. R.; van Wyk de Vries, B.; Pinkerton, H.
2010-07-01
Surface structures on 'a'ā and blocky lavas reflect the internal flow dynamics during emplacement and also influence the dynamics of developing flows. To investigate the effects of brittle, clinkery 'a'ā flow crusts on flow dynamics and surface structures, we conducted sand and silicone laboratory experiments that simulated the advance of lava into a preexisting channelized flow with a surface crust. Experiments carried out with relatively thin crusts produced apparently ductile surface deformation structures, while thick crusts behaved dominantly in a brittle manner. Increased crustal thickness led to increased strength under compression but favored more disruption under tension, as the flow core welled up through tensile fractures, entraining crustal material. At lava flow fronts, upwelling and entrainment would increase heat losses by radiation and advection, respectively, resulting in a positive-feedback cooling loop. Fracturing caused heterogeneous crustal distribution near the flow front, which resulted in lobate flow advance, despite the absence of the viscoelastic layer that has previously been inferred as the primary control on flow advance and lobe formation. We therefore conclude that the influence of a purely brittle crust on the dynamics and surface morphologies of lava flows is more significant than often thought. All of the surface structures produced in the experiments have been observed on lavas or glaciers and many also on landslides and debris flows, suggesting the results can assist in the understanding of a range of natural flows.
NASA Astrophysics Data System (ADS)
Boudam, M. K.; Saoudi, B.; Moisan, M.; Ricard, A.
2007-03-01
The flowing afterglow of an N2-O2 discharge in the 0.6-10 Torr range is examined in the perspective of achieving sterilization of medical devices (MDs) under conditions ensuring maximum UV intensity with minimum damage to polymer-based MDs. The early afterglow is shown to be responsible for creating strong erosion damage, requiring that the sterilizer be operated in a dominant late-afterglow mode. These two types of afterglow can be characterized by optical emission spectroscopy: the early afterglow is distinguished by an intense emission from the N_{2}^{+} 1st negative system (band head at 391.4 nm) while the late afterglow yields an overpopulation of the v' = 11 ro-vibrational level of the N2(B) state, indicating a reduced contribution from the early afterglow N2 metastable species. We have studied the influence of operating conditions (pressure, O2 content in the N2-O2 mixture, distance of the discharge from the entrance to the afterglow (sterilizer) chamber) in order to achieve a dominant late afterglow that also ensures maximum and almost uniform UV intensity in the sterilization chamber. As far as operating conditions are concerned, moving the plasma source sufficiently far from the chamber entrance is shown to be a practical means for significantly reducing the density of the characteristic species of the early afterglow. Using the NO titration method, we obtain the (absolute) densities of N and O atoms in the afterglow at the NO injection inlet, a few cm before the chamber entrance: the N atom density goes through a maximum at approximately 0.3-0.5% O2 and then decreases, while the O atom density increases regularly with the O2 percentage. The spatial variation of the N atom (relative) density in the chamber is obtained by recording the emission intensity from the 1st positive system at 580 nm: in the 2-5 Torr range, this density is quite uniform everywhere in the chamber. The (relative) densities of N and O atoms in the discharge are determined by using
Anderman, Evan R.; Hill, Mary Catherine
2001-01-01
Observations of the advective component of contaminant transport in steady-state flow fields can provide important information for the calibration of ground-water flow models. This report documents the Advective-Transport Observation (ADV2) Package, version 2, which allows advective-transport observations to be used in the three-dimensional ground-water flow parameter-estimation model MODFLOW-2000. The ADV2 Package is compatible with some of the features in the Layer-Property Flow and Hydrogeologic-Unit Flow Packages, but is not compatible with the Block-Centered Flow or Generalized Finite-Difference Packages. The particle-tracking routine used in the ADV2 Package duplicates the semi-analytical method of MODPATH, as shown in a sample problem. Particles can be tracked in a forward or backward direction, and effects such as retardation can be simulated through manipulation of the effective-porosity value used to calculate velocity. Particles can be discharged at cells that are considered to be weak sinks, in which the sink applied does not capture all the water flowing into the cell, using one of two criteria: (1) if there is any outflow to a boundary condition such as a well or surface-water feature, or (2) if the outflow exceeds a user specified fraction of the cell budget. Although effective porosity could be included as a parameter in the regression, this capability is not included in this package. The weighted sum-of-squares objective function, which is minimized in the Parameter-Estimation Process, was augmented to include the square of the weighted x-, y-, and z-components of the differences between the simulated and observed advective-front locations at defined times, thereby including the direction of travel as well as the overall travel distance in the calibration process. The sensitivities of the particle movement to the parameters needed to minimize the objective function are calculated for any particle location using the exact sensitivity
Evaluation of reaction rates in streambed sediments with seepage flow: a novel code
NASA Astrophysics Data System (ADS)
Boano, Fulvio; De Falco, Natalie; Arnon, Shai
2015-04-01
Streambed interfaces represent hotspots for nutrient transformations because they host different microbial species which perform many heterotrophic and autotrophic reactions. The evaluation of these reaction rates is crucial to assess the fate of nutrients in riverine environments, and it is often performed through the analysis of concentrations from water samples collected along vertical profiles. The most commonly employed evaluation tool is the Profile code developed by Berg et al. (1998), which determines reaction rates by fitting observed concentrations to a diffusion-reaction equation that neglects the presence of water flow within sediments. However, hyporheic flow is extremely common in streambeds, where solute transport is often controlled by advection rather than diffusion. There is hence a pressing need to develop new methods that can be applied even to advection-dominated sediments. This contribution fills this gap by presenting a novel approach that extends the method proposed by Berg et al. (1998). This new approach includes the influence of vertical solute transport by upwelling or downwelling water, and it is this suited to the typical flow conditions of stream sediments. The code is applied to vertical profiles of dissolved oxygen from a laboratory flume designed to mimic the complex flow conditions of real streams. The results show that it is fundamental to consider water flow to obtain reliable estimates of reaction rates in streambeds. Berg, P., N. Risgaard-Petersen, and S. Rysgaard, 1998, Interpretation of measured concentration profiles in the sediment porewater, Limnology and Oceanography, 43:1500-1510.
Experimental study of advective-diffusive gaseous CO2 transport through porous media
NASA Astrophysics Data System (ADS)
Basirat, Farzad; Sharma, Prabhakar; Niemi, Auli; Fagerlund, Fritjof
2014-05-01
Leakage of gaseous CO2 into the shallow subsurface system is one of the main concerns associated with geologic storage resources. A better understanding of CO2 leakage in the shallow subsurface plays an important role for developing leakage monitoring programs. CO2 may reach the unsaturated zone by different leak mechanisms such as exsolution from CO2 supersaturated water and continuous bubbling or gas flow along a leakage path. In the unsaturated zone, the CO2 is heavier than air and may accumulate below the ground surface and move laterally. We developed a small-scale experiment setup to study the possible gaseous CO2 transport mechanisms with different controlled conditions. In this study, the experiment setup was applied to measure CO2 distributions in time and space through homogenous dry sand in which the CO2 concentrations through the domain were measured by sensitive gas sensors. The preliminary analysis of the result suggests that the transport and distribution of gaseous CO2 is spatially and temporally sensitive for the selected experimental conditions of gas flow rate and porous media. To better understand the advection and diffusion processes through the unsaturated zone, the experimental results are coupled with the dusty gas model (DGM) of Mason et al. (1967). The dusty gas model's constitutive relationships are integrated into a numerical model for multicomponent gas mixture flow and transport in porous media. The DGM considers interactions between all gaseous species and Knudsen diffusion which is important in fine grained soils. Results from the applied model were consistent with the experimental breakthrough curves obtained in this study.
Evaporation of traffic-generated nanoparticles during advection from source
NASA Astrophysics Data System (ADS)
Harrison, Roy M.; Jones, Alan M.; Beddows, David C. S.; Dall'Osto, Manuel; Nikolova, Irina
2016-01-01
Earlier work has demonstrated the potential for volatilisation of nanoparticles emitted by road traffic as these are advected downwind from the source of emissions, but there have been few studies and the processes have yet to be elucidated in detail. Using a dataset collected at paired sampling sites located respectively in a street canyon and in a nearby park, an in depth analysis of particle number size distributions has been conducted in order to better understand the size reduction of the semi-volatile nanoparticles. By sorting the size distributions according to wind direction and fitting log normal modes, it can be seen that the mode peaking at around 22 nm at the street canyon site is on average shrinking to 6.2 nm diameter at the park site which indicates a mean shrinkage rate for these particles of 0.13 nm s-1 with temperatures within the range 12-18 °C. The diurnal variation of the shrunken mode in the park reflects the diurnal pattern of particle concentrations at the street canyon site taken as the main source area. An analysis of peak diameter for the smallest mode at the downwind park site shows an inverse relationship to wind speed suggesting that dilution rather than travel time is the main determinant of the particle shrinkage rate. An evaluation of previously collected C10 to C35 n-alkane data from a different urban location shows a good fit to Pankow partitioning theory reflecting the semi-volatility of compounds believed to be representative of the composition of diesel exhaust nanoparticles, hence confirming the feasibility of an evaporative mechanism for particle shrinkage.
Critical time scales for advection-diffusion-reaction processes
NASA Astrophysics Data System (ADS)
Ellery, Adam J.; Simpson, Matthew J.; McCue, Scott W.; Baker, Ruth E.
2012-04-01
The concept of local accumulation time (LAT) was introduced by Berezhkovskii and co-workers to give a finite measure of the time required for the transient solution of a reaction-diffusion equation to approach the steady-state solution [A. M. Berezhkovskii, C. Sample, and S. Y. Shvartsman, Biophys. J.BIOJAU0006-349510.1016/j.bpj.2010.07.045 99, L59 (2010); A. M. Berezhkovskii, C. Sample, and S. Y. Shvartsman, Phys. Rev. EPLEEE81539-375510.1103/PhysRevE.83.051906 83, 051906 (2011)]. Such a measure is referred to as a critical time. Here, we show that LAT is, in fact, identical to the concept of mean action time (MAT) that was first introduced by McNabb [A. McNabb and G. C. Wake, IMA J. Appl. Math.IJAMDM0272-496010.1093/imamat/47.2.193 47, 193 (1991)]. Although McNabb's initial argument was motivated by considering the mean particle lifetime (MPLT) for a linear death process, he applied the ideas to study diffusion. We extend the work of these authors by deriving expressions for the MAT for a general one-dimensional linear advection-diffusion-reaction problem. Using a combination of continuum and discrete approaches, we show that MAT and MPLT are equivalent for certain uniform-to-uniform transitions; these results provide a practical interpretation for MAT by directly linking the stochastic microscopic processes to a meaningful macroscopic time scale. We find that for more general transitions, the equivalence between MAT and MPLT does not hold. Unlike other critical time definitions, we show that it is possible to evaluate the MAT without solving the underlying partial differential equation (pde). This makes MAT a simple and attractive quantity for practical situations. Finally, our work explores the accuracy of certain approximations derived using MAT, showing that useful approximations for nonlinear kinetic processes can be obtained, again without treating the governing pde directly.
How does a secular instability grow in a hyperaccretion flow?
NASA Astrophysics Data System (ADS)
Kimura, Mariko; Mineshige, Shin; Kawanaka, Norita
2015-10-01
Hyperaccretion flows with mass accretion rates far above the Eddington rate have an N-shaped equilibrium curve on the Σ-dot{M} plane (with Σ and dot{M} being surface density and mass accretion rate, respectively). The accretion flow on the lower Σ branch of the N-shape is optically thick, advection-dominated accretion flow, while that on the upper one is neutrino-dominated accretion flow. The middle branch has a negative slope on the Σ-dot{M} plane, meaning that the flow on this branch is secularly unstable. To investigate how the instability affects the flow structure and what observable signatures are produced, we study the time evolution of the unstable hyperaccretion flow in response to variable mass injection rates by solving the height-averaged equations for viscous accretion flows. When a transition occurs from the lower branch to the upper branch (or from the upper branch to the lower branch), the surface density rapidly increases (decreases) around that transition region, which induces locally enhanced mass flow (referred to as non-steady mass flow) into (out of) that region. We confirm that the non-steady flow can create a kind of disturbance and that it propagates over the whole disk. However, the non-steady mass flow is not strong enough to induce coherent transition over the whole disk, unless the mass injection rate varies with time. When the injection rate continuously changes, the neutrino luminosity varies intermittently, thus producing step-function-like light curves, as the radiation efficiency discontinuously changes every time the local transition occurs. The effects of changing the N-shape and possible observational consequences on the gamma-ray burst emission are briefly discussed.
NASA Astrophysics Data System (ADS)
Crutchley, G. J.; Klaeschen, D.; Planert, L.; Bialas, J.; Berndt, C.; Papenberg, C.; Hensen, C.; Hornbach, M. J.; Krastel, S.; Brueckmann, W.
2014-09-01
Fluid flow through marine sediments drives a wide range of processes, from gas hydrate formation and dissociation, to seafloor methane seepage including the development of chemosynthetic ecosystems, and ocean acidification. Here, we present new seismic data that reveal the 3D nature of focused fluid flow beneath two mound structures on the seafloor offshore Costa Rica. These mounds have formed as a result of ongoing seepage of methane-rich fluids. We show the spatial impact of advective heat flow on gas hydrate stability due to the channelled ascent of warm fluids towards the seafloor. The base of gas hydrate stability (BGHS) imaged in the seismic data constrains peak heat flow values to ∼60 mW m and ∼70 mW m beneath two separate seep sites known as Mound 11 and Mound 12, respectively. The initiation of pronounced fluid flow towards these structures was likely controlled by fault networks that acted as efficient pathways for warm fluids ascending from depth. Through the gas hydrate stability zone, fluid flow has been focused through vertical conduits that we suggest developed as migrating fluids generated their own secondary permeability by fracturing strata as they forced their way upwards towards the seafloor. We show that Mound 11 and Mound 12 (about 1 km apart on the seafloor) are sustained by independent fluid flow systems through the hydrate system, and that fluid flow rates across the BGHS are probably similar beneath both mounds. 2D seismic data suggest that these two flow systems might merge at approximately 1 km depth, i.e. much deeper than the BGHS. This study provides a new level of detail and understanding of how channelled, anomalously-high fluid flow towards the seafloor influences gas hydrate stability. Thus, gas hydrate systems have good potential for quantifying the upward flow of subduction system fluids to seafloor seep sites, since the fluids have to interact with and leave their mark on the hydrate system before reaching the seafloor.
The contiguous domains of Arctic Ocean advection: Trails of life and death
NASA Astrophysics Data System (ADS)
Wassmann, P.; Kosobokova, K. N.; Slagstad, D.; Drinkwater, K. F.; Hopcroft, R. R.; Moore, S. E.; Ellingsen, I.; Nelson, R. J.; Carmack, E.; Popova, E.; Berge, J.
2015-12-01
The central Arctic Ocean is not isolated, but tightly connected to the northern Pacific and Atlantic Oceans. Advection of nutrient-, detritus- and plankton-rich waters into the Arctic Ocean forms lengthy contiguous domains that connect subarctic with the arctic biota, supporting both primary production and higher trophic level consumers. In turn, the Arctic influences the physical, chemical and biological oceanography of adjacent subarctic waters through southward fluxes. However, exports of biomass out of the Arctic Ocean into both the Pacific and Atlantic Oceans are thought to be far smaller than the northward influx. Thus, Arctic Ocean ecosystems are net biomass beneficiaries through advection. The biotic impact of Atlantic- and Pacific-origin taxa in arctic waters depends on the total supply of allochthonously-produced biomass, their ability to survive as adults and their (unsuccessful) reproduction in the new environment. Thus, advective transport can be thought of as trails of life and death in the Arctic Ocean. Through direct and indirect (mammal stomachs, models) observations this overview presents information about the advection and fate of zooplankton in the Arctic Ocean, now and in the future. The main zooplankton organisms subjected to advection into and inside the Arctic Ocean are (a) oceanic expatriates of boreal Atlantic and Pacific origin, (b) oceanic Arctic residents and (c) neritic Arctic expatriates. As compared to the Pacific gateway the advective supply of zooplankton biomass through the Atlantic gateways is 2-3 times higher. Advection characterises how the main planktonic organisms interact along the contiguous domains and shows how the subarctic production regimes fuel life in the Arctic Ocean. The main differences in the advective regimes through the Pacific and Atlantic gateways are presented. The Arctic Ocean is, at least in some regions, a net heterotrophic ocean that - during the foreseeable global warming trend - will more and more rely
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
Wellman, Dawn M.; Zachara, John M.; Liu, Chongxuan; Qafoku, Nikolla; Smith, Steven C.; Forrester, Steven W.
2008-11-03
Sedimentary, hydrologic, and geochemical variations in the Hanford subsurface environment, as well as compositional differences in contaminating waste streams, have created vast differences in the migration and mobility of uranium within the subsurface environment. A series of hydraulically-saturated and -unsaturated column experiments were performed to i.) assess the effect of water content on the advective desorption and migration of uranium from contaminated sediments, and ii.) evaluate the uranium concentration that can develop in porewater and/or groundwater as a result of desorption/dissolution reactions. Flow rate and moisture content were varied to evaluate the influence of contact time, pore water velocity, and macropore desaturation on aqueous uranium concentrations. Sediments were collected from the T-TX-TY tank farm complex and the 300 Area Process Ponds located on the Hanford Site, southeastern Washington State. The sediments vary in depth, mineralogy, and in contamination events. Experiments were conducted under mildly alkaline/calcareous conditions representative of conditions commonly encountered at repository sites across the arid western United States and, in particular, the Hanford site. Results illustrate the release of uranium from these sediments is kinetically controlled and low water contents encountered within the Hanford vadose zone result in the formation of mobile-immobile water regimes, which isolate a fraction of the reactive sites within the sediments, effectively reducing the concentration of uranium released into migrating porewaters.
Lewis, F.M.; Voss, C.I.; Rubin, Jacob
1986-01-01
A model was developed that can simulate the effect of certain chemical and sorption reactions simultaneously among solutes involved in advective-dispersive transport through porous media. The model is based on a methodology that utilizes physical-chemical relationships in the development of the basic solute mass-balance equations; however, the form of these equations allows their solution to be obtained by methods that do not depend on the chemical processes. The chemical environment is governed by the condition of local chemical equilibrium, and may be defined either by the linear sorption of a single species and two soluble complexation reactions which also involve that species, or binary ion exchange and one complexation reaction involving a common ion. Partial differential equations that describe solute mass balance entirely in the liquid phase are developed for each tenad (a chemical entity whose total mass is independent of the reaction process) in terms of their total dissolved concentration. These equations are solved numerically in two dimensions through the modification of an existing groundwater flow/transport computer code. (Author 's abstract)
Measurement of advection of CO2 over grasslands in complex terrain in the Alps
NASA Astrophysics Data System (ADS)
Zhao, Peng; Hammerle, Albin; Wohlfahrt, Georg
2015-04-01
The role of advection is often ignored in the estimation of net ecosystem exchange (NEE) of CO2 in ecosystems. However, some studies reported that more realistic estimates of night-time NEE could be gathered if horizontal and vertical advections are included. While most of previous advection experiments have been conducted in forest ecosystems, grassland ecosystems have a great advantage as measurements of advection can be realised with smaller infrastructure and thus less experimental effort. In a preliminary simplified study, advection showed an important contribution to NEE during night time at a sub-alpine grassland site. This three-year program is focused on the role of advection for NEE of grassland ecosystems in complex terrain in the Alps. We are going to carry out field campaigns at four sites which cover a range of terrain types typical for mountains with varying degrees of complexity, including a valley-bottom site, a steep-slope site, a mixed-terrain site, and an undulating-terrain site. Observations will take place in a notional control volume with a length varying from 50 m to 5 m at each site in order to quantify the effects of horizontal spatial scale on advection estimates. The observations at each site include vertical flux of CO2 measured by eddy-covariance technique, horizontal and vertical advections of CO2 calculated from the measurement of wind components and CO2 gradients, and NEE measured by chambers. Among all, the measurement of the horizontal advection of CO2 needs many efforts because of small-scale variability in sources/sinks of CO2. We are going to use tubes with multiple inlets, which allows sampling at multiple positions across the faces at three heights of the control volume. Thus, we would be able to quantify the contribution of advection to NEE at different grassland sites situated in complex terrain in the Alps, and to quantify the effect of spatial scale of advection measurements with a given experimental setup and accuracy on
Advective, Diffusive and Eruptive Leakage of CO2 and Brine within Fault Zone
NASA Astrophysics Data System (ADS)
Jung, N. H.; Han, W. S.
2014-12-01
This study investigated a natural analogue for CO2 leakage near the Green River, Utah, aiming to understand the influence of various factors on CO2 leakage and to reliably predict underground CO2 behavior after injection for geologic CO2 sequestration. Advective, diffusive, and eruptive characteristics of CO2 leakage were assessed via a soil CO2 flux survey and numerical modeling. The field results show anomalous CO2 fluxes (> 10 g m-2 d-1) along the faults, particularly adjacent to CO2-driven cold springs and geysers (e.g., 36,259 g m-2 d-1 at Crystal Geyser), ancient travertines (e.g., 5,917 g m-2 d-1), joint zones in sandstone (e.g., 120 g m-2 d-1), and brine discharge zones (e.g., 5,515 g m-2 d-1). Combined to similar isotopic ratios of gas and progressive evolution of brine chemistry at springs and geysers, a gradual decrease of soil CO2 flux from the Little Grand Wash (LGW; ~36,259 g m-2 d-1) to Salt Wash (SW; ~1,428 g m-2 d-1) fault zones reveals the same CO2 origin and potential southward transport of CO2 over 10-20 km. The numerical simulations overtly exhibit lateral transport of free CO2 and CO2-rich brine from the LGW to SW fault zones through the regional aquifers (e.g., Entrada, Navajo, Kayenta, Wingate, White Rim). CO2 travels predominantly as an aqueous phase (Xco2=~0.045) as previously suggested, giving rise to the convective instability that further accelerates CO2 dissolution. While the buoyant free CO2 always tends to ascend, a fraction of dense CO2-rich brine flows laterally into the aquifer and mixes with the formation fluids during upward migration along the fault. The fault always enhances advective CO2 transport regardless of its permeability (k). However, only the low-k fault scenario engenders development of CO2 anticlinal trap within the shallow aquifers (Entrada and Navajo), concentrating high CO2 fluxes (~1,273 g m-2 d-1) within the northern footwall of the LGW fault similar to the field. Moreover, eruptive CO2 leakage at a well
Technology Transfer Automated Retrieval System (TEKTRAN)
Because the Surface Energy Balance Algorithm for Land (SEBAL) tends to underestimate ET under conditions of 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 en...
NASA Astrophysics Data System (ADS)
McPhee, Miles G.; Skogseth, Ragnheid; Nilsen, Frank; Smedsrud, Lars H.
2013-08-01
Measurements near the edge of fast ice in Freemansundet, Svalbard, reveal mixing processes associated with tidal advection of a sharp front in salinity, including possible supercooling induced by double diffusion in a fully turbulent water column. The front translated back and forth with the semidiurnal tide between an area of mobile (drifting) ice in Storfjorden proper, and the narrow sound covered by fast ice. Water on each side of the front was near its salinity-determined freezing temperature. Instruments deployed about 400 m into the sound from the fast ice edge measured current, temperature, conductivity, and turbulence quantities through several tidal cycles. Turbulence data illustrate that as the steep horizontal salinity (density) gradient advected past the measurement site, vertical shear near the fast-ice base induced marked flood/ebb asymmetry in turbulent mixing. As fresher water entered the sound on the flood phase, inward transport of denser water near the upper boundary was retarded, leading to statically unstable conditions and enhanced turbulence. The opposite occurred during ebb tide, as denser water underran lighter. Transient episodes of supercooling accompanied frontal passage on both flood and ebb phases. The most likely explanation for a zone of supercooled water within the strongly mixed frontal region is that during mixing of fresher, slightly warmer (but still at freezing) water from outside with saltier, colder water in the sound, the former constituent lost heat faster than gaining salt. This interpretation (differing turbulent diffusivities for heat and salt) challenges strict application of Reynolds analogy for highly turbulent shear flow.
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
NASA Astrophysics Data System (ADS)
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), 10.1103/PhysRevE.91.013002] 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 .
Horizontal Advection and Mixing of Pollutants in the Urban Atmospheric Environment
NASA Astrophysics Data System (ADS)
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
NASA Astrophysics Data System (ADS)
Gonnermann, H. M.; Jellinek, A. M.; Richards, M. A.; Manga, M.
2002-12-01
Heat flow from the Earth's core to the mantle remains an unresolved quantity. Its value has implications for the core's thermal evolution and growth of the inner core, the geodynamo, and the relative abundance of radioactive elements in the core and mantle. Core heat flow is affected by dynamics of the lowermost mantle in three ways: (1) advection of heat by plume instabilities; (2) conductive heating of subducted material; and (3) suppression of plume instabilities, as well as advection of heat by plate-scale mantle flow. We present results from a boundary-layer analysis and laboratory experiments aimed at understanding the effects of an imposed large-scale circulation on thermal convection at high-Rayleigh number (106<=Ra<=109) in a fluid with a strongly temperature-dependent viscosity. The ultimate goal of this work is to better understand the effect of plate-scale mantle flow on heat flux across the CMB and on the dynamics of plume formation at the CMB. Our theoretical analysis is complemented by lab experiments, in which a layer of corn syrup is heated from below and a large-scale flow is induced in the fluid above the hot boundary. We identify 4 convective regions associated with high-Rayleigh number convection in the presence of a large-scale flow: (1) a subcritical TBL region (Domain I), where plume instabilities are suppressed by the advective thinning of the TBL and heat flux is increased relative to convection without large-scale flow; (2) a supercritical TBL region (Domain II), where plume instabilities are no longer suppressed and heat flux is equal to convection without large-scale flow; (3) a flow-dominated region (Domain III), which is free of plumes; and (4) a plume-dominated domain (Domain IV), where the interaction of hot buoyant plumes and imposed large-scale flow results in lateral advection and distortion of rising plumes. In addition, we present a boundary-layer analysis that predicts heat flux, Q, from a hot surface as a function of imposed
Manifolds and front propagation barriers in advection-reaction-diffusion systems
NASA Astrophysics Data System (ADS)
Solomon, Tom
2015-03-01
We present experiments on the propagation of reaction fronts in laminar, vortex-dominated flows. The fronts are produced by the excitable Belousov-Zhabotinsky chemical reaction. The flows studied are driven by magnetohydrodynamic forcing techniques and are composed of a single vortex, chains or arrays of vortices, or spatially-disordered flows. In all of these cases, one-way barriers appear that either inhibit front propagation or, in some cases, pin the reactions fronts. We analyze this behavior with a recent theory of burning invariant manifolds (BIMs) that are a generalization of the theory of invariant manifolds developed in the past to characterize chaotic mixing and transport of passive impurities. We demonstrate that the BIMs are responsible for the reaction barriers observed experimentally, and we discuss the applicability of this BIM formalism to a range of flows: time-independent, time-periodic and time-aperiodic. Supported by NSF Grants DMR-1004744, DMR-1361881 and PHY-1156964.
Flow charts: visualization of vector fields on arbitrary surfaces.
Li, Guo-Shi; Tricoche, Xavier; Weiskopf, Daniel; Hansen, Charles
2008-01-01
We introduce a novel flow visualization method called Flow Charts, which uses a texture atlas approach for the visualization of flows defined over curved surfaces. In this scheme the surface and its associated flow are segmented into overlapping patches which are then parameterized and packed in the texture domain. This scheme allows accurate particle advection across multiple charts in the texture domain, providing a flexible framework that supports various flow visualization techniques. The use of surface parameterization enables flow visualization techniques requiring the global view of the surface over long time spans, such as Unsteady Flow LIC (UFLIC), particle-based Unsteady Flow Advection-Convolution (UFAC), or dye advection. It also prevents visual artifacts normally associated with view-dependent methods. Represented as textures, Flow Charts can be naturally integrated into GPU flow visualization techniques for interactive performance. PMID:18599918
Flow Charts: Visualization of Vector Fields on Arbitrary Surfaces
Li, Guo-Shi; Tricoche, Xavier; Weiskopf, Daniel; Hansen, Charles
2009-01-01
We introduce a novel flow visualization method called Flow Charts, which uses a texture atlas approach for the visualization of flows defined over curved surfaces. In this scheme, the surface and its associated flow are segmented into overlapping patches, which are then parameterized and packed in the texture domain. This scheme allows accurate particle advection across multiple charts in the texture domain, providing a flexible framework that supports various flow visualization techniques. The use of surface parameterization enables flow visualization techniques requiring the global view of the surface over long time spans, such as Unsteady Flow LIC (UFLIC), particle-based Unsteady Flow Advection Convolution (UFAC), or dye advection. It also prevents visual artifacts normally associated with view-dependent methods. Represented as textures, Flow Charts can be naturally integrated into hardware accelerated flow visualization techniques for interactive performance. PMID:18599918
An exact peak capturing and essentially oscillation-free (EPCOF) algorithm, consisting of advection-dispersion decoupling, backward method of characteristics, forward node tracking, and adaptive local grid refinement, is developed to solve transport equations. This algorithm repr...
AN EULERIAN-LAGRANGIAN LOCALIZED ADJOINT METHOD FOR THE ADVECTION-DIFFUSION EQUATION
Many numerical methods use characteristic analysis to accommodate the advective component of transport. Such characteristic methods include Eulerian-Lagrangian methods (ELM), modified method of characteristics (MMOC), and operator splitting methods. A generalization of characteri...
Giraldo, F.X.; Neta, B.
1995-04-21
An Eulerian and semi-Lagrangian finite element methods for the solution of the two dimensional advection equation were developed. Bilinear rectangular elements were used. Linear stability analysis of the method is given.
Sensitivity of Gcm Inm Ras To The Change of Humidity Advection Scheme
NASA Astrophysics Data System (ADS)
Kostrykin, S. V.
We study the influence of change the numerical scheme used for humidity advection in the GCM INM RAS on the model results. The previously used advection scheme of the second order leap-frog was changed on the semi-lagrangian cip scheme of the third order. It has shown that the last scheme has excelent numerical properties among other common semi-lagrangian schemes dealing with precise advection of sharp gra- dients. The numerical expriments with GCM has shown that the main changes in the humidity and temperature fields has happend near tropopause. More closeness of the model fields obtained with new advection of humidity to the NCAR/NCEP reanalyses fields are shown.
EULERIAN-LAGRANGIAN LOCALIZED ADJOINT METHOD FOR THE ADVECTION-DIFFUSION EQUATION
Many numerical methods use characteristic analysis to accommodate the advective component of transport. uch characteristic methods include Eulerian-Lagrangian methods (ELM), modified method of characteristics (MMOC), and operator splitting methods. eneralization of characteristic...
Comparison of thermal advection measurements by clear-air radar and radiosonde techniques
Crochet, M.; Rougier, G.; Bazile, G. Meteorologie Nationale, Trappes )
1990-10-01
Vertical profiles of the horizontal wind have been measured every 4 min by a clear-air radar (stratospheric-troposphere radar), and vertical profiles of temperature have been obtained every 2 hours by three radiosonde soundings in the same zone in Brittany during the Mesoscale Frontal Dynamics Project FRONTS 87 campaign. Radar thermal advection is deduced from the thermal wind equation using the measured real horizontal wind instead of the geostrophic wind. Radiosonde thermal advection is determined directly from the sounding station data sets of temperature gradients and also approximately from the thermodynamic equation by the temperature tendency. These approximations, applied during a frontal passage, show the same general features and magnitude of the thermal advection, giving a preliminary but encouraging conclusion for a possible real-time utilization of clear-air radars to monitor thermal advection and to identify its characteristic features. 6 refs.
The impact of advection on stratification and chlorophyll variability in the equatorial Pacific
NASA Astrophysics Data System (ADS)
Dave, Apurva C.; Lozier, M. Susan
2015-06-01
Previously reported global-scale correlations between interannual variability in upper ocean stratification and chlorophyll a (a proxy for phytoplankton biomass) have been shown to be driven by strong associations between the two properties in the central and western equatorial Pacific. Herein, we present evidence that these correlations are not causal but instead result from the advection of heat, salt, and nutrients in the region. Specifically, we demonstrate that stratification and chlorophyll are simultaneously influenced by shifts in the horizontal advective inputs of cold/saline/nutrient-rich waters from upwelling regions to the east and warm/fresh/nutrient-poor waters to the west. We find that horizontal advection contributes substantially to the annual surface layer nutrient budget and, together with vertical advection, significantly impacts interannual variability in chlorophyll. These results highlight the importance of a three-dimensional framework for examining nutrient supply in the upper ocean—a crucial requirement for assessing future marine ecosystem responses to a changing climate.
Shadid, John Nicolas; Bochev, Pavel Blagoveston; Gunzburger, Max Donald
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.
A fully implicit method for 3D quasi-steady state magnetic advection-diffusion.
Siefert, Christopher; Robinson, Allen Conrad
2009-09-01
We describe the implementation of a prototype fully implicit method for solving three-dimensional quasi-steady state magnetic advection-diffusion problems. This method allows us to solve the magnetic advection diffusion equations in an Eulerian frame with a fixed, user-prescribed velocity field. We have verified the correctness of method and implementation on two standard verification problems, the Solberg-White magnetic shear problem and the Perry-Jones-White rotating cylinder problem.
Advection-Induced Spectrotemporal Defects in a Free-Electron Laser
Bielawski, S.; Szwaj, C.; Bruni, C.; Garzella, D.; Orlandi, G.L.; Couprie, M.E.
2005-07-15
We evidence numerically and experimentally that advection can induce spectrotemporal defects in a system presenting a localized structure. Those defects in the spectrum are associated with the breakings induced by the drift of the localized solution. The results are based on simulations and experiments performed on the super-ACO free-electron laser. However, we show that this instability can be generalized using a real Ginzburg-Landau equation with (i) advection and (ii) a finite-size supercritical region.
Thermal characteristics of time-periodic electroosmotic flow in a circular microchannel
NASA Astrophysics Data System (ADS)
Moghadam, Ali Jabari
2015-10-01
A theoretical analysis is performed to explore the thermal characteristics of electroosmotic flow in a circular microchannel under an alternating electric field. An analytical approach is presented to solve energy equation, and then, the exact solution of temperature profiles is obtained by using the Green's function method. This study reveals that the temperature field repeats itself for each half-period. Frequency has a strong influence on the thermal behavior of the flow field. For small values of the dimensionless frequency (small channel size, large kinematic viscosity, or small frequency), the advection mechanism is dominant in the whole domain and the resultant heating (Joule heating and wall heat flux) can be transferred by the complete flow field in the axial direction; while, the middle portion of the flow field at high dimensionless frequencies does not have sufficient time to transfer heat by advection, and the bulk fluid temperature, especially in heating, may consequently become greater than the wall temperature. In a particular instance of cooling mode, a constant surface temperature case is temporarily occurred in which the axial temperature gradient will be zero. For relatively high frequencies, the unsteady bulk fluid temperature in some radial positions at some moments may be equal to the wall temperature; hence instantaneous cylindrical surfaces with zero radial heat flux may occur over a period of time. Depending on the value and sign of the thermal scale ratio, the quasi-steady-state Nusselt number (time-averaged at one period) approaches a specific value as the electrokinetic radius becomes infinity.
Burning invariant manifolds in spatially disordered advection-reaction-diffusion
NASA Astrophysics Data System (ADS)
Bargteil, Dylan; Solomon, Tom; Mahoney, John; Mitchell, Kevin
2012-02-01
We introduce burning invariant manifolds (BIMs) which act as barriers to front propagation, similar to the role played by invariant manifolds as barriers to passive transport in two-dimensional flows. We present experimental studies of BIMs in a spatially disordered, time-independent flow. We generate the flow with a magnetohydrodynamic technique that uses a DC current and a disordered pattern of permanent magnets. The velocity field is determined from this flow using particle tracking velocimetry, and reaction fronts are produced using the Ferroin-catalyzed Belousov-Zhabotinsky (BZ) chemical reaction. We use the experimental velocity field and a three-dimensional set of ODEs to predict from theory the location and orientation of BIMs. These predicted BIMs are found to match up well with the propagation barriers observed experimentally in the same flow using the BZ reaction. We explore the nature of BIMs as one-sided barriers, in contrast to invariant manifolds that act as barriers for passive transport in all directions. We also explore the role of projection singularities in the theory and how these singularities affect front behavior.
Autosomal dominant vitreoretinochoroidopathy (ADVIRC).
Blair, N P; Goldberg, M F; Fishman, G A; Salzano, T
1984-01-01
We report the second family recognised to have autosomal dominant vitreoretinochoroidopathy. The clinical features were (1) autosomal dominant inheritance; (2) peripheral, coarse pigmentary degeneration of the fundus for 360 degrees, with a relatively discrete posterior border in the equatorial region (this finding may be pathognomonic); (3) superficial punctate yellowish-white opacities in the retina; (4) various vascular abnormalities; (5) breakdown of the blood-retinal barrier; (6) retinal neovascularisation; (7) vitreous abnormalities; and (8) choroidal atrophy. Visual reduction was mainly due to macular oedema or vitreous haemorrhage. Images PMID:6689931
Language after dominant hemispherectomy
Gott, Piggy S.
1973-01-01
Linguistic and related cognitive abilities were investigated two years after dominant left hemispherectomy for cerebral malignancy in a 12 year old female. Auditory comprehension of speech was superior to other modes of language abilities with expressive speech being the least developed. Findings suggested an isolation or non-communication between the systems for speaking and for writing and visual perception. It was concluded that language mechanisms in the right hemisphere were not just at a low level of development of the functions found in the dominant hemisphere but were modified as a result of interference by preexistent spatioperceptual systems. Images PMID:4772723
NASA Astrophysics Data System (ADS)
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
Learning dominance relations in combinatorial search problems
NASA Technical Reports Server (NTRS)
Yu, Chee-Fen; Wah, Benjamin W.
1988-01-01
Dominance relations commonly are used to prune unnecessary nodes in search graphs, but they are problem-dependent and cannot be derived by a general procedure. The authors identify machine learning of dominance relations and the applicable learning mechanisms. A study of learning dominance relations using learning by experimentation is described. This system has been able to learn dominance relations for the 0/1-knapsack problem, an inventory problem, the reliability-by-replication problem, the two-machine flow shop problem, a number of single-machine scheduling problems, and a two-machine scheduling problem. It is considered that the same methodology can be extended to learn dominance relations in general.
Benchmarking transport solvers for fracture flow problems
NASA Astrophysics Data System (ADS)
Olkiewicz, Piotr; Dabrowski, Marcin
2015-04-01
Fracture flow may dominate in rocks with low porosity and it can accompany both industrial and natural processes. Typical examples of such processes are natural flows in crystalline rocks and industrial flows in geothermal systems or hydraulic fracturing. Fracture flow provides an important mechanism for transporting mass and energy. For example, geothermal energy is primarily transported by the flow of the heated water or steam rather than by the thermal diffusion. The geometry of the fracture network and the distribution of the mean apertures of individual fractures are the key parameters with regard to the fracture network transmissivity. Transport in fractures can occur through the combination of advection and diffusion processes like in the case of dissolved chemical components. The local distribution of the fracture aperture may play an important role for both flow and transport processes. In this work, we benchmark various numerical solvers for flow and transport processes in a single fracture in 2D and 3D. Fracture aperture distributions are generated by a number of synthetic methods. We examine a single-phase flow of an incompressible viscous Newtonian fluid in the low Reynolds number limit. Periodic boundary conditions are used and a pressure difference is imposed in the background. The velocity field is primarly found using the Stokes equations. We systematically compare the obtained velocity field to the results obtained by solving the Reynolds equation. This allows us to examine the impact of the aperture distribution on the permeability of the medium and the local velocity distribution for two different mathematical descriptions of the fracture flow. Furthermore, we analyse the impact of aperture distribution on the front characteristics such as the standard deviation and the fractal dimension for systems in 2D and 3D.
Fischer, G.E.
1985-07-01
These two lectures on iron dominated magnets are meant for the student of accelerator science and contain general treatments of the subjects design and construction. The material is arranged in the categories: General Concepts and Cost Considerations, Profile Configuration and Harmonics, Magnetic Measurements, a few examples of ''special magnets'' and Materials and Practices. Extensive literature is provided.
Parashar, R.; Cushman, J.H.
2008-06-20
Microbial motility is often characterized by 'run and tumble' behavior which consists of bacteria making sequences of runs followed by tumbles (random changes in direction). As a superset of Brownian motion, Levy motion seems to describe such a motility pattern. The Eulerian (Fokker-Planck) equation describing these motions is similar to the classical advection-diffusion equation except that the order of highest derivative is fractional, {alpha} element of (0, 2]. The Lagrangian equation, driven by a Levy measure with drift, is stochastic and employed to numerically explore the dynamics of microbes in a flow cell with sticky boundaries. The Eulerian equation is used to non-dimensionalize parameters. The amount of sorbed time on the boundaries is modeled as a random variable that can vary over a wide range of values. Salient features of first passage time are studied with respect to scaled parameters.
NASA Astrophysics Data System (ADS)
van Gorsel, E.; Leuning, R.; Delpierre, N.; Haverd, V.; Davy, R.; Cleugh, H.
2007-12-01
Even moderately complex topography can lead to significant horizontal and vertical advection and a consequent underestimation of nocturnal CO2 fluxes derived from eddy covariance measurements on a single tower. The presence of advective transport is identified using the time series of CO2 concentrations. Given a continuous input of carbon (soil-, wood- and leaf respiration) into a control volume (CV) we expect concentrations in that control volume to increase through time if there is no flux through the upper lid and no advective transport. Time series measurements usually show a strong increase in carbon concentration once the atmosphere is stably stratified, but after this initially strong increase the temporal build-up of concentrations is slower and may even remain relatively constant. As this steady-state situation is not associated with fluxes through the top of the CV we can assume that advection is draining CO2 away. We have analysed data from 24 Fluxnet sites where turbulent flux (Fc) and change of storage (Sc) of CO2 are routinely measured. Analysis of Sc confirms the observation by Aubinet et al. [1] that a common feature in canopy flows is that a maximum rate of change of CO2 occurs in the early evening. This suggests that after this maximum, the advection terms in the mass balance become non negligible. Based on this observation we have developed an alternative to the u*-threshold filtering technique [2]. We have shown that applying this alternative approach leads to good agreement between eddy covariance derived estimates of respiration and independent chamber measurements on a study site in a medium dense Eucalyptus forest in south-east Australia. In this contribution we discuss the applicability of this approach for several sites ranging from the tropics to subpolar latitudes and located in terrain that varies from almost ideally flat to very complex. We compare results from three different estimates of respiration and discuss differences between
NASA Technical Reports Server (NTRS)
Otterman, J.; Ardizzone, J.; Atlas, R.; Demaree, G.; Huth, R.; Jaagus, J.; Koslowsky, D.; Przybylak, R.; Wos, A.; Atlas, Robert (Technical Monitor)
1999-01-01
It is well recognized that advection from the North Atlantic has a profound effect on the climatic conditions in central Europe. A new dataset of the ocean-surface winds, derived from the Special Sensor Microwave Imager, SSM/1, is now available. This satellite instrument measures the wind speed, but not the direction. However, variational analysis developed at the Data Assimilation Office, NASA Goddard Space Flight Center, by combining the SSM/I measurements with wind vectors measured from ships, etc., produced global maps of the ocean surface winds suitable for climate analysis. From this SSM/I dataset, a specific index I(sub na) of the North Atlantic surface winds has been developed, which pertinently quantifies the low-level advection into central Europe. For a selected time-period, the index I(sub na) reports the average of the amplitude of the wind, averaging only the speed when the direction is from the southwest (when the wind is from another direction, the contribution counts to the average as zero speed). Strong correlations were found between February I(sub na) and the surface air temperatures in Europe 50-60 deg N. In the present study, we present the correlations between I(sub na) and temperature I(sub s), and also the sensitivity of T(sub s), to an increase in I(sub na), in various seasons and various regions. We specifically analyze the flow of maritime-air from the North Atlantic that produced two extraordinary warm periods: February 1990, and early-winter 2000/2001. The very cold December 2001 was clearly due to a northerly flow. Our conclusion is that the SSM/I dataset is very useful for providing insight to the forcing of climatic fluctuations in Europe.
Xiaoyi Li; Hai Huang; Paul Meakin
2008-09-01
The nonlinear coupling of fluid flow, reactive chemical transport and pore structure changes due to mineral precipitation (or dissolution) in porous media play a key role in a wide variety of processes of scientific interest and practical importance. Significant examples include the evolution of fracture apertures in the subsurface, acid fracturing stimulation for enhanced oil recovery and immobilizations of radionuclides and heavy metals in contaminated groundwater. We have developed a pore-scale simulation technique for modeling coupled reactive flow and structure evolution in porous media and fracture apertures. Advection, diffusion, and mineral precipitation resulting in changes in pore geometries are treated simultaneously by solving fully coupled fluid momentum and reactive solute transport equations. In this model, the reaction-induced evolution of solid grain surfaces is captured using a level set method. A sub-grid representation of the interface, based on the level set approach, is used instead of pixel representations of the interface often used in cellular-automata and most lattice-Boltzmann methods. The model is validated against analytical solutions for simplified geometries. Precipitation processes were simulated under various flow conditions and reaction rates, and the resulting pore geometry changes are discussed. Quantitative relationships between permeability and porosity under various flow conditions and reaction rates are reported.
NASA Astrophysics Data System (ADS)
Maghrebi, M.; Jankovic, I.; Rabideau, A. J.; Allen-King, R. M.; Weissmann, G. S.
2011-12-01
Effects of three key transport mechanisms (advection, diffusion and sorption) on transport and contaminant tailing of chlorinated solvents have been investigated using a numerical model. Thousands of model simulations have been conducted for various combinations of transport parameters that govern three key mechanisms in order to quantify tailing and relative importance of each mechanism. Hydraulic conductivity model contains a single inclusion of constant conductivity K embedded in a homogeneous anisotropic background of conductivity Kh,Kv. The inclusion is shaped as an oblate ellipsoid and subject to uniform flow. The background represents "average" conductivity of a heterogeneous formation while inclusion is used to represent geologic units that are more or less conductive than the background. The ratio of long to short semi-axis of the inclusion (a/b) models the ratio of horizontal to vertical integral scales (Ih/Iv) of different geologic units, where integral scales can be obtained, for example, using indicator variograms. The flow solution for present problem is obtained analytically as a closed form solution with exact expressions for Darcy velocity valid both inside and outside the inclusion. Sorption is modeled as an equilibrium process governed by a linear isotherm. The effects on transport and tailing are accounted for using retardation factors. Sorption heterogeneity is created by allowing different values of retardation factor for the interior (Ri) and the exterior of the inclusion (Rb). Diffusive displacements have been added to retarded advective displacements using random walk method. Peclet number, defined as Pe=U Ih/D (U is the groundwater velocity, D is the molecular diffusion coefficient for chlorinated solvents), is used to quantify the diffusion process. Very large numbers of particles (hundreds of thousands) have been tracked using very small time steps (as small as a/10,000) to provide sufficient resolution to breakthrough curves and to
NASA Astrophysics Data System (ADS)
Erol, Selcuk; Francois, Bertrand
2016-04-01
The advection/dispersion mechanism of the groundwater flow in the ground has a significant effect on a borehole heat exchanger (BHE) to enhance its thermal performance. However, the amount of energy extracted from the ground never disappears and only shifts with the magnitude of the effective thermal velocity in the infinite domain. In this work, we focus on the temperature and the energy balance of the ground in an advection/dispersion dominated heat transfer system during the operation period of a BHE and the subsequent recovery phase when the system is idle. The problem is treated with single BHE and multi-BHEs systems, for different representative geology and different groundwater flow velocity. In order to assess the thermal energy deficit due to heat extraction from the ground, we used the finite line source analytical model, developed recently (Erol et al., 2015) that provides the temperature distributions around the boreholes for discontinuous heat extraction. The model is developed based on the Green's function, which is the solution of heat conduction/advection/dispersion equation in porous media, for discontinuous heat extraction by analytically convoluting rectangular function or pulses in time domain. The results demonstrate the significant positive impact of the groundwater flow for the recovery in terms of temperature deficit at the location of the borehole. However, the total thermal energy deficit is not affected by the groundwater movement. The energy balance of the ground is the same no matter the prevailing heat transfer system, which can be only conduction or advection/dispersion. In addition, the energy balance of the ground is not based on either the duration of the production period operation or of the recovery phase, but depends on the total amount of heat that is extracted and on the bulk volumetric heat capacity of the ground.
NASA Astrophysics Data System (ADS)
Liu, Hui-Hai
2014-05-01
In clay or other low-permeability media, water flow becomes non-Darcian and characterized by the non-linear relationship between water flux and hydraulic gradient. This work is devoted to addressing a number of key issues related to geological disposal of high-level nuclear waste in clay/shale formations. It is demonstrated that water flow velocity in the damaged zone (often considered as a potential preferential advection paths in a repository) surrounding the tunnel is extremely small, as a result of non-Darcian flow behavior, such that solute transport is dominated by diffusion, rather than advection. The finding is also consistent with the often-observed existence of persistent abnormal pressures in shale formations. While relative permeability is the key parameter for modeling the unsaturated flow process, without incorporating non-Darcian flow behavior, significant errors can occur in the determination of relative permeability values from traditional measurement methods. An approach for dealing with temperature impact on non-Darcian flow and a formulation to calculate non-Darcian water flux in an anisotropic medium are presented, taking into consideration that a geological repository is subject to temperature evolution in the near field as a result of heat generated by nuclear waste, and that shale formations are generally anisotropic.
[Dominant, motivation and behavior].
Batuev, A S
1982-01-01
It was shown in experiments on cats with elaborated conditioned running to the left (with fresh food) and right (with salted food) feeding troughs that conditioned signals may change the current behaviour in spite of real unconditioned stimuli. The fresh food signal produces a conditioned "freshening" of the salt meat, which may be regarded as a successful physiological model of gustatory illusions. With a free choice of different salinity of food from different cups of each feeding though, behaviour is corrected by unconditioned factors, i.e. real salinity of food. As a result the thresholds of eating salt food from both feeding troughs are equalized. The facts are discussed in the light of the dominant principle, i.e. that central program which is built on the basis of the dominant motivation, of previous experience and current analysis of surroundings. PMID:7164569
[Dominant Thalamus and Aphasia].
Nakano, Akiko; Shimomura, Tatsuo
2015-12-01
Many studies have shown that lesions of the dominant thalamus precipitate language disorders in a similar manner to transcortical aphasias, in a phenomenon known as "thalamic aphasia." In some cases, however, aphasia may not occur or may appear transiently following thalamic lesions. Furthermore, dominant thalamic lesions can produce changes in character, as observed in patients with amnesic disorder. Previous work has explored the utility of thalamic aphasia as a discriminative feature for classification of aphasia. Although the thalamus may be involved in the function of the brainstem reticular activating system and play a role in attentional network and in memory of Papez circuit or Yakovlev circuit, the mechanism by which thalamic lesion leads to the emergence of aphasic disorders is unclear. In this review, we we survey historical and recent literature on thalamic aphasia in an attempt to understand the neural processes affected by thalamic lesions. PMID:26618763
Horizontal advection and dispersion in a stratified shelf sea: The role of inertial oscillations
NASA Astrophysics Data System (ADS)
Inall, Mark E.; Aleynik, Dmitry; Neil, Clare
2013-10-01
The role played by inertial motions in horizontal dispersion within the thermocline of a broad, mid-latitude shelf sea is examined through the analysis of a deliberately released dye tracer. Our analysis is of the horizontal and vertical evolution over 40 h of a dye tracer injected into the seasonally stratified thermocline of the Celtic Sea on the NW European Shelf. The inferred diapycnal diffusivity was 1.3-1.5 × 10-5 m2 s-1, and the radial horizontal diffusivities of the depth integrated dye patch ranged from 1.9 to 4.0 m2 s-1. The inferred vertical diffusivity is in agreement with microstructure based estimates, and the depth integrated horizontal diffusivity is broadly in agreement with previous dye release derived estimates made over similar scales and time periods. Asymmetry in the horizontal evolution of the dye patch was evident. We argue that mean shear dispersion was responsible for lateral elongation of the dye patch, particularly between hours 23 and 35 after release, during which time horizontal diffusivity along the major axis, Ka, exceeded that along the minor axis, Kb, by more than a factor of 10. We further show that along-patch shear was predominantly a result of differential advection between a deep residual flow to the south-east and an oscillating wind-driven surface Ekman layer. In this region of strong low frequency (inertial) shear a time dependent model of shear dispersion (Young et al., 1982) was able to account for the observed rate of horizontal dispersion calculated on the target isopycnal surface.
NASA Astrophysics Data System (ADS)
Mudunuru, M. K.; Shabouei, M.; Nakshatrala, K.
2015-12-01
Advection-diffusion-reaction (ADR) equations appear in various areas of life sciences, hydrogeological systems, and contaminant transport. Obtaining stable and accurate numerical solutions can be challenging as the underlying equations are coupled, nonlinear, and non-self-adjoint. Currently, there is neither a robust computational framework available nor a reliable commercial package known that can handle various complex situations. Herein, the objective of this poster presentation is to present a novel locally conservative non-negative finite element formulation that preserves the underlying physical and mathematical properties of a general linear transient anisotropic ADR equation. In continuous setting, governing equations for ADR systems possess various important properties. In general, all these properties are not inherited during finite difference, finite volume, and finite element discretizations. The objective of this poster presentation is two fold: First, we analyze whether the existing numerical formulations (such as SUPG and GLS) and commercial packages provide physically meaningful values for the concentration of the chemical species for various realistic benchmark problems. Furthermore, we also quantify the errors incurred in satisfying the local and global species balance for two popular chemical kinetics schemes: CDIMA (chlorine dioxide-iodine-malonic acid) and BZ (Belousov--Zhabotinsky). Based on these numerical simulations, we show that SUPG and GLS produce unphysical values for concentration of chemical species due to the violation of the non-negative constraint, contain spurious node-to-node oscillations, and have large errors in local and global species balance. Second, we proposed a novel finite element formulation to overcome the above difficulties. The proposed locally conservative non-negative computational framework based on low-order least-squares finite elements is able to preserve these underlying physical and mathematical properties
NASA Technical Reports Server (NTRS)
Lang, Steve; Tao, W.-K.; Simpson, J.; Ferrier, B.; Einaudi, Franco (Technical Monitor)
2001-01-01
Six different convective-stratiform separation techniques, including a new technique that utilizes the ratio of vertical and terminal velocities, are compared and evaluated using two-dimensional numerical simulations of a tropical [Tropical Ocean Global Atmosphere Coupled Ocean-Atmosphere Response Experiment (TOGA COARE)] and midlatitude continental [Preliminary Regional Experiment for STORM-Central (PRESTORM)] squall line. The simulations are made using two different numerical advection schemes: 4th order and positive definite advection. Comparisons are made in terms of rainfall, cloud coverage, mass fluxes, apparent heating and moistening, mean hydrometeor profiles, CFADs (Contoured Frequency with Altitude Diagrams), microphysics, and latent heating retrieval. Overall, it was found that the different separation techniques produced results that qualitatively agreed. However, the quantitative differences were significant. Observational comparisons were unable to conclusively evaluate the performance of the techniques. Latent heating retrieval was shown to be sensitive to the use of separation technique mainly due to the stratiform region for methods that found very little stratiform rain. The midlatitude PRESTORM simulation was found to be nearly invariant with respect to advection type for most quantities while for TOGA COARE fourth order advection produced numerous shallow convective cores and positive definite advection fewer cells that were both broader and deeper penetrating above the freezing level.
Estimation of the advection effects induced by surface heterogeneities in the surface energy budget
NASA Astrophysics Data System (ADS)
Cuxart, Joan; Wrenger, Burkhard; Martínez-Villagrasa, Daniel; Reuder, Joachim; Jonassen, Marius O.; Jiménez, Maria A.; Lothon, Marie; Lohou, Fabienne; Hartogensis, Oscar; Dünnermann, Jens; Conangla, Laura; Garai, Anirban
2016-07-01
The effect of terrain heterogeneities in one-point measurements is a continuous subject of discussion. Here we focus on the order of magnitude of the advection term in the equation of the evolution of temperature as generated by documented terrain heterogeneities and we estimate its importance as a term in the surface energy budget (SEB), for which the turbulent fluxes are computed using the eddy-correlation method. The heterogeneities are estimated from satellite and model fields for scales near 1 km or broader, while the smaller scales are estimated through direct measurements with remotely piloted aircraft and thermal cameras and also by high-resolution modelling. The variability of the surface temperature fields is not found to decrease clearly with increasing resolution, and consequently the advection term becomes more important as the scales become finer. The advection term provides non-significant values to the SEB at scales larger than a few kilometres. In contrast, surface heterogeneities at the metre scale yield large values of the advection, which are probably only significant in the first centimetres above the ground. The motions that seem to contribute significantly to the advection term in the SEB equation in our case are roughly those around the hectometre scales.
NASA Astrophysics Data System (ADS)
Reiter, M. A.
2004-12-01
60m to 120m, the expression representing horizontal advection is a generally preferred fit to the T log. Perhaps horizontal liquid flow through perched water zones, steps in the ground water table elevation caused by normal faulting, horizontal variations in barometric pressure effects at depth, and sub horizontal vapor flow moving around permeability barriers on its way to the surface, promote horizontal advection at the Tome and Mesa del Sol sites.
Flow visualization using moving textures
Max, N.; Becker, B.
1995-04-01
An intuitive way to visualize a flow is to watch particles or textures move in the flow. In this paper, the authors show how texture mapping hardware can produce near-real-time texture motion, using a polygon grid, and one fixed texture. However, the authors make no attempt to indicate the flow direction in a still frame. As discussed here, any anisotropic stretching comes from the velocity gradient, not the velocity itself. The basic idea is to advect the texture by the flow field. In a cited paper, they gave an indication of the wind velocity by advecting the 3D texture coordinates on the polygon vertices of a cloudiness contour surface in a climate simulation. This was slow, because the 3D texture was rendered in software, and because advecting the texture was difficult for time-varying flows. In this paper, they replace the 3D textures by 2D texture maps compatible with hardware rendering, and give techniques for handling time-varying flows more efficiently. The next section gives their technique for the case of 2D steady flows, and the following one discusses the problems of texture distortion. Then they discuss the problems with extending method to time-varying flows, and two solutions. Next they develop compositing methods for visualizing 3D flows. The final section gives their results and conclusions.
Thermophoretically Dominated Aerosol Coagulation
NASA Astrophysics Data System (ADS)
Rosner, Daniel E.; Arias-Zugasti, Manuel
2011-01-01
A theory of aerosol coagulation due to size-dependent thermophoresis is presented. This previously overlooked effect is important when local temperature gradients are large, the sol population is composed of particles of much greater thermal conductivity than the carrier gas, with mean diameters much greater than the prevailing gas mean free path, and an adequate “spread” in sizes (as in metallurgical mists or fumes). We illustrate this via a population-balance analysis of the evolution of an initially log-normal distribution when this mechanism dominates ordinary Brownian diffusion.
Advection of methane in the hydrate zone: model, analysis and examples
NASA Astrophysics Data System (ADS)
Peszynska, Malgorzata; Showalter, Ralph E.; Webster, Justin T.
2015-12-01
A two-phase two-component model is formulated for the advective-diffusive transport of methane in liquid phase through sediment with the accompanying formation and dissolution of methane hydrate. This free-boundary problem has a unique generalized solution in $L^1$; the proof combines analysis of the stationary semilinear elliptic Dirichlet problem with the nonlinear semigroup theory in Banach space for an m-accretive multi-valued operator. Additional estimates of maximum principle type are obtained, and these permit appropriate maximal extensions of the phase-change relations. An example with pure advection indicates the limitations of these estimates and of the model developed here. We also consider and analyze the coupled pressure equation that determines the advective flux in the transport model.
First-Order Hyperbolic System Method for Time-Dependent Advection-Diffusion Problems
NASA Technical Reports Server (NTRS)
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.
Warm-air advection, air mass transformation and fog causes rapid ice melt
NASA Astrophysics Data System (ADS)
Tjernström, Michael; Shupe, Matthew D.; Brooks, Ian M.; Persson, P. Ola G.; Prytherch, John; Salisbury, Dominic J.; Sedlar, Joseph; Achtert, Peggy; Brooks, Barbara J.; Johnston, Paul E.; Sotiropoulou, Georgia; Wolfe, Dan
2015-07-01
Direct observations during intense warm-air advection over the East Siberian Sea reveal a period of rapid sea-ice melt. A semistationary, high-pressure system north of the Bering Strait forced northward advection of warm, moist air from the continent. Air-mass transformation over melting sea ice formed a strong, surface-based temperature inversion in which dense fog formed. This induced a positive net longwave radiation at the surface while reducing net solar radiation only marginally; the inversion also resulted in downward turbulent heat flux. The sum of these processes enhanced the surface energy flux by an average of ~15 W m-2 for a week. Satellite images before and after the episode show sea-ice concentrations decreasing from > 90% to ~50% over a large area affected by the air-mass transformation. We argue that this rapid melt was triggered by the increased heat flux from the atmosphere due to the warm-air advection.
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
Evaporative loss from irrigated interrows in a highly advective semi-arid agricultural area
NASA Astrophysics Data System (ADS)
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
Altimetric lagrangian advection to reconstruct Pacific Ocean fine scale surface tracer fields
NASA Astrophysics Data System (ADS)
Rogé, Marine; Morrow, Rosemary; Dencausse, Guillaume
2015-04-01
In past studies, lagrangian stirring of surface tracer fields by altimetric surface geostrophic currents has been performed in different mid to high-latitude regions, showing good results in reconstructing finer-scale tracer patterns. Here we apply the technique to three different regions in the eastern and western tropical Pacific, and in the subtropical southwest Pacific. Initial conditions are derived from weekly gridded temperature and salinity fields, based on hydrographic data and Argo. Validation of the improved fine-scale surface tracer fields is performed using satellite AMSRE SST data, and high-resolution ship thermosalinograph data. We test two kinds of lagrangian advection. The standard one-way advection is shown to introduce an increased tracer bias as the advection time increases. Indeed, since we only use passive stirring, a bias is introduced from the missing physics, such as air-sea fluxes or mixing. A second "backward-forward" advection technique is shown to reduce the seasonal bias, but more data is lost around coasts and islands, a strong handicap in the tropical Pacific with many small islands. In the subtropical Pacific Ocean, the mesoscale temperature and salinity fronts are well represented by the one-way advection over a 10-day advection time, including westward propagating features not apparent in the initial fields. In the tropics, the results are less clear. The validation is hampered by the complex vertical stratification, and the technique is limited by the lack of accurate surface currents for the stirring - the gridded altimetric fields poorly represent the meridional currents, and are not detecting the fast tropical instability waves, nor the wind-driven circulation. We suggest that the passive lateral stirring technique is efficient in regions with moderate the high mesoscale energy and correlated mesoscale surface temperature and surface height. In other regions, more complex dynamical processes may need to be included.
Altimetric Lagrangian advection to reconstruct Pacific Ocean fine-scale surface tracer fields
NASA Astrophysics Data System (ADS)
Rogé, Marine; Morrow, Rosemary A.; Dencausse, Guillaume
2015-09-01
In past studies, Lagrangian stirring of surface tracer fields by altimetric surface geostrophic currents has been performed in different mid- to high-latitude regions, showing good results in reconstructing finer scale tracer patterns. Here, we explore the pertinence of the technique in the western equatorial Pacific and in the subtropical southwest Pacific. Initial conditions are derived from weekly gridded low-resolution temperature and salinity fields based on in situ hydrographic data. Validation of the reconstructed fine-scale surface tracer fields is performed using satellite AMSRE Sea Surface Temperature data and high-resolution ship thermosalinograph data. We test two kinds of Lagrangian advection. The standard one-way advection leads to an increased error as the advection time increases, due to the missing physics, such as air-sea fluxes or non-geostrophic dynamics. A second "backward-forward" advection technique is explored to reduce this bias in the tracer field, with improved results. In the subtropical southwest Pacific Ocean, the mesoscale temperature and salinity fronts are well represented by both Lagrangian advection techniques over a short 7- to 14-day advection time, including westward-propagating features not apparent in the initial fields. In the tropics, the results are less clear. The validation is hampered by the complex vertical stratification, and the lateral stirring technique is limited by the pertinence of using geostrophic surface current fields in the tropics. We suggest that the passive lateral stirring technique is efficient in regions with moderate to high mesoscale energy, where mesoscale surface tracer and surface height fields are correlated. In other regions, more complex dynamical processes may need to be included.
NASA Astrophysics Data System (ADS)
Cornaton, F.; Perrochet, P.
2006-09-01
Groundwater age and life expectancy probability density functions (pdf) have been defined, and solved in a general three-dimensional context by means of forward and backward advection-dispersion equations [Cornaton F, Perrochet P. Groundwater age, life expectancy and transit time distributions in advective-dispersive systems; 1. Generalized reservoir theory. Adv Water Res (xxxx)]. The discharge and recharge zones transit time pdfs were then derived by applying the reservoir theory (RT) to the global system, thus considering as ensemble the union of all inlet boundaries on one hand, and the union of all outlet boundaries on the other hand. The main advantages in using the RT to calculate the transit time pdf is that the outlet boundary geometry does not represent a computational limiting factor (e.g. outlets of small sizes), since the methodology is based on the integration over the entire domain of each age, or life expectancy, occurrence. In the present paper, we extend the applicability of the RT to sub-drainage basins of groundwater reservoirs by treating the reservoir flow systems as compartments which transfer the water fluxes to a particular discharge zone, and inside which mixing and dispersion processes can take place. Drainage basins are defined by the field of probability of exit at outlet. In this way, we make the RT applicable to each sub-drainage system of an aquifer of arbitrary complexity and configuration. The case of the well-head protection problem is taken as illustrative example, and sensitivity analysis of the effect of pore velocity variations on the simulated ages is carried out.
NASA Astrophysics Data System (ADS)
Ho, D. T.; Schlosser, P.; Schlosser, P.; Schlosser, P.; Caplow, T.; Garrison, M. R.
2001-12-01
In recent years, deliberate tracer release experiments have been used in the ocean, rivers, lakes, and groundwater flow systems to study advection, mixing, air-water gas exchange, and exchanges between subsystems. Here we report results from a recent deliberate tracer release experiment conducted in the tidal Hudson River. On July 25, 2001, ca. 3.3 moles of the inert gas SF6 were injected into the Hudson River near Newburgh, NY at a depth of about 6 m. Subsequently, the SF6 was monitored from a boat (Riverkeeper) by pumping water (from 2 m depth) via a submersed pump mounted on the front of the boat, through a gas extraction unit, followed by measurement using an onboard gas chromatograph. The measurement interval was about 2 minutes and the maximum speed of the boat was about 15 km h-1. This allowed us to obtain detailed surveys of the temporal evolution of the tracer plume for 14 days. Initial results from the experiment show that during July/August 2001, there was virtually no net downward advection of the water body originally tagged with SF6. Instead, we observed rapid mixing of the tracer-tagged water up- and down-river. After one week, the tracer-tagged water could be detected over a stretch of 70 km along the axis of the river channel. At this time, the stretch of river labeled with concentrations >50% of the peak value was about 14 km. After two weeks, the tracer-tagged water had extended to over 90 km, while 28 km had SF6 concentrations >50% of the peak value. Vertical mixing into depressions on the bottom of the river reaching more than 175 feet seemed to be rapid. Dispersion coefficients and vertical turbulent exchange coefficients will be discussed.
Large-eddy Advection in Evapotranspiration Estimates from an Array of Eddy Covariance Towers
NASA Astrophysics Data System (ADS)
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.
NASA Astrophysics Data System (ADS)
Vidal L., Francisco V.; Vidal L., Victor M. V.; Molero, José María Pérez
Surface and deep circulation of the central and western Gulf of Mexico is controlled by interactions of rings of water pinched from the gulf's Loop Current. The discovery was made by Mexican oceanographers who are preparing a full-color, 8-volume oceanographic atlas of the gulf.Anticyclonic warm-core rings pinch off the Loop Current at a rate of about one to two per year, the scientists of the Grupo de Estudios Oceanográficos of the Instituto de Investigaciones Eléctricas (GEO-IIE) found. The rings migrate west until they collide with the continental shelf break of the western gulf, almost always between 22° and 23°N latitude. On their westward travel they transfer angular momentum and vorticity to the surrounding water, generating cyclonic circulations and vortex pairs that completely dominate the entire surface and deep circulation of the central and western gulf.
Advection of Microphysical Scalars in Terminal Area Simulation System (TASS)
NASA Technical Reports Server (NTRS)
Ahmad, Nashat N.; Proctor, Fred H.
2011-01-01
The Terminal Area Simulation System (TASS) is a large eddy scale atmospheric flow model with extensive turbulence and microphysics packages. It has been applied successfully in the past to a diverse set of problems ranging from prediction of severe convective events (Proctor et al. 2002), tracking storms and for simulating weapons effects such as the dispersion and fallout of fission debris (Bacon and Sarma 1991), etc. More recently, TASS has been used for predicting the transport and decay of wake vortices behind aircraft (Proctor 2009). An essential part of the TASS model is its comprehensive microphysics package, which relies on the accurate computation of microphysical scalar transport. This paper describes an evaluation of the Leonard scheme implemented in the TASS model for transporting microphysical scalars. The scheme is validated against benchmark cases with exact solutions and compared with two other schemes - a Monotone Upstream-centered Scheme for Conservation Laws (MUSCL)-type scheme after van Leer and LeVeque's high-resolution wave propagation method. Finally, a comparison between the schemes is made against an incident of severe tornadic super-cell convection near Del City, Oklahoma.
Climatology of Wave-Mean Flow Interaction and Stratospheric Ozone Transport
NASA Astrophysics Data System (ADS)
Monier, E.; Weare, B. C.
2008-12-01
The troposphere-stratosphere coupling is currently drawing a lot of interest since the stratosphere was shown to have a significant impact on climate change. In this study, the Transformed Eulerian-Mean formulation and the ECMWF ERA-40 reanalysis are used to investigate the processes responsible for the wave-mean flow interaction. In addition, ozone seasonal variability is also studied in order to better understand the dynamical transport of ozone and its significance compared to the radiative-chemical effects. Results show that the dissipative forces and the advection by the residual mean meridional circulation have a significant contribution to the time rate of change of the stratospheric polar vortex. The dissipative forces has a magnitude comparable to that of the Eliassen-Palm Flux divergence or the residual mean meridional circulation and is consistent in location and magnitude with an orographic gravity wave drag forcing or the fact that the Brewer Dobson circulation is too strong in the ERA-40 reanalysis. In addition, the ozone chemical net production term is consistent with ozone production in the Tropics and ozone loss in early winter at midlatitude. The ozone transport is dominated by advection by the vertical component of the residual mean meridional circulation and by the divergence of the net eddy flux horizontal component. Overall, the Northern hemisphere is dominated by stationary processes due to the influence of orography and land-sea heating contrasts while the Southern hemisphere is marked by a combination of stationary and transient processes that have very different contributions.
General solution of a fractional diffusion-advection equation for solar cosmic-ray transport
NASA Astrophysics Data System (ADS)
Rocca, M. C.; Plastino, A. R.; Plastino, A.; Ferri, G. L.; de Paoli, A.
2016-04-01
In this effort we exactly solve the fractional diffusion-advection equation for solar cosmic-ray transport and give its general solution in terms of hypergeometric distributions. Numerical analysis of this equation shows that its solutions resemble power-laws.
NASA Astrophysics Data System (ADS)
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.
Technology Transfer Automated Retrieval System (TEKTRAN)
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...
A Study of the Physical Processes of an Advection Fog Boundary Layer
NASA Astrophysics Data System (ADS)
Liu, Duan Yang; Yan, Wen Lian; Yang, Jun; Pu, Mei Juan; Niu, Sheng Jie; Li, Zi Hua
2016-01-01
A large quantity of advection fog appeared in the Yangtze River delta region between 1 and 2 December 2009. Here, we detail the fog formation and dissipation processes and the background weather conditions. The fog boundary layer and its formation and dissipation mechanisms have also been analyzed using field data recorded in a northern suburb of Nanjing. The results showed the following: (1) This advection fog was generated by interaction between advection of a north-east cold ground layer and a south-east warm upper layer. The double-inversion structure generated by this interaction between the cold and warm advections and steady south-east vapour transport was the main cause of this long-lasting fog. The double-inversion structure provided good thermal conditions for the thick fog, and the south-east vapour transport was not only conducive to maintaining the thickness of the fog but also sustained its long duration. (2) The fog-top altitude was over 600 m for most of the time, and the fog reduced visibility to less than 100 m for approximately 12 h. (3) The low-level jet near the lower inversion layer also played a role in maintaining the thick fog system by promoting heat, momentum and south-east vapour transport.
ADVECTION, EDGE, AND OASIS EFFECTS ON SPATIAL MOISTURE AND FLUX FIELDS FROM LIDAR
Technology Transfer Automated Retrieval System (TEKTRAN)
Relatively narrow forest stands such as the riparian Tamarisk bordering the Rio Grande are subject to dry air advection from the adjacent semi-desert environment. The transport of warm dry air into the canopy has a profound effect upon the spatial properties of the moisture field and associated lat...
Lagrangian statistics and flow topology in forced 2-D turbulence
Kadoch, B.; Del-Castillo-Negrete, Diego B; Bos, W.J.T.; Schneider, Kai
2011-01-01
A study of the relationship between Lagrangian statistics and flow topology in fluid turbulence is presented. The topology is characterized using the Weiss criterion, which provides a conceptually simple tool to partition the flow into topologically different regions: elliptic (vortex dominated), hyperbolic (deformation dominated), and intermediate (turbulent background). The flow corresponds to forced two-dimensional Navier-Stokes turbulence in doubly periodic and circular bounded domains, the latter with no-slip boundary conditions. In the double periodic domain, the probability density function (pdf) of the Weiss field exhibits a negative skewness consistent with the fact that in periodic domains the flow is dominated by coherent vortex structures. On the other hand, in the circular domain, the elliptic and hyperbolic regions seem to be statistically similar. We follow a Lagrangian approach and obtain the statistics by tracking large ensembles of passively advected tracers. The pdfs of residence time in the topologically different regions are computed introducing the Lagrangian Weiss field, i.e., the Weiss field computed along the particles' trajectories. In elliptic and hyperbolic regions, the pdfs of the residence time have self-similar algebraic decaying tails. In contrast, in the intermediate regions the pdf has exponential decaying tails. The conditional pdfs (with respect to the flow topology) of the Lagrangian velocity exhibit Gaussian-like behavior in the periodic and in the bounded domains. In contrast to the freely decaying turbulence case, the conditional pdfs of the Lagrangian acceleration in forced turbulence show a comparable level of intermittency in both the periodic and the bounded domains. The conditional pdfs of the Lagrangian curvature are characterized, in all cases, by self-similar power-law behavior with a decay exponent of order - 2.
NASA Astrophysics Data System (ADS)
Kourim, Fatna; Vauchez, Alain; Bodinier, Jean-Louis; Alard, Olivier; Bendaoud, Abderrahmane
2015-05-01
In the Tahalgha district (southwestern Hoggar, Algeria), the Cenozoic volcanism has sampled subcontinental mantle beneath two crustal terranes that collided during the Pan-African orogeny: the "Polycyclic Central Hoggar" to the east and the "Western Hoggar" to the west. Two major lithospheric shear zones separate these terranes: the "4°35" and the "4°50" faults. Mantle xenoliths were collected between the two faults and across the 4°35 fault. In addition to a range in equilibrium temperatures and chemical compositions reported elsewhere, the samples show variations in their microstructures and crystallographic preferred orientations. Equilibrium temperatures and geochemical characteristics allow dividing them into low - (LT; 700-900 °C), intermediate - (IT; 900-1000 °C), and high-temperature (HT; 1000-1100 °C) xenoliths. The LT and IT peridotites occur on both sides of the 4°35 fault; they are usually coarse-grained. HT xenoliths are present only east of the 4°35 fault, in the narrow domain stuck between the two faults; they are fine-grained and extensively affected by annealing and melt-rock reactions. Microstructures and crystallographic textures indicate that deformation in the LT- and IT-xenoliths occurred through dislocation creep under relatively high-temperature, low-pressure conditions, followed by post-kinematic cooling. The fine-grained HT-xenoliths were deformed under relatively high-stress conditions before being annealed. Combining microstructural and CPO data with petrological and geochemical informations suggests that: (1) the LT xenoliths are remnants of the Neoproterozoic lithospheric mantle that preserved microstructural and chemical characteristics inherited from the Pan-African orogeny, and (2) the HT xenoliths record localized Cenozoic deformation associated with melt channeling through feed-back processes that culminated in the formation of high-permeability porous-flow conduits. Limited grain-growth in HT xenoliths suggests that
NASA Astrophysics Data System (ADS)
Benson, D. A.; Zhang, Y.
2006-12-01
Conservative solute transport through natural media is typically "anomalous" or non-Fickian. The anomalous transport may be characterized by faster than linear growth of the centered second moment, or non-Gaussian leading or trailing edges of a plume emanating from a point source. These characteristics develop because of non-local dependence on either past (time) or far upstream (space) concentrations. Non-local equations developed to describe anomalous dispersion usually focus on constant transport parameters and/or independence of the transport on space dimension. These simplifications have been useful for fitting simple transport processes, such as laboratory column tests or 1-D projections of field data. However, they may be insufficient for real field settings, where direction-dependent depositional processes and nonstationary heterogeneity can occur. We develop a generalized, multi-dimensional, spatiotemporal fractional advection- dispersion equation (fADE) with variable parameters to characterize regional-scale anomalous dispersion processes including trapping in immobile zones and/or super-Fickian rapid transport. A Lagrangian numerical model of the space-time fractional transport equation is developed in which solute particles can disperse in both space and time, depending on the medium heterogeneity properties, such as the connectivity and statistical distributions of high versus low-permeability deposits. In the generalized fADE, the range of the order of fractional time derivative is (0 2], representing a wide range of possible trapping behavior. The extension of the order to the range (1 2] is novel to transport theory. We apply the numerical model in 1-D and 2-D to the MADE site tritium plumes, and results indicate that this method can capture the main behaviors of realistic plumes, including local variations of spreading, direction-dependent scaling rates, and arbitrary rapid transport along preferential flow paths. Since the governing equation
NASA Astrophysics Data System (ADS)
Geiger, S.; Driesner, T.; Coumou, D.
2005-12-01
We compare temperature-based and enthalpy-based numerical schemes for compressible non-isothermal subsurface fluid flow. We formulate a diffusion equation for the fluid pressure, a diffusion equation for heat conduction, and an equation for the advective transport of temperature or enthalpy in the fluid. These equations can readily be solved by a combination of finite element and higher-order finite volume methods, which are capable of preserving steep temperature gradients in advection dominated flows and handling complex two- and three-dimensional geologic structures with orders of magnitude variation in permeability. Since the time-scale of pressure diffusion is slower than the time-scale for advective fluid flow, it is possible to decouple the equations and use implicit finite element methods for the parabolic (diffusion) equations and explicit finite volume methods for the hyperbolic (advection) equations. For single-phase flow, we use the thermal wave speed to compute the advection of the temperature field on the finite volumes. Since the thermal front is advected at a slower rate than the actual fluid flow, a significant (i.e., a factor 10 at liquid and a factor 1000 at vapor conditions) computational speedup can be achieved in comparison to the formulation where enthalpy is advected. The results for temperature-based and enthalpy-based formulations at vapor or liquid conditions, however, are identical and compare extremely well with results obtained from other codes that use fully coupled solution techniques. Our results do not improve if we use Picard iteration to couple the pressure, conduction, and advection equations. For the enthalpy-based transport schemes, we use a Newton iteration to equilibrate the energy in the fluid and rock. This also allows us to use more modern equation of states for complex multi-component systems, that are formulated in terms of pressure p, temperature T, and composition X, and hence cannot use the specific enthalpy h to
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...
Technology Transfer Automated Retrieval System (TEKTRAN)
This paper presents a formal exact solution of the linear advection-diffusion transport equation with constant coefficients for both transient and steady-state regimes. A classical mathematical substitution transforms the original advection-diffusion equation into an exclusively diffusive equation. ...
Technology Transfer Automated Retrieval System (TEKTRAN)
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...
Effects of High-energy Particles on Accretion Flows onto a Supermassive Black Hole
NASA Astrophysics Data System (ADS)
Kimura, Shigeo S.; Toma, Kenji; Takahara, Fumio
2014-08-01
We study the effects of high-energy particles (HEPs) on the accretion flows onto a supermassive black hole and luminosities of escaping particles such as protons, neutrons, gamma rays, and neutrinos. We formulate a one-dimensional model of the two-component accretion flow consisting of thermal particles and HEPs, supposing that some fraction of the released energy is converted to the acceleration of HEPs. The thermal component is governed by fluid dynamics while the HEPs obey the moment equations of the diffusion-convection equation. By solving the time evolution of these equations, we obtain advection-dominated flows as the steady state solutions. The effects of the HEPs on the flow structures turn out to be small even if the pressure of the HEPs dominates over the thermal pressure. For a model in which the escaping protons take away almost all the energy released, the HEPs have a large enough influence to make the flow have a Keplerian angular velocity at the inner region. We calculate the luminosities of the escaping particles for these steady solutions. The escaping particles can extract the energy from about 10^{-4}\\dot{M} c^2 to 10^{-2}\\dot{M} c^2, where \\dot{M} is the mass accretion rate. The luminosities of the escaping particles depend on parameters such as the injection Lorentz factors, the mass accretion rates, and the diffusion coefficients. We also discuss some implications on the relativistic jet production by the escaping particles.
Debris-flow observations in the Zermatt Valley
NASA Astrophysics Data System (ADS)
Graf, Christoph
2015-04-01
related slide and fall processes, increasingly large amounts of loose sediment are delivered into debris-flow systems. Extensive till, scree slopes and rock glaciers represent the principal and extensive sediment sources for debris flows which are commonly triggered at elevations between 2000 and 3000 m asl. Here, high annual and daily thermal ranges favour frost weathering and regolith production delivered to scree slopes. Slope angles in the initiation zones range from 27 to 41° and are dominated by permafrost in all of the catchments. Debris flows are triggered either through the wetting of material continuously delivered by the permafrost body to the channel or due to release at the rock glacier fronts during exceptional water input. The wetting typically occurs during rainstorms, but debris flows at these sites also happen when sediment shear resistance is reduced by the melting of ice particles, by snow melting and/or a combination of both. In the Dorfbach torrent near Randa, WSL operates an automated debris-flow observation station, measuring the typical parameters such as flow heights and velocities since several years. As part of an interdisciplinary project on data acquisition and numerical modelling of debris flows for hazard mapping, we monitor several other debris-flow prone torrents in the valley and combine these data with observations of ongoing processes in the headwater of the catchments. Several debris-flow events in some of the torrents could be observed and measured in the last years. Total volume, discharge per surge, frontal speed, run out length and impact on the inhabited fans varied considerably. Typically one first event cluster is dominated by snow melting controlled conditions starting late May until end of June and a second cluster are the rainstorm dominated events in midsummer. The largest events are expected in late summer or in fall, when long-lasting advective precipitation events over several days prevail.
Modeling Arteriolar Flow and Mass Transport Using the Immersed Boundary Method
NASA Astrophysics Data System (ADS)
Arthurs, Kayne M.; Moore, Leon C.; Peskin, Charles S.; Pitman, E. Bruce; Layton, H. E.
1998-12-01
Flow in arterioles is determined by a number of interacting factors, including perfusion pressure, neural stimulation, vasoactive substances, the intrinsic contractility of arteriolar walls, and wall shear stress. We have developed a two-dimensional model of arteriolar fluid flow and mass transport. The model includes a phenomenological representation of the myogenic response of the arteriolar wall, in which an increase in perfusion pressure stimulates vasoconstriction. The model also includes the release, advection, diffusion, degradation, and dilatory action of nitric oxide (NO), a potent, but short-lived, vasodilatory agent. Parameters for the model were taken primarily from the experimental literature of the rat renal afferent arteriole. Solutions to the incompressible Navier-Stokes equations were approximated by means of a splitting that used upwind differencing for the inertial term and a spectral method for the viscous term and incompressibility condition. The immersed boundary method was used to include the forces arising from the arteriolar walls. The advection of NO was computed by means of a high-order flux-corrected transport scheme; the diffusion of NO was computed by a spectral solver. Simulations demonstrated the efficacy of the numerical methods employed, and grid refinement studies confirmed anticipated first-order temporal convergence and demonstrated second-order spatial convergence in key quantities. By providing information about the effective width of the immersed boundary and sheer stress magnitude near that boundary, the grid refinement studies indicate the degree of spatial refinement required for quantitatively reliable simulations. Owing to the dominating effect of NO advection, relative to degradation and diffusion, simulations indicate that NO has the capacity to produce dilation along the entire length of the arteriole.
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.
Flow and transport in single fracture with roughness.
NASA Astrophysics Data System (ADS)
Olkiewicz, Piotr; Dabrowski, Marcin
2016-04-01
Fracture flow may dominate in rocks with low porosity and it can accompany both industrial and natural processes. Typical examples of such processes are natural flows in crystalline rocks and industrial flows in geothermal systems or hydraulic fracturing. Fracture flow provides an important mechanism for transporting mass and energy. For example, geothermal energy is primarily transported by the flow of the heated water or steam rather than by the thermal diffusion. The geometry of the fracture network and the distribution of the mean apertures of individual fractures are the key parameters with regard to the fracture network transmissivity. Transport in fractures can occur through the combination of advection and diffusion processes like in the case of dissolved chemical components. The local distribution of the fracture aperture may play an important role for both flow and transport processes. In this work, we compare numerical solution for flow and transport processes in a single fracture in 2D and 3D. Fracture aperture distributions are generated by random correlated field method. We examine a single-phase flow of an incompressible viscous Newtonian fluid in the low Reynolds number limit. The velocity field is found using the Stokes equations with periodic boundary condition and a gravity force is imposed in the background. We systematically compare the obtained velocity field to the results obtained by solving the Reynolds equation, where pressure difference is imposed in the background. This allows us to examine the impact of the aperture distribution on the permeability of the medium and the local velocity distribution for two different mathematical descriptions of the fracture flow. Furthermore, we analyse the impact of aperture distribution on the front characteristics.
Particulate export vs lateral advection in the Antarctic Polar Front (Southern Pacific Ocean)
NASA Astrophysics Data System (ADS)
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
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
Mixing layers and coherent structures in vegetated aquatic flows
NASA Astrophysics Data System (ADS)
Ghisalberti, Marco; Nepf, Heidi M.
2002-02-01
To date, flow through submerged aquatic vegetation has largely been viewed as perturbed boundary layer flow, with vegetative drag treated as an extension of bed drag. However, recent studies of terrestrial canopies demonstrate that the flow structure within and just above an unconfined canopy more strongly resembles a mixing layer than a boundary layer. This paper presents laboratory measurements, obtained from a scaled seagrass model, that demonstrate the applicability of the mixing layer analogy to aquatic systems. Specifically, all vertical profiles of mean velocity contained an inflection point, which makes the flow susceptible to Kelvin-Helmholtz instability. This instability leads to the generation of large, coherent vortices within the mixing layer (observed in the model at frequencies between 0.01 and 0.11 Hz), which dominate the vertical transport of momentum through the layer. The downstream advection of these vortices is shown to cause the progressive, coherent waving of aquatic vegetation, known as the monami. When the monami is present, the turbulent vertical transport of momentum is enhanced, with turbulent stresses penetrating an additional 30% of the plant height into the canopy.
A balancing domain decomposition method by constraints for advection-diffusion problems
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.
Advective-diffusive motion on large scales from small-scale dynamics with an internal symmetry
NASA Astrophysics Data System (ADS)
Marino, Raffaele; Aurell, Erik
2016-06-01
We consider coupled diffusions in n -dimensional space and on a compact manifold and the resulting effective advective-diffusive motion on large scales in space. The effective drift (advection) and effective diffusion are determined as a solvability conditions in a multiscale analysis. As an example, we consider coupled diffusions in three-dimensional space and on the group manifold SO(3) of proper rotations, generalizing results obtained by H. Brenner [J. Colloid Interface Sci. 80, 548 (1981), 10.1016/0021-9797(81)90214-9]. We show in detail how the analysis can be conveniently carried out using local charts and invariance arguments. As a further example, we consider coupled diffusions in two-dimensional complex space and on the group manifold SU(2). We show that although the local operators may be the same as for SO(3), due to the global nature of the solvability conditions the resulting diffusion will differ and generally be more isotropic.
NASA Astrophysics Data System (ADS)
Yochelis, Arik; Bar-On, Tomer; Gov, Nir S.
2016-04-01
Unconventional myosins belong to a class of molecular motors that walk processively inside cellular protrusions towards the tips, on top of actin filament. Surprisingly, in addition, they also form retrograde moving self-organized aggregates. The qualitative properties of these aggregates are recapitulated by a mass conserving reaction-diffusion-advection model and admit two distinct families of modes: traveling waves and pulse trains. Unlike the traveling waves that are generated by a linear instability, pulses are nonlinear structures that propagate on top of linearly stable uniform backgrounds. Asymptotic analysis of isolated pulses via a simplified reaction-diffusion-advection variant on large periodic domains, allows to draw qualitative trends for pulse properties, such as the amplitude, width, and propagation speed. The results agree well with numerical integrations and are related to available empirical observations.
NASA Technical Reports Server (NTRS)
Shia, Run-Lie; Ha, Yuk Lung; Wen, Jun-Shan; Yung, Yuk L.
1990-01-01
Extensive testing of the advective scheme proposed by Prather (1986) has been carried out in support of the California Institute of Technology-Jet Propulsion Laboratory two-dimensional model of the middle atmosphere. The original scheme is generalized to include higher-order moments. In addition, it is shown how well the scheme works in the presence of chemistry as well as eddy diffusion. Six types of numerical experiments including simple clock motion and pure advection in two dimensions have been investigated in detail. By comparison with analytic solutions, it is shown that the new algorithm can faithfully preserve concentration profiles, has essentially no numerical diffusion, and is superior to a typical fourth-order finite difference scheme.
A study of turbulent transport of an advective nature in a fluid plasma
NASA Astrophysics Data System (ADS)
Min, Byunghoon; An, Chan-Yong; Kim, Chang-Bae
2014-08-01
The advective nature of the electrostatic turbulent flux of plasma energy in Fourier space is studied numerically in a nearly adiabatic state. Such a state is represented by the Hasegawa-Mima equation, which is driven by a noise that may model the destabilization due to the phase mismatch of the plasma density and the electric potential. The noise is assumed to be Gaussian and not to be invariant under reflection along a direction ŝ. The flux density induced by such noise is found to be anisotropic: While it is random along ŝ, it is not along the perpendicular direction ŝ ⊥, and the flux is not diffusive. The renormalized response may be approximated as advective, with the velocity being proportional to ( kρ s )2, in the Fourier space.
DPDC (double-pass donor cell): A second-order monotone scheme for advection
Beason, C W; Margolin, L G
1988-09-26
We are developing a new, second-order, monotone scheme for advection. DPDC (i.e., double-pass donor cell) is based on Smolarkiewicz' simple, positive definite method. Both schemes are multipass methods in which upstream approximations to the truncation error are subtracted from the equations. We describe two significant improvements to Smolarkiewicz' method. First, we use a local gauge transformation to convert the method from being positive definite to the stronger condition of being monotone. Second, we analytically approximate the sum of the corrections of all the passes to use in a single corrective pass. This increases the accuracy of the method, but does not increase the order of accuracy. We compare DPDC with van Leer's method for advection of several different pulses in a constant velocity field. 5 refs., 4 figs.
Multi-moment advection scheme in three dimension for Vlasov simulations of magnetized plasma
Minoshima, Takashi; Matsumoto, Yosuke; Amano, Takanobu
2013-03-01
We present an extension of the multi-moment advection scheme [T. Minoshima, Y. Matsumoto, T. Amano, Multi-moment advection scheme for Vlasov simulations, Journal of Computational Physics 230 (2011) 6800–6823] to the three-dimensional case, for full electromagnetic Vlasov simulations of magnetized plasma. The scheme treats not only point values of a profile but also its zeroth to second order piecewise moments as dependent variables, and advances them on the basis of their governing equations. Similar to the two-dimensional scheme, the three-dimensional scheme can accurately solve the solid body rotation problem of a gaussian profile with little numerical dispersion or diffusion. This is a very important property for Vlasov simulations of magnetized plasma. We apply the scheme to electromagnetic Vlasov simulations. Propagation of linear waves and nonlinear evolution of the electron temperature anisotropy instability are successfully simulated with a good accuracy of the energy conservation.
NASA Astrophysics Data System (ADS)
Huber, Markus; Tailleux, Remi; Ferreira, David; Kuhlbrodt, Till; Gregory, Jonathan
2015-04-01
The classic vertical advection-diffusion (VAD) balance is a central concept in studying the ocean heat budget, in particular in simple climate models (SCMs). Here we present a new framework to calibrate the parameters of the VAD equation to the vertical ocean heat balance of two fully-coupled climate models that is traceable to the models' circulation as well as to vertical mixing and diffusion processes. Based on temperature diagnostics, we derive an effective vertical velocity w∗ and turbulent diffusivity kν∗ for each individual physical process. In steady state, we find that the residual vertical velocity and diffusivity change sign in middepth, highlighting the different regional contributions of isopycnal and diapycnal diffusion in balancing the models' residual advection and vertical mixing. We quantify the impacts of the time evolution of the effective quantities under a transient 1% CO2 simulation and make the link to the parameters of currently employed SCMs.
Numerical advection algorithms and their role in atmospheric transport and chemistry models
NASA Technical Reports Server (NTRS)
Rood, Richard B.
1987-01-01
During the last 35 years, well over 100 algorithms for modeling advection processes have been described and tested. This review summarizes the development and improvements that have taken place. The nature of the errors caused by numerical approximation to the advection equation are highlighted. Then the particular devices that have been proposed to remedy these errors are discussed. The extensive literature comparing transport algorithms is reviewed. Although there is no clear cut 'best' algorithm, several conclusions can be made. Spectral and pseudospectral techniques consistently provide the highest degree of accuracy, but expense and difficulties assuring positive mixing ratios are serious drawbacks. Schemes which consider fluid slabs bounded by grid points (volume schemes), rather than the simple specification of constituent values at the grid points, provide accurate positive definite results.
NASA Technical Reports Server (NTRS)
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.
NASA Technical Reports Server (NTRS)
Mcfarland, M. J.
1975-01-01
Temperature and moisture advection patterns of dry air intrusion were analyzed by a variational optimization method to relate mesoscale advection to a severe thunderstorm environment. The analysis results presented here were obtained from a case study, May 26, 1973, when a tornado squall line developed in Oklahoma in conjunction with a clearly delineated dry air intrusion. Observations from the synoptic upper air network were used for inputs of horizontal wind components, potential temperature, and mixing ratio at each 50 mb increment from 950 to 100 mb. An objective analysis was performed to assign values of the variables to grid points of a 15 x 14 horizontal grid with approximate 125 km grid spacing at each pressure level. After the analysis the data fields were smoothed using a variational formalism.
Differences between tangential geostrophy and columnar flow
NASA Astrophysics Data System (ADS)
Amit, Hagay; Pais, Maria Alexandra
2013-07-01
Core flows inverted from time-dependent geomagnetic field models image the geodynamo at the top of its generation region, the Earth's outer core. Physical assumptions incorporated in these inversions affect the resulting flows. Based on rapid rotation dominance, two assumptions similar in form yet different in essence have been proposed: tangential geostrophy (TG, LeMouël 1984) and columnar flow (CF, Amit & Olson 2004). We recall that CF is theoretically consistent with the quasi-geostrophy (QG) theory for an incompressible fluid with spherical solid boundaries whereas TG is not. As such, we highlight the importance of applying the CF assumption when inverting geomagnetic data for interior core (columnar) flows that can be used in kinematic dynamo and thermal convection models in the Boussinesq approximation. Next we evaluate the non-uniqueness associated with CF flows. The areas of ambiguous patches at the core surface where invisible TG or CF flows reside are roughly comparable. The spatial distribution of ambiguous patches for both TG and CF is quite asymmetric about the equator, so assuming equatorial symmetry is expected to reduce the non-uniqueness significantly. In fact, for assumed equatorial symmetry, the only possible non-unique flows will be those along hypothetical ζ-contours in the opposite hemispheres that their equatorial plane projections are parallel. TG flows exhibit a strong Atlantic/Pacific hemispheric dichotomy and a well-defined eccentric gyre whereas in CF flows the dichotomy between these two hemispheres is weaker and the gyre is less clear suggesting that the eccentric gyre might not conserve mass. Both TG and CF upwelling/downwelling patterns are strongly localized in the equatorial region. In addition, in both cases upwelling/downwelling is correlated with equatorward/poleward flow respectively, as expected for QG convection. CF upwelling is more intense than TG upwelling but the magnitude ratio is smaller than the factor 2
Scyphozoa in the Bornholm Basin (central Baltic Sea) The role of advection
NASA Astrophysics Data System (ADS)
Barz, Kristina; Hinrichsen, Hans-Harald; Hirche, Hans-Jürgen
2006-04-01
The usual absence of ephyrae and late appearance of medusae of the Scyphozoa Aurelia aurita and Cyanea capillata in the Bornholm Basin (BB; central Baltic Sea) indicate that these species are not strobilating in the region and their presence depends on advection. To study their potential origin we compared drift from historically known strobilation areas derived from a circulation model with spatial distributions observed during 19 cruises in the BB during 2002 and 2003. The model results are in good accordance with the field observations. According to the model results inter-annual differences in the timing of first appearance and life stage at appearance of A. aurita were clearly related to differences in the hydrodynamic regime during the investigation periods. During the stagnation regime in 2002 young medusae occurred first in June in the BB. In contrast, in 2003 fast transport due to several inflow events advected ephyrae released between January and March in the western Baltic already in April to the BB. Although the Gullmar Fjord (western Sweden) is the nearest known strobilation area for C. capillata, the model did not support advection from there in numbers explaining the occurrence of this species in the BB in 2002 and 2003. If the model works adequately in this regions we have to assume that the Gullmar Fjord is not a main source region of C. capillata in the BB, but other strobilation areas in the Kattegat or the North Sea appear more important. Our results imply that advection and inflow events are critical for the occurrence and distribution of early stages of jellyfish in the central Baltic Sea. They demonstrate the potential of circulation models as tools to study the effect of long-range transport on the spatial composition of these organisms.
İbiş, Birol
2014-01-01
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. PMID:24578662
Carbon dioxide seasonality in dynamically ventilated caves: the role of advective fluxes
NASA Astrophysics Data System (ADS)
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.
Ibiş, Birol; Bayram, Mustafa
2014-01-01
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. PMID:24578662
A Lagrangian-Eulerian finite element method with adaptive gridding for advection-dispersion problems
Ijiri, Y.; Karasaki, K.
1994-02-01
In the present paper, a Lagrangian-Eulerian finite element method with adaptive gridding for solving advection-dispersion equations is described. The code creates new grid points in the vicinity of sharp fronts at every time step in order to reduce numerical dispersion. The code yields quite accurate solutions for a wide range of mesh Peclet numbers and for mesh Courant numbers well in excess of 1.
Oldenburg, Curtis; Moridis, George
1998-03-24
We have developed EOS7M, a ferrofluid flow and transport module for TOUGH2. EOS7M calculates the magnetic forces on ferrofluid caused by an external magnetic field and allows simulation of flow and advective transport of ferrofluid-water mixtures through porous media. Such flow problems are strongly coupled and well suited to the TOUGH2 framework. Preliminary applications of EOS7M to some simple pressure and flow problems for which experiments were carried out in the lab show good qualitative agreement with the laboratory results.
NASA Astrophysics Data System (ADS)
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.
NASA Astrophysics Data System (ADS)
Backeberg, B. C.; Bertino, L.; Johannessen, J. A.
2009-06-01
A 4th order advection scheme is applied in a nested eddy-resolving Hybrid Coordinate Ocean Model (HYCOM) of the greater Agulhas Current system for the purpose of testing advanced numerics as a means for improving the model simulation for eventual operational implementation. Model validation techniques comparing sea surface height variations, sea level skewness and variogram analyses to satellite altimetry measurements quantify that generally the 4th order advection scheme improves the realism of the model simulation. The most striking improvement over the standard 2nd order momentum advection scheme, is that the southern Agulhas Current is simulated as a well-defined meandering current, rather than a train of successive eddies. A better vertical structure and stronger poleward transports in the Agulhas Current core contribute toward a better southwestward penetration of the current, and its temperature field, implying a stronger Indo-Atlantic inter-ocean exchange. It is found that the transport, and hence this exchange, is sensitive to the occurrences of mesoscale features originating upstream in the Mozambique Channel and southern East Madagascar Current, and that the improved HYCOM simulation is well suited for further studies of these inter-actions.
NASA Astrophysics Data System (ADS)
Backeberg, B. C.; Bertino, L.; Johannessen, J. A.
2009-02-01
A 4th order advection scheme is applied in a nested eddy-resolving Hybrid Coordinate Ocean Model (HYCOM) of the greater Agulhas Current system for the purpose of testing advanced numerics as a means for improving the model simulation for eventual operational implementation. Model validation techniques comparing sea surface height variations, sea level skewness and variogram analyses to satellite altimetry measurements quantify that generally the 4th order advection scheme improves the realism of the model simulation. The most striking improvement over the standard 2nd order momentum advection scheme, is that the Southern Agulhas Current is simulated as a well-defined meandering current, rather than a train of successive eddies. A better vertical structure and stronger poleward transports in the Agulhas Current core contribute toward a better southwestward penetration of the current, and its temperature field, implying a stronger Indo-Atlantic inter-ocean exchange. It is found that the transport, and hence this exchange, is sensitive to the occurrences of mesoscale features originating upstream in the Mozambique Channel and Southern East Madagascar Current, and that the improved HYCOM simulation is well suited for further studies of these inter-actions.
Advective pore water input of nutrients to the Satilla River Estuary, Georgia, USA
NASA Astrophysics Data System (ADS)
Jahnke, R. A.; Alexander, C. R.; Kostka, J. E.
2003-03-01
In situ benthic flux measurements, pore water nutrient profiles, water column nutrient distributions, sediment grain size distributions and side-scan sonar observations suggest that advective transport of pore waters may be a major input pathway of nutrients into the Satilla River Estuary (coastal Georgia, USA). In situ benthic chamber incubations demonstrate the occurrence of highly variable, but occasionally very large sea floor fluxes of silicate, phosphate, and ammonium. Locally occurring benthic microbial mineralization of organic matter, as estimated by S 35-sulphate reduction rate measurements, is insufficient to support these large fluxes. We hypothesize that the observed interlayering of permeable, sandy sediments with fine-grained, organic-rich sediments in the estuary provides conduits for advective transport of pore water constituents out of the sediments. Because permeable layers may extend significant distances beneath the salt marsh, the large fluxes observed may be supported by remineralization occurring over large areas adjacent to the estuary. Advective transport may be induced by pressure gradients generated by a variety of processes, including landward recharge by meteoric or rain waters if sand layers extend far enough into the maritime coastal lands. Alternatively, tidal variations across the salt marsh sediment surface may hydraulically pump water through the sediment system. Because these fluxes appear to be concentrated into small layers, this source may be a significant input of nutrients to the estuary even if permeable, sandy layers comprise a very small proportion of the seabed.
A deterministic Lagrangian particle separation-based method for advective-diffusion problems
NASA Astrophysics Data System (ADS)
Wong, Ken T. M.; Lee, Joseph H. W.; Choi, K. W.
2008-12-01
A simple and robust Lagrangian particle scheme is proposed to solve the advective-diffusion transport problem. The scheme is based on relative diffusion concepts and simulates diffusion by regulating particle separation. This new approach generates a deterministic result and requires far less number of particles than the random walk method. For the advection process, particles are simply moved according to their velocity. The general scheme is mass conservative and is free from numerical diffusion. It can be applied to a wide variety of advective-diffusion problems, but is particularly suited for ecological and water quality modelling when definition of particle attributes (e.g., cell status for modelling algal blooms or red tides) is a necessity. The basic derivation, numerical stability and practical implementation of the NEighborhood Separation Technique (NEST) are presented. The accuracy of the method is demonstrated through a series of test cases which embrace realistic features of coastal environmental transport problems. Two field application examples on the tidal flushing of a fish farm and the dynamics of vertically migrating marine algae are also presented.
The effects of advection solvers on the performance of air quality models
Tanrikulu, S.; Odman, M.T.
1996-12-31
The available numerical solvers for the advection term in the chemical species conservation equation have different properties, and consequently introduce different types of errors. These errors can affect the performance of air quality models and lead to biases in model results. In this study, a large number of advection solvers have been studied and six of them were identified as having potential for use in photochemical models. The identified solvers were evaluated extensively using various numerical tests that are relevant to air quality simulations. Among the solvers evaluated, three of them showed better performance in terms of accuracy and some other characteristics such as conservation of mass and positivity. They are the solvers by Bott, Yuamartino, and Dabdub and Seinfeld. These three solvers were incorporated into the SARMAP Air Quality Model (SAQM) and the August 3-6, 1990 ozone episode in the San Joaquin Valley of California was simulated with each. A model performance analysis was conducted for each simulation using the rich air quality database of the 1990 San Joaquin Valley Air Quality Study. The results of the simulations were compared with each other and the effects of advection solvers on the performance of the model are discussed.
Dissecting diffusive and advective motion in colloidal sedimentation by multi-