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.
Numerical advection algorithms and their role in atmospheric transport and chemistry models
NASA Astrophysics Data System (ADS)
Rood, Richard B.
1987-02-01
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)
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.
Shia, R L; Ha, Y L; Wen, J S; Yung, Y L
1990-05-20
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. We generalize the original scheme to include higher-order moments. In addition, we show 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.
High-resolution two dimensional advective transport
Smith, P.E.; Larock, B.E.
1989-01-01
The paper describes a two-dimensional high-resolution scheme for advective transport that is based on a Eulerian-Lagrangian method with a flux limiter. The scheme is applied to the problem of pure-advection of a rotated Gaussian hill and shown to preserve the monotonicity property of the governing conservation law.
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.
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
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...
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).
An operator splitting algorithm for the three-dimensional advection-diffusion equation
NASA Astrophysics Data System (ADS)
Khan, Liaqat Ali; Liu, Philip L.-F.
1998-09-01
Operator splitting algorithms are frequently used for solving the advection-diffusion equation, especially to deal with advection dominated transport problems. In this paper an operator splitting algorithm for the three-dimensional advection-diffusion equation is presented. The algorithm represents a second-order-accurate adaptation of the Holly and Preissmann scheme for three-dimensional problems. The governing equation is split into an advection equation and a diffusion equation, and they are solved by a backward method of characteristics and a finite element method, respectively. The Hermite interpolation function is used for interpolation of concentration in the advection step. The spatial gradients of concentration in the Hermite interpolation are obtained by solving equations for concentration gradients in the advection step. To make the composite algorithm efficient, only three equations for first-order concentration derivatives are solved in the diffusion step of computation. The higher-order spatial concentration gradients, necessary to advance the solution in a computational cycle, are obtained by numerical differentiations based on the available information. The simulation characteristics and accuracy of the proposed algorithm are demonstrated by several advection dominated transport problems.
Coupling of active motion and advection shapes intracellular cargo transport.
Khuc Trong, Philipp; Guck, Jochen; Goldstein, Raymond E
2012-07-13
Intracellular cargo transport can arise from passive diffusion, active motor-driven transport along cytoskeletal filament networks, and passive advection by fluid flows entrained by such cargo-motor motion. Active and advective transport are thus intrinsically coupled as related, yet different representations of the same underlying network structure. A reaction-advection-diffusion system is used here to show that this coupling affects the transport and localization of a passive tracer in a confined geometry. For sufficiently low diffusion, cargo localization to a target zone is optimized either by low reaction kinetics and decoupling of bound and unbound states, or by a mostly disordered cytoskeletal network with only weak directional bias. These generic results may help to rationalize subtle features of cytoskeletal networks, for example as observed for microtubules in fly oocytes.
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.
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.
Anomalous transport and chaotic advection in homogeneous porous media.
Lester, D R; Metcalfe, G; Trefry, M G
2014-12-01
The topological complexity inherent to all porous media imparts persistent chaotic advection under steady flow conditions, which, in concert with the no-slip boundary condition, generates anomalous transport. We explore the impact of this mechanism upon longitudinal dispersion via a model random porous network and develop a continuous-time random walk that predicts both preasymptotic and asymptotic transport. In the absence of diffusion, the ergodicity of chaotic fluid orbits acts to suppress longitudinal dispersion from ballistic to superdiffusive transport, with asymptotic variance scaling as σ(L)(2)(t)∼t(2)/(ln t)(3). These results demonstrate that anomalous transport is inherent to homogeneous porous media and has significant implications for macrodispersion.
Anomalous transport and chaotic advection in homogeneous porous media.
Lester, D R; Metcalfe, G; Trefry, M G
2014-12-01
The topological complexity inherent to all porous media imparts persistent chaotic advection under steady flow conditions, which, in concert with the no-slip boundary condition, generates anomalous transport. We explore the impact of this mechanism upon longitudinal dispersion via a model random porous network and develop a continuous-time random walk that predicts both preasymptotic and asymptotic transport. In the absence of diffusion, the ergodicity of chaotic fluid orbits acts to suppress longitudinal dispersion from ballistic to superdiffusive transport, with asymptotic variance scaling as σ(L)(2)(t)∼t(2)/(ln t)(3). These results demonstrate that anomalous transport is inherent to homogeneous porous media and has significant implications for macrodispersion. PMID:25615192
Technology Transfer Automated Retrieval System (TEKTRAN)
Mathematical models describing contaminant transport in heterogeneous porous media are often formulated as an advection-dispersion transport equation with distance-dependent transport coefficients. In this work, a general analytical solution is presented for the linear, one-dimensional advection-di...
Advective transport in heterogeneous aquifers: Are proxy models predictive?
NASA Astrophysics Data System (ADS)
Fiori, A.; Zarlenga, A.; Gotovac, H.; Jankovic, I.; Volpi, E.; Cvetkovic, V.; Dagan, G.
2015-12-01
We examine the prediction capability of two approximate models (Multi-Rate Mass Transfer (MRMT) and Continuous Time Random Walk (CTRW)) of non-Fickian transport, by comparison with accurate 2-D and 3-D numerical simulations. Both nonlocal in time approaches circumvent the need to solve the flow and transport equations by using proxy models to advection, providing the breakthrough curves (BTC) at control planes at any x, depending on a vector of five unknown parameters. Although underlain by different mechanisms, the two models have an identical structure in the Laplace Transform domain and have the Markovian property of independent transitions. We show that also the numerical BTCs enjoy the Markovian property. Following the procedure recommended in the literature, along a practitioner perspective, we first calibrate the parameters values by a best fit with the numerical BTC at a control plane at x1, close to the injection plane, and subsequently use it for prediction at further control planes for a few values of σY2≤8. Due to a similar structure and Markovian property, the two methods perform equally well in matching the numerical BTC. The identified parameters are generally not unique, making their identification somewhat arbitrary. The inverse Gaussian model and the recently developed Multi-Indicator Model (MIM), which does not require any fitting as it relates the BTC to the permeability structure, are also discussed. The application of the proxy models for prediction requires carrying out transport field tests of large plumes for a long duration.
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...
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.
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.
Modifying SEBAL ET Algorithm to account for advection by using daily averages of weather data
NASA Astrophysics Data System (ADS)
Mkhwanazi, M. M.; Chavez, J. L.
2013-12-01
The use of Remote Sensing (RS) in crop evapotranspiration (ET) estimation is aimed at improving agricultural water management. The Surface Energy Balance Algorithm for Land (SEBAL) is one of several methods that have been developed for this purpose. This has been a preferred model as it requires minimal climate data. However, it has a noted downside of underestimating ET under advective conditions. This is primarily due to the use of evaporative fraction (EF) to extrapolate instantaneous ET to daily values, with the assumption that EF is constant throughout the day. A modified SEBAL model was used in this study, which requires daily averages of weather data to estimate advection which is then introduced into the 24-hour ET sub-model of SEBAL. The study was carried out in southeastern Colorado, a semi-arid area where afternoon advection is a common feature. ET estimated using the original and modified SEBAL was compared to the lysimeter-measured ET. Results showed that the modified SEBAL algorithm performed better in estimating daily ET in overall, but especially on days when there was advection. On non-advective days, the original SEBAL was more accurate. It is therefore recommended that the modified SEBAL be used only on advective days, and guidelines to help identify such days were proposed.
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...
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...
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 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.
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.
Analytical Advection-Dispersion Model for Transport and Plant Uptake of Solutes in the Root Zone
Technology Transfer Automated Retrieval System (TEKTRAN)
We develop an advective-dispersive solute transport equation that includes plant uptake of water and solute, and present an analytical solution. Assumptions underlying the transport model include linear solute sorption, first-order plant uptake, and a uniform soil water content. We examine the lat...
Two-Dimensional Advective Transport in Ground-Water Flow Parameter Estimation
Anderman, E.R.; Hill, M.C.; Poeter, E.P.
1996-01-01
Nonlinear regression is useful in ground-water flow parameter estimation, but problems of parameter insensitivity and correlation often exist given commonly available hydraulic-head and head-dependent flow (for example, stream and lake gain or loss) observations. To address this problem, advective-transport observations are added to the ground-water flow, parameter-estimation model MODFLOWP using particle-tracking methods. The resulting model is used to investigate the importance of advective-transport observations relative to head-dependent flow observations when either or both are used in conjunction with hydraulic-head observations in a simulation of the sewage-discharge plume at Otis Air Force Base, Cape Cod, Massachusetts, USA. The analysis procedure for evaluating the probable effect of new observations on the regression results consists of two steps: (1) parameter sensitivities and correlations calculated at initial parameter values are used to assess the model parameterization and expected relative contributions of different types of observations to the regression; and (2) optimal parameter values are estimated by nonlinear regression and evaluated. In the Cape Cod parameter-estimation model, advective-transport observations did not significantly increase the overall parameter sensitivity; however: (1) inclusion of advective-transport observations decreased parameter correlation enough for more unique parameter values to be estimated by the regression; (2) realistic uncertainties in advective-transport observations had a small effect on parameter estimates relative to the precision with which the parameters were estimated; and (3) the regression results and sensitivity analysis provided insight into the dynamics of the ground-water flow system, especially the importance of accurate boundary conditions. In this work, advective-transport observations improved the calibration of the model and the estimation of ground-water flow parameters, and use of
Scaling of geochemical reaction rates via advective solute transport.
Hunt, A G; Ghanbarian, B; Skinner, T E; Ewing, R P
2015-07-01
Transport in porous media is quite complex, and still yields occasional surprises. In geological porous media, the rate at which chemical reactions (e.g., weathering and dissolution) occur is found to diminish by orders of magnitude with increasing time or distance. The temporal rates of laboratory experiments and field observations differ, and extrapolating from laboratory experiments (in months) to field rates (in millions of years) can lead to order-of-magnitude errors. The reactions are transport-limited, but characterizing them using standard solute transport expressions can yield results in agreement with experiment only if spurious assumptions and parameters are introduced. We previously developed a theory of non-reactive solute transport based on applying critical path analysis to the cluster statistics of percolation. The fractal structure of the clusters can be used to generate solute distributions in both time and space. Solute velocities calculated from the temporal evolution of that distribution have the same time dependence as reaction-rate scaling in a wide range of field studies and laboratory experiments, covering some 10 decades in time. The present theory thus both explains a wide range of experiments, and also predicts changes in the scaling behavior in individual systems with increasing time and/or length scales. No other theory captures these variations in scaling by invoking a single physical mechanism. Because the successfully predicted chemical reactions include known results for silicate weathering rates, our theory provides a framework for understanding changes in the global carbon cycle, including its effects on extinctions, climate change, soil production, and denudation rates. It further provides a basis for understanding the fundamental time scales of hydrology and shallow geochemistry, as well as the basis of industrial agriculture. PMID:26232976
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...
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.
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...
It is well known that the fate and transport of contaminants in the subsurface are controlled by complex processes including advection, dispersion-diffusion, and chemical reactions. However, the interplay between the physical transport processes and chemical reactions, and their...
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.
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. ...
NASA Astrophysics Data System (ADS)
Juckes, M. N.
2006-05-01
A new data assimilation algorithm, using the isentropic advection equation, is applied to MIPAS and SBUV measurements of stratospheric ozone. The system is solved separately on each isentropic level, with neither vertical advection nor chemical reactions represented. The results are validated against HALOE, POAM III, SAGE II & III, OSIRIS and ozone sonde data. The new assimilation algorithm has the accuracy of the Kalman smoother but is, for the systems studied here with up to 200 000 variables per time step and 61 million control variables in total, many orders of magnitude less computationally expensive. The analysis produced minimises a single penalty function evaluated over an analysis window of over one month. The cost of the analysis is found to increase nearly linearly with the number of control variables. Compared with over 800 profiles from Electrochemical Concentration Cell sondes at 29 sites the analysis is found to be merely 0.1% high at 420 K, rising to 0.4% at 650 K. Comparison against the other satellites imply that the bias remains small up to 1250 K (38 km) and then increases to around -10% at 1650 K (44 km). Between 20 and 35 km the root-mean-square difference relative to HALOE, SAGE II & III, and POAM is in the 5 to 10% range, with larger discrepancies relative to other instruments. Outside this height range rms differences are generally larger, though agreement with HALOE remains good up to 50 km. The assimilation has closer agreement to independent observations than found in direct near-neighbour comparisons between profiles, demonstrating that the assimilation can add value to the observations.
Developing a modified SEBAL algorithm that is responsive to advection by using limited weather data
NASA Astrophysics Data System (ADS)
Mkhwanazi, Mcebisi
The use of Remote Sensing ET algorithms in water management, especially for agricultural purposes is increasing, and there are more models being introduced. The Surface Energy Balance Algorithm for Land (SEBAL) and its variant, Mapping Evapotranspiration with Internalized Calibration (METRIC) are some of the models that are being widely used. While SEBAL has several advantages over other RS models, including that it does not require prior knowledge of soil, crop and other ground details, it has the downside of underestimating evapotranspiration (ET) on days when there is advection, which may be in most cases in arid and semi-arid areas. METRIC, however has been modified to be able to account for advection, but in doing so it requires hourly weather data. In most developing countries, while accurate estimates of ET are required, the weather data necessary to use METRIC may not be available. This research therefore was meant to develop a modified version of SEBAL that would require minimal weather data that may be available in these areas, and still estimate ET accurately. The data that were used to develop this model were minimum and maximum temperatures, wind data, preferably the run of wind in the afternoon, and wet bulb temperature. These were used to quantify the advected energy that would increase ET in the field. This was a two-step process; the first was developing the model for standard conditions, which was described as a healthy cover of alfalfa, 40-60 cm tall and not short of water. Under standard conditions, when estimated ET using modified SEBAL was compared with lysimeter-measured ET, the modified SEBAL model had a Mean Bias Error (MBE) of 2.2 % compared to -17.1 % from the original SEBAL. The Root Mean Square Error (RMSE) was lower for the modified SEBAL model at 10.9 % compared to 25.1 % for the original SEBAL. The modified SEBAL model, developed on an alfalfa field in Rocky Ford, was then tested on other crops; beans and wheat. It was also tested on
NASA Astrophysics Data System (ADS)
Huhn, F.; von Kameke, A.; Pérez-Muñuzuri, V.; Olascoaga, M. J.; Beron-Vera, F. J.
2012-03-01
Based on ten years (1998-2007) of satellite ocean color data we analyze the spatiotemporal patterns in the seasonal Madagascar plankton bloom with respect to the advection of the recently discovered Southern Indian Ocean Countercurrent (SICC). In maps of Finite-time Lyapunov Exponents (FTLE) and Finite-Time Zonal Drift (FTZD) computed from altimetry derived velocities we observe a narrow zonal jet that starts at ˜25°S at the southern tip of Madagascar, an important upwelling region, and extends to the east further than the largest plankton blooms (˜2500 km). In bloom years, the jet coincides with large parts of the northern boundary of the plankton bloom, acting as a barrier to meridional transport. Our findings suggest that advection is an important and so far underestimated mechanism for the eastward propagation and the extent of the plankton bloom. This supports the hypothesis of a single nutrient source south of Madagascar.
NASA Astrophysics Data System (ADS)
Sofiev, M.; Vira, J.; Kouznetsov, R.; Prank, M.; Soares, J.; Genikhovich, E.
2015-03-01
The paper presents dynamic cores v.4 and v.5 of the System for Integrated modeLling of Atmospheric coMposition SILAM v.5.5 based on the advection algorithm of Michael Galperin. This advection routine, so far weakly presented in international literature, is non-diffusive, positively defined, stable with regard to Courant number significantly above one, and very efficient computationally. For the first time, we present a rigorous description of its original version, along with several updates that improve its monotonicity and allow applications to long-living species in conditions of complex atmospheric flows. The other extension allows the scheme application to dynamics of aerosol spectra. The scheme is accompanied with the previously developed vertical diffusion algorithm, which encapsulates the dry deposition process as a boundary condition. Connection to chemical transformation modules is outlined, accounting for the specifics of transport scheme. 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 models. The basic tests were repeated for the updated scheme, along with demanding global 2-D tests recently suggested in literature, which allowed positioning the scheme with regard to sophisticated state-of-the-art approaches. The model performance appeared close to the top of the list with very modest computational costs.
NASA Astrophysics Data System (ADS)
Ancey, C.; Bohorquez, P.; Heyman, J.
2015-12-01
The advection-diffusion equation is one of the most widespread equations in physics. It 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). Phenomenological laws are usually sufficient to derive this equation and interpret its terms. Stochastic models can also be used to derive it, with the significant advantage that they provide information on the statistical properties of particle activity. These models are quite useful when sediment transport exhibits large fluctuations (typically at low transport rates), making the measurement of mean values difficult. Among these stochastic models, the most common approach consists of random walk models. For instance, they have been used to model the random displacement of tracers in rivers. Here we explore an alternative approach, which involves monitoring the evolution of the number of particles moving within an array of cells of finite length. Birth-death Markov processes are well suited to this objective. While the topic has been explored in detail for diffusion-reaction systems, the treatment of advection has received no attention. We therefore look into the possibility of deriving the advection-diffusion equation (with a source term) within the framework of birth-death Markov processes. We show that in the continuum limit (when the cell size becomes vanishingly small), we can derive an advection-diffusion equation for particle activity. Yet while this derivation is formally valid in the continuum limit, it runs into difficulty in practical applications involving cells or meshes of finite length. Indeed, within our stochastic framework, 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
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.
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.
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.
Really TVD advection schemes for the depth-integrated transport equation
NASA Astrophysics Data System (ADS)
Mercier, Ch.; Delhez, E. J. M.
This paper explores the use of TVD advection schemes to solve the depth-integrated transport equation for tracers in finite volume marine models. Numerical experiments show that the blind application of the usual TVD schemes and associated flux limiters can lead to non-TVD solutions when applied in complex geometries. Spatial and/or temporal variations of the local bathymetry can indeed break the TVD property of the usual schemes. Really TVD schemes can be recovered by taking into account the local depth and its variations in the formulation of the flux limiters. Using this approach, a generalized superbee limiter is introduced and validated.
Analytical Solutions of a Fractional Diffusion-advection Equation for Solar Cosmic-Ray Transport
NASA Astrophysics Data System (ADS)
Litvinenko, Yuri E.; Effenberger, Frederic
2014-12-01
Motivated by recent applications of superdiffusive transport models to shock-accelerated particle distributions in the heliosphere, we analytically solve a one-dimensional fractional diffusion-advection equation for the particle density. We derive an exact Fourier transform solution, simplify it in a weak diffusion approximation, and compare the new solution with previously available analytical results and with a semi-numerical solution based on a Fourier series expansion. We apply the results to the problem of describing the transport of energetic particles, accelerated at a traveling heliospheric shock. Our analysis shows that significant errors may result from assuming an infinite initial distance between the shock and the observer. We argue that the shock travel time should be a parameter of a realistic superdiffusive transport model.
Analytical solutions of a fractional diffusion-advection equation for solar cosmic-ray transport
Litvinenko, Yuri E.; Effenberger, Frederic
2014-12-01
Motivated by recent applications of superdiffusive transport models to shock-accelerated particle distributions in the heliosphere, we analytically solve a one-dimensional fractional diffusion-advection equation for the particle density. We derive an exact Fourier transform solution, simplify it in a weak diffusion approximation, and compare the new solution with previously available analytical results and with a semi-numerical solution based on a Fourier series expansion. We apply the results to the problem of describing the transport of energetic particles, accelerated at a traveling heliospheric shock. Our analysis shows that significant errors may result from assuming an infinite initial distance between the shock and the observer. We argue that the shock travel time should be a parameter of a realistic superdiffusive transport model.
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.
Modeling of advection-diffusion-reaction processes using transport dissipative particle dynamics
NASA Astrophysics Data System (ADS)
Li, Zhen; Yazdani, Alireza; Tartakovsky, Alexandre; Karniadakis, George Em
2015-11-01
We present a transport dissipative particle dynamics (tDPD) model for simulating mesoscopic problems involving advection-diffusion-reaction (ADR) processes, along with a methodology for implementation of the correct Dirichlet and Neumann boundary conditions in tDPD simulations. In particular, the transport of concentration is modeled by a Fickian flux and a random flux between tDPD particles, and the advection is implicitly considered by the movements of Lagrangian particles. To validate the proposed tDPD model and the boundary conditions, three benchmark simulations of one-dimensional diffusion with different boundary conditions are performed, and the results show excellent agreement with the theoretical solutions. Also, two-dimensional simulations of ADR systems are performed and the tDPD simulations agree well with the results obtained by the spectral element method. Finally, an application of tDPD to the spatio-temporal dynamics of blood coagulation involving twenty-five reacting species is performed to demonstrate the promising biological applications of the tDPD model. Supported by the DOE Center on Mathematics for Mesoscopic Modeling of Materials (CM4) and an INCITE grant.
Simulation of the advective methane transport and AOM in Shenhu area, the Northern South China Sea
NASA Astrophysics Data System (ADS)
Liu, L.; Wu, N.
2012-04-01
Anaerobic Oxidation of Methane (AOM) occurs in the transition zone between the presence of sulfate and methane. This reaction is an important process for methane and the global carbon cycle. Methane gas hydrates bearing sediments were recovered in Shenhu Area, the Northern South China Sea, and methane advective transport was detected in this area as well. A one dimension numerical simulation tool was implemented to study the AOM process combined with the advective methane transport in Shenhu Area according to the local drilling data and geochemical information. The modeled results suggest that local methane flux will be consumed in the sediment column via dissolution, sorption and AOM reaction. A portion of methane will enter water column and possibly atmosphere if the methane flux was one order of magnitude higher than current level. Furthermore, the calculated rates of AOM in Shenhu area range similar to that of gas hydrate mounds in Mexico Golf. However, AOM is ability to consume more methane than that in Golf of Mexico due to the lower permeable sediment associated with a deeper sulfate methane transition layer.
NASA Technical Reports Server (NTRS)
Zhou, YE; Vahala, George
1993-01-01
The advection of a passive scalar by incompressible turbulence is considered using recursive renormalization group procedures in the differential sub grid shell thickness limit. It is shown explicitly that the higher order nonlinearities induced by the recursive renormalization group procedure preserve Galilean invariance. Differential equations, valid for the entire resolvable wave number k range, are determined for the eddy viscosity and eddy diffusivity coefficients, and it is shown that higher order nonlinearities do not contribute as k goes to 0, but have an essential role as k goes to k(sub c) the cutoff wave number separating the resolvable scales from the sub grid scales. The recursive renormalization transport coefficients and the associated eddy Prandtl number are in good agreement with the k-dependent transport coefficients derived from closure theories and experiments.
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.
NASA Astrophysics Data System (ADS)
Ojha, Richa; Prakash, A.; Govindaraju, Rao S.
2014-08-01
Description of field-scale solute transport in unsaturated soils is essential for assessing the degree of contamination, estimating fluxes past a control plane and for designing remedial measures. The flow field is usually described by numerical solution of the Richards equation followed by numerical solution of the advection-dispersion equation to describe contaminant movement. These numerical solutions are highly complex, and do not provide the insights that are possible from simpler analytical representations. In this study, analytical solutions at the local scale are developed to describe purely advective vertical transport of a conservative solute along the principle characteristic of the flow field. Local-scale model development is simplified by using a sharp-front approximation for water movement. These local solutions are then upscaled to field-scale solute transport by adopting a lognormally distributed horizontal hydraulic conductivity field to represent the natural heterogeneity observed in field soils. Analytical expressions are developed for the mean behavior of solute transport at the field scale. Comparisons with experimental observations find that trends of field-scale solute behavior are reasonably reproduced by the model. The accuracy of the proposed solution improves with increasing spatial variability in the hydraulic conductivity as revealed by further comparisons with numerical results of the Richards equation-based field-scale solute movement. In some cases, the sharp-front approximation may lead to anomalous field-scale behavior depending on the role of pre and postponded conditions in the field, and this limitation is discussed. The proposed method shows promise for describing field-scale solute movement in loamy sand and sandy loam soils.
Perko, Janez; Patel, Ravi A
2014-05-01
The paper presents an approach that extends the flexibility of the standard lattice Boltzmann single relaxation time scheme in terms of spatial variation of dissipative terms (e.g., diffusion coefficient) and stability for high Péclet mass transfer problems. Spatial variability of diffusion coefficient in SRT is typically accommodated through the variation of relaxation time during the collision step. This method is effective but cannot deal with large diffusion coefficient variations, which can span over several orders of magnitude in some natural systems. The approach explores an alternative way of dealing with large diffusion coefficient variations in advection-diffusion transport systems by introducing so-called diffusion velocity. The diffusion velocity is essentially an additional convective term that replaces variations in diffusion coefficients vis-à-vis a chosen reference diffusion coefficient which defines the simulation time step. Special attention is paid to the main idea behind the diffusion velocity formulation and its implementation into the lattice Boltzmann framework. Finally, the performance, stability, and accuracy of the diffusion velocity formulation are discussed via several advection-diffusion transport benchmark examples. These examples demonstrate improved stability and flexibility of the proposed scheme with marginal consequences on the numerical performance.
Transport dissipative particle dynamics model for mesoscopic advection-diffusion-reaction problems
NASA Astrophysics Data System (ADS)
Li, Zhen; Yazdani, Alireza; Tartakovsky, Alexandre; Karniadakis, George Em
2015-07-01
We present a transport dissipative particle dynamics (tDPD) model for simulating mesoscopic problems involving advection-diffusion-reaction (ADR) processes, along with a methodology for implementation of the correct Dirichlet and Neumann boundary conditions in tDPD simulations. tDPD is an extension of the classic dissipative particle dynamics (DPD) framework with extra variables for describing the evolution of concentration fields. The transport of concentration is modeled by a Fickian flux and a random flux between tDPD particles, and the advection is implicitly considered by the movements of these Lagrangian particles. An analytical formula is proposed to relate the tDPD parameters to the effective diffusion coefficient. To validate the present tDPD model and the boundary conditions, we perform three tDPD simulations of one-dimensional diffusion with different boundary conditions, and the results show excellent agreement with the theoretical solutions. We also performed two-dimensional simulations of ADR systems and the tDPD simulations agree well with the results obtained by the spectral element method. Finally, we present an application of the tDPD model to the dynamic process of blood coagulation involving 25 reacting species in order to demonstrate the potential of tDPD in simulating biological dynamics at the mesoscale. We find that the tDPD solution of this comprehensive 25-species coagulation model is only twice as computationally expensive as the conventional DPD simulation of the hydrodynamics only, which is a significant advantage over available continuum solvers.
Transport dissipative particle dynamics model for mesoscopic advection-diffusion-reaction problems.
Li, Zhen; Yazdani, Alireza; Tartakovsky, Alexandre; Karniadakis, George Em
2015-07-01
We present a transport dissipative particle dynamics (tDPD) model for simulating mesoscopic problems involving advection-diffusion-reaction (ADR) processes, along with a methodology for implementation of the correct Dirichlet and Neumann boundary conditions in tDPD simulations. tDPD is an extension of the classic dissipative particle dynamics (DPD) framework with extra variables for describing the evolution of concentration fields. The transport of concentration is modeled by a Fickian flux and a random flux between tDPD particles, and the advection is implicitly considered by the movements of these Lagrangian particles. An analytical formula is proposed to relate the tDPD parameters to the effective diffusion coefficient. To validate the present tDPD model and the boundary conditions, we perform three tDPD simulations of one-dimensional diffusion with different boundary conditions, and the results show excellent agreement with the theoretical solutions. We also performed two-dimensional simulations of ADR systems and the tDPD simulations agree well with the results obtained by the spectral element method. Finally, we present an application of the tDPD model to the dynamic process of blood coagulation involving 25 reacting species in order to demonstrate the potential of tDPD in simulating biological dynamics at the mesoscale. We find that the tDPD solution of this comprehensive 25-species coagulation model is only twice as computationally expensive as the conventional DPD simulation of the hydrodynamics only, which is a significant advantage over available continuum solvers.
Transport dissipative particle dynamics model for mesoscopic advection-diffusion-reaction problems
Yazdani, Alireza; Tartakovsky, Alexandre; Karniadakis, George Em
2015-01-01
We present a transport dissipative particle dynamics (tDPD) model for simulating mesoscopic problems involving advection-diffusion-reaction (ADR) processes, along with a methodology for implementation of the correct Dirichlet and Neumann boundary conditions in tDPD simulations. tDPD is an extension of the classic dissipative particle dynamics (DPD) framework with extra variables for describing the evolution of concentration fields. The transport of concentration is modeled by a Fickian flux and a random flux between tDPD particles, and the advection is implicitly considered by the movements of these Lagrangian particles. An analytical formula is proposed to relate the tDPD parameters to the effective diffusion coefficient. To validate the present tDPD model and the boundary conditions, we perform three tDPD simulations of one-dimensional diffusion with different boundary conditions, and the results show excellent agreement with the theoretical solutions. We also performed two-dimensional simulations of ADR systems and the tDPD simulations agree well with the results obtained by the spectral element method. Finally, we present an application of the tDPD model to the dynamic process of blood coagulation involving 25 reacting species in order to demonstrate the potential of tDPD in simulating biological dynamics at the mesoscale. We find that the tDPD solution of this comprehensive 25-species coagulation model is only twice as computationally expensive as the conventional DPD simulation of the hydrodynamics only, which is a significant advantage over available continuum solvers. PMID:26156459
Transport dissipative particle dynamics model for mesoscopic advection-diffusion-reaction problems.
Li, Zhen; Yazdani, Alireza; Tartakovsky, Alexandre; Karniadakis, George Em
2015-07-01
We present a transport dissipative particle dynamics (tDPD) model for simulating mesoscopic problems involving advection-diffusion-reaction (ADR) processes, along with a methodology for implementation of the correct Dirichlet and Neumann boundary conditions in tDPD simulations. tDPD is an extension of the classic dissipative particle dynamics (DPD) framework with extra variables for describing the evolution of concentration fields. The transport of concentration is modeled by a Fickian flux and a random flux between tDPD particles, and the advection is implicitly considered by the movements of these Lagrangian particles. An analytical formula is proposed to relate the tDPD parameters to the effective diffusion coefficient. To validate the present tDPD model and the boundary conditions, we perform three tDPD simulations of one-dimensional diffusion with different boundary conditions, and the results show excellent agreement with the theoretical solutions. We also performed two-dimensional simulations of ADR systems and the tDPD simulations agree well with the results obtained by the spectral element method. Finally, we present an application of the tDPD model to the dynamic process of blood coagulation involving 25 reacting species in order to demonstrate the potential of tDPD in simulating biological dynamics at the mesoscale. We find that the tDPD solution of this comprehensive 25-species coagulation model is only twice as computationally expensive as the conventional DPD simulation of the hydrodynamics only, which is a significant advantage over available continuum solvers. PMID:26156459
A subordinated advection model for uniform bed load transport from local to regional scales
NASA Astrophysics Data System (ADS)
Zhang, Yong; Martin, Raleigh L.; Chen, Dong; Baeumer, Boris; Sun, Hongguang; Chen, Li
2014-12-01
Sediment tracers moving as bed load can exhibit anomalous dispersion behavior deviating from Fickian diffusion. The presence of heavy-tailed resting time distributions and thin-tailed step length distributions motivate adoption of fractional-derivative models (FDMs) to describe sediment dispersion, but these models require many parameters that are difficult to quantify. Here we propose a considerably simplified FDM for anomalous transport of uniformly sized grains along straight channels, the subordinated advection equation (SAE), which is based on the concept of time subordination. Unlike previous FDM models with time index γ between 0 and 1, our SAE model adopts a value of γ between 1 and 2. This γ describes random velocities deviating significantly from the mean velocity and models both long resting periods and relatively fast displacements. We show that the model quantifies the dynamics of four bed load transport experiments recorded in the literature. In addition to γ, SAE model parameters—velocity and capacity coefficient—are related to the mean and variance of particle velocities, respectively. Successful application of the SAE model also implies a universal probability density for the heavy-tailed waiting time distribution (with finite mean) and a relatively lighter tailed step length distribution for uniform bed load transport from local to regional scales.
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)
Fan, Niannian; Singh, Arvind; Guala, Michele; Foufoula-Georgiou, Efi; Wu, Baosheng
2016-04-01
Bed load transport is a highly stochastic, multiscale process, where particle advection and diffusion regimes are governed by the dynamics of each sediment grain during its motion and resting states. Having a quantitative understanding of the macroscale behavior emerging from the microscale interactions is important for proper model selection in the absence of individual grain-scale observations. Here we develop a semimechanistic sediment transport model based on individual particle dynamics, which incorporates the episodic movement (steps separated by rests) of sediment particles and study their macroscale behavior. By incorporating different types of probability distribution functions (PDFs) of particle resting times Tr, under the assumption of thin-tailed PDF of particle velocities, we study the emergent behavior of particle advection and diffusion regimes across a wide range of spatial and temporal scales. For exponential PDFs of resting times Tr, we observe normal advection and diffusion at long time scales. For a power-law PDF of resting times (i.e., f>(Tr>)˜Tr-ν), the tail thickness parameter ν is observed to affect the advection regimes (both sub and normal advective), and the diffusion regimes (both subdiffusive and superdiffusive). By comparing our semimechanistic model with two random walk models in the literature, we further suggest that in order to reproduce accurately the emerging diffusive regimes, the resting time model has to be coupled with a particle motion model able to produce finite particle velocities during steps, as the episodic model discussed here.
Technology Transfer Automated Retrieval System (TEKTRAN)
The classical model to describe solute transport in soil is based on the advective-dispersive equation where Fick’s law is used to explain dispersion. From the microscopic point of view this is equivalent to consider that the motion of the particles of solute may be simulated by the Brownian motion....
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.
Removing volatile contaminants from the unsaturated zone by inducing advective air-phase transport
Baehr, A.L.; Hoag, G.E.; Marley, M.C.
1989-01-01
Organic liquids inadvertently spilled and then distributed in the unsaturated zone can pose a long-term threat to ground water. Many of these substances have significant volatility, and thereby establish a premise for contaminant removal from the unsaturated zone by inducing advective air-phase transport with wells screened in the unsaturated zone. In order to focus attention on the rates of mass transfer from liquid to vapour phases, sand columns were partially saturated with gasoline and vented under steady air-flow conditions. The ability of an equilibrium-based transport model to predict the hydrocarbon vapor flux from the columns implies an efficient rate of local phase transfer for reasonably high air-phase velocities. Thus the success of venting remediations will depend primarily on the ability to induce an air-flow field in a heterogeneous unsaturated zone that will intersect the distributed contaminant. To analyze this aspect of the technique, a mathematical model was developed to predict radially symmetric air flow induced by venting from a single well. This model allows for in-situ determinations of air-phase permeability, which is the fundamental design parameter, and for the analysis of the limitations of a single well design. A successful application of the technique at a site once contaminated by gasoline supports the optimism derived from the experimental and modeliing phases of this study, and illustrates the well construction and field methods used to document the volatile contaminant recovery. ?? 1989.
Transport dissipative particle dynamics model for mesoscopic advection- diffusion-reaction problems
Zhen, Li; Yazdani, Alireza; Tartakovsky, Alexandre M.; Karniadakis, George E.
2015-07-07
We present a transport dissipative particle dynamics (tDPD) model for simulating mesoscopic problems involving advection-diffusion-reaction (ADR) processes, along with a methodology for implementation of the correct Dirichlet and Neumann boundary conditions in tDPD simulations. tDPD is an extension of the classic DPD framework with extra variables for describing the evolution of concentration fields. The transport of concentration is modeled by a Fickian flux and a random flux between particles, and an analytical formula is proposed to relate the mesoscopic concentration friction to the effective diffusion coefficient. To validate the present tDPD model and the boundary conditions, we perform three tDPD simulations of one-dimensional diffusion with different boundary conditions, and the results show excellent agreement with the theoretical solutions. We also performed two-dimensional simulations of ADR systems and the tDPD simulations agree well with the results obtained by the spectral element method. Finally, we present an application of the tDPD model to the dynamic process of blood coagulation involving 25 reacting species in order to demonstrate the potential of tDPD in simulating biological dynamics at the mesoscale. We find that the tDPD solution of this comprehensive 25-species coagulation model is only twice as computationally expensive as the DPD simulation of the hydrodynamics only, which is a significant advantage over available continuum solvers.
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)
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)
Biamonte, Mason; Idarraga, John
2013-04-01
A classical hybrid alternating-direction implicit difference scheme is used to simulate two-dimensional charge carrier advection-diffusion induced by alpha particles incident upon silicon pixel detectors at room temperature in vacuum. A mapping between the results of the simulation and a projection of the cluster size for each incident alpha is constructed. The error between the simulation and the experimental data diminishes with the increase in the applied voltage for the pixels in the central region of the cluster. Simulated peripheral pixel TOT values do not match the data for any value of applied voltage, suggesting possible modifications to the current algorithm from first principles. Coulomb repulsion between charge carriers is built into the algorithm using the Barnes-Hut tree algorithm. The plasma effect arising from the initial presence of holes in the silicon is incorporated into the simulation. The error between the simulation and the data helps identify physics not accounted for in standard literature simulation techniques.
Seirin Lee, Sungrim; Shibata, Tatsuo
2015-10-01
Anterior-Posterior (AP) polarity formation of cell membrane proteins plays a crucial role in determining cell asymmetry, which depends not only on the several genetic process but also biochemical and biophysical interactions. The mechanism of AP formation of Caenorhabditis elegans embryo is characterized into the three processes: (i) membrane association and dissociation of posterior and anterior proteins, (ii) diffusion into the membrane and cytosol, and (iii) active cortical and cytoplasmic flows induced by the contraction of the acto-myosin cortex. We explored the mechanism of symmetry breaking and AP polarity formation using self-recruitment model of posterior proteins. We found that the AP polarity pattern is established over wide range in the total mass of polarity proteins and the diffusion ratio in the cytosol to the membrane. We also showed that the advective transport in both membrane and cytosol during the establishment phase affects optimal time interval of establishment and positioning of the posterior domain, and plays a role to increase the robustness in the AP polarity formation by reducing the number of posterior domains for the sensitivity of initial conditions. We also demonstrated that a proper ratio of the total mass to cell size robustly regulate the length scale of the posterior domain.
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
NASA Astrophysics Data System (ADS)
Beisman, J. J., III; Maxwell, R. M.; Navarre-Sitchler, A.; Steefel, C. I.
2014-12-01
Understanding the interactions between physical, geochemical, and biological processes in the shallow subsurface is prerequisite to the development of effective contamination remediation techniques, or the accurate quantification of nutrient fluxes and biogeochemical cycling. Here we present recent developments to the massively parallel reactive transport code ParCrunchFlow. This model, previously applicable only to steady-state, saturated subsurface flows, has been extended to transient, surface-subsurface systems. Proof-of-concept simulations detailing reactive transport processes in hillslope and floodplain settings will be presented. In order to reduce the numerical dispersion inherent in grid based advection schemes, which can lead to an over prediction of reaction rates, a weighted, essentially non-oscillatory (WENO) advection scheme has been implemented, providing formal fifth-order spatial and third-order temporal accuracy. We use a mass-conservative, positivity-preserving flux limiter while advecting solute concentrations to prevent non-physical solutions. The effects of advection schemes and their associated numerical dispersion on reaction rates are evaluated by comparing our scheme to a monotonic lower order scheme in a transverse mixing scenario. The work presented here allows a better understanding of nutrient cycling dynamics in watershed systems.
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
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
Merritt, M.L.
1993-01-01
The simulation of the transport of injected freshwater in a thin brackish aquifer, overlain and underlain by confining layers containing more saline water, is shown to be influenced by the choice of the finite-difference approximation method, the algorithm for representing vertical advective and dispersive fluxes, and the values assigned to parametric coefficients that specify the degree of vertical dispersion and molecular diffusion that occurs. Computed potable water recovery efficiencies will differ depending upon the choice of algorithm and approximation method, as will dispersion coefficients estimated based on the calibration of simulations to match measured data. A comparison of centered and backward finite-difference approximation methods shows that substantially different transition zones between injected and native waters are depicted by the different methods, and computed recovery efficiencies vary greatly. Standard and experimental algorithms and a variety of values for molecular diffusivity, transverse dispersivity, and vertical scaling factor were compared in simulations of freshwater storage in a thin brackish aquifer. Computed recovery efficiencies vary considerably, and appreciable differences are observed in the distribution of injected freshwater in the various cases tested. The results demonstrate both a qualitatively different description of transport using the experimental algorithms and the interrelated influences of molecular diffusion and transverse dispersion on simulated recovery efficiency. When simulating natural aquifer flow in cross-section, flushing of the aquifer occurred for all tested coefficient choices using both standard and experimental algorithms. ?? 1993.
Rigorous upper bounds for transport due to passive advection by inhomogeneous turbulence
Krommes, J.A.; Smith, R.A.
1987-05-01
A variational procedure, due originally to Howard and explored by Busse and others for self-consistent turbulence problems, is employed to determine rigorous upper bounds for the advection of a passive scalar through an inhomogeneous turbulent slab with arbitrary generalized Reynolds number R and Kubo number K. In the basic version of the method, the steady-state energy balance is used as a constraint; the resulting bound, though rigorous, is independent of K. A pedagogical reference model (one dimension, K = infinity) is described in detail; the bound compares favorably with the exact solution. The direct-interaction approximation is also worked out for this model; it is somewhat more accurate than the bound, but requires considerably more labor to solve. For the basic bound, a general formalism is presented for several dimensions, finite correlation length, and reasonably general boundary conditions. Part of the general method, in which a Green's function technique is employed, applies to self-consistent as well as to passive problems, and thereby generalizes previous results in the fluid literature. The formalism is extended for the first time to include time-dependent constraints, and a bound is deduced which explicitly depends on K and has the correct physical scalings in all regimes of R and K. Two applications from the theory of turbulent plasmas ae described: flux in velocity space, and test particle transport in stochastic magnetic fields. For the velocity space problem the simplest bound reproduces Dupree's original scaling for the strong turbulence diffusion coefficient. For the case of stochastic magnetic fields, the scaling of the bounds is described for the magnetic diffusion coefficient as well as for the particle diffusion coefficient in the so-called collisionless, fluid, and double-streaming regimes.
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.
NASA Astrophysics Data System (ADS)
Klammler, Harald; Hatfield, Kirk; Mohamed, Mohamed M.; Perminova, Irina V.; Perlmutter, Mike
2014-07-01
The problem of permeable reactive barrier (PRB) capture and release behavior is investigated by means of an approximate analytical approach exploring the invariance of steady-state solutions of the advection-dispersion equation to conformal mapping. PRB configurations considered are doubly-symmetric funnel-and-gate as well as less frequent drain-and-gate systems. The effect of aquifer heterogeneity on contaminant plume spreading is hereby incorporated through an effective transverse macro-dispersion coefficient, which has to be known. Results are normalized and graphically represented in terms of a relative capture efficiency M of contaminant mass or groundwater passing a control plane (transect) at a sufficient distance up-stream of a PRB as to comply with underlying assumptions. Factors of safety FS are given as the ratios of required capture width under advective-dispersive and purely advective transport for achieving equal capture efficiency M. It is found that M also applies to the release behavior down-stream of a PRB, i.e., it describes the spreading and dilution of PRB treated groundwater possibly containing incompletely remediated contamination and/or remediation reaction products. Hypothetical examples are given to demonstrate results.
NASA Astrophysics Data System (ADS)
Ebner, P. P.; Grimm, S.; Steen-Larsen, H. C.; Schneebeli, M.; Steinfeld, A.
2014-12-01
The metamorphism of snow under advective air flow, with and without temperature gradient, was never experimentally investigated. We developed a new sample holder where metamorphism under advective conditions can be observed and measured using time-lapse micro-tomography [1]. Long-term experiments were performed and direct pore-level simulation (DPLS) [2,3] was directly applied on the extracted 3D digital geometry of the snow to calculate the effective transport properties by solving the governing fluid flow equations. The results showed no effect of isothermal advection, compared to rates typical for isothermal metamorphism. Appling a temperature gradient, the results showed increased snow metamorphism compared to rates typical for temperature gradient metamorphism. However, for both cases a change in the isotopic composition in the air as well as in the snow sample could be observed. These measurements could be influential to better understand snow-air exchange processes relevant for atmospheric chemistry and isotopic composition. REFERENCES[1] Ebner P. P., Grimm S., Schneebeli M., and Steinfeld A.: An instrumented sample holder for time-lapse micro-tomography measurements of snow under advective airflow. Geoscientific Instrumentation, Methods and Data Systems 4(2014), 353-373. [2] Zermatten E., Haussener S., Schneebeli M., and Steinfeld A.: Tomography-based determination of permeability and Dupuit-Forchheimer coefficient of characteristic snow samples. Journal of Glaciology 57(2011), 811-816. [3] Zermatten E., Schneebeli M., Arakawa H., and Steinfeld A.: Tomography-based determination of porosity, specific area and permeability of snow and comparison with measurements. Cold Regions Science and Technology 97 (2014), 33-40. Fig. 1: 3-D surface rendering of a refrozen wet snow sample with fluid flow streamline.
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
Novak, C.F.
1993-12-31
The Fracture-Matrix Transport (FMT) code couples saturated porous media advection and diffusion with mechanistic chemical models for speciation and interphase reactions. FMT is being developed to support actinide solubility and retardation studies for the Waste Isolation Pilot Plant (WIPP), USDOE facility for demonstrating safe disposal of transuranic waste. Hydrologic studies of water-bearing units above the WIPP indicate double-porosity transport behavior in some locations, with groundwater concentrations ranging which potable to highly concentrated. Previously, FMT simulated such systems in two-dimensions on the continuum from advection- to diffusion-dominated, with a user-specified velocity field that allows double-porosity transport. However, aqueous density was assumed constant, and reactive minerals were assumed to occupy negligible volume. Both of these assumptions can be considered poor for evaporite systems, where large changes in porosity and aqueous density can result from high mineral solubilities. Therefore, further development of FMT has relaxed these restrictions, allowing aqueous density to vary with phase composition, and allowing void volume to change as minerals dissolve and precipitate. This paper describes the additional mathematical complexity required to simulate such systems. The sensitivity of advection-dominated transport to these variables is explored through an extended example.
NASA Astrophysics Data System (ADS)
Lester, D. R.; Trefry, M. G.; Metcalfe, G.
2016-11-01
The macroscopic spreading and mixing of solute plumes in saturated porous media is ultimately controlled by processes operating at the pore scale. Whilst the conventional picture of pore-scale mechanical dispersion and molecular diffusion leading to persistent hydrodynamic dispersion is well accepted, this paradigm is inherently two-dimensional (2D) in nature and neglects important three-dimensional (3D) phenomena. We discuss how the kinematics of steady 3D flow at the pore scale generate chaotic advection-involving exponential stretching and folding of fluid elements-the mechanisms by which it arises and implications of microscopic chaos for macroscopic dispersion and mixing. Prohibited in steady 2D flow due to topological constraints, these phenomena are ubiquitous due to the topological complexity inherent to all 3D porous media. Consequently 3D porous media flows generate profoundly different fluid deformation and mixing processes to those of 2D flow. The interplay of chaotic advection and broad transit time distributions can be incorporated into a continuous-time random walk (CTRW) framework to predict macroscopic solute mixing and spreading. We show how these results may be generalised to real porous architectures via a CTRW model of fluid deformation, leading to stochastic models of macroscopic dispersion and mixing which both honour the pore-scale kinematics and are directly conditioned on the pore-scale architecture.
Advection dispersion mass transport associated with a non-aqueous-phase liquid pool
NASA Astrophysics Data System (ADS)
Fyrillas, Marios M.
2000-06-01
The two-dimensional problem of advection dispersion associated with a non-aqueous-phase liquid (NAPL) pool is addressed using the boundary element method. The problem is appropriately posed with an inhomogeneous boundary condition taking into consideration the presence of the pool and the impermeable layer. We derive a Fredholm integral equation of the first kind for the concentration gradient along the pool location and compute the average mass transfer coefficient numerically using the boundary-element method. Numerical results are in agreement with asymptotic analytical solutions obtained for the cases of small and large Péclet number (Pex). The asymptotic solution for small Pex, which is obtained by applying a novel perturbation technique to the integral equation, is used to de-singularize the integral equation. Results predicted by this analysis are in good agreement with experimentally determined overall mass transfer coefficients.
Advective excess Ba transport as shown from sediment and trap geochemical signatures
Fagel, N.; Andre, L.; Dehairs, F.
1999-08-01
The authors report the results of a geochemical study of sediment and trap material. Major and trace elements (Zr, Ba, rare earth elements, and Th) were analyzed on bulk sedimentary material collected along the NE Atlantic margin. The aim is to test the widespread use of Ba-barite as a proxy for paleoproductivity in a continental margin area. This environment is of great interest because atmospheric-oceanic exchanges are important. In sediments, the geochemical signatures remain close to an upper crust reference, with flat shale-normalized rare earth elements patterns and constant elementary ratios. The calculated biogenic fraction of Ba or excess Ba (20--45%) remains lower than the excess Ba record in trap material (80--99%). The evolution of the geochemical signature along the margin reflects variable dilution of a detrital Post Archean Australian Shale-like component by a biogenic carbonaceous seawater-derived component. The trap material displays a wide range of variation in its trace element content (e.g., Ba {approximately}150--3,000 ppm, Zr {approximately}2--100 ppm), except for the abyssal site, which is characterized by constant signature. In the two other sites, all of the trace element contents increase with water depth and present pronounced seasonal changes at each sampled water depth. The amount of excess Ba also increases in the deepest traps, and its evolution throughout the year mimics the change of the other analyzed trace elements. In contrast, its relationships with particulate organic carbon are not obvious. In terms of fluxes, two periods of enhanced excess Ba fluxes are observed: (1) excess Ba flux increases with the detrital-like elements like Th especially during winter, and (2) excess Ba flux is enhanced without any change for the other trace elements during spring. To explain the first case, a supply through lateral advection is proposed. Such transient input of significant excess Ba flux will have a great impact on the yearly averaged
Zhou, Quanlin; Birkholzer, Jens T.; Javandel, Iraj; Jordan, Preston D.
2004-01-14
A calibrated groundwater flow model for a contaminated site can provide substantial information for assessing and improving hydraulic measures implemented for remediation. A three-dimensional transient groundwater flow model was developed for a contaminated mountainous site, at which interim corrective measures were initiated to limit further spreading of contaminants. This flow model accounts for complex geologic units that vary considerably in thickness, slope, and hydrogeologic properties, as well as large seasonal fluctuations of the groundwater table and flow rates. Other significant factors are local recharge from leaking underground storm drains and recharge from steep uphill areas. The zonation method was employed to account for the clustering of high and low hydraulic conductivities measured in a geologic unit. A composite model was used to represent the bulk effect of thin layers of relatively high hydraulic conductivity found within bedrock of otherwise low conductivity. The inverse simulator ITOUGH2 was used to calibrate the model for the distribution of rock properties. The model was initially calibrated using data collected between 1994 and 1996. To check the validity of the model, it was subsequently applied to predicting groundwater level fluctuation and groundwater flux between 1996 and 1998. Comparison of simulated and measured data demonstrated that the model is capable of predicting the complex flow reasonably well. Advective transport was approximated using pathways of particles originating from source areas of the plumes. The advective transport approximation was in good agreement with the trend of contaminant plumes observed over the years. The validated model was then refined to focus on a subsection of the large system. The refined model was subsequently used to assess the efficiency of hydraulic measures implemented for remediation.
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...
Parkhurst, D.L.
1995-01-01
PHREEQC is a computer program written in the C pwgranuning language that is designed to perform a wide variety of aqueous geochemical calculations. PHREEQC is based on an ion-association aqueous model and has capabilities for (1) speciation and saturation-index calculations, (2) reaction-path and advective-transport calculations involving specified irreversible reactions, mixing of solutions, mineral and gas equilibria surface-complex-ation reactions, and ion-exchange reactions, and (3) inverse modeling, which finds sets of mineral and gas mole transfers that account for composition differences between waters, within specified compositional uncertainties. PHREEQC is derived from the Fortran program PHREEQE, but it has been completely rewritten in C with the addition many new capabilities. New features include the capabilities to use redox couples to distribute redox elements among their valence states in speciation calculations; to model ion-exchange and surface-compiexation reactions; to model reactions with a fixed-pressure, multicomponent gas phase (that is, a gas bubble); to calculate the mass of water in the aqueous phase during reaction and transport calculations; to keep track of the moles of minerals present in the solid phases and determine antomaticaHy the thermodynamically stable phase assemblage; to simulate advective transport in combination with PHREEQC's reaction-modeling capability; and to make inverse modeling calculations that allow for uncertainties in the analytical data. The user interface is improved through the use of a simplified approach to redox reactions, which includes explicit mole-balance equations for hydrogen and oxygen; the use of a revised input that is modular and completely free format; and the use of mineral names and standard chemical symbolism rather than index numbers. The use of (2 eliminates nearly all limitations on army sizes, including numbers of elements, aqueous species, solutions, phases, and lengths of character
Kim, Chang-Bae; Krommes, J.A.
1988-08-01
The work of Krommes and Smith on rigorous upper bounds for the turbulent transport of a passively advected scalar (/ital Ann. Phys./ 177:246 (1987)) is extended in two directions: (1) For their ''reference model,'' improved upper bounds are obtained by utilizing more sophisticated two-time constraints which include the effects of cross-correlations up to fourth order. Numerical solutions of the model stochastic differential equation are also obtained; they show that the new bounds compare quite favorably with the exact results, even at large Reynolds and Kubo numbers. (2) The theory is extended to take account of a finite spatial autocorrelation length L/sub c/. As a reasonably generic example, the problem of particle transport due to statistically specified stochastic magnetic fields in a collisionless turbulent plasma is revisited. A bound is obtained which reduces for small L/sub c/ to the quasilinear limit and for large L/sub c/ to the strong turbulence limit, and which provides a reasonable and rigorous interpolation for intermediate values of L/sub c/. 18 refs., 6 figs.
NASA Astrophysics Data System (ADS)
Bodin, Jacques
2015-03-01
In this study, new multi-dimensional time-domain random walk (TDRW) algorithms are derived from approximate one-dimensional (1-D), two-dimensional (2-D), and three-dimensional (3-D) analytical solutions of the advection-dispersion equation and from exact 1-D, 2-D, and 3-D analytical solutions of the pure-diffusion equation. These algorithms enable the calculation of both the time required for a particle to travel a specified distance in a homogeneous medium and the mass recovery at the observation point, which may be incomplete due to 2-D or 3-D transverse dispersion or diffusion. The method is extended to heterogeneous media, represented as a piecewise collection of homogeneous media. The particle motion is then decomposed along a series of intermediate checkpoints located on the medium interface boundaries. The accuracy of the multi-dimensional TDRW method is verified against (i) exact analytical solutions of solute transport in homogeneous media and (ii) finite-difference simulations in a synthetic 2-D heterogeneous medium of simple geometry. The results demonstrate that the method is ideally suited to purely diffusive transport and to advection-dispersion transport problems dominated by advection. Conversely, the method is not recommended for highly dispersive transport problems because the accuracy of the advection-dispersion TDRW algorithms degrades rapidly for a low Péclet number, consistent with the accuracy limit of the approximate analytical solutions. The proposed approach provides a unified methodology for deriving multi-dimensional time-domain particle equations and may be applicable to other mathematical transport models, provided that appropriate analytical solutions are available.
ADVECTIVE TRANSPORT OF INTERSTELLAR PLASMA INTO THE HELIOSPHERE ACROSS THE RECONNECTING HELIOPAUSE
Strumik, M.; Grzedzielski, S.; Czechowski, A.; Macek, W. M.; Ratkiewicz, R.
2014-02-10
We discuss results of magnetohydrodynamical model simulations of plasma dynamics in the proximity of the heliopause (HP). The model is shown to fit details of the magnetic field variations observed by the Voyager 1 spacecraft during the transition from the heliosphere to the local interstellar medium (LISM). We propose an interpretation of magnetic field structures observed by Voyager 1 in terms of fine-scale physical processes. Our simulations reveal an effective transport mechanism of relatively dense LISM plasma across the reconnecting HP into the heliosphere. The mechanism is associated with annihilation of magnetic sectors in the heliospheric plasma near the HP.
McCaulou, D.R.
1993-10-01
Replicate column experiments were done to quantify the effects of temperature and bacterial motility on advective transport through repacked, but otherwise unaltered, natural aquifer sediment. The bacteria used in this study, A0500, was a flagellated, spore-forming rod isolated from the deep subsurface at DOE`s Savannah River Laboratory. Motility was controlled by turning on flagellar metabolism at 18{degrees}C but off at 40{degrees}C. Microspheres were used to independently quantify the effects of temperature on the sticking efficiency ({alpha}), estimated using a steady-state filtration model. The observed greater microsphere removal at the higher temperature agreed with the physical-chemical model, but bacteria removal at 18{degrees}C was only half that at 4{degrees}C. The sticking efficiency for non-motile A0500 (4{degrees}C) was over three times that of the motile A0500 (18{degrees}C), 0.073 versus 0.022 respectively. Analysis of complete breakthrough curves using a non-steady, kinetically limited, transport model to estimate the time scales of attachment and detachment suggested that motile A 0500 bacteria traveled twice as far as non-motile A 0500 bacteria before becoming attached. Once attached, non-motile colloids detached on the time scale of 9 to 17 days. The time scale for detachment of motile A0500 bacteria was shorter, 4 to 5 days. Results indicate that bacterial attachment was reversible and detachment was enhanced by bacterial motifity. The kinetic energy of bacterial motility changed the attachment-detachment kinetics in favor of the detached state. The chemical factors responsible for the enhanced transport are not known. However, motility may have caused weakly held bacteria to detach from the secondary minimum, and possibly from the primary minimum, as described by DLVO theory.
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
JIT-transportation problem and its algorithm
NASA Astrophysics Data System (ADS)
Bai, Guozhong; Gan, Xiao-Xiong
2011-12-01
This article introduces the (just-in-time) JIT-transportation problem, which requires that all demanded goods be shipped to their destinations on schedule, at a zero or minimal destination-storage cost. The JIT-transportation problem is a special goal programming problem with discrete constraints. This article provides a mathematical model for such a transportation problem and introduces the JIT solution, the deviation solution, the JIT deviation, etc. By introducing the B(λ)-problem, this article establishes the equivalence between the optimal solutions of the B(λ)-problem and the optimal solutions of the JIT-transportation problem, and then provides an algorithm for the JIT-transportation problems. This algorithm is proven mathematically and is also illustrated by an example.
An implicit dispersive transport algorithm for the US Geological Survey MOC3D solute-transport model
Kipp, K.L.; Konikow, L.F.; Hornberger, G.Z.
1998-01-01
This report documents an extension to the U.S. Geological Survey MOC3D transport model that incorporates an implicit-in-time difference approximation for the dispersive transport equation, including source/sink terms. The original MOC3D transport model (Version 1) uses the method of characteristics to solve the transport equation on the basis of the velocity field. The original MOC3D solution algorithm incorporates particle tracking to represent advective processes and an explicit finite-difference formulation to calculate dispersive fluxes. The new implicit procedure eliminates several stability criteria required for the previous explicit formulation. This allows much larger transport time increments to be used in dispersion-dominated problems. The decoupling of advective and dispersive transport in MOC3D, however, is unchanged. With the implicit extension, the MOC3D model is upgraded to Version 2. A description of the numerical method of the implicit dispersion calculation, the data-input requirements and output options, and the results of simulator testing and evaluation are presented. Version 2 of MOC3D was evaluated for the same set of problems used for verification of Version 1. These test results indicate that the implicit calculation of Version 2 matches the accuracy of Version 1, yet is more efficient than the explicit calculation for transport problems that are characterized by a grid Peclet number less than about 1.0.
Alcaraz, Mar; García-Gil, Alejandro; Vázquez-Suñé, Enric; Velasco, Violeta
2016-02-01
Borehole Heat Exchangers (BHEs) are increasingly being used to exploit shallow geothermal energy. This paper presents a new methodology to provide a response to the need for a regional quantification of the geothermal potential that can be extracted by BHEs and the associated environmental impacts. A set of analytical solutions facilitates accurate calculation of the heat exchange of BHEs with the ground and its environmental impacts. For the first time, advection and dispersion heat transport mechanisms and the temporal evolution from the start of operation of the BHE are taken into account in the regional estimation of shallow geothermal resources. This methodology is integrated in a GIS environment, which facilitates the management of input and output data at a regional scale. An example of the methodology's application is presented for Barcelona, in Spain. As a result of the application, it is possible to show the strengths and improvements of this methodology in the development of potential maps of low temperature geothermal energy as well as maps of environmental impacts. The minimum and maximum energy potential values for the study site are 50 and 1800 W/m(2) for a drilled depth of 100 m, proportionally to Darcy velocity. Regarding to thermal impacts, the higher the groundwater velocity and the energy potential, the higher the size of the thermal plume after 6 months of exploitation, whose length ranges from 10 to 27 m long. A sensitivity analysis was carried out in the calculation of heat exchange rate and its impacts for different scenarios and for a wide range of Darcy velocities. The results of this analysis lead to the conclusion that the consideration of dispersion effects and temporal evolution of the exploitation prevent significant differences up to a factor 2.5 in the heat exchange rate accuracy and up to several orders of magnitude in the impacts generated.
Alcaraz, Mar; García-Gil, Alejandro; Vázquez-Suñé, Enric; Velasco, Violeta
2016-02-01
Borehole Heat Exchangers (BHEs) are increasingly being used to exploit shallow geothermal energy. This paper presents a new methodology to provide a response to the need for a regional quantification of the geothermal potential that can be extracted by BHEs and the associated environmental impacts. A set of analytical solutions facilitates accurate calculation of the heat exchange of BHEs with the ground and its environmental impacts. For the first time, advection and dispersion heat transport mechanisms and the temporal evolution from the start of operation of the BHE are taken into account in the regional estimation of shallow geothermal resources. This methodology is integrated in a GIS environment, which facilitates the management of input and output data at a regional scale. An example of the methodology's application is presented for Barcelona, in Spain. As a result of the application, it is possible to show the strengths and improvements of this methodology in the development of potential maps of low temperature geothermal energy as well as maps of environmental impacts. The minimum and maximum energy potential values for the study site are 50 and 1800 W/m(2) for a drilled depth of 100 m, proportionally to Darcy velocity. Regarding to thermal impacts, the higher the groundwater velocity and the energy potential, the higher the size of the thermal plume after 6 months of exploitation, whose length ranges from 10 to 27 m long. A sensitivity analysis was carried out in the calculation of heat exchange rate and its impacts for different scenarios and for a wide range of Darcy velocities. The results of this analysis lead to the conclusion that the consideration of dispersion effects and temporal evolution of the exploitation prevent significant differences up to a factor 2.5 in the heat exchange rate accuracy and up to several orders of magnitude in the impacts generated. PMID:26605833
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.
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
A transport-based condensed history algorithm
Tolar Jr, D R
1999-01-06
Condensed history algorithms are approximate electron transport Monte Carlo methods in which the cumulative effects of multiple collisions are modeled in a single step of (user-specified) path length s{sub 0}. This path length is the distance each Monte Carlo electron travels between collisions. Current condensed history techniques utilize a splitting routine over the range 0 {le} s {le} s{sub 0}. For example, the PEnELOPE method splits each step into two substeps; one with length {xi}s{sub 0} and one with length (1 {minus}{xi})s{sub 0}, where {xi} is a random number from 0 < {xi} < 1. because s{sub 0} is fixed (not sampled from an exponential distribution), conventional condensed history schemes are not transport processes. Here the authors describe a new condensed history algorithm that is a transport process. The method simulates a transport equation that approximates the exact Boltzmann equation. The new transport equation has a larger mean free path than, and preserves two angular moments of, the Boltzmann equation. Thus, the new process is solved more efficiently by Monte Carlo, and it conserves both particles and scattering power.
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.
Fast algorithms for transport models. Final report
Manteuffel, T.A.
1994-10-01
This project has developed a multigrid in space algorithm for the solution of the S{sub N} equations with isotropic scattering in slab geometry. The algorithm was developed for the Modified Linear Discontinuous (MLD) discretization in space which is accurate in the thick diffusion limit. It uses a red/black two-cell {mu}-line relaxation. This relaxation solves for all angles on two adjacent spatial cells simultaneously. It takes advantage of the rank-one property of the coupling between angles and can perform this inversion in O(N) operations. A version of the multigrid in space algorithm was programmed on the Thinking Machines Inc. CM-200 located at LANL. It was discovered that on the CM-200 a block Jacobi type iteration was more efficient than the block red/black iteration. Given sufficient processors all two-cell block inversions can be carried out simultaneously with a small number of parallel steps. The bottleneck is the need for sums of N values, where N is the number of discrete angles, each from a different processor. These are carried out by machine intrinsic functions and are well optimized. The overall algorithm has computational complexity O(log(M)), where M is the number of spatial cells. The algorithm is very efficient and represents the state-of-the-art for isotropic problems in slab geometry. For anisotropic scattering in slab geometry, a multilevel in angle algorithm was developed. A parallel version of the multilevel in angle algorithm has also been developed. Upon first glance, the shifted transport sweep has limited parallelism. Once the right-hand-side has been computed, the sweep is completely parallel in angle, becoming N uncoupled initial value ODE`s. The author has developed a cyclic reduction algorithm that renders it parallel with complexity O(log(M)). The multilevel in angle algorithm visits log(N) levels, where shifted transport sweeps are performed. The overall complexity is O(log(N)log(M)).
Parallel processing of numerical transport algorithms
Wienke, B.R.; Hiromoto, R.E.
1984-01-01
The multigroup, discrete ordinates representation for the linear transport equation enjoys widespread computational use and popularity. Serial solution schemes and numerical algorithms developed over the years provide a timely framework for parallel extension. On the Denelcor HEP, we investigate the parallel structure and extension of a number of standard S/sub n/ approaches. Concurrent inner sweeps, coupled acceleration techniques, synchronized inner-outer loops, and chaotic iteration are described, and results of computations are contrasted. The multigroup representation and serial iteration methods are also detailed. The basic iterative S/sub n/ method lends itself to parallel tasking, portably affording an effective medium for performing transport calculations on future architectures. This analysis represents a first attempt to extend serial S/sub n/ algorithms to parallel environments and provides good baseline estimates on ease of parallel implementation, relative algorithm efficiency, comparative speedup, and some future directions. We find basic inner-outer and chaotic iteration strategies both easily support comparably high degrees of parallelism. Both accommodate parallel rebalance and diffusion acceleration and appear as robust and viable parallel techniques for S/sub n/ production work.
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.
Monger, Gregg R.; Duncan, Candice Morrison; Brusseau, Mark L.
2015-01-01
A gas-phase tracer test (GTT) was conducted at a landfill in Tucson, AZ, to help elucidate the impact of landfill gas generation on the transport and fate of chlorinated aliphatic volatile organic contaminants (VOCs). Sulfur hexafluoride (SF6) was used as the non-reactive gas tracer. Gas samples were collected from a multiport monitoring well located 15.2 m from the injection well, and analyzed for SF6, CH4, CO2, and VOCs. The travel times determined for SF6 from the tracer test are approximately two to ten times smaller than estimated travel times that incorporate transport by only gas-phase diffusion. In addition, significant concentrations of CH4 and CO2 were measured, indicating production of landfill gas. Based on these results, it is hypothesized that the enhanced rates of transport observed for SF6 are caused by advective transport associated with landfill gas generation. The rates of transport varied vertically, which is attributed to multiple factors including spatial variability of water content, refuse mass, refuse permeability, and gas generation. PMID:26380532
An Improved Neutron Transport Algorithm for HZETRN
NASA Technical Reports Server (NTRS)
Slaba, Tony C.; Blattnig, Steve R.; Clowdsley, Martha S.; Walker, Steven A.; Badavi, Francis F.
2010-01-01
Long term human presence in space requires the inclusion of radiation constraints in mission planning and the design of shielding materials, structures, and vehicles. In this paper, the numerical error associated with energy discretization in HZETRN is addressed. An inadequate numerical integration scheme in the transport algorithm is shown to produce large errors in the low energy portion of the neutron and light ion fluence spectra. It is further shown that the errors result from the narrow energy domain of the neutron elastic cross section spectral distributions, and that an extremely fine energy grid is required to resolve the problem under the current formulation. Two numerical methods are developed to provide adequate resolution in the energy domain and more accurately resolve the neutron elastic interactions. Convergence testing is completed by running the code for various environments and shielding materials with various energy grids to ensure stability of the newly implemented method.
NASA Astrophysics Data System (ADS)
Neuman, Shlomo P.
2016-07-01
Fiori et al. (2015) examine the predictive capabilities of (among others) two "proxy" non-Fickian transport models, MRMT (Multi-Rate Mass Transfer) and CTRW (Continuous-Time Random Walk). In particular, they compare proxy model predictions of mean breakthrough curves (BTCs) at a sequence of control planes with near-ergodic BTCs generated through two- and three-dimensional simulations of nonreactive, mean-uniform advective transport in single realizations of stationary, randomly heterogeneous porous media. The authors find fitted proxy model parameters to be nonunique and devoid of clear physical meaning. This notwithstanding, they conclude optimistically that "i. Fitting the proxy models to match the BTC at [one control plane] automatically ensures prediction at downstream control planes [and thus] ii. … the measured BTC can be used directly for prediction, with no need to use models underlain by fitting." I show that (a) the authors' findings follow directly from (and thus confirm) theoretical considerations discussed earlier by Neuman and Tartakovsky (2009), which (b) additionally demonstrate that proxy models will lack similar predictive capabilities under more realistic, non-Markovian flow and transport conditions that prevail under flow through nonstationary (e.g., multiscale) media in the presence of boundaries and/or nonuniformly distributed sources, and/or when flow/transport are conditioned on measurements.
Hill, Mary C.; Ely, D. Matthew; Tiedeman, Claire R.; O'Brien, Grady M.; D'Agnese, Frank A.; Faunt, Claudia C.
2001-01-01
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. The predictions of interest are subsurface transport from beneath Yucca Mountain and 14 Underground Test Areas. The advective component of transport is considered because it is the component most affected by the system dynamics represented by the 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. The methods presented in this report are used in three ways. (1) The ratings for individual observations are obtained by manipulating the measures of prediction uncertainty, and do not involve recalibrating the model. In this analysis, observation locations are each omitted individually and the resulting increase in uncertainty in the predictions is calculated. The uncertainty is quantified as standard deviations on the simulated advective transport. The increase in uncertainty is quantified as the percent increase in the standard deviations caused by omitting the one observation location from the calculation of standard deviations. In general, observation locations associated with larger increases are rated as more important. (2) Ratings for largely geographically based groups are obtained using a straightforward extension of the method used for
Wagner, Brian J.; Gorelick, Steven M.
1986-01-01
A simulation nonlinear multiple-regression methodology for estimating parameters that characterize the transport of contaminants is developed and demonstrated. Finite difference containment transport simulation is combined with a nonlinear weighted least squares multiple-regression procedure. The technique provides optimal parameter estimates and gives statistics for assessing the reliability of these estimates under certain general assumptions about the distributions of the random measurement errors. Monte Carlo analysis is used to estimate parameter reliability for a hypothetical homogeneous soil column for which concentration data contain large random measurement errors. The value of data collected spatially versus data collected temporally was investigated for estimation of velocity, dispersion coefficient, effective porosity, first-order decay rate, and zero-order production. The use of spatial data gave estimates that were 2-3 times more reliable than estimates based on temporal data for all parameters except velocity. (Estimated author abstract) Refs.
NASA Astrophysics Data System (ADS)
Baechler, S.; Croisé, J.; Altmann, S.
2012-12-01
Chemico-osmosis is a recognized phenomenon taking place in clay mineral-rich sedimentary formations and a number of questions have been raised concerning its potential effects on pressure fields in and around underground radioactive waste repositories installed in such formations. Certain radioactive waste packages contain large quantities of nitrate salts whose release might result in the presence of highly concentrated salt solutions in the disposal cells, during their resaturation after closure of the facility. This would lead to large solute concentration gradients within the formation's porewater which could then potentially induce significant chemico-osmotic fluxes. In this paper, we assess the impact of chemico-osmotic fluxes on the water pressure during the post-closure period of a typical disposal cell for intermediate-level, long-lived bituminised radioactive waste in the Callovo-Oxfordian Clay formation. A numerical model of chemico-osmotic water flow and solute transport has been developed based on the work of Bader and Kooi (2005) [5], and including Bresler's dependence of osmotic efficiency on concentration and compaction state [9]. Model validity has been extended to highly concentrated solutions by incorporating a concentration-dependent activity coefficient, based on the Pitzer's equations. Results show that due to the strong dependence of the osmotic coefficient on concentration, the impact of chemico-osmosis on water flow and on the pressure field around the disposal cell is relatively low. A maximum overpressure of the order of 1 MPa was obtained. No difference in the simulation results were noticed for disposal cell solutions having concentrations higher than 1 M NaNO3. Differences between simulations were found to be almost entirely due to Bresler's relationship i.e., the model of the dependence between osmotic efficiency and concentration, and only slightly on the activity coefficient correction. Questions remain regarding the appropriate
A computational study of routing algorithms for realistic transportation networks
Jacob, R.; Marathe, M.V.; Nagel, K.
1998-12-01
The authors carry out an experimental analysis of a number of shortest path (routing) algorithms investigated in the context of the TRANSIMS (Transportation Analysis and Simulation System) project. The main focus of the paper is to study how various heuristic and exact solutions, associated data structures affected the computational performance of the software developed especially for realistic transportation networks. For this purpose the authors have used Dallas Fort-Worth road network with very high degree of resolution. The following general results are obtained: (1) they discuss and experimentally analyze various one-one shortest path algorithms, which include classical exact algorithms studied in the literature as well as heuristic solutions that are designed to take into account the geometric structure of the input instances; (2) they describe a number of extensions to the basic shortest path algorithm. These extensions were primarily motivated by practical problems arising in TRANSIMS and ITS (Intelligent Transportation Systems) related technologies. Extensions discussed include--(i) time dependent networks, (ii) multi-modal networks, (iii) networks with public transportation and associated schedules. Computational results are provided to empirically compare the efficiency of various algorithms. The studies indicate that a modified Dijkstra`s algorithm is computationally fast and an excellent candidate for use in various transportation planning applications as well as ITS related technologies.
Mohanram, Arvind; Ray, Chittaranjan; Harvey, Ronald W; Metge, David W; Ryan, Joseph N; Chorover, Jon; Eberl, D D
2010-10-01
In order to gain more information about the fate of Cryptosporidium parvum oocysts in tropical volcanic soils, the transport and attachment behaviors of oocysts and oocyst-sized polystyrene microspheres were studied in the presence of two soils. These soils were chosen because of their differing chemical and physical properties, i.e., an organic-rich (43-46% by mass) volcanic ash-derived soil from the island of Hawaii, and a red, iron (22-29% by mass), aluminum (29-45% by mass), and clay-rich (68-76% by mass) volcanic soil from the island of Oahu. A third agricultural soil, an organic- (13% by mass) and quartz-rich (40% by mass) soil from Illinois, was included for reference. In 10-cm long flow-through columns, oocysts and microspheres advecting through the red volcanic soil were almost completely (98% and 99%) immobilized. The modest breakthrough resulted from preferential flow-path structure inadvertently created by soil-particle aggregation during the re-wetting process. Although a high (99%) removal of oocysts and microsphere within the volcanic ash soil occurred initially, further examination revealed that transport was merely retarded because of highly reversible interactions with grain surfaces. Judging from the slope of the substantive and protracted tail of the breakthrough curve for the 1.8-μm microspheres, almost all (>99%) predictably would be recovered within ∼4000 pore volumes. This suggests that once contaminated, the volcanic ash soil could serve as a reservoir for subsequent contamination of groundwater, at least for pathogens of similar size or smaller. Because of the highly reversible nature of organic colloid immobilization in this soil type, C. parvum could contaminate surface water should overland flow during heavy precipitation events pick up near-surface grains to which they are attached. Surprisingly, oocyst and microsphere attachment to the reference soil from Illinois appeared to be at least as sensitive to changes in pH as was
Mohanram, A.; Ray, C.; Harvey, R.W.; Metge, D.W.; Ryan, J.N.; Chorover, J.; Eberl, D.D.
2010-01-01
In order to gain more information about the fate of Cryptosporidium parvum oocysts in tropical volcanic soils, the transport and attachment behaviors of oocysts and oocyst-sized polystyrene microspheres were studied in the presence of two soils. These soils were chosen because of their differing chemical and physical properties, i.e., an organic-rich (43-46% by mass) volcanic ash-derived soil from the island of Hawaii, and a red, iron (22-29% by mass), aluminum (29-45% by mass), and clay-rich (68-76% by mass) volcanic soil from the island of Oahu. A third agricultural soil, an organic- (13% by mass) and quartz-rich (40% by mass) soil from Illinois, was included for reference. In 10-cm long flow-through columns, oocysts and microspheres advecting through the red volcanic soil were almost completely (98% and 99%) immobilized. The modest breakthrough resulted from preferential flow-path structure inadvertently created by soil-particle aggregation during the re-wetting process. Although a high (99%) removal of oocysts and microsphere within the volcanic ash soil occurred initially, further examination revealed that transport was merely retarded because of highly reversible interactions with grain surfaces. Judging from the slope of the substantive and protracted tail of the breakthrough curve for the 1.8-??m microspheres, almost all (>99%) predictably would be recovered within ~4000 pore volumes. This suggests that once contaminated, the volcanic ash soil could serve as a reservoir for subsequent contamination of groundwater, at least for pathogens of similar size or smaller. Because of the highly reversible nature of organic colloid immobilization in this soil type, C. parvum could contaminate surface water should overland flow during heavy precipitation events pick up near-surface grains to which they are attached. Surprisingly, oocyst and microsphere attachment to the reference soil from Illinois appeared to be at least as sensitive to changes in pH as was observed
Mohanram, Arvind; Ray, Chittaranjan; Harvey, Ronald W; Metge, David W; Ryan, Joseph N; Chorover, Jon; Eberl, D D
2010-10-01
In order to gain more information about the fate of Cryptosporidium parvum oocysts in tropical volcanic soils, the transport and attachment behaviors of oocysts and oocyst-sized polystyrene microspheres were studied in the presence of two soils. These soils were chosen because of their differing chemical and physical properties, i.e., an organic-rich (43-46% by mass) volcanic ash-derived soil from the island of Hawaii, and a red, iron (22-29% by mass), aluminum (29-45% by mass), and clay-rich (68-76% by mass) volcanic soil from the island of Oahu. A third agricultural soil, an organic- (13% by mass) and quartz-rich (40% by mass) soil from Illinois, was included for reference. In 10-cm long flow-through columns, oocysts and microspheres advecting through the red volcanic soil were almost completely (98% and 99%) immobilized. The modest breakthrough resulted from preferential flow-path structure inadvertently created by soil-particle aggregation during the re-wetting process. Although a high (99%) removal of oocysts and microsphere within the volcanic ash soil occurred initially, further examination revealed that transport was merely retarded because of highly reversible interactions with grain surfaces. Judging from the slope of the substantive and protracted tail of the breakthrough curve for the 1.8-μm microspheres, almost all (>99%) predictably would be recovered within ∼4000 pore volumes. This suggests that once contaminated, the volcanic ash soil could serve as a reservoir for subsequent contamination of groundwater, at least for pathogens of similar size or smaller. Because of the highly reversible nature of organic colloid immobilization in this soil type, C. parvum could contaminate surface water should overland flow during heavy precipitation events pick up near-surface grains to which they are attached. Surprisingly, oocyst and microsphere attachment to the reference soil from Illinois appeared to be at least as sensitive to changes in pH as was
Mobile transporter path planning using a genetic algorithm approach
NASA Technical Reports Server (NTRS)
Baffes, Paul; Wang, Lui
1988-01-01
The use of an optimization technique known as a genetic algorithm for solving the mobile transporter path planning problem is investigated. The mobile transporter is a traveling robotic vehicle proposed for the Space Station which must be able to reach any point of the structure autonomously. Specific elements of the genetic algorithm are explored in both a theoretical and experimental sense. Recent developments in genetic algorithm theory are shown to be particularly effective in a path planning problem domain, though problem areas can be cited which require more research. However, trajectory planning problems are common in space systems and the genetic algorithm provides an attractive alternative to the classical techniques used to solve these problems.
Mobile Transporter Path Planning Using A Genetic Algorithm Approach
NASA Astrophysics Data System (ADS)
Baffes, Paul; Wang, Lui
1988-10-01
The use of an optimization technique known as a genetic algorithm for solving the mobile transporter path planning problem is investigated. The mobile transporter is a traveling robotic vehicle proposed for the space station which must be able to reach any point of the structure autonomously. Specific elements of the genetic algorithm are explored in both a theoretical and experimental sense. Recent developments in genetic algorithm theory are shown to be particularly effective in a path planning problem domain, though problem areas can be cited which require more research. However, trajectory planning problems are common in space systems and the genetic algorithm provides an attractive alternative to the classical techniques used to solve these problems.
Improved metropolis light transport algorithm based on multiple importance sampling
NASA Astrophysics Data System (ADS)
He, Huaiqing; Yang, Jiaqian; Liu, Haohan
2015-12-01
Metropolis light transport was an unbiased and robust Monte Carlo method, which could efficiently reduce noise during rendering the realistic graphics to resolve the global illumination problem. The basic Metropolis light transport was improved by combining with multiple importance sampling, which better solved the large correlation and high variance between samples caused by the basic Metropolis light transport. The experiences manifested that the quality of images generated by improved algorithm was better compared with the basic Metropolis light transport in the same scenes settings.
Sharp, R.W. Jr.; Barton, R.T.
1981-01-21
A continuous rezoning procedure has been implemented in the computational cycle of a version of the HEMP two-dimensional, Lagrange, fluid dynamics code. The rezoning problem is divided into two steps. The first step requires the solving of ordinary Lagrange equations of motion; the second step consists of adding equipotential grid relaxation along with an advective remapping scheme.
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.
Monte Carlo Particle Transport: Algorithm and Performance Overview
Gentile, N; Procassini, R; Scott, H
2005-06-02
Monte Carlo methods are frequently used for neutron and radiation transport. These methods have several advantages, such as relative ease of programming and dealing with complex meshes. Disadvantages include long run times and statistical noise. Monte Carlo photon transport calculations also often suffer from inaccuracies in matter temperature due to the lack of implicitness. In this paper we discuss the Monte Carlo algorithm as it is applied to neutron and photon transport, detail the differences between neutron and photon Monte Carlo, and give an overview of the ways the numerical method has been modified to deal with issues that arise in photon Monte Carlo simulations.
An evolutionary algorithm for interval solid transportation problems.
Jiménez, F; Verdegay, J L
1999-01-01
The Solid Transportation Problem arises when bounds are given on three item properties. Usually, these properties are source, destination and mode of transport (conveyance), and may be given in an interval way. This paper deals with solid transportation problems in which the data in the constraint set are expressed in an interval form, i.e. when sources, destinations and conveyances have interval values instead of point values. An arbitrary linear or nonlinear objective function is also considered. To solve the problem, an Evolutionary Algorithm which extends and generalizes other approaches considering only point values, is proposed.
Karniadakis, George Em
2014-03-11
The main objective of this project is to develop new computational tools for uncertainty quantifica- tion (UQ) of systems governed by stochastic partial differential equations (SPDEs) with applications to advection-diffusion-reaction systems. We pursue two complementary approaches: (1) generalized polynomial chaos and its extensions and (2) a new theory on deriving PDF equations for systems subject to color noise. The focus of the current work is on high-dimensional systems involving tens or hundreds of uncertain parameters.
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
NASA Astrophysics Data System (ADS)
Zamani, K.; Bombardelli, F.
2011-12-01
Almost all natural phenomena on Earth are highly nonlinear. Even simplifications to the equations describing nature usually end up being nonlinear partial differential equations. Transport (ADR) equation is a pivotal equation in atmospheric sciences and water quality. This nonlinear equation needs to be solved numerically for practical purposes so academicians and engineers thoroughly rely on the assistance of numerical codes. Thus, numerical codes require verification before they are utilized for multiple applications in science and engineering. Model verification is a mathematical procedure whereby a numerical code is checked to assure the governing equation is properly solved as it is described in the design document. CFD verification is not a straightforward and well-defined course. Only a complete test suite can uncover all the limitations and bugs. Results are needed to be assessed to make a distinction between bug-induced-defect and innate limitation of a numerical scheme. As Roache (2009) said, numerical verification is a state-of-the-art procedure. Sometimes novel tricks work out. This study conveys the synopsis of the experiences we gained during a comprehensive verification process which was done for a transport solver. A test suite was designed including unit tests and algorithmic tests. Tests were layered in complexity in several dimensions from simple to complex. Acceptance criteria defined for the desirable capabilities of the transport code such as order of accuracy, mass conservation, handling stiff source term, spurious oscillation, and initial shape preservation. At the begining, mesh convergence study which is the main craft of the verification is performed. To that end, analytical solution of ADR equation gathered. Also a new solution was derived. In the more general cases, lack of analytical solution could be overcome through Richardson Extrapolation and Manufactured Solution. Then, two bugs which were concealed during the mesh convergence
Parallel radiation transport algorithms and associated architectural requirements
Morel, J. E.; Baker, R. S.; Warsa, J. S.
2004-01-01
The radiation transport equation is a seven-dimensional equation that can be extremely expensive to solve. In general, transport can be expected to completely dominate the memory and CPU time requirements for the ASCI codes. Both traditional iterative transport solution methods and modern Krylov-subspace solution methods require the inversion of a large number of block lower-diagonal matrices. While such inversions are easily done in serial, a high level of sophistication is needed for implementations on massively parallel platforms. Rectangular-mesh methods are well-established and generally quite efficient but unstructured-mesh methods remain a research topic. Nonetheless, considerable progress has been made in unstructured-mesh methods over the last several years. In general, the efficiency of transport solution algorithms are quite sensitive to communication latencies and bandwidth, but there are other significant considerations as well. Some new parallel algorithms have recently been defined that may be significantly better than existing methods for time-dependent problems, but will be significantly less effective for steady-state problems in some circumstances. Transport methods would benefit from a machine architecture with low latencies, high bandwidth, and on the order of one thousand very fast, large-memory processors, as opposed to an architecture that consists of a very large number of slower processors with less memory. In addition, a lightweight operating system is highly desirable.
Inverse transport calculations in optical imaging with subspace optimization algorithms
Ding, Tian Ren, Kui
2014-09-15
Inverse boundary value problems for the radiative transport equation play an important role in optics-based medical imaging techniques such as diffuse optical tomography (DOT) and fluorescence optical tomography (FOT). Despite the rapid progress in the mathematical theory and numerical computation of these inverse problems in recent years, developing robust and efficient reconstruction algorithms remains a challenging task and an active research topic. We propose here a robust reconstruction method that is based on subspace minimization techniques. The method splits the unknown transport solution (or a functional of it) into low-frequency and high-frequency components, and uses singular value decomposition to analytically recover part of low-frequency information. Minimization is then applied to recover part of the high-frequency components of the unknowns. We present some numerical simulations with synthetic data to demonstrate the performance of the proposed algorithm.
An Improved Neutron Transport Algorithm for Space Radiation
NASA Technical Reports Server (NTRS)
Heinbockel, John H.; Clowdsley, Martha S.; Wilson, John W.
2000-01-01
A low-energy neutron transport algorithm for use in space radiation protection is developed. The algorithm is based upon a multigroup analysis of the straight-ahead Boltzmann equation by using a mean value theorem for integrals. This analysis is accomplished by solving a realistic but simplified neutron transport test problem. The test problem is analyzed by using numerical and analytical procedures to obtain an accurate solution within specified error bounds. Results from the test problem are then used for determining mean values associated with rescattering terms that are associated with a multigroup solution of the straight-ahead Boltzmann equation. The algorithm is then coupled to the Langley HZETRN code through the evaporation source term. Evaluation of the neutron fluence generated by the solar particle event of February 23, 1956, for a water and an aluminum-water shield-target configuration is then compared with LAHET and MCNPX Monte Carlo code calculations for the same shield-target configuration. The algorithm developed showed a great improvement in results over the unmodified HZETRN solution. In addition, a two-directional solution of the evaporation source showed even further improvement of the fluence near the front of the water target where diffusion from the front surface is important.
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
NASA Astrophysics Data System (ADS)
Moltyaner, G. L.
1993-10-01
In situ sensing technology, used in a series of natural-gradient tracer tests at the Chalk River Laboratories in Ontario, leads to the introduction of a conceptually new approach to the study of groundwater motion in porous media. As opposed to the conventional approach, based on the consideration of a fictitious fluid continuum with fluid properties distributed over both voids and solids, in the new approach the actual groundwater motion in the void space of a porous medium is considered and described at the local scale by the statistical characterization of the propagation of gamma-radiation energy associated with the moving water as a tracer. The essential feature of the new approach is that the mean free path of a gamma-energy photon instead of the porosity is used as a scaling factor in transferring information associated with pore-scale fluid motion to the local scale. This scaling factor is employed for reintroducing the familiar particle model of fluid motion but at the local scale. It is shown that when the local-scale dispersion is neglected, the evolution of local-scale fluid particles making up the tracer plume can be described by the advection equation; its equation of characteristics describes trajectories of local-scale particles. A simple analytical solution to the advection equation is then used to produce three-dimensional images of the spatial distribution of local-scale particles observed in the Twin Lake test. It is also shown that the spatial averaging procedure with regard to the weighting function for a spherical averaging volume of one mean free path radius may be used to introduce the three-dimensional field of local-scale concentration. The averaging procedure is then used to illustrate that the concept of the three-dimensional field of plume-scale concentration does not make physical sense and only the one-dimensional plume-scale concentration field may be introduced in shallow aquifers.
An Algorithm for the Mixed Transportation Network Design Problem.
Liu, Xinyu; Chen, Qun
2016-01-01
This paper proposes an optimization algorithm, the dimension-down iterative algorithm (DDIA), for solving a mixed transportation network design problem (MNDP), which is generally expressed as a mathematical programming with equilibrium constraint (MPEC). The upper level of the MNDP aims to optimize the network performance via both the expansion of the existing links and the addition of new candidate links, whereas the lower level is a traditional Wardrop user equilibrium (UE) problem. The idea of the proposed solution algorithm (DDIA) is to reduce the dimensions of the problem. A group of variables (discrete/continuous) is fixed to optimize another group of variables (continuous/discrete) alternately; then, the problem is transformed into solving a series of CNDPs (continuous network design problems) and DNDPs (discrete network design problems) repeatedly until the problem converges to the optimal solution. The advantage of the proposed algorithm is that its solution process is very simple and easy to apply. Numerical examples show that for the MNDP without budget constraint, the optimal solution can be found within a few iterations with DDIA. For the MNDP with budget constraint, however, the result depends on the selection of initial values, which leads to different optimal solutions (i.e., different local optimal solutions). Some thoughts are given on how to derive meaningful initial values, such as by considering the budgets of new and reconstruction projects separately.
An Algorithm for the Mixed Transportation Network Design Problem
Liu, Xinyu; Chen, Qun
2016-01-01
This paper proposes an optimization algorithm, the dimension-down iterative algorithm (DDIA), for solving a mixed transportation network design problem (MNDP), which is generally expressed as a mathematical programming with equilibrium constraint (MPEC). The upper level of the MNDP aims to optimize the network performance via both the expansion of the existing links and the addition of new candidate links, whereas the lower level is a traditional Wardrop user equilibrium (UE) problem. The idea of the proposed solution algorithm (DDIA) is to reduce the dimensions of the problem. A group of variables (discrete/continuous) is fixed to optimize another group of variables (continuous/discrete) alternately; then, the problem is transformed into solving a series of CNDPs (continuous network design problems) and DNDPs (discrete network design problems) repeatedly until the problem converges to the optimal solution. The advantage of the proposed algorithm is that its solution process is very simple and easy to apply. Numerical examples show that for the MNDP without budget constraint, the optimal solution can be found within a few iterations with DDIA. For the MNDP with budget constraint, however, the result depends on the selection of initial values, which leads to different optimal solutions (i.e., different local optimal solutions). Some thoughts are given on how to derive meaningful initial values, such as by considering the budgets of new and reconstruction projects separately. PMID:27626803
An Algorithm for the Mixed Transportation Network Design Problem.
Liu, Xinyu; Chen, Qun
2016-01-01
This paper proposes an optimization algorithm, the dimension-down iterative algorithm (DDIA), for solving a mixed transportation network design problem (MNDP), which is generally expressed as a mathematical programming with equilibrium constraint (MPEC). The upper level of the MNDP aims to optimize the network performance via both the expansion of the existing links and the addition of new candidate links, whereas the lower level is a traditional Wardrop user equilibrium (UE) problem. The idea of the proposed solution algorithm (DDIA) is to reduce the dimensions of the problem. A group of variables (discrete/continuous) is fixed to optimize another group of variables (continuous/discrete) alternately; then, the problem is transformed into solving a series of CNDPs (continuous network design problems) and DNDPs (discrete network design problems) repeatedly until the problem converges to the optimal solution. The advantage of the proposed algorithm is that its solution process is very simple and easy to apply. Numerical examples show that for the MNDP without budget constraint, the optimal solution can be found within a few iterations with DDIA. For the MNDP with budget constraint, however, the result depends on the selection of initial values, which leads to different optimal solutions (i.e., different local optimal solutions). Some thoughts are given on how to derive meaningful initial values, such as by considering the budgets of new and reconstruction projects separately. PMID:27626803
Pangolin v1.0, a conservative 2-D advection model towards large-scale parallel calculation
NASA Astrophysics Data System (ADS)
Praga, A.; Cariolle, D.; Giraud, L.
2015-02-01
To exploit the possibilities of parallel computers, we designed a large-scale bidimensional atmospheric advection model named Pangolin. As the basis for a future chemistry-transport model, a finite-volume approach for advection was chosen to ensure mass preservation and to ease parallelization. To overcome the pole restriction on time steps for a regular latitude-longitude grid, Pangolin uses a quasi-area-preserving reduced latitude-longitude grid. The features of the regular grid are exploited to reduce the memory footprint and enable effective parallel performances. In addition, a custom domain decomposition algorithm is presented. To assess the validity of the advection scheme, its results are compared with state-of-the-art models on algebraic test cases. Finally, parallel performances are shown in terms of strong scaling and confirm the efficient scalability up to a few hundred cores.
A generic algorithm for Monte Carlo simulation of proton transport
NASA Astrophysics Data System (ADS)
Salvat, Francesc
2013-12-01
A mixed (class II) algorithm for Monte Carlo simulation of the transport of protons, and other heavy charged particles, in matter is presented. The emphasis is on the electromagnetic interactions (elastic and inelastic collisions) which are simulated using strategies similar to those employed in the electron-photon code PENELOPE. Elastic collisions are described in terms of numerical differential cross sections (DCSs) in the center-of-mass frame, calculated from the eikonal approximation with the Dirac-Hartree-Fock-Slater atomic potential. The polar scattering angle is sampled by employing an adaptive numerical algorithm which allows control of interpolation errors. The energy transferred to the recoiling target atoms (nuclear stopping) is consistently described by transformation to the laboratory frame. Inelastic collisions are simulated from DCSs based on the plane-wave Born approximation (PWBA), making use of the Sternheimer-Liljequist model of the generalized oscillator strength, with parameters adjusted to reproduce (1) the electronic stopping power read from the input file, and (2) the total cross sections for impact ionization of inner subshells. The latter were calculated from the PWBA including screening and Coulomb corrections. This approach provides quite a realistic description of the energy-loss distribution in single collisions, and of the emission of X-rays induced by proton impact. The simulation algorithm can be readily modified to include nuclear reactions, when the corresponding cross sections and emission probabilities are available, and bremsstrahlung emission.
On the tensorial nature of advective porosity
NASA Astrophysics Data System (ADS)
Neuman, Shlomo P.
2005-02-01
Field tracer tests indicate that advective porosity, the quantity relating advective velocity to Darcy flux, may exhibit directional dependence. Hydraulic anisotropy explains some but not all of the reported directional results. The present paper shows mathematically that directional variations in advective porosity may arise simply from incomplete mixing of an inert tracer between directional flow channels within a sampling (or support) volume ω of soil or rock that may be hydraulically isotropic or anisotropic. In the traditional fully homogenized case, our theory yields trivially a scalar advective porosity equal to the interconnected porosity ϕ, thus explaining neither the observed directional effects nor the widely reported experimental finding that advective porosity is generally smaller than ϕ. We consider incomplete mixing under conditions in which the characteristic time tD of longitudinal diffusion along channels across ω is much shorter than the characteristic time tH required for homogenization through transverse diffusion between channels. This may happen where flow takes place preferentially through relatively conductive channels and/or fractures of variable orientation separated by material that forms a partial barrier to diffusive transport. Our solution is valid for arbitrary channel Peclet numbers on a correspondingly wide range of time scales tD ⩽ t ≪ tH. It shows that the tracer center of mass is advected at a macroscopic velocity which is generally not collinear with the macroscopic Darcy flux and exceeds it in magnitude. These two vectors are related through a second-rank symmetric advective dispersivity tensor Φ. If the permeability k of ω is a symmetric positive-definite tensor, so is Φ. However, the principal directions and values of these two tensors are generally not the same; whereas those of k are a fixed property of the medium and the length-scale of ω, those of Φ depend additionally on the direction and magnitude of the
Parker, Jack C; Kim, Ungtae
2015-11-01
The mono-continuum advection-dispersion equation (mADE) is commonly regarded as unsuitable for application to media that exhibit rapid breakthrough and extended tailing associated with diffusion between high and low permeability regions. This paper demonstrates that the mADE can be successfully used to model such conditions if certain issues are addressed. First, since hydrodynamic dispersion, unlike molecular diffusion, cannot occur upstream of the contaminant source, models must be formulated to prevent "back-dispersion." Second, large variations in aquifer permeability will result in differences between volume-weighted average concentration (resident concentration) and flow-weighted average concentration (flux concentration). Water samples taken from wells may be regarded as flux concentrations, while soil samples may be analyzed to determine resident concentrations. While the mADE is usually derived in terms of resident concentration, it is known that a mADE of the same mathematical form may be written in terms of flux concentration. However, when solving the latter, the mathematical transformation of a flux boundary condition applied to the resident mADE becomes a concentration type boundary condition for the flux mADE. Initial conditions must also be consistent with the form of the mADE that is to be solved. Thus, careful attention must be given to the type of concentration data that is available, whether resident or flux concentrations are to be simulated, and to boundary and initial conditions. We present 3-D analytical solutions for resident and flux concentrations, discuss methods of solving numerical models to obtain resident and flux concentrations, and compare results for hypothetical problems. We also present an upscaling method for computing "effective" dispersivities and other mADE model parameters in terms of physically meaningful parameters in a diffusion-limited mobile-immobile model. Application of the latter to previously published studies of
Parker, Jack C; Kim, Ungtae
2015-11-01
The mono-continuum advection-dispersion equation (mADE) is commonly regarded as unsuitable for application to media that exhibit rapid breakthrough and extended tailing associated with diffusion between high and low permeability regions. This paper demonstrates that the mADE can be successfully used to model such conditions if certain issues are addressed. First, since hydrodynamic dispersion, unlike molecular diffusion, cannot occur upstream of the contaminant source, models must be formulated to prevent "back-dispersion." Second, large variations in aquifer permeability will result in differences between volume-weighted average concentration (resident concentration) and flow-weighted average concentration (flux concentration). Water samples taken from wells may be regarded as flux concentrations, while soil samples may be analyzed to determine resident concentrations. While the mADE is usually derived in terms of resident concentration, it is known that a mADE of the same mathematical form may be written in terms of flux concentration. However, when solving the latter, the mathematical transformation of a flux boundary condition applied to the resident mADE becomes a concentration type boundary condition for the flux mADE. Initial conditions must also be consistent with the form of the mADE that is to be solved. Thus, careful attention must be given to the type of concentration data that is available, whether resident or flux concentrations are to be simulated, and to boundary and initial conditions. We present 3-D analytical solutions for resident and flux concentrations, discuss methods of solving numerical models to obtain resident and flux concentrations, and compare results for hypothetical problems. We also present an upscaling method for computing "effective" dispersivities and other mADE model parameters in terms of physically meaningful parameters in a diffusion-limited mobile-immobile model. Application of the latter to previously published studies of
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 Technical Reports Server (NTRS)
Pawson, S.; Nielsen, Jon E.; Oman, L.; Douglass, A. R.; Duncan, B. N.; Zhu, Z.
2012-01-01
Convective transport is one of the dominant factors in determining the composition of the troposphere. It is the main mechanism for lofting constituents from near-surface source regions to the middle and upper troposphere, where they can subsequently be advected over large distances. Gases reaching the upper troposphere can also be injected through the tropopause and play a subsequent role in the lower stratospheric ozone balance. Convection codes in climate models remain a great source of uncertainty for both the energy balance of the general circulation and the transport of constituents. This study uses the Goddard Earth Observing System Chemistry-Climate Model (GEOS CCM) to perform a controlled experiment that isolates the impact of convective transport of constituents from the direct changes on the atmospheric energy balance. Two multi-year simulations are conducted. In the first, the thermodynamic variable, moisture, and all trace gases are transported using the multi-plume Relaxed-Arakawa-Schubert (RAS) convective parameterization. In the second simulation, RAS impacts the thermodynamic energy and moisture in this standard manner, but all other constituents are transported differently. The accumulated convective mass fluxes (including entrainment and detrainment) computed at each time step of the GCM are used with a diffusive (bulk) algorithm for the vertical transport, which above all is less efficient at transporting constituents from the lower to the upper troposphere. Initial results show the expected differences in vertical structure of trace gases such as carbon monoxide, but also show differences in lower stratospheric ozone, in a region where it can potentially impact the climate state of the model. This work will investigate in more detail the impact of convective transport changes by comparing the two simulations over many years (1996-2010), focusing on comparisons with observed constituent distributions and similarities and differences of patterns
NASA Astrophysics Data System (ADS)
Pawson, S.; Nielsen, J. E.; Oman, L.; Douglass, A. R.; Duncan, B. N.; Zhu, Z.
2012-12-01
Convective transport is one of the dominant factors in determining the composition of the troposphere. It is the main mechanism for lofting constituents from near-surface source regions to the middle and upper troposphere, where they can subsequently be advected over large distances. Gases reaching the upper troposphere can also be injected through the tropopause and play a subsequent role in the lower stratospheric ozone balance. Convection codes in climate models remain a great source of uncertainty for both the energy balance of the general circulation and the transport of constituents. This study uses the Goddard Earth Observing System Chemistry-Climate Model (GEOS CCM) to perform a controlled experiment that isolates the impact of convective transport of constituents from the direct changes on the atmospheric energy balance. Two multi-year simulations are conducted. In the first, the thermodynamic variable, moisture, and all trace gases are transported using the multi-plume "Relaxed-Arakawa-Schubert" (RAS) convective parameterization. In the second simulation, RAS impacts the thermodynamic energy and moisture in this standard manner, but all other constituents are transported differently. The accumulated convective mass fluxes (including entrainment and detrainment) computed at each time step of the GCM are used with a diffusive (bulk) algorithm for the vertical transport, which above all is less efficient at transporting constituents from the lower to the upper troposphere. Initial results show the expected differences in vertical structure of trace gases such as carbon monoxide, but also show differences in lower stratospheric ozone, in a region where it can potentially impact the climate state of the model. This work will investigate in more detail the impact of convective transport changes by comparing the two simulations over many years (1996-2010), focusing on comparisons with observed constituent distributions and similarities and differences of
An Improved Neutron Transport Algorithm for HZETRN2006
NASA Astrophysics Data System (ADS)
Slaba, Tony
NASA's new space exploration initiative includes plans for long term human presence in space thereby placing new emphasis on space radiation analyses. In particular, a systematic effort of verification, validation and uncertainty quantification of the tools commonly used for radiation analysis for vehicle design and mission planning has begun. In this paper, the numerical error associated with energy discretization in HZETRN2006 is addressed; large errors in the low-energy portion of the neutron fluence spectrum are produced due to a numerical truncation error in the transport algorithm. It is shown that the truncation error results from the narrow energy domain of the neutron elastic spectral distributions, and that an extremely fine energy grid is required in order to adequately resolve the problem under the current formulation. Since adding a sufficient number of energy points will render the code computationally inefficient, we revisit the light-ion transport theory developed for HZETRN2006 and focus on neutron elastic interactions. The new approach that is developed numerically integrates with adequate resolution in the energy domain without affecting the run-time of the code and is easily incorporated into the current code. Efforts were also made to optimize the computational efficiency of the light-ion propagator; a brief discussion of the efforts is given along with run-time comparisons between the original and updated codes. Convergence testing is then completed by running the code for various environments and shielding materials with many different energy grids to ensure stability of the proposed method.
Dynamic airspace configuration algorithms for next generation air transportation system
NASA Astrophysics Data System (ADS)
Wei, Jian
The National Airspace System (NAS) is under great pressure to safely and efficiently handle the record-high air traffic volume nowadays, and will face even greater challenge to keep pace with the steady increase of future air travel demand, since the air travel demand is projected to increase to two to three times the current level by 2025. The inefficiency of traffic flow management initiatives causes severe airspace congestion and frequent flight delays, which cost billions of economic losses every year. To address the increasingly severe airspace congestion and delays, the Next Generation Air Transportation System (NextGen) is proposed to transform the current static and rigid radar based system to a dynamic and flexible satellite based system. New operational concepts such as Dynamic Airspace Configuration (DAC) have been under development to allow more flexibility required to mitigate the demand-capacity imbalances in order to increase the throughput of the entire NAS. In this dissertation, we address the DAC problem in the en route and terminal airspace under the framework of NextGen. We develop a series of algorithms to facilitate the implementation of innovative concepts relevant with DAC in both the en route and terminal airspace. We also develop a performance evaluation framework for comprehensive benefit analyses on different aspects of future sector design algorithms. First, we complete a graph based sectorization algorithm for DAC in the en route airspace, which models the underlying air route network with a weighted graph, converts the sectorization problem into the graph partition problem, partitions the weighted graph with an iterative spectral bipartition method, and constructs the sectors from the partitioned graph. The algorithm uses a graph model to accurately capture the complex traffic patterns of the real flights, and generates sectors with high efficiency while evenly distributing the workload among the generated sectors. We further improve
NASA Technical Reports Server (NTRS)
Kritz, Mark A.; Le Roulley, Jean-Claude; Danielsen, Edwin F.
1990-01-01
A series of upper tropospheric radon concentration measurements made over the eastern Pacific and west coast of the U.S. during the summers of 1983 and 1984 has revealed the occurrence of unexpectedly high radon concentrations for 9 of the 61 measurements. A frequency distribution plot of the set of 61 observations shows a distinct bimodal distribution, with approximately 2/5 of the observations falling close to 1 pCi/SCM, and 3/5 falling in a high concentration mode centered at about 11 pCi/SCM. Trajectory and synoptic analyses for two of the flights on which such high radon concentrations were observed indicate that this radon-rich air originated in the Asian boundary layer, ascended in cumulus updrafts, and was carried eastward in the fast moving air on the anticyclonic side of the upper tropospheric jet. The results suggest that the combination of rapid vertical transport from the surface boundary layer to the upper troposphere, followed by rapid horizontal transport eastward represents an efficient mode of long-transport for other, chemically reactive atmospheric trace constituents.
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.
Algorithm for Public Electric Transport Schedule Control for Intelligent Embedded Devices
NASA Astrophysics Data System (ADS)
Alps, Ivars; Potapov, Andrey; Gorobetz, Mikhail; Levchenkov, Anatoly
2010-01-01
In this paper authors present heuristics algorithm for precise schedule fulfilment in city traffic conditions taking in account traffic lights. The algorithm is proposed for programmable controller. PLC is proposed to be installed in electric vehicle to control its motion speed and signals of traffic lights. Algorithm is tested using real controller connected to virtual devices and real functional models of real tram devices. Results of experiments show high precision of public transport schedule fulfilment using proposed algorithm.
An amoeboid algorithm for solving linear transportation problem
NASA Astrophysics Data System (ADS)
Gao, Cai; Yan, Chao; Zhang, Zili; Hu, Yong; Mahadevan, Sankaran; Deng, Yong
2014-03-01
Transportation Problem (TP) is one of the basic operational research problems, which plays an important role in many practical applications. In this paper, a bio-inspired mathematical model is proposed to handle the Linear Transportation Problem (LTP) in directed networks by modifying the original amoeba model Physarum Solver. Several examples are used to prove that the provided model can effectively solve Balanced Transportation Problem (BTP), Unbalanced Transportation Problem (UTP), especially the Generalized Transportation Problem (GTP), in a nondiscrete way.
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.
Concentration polarization, surface currents, and bulk advection in a microchannel.
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. PMID:25375606
EBS Radionuclide Transport Abstraction
J. Prouty
2006-07-14
The purpose of this report is to develop and analyze the engineered barrier system (EBS) radionuclide transport abstraction model, consistent with Level I and Level II model validation, as identified in Technical Work Plan for: Near-Field Environment and Transport: Engineered Barrier System: Radionuclide Transport Abstraction Model Report Integration (BSC 2005 [DIRS 173617]). The EBS radionuclide transport abstraction (or EBS RT Abstraction) is the conceptual model used in the total system performance assessment (TSPA) to determine the rate of radionuclide releases from the EBS to the unsaturated zone (UZ). The EBS RT Abstraction conceptual model consists of two main components: a flow model and a transport model. Both models are developed mathematically from first principles in order to show explicitly what assumptions, simplifications, and approximations are incorporated into the models used in the TSPA. The flow model defines the pathways for water flow in the EBS and specifies how the flow rate is computed in each pathway. Input to this model includes the seepage flux into a drift. The seepage flux is potentially split by the drip shield, with some (or all) of the flux being diverted by the drip shield and some passing through breaches in the drip shield that might result from corrosion or seismic damage. The flux through drip shield breaches is potentially split by the waste package, with some (or all) of the flux being diverted by the waste package and some passing through waste package breaches that might result from corrosion or seismic damage. Neither the drip shield nor the waste package survives an igneous intrusion, so the flux splitting submodel is not used in the igneous scenario class. The flow model is validated in an independent model validation technical review. The drip shield and waste package flux splitting algorithms are developed and validated using experimental data. The transport model considers advective transport and diffusive transport
A positive finite-difference advection scheme
Hundsdorfer, W.; Koren, B.; Loon, M. van
1995-03-01
This paper examines a class of explicit finite-difference advection schemes derived along the method of lines. An important application field is large-scale atmospheric transport. The paper therefore focuses on the demand of positivity. For the spatial discretization, attention is confined to conservative schemes using five points per direction. The fourth-order central scheme and the family of {kappa}-schemes, comprising the second-order central, the second-order upwind, and the third-order upwind biased, are studied. Positivity is enforced through flux limiting. It is concluded that the limited third-order upwind discretization is the best candidate from the four examined. For the time integration attention is confined to a number of explicit Runge-Kutta methods of orders two to four. With regard to the demand of positivity, these integration methods turn out to behave almost equally and no best method could be identified. 16 refs., 4 figs., 4 tabs.
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.
Algorithm for resistance to flow and transport in sand-bed channels
Bennett, J.P.
1995-01-01
An algorithm is developed that relates depth to discharge and determines bed- and suspended-load transport for the entire range of bed forms found in sand-bed channels; equilibrium-state geometry of lower flow regime bedforms is also predicted. A Meyer-Peter-type formulation is used to compute sand transport in the bed-load layer and for computing suspended sand transport, McLean's procedure is adopted. A bed-form classifcation scheme is developed. The algorithm produces overall geometric averages of predicted to observed depth and predicted to observed transport of 1.00. For a verification data set of 855 observations, mostly from rivers and canals, the overall geometric averages of predicted to observed depth and transport are 0.87 and 1.14. -from Author
Palanichamy, Jegathambal; Schüttrumpf, Holger; Köngeter, Jürgen; Becker, Torsten; Palani, Sundarambal
2009-01-01
The migration of the species of chromium and ammonium in groundwater and their effective remediation depend on the various hydro-geological characteristics of the system. The computational modeling of the reactive transport problems is one of the most preferred tools for field engineers in groundwater studies to make decision in pollution abatement. The analytical models are less modular in nature with low computational demand where the modification is difficult during the formulation of different reactive systems. Numerical models provide more detailed information with high computational demand. Coupling of linear partial differential Equations (PDE) for the transport step with a non-linear system of ordinary differential equations (ODE) for the reactive step is the usual mode of solving a kinetically controlled reactive transport equation. This assumption is not appropriate for a system with low concentration of species such as chromium. Such reaction systems can be simulated using a stochastic algorithm. In this paper, a finite difference scheme coupled with a stochastic algorithm for the simulation of the transport of ammonium and chromium in subsurface media has been detailed.
NASA Astrophysics Data System (ADS)
Yin, Y.; Sykes, J. F.
2006-12-01
Transport parameter estimation and contaminant source identification are critical steps in the development of a physically based groundwater contaminant transport model. For most transient field scale problems, the high computational burden required by parameter identification algorithms combined with sparse data sets often limits calibration. However, when data are available, a high performance computing system and parallel computing may make the calibration process feasible. The selection of the optimization algorithm is also critical. In this paper, the contaminant transport and source parameters were estimated and compared using optimization with two heuristic search algorithms (a dynamically dimensioned search and a parallelized micro genetic algorithm) and a gradient based multi-start PEST algorithm which were implemented on the Shared Hierarchical Academic Research Computing Network (Sharcnet). The case study is located in New Jersey where improper waste disposal resulted in the contamination of down gradient public water supply wells. Using FRAC3DVS, a physically based transient three-dimensional groundwater flow model with spatially and temporally varying recharge was developed and calibrated using both approximately 9 years of head data from continuous well records and data over a period of approximately 30 years from traditional monitoring wells. For the contaminant system, the parameters that were estimated include source leaching rate, source concentration, dispersivities, and retardation coefficient. The groundwater domain was discretized using 214,520 elements. With highly changing pump rates at the 7 municipal wells, time increments over the approximately 30 year simulation period varied dynamically between several days and 3 months. On Sharcnet, one forward simulation on a single processor of both transient flow and contaminant transport takes approximately 3 to 4 hours. The contaminant transport model calibration results indicate that overall
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...
Advective coalescence in chaotic flows.
Nishikawa, T; Toroczkai, Z; Grebogi, C
2001-07-16
We investigate the reaction kinetics of small spherical particles with inertia, obeying coalescence type of reaction, B+B-->B, and being advected by hydrodynamical flows with time-periodic forcing. In contrast to passive tracers, the particle dynamics is governed by the strongly nonlinear Maxey-Riley equations, which typically create chaos in the spatial component of the particle dynamics, appearing as filamental structures in the distribution of the reactants. Defining a stochastic description supported on the natural measure of the attractor, we show that, in the limit of slow reaction, the reaction kinetics assumes a universal behavior exhibiting a t(-1) decay in the amount of reagents, which become distributed on a subset of dimension D2, where D2 is the correlation dimension of the chaotic flow. PMID:11461595
Chaotic advection of immiscible fluids
NASA Astrophysics Data System (ADS)
Vollmayr-Lee, Benjamin; Beller, Daniel; Yasuda, Sohei
2012-02-01
We consider a system of two immiscible fluids advected by a chaotic flow field. A nonequilibrium steady state arises from the competition between the coarsening of the immiscible fluids and the domain bursting caused by the chaotic flow. It has been established that the average domain size in this steady state scales as a inverse power of the Lyapunov exponent. We examine the issue of local structure and look for correlations between the local domain size and the finite-time Lyapunov exponent (FTLE) field. For a variety of chaotic flows, we consistently find the domains to be smallest in regions where the FTLE field is maximal. This raises the possibility of making universal predictions of steady-state characteristics based on Lyapunov analysis of the flow field.
Tomography-based monitoring of isothermal snow metamorphism under advective conditions
NASA Astrophysics Data System (ADS)
Ebner, P. P.; Schneebeli, M.; Steinfeld, A.
2015-02-01
Time-lapse X-ray micro-tomography was used to investigate the structural dynamics of isothermal snow metamorphism exposed to an advective airflow. Diffusion and advection across the snow pores were analysed in controlled laboratory experiments. The 3-D digital geometry obtained by tomographic scans was used in direct pore-level numerical simulations to determine the effective transport properties. The results showed that isothermal advection with saturated air have no influence on the coarsening rate that is typical for isothermal snow metamorphism. Diffusion originating in the Kelvin effect between snow structures dominates and is the main transport process in isothermal snow packs.
James, Andrew I.; Jawitz, James W.; Munoz-Carpena, Rafael
2009-01-01
A model to simulate transport of materials in surface water and ground water has been developed to numerically approximate solutions to the advection-dispersion equation. This model, known as the Transport and Reaction Simulation Engine (TaRSE), uses an algorithm that incorporates a time-splitting technique where the advective part of the equation is solved separately from the dispersive part. An explicit finite-volume Godunov method is used to approximate the advective part, while a mixed-finite element technique is used to approximate the dispersive part. The dispersive part uses an implicit discretization, which allows it to run stably with a larger time step than the explicit advective step. The potential exists to develop algorithms that run several advective steps, and then one dispersive step that encompasses the time interval of the advective steps. Because the dispersive step is computationally most expensive, schemes can be implemented that are more computationally efficient than non-time-split algorithms. This technique enables scientists to solve problems with high grid Peclet numbers, such as transport problems with sharp solute fronts, without spurious oscillations in the numerical approximation to the solution and with virtually no artificial diffusion.
Analysis of Massively Parallel Discrete-Ordinates Transport Sweep Algorithms with Collisions
Bailey, T S; Falgout, R D
2008-10-14
We present theoretical scaling models for a variety of discrete-ordinates sweep algorithms. In these models, we pay particular attention to the way each algorithm handles collisions. A collision is defined as a processor having multiple angles with ready to be swept during one stage of the sweep. The models also take into account how subdomains are assigned to processors and how angles are grouped during the sweep. We describe a data driven algorithm that resolves collisions efficiently during the sweep as well as other algorithms that have been designed to avoid collisions completely. Our models are validated using the ARGES and AMTRAN transport codes. We then use the models to study and predict scaling trends in all of the sweep algorithms.
An Algorithm for the Transport of Anisotropic Neutrons
NASA Technical Reports Server (NTRS)
Tweed, J.
2005-01-01
One major obstacle to human space exploration is the possible limitations imposed by the adverse effect of long-term exposure to the space environment. Even before human spaceflight began, the potentially brief exposure of astronauts to the very intense random solar particle events (SPE) were of great concern. A new challenge appears in deep space exploration from exposure to the low-intensity heavy-ion flux of the galactic cosmic rays (GCR) since the missions are of long duration and the accumulated GCR exposures can be high. Because cancer induction rates increase behind low to rather large thicknesses of aluminum shielding, according to available biological data on mammalian exposures to GCR like ions, the shield requirements for a Mars mission are prohibitively expensive in terms of mission launch costs. Therefore, a critical issue in the Human Exploration and Development of Space enterprise is cost effective mitigation of risk associated with ionizing radiation exposure. In order to estimate astronaut risk to GCR exposure and associated cancer risks and health hazards, it is necessary to do shield material studies. To determine an optimum radiation shield material it is necessary to understand nuclear interaction processes such as fragmentation and secondary particle production which is a function of energy dependent cross sections. This requires knowledge of material transmission characteristics either through laboratory testing or improved theoretical modeling. Here ion beam transport theory is of importance in that testing of materials in the laboratory environment generated by particle accelerators is a necessary step in materials development and evaluation for space use. The approximations used in solving the Boltzmann transport equation for the space setting are often not sufficient for laboratory work and those issues are a major emphasis of the present work.
Algorithm and data support of traffic congestion forecasting in the controlled transport
NASA Astrophysics Data System (ADS)
Dmitriev, S. V.
2015-06-01
The topicality of problem of the traffic congestion forecasting in the logistic systems of product movement highways is considered. The concepts: the controlled territory, the highway occupancy by vehicles, the parking and the controlled territory are introduced. Technical realizabilityof organizing the necessary flow of information on the state of the transport system for its regulation has been marked. Sequence of practical implementation of the solution is given. An algorithm for predicting traffic congestion in the controlled transport system is suggested.
Parallel algorithms for 2-D cylindrical transport equations of Eigenvalue problem
Wei, J.; Yang, S.
2013-07-01
In this paper, aimed at the neutron transport equations of eigenvalue problem under 2-D cylindrical geometry on unstructured grid, the discrete scheme of Sn discrete ordinate and discontinuous finite is built, and the parallel computation for the scheme is realized on MPI systems. Numerical experiments indicate that the designed parallel algorithm can reach perfect speedup, it has good practicality and scalability. (authors)
Berkolaiko, G.; Kuipers, J.
2013-12-15
Electronic transport through chaotic quantum dots exhibits universal behaviour which can be understood through the semiclassical approximation. Within the approximation, calculation of transport moments reduces to codifying classical correlations between scattering trajectories. These can be represented as ribbon graphs and we develop an algorithmic combinatorial method to generate all such graphs with a given genus. This provides an expansion of the linear transport moments for systems both with and without time reversal symmetry. The computational implementation is then able to progress several orders further than previous semiclassical formulae as well as those derived from an asymptotic expansion of random matrix results. The patterns observed also suggest a general form for the higher orders.
Numerical experiments for advection equation
Sun, Wen-Yih )
1993-10-01
We propose to combine the Crowley fourth-order scheme and the Gadd scheme for solving the linear advection equation. Two new schemes will be presented: the first is to integrate the Crowley scheme and the Gadd scheme alternately (referred to as New1); the second is to integrate the Crowley scheme twice before we apply the Gadd scheme once (referred to as New2). The new schemes are designed such that no additional restriction is placed on the CFL criterion in an integration. The performance of the new schemes is better than that of the original Crowley or Gadd schemes. It is noted that the amplitude obtained from New2 is more accurate than that from New1 for long waves, but less accurate for short waves. The phase speed calculated from New2 is very close to the real phase speed in most cases tested here, but the phase speed of New 1 is faster than the real phase speed. Hence, New2 is a better choice, especially for a model that includes horizontal smoothing to dampen the short waves. 9 refs., 5 figs., 8 tabs.
Chacon, Luis; del-Castillo-Negrete, Diego; Hauck, Cory D.
2014-09-01
We propose a Lagrangian numerical algorithm for a time-dependent, anisotropic temperature transport equation in magnetized plasmas in the large guide field regime. The approach is based on an analytical integral formal solution of the parallel (i.e., along the magnetic field) transport equation with sources, and it is able to accommodate both local and non-local parallel heat flux closures. The numerical implementation is based on an operator-split formulation, with two straightforward steps: a perpendicular transport step (including sources), and a Lagrangian (field-line integral) parallel transport step. Algorithmically, the first step is amenable to the use of modern iterative methods, while the second step has a fixed cost per degree of freedom (and is therefore scalable). Accuracy-wise, the approach is free from the numerical pollution introduced by the discrete parallel transport term when the perpendicular to parallel transport coefficient ratio X_{⊥} /X_{∥} becomes arbitrarily small, and is shown to capture the correct limiting solution when ε = X⊥L^{2}_{∥}/X1L^{2}_{⊥} → 0 (with L∥∙ L⊥ , the parallel and perpendicular diffusion length scales, respectively). Therefore, the approach is asymptotic-preserving. We demonstrate the capabilities of the scheme with several numerical experiments with varying magnetic field complexity in two dimensions, including the case of transport across a magnetic island.
Sensitivity of CO2 Simulation in a GCM to the Convective Transport Algorithms
NASA Technical Reports Server (NTRS)
Zhu, Z.; Pawson, S.; Collatz, G. J.; Gregg, W. W.; Kawa, S. R.; Baker, D.; Ott, L.
2014-01-01
Convection plays an important role in the transport of heat, moisture and trace gases. In this study, we simulated CO2 concentrations with an atmospheric general circulation model (GCM). Three different convective transport algorithms were used. One is a modified Arakawa-Shubert scheme that was native to the GCM; two others used in two off-line chemical transport models (CTMs) were added to the GCM here for comparison purposes. Advanced CO2 surfaced fluxes were used for the simulations. The results were compared to a large quantity of CO2 observation data. We find that the simulation results are sensitive to the convective transport algorithms. Overall, the three simulations are quite realistic and similar to each other in the remote marine regions, but are significantly different in some land regions with strong fluxes such as Amazon and Siberia during the convection seasons. Large biases against CO2 measurements are found in these regions in the control run, which uses the original GCM. The simulation with the simple diffusive algorithm is better. The difference of the two simulations is related to the very different convective transport speed.
Lewis-Brown, Jean C.; Carleton, Glen B.; Imbrigiotta, Thomas E.
2006-01-01
Volatile organic compounds, predominantly trichloroethylene and its degradation products, have been detected in ground water at the Naval Air Warfare Center (NAWC), West Trenton, New Jersey. An air-stripping pump-and-treat system has been in operation at the NAWC since 1998. An existing ground-water-flow model was used to evaluate the effect of a change in the configuration of the network of recovery wells in the pump-and-treat system on flow paths of contaminated ground water. The NAWC is underlain by a fractured-rock aquifer composed of dipping layers of sedimentary rocks of the Lockatong and Stockton Formations. Hydraulic and solute-transport properties of the part of the aquifer composed of the Lockatong Formation were measured using aquifer tests and tracer tests. The heterogeneity of the rocks causes a wide range of values of each parameter measured. Transmissivity ranges from 95 to 1,300 feet squared per day; the storage coefficient ranges from 9 x 10-5 to 5 x 10-3; and the effective porosity ranges from 0.0003 to 0.002. The average linear velocity of contaminated ground water was determined for ambient conditions (when no wells at the site are pumped) using an existing ground-water-flow model, particle-tracking techniques, and the porosity values determined in this study. The average linear velocity of flow paths beginning at each contaminated well and ending at the streams where the flow paths terminate ranges from 0.08 to 130 feet per day. As a result of a change in the pump-and-treat system (adding a 165-foot-deep well pumped at 5 gallons per minute and reducing the pumping rate at a nearby 41-foot-deep well by the same amount), water in the vicinity of three 100- to 165-foot-deep wells flows to the deep well rather than the shallower well.
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.
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
Solute transport via alternating-direction collocation using the modified method of characteristics
NASA Astrophysics Data System (ADS)
Allen, Myron B.; Khosravani, Azar
We present a finite-element collocation method for modeling underground solute transport in two space dimensions when advection is dominant. The scheme uses a modified method of characteristics to approximate advective terms, thereby reducing the temporal truncation error and allowing accurate transport of solute by the velocity field. In conjunction with this approach, we employ an alternating-direction algorithm to yield a highly parallelizable algorithm for solving two-dimensional problems as sequences of simpler problems having one-dimensional matrix structure.
Bouchard, Hugo; Bielajew, Alex
2015-07-01
To establish a theoretical framework for generalizing Monte Carlo transport algorithms by adding external electromagnetic fields to the Boltzmann radiation transport equation in a rigorous and consistent fashion. Using first principles, the Boltzmann radiation transport equation is modified by adding a term describing the variation of the particle distribution due to the Lorentz force. The implications of this new equation are evaluated by investigating the validity of Fano's theorem. Additionally, Lewis' approach to multiple scattering theory in infinite homogeneous media is redefined to account for the presence of external electromagnetic fields. The equation is modified and yields a description consistent with the deterministic laws of motion as well as probabilistic methods of solution. The time-independent Boltzmann radiation transport equation is generalized to account for the electromagnetic forces in an additional operator similar to the interaction term. Fano's and Lewis' approaches are stated in this new equation. Fano's theorem is found not to apply in the presence of electromagnetic fields. Lewis' theory for electron multiple scattering and moments, accounting for the coupling between the Lorentz force and multiple elastic scattering, is found. However, further investigation is required to develop useful algorithms for Monte Carlo and deterministic transport methods. To test the accuracy of Monte Carlo transport algorithms in the presence of electromagnetic fields, the Fano cavity test, as currently defined, cannot be applied. Therefore, new tests must be designed for this specific application. A multiple scattering theory that accurately couples the Lorentz force with elastic scattering could improve Monte Carlo efficiency. The present study proposes a new theoretical framework to develop such algorithms.
A new algorithm for generating highly accurate benchmark solutions to transport test problems
Azmy, Y.Y.
1997-06-01
We present a new algorithm for solving the neutron transport equation in its discrete-variable form. The new algorithm is based on computing the full matrix relating the scalar flux spatial moments in all cells to the fixed neutron source spatial moments, foregoing the need to compute the angular flux spatial moments, and thereby eliminating the need for sweeping the spatial mesh in each discrete-angular direction. The matrix equation is solved exactly in test cases, producing a solution vector that is free from iteration convergence error, and subject only to truncation and roundoff errors. Our algorithm is designed to provide method developers with a quick and simple solution scheme to test their new methods on difficult test problems without the need to develop sophisticated solution techniques, e.g. acceleration, before establishing the worthiness of their innovation. We demonstrate the utility of the new algorithm by applying it to the Arbitrarily High Order Transport Nodal (AHOT-N) method, and using it to solve two of Burre`s Suite of Test Problems (BSTP). Our results provide highly accurate benchmark solutions, that can be distributed electronically and used to verify the pointwise accuracy of other solution methods and algorithms.
Utilizing Kernelized Advection Schemes in Ocean Models
NASA Astrophysics Data System (ADS)
Zadeh, N.; Balaji, V.
2008-12-01
There has been a recent effort in the ocean model community to use a set of generic FORTRAN library routines for advection of scalar tracers in the ocean. In a collaborative project called Hybrid Ocean Model Environement (HOME), vastly different advection schemes (space-differencing schemes for advection equation) become available to modelers in the form of subroutine calls (kernels). In this talk we explore the possibility of utilizing ESMF data structures in wrapping these kernels so that they can be readily used in ESMF gridded components.
Transport implementation of the Bernstein–Vazirani algorithm with ion qubits
NASA Astrophysics Data System (ADS)
Fallek, S. D.; Herold, C. D.; McMahon, B. J.; Maller, K. M.; Brown, K. R.; Amini, J. M.
2016-08-01
Using trapped ion quantum bits in a scalable microfabricated surface trap, we perform the Bernstein–Vazirani algorithm. Our architecture takes advantage of the ion transport capabilities of such a trap. The algorithm is demonstrated using two- and three-ion chains. For three ions, an improvement is achieved compared to a classical system using the same number of oracle queries. For two ions and one query, we correctly determine an unknown bit string with probability 97.6(8)%. For three ions, we succeed with probability 80.9(3)%.
NASA Astrophysics Data System (ADS)
Romano, Paul Kollath
Monte Carlo particle transport methods are being considered as a viable option for high-fidelity simulation of nuclear reactors. While Monte Carlo methods offer several potential advantages over deterministic methods, there are a number of algorithmic shortcomings that would prevent their immediate adoption for full-core analyses. In this thesis, algorithms are proposed both to ameliorate the degradation in parallel efficiency typically observed for large numbers of processors and to offer a means of decomposing large tally data that will be needed for reactor analysis. A nearest-neighbor fission bank algorithm was proposed and subsequently implemented in the OpenMC Monte Carlo code. A theoretical analysis of the communication pattern shows that the expected cost is O( N ) whereas traditional fission bank algorithms are O(N) at best. The algorithm was tested on two supercomputers, the Intrepid Blue Gene/P and the Titan Cray XK7, and demonstrated nearly linear parallel scaling up to 163,840 processor cores on a full-core benchmark problem. An algorithm for reducing network communication arising from tally reduction was analyzed and implemented in OpenMC. The proposed algorithm groups only particle histories on a single processor into batches for tally purposes---in doing so it prevents all network communication for tallies until the very end of the simulation. The algorithm was tested, again on a full-core benchmark, and shown to reduce network communication substantially. A model was developed to predict the impact of load imbalances on the performance of domain decomposed simulations. The analysis demonstrated that load imbalances in domain decomposed simulations arise from two distinct phenomena: non-uniform particle densities and non-uniform spatial leakage. The dominant performance penalty for domain decomposition was shown to come from these physical effects rather than insufficient network bandwidth or high latency. The model predictions were verified with
Nemanic, M K; Nowak, P
1999-04-12
We consider the solution of time-dependent, energy-dependent, discrete ordinates, and nonlinear radiative transfer problems on three-dimensional unstructured spatial grids. We discuss the solution of this class of transport problems, using the code TETON, on large distributed-memory multinode computers having multiple processors per ''node'' (e.g. the IBM-SP). We discuss the use of both spatial decomposition using message passing between ''nodes'' and a threading algorithm in angle on each ''node''. We present timing studies to show how this algorithm scales to hundreds and thousands of processors. We also present an energy group ''batching'' algorithm that greatly enhances cache performance. Our conclusion, after considering cache performance, storage limitations and dependencies inherent in the physics, is that a model that uses a combination of message-passing and threading is superior to one that uses message-passing alone. We present numerical evidence to support our conclusion.
NASA Astrophysics Data System (ADS)
Penenko, Alexey; Penenko, Vladimir; Nuterman, Roman; Baklanov, Alexander; Mahura, Alexander
2015-11-01
Atmospheric chemistry dynamics is studied with convection-diffusion-reaction model. The numerical Data Assimilation algorithm presented is based on the additive-averaged splitting schemes. It carries out ''fine-grained'' variational data assimilation on the separate splitting stages with respect to spatial dimensions and processes i.e. the same measurement data is assimilated to different parts of the split model. This design has efficient implementation due to the direct data assimilation algorithms of the transport process along coordinate lines. Results of numerical experiments with chemical data assimilation algorithm of in situ concentration measurements on real data scenario have been presented. In order to construct the scenario, meteorological data has been taken from EnviroHIRLAM model output, initial conditions from MOZART model output and measurements from Airbase database.
Watanabe, Shin; Takamatsu, Atsuko
2014-01-01
In this paper, we propose designing transportation network topology and traffic distribution under fluctuating conditions using a bio-inspired algorithm. The algorithm is inspired by the adaptive behavior observed in an amoeba-like organism, plasmodial slime mold, more formally known as plasmodium of Physarum plycephalum. This organism forms a transportation network to distribute its protoplasm, the fluidic contents of its cell, throughout its large cell body. In this process, the diameter of the transportation tubes adapts to the flux of the protoplasm. The Physarum algorithm, which mimics this adaptive behavior, has been widely applied to complex problems, such as maze solving and designing the topology of railroad grids, under static conditions. However, in most situations, environmental conditions fluctuate; for example, in power grids, the consumption of electric power shows daily, weekly, and annual periodicity depending on the lifestyles or the business needs of the individual consumers. This paper studies the design of network topology and traffic distribution with oscillatory input and output traffic flows. The network topology proposed by the Physarum algorithm is controlled by a parameter of the adaptation process of the tubes. We observe various rich topologies such as complete mesh, partial mesh, Y-shaped, and V-shaped networks depending on this adaptation parameter and evaluate them on the basis of three performance functions: loss, cost, and vulnerability. Our results indicate that consideration of the oscillatory conditions and the phase-lags in the multiple outputs of the network is important: The building and/or maintenance cost of the network can be reduced by introducing the oscillating condition, and when the phase-lag among the outputs is large, the transportation loss can also be reduced. We use stability analysis to reveal how the system exhibits various topologies depending on the parameter. PMID:24586616
NASA Technical Reports Server (NTRS)
Kumar, Vivek; Horio, Brant M.; DeCicco, Anthony H.; Hasan, Shahab; Stouffer, Virginia L.; Smith, Jeremy C.; Guerreiro, Nelson M.
2015-01-01
This paper presents a search algorithm based framework to calibrate origin-destination (O-D) market specific airline ticket demands and prices for the Air Transportation System (ATS). This framework is used for calibrating an agent based model of the air ticket buy-sell process - Airline Evolutionary Simulation (Airline EVOS) -that has fidelity of detail that accounts for airline and consumer behaviors and the interdependencies they share between themselves and the NAS. More specificially, this algorithm simultaneous calibrates demand and airfares for each O-D market, to within specified threshold of a pre-specified target value. The proposed algorithm is illustrated with market data targets provided by the Transportation System Analysis Model (TSAM) and Airline Origin and Destination Survey (DB1B). Although we specify these models and datasources for this calibration exercise, the methods described in this paper are applicable to calibrating any low-level model of the ATS to some other demand forecast model-based data. We argue that using a calibration algorithm such as the one we present here to synchronize ATS models with specialized forecast demand models, is a powerful tool for establishing credible baseline conditions in experiments analyzing the effects of proposed policy changes to the ATS.
Drift by drift: effective population size is limited by advection
2008-01-01
Background Genetic estimates of effective population size often generate surprising results, including dramatically low ratios of effective population size to census size. This is particularly true for many marine species, and this effect has been associated with hypotheses of "sweepstakes" reproduction and selective hitchhiking. Results Here we show that in advective environments such as oceans and rivers, the mean asymmetric transport of passively dispersed reproductive propagules will act to limit the effective population size in species with a drifting developmental stage. As advection increases, effective population size becomes decoupled from census size as the persistence of novel genetic lineages is restricted to those that arise in a small upstream portion of the species domain. Conclusion This result leads to predictions about the maintenance of diversity in advective systems, and complements the "sweepstakes" hypothesis and other hypotheses proposed to explain cases of low allelic diversity in species with high fecundity. We describe the spatial extent of the species domain in which novel allelic diversity will be retained, thus determining how large an appropriately placed marine reserve must be to allow the persistence of endemic allelic diversity. PMID:18710549
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.
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
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
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.
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.
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.
An Improved Elastic and Nonelastic Neutron Transport Algorithm for Space Radiation
NASA Technical Reports Server (NTRS)
Clowdsley, Martha S.; Wilson, John W.; Heinbockel, John H.; Tripathi, R. K.; Singleterry, Robert C., Jr.; Shinn, Judy L.
2000-01-01
A neutron transport algorithm including both elastic and nonelastic particle interaction processes for use in space radiation protection for arbitrary shield material is developed. The algorithm is based upon a multiple energy grouping and analysis of the straight-ahead Boltzmann equation by using a mean value theorem for integrals. The algorithm is then coupled to the Langley HZETRN code through a bidirectional neutron evaporation source term. Evaluation of the neutron fluence generated by the solar particle event of February 23, 1956, for an aluminum water shield-target configuration is then compared with MCNPX and LAHET Monte Carlo calculations for the same shield-target configuration. With the Monte Carlo calculation as a benchmark, the algorithm developed in this paper showed a great improvement in results over the unmodified HZETRN solution. In addition, a high-energy bidirectional neutron source based on a formula by Ranft showed even further improvement of the fluence results over previous results near the front of the water target where diffusion out the front surface is important. Effects of improved interaction cross sections are modest compared with the addition of the high-energy bidirectional source terms.
Iterative feedback algorithm for phase retrieval based on transport of intensity equation
NASA Astrophysics Data System (ADS)
Liu, Kaifeng; Cheng, Hong; Zhang, Cheng; Shen, Chuan; Zhang, Fen; Wei, Sui
2015-12-01
In this paper, a novel phase retrieval algorithm is presented which combines the advantages of the Transport of Intensity Equation (TIE) method and the iteration method. TIE method is fast, but its precision is not high. Though the convergence rate of iteration method is slow, its result is more accurate. This algorithm consists of Iterative Angular Spectrum (IAS) method to utilize the physical constraints between the object and the spectral domain, and the relationship between the intensity and phase among the wave propagation. Firstly, the phase at the object plane is calculated from two intensity images by TIE. Then this result is treated as the initial phase of the IAS. Finally, the phase information at the object plane is acquired according the reversibility of the optical path. During the iteration process, the feedback mechanism is imposed on it that improve the convergence rate and the precision of phase retrieval and the simulation results are given.
Aungkulanon, Pasura; Luangpaiboon, Pongchanun
2016-01-01
Response surface methods via the first or second order models are important in manufacturing processes. This study, however, proposes different structured mechanisms of the vertical transportation systems or VTS embedded on a shuffled frog leaping-based approach. There are three VTS scenarios, a motion reaching a normal operating velocity, and both reaching and not reaching transitional motion. These variants were performed to simultaneously inspect multiple responses affected by machining parameters in multi-pass turning processes. The numerical results of two machining optimisation problems demonstrated the high performance measures of the proposed methods, when compared to other optimisation algorithms for an actual deep cut design. PMID:27386280
NASA Astrophysics Data System (ADS)
Stevens, D.; Power, H.
2015-10-01
We propose a node-based local meshless method for advective transport problems that is capable of operating on centrally defined stencils and is suitable for shock-capturing purposes. High spatial convergence rates can be achieved; in excess of eighth-order in some cases. Strongly-varying smooth profiles may be captured at infinite Péclet number without instability, and for discontinuous profiles the solution exhibits neutrally stable oscillations that can be damped by introducing a small artificial diffusion parameter, allowing a good approximation to the shock-front to be maintained for long travel times without introducing spurious oscillations. The proposed method is based on local collocation with radial basis functions (RBFs) in a "finite collocation" configuration. In this approach the PDE governing and boundary equations are enforced directly within the local RBF collocation systems, rather than being reconstructed from fixed interpolating functions as is typical of finite difference, finite volume or finite element methods. In this way the interpolating basis functions naturally incorporate information from the governing PDE, including the strength and direction of the convective velocity field. By using these PDE-enhanced interpolating functions an "implicit upwinding" effect is achieved, whereby the flow of information naturally respects the specifics of the local convective field. This implicit upwinding effect allows high-convergence solutions to be obtained on centred stencils for advection problems. The method is formulated using a high-convergence implicit timestepping algorithm based on Richardson extrapolation. The spatial and temporal convergence of the proposed approach is demonstrated using smooth functions with large gradients. The capture of discontinuities is then investigated, showing how the addition of a dynamic stabilisation parameter can damp the neutrally stable oscillations with limited smearing of the shock front.
Basconi, Joseph E; Shirts, Michael R
2013-07-01
Temperature control algorithms in molecular dynamics (MD) simulations are necessary to study isothermal systems. However, these thermostatting algorithms alter the velocities of the particles and thus modify the dynamics of the system with respect to the microcanonical ensemble, which could potentially lead to thermostat-dependent dynamical artifacts. In this study, we investigate how six well-established thermostat algorithms applied with different coupling strengths and to different degrees of freedom affect the dynamics of various molecular systems. We consider dynamic processes occurring on different times scales by measuring translational and rotational self-diffusion as well as the shear viscosity of water, diffusion of a small molecule solvated in water, and diffusion and the dynamic structure factor of a polymer chain in water. All of these properties are significantly dampened by thermostat algorithms which randomize particle velocities, such as the Andersen thermostat and Langevin dynamics, when strong coupling is used. For the solvated small molecule and polymer, these dampening effects are reduced somewhat if the thermostats are applied to the solvent alone, such that the solute's temperature is maintained only through thermal contact with solvent particles. Algorithms which operate by scaling the velocities, such as the Berendsen thermostat, the stochastic velocity rescaling approach of Bussi and co-workers, and the Nosé-Hoover thermostat, yield transport properties that are statistically indistinguishable from those of the microcanonical ensemble, provided they are applied globally, i.e. coupled to the system's kinetic energy. When coupled to local kinetic energies, a velocity scaling thermostat can have dampening effects comparable to a velocity randomizing method, as we observe when a massive Nose-Hoover coupling scheme is used to simulate water. Correct dynamical properties, at least those studied in this paper, are obtained with the Berendsen
NASA Technical Reports Server (NTRS)
Fleming, E. L.; Jackman, C. H.; Stolarski, R. S.; Considine, D. B.
1998-01-01
We have developed a new empirically-based transport algorithm for use in our GSFC two-dimensional transport and chemistry model. The new algorithm contains planetary wave statistics, and parameterizations to account for the effects due to gravity waves and equatorial Kelvin waves. As such, this scheme utilizes significantly more information compared to our previous algorithm which was based only on zonal mean temperatures and heating rates. The new model transport captures much of the qualitative structure and seasonal variability observed in long lived tracers, such as: isolation of the tropics and the southern hemisphere winter polar vortex; the well mixed surf-zone region of the winter sub-tropics and mid-latitudes; the latitudinal and seasonal variations of total ozone; and the seasonal variations of mesospheric H2O. The model also indicates a double peaked structure in methane associated with the semiannual oscillation in the tropical upper stratosphere. This feature is similar in phase but is significantly weaker in amplitude compared to the observations. The model simulations of carbon-14 and strontium-90 are in good agreement with observations, both in simulating the peak in mixing ratio at 20-25 km, and the decrease with altitude in mixing ratio above 25 km. We also find mostly good agreement between modeled and observed age of air determined from SF6 outside of the northern hemisphere polar vortex. However, observations inside the vortex reveal significantly older air compared to the model. This is consistent with the model deficiencies in simulating CH4 in the northern hemisphere winter high latitudes and illustrates the limitations of the current climatological zonal mean model formulation. The propagation of seasonal signals in water vapor and CO2 in the lower stratosphere showed general agreement in phase, and the model qualitatively captured the observed amplitude decrease in CO2 from the tropics to midlatitudes. However, the simulated seasonal
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.
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
EBS Radionuclide Transport Abstraction
J.D. Schreiber
2005-08-25
The purpose of this report is to develop and analyze the engineered barrier system (EBS) radionuclide transport abstraction model, consistent with Level I and Level II model validation, as identified in ''Technical Work Plan for: Near-Field Environment and Transport: Engineered Barrier System: Radionuclide Transport Abstraction Model Report Integration'' (BSC 2005 [DIRS 173617]). The EBS radionuclide transport abstraction (or EBS RT Abstraction) is the conceptual model used in the total system performance assessment for the license application (TSPA-LA) to determine the rate of radionuclide releases from the EBS to the unsaturated zone (UZ). The EBS RT Abstraction conceptual model consists of two main components: a flow model and a transport model. Both models are developed mathematically from first principles in order to show explicitly what assumptions, simplifications, and approximations are incorporated into the models used in the TSPA-LA. The flow model defines the pathways for water flow in the EBS and specifies how the flow rate is computed in each pathway. Input to this model includes the seepage flux into a drift. The seepage flux is potentially split by the drip shield, with some (or all) of the flux being diverted by the drip shield and some passing through breaches in the drip shield that might result from corrosion or seismic damage. The flux through drip shield breaches is potentially split by the waste package, with some (or all) of the flux being diverted by the waste package and some passing through waste package breaches that might result from corrosion or seismic damage. Neither the drip shield nor the waste package survives an igneous intrusion, so the flux splitting submodel is not used in the igneous scenario class. The flow model is validated in an independent model validation technical review. The drip shield and waste package flux splitting algorithms are developed and validated using experimental data. The transport model considers
O'Brien, M. J.; Brantley, P. S.
2015-01-20
In order to run Monte Carlo particle transport calculations on new supercomputers with hundreds of thousands or millions of processors, care must be taken to implement scalable algorithms. This means that the algorithms must continue to perform well as the processor count increases. In this paper, we examine the scalability of:(1) globally resolving the particle locations on the correct processor, (2) deciding that particle streaming communication has finished, and (3) efficiently coupling neighbor domains together with different replication levels. We have run domain decomposed Monte Carlo particle transport on up to 2^{21} = 2,097,152 MPI processes on the IBM BG/Q Sequoia supercomputer and observed scalable results that agree with our theoretical predictions. These calculations were carefully constructed to have the same amount of work on every processor, i.e. the calculation is already load balanced. We also examine load imbalanced calculations where each domain’s replication level is proportional to its particle workload. In this case we show how to efficiently couple together adjacent domains to maintain within workgroup load balance and minimize memory usage.
NASA Astrophysics Data System (ADS)
Walsh, Jonathan A.; Romano, Paul K.; Forget, Benoit; Smith, Kord S.
2015-11-01
In this work we propose, implement, and test various optimizations of the typical energy grid-cross section pair lookup algorithm in Monte Carlo particle transport codes. The key feature common to all of the optimizations is a reduction in the length of the vector of energies that must be searched when locating the index of a particle's current energy. Other factors held constant, a reduction in energy vector length yields a reduction in CPU time. The computational methods we present here are physics-informed. That is, they are designed to utilize the physical information embedded in a simulation in order to reduce the length of the vector to be searched. More specifically, the optimizations take advantage of information about scattering kinematics, neutron cross section structure and data representation, and also the expected characteristics of a system's spatial flux distribution and energy spectrum. The methods that we present are implemented in the OpenMC Monte Carlo neutron transport code as part of this work. The gains in computational efficiency, as measured by overall code speedup, associated with each of the optimizations are demonstrated in both serial and multithreaded simulations of realistic systems. Depending on the system, simulation parameters, and optimization method employed, overall code speedup factors of 1.2-1.5, relative to the typical single-nuclide binary search algorithm, are routinely observed.
Hoisie, A.; Lubeck, O.; Wasserman, H.
1998-12-31
The authors develop a model for the parallel performance of algorithms that consist of concurrent, two-dimensional wavefronts implemented in a message passing environment. The model, based on a LogGP machine parameterization, combines the separate contributions of computation and communication wavefronts. They validate the model on three important supercomputer systems, on up to 500 processors. They use data from a deterministic particle transport application taken from the ASCI workload, although the model is general to any wavefront algorithm implemented on a 2-D processor domain. They also use the validated model to make estimates of performance and scalability of wavefront algorithms on 100-TFLOPS computer systems expected to be in existence within the next decade as part of the ASCI program and elsewhere. In this context, the authors analyze two problem sizes. Their model shows that on the largest such problem (1 billion cells), inter-processor communication performance is not the bottleneck. Single-node efficiency is the dominant factor.
A fast, parallel algorithm to solve the basic fluvial erosion/transport equations
NASA Astrophysics Data System (ADS)
Braun, J.
2012-04-01
Quantitative models of landform evolution are commonly based on the solution of a set of equations representing the processes of fluvial erosion, transport and deposition, which leads to predict the geometry of a river channel network and its evolution through time. The river network is often regarded as the backbone of any surface processes model (SPM) that might include other physical processes acting at a range of spatial and temporal scales along hill slopes. The basic laws of fluvial erosion requires the computation of local (slope) and non-local (drainage area) quantities at every point of a given landscape, a computationally expensive operation which limits the resolution of most SPMs. I present here an algorithm to compute the various components required in the parameterization of fluvial erosion (and transport) and thus solve the basic fluvial geomorphic equation, that is very efficient because it is O(n) (the number of required arithmetic operations is linearly proportional to the number of nodes defining the landscape), and is fully parallelizable (the computation cost decreases in a direct inverse proportion to the number of processors used to solve the problem). The algorithm is ideally suited for use on latest multi-core processors. Using this new technique, geomorphic problems can be solved at an unprecedented resolution (typically of the order of 10,000 X 10,000 nodes) while keeping the computational cost reasonable (order 1 sec per time step). Furthermore, I will show that the algorithm is applicable to any regular or irregular representation of the landform, and is such that the temporal evolution of the landform can be discretized by a fully implicit time-marching algorithm, making it unconditionally stable. I will demonstrate that such an efficient algorithm is ideally suited to produce a fully predictive SPM that links observationally based parameterizations of small-scale processes to the evolution of large-scale features of the landscapes on
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.
Powell, B. P.; Azmy, Y. Y.
2013-07-01
The Integral Transport Matrix Method (ITMM) has been shown to be an effective method for solving the neutron transport equation in large domains on massively parallel architectures. In the limit of very large number of processors, the speed of the algorithm, and its suitability for unstructured meshes, i.e. other than an ordered Cartesian grid, is limited by the construction of four matrix operators required for obtaining the solution in each sub-domain. The existing algorithm used for construction of these matrix operators, termed the differential mesh sweep, is computationally expensive and was developed for a structured grid. This work proposes the use of a new algorithm for construction of these operators based on the construction of a single, fundamental matrix representing the transport of a particle along every possible path throughout the sub-domain mesh. Each of the operators is constructed by multiplying an element of this fundamental matrix by two factors dependent only upon the operator being constructed and on properties of the emitting and incident cells. The ITMM matrix operator construction time for the new algorithm is demonstrated to be shorter than the existing algorithm in all tested cases with both isotropic and anisotropic scattering considered. While also being a more efficient algorithm on a structured Cartesian grid, the new algorithm is promising in its geometric robustness and potential for being applied to an unstructured mesh, with the ultimate goal of application to an unstructured tetrahedral mesh on a massively parallel architecture. (authors)
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...
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).
Numerical modeling of DNA-chip hybridization with chaotic advection
Raynal, Florence; Beuf, Aurélien; Carrière, Philippe
2013-01-01
We present numerical simulations of DNA-chip hybridization, both in the “static” and “dynamical” cases. In the static case, transport of free targets is limited by molecular diffusion; in the dynamical case, an efficient mixing is achieved by chaotic advection, with a periodic protocol using pumps in a rectangular chamber. This protocol has been shown to achieve rapid and homogeneous mixing. We suppose in our model that all free targets are identical; the chip has different spots on which the probes are fixed, also all identical, and complementary to the targets. The reaction model is an infinite sink potential of width dh, i.e., a target is captured as soon as it comes close enough to a probe, at a distance lower than dh. Our results prove that mixing with chaotic advection enables much more rapid hybridization than the static case. We show and explain why the potential width dh does not play an important role in the final results, and we discuss the role of molecular diffusion. We also recover realistic reaction rates in the static case. PMID:24404027
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.
F--Ray: A new algorithm for efficient transport of ionizing radiation
NASA Astrophysics Data System (ADS)
Mao, Yi; Zhang, J.; Wandelt, B. D.; Shapiro, P. R.; Iliev, I. T.
2014-04-01
We present a new algorithm for the 3D transport of ionizing radiation, called F
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.
Tomography-based monitoring of isothermal snow metamorphism under advective conditions
NASA Astrophysics Data System (ADS)
Ebner, P. P.; Schneebeli, M.; Steinfeld, A.
2015-07-01
Time-lapse X-ray microtomography was used to investigate the structural dynamics of isothermal snow metamorphism exposed to an advective airflow. The effect of diffusion and advection across the snow pores on the snow microstructure were analysed in controlled laboratory experiments and possible effects on natural snowpacks discussed. The 3-D digital geometry obtained by tomographic scans was used in direct pore-level numerical simulations to determine the effective permeability. The results showed that isothermal advection with saturated air have no influence on the coarsening rate that is typical for isothermal snow metamorphism. Isothermal snow metamorphism is driven by sublimation deposition caused by the Kelvin effect and is the limiting factor independently of the transport regime in the pores.
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.
Azmy, Yousry
2014-06-10
We employ the Integral Transport Matrix Method (ITMM) as the kernel of new parallel solution methods for the discrete ordinates approximation of the within-group neutron transport equation. The ITMM abandons the repetitive mesh sweeps of the traditional source iterations (SI) scheme in favor of constructing stored operators that account for the direct coupling factors among all the cells' fluxes and between the cells' and boundary surfaces' fluxes. The main goals of this work are to develop the algorithms that construct these operators and employ them in the solution process, determine the most suitable way to parallelize the entire procedure, and evaluate the behavior and parallel performance of the developed methods with increasing number of processes, P. The fastest observed parallel solution method, Parallel Gauss-Seidel (PGS), was used in a weak scaling comparison with the PARTISN transport code, which uses the source iteration (SI) scheme parallelized with the Koch-baker-Alcouffe (KBA) method. Compared to the state-of-the-art SI-KBA with diffusion synthetic acceleration (DSA), this new method- even without acceleration/preconditioning-is completitive for optically thick problems as P is increased to the tens of thousands range. For the most optically thick cells tested, PGS reduced execution time by an approximate factor of three for problems with more than 130 million computational cells on P = 32,768. Moreover, the SI-DSA execution times's trend rises generally more steeply with increasing P than the PGS trend. Furthermore, the PGS method outperforms SI for the periodic heterogeneous layers (PHL) configuration problems. The PGS method outperforms SI and SI-DSA on as few as P = 16 for PHL problems and reduces execution time by a factor of ten or more for all problems considered with more than 2 million computational cells on P = 4.096.
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
Xie, Dexuan; Dash, Ranjan K.; Beard, Daniel A.
2009-01-01
Fast algorithms for simulating mathematical models of coupled blood-tissue transport and metabolism are critical for the analysis of data on transport and reaction in tissues. Here, by combining the method of characteristics with the standard grid discretization technique, a novel algorithm is introduced for solving a general blood-tissue transport and metabolism model governed by a large system of one-dimensional semilinear first order partial differential equations. The key part of the algorithm is to approximate the model as a group of independent ordinary differential equation (ODE) systems such that each ODE system has the same size as the model and can be integrated independently. Thus the method can be easily implemented in parallel on a large scale multiprocessor computer. The accuracy of the algorithm is demonstrated for solving a simple blood-tissue exchange model introduced by Sangren and Sheppard (Bull. Math. Biophys. 15:387–394, 1953), which has an analytical solution. Numerical experiments made on a distributed-memory parallel computer (an HP Linux cluster) and a shared-memory parallel computer (a SGI Origin 2000) demonstrate the parallel efficiency of the algorithm. PMID:20161089
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.
Zhou, Jianzhong; Song, Lixiang; Kursan, Suncana; Liu, Yi
2015-05-01
A two-dimensional coupled water quality model is developed for modeling the flow-mass transport in shallow water. To simulate shallow flows on complex topography with wetting and drying, an unstructured grid, well-balanced, finite volume algorithm is proposed for numerical resolution of a modified formulation of two-dimensional shallow water equations. The slope-limited linear reconstruction method is used to achieve second-order accuracy in space. The algorithm adopts a HLLC-based integrated solver to compute the flow and mass transport fluxes simultaneously, and uses Hancock's predictor-corrector scheme for efficient time stepping as well as second-order temporal accuracy. The continuity and momentum equations are updated in both wet and dry cells. A new hybrid method, which can preserve the well-balanced property of the algorithm for simulations involving flooding and recession, is proposed for bed slope terms approximation. The effectiveness and robustness of the proposed algorithm are validated by the reasonable good agreement between numerical and reference results of several benchmark test cases. Results show that the proposed coupled flow-mass transport model can simulate complex flows and mass transport in shallow water.
Zhou, Jianzhong; Song, Lixiang; Kursan, Suncana; Liu, Yi
2015-05-01
A two-dimensional coupled water quality model is developed for modeling the flow-mass transport in shallow water. To simulate shallow flows on complex topography with wetting and drying, an unstructured grid, well-balanced, finite volume algorithm is proposed for numerical resolution of a modified formulation of two-dimensional shallow water equations. The slope-limited linear reconstruction method is used to achieve second-order accuracy in space. The algorithm adopts a HLLC-based integrated solver to compute the flow and mass transport fluxes simultaneously, and uses Hancock's predictor-corrector scheme for efficient time stepping as well as second-order temporal accuracy. The continuity and momentum equations are updated in both wet and dry cells. A new hybrid method, which can preserve the well-balanced property of the algorithm for simulations involving flooding and recession, is proposed for bed slope terms approximation. The effectiveness and robustness of the proposed algorithm are validated by the reasonable good agreement between numerical and reference results of several benchmark test cases. Results show that the proposed coupled flow-mass transport model can simulate complex flows and mass transport in shallow water. PMID:25686488
Aplication of LIRIC algorithm to study aerosol transport over Belsk, Poland
NASA Astrophysics Data System (ADS)
Pietruczuk, Aleksander; Posyniak, Michał
2015-04-01
In this work synergy of measurements done by of a LIDAR and a sun-sky scanning photometer is presented. The LIdar-Radiometer Inversion Code (LIRIC) was applied to study periodic events of increased values of the aerosol optical depth (AOD) observed at Belsk (Poland). Belsk is a background site located in a rural area around 50 km south from Warsaw. Events of increased AOD occur mainly during spring and they coincide with events of elevated concentrations of particulate matter (PM10). This phenomenon is observed in all eastern Europe, e.g. in Minsk, and is caused by long range aerosol transport. Our previous work showed aerosol transport from the border between Belarus, Ukraine and Russia in the planetary boundary layer (PBL), and from north Africa in the free troposphere. The LIRIC algorithm, which uses optical and microphysical properties of the aerosol derived from photometric measurements and LIDAR profiles, was applied to study vertical distribution of fine and coarse modes of aerosol. The analysis of the airmass backward trajectories and models results (DREAM and NAAPS)was also used to determine a possible aerosol type and its source region. This study proved our previous findings. Most of events with increased AODs are observed during spring. In this season the fine mode aerosol is mainly present in the PBL. On the basis of the trajectory analysis and the NAAPS results we presume that it is the absorbing aerosol originating from the regions of seasonal biomass burning in eastern Europe, i.e. the area mentioned above. The events with increased AODs were also found during summer. In this case the fine mode aerosol is transported in the PBL a like to spring season. However, our analysis of trajectories and model results indicated western Europe as a source region. It is probably urban/industrial aerosol. The coarse mode aerosol is transported mainly in the free troposphere as separate layers. The analysis of backward trajectories indicates northern Africa as a
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.
Han Tao; Followill, David; Repchak, Roman; Molineu, Andrea; Howell, Rebecca; Salehpour, Mohammad; Mikell, Justin; Mourtada, Firas
2013-05-15
Purpose: The novel deterministic radiation transport algorithm, Acuros XB (AXB), has shown great potential for accurate heterogeneous dose calculation. However, the clinical impact between AXB and other currently used algorithms still needs to be elucidated for translation between these algorithms. The purpose of this study was to investigate the impact of AXB for heterogeneous dose calculation in lung cancer for intensity-modulated radiation therapy (IMRT) and volumetric-modulated arc therapy (VMAT). Methods: The thorax phantom from the Radiological Physics Center (RPC) was used for this study. IMRT and VMAT plans were created for the phantom in the Eclipse 11.0 treatment planning system. Each plan was delivered to the phantom three times using a Varian Clinac iX linear accelerator to ensure reproducibility. Thermoluminescent dosimeters (TLDs) and Gafchromic EBT2 film were placed inside the phantom to measure delivered doses. The measurements were compared with dose calculations from AXB 11.0.21 and the anisotropic analytical algorithm (AAA) 11.0.21. Two dose reporting modes of AXB, dose-to-medium in medium (D{sub m,m}) and dose-to-water in medium (D{sub w,m}), were studied. Point doses, dose profiles, and gamma analysis were used to quantify the agreement between measurements and calculations from both AXB and AAA. The computation times for AAA and AXB were also evaluated. Results: For the RPC lung phantom, AAA and AXB dose predictions were found in good agreement to TLD and film measurements for both IMRT and VMAT plans. TLD dose predictions were within 0.4%-4.4% to AXB doses (both D{sub m,m} and D{sub w,m}); and within 2.5%-6.4% to AAA doses, respectively. For the film comparisons, the gamma indexes ({+-}3%/3 mm criteria) were 94%, 97%, and 98% for AAA, AXB{sub Dm,m}, and AXB{sub Dw,m}, respectively. The differences between AXB and AAA in dose-volume histogram mean doses were within 2% in the planning target volume, lung, heart, and within 5% in the spinal cord
Han, Tao; Followill, David; Mikell, Justin; Repchak, Roman; Molineu, Andrea; Howell, Rebecca; Salehpour, Mohammad; Mourtada, Firas
2013-01-01
Purpose: The novel deterministic radiation transport algorithm, Acuros XB (AXB), has shown great potential for accurate heterogeneous dose calculation. However, the clinical impact between AXB and other currently used algorithms still needs to be elucidated for translation between these algorithms. The purpose of this study was to investigate the impact of AXB for heterogeneous dose calculation in lung cancer for intensity-modulated radiation therapy (IMRT) and volumetric-modulated arc therapy (VMAT). Methods: The thorax phantom from the Radiological Physics Center (RPC) was used for this study. IMRT and VMAT plans were created for the phantom in the Eclipse 11.0 treatment planning system. Each plan was delivered to the phantom three times using a Varian Clinac iX linear accelerator to ensure reproducibility. Thermoluminescent dosimeters (TLDs) and Gafchromic EBT2 film were placed inside the phantom to measure delivered doses. The measurements were compared with dose calculations from AXB 11.0.21 and the anisotropic analytical algorithm (AAA) 11.0.21. Two dose reporting modes of AXB, dose-to-medium in medium (Dm,m) and dose-to-water in medium (Dw,m), were studied. Point doses, dose profiles, and gamma analysis were used to quantify the agreement between measurements and calculations from both AXB and AAA. The computation times for AAA and AXB were also evaluated. Results: For the RPC lung phantom, AAA and AXB dose predictions were found in good agreement to TLD and film measurements for both IMRT and VMAT plans. TLD dose predictions were within 0.4%–4.4% to AXB doses (both Dm,m and Dw,m); and within 2.5%–6.4% to AAA doses, respectively. For the film comparisons, the gamma indexes (±3%/3 mm criteria) were 94%, 97%, and 98% for AAA, AXB_Dm,m, and AXB_Dw,m, respectively. The differences between AXB and AAA in dose–volume histogram mean doses were within 2% in the planning target volume, lung, heart, and within 5% in the spinal cord. However, differences up to 8
Wang, H.; Man, S.; Ewing, R.E.; Qin, G.; Lyons, S.L.; Al-Lawatia, M.
1999-06-10
Many difficult problems arise in the numerical simulation of fluid flow processes within porous media in petroleum reservoir simulation and in subsurface contaminant transport and remediation. The authors develop a family of Eulerian-Lagrangian localized adjoint methods for the solution of the initial-boundary value problems for first-order advection-reaction equations on general multi-dimensional domains. Different tracking algorithms, including the Euler and Runge-Kutta algorithms, are used. The derived schemes, which are full mass conservative, naturally incorporate inflow boundary conditions into their formulations and do not need any artificial outflow boundary conditions. Moreover, they have regularly structured, well-conditioned, symmetric, and positive-definite coefficient matrices, which can be efficiently solved by the conjugate gradient method in an optimal order number of iterations without any preconditioning needed. Numerical results are presented to compare the performance of the ELLAM schemes with many well studied and widely used methods, including the upwind finite difference method, the Galerkin and the Petrov-Galerkin finite element methods with backward-Euler or Crank-Nicolson temporal discretization, the streamline diffusion finite element methods, the monotonic upstream-centered scheme for conservation laws (MUSCL), and the Minmod scheme.
McGhee, J.M.; Roberts, R.M.; Morel, J.E.
1997-06-01
A spherical harmonics research code (DANTE) has been developed which is compatible with parallel computer architectures. DANTE provides 3-D, multi-material, deterministic, transport capabilities using an arbitrary finite element mesh. The linearized Boltzmann transport equation is solved in a second order self-adjoint form utilizing a Galerkin finite element spatial differencing scheme. The core solver utilizes a preconditioned conjugate gradient algorithm. Other distinguishing features of the code include options for discrete-ordinates and simplified spherical harmonics angular differencing, an exact Marshak boundary treatment for arbitrarily oriented boundary faces, in-line matrix construction techniques to minimize memory consumption, and an effective diffusion based preconditioner for scattering dominated problems. Algorithm efficiency is demonstrated for a massively parallel SIMD architecture (CM-5), and compatibility with MPP multiprocessor platforms or workstation clusters is anticipated.
Advective-diffusive mass transfer in fractured porous media with variable rock matrix block size.
Sharifi Haddad, Amin; Hassanzadeh, Hassan; Abedi, Jalal
2012-05-15
Traditional dual porosity models do not take into account the effect of matrix block size distribution on the mass transfer between matrix and fracture. In this study, we introduce the matrix block size distributions into an advective-diffusive solute transport model of a divergent radial system to evaluate the mass transfer shape factor, which is considered as a first-order exchange coefficient between the fracture and matrix. The results obtained lead to a better understanding of the advective-diffusive mass transport in fractured porous media by identifying two early and late time periods of mass transfer. Results show that fractured rock matrix block size distribution has a great impact on mass transfer during early time period. In addition, two dimensionless shape factors are obtained for the late time, which depend on the injection flow rate and the distance of the rock matrix from the injection point.
NASA Astrophysics Data System (ADS)
Ebner, P. P.; Grimm, S. A.; Schneebeli, M.; Steinfeld, A.
2014-09-01
An instrumented sample holder was developed for time-lapse microtomography of snow samples to enable in situ nondestructive spatial and temporal measurements under controlled advective airflows, temperature gradients, and air humidities. The design was aided by computational fluid dynamics simulations to evaluate the airflow uniformity across the snow sample. Morphological and mass transport properties were evaluated during a 4-day test run. This instrument allows the experimental characterization of metamorphism of snow undergoing structural changes with time.
Advection-Dominated Accretion Disks: Geometrically Slim or Thick?
NASA Astrophysics Data System (ADS)
Gu, Wei-Min; Xue, Li; Liu, Tong; Lu, Ju-Fu
2009-12-01
We revisit the vertical structure of black-hole accretion disks in spherical coordinates. By comparing the advective cooling with the viscous heating, we show that advection-dominated disks are geometrically thick, i.e., with a half-opening angle of Δθ > 2π/5, rather than being slim, as supposed previously in the literature.
Time Acceleration Methods for Advection on the Cubed Sphere
Archibald, Richard K; Evans, Katherine J; White III, James B; Drake, John B
2009-01-01
Climate simulation will not grow to the ultrascale without new algorithms to overcome the scalability barriers blocking existing implementations. Until recently, climate simulations concentrated on the question of whether the climate is changing. The emphasis is now shifting to impact assessments, mitigation and adaptation strategies, and regional details. Such studies will require significant increases in spatial resolution and model complexity while maintaining adequate throughput. The barrier to progress is the resulting decrease in time step without increasing single-thread performance. In this paper we demonstrate how to overcome this time barrier for the first standard test defined for the shallow-water equations on a sphere. This paper explains how combining a multiwavelet discontinuous Galerkin method with exact linear part time-evolution schemes can overcome the time barrier for advection equations on a sphere. The discontinuous Galerkin method is a high-order method that is conservative, flexible, and scalable. The addition of multiwavelets to discontinuous Galerkin provides a hierarchical scale structure that can be exploited to improve computational efficiency in both the spatial and temporal dimensions. Exact linear part time-evolution schemes are explicit schemes that remain stable for implicit-size time steps.
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.
Oxygen Advection and Diffusion in a Three Dimensional Vascular Anatomical Network
Fang, Qianqian; Sakadžić, Sava; Ruvinskaya, Lana; Devor, Anna; Dale, Anders M.; Boas, David A.
2008-01-01
There is an increasing need for quantitative and computationally affordable models for analyzing tissue metabolism and hemodynamics in microvascular networks. In this work, we develop a hybrid model to solve for the time-varying oxygen advection-diffusion equation in the vessels and tissue. To obtain a three-dimensional temporal evolution of tissue oxygen concentration for realistic complex vessel networks, we used a graph-based advection model combined with a finite-element based diffusion model and an implicit time-advancing scheme. We validated this algorithm for both static and dynamic conditions. We also applied it to a complex vascular network obtained from a rodent somatosensory cortex. Qualitative agreement was found with in-vivo experiments. PMID:18958033
A tracer-based inversion method for diagnosing eddy-induced diffusivity and advection
NASA Astrophysics Data System (ADS)
Bachman, S. D.; Fox-Kemper, B.; Bryan, F. O.
2015-02-01
A diagnosis method is presented which inverts a set of tracer flux statistics into an eddy-induced transport intended to apply for all tracers. The underlying assumption is that a linear flux-gradient relationship describes eddy-induced tracer transport, but a full tensor coefficient is assumed rather than a scalar coefficient which allows for down-gradient and skew transports. Thus, Lagrangian advection and anisotropic diffusion not necessarily aligned with the tracer gradient can be diagnosed. In this method, multiple passive tracers are initialized in an eddy-resolving flow simulation. Their spatially-averaged gradients form a matrix, where the gradient of each tracer is assumed to satisfy an identical flux-gradient relationship. The resulting linear system, which is overdetermined when using more than three tracers, is then solved to obtain an eddy transport tensor R which describes the eddy advection (antisymmetric part of R) and potentially anisotropic diffusion (symmetric part of R) in terms of coarse-grained variables. The mathematical basis for this inversion method is presented here, along with practical guidelines for its implementation. We present recommendations for initialization of the passive tracers, maintaining the required misalignment of the tracer gradients, correcting for nonconservative effects, and quantifying the error in the diagnosed transport tensor. A method is proposed to find unique, tracer-independent, distinct rotational and divergent Lagrangian transport operators, but the results indicate that these operators are not meaningfully relatable to tracer-independent eddy advection or diffusion. With the optimal method of diagnosis, the diagnosed transport tensor is capable of predicting the fluxes of other tracers that are withheld from the diagnosis, including even active tracers such as buoyancy, such that relative errors of 14% or less are found.
NASA Astrophysics Data System (ADS)
Pirayesh Neghab, Mohammadali; Haji, Rasoul
This study considers a two-level supply chain system consisting of one warehouse and a number of identical retailers. In this system, we incorporate transportation costs into inventory replenishment decisions. The transportation cost contains a fixed cost and a variable cost. We assume that the demand rate at each retailer is known and the demand is confined to a single item. First, we derive the total cost which is the sum of the holding and ordering cost at the warehouse and retailers as well as the transportation cost from the warehouse to retailers. Then, we propose a search algorithm to find the economic order quantities for the warehouse and retailers which minimize the total cost.
Detwiler, R.L.; Mehl, S.; Rajaram, H.; Cheung, W.W.
2002-01-01
Numerical solution of large-scale ground water flow and transport problems is often constrained by the convergence behavior of the iterative solvers used to solve the resulting systems of equations. We demonstrate the ability of an algebraic multigrid algorithm (AMG) to efficiently solve the large, sparse systems of equations that result from computational models of ground water flow and transport in large and complex domains. Unlike geometric multigrid methods, this algorithm is applicable to problems in complex flow geometries, such as those encountered in pore-scale modeling of two-phase flow and transport. We integrated AMG into MODFLOW 2000 to compare two- and three-dimensional flow simulations using AMG to simulations using PCG2, a preconditioned conjugate gradient solver that uses the modified incomplete Cholesky preconditioner and is included with MODFLOW 2000. CPU times required for convergence with AMG were up to 140 times faster than those for PCG2. The cost of this increased speed was up to a nine-fold increase in required random access memory (RAM) for the three-dimensional problems and up to a four-fold increase in required RAM for the two-dimensional problems. We also compared two-dimensional numerical simulations of steady-state transport using AMG and the generalized minimum residual method with an incomplete LU-decomposition preconditioner. For these transport simulations, AMG yielded increased speeds of up to 17 times with only a 20% increase in required RAM. The ability of AMG to solve flow and transport problems in large, complex flow systems and its ready availability make it an ideal solver for use in both field-scale and pore-scale modeling.
NASA Technical Reports Server (NTRS)
Mitra, Debasis; Thomas, Ajai; Hemminger, Joseph; Sakowski, Barbara
2001-01-01
In this research we have developed an algorithm for the purpose of constraint processing by utilizing relational algebraic operators. Van Beek and others have investigated in the past this type of constraint processing from within a relational algebraic framework, producing some unique results. Apart from providing new theoretical angles, this approach also gives the opportunity to use the existing efficient implementations of relational database management systems as the underlying data structures for any relevant algorithm. Our algorithm here enhances that framework. The algorithm is quite general in its current form. Weak heuristics (like forward checking) developed within the Constraint-satisfaction problem (CSP) area could be also plugged easily within this algorithm for further enhancements of efficiency. The algorithm as developed here is targeted toward a component-oriented modeling problem that we are currently working on, namely, the problem of interactive modeling for batch-simulation of engineering systems (IMBSES). However, it could be adopted for many other CSP problems as well. The research addresses the algorithm and many aspects of the problem IMBSES that we are currently handling.
Electrohydrodynamically Driven Chaotic Advection in Drops
NASA Astrophysics Data System (ADS)
Ward, Thomas; Homsy, G. M.
2002-11-01
When a liquid drop of given dielectric constant, resistivity and viscosity is translating in a liquid of different dielectric constant, resistivity and viscosity under Stokes flow conditions in the presence of an electric field, the resulting internal circulation is a superposition of the Hadamard-Rybcynski circulation and the circulation first described theoretically by G. I. Taylor. For sufficiently strong electric field strengths, the quadrapole structure of the Taylor circulation can cause an internal stagnation disk to occur. Our interest is in the situation where a modulation of the electric field causes the stagnation disk to modulate its position, potentially leading to chaotic flows within the drop. The dimensionless electric field strength is characterized by W = 4V(1+lambda)/U where V is the maximum interfacial velocity of the Taylor circulation, U the translational velocity, and lambda the viscosity ratio. The streamfunction for the flow is: 1) psi = (r4-r2) sin2)(theta + W(t) (r3 - r5) sin2 (theta) cos(theta) 2) W(t) = W1 + W2 cos ((epsilon)t) where epsilon is the dimensionless frequency, and W1, W2 are the amplitudes of the DC and AC components, respectively. We have found it useful to replace these parameters by a secondary set, epsilon, Wmax and delta = (1 / W1 - 1 / W2) - (1 / W1 + 1 / W2). As shown in Figure 1a, delta is the dimensionless distance the stagnation disk moves over one period of modulation. The advection equations corresponding to the flow were integrated by standard techniques, and it was found that the trajectories were chaotic over a wide range of parameters. Experiments were conducted to test the predictions of rapid mixing on convective time scales. Drops of silicon oil were suspended in a small 60 mm x 120 mm x 120 mm test cell filled with castor oil, and subject to time-modulated axial electric fields with a wave form corresponding to eq(2). The drops were typically 5 mm in diameter and settled with typical speeds of O(10-1 mm
NASA Technical Reports Server (NTRS)
Yorks, John E.; Mcgill, Matthew J.; Scott, V. Stanley; Kupchock, Andrew; Wake, Shane; Hlavka, Dennis; Hart, William; Selmer, Patrick
2014-01-01
The Airborne Cloud-Aerosol Transport System (ACATS) is a multi-channel Doppler lidar system recently developed at NASA Goddard Space Flight Center (GSFC). A unique aspect of the multi-channel Doppler lidar concept such as ACATS is that it is also, by its very nature, a high spectral resolution lidar (HSRL). Both the particulate and molecular scattered signal can be directly and unambiguously measured, allowing for direct retrievals of particulate extinction. ACATS is therefore capable of simultaneously resolving the backscatterextinction properties and motion of a particle from a high altitude aircraft. ACATS has flown on the NASA ER-2 during test flights over California in June 2012 and science flights during the Wallops Airborne Vegetation Experiment (WAVE) in September 2012. This paper provides an overview of the ACATS method and instrument design, describes the ACATS retrieval algorithms for cloud and aerosol properties, and demonstrates the data products that will be derived from the ACATS data using initial results from the WAVE project. The HSRL retrieval algorithms developed for ACATS have direct application to future spaceborne missions such as the Cloud-Aerosol Transport System (CATS) to be installed on the International Space Station (ISS). Furthermore, the direct extinction and particle wind velocity retrieved from the ACATS data can be used for science applications such 27 as dust or smoke transport and convective outflow in anvil cirrus clouds.
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.
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.
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.
Predicting salt advection in groundwater from saline aquaculture ponds
NASA Astrophysics Data System (ADS)
Verrall, D. P.; Read, W. W.; Narayan, K. A.
2009-01-01
SummaryThis paper predicts saltwater advection in groundwater from leaky aquaculture ponds. A closed form solution for the potential function, stream function and velocity field is derived via the series solutions method. Numerically integrating along different streamlines gives the location (or advection front) of saltwater throughout the domain for any predefined upper time limit. Extending this process produces a function which predicts advection front location against time. The models considered in this paper are easily modified given knowledge of the required physical parameters.
Advection and the Efficiency of Spectral Energy Transfer in Two-Dimensional Turbulence.
Fang, Lei; Ouellette, Nicholas T
2016-09-01
We report measurements of the geometric alignment of the small-scale turbulent stress and the large-scale rate of strain that together lead to the net flux of energy from small scales to large scales in two-dimensional turbulence. We find that the instantaneous alignment between these two tensors is weak and, thus, that the spectral transport of energy is inefficient. We show, however, that the strain rate is much better aligned with the stress at times in the past, suggesting that the differential advection of the two is responsible for the inefficient spectral transfer. We provide evidence for this conjecture by measuring the alignment statistics conditioned on weakly changing stress history. Our results give new insight into the relationship between scale-to-scale energy transfer, geometric alignment, and advection in turbulent flows.
Advection and the Efficiency of Spectral Energy Transfer in Two-Dimensional Turbulence
NASA Astrophysics Data System (ADS)
Fang, Lei; Ouellette, Nicholas T.
2016-09-01
We report measurements of the geometric alignment of the small-scale turbulent stress and the large-scale rate of strain that together lead to the net flux of energy from small scales to large scales in two-dimensional turbulence. We find that the instantaneous alignment between these two tensors is weak and, thus, that the spectral transport of energy is inefficient. We show, however, that the strain rate is much better aligned with the stress at times in the past, suggesting that the differential advection of the two is responsible for the inefficient spectral transfer. We provide evidence for this conjecture by measuring the alignment statistics conditioned on weakly changing stress history. Our results give new insight into the relationship between scale-to-scale energy transfer, geometric alignment, and advection in turbulent flows.
Advection and the Efficiency of Spectral Energy Transfer in Two-Dimensional Turbulence.
Fang, Lei; Ouellette, Nicholas T
2016-09-01
We report measurements of the geometric alignment of the small-scale turbulent stress and the large-scale rate of strain that together lead to the net flux of energy from small scales to large scales in two-dimensional turbulence. We find that the instantaneous alignment between these two tensors is weak and, thus, that the spectral transport of energy is inefficient. We show, however, that the strain rate is much better aligned with the stress at times in the past, suggesting that the differential advection of the two is responsible for the inefficient spectral transfer. We provide evidence for this conjecture by measuring the alignment statistics conditioned on weakly changing stress history. Our results give new insight into the relationship between scale-to-scale energy transfer, geometric alignment, and advection in turbulent flows. PMID:27636478
Choi, Jee-Won; Tillman, Fred D; Smith, James A
2002-07-15
It was hypothesized that atmospheric pressure changes can induce gas flow in the unsaturated zone to such an extent that the advective flux of organic vapors in unsaturated-zone soil gas can be significant relative to the gas-phase diffusion flux of these organic vapors. To test this hypothesis, a series of field measurements and computer simulations were conducted to simulate and compare diffusion and advection fluxes at a trichloroethene-contaminated field site at Picatinny Arsenal in north-central New Jersey. Moisture content temperature, and soil-gas pressure were measured at multiple depths (including at land surface) and times for three distinct sampling events in August 1996, October 1996, and August 1998. Gas pressures in the unsaturated zone changed significantly over time and followed changes measured in the atmosphere. Gas permeability of the unsaturated zone was estimated using data from a variety of sources, including laboratory gas permeability measurements made on intact soil cores from the site, a field air pump test, and calibration of a gas-flow model to the transient, one-dimensional gas pressure data. The final gas-flow model reproduced small pressure gradients as observed in the field during the three distinct sampling events. The velocities calculated from the gas-flow model were used in transient, one-dimensional transport simulations to quantify advective and diffusive fluxes of TCE vapor from the subsurface to the atmosphere as a function of time for each sampling event. Effective diffusion coefficients used for these simulations were determined from independent laboratory measurements made on intact soil cores collected from the field site. For two of the three sampling events (August 1996 and August 1998), the TCE gas-phase diffusion flux at land surface was significantly greater than the advection flux over the entire sampling period. For the second sampling event (October 1996), the advection flux was frequently larger than the
Comparative Study of Multicast Protection Algorithms Using Shared Links in 100GET Transport Network
NASA Astrophysics Data System (ADS)
Sulaiman, Samer; Haidine, Abdelfattah; Lehnert, Ralf; Tuerk, Stefan
In recent years new challenges have emerged in the telecommunications market resulting from the increase of network traffic and strong competition. Because of that, service providers feel constrained to replace expensive and complex IP-routers with a cheap and simple solution which guarantees the requested quality of services (QoS) with low cost. One of these solutions is to use the Ethernet technology as a switching layer, which results in using the cheap Ethernet services (E-Line, E-LAN and E-Tree) and to replace the expensive IP-routers. To achieve this migration step, new algorithms that support the available as well as the future services have to be developed. In this paper, we investigate the multicast protection issue. Three multicast protection algorithms based on the shared capacity between primary and backup solutions are proposed and evaluated. The blocking probability is used to evaluate the performance of the proposed algorithms. The sub-path algorithm resulted in a low blocking probability compared with the other algorithms.
Conditions and processes affecting radionuclide transport
Simmons, Ardyth M.; Neymark, Leonid A.
2012-01-01
Understanding of unsaturated-zone transport is based on laboratory and field-scale experiments. Fractures provide advective transport pathways. Sorption and matrix diffusion may contribute to retardation of radionuclides. Conversely, sorption onto mobile colloids may enhance radionuclide transport.
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.
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.
A comparison of transport algorithms for premixed, laminar steady state flames
NASA Technical Reports Server (NTRS)
Coffee, T. P.; Heimerl, J. M.
1980-01-01
The effects of different methods of approximating multispecies transport phenomena in models of premixed, laminar, steady state flames were studied. Five approximation methods that span a wide range of computational complexity were developed. Identical data for individual species properties were used for each method. Each approximation method is employed in the numerical solution of a set of five H2-02-N2 flames. For each flame the computed species and temperature profiles, as well as the computed flame speeds, are found to be very nearly independent of the approximation method used. This does not indicate that transport phenomena are unimportant, but rather that the selection of the input values for the individual species transport properties is more important than the selection of the method used to approximate the multispecies transport. Based on these results, a sixth approximation method was developed that is computationally efficient and provides results extremely close to the most sophisticated and precise method used.
Development of sub-daily erosion and sediment transport algorithms in SWAT
Technology Transfer Automated Retrieval System (TEKTRAN)
New Soil and Water Assessment Tool (SWAT) algorithms for simulation of stormwater best management practices (BMPs) such as detention basins, wet ponds, sedimentation filtration ponds, and retention irrigation systems are under development for modeling small/urban watersheds. Modeling stormwater BMPs...
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.
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.
Driessen, B.J.; Dohner, J.L.
1998-08-01
In this paper a hybrid, finite element--boundary element method which can be used to solve for particle advection-diffusion in infinite domains with variable advective fields is presented. In previous work either boundary element, finite element, or difference methods have been used to solve for particle motion in advective-diffusive domains. These methods have a number of limitations. Due to the complexity of computing spatially dependent Green`s functions, the boundary element method is limited to domains containing only constant advective fields, and due to their inherent formulation, finite element and finite difference methods are limited to only domains of finite spatial extent. Thus, finite element and finite difference methods are limited to finite space problems for which the boundary element method is not, and the boundary element method is limited to constant advection field problems for which finite element and finite difference methods are not. In this paper it is proposed to split a domain into two sub-domains, and for each of these sub domains, apply the appropriate solution method; thereby, producing a method for the total infinite space, variable advective field domain.
A Method for Measuring Subcanopy CO2 Advection
NASA Astrophysics Data System (ADS)
Staebler, R. M.; Fitzjarrald, D. R.
2004-12-01
Underestimation of nocturnal CO2 respiration under calm conditions remains an unsolved problem at many forest flux stations, and several groups are currently investigating the direct measurement of horizontal advection of CO2. This presentation will describe a systematic, relatively low-cost methodology developed to determine whether horizontal mean transport of CO2 accounts for the missing CO2 at the Harvard Forest (Petersham, MA). This methodology includes the characterization of subcanopy motions, determining the appropriate size of the subcanopy network required to make the measurements, developing a method of integrating the measurements in the vertical, and determining the required averaging time. Measurements were conducted over 4 years and produced data for 310 nights covering all seasons. Subcanopy flows were decoupled from the flows aloft 75% of the time. Conditions conducive to the generation of negative buoyancy near the forest floor, necessary for drainage flows to develop, were given in 92% of all nights. The occurrence of nocturnal drainage flows correlated well with "missing flux" problems ("deficit nights"), prompting us to propose an improvement on the commonly used friction velocity criterion (which requires u* to be larger than some empirical cut-off for the eddy fluxes to be considered credible). The "negative buoyancy forcing fraction", i.e. negative buoyancy as a fraction of the sum of the dynamic driving forces, can be shown to predict deficit nights significantly better than the u* cut-off. The appropriate horizontal size of the network of wind and CO2 sensors at the Harvard Forest was shown to be on the order of 100 m, ensuring that sensors were generally observing coherent processes on this scale or larger and thus displaying some correlation. Horizontal transport of CO2 was found to be restricted to the bottom ~10 m of the forest, facilitating the development of a method of integrating the horizontal CO2 gradients in the vertical
NASA Astrophysics Data System (ADS)
Ebner, P. P.; Schneebeli, M.; Steinfeld, A.
2015-09-01
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 micro-tomography is applied to investigate the structural dynamics of temperature gradient snow metamorphism exposed to an advective airflow in controlled laboratory conditions. The sublimation of water vapor for saturated air flowing across the snow sample was experimentally determined via variations of the porous ice structure. The results showed that the exothermic gas-to-solid phase change is favorable vis-a-vis the endothermic solid-to-gas phase change, thus leading to more ice deposition than ice sublimation. Sublimation has a marked effect on the structural change of the ice matrix but diffusion of water vapor in 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 reposition process of water molecules on the ice grains is relevant for atmospheric chemistry.
NASA Astrophysics Data System (ADS)
Weston, Joseph; Waintal, Xavier
2016-04-01
We report on a "source-sink" algorithm which allows one to calculate time-resolved physical quantities from a general nanoelectronic quantum system (described by an arbitrary time-dependent quadratic Hamiltonian) connected to infinite electrodes. Although mathematically equivalent to the nonequilibrium Green's function formalism, the approach is based on the scattering wave functions of the system. It amounts to solving a set of generalized Schrödinger equations that include an additional "source" term (coming from the time-dependent perturbation) and an absorbing "sink" term (the electrodes). The algorithm execution time scales linearly with both system size and simulation time, allowing one to simulate large systems (currently around 106 degrees of freedom) and/or large times (currently around 105 times the smallest time scale of the system). As an application we calculate the current-voltage characteristics of a Josephson junction for both short and long junctions, and recover the multiple Andreev reflection physics. We also discuss two intrinsically time-dependent situations: the relaxation time of a Josephson junction after a quench of the voltage bias, and the propagation of voltage pulses through a Josephson junction. In the case of a ballistic, long Josephson junction, we predict that a fast voltage pulse creates an oscillatory current whose frequency is controlled by the Thouless energy of the normal part. A similar effect is found for short junctions; a voltage pulse produces an oscillating current which, in the absence of electromagnetic environment, does not relax.
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.
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
Heavy clay sediments are regarded "safe" from the hydrological point of view due to their low hydraulic conductivities. However, the formation of desiccation cracks in dispersive clays may dramatically change their bulk hydraulic properties. The impact of desiccation cracks on water percolation, dissolved salts and contaminants transport and redox related reactions (microbial ammonium oxidation and denitrification) were investigated in 6 -12 m clay layer near a diary farm waste lagoon. The study implemented unique vadose-zone monitoring systems that enable in-situ measurements of the temporal variation of the sediment's water content along with frequent sampling of the sediment's pore water along the entire vadose zone (> 30 m). Results from four years of continuous measurements showed quick rises in sediment water content following rain events and temporal wastewater overflows. The percolation pattern indicated dominance of preferential flow through a desiccation-cracks network crossing the entire clay sediment layer. High water-propagation velocities (0.4 - 23.6 m h-1) were observed, indicating that the desiccation-crack network remains open and serves as a preferential flow pathway year-round, even at high sediment water content (~0.50 m3 m-3). The rapid percolation bypassed the most bio-geo-active parts of the soil, transporting even highly sorptive contaminants (testosterone and estrogen) in to the deep sections of the vadose zone, accelerating the underlying groundwater contamination. The ammonium and nitrate concentrations in the vadose zone and the high number of nitrifying and denitrifying bacteria (~108 gene copies gdry-sediemt-1, each) found in the sediment indicated that the entire vadose zone is aerated even at high water content conditions (~0.55 m3 m-3). The dissolved salts concentration in the pore-water and the δ2H-H2O and δ18O-H2O values of the pore-water substantially increased with depth (becoming less depleted) in the clay sediment
Yaqi Wang; Cristian Rabiti; Giuseppe Palmiotti
2011-06-01
The Red-Black algorithm has been successfully applied on solving the second-order parity transport equation with the PN approximation in angle and the Hybrid Finite Element Method (HFEM) in space, i.e., the Variational Nodal Method (VNM) [1,2,3,4,5]. Any transport solving techniques, including the Red-Black algorithm, need to be parallelized in order to take the advantage of the development of supercomputers with multiple processors for the advanced modeling and simulation. To our knowledge, an attempt [6] was done to parallelize it, but it was devoted only to the z axis plans in three-dimensional calculations. General parallelization of the Red-Black algorithm with the spatial domain decomposition has not been reported in the literature. In this summary, we present our implementation of the parallelization of the Red-Black algorithm and its efficiency results.
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.
Cunningham, Andrew J.; Frank, Adam; Varniere, Peggy; Mitran, Sorin; Jones, Thomas W.
2009-06-15
A description is given of the algorithms implemented in the AstroBEAR adaptive mesh-refinement code for ideal magnetohydrodynamics. The code provides several high-resolution shock-capturing schemes which are constructed to maintain conserved quantities of the flow in a finite-volume sense. Divergence-free magnetic field topologies are maintained to machine precision by collating the components of the magnetic field on a cell-interface staggered grid and utilizing the constrained transport approach for integrating the induction equations. The maintenance of magnetic field topologies on adaptive grids is achieved using prolongation and restriction operators which preserve the divergence and curl of the magnetic field across collocated grids of different resolutions. The robustness and correctness of the code is demonstrated by comparing the numerical solution of various tests with analytical solutions or previously published numerical solutions obtained by other codes.
NASA Astrophysics Data System (ADS)
Feldman, Baruch; Zhou, Yunkai
2016-10-01
We present an eigenspectrum partitioning scheme without inversion for the recently described real-space electronic transport code, TRANSEC. The primary advantage of TRANSEC is its highly parallel algorithm, which enables studying conductance in large systems. The present scheme adds a new source of parallelization, significantly enhancing TRANSEC's parallel scalability, especially for systems with many electrons. In principle, partitioning could enable super-linear parallel speedup, as we demonstrate in calculations within TRANSEC. In practical cases, we report better than five-fold improvement in CPU time and similar improvements in wall time, compared to previously-published large calculations. Importantly, the suggested scheme is relatively simple to implement. It can be useful for general large Hermitian or weakly non-Hermitian eigenvalue problems, whenever relatively accurate inversion via direct or iterative linear solvers is impractical.
Parvizi, A; Van den Broek, W; Koch, C T
2016-04-18
The transport of intensity equation (TIE) is widely applied for recovering wave fronts from an intensity measurement and a measurement of its variation along the direction of propagation. In order to get around the problem of non-uniqueness and ill-conditionedness of the solution of the TIE in the very common case of unspecified boundary conditions or noisy data, additional constraints to the solution are necessary. Although from a numerical optimization point of view, convex constraint as imposed to by total variation minimization is preferable, we will show that in many cases non-convex constraints are necessary to overcome the low-frequency artifacts so typical for convex constraints. We will provide simulated and experimental examples that demonstrate the superiority of solutions to the TIE obtained by our recently introduced gradient flipping algorithm over a total variation constrained solution. PMID:27137272
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.
NASA Technical Reports Server (NTRS)
Guo, Liwen; Cardullo, Frank M.; Kelly, Lon C.
2007-01-01
This report summarizes the results of delay measurement and piloted performance tests that were conducted to assess the effectiveness of the adaptive compensator and the state space compensator for alleviating the phase distortion of transport delay in the visual system in the VMS at the NASA Langley Research Center. Piloted simulation tests were conducted to assess the effectiveness of two novel compensators in comparison to the McFarland predictor and the baseline system with no compensation. Thirteen pilots with heterogeneous flight experience executed straight-in and offset approaches, at various delay configurations, on a flight simulator where different predictors were applied to compensate for transport delay. The glideslope and touchdown errors, power spectral density of the pilot control inputs, NASA Task Load Index, and Cooper-Harper rating of the handling qualities were employed for the analyses. The overall analyses show that the adaptive predictor results in slightly poorer compensation for short added delay (up to 48 ms) and better compensation for long added delay (up to 192 ms) than the McFarland compensator. The analyses also show that the state space predictor is fairly superior for short delay and significantly superior for long delay than the McFarland compensator.
The conservative characteristic FD methods for atmospheric aerosol transport problems
NASA Astrophysics Data System (ADS)
Fu, Kai; Liang, Dong
2016-01-01
In the paper, we develop the new conservative characteristic finite difference methods (C-CFD) for the atmospheric aerosol transport problems. We propose the time second-order and spatial high-order conservative characteristic finite difference methods for the aerosol vertical advection-diffusion process and the two-dimensional conservative characteristic finite difference methods for aerosol horizontal transport process in the second-order splitting algorithm. Based on the characteristic form of advection-diffusion equations tracking back along the characteristic curve, we treat the integrals over the tracking cells at the previous time level by the conservative interpolations and propose to treat the diffusion terms by the average along the characteristics, where the high-order discrete fluxes are obtained by approximating the cumulative mass function and are continuous at the tracking points. The important feature is that the proposed C-CFD schemes preserve mass and have second-order accuracy in time and high-order accuracy in space. Numerical tests are taken to show the accuracy in time and space and mass conservation of our C-CFD schemes, compared with the standard CFD method. A real case of air quality modelling during the 2008 Beijing Olympics and a severe haze in North China are further simulated and analyzed by using our C-CFD algorithm. Simulated results are in good agreement with observations. The developed C-CFD algorithm can be used for efficiently solving large scale atmospheric aerosol transport problems.
Garcia-Pareja, S.; Galan, P.; Manzano, F.; Brualla, L.; Lallena, A. M.
2010-07-15
Purpose: In this work, the authors describe an approach which has been developed to drive the application of different variance-reduction techniques to the Monte Carlo simulation of photon and electron transport in clinical accelerators. Methods: The new approach considers the following techniques: Russian roulette, splitting, a modified version of the directional bremsstrahlung splitting, and the azimuthal particle redistribution. Their application is controlled by an ant colony algorithm based on an importance map. Results: The procedure has been applied to radiosurgery beams. Specifically, the authors have calculated depth-dose profiles, off-axis ratios, and output factors, quantities usually considered in the commissioning of these beams. The agreement between Monte Carlo results and the corresponding measurements is within {approx}3%/0.3 mm for the central axis percentage depth dose and the dose profiles. The importance map generated in the calculation can be used to discuss simulation details in the different parts of the geometry in a simple way. The simulation CPU times are comparable to those needed within other approaches common in this field. Conclusions: The new approach is competitive with those previously used in this kind of problems (PSF generation or source models) and has some practical advantages that make it to be a good tool to simulate the radiation transport in problems where the quantities of interest are difficult to obtain because of low statistics.
Performance Analysis of high-order remap-type advection scheme on icosahedral-hexagonal grid
NASA Astrophysics Data System (ADS)
Mittal, Rashmi; Dubey, Sarvesh; Saxena, Vaibhav; Meurdesoif, Yann
2014-05-01
A comparative performance analysis on computational cost of second order advection schemes FF-CSLAM (Flux form conservative semi-Lagrangian multi-tracer transport scheme) and it's two simplifications on Icosahedral grid has been presented. Tracer transport is one of the main building blocks in atmospheric models and hence their performance greatly determines the overall performance of the model. FF-CSLAM falls in the category of arbitrary Lagrangian Eulerian (ALE) scheme. It exploits the finite volume formulation and therefore it is inherently conservative. Flux-area through edges are approximated with great circle arcs in an upwind fashion. Bi-quadratic sub-grid scale reconstructions using weighted least-squares method is employed to approximate trace field. Area integrals on the overlapped region of flux-area and static Eulerian meshes are evaluated via line-integrals. A brief description of implementation of FF-CSLAM on icosahedral -hexagonal meshes along with and its numerical accuracy in terms of standard test cases will be presented. A comparative analysis of the computational overhead is necessary to assess the suitability of FF-CSLAM for massively parallel and multi-threading computer architectures in comparison to other advection schemes implemented on icosahedral grids. The main focus of this work is to present the implementation of the shared memory parallelization and to describe the memory access pattern of the numerical scheme. FF-CSLAM is a remap-type advection scheme, thus extra calculation are done in comparison to the other advection schemes. The additional computations are associated with the search required to find the overlap area between the area swept through the edge and the underlining grid. But the experiments shows that the associated computational overhead is minimal for multi-tracer transport. It will be shown that for the Courant Number less than one, FF-CSLAM, the computations are not expensive. Since the grid cells are arranged in
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
Invasions in heterogeneous habitats in the presence of advection.
Vergni, Davide; Iannaccone, Sandro; Berti, Stefano; Cencini, Massimo
2012-05-21
We investigate invasions from a biological reservoir to an initially empty, heterogeneous habitat in the presence of advection. The habitat consists of a periodic alternation of favorable and unfavorable patches. In the latter the population dies at fixed rate. In the former it grows either with the logistic or with an Allee effect type dynamics, where the population has to overcome a threshold to grow. We study the conditions for successful invasions and the speed of the invasion process, which is numerically and analytically investigated in several limits. Generically advection enhances the downstream invasion speed but decreases the population size of the invading species, and can even inhibit the invasion process. Remarkably, however, the rate of population increase, which quantifies the invasion efficiency, is maximized by an optimal advection velocity. In models with Allee effect, differently from the logistic case, above a critical unfavorable patch size the population localizes in a favorable patch, being unable to invade the habitat. However, we show that advection, when intense enough, may activate the invasion process.
Black Hole Advective Accretion Disks with Optical Depth Transition
Artemove, Y.V.; Bisnovatyi-Kogan, G.S.; Igumenshchev, I.V.; Novikov, I.D.
2006-02-01
We have constructed numerically global solutions of advective accretion disks around black holes that describe a continuous transition between the effectively optically thick outer and optically thin inner disk regions. We have concentrated on models of accretion flows with large mass accretion rates, and we have employed a bridging formula for radiative losses at high and low effective optical depths.
Radiation transport algorithms on trans-petaflops supercomputers of different architectures.
Christopher, Thomas Woods
2003-08-01
We seek to understand which supercomputer architecture will be best for supercomputers at the Petaflops scale and beyond. The process we use is to predict the cost and performance of several leading architectures at various years in the future. The basis for predicting the future is an expanded version of Moore's Law called the International Technology Roadmap for Semiconductors (ITRS). We abstract leading supercomputer architectures into chips connected by wires, where the chips and wires have electrical parameters predicted by the ITRS. We then compute the cost of a supercomputer system and the run time on a key problem of interest to the DOE (radiation transport). These calculations are parameterized by the time into the future and the technology expected to be available at that point. We find the new advanced architectures have substantial performance advantages but conventional designs are likely to be less expensive (due to economies of scale). We do not find a universal ''winner'', but instead the right architectural choice is likely to involve non-technical factors such as the availability of capital and how long people are willing to wait for results.
Implementation of a Semi-Lagrangian scheme for water vapour and tracer advection in RegCM4
NASA Astrophysics Data System (ADS)
Tefera Diro, Gulilat; Tompkins, Adrian; Giorgi, Filippo; Bonaventura, Luca
2013-04-01
A semi-Lagrangian approach is introduced in the latest version of the ICTP regional climate model (RegCM4) for water vapor and tracer advection. A 'quasi' cubic interpolation and McGregor's third order accurate trajectory calculation are used in the advection scheme. The modified scheme is evaluated on idealized as well as realistic case studies and its results are compared against those of the Eulerian scheme originally employed in RegCM4. In the idealized test cases the semi-Lagrangian scheme appears to be superior to the Eulerian scheme in terms of the dissipative and dispersive errors, especially when large gradients are present in the advected quantity. Two realistic cases of meso-scale phenomena over the European domain were also tested in a short range mode for specific humidity transport. In both cases, the semi-Lagrangian scheme has captured better the detailed structure and improved the overall pattern of the vertically integrated humidity field. In the present preliminary implementation, the scheme is more expensive than the Eulerian one. This is because the same time step is used for tracer advection as the explicit time discretization employed by the dynamical core. However, greater computational gains are expected as the number of tracers considered increases, for instance when the gas phase chemistry is switched on.
Stevens, D.E.; Bretherton, S.
1996-12-01
This paper presents a new forward-in-time advection method for nearly incompressible flow, MU, and its application to an adaptive multilevel flow solver for atmospheric flows. MU is a modification of Leonard et al.`s UTOPIA scheme. MU, like UTOPIA, is based on third-order accurate semi-Lagrangian multidimensional upwinding for constant velocity flows. for varying velocity fields, MU is a second-order conservative method. MU has greater stability and accuracy than UTOPIA and naturally decomposes into a monotone low-order method and a higher-order accurate correction for use with flux limiting. Its stability and accuracy make it a computationally efficient alternative to current finite-difference advection methods. We present a fully second-order accurate flow solver for the anelastic equations, a prototypical low Mach number flow. The flow solver is based on MU which is used for both momentum and scalar transport equations. This flow solver can also be implemented with any forward-in-time advection scheme. The multilevel flow solver conserves discrete global integrals of advected quantities and includes adaptive mesh refinements. Its second-order accuracy is verified using a nonlinear energy conservation integral for the anelastic equations. For a typical geophysical problem in which the flow is most rapidly varying in a small part of the domain, the multilevel flow solver achieves global accuracy comparable to uniform-resolution simulation for 10% of the computational cost. 36 refs., 10 figs.
NASA Astrophysics Data System (ADS)
Ebner, P. P.; Grimm, S. A.; Schneebeli, M.; Steinfeld, A.
2014-06-01
An instrumented sample holder was developed for time-lapse micro-tomography of snow samples to enable in-situ nondestructive spatial and temporal measurements under controlled advective airflows, temperature gradients, and air humidities. The design was aided by computational fluid dynamics simulations to evaluate the airflow uniformity across the snow sample. Morphological and mass transport properties were evaluated during a 4 day test run. This instrument allows the experimental characterization of metamorphism of snow undergoing structural changes with time.
Toxic Alexandrium blooms in the western Gulf of Maine: The plume advection hypothesis revisited
Anderson, D.M.; Keafer, B.A.; Geyer, W.R.; Signell, R.P.; Loder, T.C.
2005-01-01
The plume advection hypothesis links blooms of the toxic dinoflagellate Alexandrium fundyense in the western Gulf of Maine (GOM) to a buoyant plume derived from river outflows. This hypothesis was examined with cruise and moored-instrument observations in 1993 when levels of paralytic shellfish poisoning (PSP) toxins were high, and in 1994 when toxicity was low. A coupled physical-biological model simulated hydrography and A. fundyense distributions. Initial A. fundyense populations were restricted to low-salinity nearshore waters near Casco Bay, but also occurred in higher salinity waters along the plume boundary. This suggests two sources of cells - those from shallow-water cyst populations and those transported to shore from offshore blooms in the eastern segment of the Maine coastal current (EMCC). Observations confirm the role of the plume in A. fundyense transport and growth. Downwelling-favorable winds in 1993 transported the plume and its cells rapidly alongshore, enhancing toxicity and propagating PSP to the south. In 1994, sustained upwelling moved the plume offshore, resulting in low toxicity in intertidal shellfish. A. fundyense blooms were likely nutrient limited, leading to low growth rates and moderate cell abundances. These observations and mechanisms were reproduced by coupled physical-biological model simulations. The plume advection hypothesis provides a viable explanation for outbreaks of PSP in the western GOM, but should be refined to include two sources for cells that populate the plume and two major pathways for transport: one within the low-salinity plume and another where A. fundyense cells originating in the EMCC are transported along the outer boundary of the plume front with the western segment of the Maine coastal current.
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.
Pollutant advective spreading in beach sand exposed to high-energy tides
NASA Astrophysics Data System (ADS)
Itugha, Okuroghoboye D.; Chen, Daoyi; Guo, Yakun
2016-11-01
This paper presents field measurements in which dye solute was injected into coastal sand to investigate contaminant advection in intertidal beach sand. The measurements show the pathways of a contaminated plume in the unsaturated zone during both the flood and ebb tides. A prescribed amount of dye tracer solution was directly injected through the topsoil, with average porosity 0.3521 ± 0.01, at predetermined locations of the River Mersey's outer estuarial beach during ebb-tide. The injected dye was monitored, sampled and photographed over several tidal cycles. The distinctive features of the plume (full two dimensional cross-sections), sediments and water-table depth were sampled in-situ, close to the injection point (differing from previous contaminant monitoring tests in aquifers). The advective movement is attributed to tidal impact which is different from contaminant transport in aquifers. The experimental results show that plumes have significantly large spatial variability, diverging upwards and converging downwards, with a conical geometric shape which is different from the usual spherical/elliptical shape reported in literature. The mean vertical motion of the plume reaches three times the top-width within ten tidal cycles, exceeding the narrow bottom-width by a factor of order 2. The observed transport features of the plume within the beach sand have significant relevance to saltwater intrusion, surface water and groundwater quality. The field observations are unique and can serve as a valuable benchmark database for relevant numerical studies.
Advection of surface-derived organic carbon fuels microbial reduction in Bangladesh groundwater
NASA Astrophysics Data System (ADS)
Mailloux, Brian J.; Trembath-Reichert, Elizabeth; Cheung, Jennifer; Watson, Marlena; Stute, Martin; Freyer, Greg A.; Ferguson, Andrew S.; Matin Ahmed, Kazi; Jahangir Alam, Md.; Buchholz, Bruce A.; Thomas, James; Layton, Alice C.; Zheng, Yan; Bostick, Benjamin C.; van Geen, Alexander
2013-04-01
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.
Coupling Flow and Thermal and Reactive Geochemical Transport
NASA Astrophysics Data System (ADS)
Yeh, G.
2004-12-01
The couplings among fluid flows, thermal transport, geochemical reactions, advective and diffusive transport of solutes in fractured media or soils, and changes in hydraulic properties due to precipitation and dissolution along fractures and rock matrix are important for understanding interplays between fluid flows and dynamic transport processes. This paper describes the development and demonstrative applications of a mechanistic-based numerical model of coupled fluid flow and thermal and reactive geochemical transport, including both fast and slow reactions, in variably saturated media. Theoretical bases, numerical implementations, and two numerical experiments using the model will be presented. The first example deals with the effect of precipitation-dissolution on fluid flow and matrix diffusion in a two-dimensional fractured media. Because of the precipitation and decreased diffusion of solute from the fracture into the matrix, retardation in the fractured medium is not as large as the case wherein interactions between geochemical reactions and transport are not considered. The second example focuses on a complicated but realistic advective-dispersive-reactive transport problem. This example exemplifies the need for innovative numerical algorithms to solve problems involving stiff geochemical reactions.
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.
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.
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.
NASA Astrophysics Data System (ADS)
Kotegawa, Tatsuya
Complexity in the Air Transportation System (ATS) arises from the intermingling of many independent physical resources, operational paradigms, and stakeholder interests, as well as the dynamic variation of these interactions over time. Currently, trade-offs and cost benefit analyses of new ATS concepts are carried out on system-wide evaluation simulations driven by air traffic forecasts that assume fixed airline routes. However, this does not well reflect reality as airlines regularly add and remove routes. A airline service route network evolution model that projects route addition and removal was created and combined with state-of-the-art air traffic forecast methods to better reflect the dynamic properties of the ATS in system-wide simulations. Guided by a system-of-systems framework, network theory metrics and machine learning algorithms were applied to develop the route network evolution models based on patterns extracted from historical data. Constructing the route addition section of the model posed the greatest challenge due to the large pool of new link candidates compared to the actual number of routes historically added to the network. Of the models explored, algorithms based on logistic regression, random forests, and support vector machines showed best route addition and removal forecast accuracies at approximately 20% and 40%, respectively, when validated with historical data. The combination of network evolution models and a system-wide evaluation tool quantified the impact of airline route network evolution on air traffic delay. The expected delay minutes when considering network evolution increased approximately 5% for a forecasted schedule on 3/19/2020. Performance trade-off studies between several airline route network topologies from the perspectives of passenger travel efficiency, fuel burn, and robustness were also conducted to provide bounds that could serve as targets for ATS transformation efforts. The series of analysis revealed that high
NASA Technical Reports Server (NTRS)
Guo, Liwen; Cardullo, Frank M.; Kelly, Lon C.
2007-01-01
The desire to create more complex visual scenes in modern flight simulators outpaces recent increases in processor speed. As a result, simulation transport delay remains a problem. New approaches for compensating the transport delay in a flight simulator have been developed and are presented in this report. The lead/lag filter, the McFarland compensator and the Sobiski/Cardullo state space filter are three prominent compensators. The lead/lag filter provides some phase lead, while introducing significant gain distortion in the same frequency interval. The McFarland predictor can compensate for much longer delay and cause smaller gain error in low frequencies than the lead/lag filter, but the gain distortion beyond the design frequency interval is still significant, and it also causes large spikes in prediction. Though, theoretically, the Sobiski/Cardullo predictor, a state space filter, can compensate the longest delay with the least gain distortion among the three, it has remained in laboratory use due to several limitations. The first novel compensator is an adaptive predictor that makes use of the Kalman filter algorithm in a unique manner. In this manner the predictor can accurately provide the desired amount of prediction, while significantly reducing the large spikes caused by the McFarland predictor. Among several simplified online adaptive predictors, this report illustrates mathematically why the stochastic approximation algorithm achieves the best compensation results. A second novel approach employed a reference aircraft dynamics model to implement a state space predictor on a flight simulator. The practical implementation formed the filter state vector from the operator s control input and the aircraft states. The relationship between the reference model and the compensator performance was investigated in great detail, and the best performing reference model was selected for implementation in the final tests. Theoretical analyses of data from offline
NASA Astrophysics Data System (ADS)
Biavati, G.; Kretschmer, R.; Gerbig, C.; Feist, D. G.
2012-04-01
The retrieval of mixing height [MH] is a common target of several scientific community all over the world. A strong effort is needed to the fact that modeling of MH generally fails introducing strong errors in the estimate of the concentrations of pollutants and green house gasses within the boundary layer. In Europe local meteorological services and international projects are implementing networks of instruments that can provide atmospheric profiles of different quantities. These networks will continuously provide data which could be used to constrain MH values. The current availability of atmospheric profiles of different nature, such as radiosondes, ground based lidar and ceilometers as well as satellites over Europe grant a spatial coverage that allow to estimate the impact of the knowledge of MH on transport models at synoptic scale of quantities as CO2 and CH4 mixing ratios. In this study we apply several algorithms to retrieve MH from different data sources: the ceilometers network installed by the German Weather Service; the data from CALIPSO satellite and all the WMO radio-soundings available over Europe during the IMECC (Infrastructure for Measurements of the European Carbon Cycle) in 2009. The values obtained from the optical instruments are validated using as reference the estimation retrieved by the virtual potential temperature profiles obtained by the radiosondes where co-location occurs and using statistical interpolation to evaluate the estimates from satellite and non co-located stations.. The impact of this estimates of MH on CO2 mixing ratios will be evaluated with the Stochastic Time Inverted Lagrangian Transport model (STILT) driven by WRF meteorology in comparison with in-situ measurements.
NASA Astrophysics Data System (ADS)
Renner, Angelika H. H.; Thorpe, Sally E.; Heywood, Karen J.; Murphy, Eugene J.; Watkins, Jon L.; Meredith, Michael P.
2012-05-01
Pathways and rates of ocean flow near the Antarctic Peninsula are strongly affected by frontal features, forcings from the atmosphere and the cryosphere. In the surface mixed layer, the currents advect material from the northwestern Weddell Sea on the eastern side of the Peninsula around the tip of the Peninsula to its western side and into the Scotia Sea, connecting populations of Antarctic krill (Euphausia superba) and supporting the ecosystem of the region. Modelling of subsurface drifters using a particle tracking algorithm forced by the velocity fields of a coupled sea ice-ocean model (ORCA025-LIM2) allows analysis of the seasonal and interannual variability of drifter pathways over 43 years. The results show robust and persistent connections from the Weddell Sea both to the west into the Bellingshausen Sea and across the Scotia Sea towards South Georgia, reproducing well the observations. The fate of the drifters is sensitive to their deployment location, in addition to other factors. From the shelf of the eastern Antarctic Peninsula, the majority enter the Bransfield Strait and subsequently the Bellingshausen Sea. When originating further offshore over the deeper Weddell Sea, drifters are more likely to cross the South Scotia Ridge and reach South Georgia. However, the wind field east and southeast of Elephant Island, close to the tip of the Peninsula, is crucial for the drifter trajectories and is highly influenced by the Southern Annular Mode (SAM). Increased advection and short travel times to South Georgia, and reduced advection to the western Antarctic Peninsula can be linked to strong westerlies, a signature of the positive phase of the SAM. The converse is true for the negative phase. Strong westerlies and shifts of ocean fronts near the tip of the Peninsula that are potentially associated with both the SAM and the El Niño-Southern Oscillation restrict the connection from the Weddell Sea to the west, and drifters then predominantly follow the open
Glacial disparities in Intermediate Mode Water advection in the South Pacific Gyre
NASA Astrophysics Data System (ADS)
Tapia, R.; Nuernberg, D.; Ronge, T.; Tiedemann, R.
2014-12-01
The Intermediate Mode Waters formed in the Southern Ocean are critical for the lower thermocline ventilation process in the Southern Hemisphere Gyres. They also might have served as the most relevant pathways transporting climatic signals from high to low latitudes via the "oceanic tunneling" on glacial/interglacial time scales. Despite the importance of the Southern Ocean Intermediate Waters (SOIWs), our understanding on the long-term evolution, exact advection paths, and impact on the South Pacific Gyre's thermocline is still fragmentary. Here, we present a 200 kyr record of paired Mg/Ca ratios and stable oxygen isotope from surface dweller and deep dwelling planktonic foraminifera, from the South Pacific Gyre (SPG). On average, the Mg/Ca-derived sea Surface Temperatures (Globigerina bulloides) show similar conditions during the LGM and Marine Isotope Stage (MIS) 6 (9.4 °C versus 9.9 °C). In contrast, our Mg/Ca-derived subsurface temperatures (Globorotalia inflata and Globorotalia truncatulinoides) suggest LGM from ~3 to ~2 °C colder than MIS 6. The reconstructed subsurface ice volume corrected stable oxygen isotope ratio of seawater (δ18Osw-ivc, proxy for local salinity changes) suggests opposing glacial subsurface conditions, i.e., slightly saltier-than-Holocene during MIS 6 to fresher-than-Holocene during MIS 2. Considering that subsurface hydrography at the core site is plausibly driven by the formation and/or advection of SOIWs from the South East Pacific, our results provide further support on the relevance of subsurface processes in the Southern Ocean transferring climatic signals (temperature and salinity) to the SPG. Furthermore, the contrasting subsurface glacial scenarios at the SPG's thermocline imply that the advection of SOIWs during glacial stages could be highly variable during different glacial stages.
NASA Astrophysics Data System (ADS)
Georghiou, G. E.; Morrow, R.; Metaxas, A. C.
2000-10-01
An improved finite-element flux-corrected transport (FE-FCT) scheme, which was demonstrated in one dimension by the authors, is now extended to two dimensions and applied to gas discharge problems. The low-order positive ripple-free scheme, required to produce a FCT algorithm, is obtained by introducing diffusion to the high-order scheme (two-step Taylor-Galerkin). A self-adjusting variable diffusion coefficient is introduced, which reduces the high-order scheme to the equivalent of the upwind difference scheme, but without the complexities of an upwind scheme in a finite-element setting. Results are presented which show that the high-order scheme reduces to the equivalent of upwinding when the new diffusion coefficient is used. The proposed FCT scheme is shown to give similar results in comparison to a finite-difference time-split FCT code developed by Boris and Book. Finally, the new method is applied for the first time to a streamer propagation problem in its two-dimensional form.
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.
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.
A high order characteristic discontinuous Galerkin scheme for advection on unstructured meshes
NASA Astrophysics Data System (ADS)
Lee, D.; Lowrie, R.; Petersen, M.; Ringler, T.; Hecht, M.
2016-11-01
A new characteristic discontinuous Galerkin (CDG) advection scheme is presented. In contrast to standard discontinuous Galerkin schemes, the test functions themselves follow characteristics in order to ensure conservation and the edges of each element are also traced backwards along characteristics in order to create a swept region, which is integrated in order to determine the mass flux across the edge. Both the accuracy and performance of the scheme are greatly improved by the use of large Courant-Friedrichs-Lewy numbers for a shear flow test case and the scheme is shown to scale sublinearly with the number of tracers being advected, outperforming a standard flux corrected transport scheme for 10 or more tracers with a linear basis. Moreover the CDG scheme may be run to arbitrarily high order spatial accuracy and on unstructured grids, and is shown to give the correct order of error convergence for piecewise linear and quadratic bases on regular quadrilateral and hexahedral planar grids. Using a modal Taylor series basis, the scheme may be made monotone while preserving conservation with the use of a standard slope limiter, although this reduces the formal accuracy of the scheme to first order. The second order scheme is roughly as accurate as the incremental remap scheme with nonlocal gradient reconstruction at half the horizontal resolution. The scheme is being developed for implementation within the Model for Prediction Across Scales (MPAS) Ocean model, an unstructured grid finite volume ocean model.
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
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
A reaction between two chemical species can only happen if molecules collide and react. Thus, the mixing of a system can become a limiting factor in the onset of reaction. Solving for reaction rate in a well-mixed system is typically a straightforward task. However, when incomplete mixing kicks in, obtaining a solution becomes more challenging. Since reaction can only happen in regions where both reactants co-exist, the incomplete mixing may slow down the reaction rate, when compared to a well-mixed system. The effect of incomplete mixing upon reaction is a highly important aspect of various processes in natural and engineered systems, ranging from mineral precipitation in geological formations to groundwater remediation in aquifers. We study a relatively simple system with a bi-molecular irreversible kinetic reaction A+B → Ø where the underlying transport of reactants is governed by an advection-diffusion equation, and the initial concentrations are given in terms of an average and a perturbation. Such a system does not have an analytical solution to date, even for the zero advection case. We model the system by a Monte Carlo particle tracking method, where particles represent some reactant mass. In this method, diffusion is modeled by a random walk of the particles, and reaction is modeled by annihilation of particles. The probability of the annihilation is proportional to the reaction rate constant and the probability density associated with particle co-location. We study the numerical method in depth, characterizing typical numerical errors and time step restrictions. In particular, we show that the numerical method converges to the advection-diffusion-reaction equation at the limit Δt →0. We also rigorously derive the relationship between the initial number of particles in the system and the initial concentrations perturbations represented by that number. We then use the particle simulations of zero-advection system to demonstrate the well
NASA Astrophysics Data System (ADS)
Fischer, G.; Reuter, C.; Karakas, G.; Nowald, N.; Wefer, G.
2009-12-01
This article will review major features of the ‘giant’ Cape Blanc filament off Mauritania with regard to the transport of chlorophyll and organic carbon from the shelf to the open ocean. Within the filament, chlorophyll is transported about 400 km offshore. Modelled particle distributions along a zonal transect at 21°N showed that particles with a sinking velocity of 5 m d -1 are advected offshore by up to 600 km in subsurface particle clouds generally located between 400 m and 800 m water depth, forming an Intermediate Nepheloid Layer (INL). It corresponds to the depth of the oxygen minimum zone. Heavier particles with a sinking velocity of 30 m d -1 are transported from the shelf within the Bottom Layer (BL) of more than 1000 m thickness, largely following the topography of the bottom slope. The particles advected within the BL contribute to the enhanced winter-spring mass fluxes collected at the open-ocean mesotrophic sediment trap site CB-13 (∼200 nm offshore), due to a long distance advection in deeper waters. The lateral contribution to the deep sediment trap in winter-spring is estimated to be 63% and 72% for organic carbon and total mass, respectively, whereas the lateral input for both components on an annual basis is estimated to be in the order of 15%. Biogenic opal increases almost fivefold from the upper to the lower mesotrophic CB-13 trap, also pointing to an additional source for biogenic silica from eutrophic coastal waters. Blooms obviously sink in smaller, probably mesoscale-sized patches with variable settling rates, depending on the type of aggregated particles and their ballast content. Generally, particle sinking rates are exceptionally high off NW Africa. Very high chlorophyll values and a large size of the Cape Blanc filament in 1998-1999 are also documented in enhanced total mass and organic carbon fluxes. An increasing trend in satellite chlorophyll concentrations and the size of the Cape Blanc filament between 1997 and 2008 as
ERIC Educational Resources Information Center
Crank, Ron
This instructional unit is one of 10 developed by students on various energy-related areas that deals specifically with transportation and energy use. Its objective is for the student to be able to discuss the implication of energy usage as it applies to the area of transportation. Some topics covered are efficiencies of various transportation…
NASA Astrophysics Data System (ADS)
Matsui, H.; Koike, M.
2012-08-01
We have developed a new source and process apportionment method, the Process, Age, and Source region Chasing ALgorithm (PASCAL), and implemented it in a three-dimensional chemical transport model, the Community Multiscale Air Quality (CMAQ) model. By adding new variables (tagged species), PASCAL traces 1) the source region of emissions (source apportionment), 2) the age of individual species (elapsed time from emissions), 3) net and gross production and loss amounts from individual physical and chemical processes during transport (Lagrangian way), and 4) local production and loss rates at individual grid cells (Eulerian way) for primary and secondary aerosols and their precursor gases. The main advantage of PASCAL is the third one, which can trace accumulated production and loss amounts of individual processes during transport from source regions to each grid cell (Lagrangian type of integration) for both gross (production and loss) and net (gross production - loss) concentrations. Currently the method is applied for mixing ratios of CO and SO2 and mass concentrations of black carbon and sulfate aerosols. This algorithm is not impacted by the non-linearity of chemical reactions and is computationally efficient. CMAQ/PASCAL model calculations were conducted over the East Asian region to test its performance. The overall validity of PASCAL calculations is confirmed for all species, periods, altitudes, and regions. This algorithm will be a useful tool in evaluating source regions as well as formation and loss processes of aerosols in the atmosphere in order to make effective strategies for emissions reduction.
NASA Astrophysics Data System (ADS)
Wilderbuer, Thomas; Duffy-Anderson, Janet T.; Stabeno, Phyllis; Hermann, Albert
2016-05-01
effect on horizontal eddy diffusion, increasing its value by a factor of five in the case of fixed-depth floats, as compared with a factor of two in the case of neutrally buoyant floats. Further, the incorporation of diurnal vertical behavior in phase with favorable (on shelf) tides transported the "larvae" ~ 400 km within 40 days of their release date. Empirical drifter data coupled with model evidence suggest that semi-diurnal tidal forcing is the primary mechanism of eastward advection over the Bering Sea shelf, and larval observational data suggest that northern rock sole larvae can maximize their eastward transport to nursery grounds by synchronizing their vertical movements to tidal periodicity during the postflexion stage.
NASA Astrophysics Data System (ADS)
Rubbab, Qammar; Mirza, Itrat Abbas; Qureshi, M. Zubair Akbar
2016-07-01
The time-fractional advection-diffusion equation with Caputo-Fabrizio fractional derivatives (fractional derivatives without singular kernel) is considered under the time-dependent emissions on the boundary and the first order chemical reaction. The non-dimensional problem is formulated by using suitable dimensionless variables and the fundamental solutions to the Dirichlet problem for the fractional advection-diffusion equation are determined using the integral transforms technique. The fundamental solutions for the ordinary advection-diffusion equation, fractional and ordinary diffusion equation are obtained as limiting cases of the previous model. Using Duhamel's principle, the analytical solutions to the Dirichlet problem with time-dependent boundary pulses have been obtained. The influence of the fractional parameter and of the drift parameter on the solute concentration in various spatial positions was analyzed by numerical calculations. It is found that the variation of the fractional parameter has a significant effect on the solute concentration, namely, the memory effects lead to the retardation of the mass transport.
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.
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.
A Dynamic and Spatial Scaling Approach to Advection Forecasting.
NASA Astrophysics Data System (ADS)
Seed, A. W.
2003-03-01
Quantitative nowcasts of rainfall are frequently based on the advection of rain fields observed by weather radar. Spectral Prognosis (S-PROG) is an advection-based nowcasting system that uses the observations that rain fields commonly exhibit both spatial and dynamic scaling properties, that is, the lifetime of a feature in the field is dependent on the scale of the feature (large features evolve more slowly than small features), and that features at all scales between the outer and inner observed scales are present in the field. The logarithm of the radar reflectivity field is disaggregated into a set or cascade of fields, in which each field in the set (or level in the cascade) represents the features of the original field over a limited range of scales. The Lagrangian temporal evolution of each level in the cascade is modeled using a simple autoregressive (lag 2) model, which automatically causes the forecast field to become smooth as the structures at the various scales evolve through their life cycles, or can be used to generate conditional simulations if the noise term is included. This paper describes the model and presents preliminary results.
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.
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.
Toward enhanced subsurface intervention methods using chaotic advection
NASA Astrophysics Data System (ADS)
Trefry, Michael G.; Lester, Daniel R.; Metcalfe, Guy; Ord, Alison; Regenauer-Lieb, Klaus
2012-01-01
Many intervention activities in the terrestrial subsurface involve the need to recover/emplace distributions of scalar quantities (e.g. dissolved phase concentrations or heat) from/in volumes of saturated porous media. These scalars can be targeted by pump-and-treat methods or by amendment technologies. Application examples include in-situ leaching for metals, recovery of dissolved contaminant plumes, or utilizing heat energy in geothermal reservoirs. While conventional pumping methods work reasonably well, costs associated with maintaining pumping schedules are high and improvements in efficiency would be welcome. In this paper we discuss how transient switching of the pressure at different wells can intimately control subsurface flow, generating a range of "programmed" flows with various beneficial characteristics. Some programs produce chaotic flows which accelerate mixing, while others create encapsulating flows which can isolate fluid zones for lengthy periods. In a simplified model of an aquifer subject to balanced pumping, chaotic flow topologies have been predicted theoretically and verified experimentally using Hele-Shaw cells. Here, a survey of the key characteristics of chaotic advection is presented. Mathematical methods are used to show how these characteristics may translate into practical situations involving regional flows and heterogeneity. The results are robust to perturbations, and withstand significant aquifer heterogeneity. It is proposed that chaotic advection may form the basis of new efficient technologies for groundwater interventions.
A cryogenic circulating advective multi-pass absorption cell
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.
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.
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
Dense-gas dispersion advection-diffusion model
Ermak, D.L.
1992-07-01
A dense-gas version of the ADPIC particle-in-cell, advection- diffusion model was developed to simulate the atmospheric dispersion of denser-than-air releases. In developing the model, it was assumed that the dense-gas effects could be described in terms of the vertically-averaged thermodynamic properties and the local height of the cloud. The dense-gas effects were treated as a perturbation to the ambient thermodynamic properties (density and temperature), ground level heat flux, turbulence level (diffusivity), and windfield (gravity flow) within the local region of the dense-gas cloud. These perturbations were calculated from conservation of energy and conservation of momentum principles along with the ideal gas law equation of state for a mixture of gases. ADPIC, which is generally run in conjunction with a mass-conserving wind flow model to provide the advection field, contains all the dense-gas modifications within it. This feature provides the versatility of coupling the new dense-gas ADPIC with alternative wind flow models. The new dense-gas ADPIC has been used to simulate the atmospheric dispersion of ground-level, colder-than-ambient, denser-than-air releases and has compared favorably with the results of field-scale experiments.
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.
Quantification of Stokes Drift as a Mechanism for Surface Oil Advection in the DWH Oil Spill
NASA Astrophysics Data System (ADS)
Clark, M.
2013-12-01
Stokes drift has previously been qualitatively shown to be a factor in ocean surface particle transport, but has never been comprehensively quantified. In addition, most operational ocean particle advection models used during the Deepwater Horizon oil spill do not explicitly account for Stokes drift, instead using a simple parameterization based on wind drift (or ignoring it completely). This research works to quantify Stokes drift via direct calculation, with a focus on shallow water, where Stokes drift is more likely to have a relatively large impact compared to other transport processes such as ocean currents. For this study, WaveWatch III modeled waves in the Gulf of Mexico are used, from which Stokes drift is calculated using the peak wave period and significant wave height outputs. Trajectories are also calculated to examine the role Stokes drift plays in bringing surface particles (and specifically surface oil slicks) onshore. The impact of Stokes drift is compared to transport by currents and traditional estimates of wind drift.
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
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
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
NASA Astrophysics Data System (ADS)
Sedlar, J.
2015-12-01
Atmospheric advection of heat and moisture from lower latitudes to the high-latitude Arctic is a critical component of Earth's energy cycle. Large-scale advective events have been shown to make up a significant portion of the moist static energy budget of the Arctic atmosphere, even though such events are typically infrequent. The transport of heat and moisture over surfaces covered by ice and snow results in dynamic changes to the boundary layer structure, stability and turbulence, as well as to diabatic processes such as cloud distribution, microphysics and subsequent radiative effects. Recent studies have identified advection into the Arctic as a key mechanism for modulating the melt and freeze of snow and sea ice, via modification to all-sky longwave radiation. This paper examines the radiative impact during summer of such Arctic advective events at the top of the atmosphere (TOA), considering also the important role they play for the surface energy budget. Using infrared sounder measurements from the AIRS satellite, the summer frequency of significantly stable and moist advective events from 2003-2014 are characterized; justification of AIRS profiles over the Arctic are made using radiosoundings during a 3-month transect (ACSE) across the Eastern Arctic basin. One such event was observed within the East Siberian Sea in August 2014 during ACSE, providing in situ verification on the robustness and capability of AIRS to monitor advective cases. Results will highlight the important surface warming aspect of stable, moist instrusions. However a paradox emerges as such events also result in a cooling at the TOA evident on monthly mean TOA radiation. Thus such events have a climatic importance over ice and snow covered surfaces across the Arctic. ERA-Interim reanalyses are examined to provide a longer term perspective on the frequency of such events as well as providing capability to estimate meridional fluxes of moist static energy.
NASA Astrophysics Data System (ADS)
Kirchner, James W.; Feng, Xiahong; Neal, Colin
2001-12-01
Time series of chemical tracers in rainfall and streamflow can be used to probe the internal workings of catchments. We have recently proposed that catchments act as fractal filters for inert chemical tracers like chloride, converting 'white noise' rainfall chemistry inputs into fractal ' 1/f noise' chemical time series in runoff [Nature 403 (2000) 524]. This implies that catchments have long-tailed travel-time distributions, and thus retain soluble contaminants for unexpectedly long timespans. Here we show that these long-tailed travel-time distributions, and the fractal tracer time series that they imply, can be generated by advection and dispersion of spatially distributed rainfall inputs as they travel toward a channel. Tracer pulses that land close to the stream reach it promptly, with relatively little dispersion. Tracer pulses that land farther upslope must travel farther to reach the stream, and undergo more dispersion. The tracer signal in the stream will be the integral of the contributions from each point along the length of the hillslope, with a peak at short lag times (reflecting tracers landing near the stream) and a long tail (reflecting tracers landing farther from the stream). Here we integrate the advection-dispersion equation for rainfall tracers landing at all points on a simple model hillslope, and show that it yields fractal tracer behavior, as well as a travel-time distribution nearly equivalent to that found empirically [Nature 403 (2000) 524]. However, it does so only when the dispersion length scale approaches the length of the hillslope, implying that subsurface transport is dominated by large conductivity contrasts related to macropores, fracture networks, and similar large-scale heterogeneities in subsurface conductivity. Thus, the 1/ f scaling observed at our study sites indicates that these catchments are dominated by flowpaths that exhibit macro-dispersion over the longest possible length scales.
Kariuk, Iu A
2009-01-01
An algorithm of early diagnosis and treatment of nasal cavity and accessory sinuses of the nose in students of educational establishments of the water-borne transport system has been developed. Inclusion of such methods as screening diagnosis of inflammatory diseases of paranasal sinuses, original roentgenologic and zonographic imaging of paranasal and frontal sinuses made it possible to substantially improve the quality of diagnosis, shorten duration of the examination, and reduce radiation exposure of the patients. The proposed algorithm was used to provide therapeutic and rehabilitation services to 260 patients admitted to the Clinical Hospital No 1 of the federal state institution
Finite amplitude gravity waves: Harmonics, advective steepening, breaking and saturation
NASA Technical Reports Server (NTRS)
Weinstock, J.
1985-01-01
A simple theory is presented which determines details of the breaking and saturation of a gravity wave as it propagates upward in the atmosphere. Breaking and saturation are here due to nonlinear advection analogous to the breaching of a surface wave and to the breaking of a planetary wave. Much simplification is obtained by the assumption that in a wave packet consisting of a primary wave and its harmonics, the primary wave remains dominant. This assumption, referred to a quasi-monochromatic approximation, is suggested by observations. Determined by this approximate theory are: a detailed picture of the waveform as it steepens and breaks; harmonics of the wave; the turbulence generation; and an underlying relationship between superadiabatic lapse rate and saturation by wave-wave interactions.
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.
Magnetic field advection in two interpenetrating plasma streams
Ryutov, D. D.; Kugland, N. L.; Levy, M. C.; Plechaty, C.; Ross, J. S.; Park, H. S.
2013-03-15
Laser-generated colliding plasma streams can serve as a test-bed for the study of various astrophysical phenomena and the general physics of self-organization. For streams of a sufficiently high kinetic energy, collisions between the ions of one stream with the ions of the other stream are negligible, and the streams can penetrate through each other. On the other hand, the intra-stream collisions for high-Mach-number flows can still be very frequent, so that each stream can be described hydrodynamically. This paper presents an analytical study of the effects that these interpenetrating streams have on large-scale magnetic fields either introduced by external coils or generated in the plasma near the laser targets. Specifically, a problem of the frozen-in constraint is assessed and paradoxical features of the field advection in this system are revealed. A possibility of using this system for studies of magnetic reconnection is mentioned.
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.
Magnetic method for stimulating transport in fluids
Martin, James E.; Solis, Kyle J.
2016-10-18
A method for producing mass and heat transport in fluids, wherein the method does not rely on conventional convection, that is, it does not require gravity, a thermal gradient, or a magnetic field gradient. This method gives rise to a unique class of vigorous, field-controllable flow patterns termed advection lattices. The advection lattices can be used to transport heat and/or mass in any desired direction using only magnetic fields.
Diapycnal advection by double diffusion and turbulence in the ocean
NASA Astrophysics Data System (ADS)
St. Laurent, Louis Christopher
1999-11-01
Observations of diapycnal mixing rates are examined and related to diapycnal advection for both double-diffusive and turbulent regimes. The role of double-diffusive mixing at the site of the North Atlantic Tracer Release Experiment is considered. The strength of salt-finger mixing is analyzed in terms of the stability parameters for shear and double- diffusive convection, and a nondimensional ratio of the thermal and energy dissipation rates. While the model for turbulence describes most dissipation occurring in high shear, dissipation in low shear is better described by the salt-finger model, and a method for estimating the salt-finger enhancement of the diapycnal haline diffusivity over the thermal diffusivity is proposed. Best agreement between tracer-inferred mixing rates and microstructure based estimates is achieved when the salt- finger enhancement of haline flux is taken into account. The role of turbulence occurring above rough bathymetry in the abyssal Brazil Basin is also considered. The mixing levels along sloping bathymetry exceed the levels observed on ridge crests and canyon floors. Additionally, mixing levels modulate in phase with the spring-neap tidal cycle. A model of the dissipation rate is derived and used to specify the turbulent mixing rate and constrain the diapycnal advection in an inverse model for the steady circulation. The inverse model solution reveals the presence of a secondary circulation with zonal character. These results suggest that mixing in abyssal canyons plays an important role in the mass budget of Antarctic Bottom Water. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617-253-5668; Fax 617-253-1690.)
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)
Areshkin, Denis A.; Nikolić, Branislav K.
2010-04-01
The recent fabrication of graphene nanoribbon (GNR) field-effect transistors poses a challenge for first-principles modeling of carbon nanoelectronics due to many thousand atoms present in the device. The state of the art quantum transport algorithms, based on the nonequilibrium Green function formalism combined with the density-functional theory (NEGF-DFT), were originally developed to calculate self-consistent electron density in equilibrium and at finite bias voltage (as a prerequisite to obtain conductance or current-voltage characteristics, respectively) for small molecules attached to metallic electrodes where only a few hundred atoms are typically simulated. Here we introduce combination of two numerically efficient algorithms which make it possible to extend the NEGF-DFT framework to device simulations involving large number of atoms. Our first algorithm offers an alternative to the usual evaluation of the equilibrium part of electron density via numerical contour integration of the retarded Green function in the upper complex half-plane. It is based on the replacement of the Fermi function f(E) with an analytic function f˜(E) coinciding with f(E) inside the integration range along the real axis, but decaying exponentially in the upper complex half-plane. Although f˜(E) has infinite number of poles, whose positions and residues are determined analytically, only a finite number of those poles have non-negligible residues. We also discuss how this algorithm can be extended to compute the nonequilibrium contribution to electron density, thereby evading cumbersome real-axis integration (within the bias voltage window) of NEGFs which is very difficult to converge for systems with large number of atoms while maintaining current conservation. Our second algorithm combines the recursive formulas with the geometrical partitioning of an arbitrary multiterminal device into nonuniform segments in order to reduce the computational complexity of the retarded Green
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
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
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
Algorithms and Algorithmic Languages.
ERIC Educational Resources Information Center
Veselov, V. M.; Koprov, V. M.
This paper is intended as an introduction to a number of problems connected with the description of algorithms and algorithmic languages, particularly the syntaxes and semantics of algorithmic languages. The terms "letter, word, alphabet" are defined and described. The concept of the algorithm is defined and the relation between the algorithm and…
NASA Astrophysics Data System (ADS)
Su, Zhenpeng; Zhu, Hui; Xiao, Fuliang; Zheng, Huinan; Shen, Chao; Wang, Yuming; Wang, Shui
2012-09-01
The electromagnetic ion cyclotron (EMIC) wave has long been suggested to be responsible for the rapid loss of radiation belt relativistic electrons. The test-particle simulations are performed to calculate the bounce-averaged pitch angle advection and diffusion coefficients for parallel-propagating monochromatic EMIC waves. The comparison between test-particle (TP) and quasi-linear (QL) transport coefficients is further made to quantify the influence of nonlinear processes. For typical EMIC waves, four nonlinear physical processes, i.e., the boundary reflection effect, finite perturbation effect, phase bunching and phase trapping, are found to occur sequentially from small to large equatorial pitch angles. The pitch angle averaged finite perturbation effect yields slight differences between the transport coefficients of TP and QL models. The boundary reflection effect and phase bunching produce an average reduction of >80% in the diffusion coefficients but a small change in the corresponding average advection coefficients, tending to lower the loss rate predicted by QL theory. In contrast, the phase trapping causes continuous negative advection toward the loss cone and a minor change in the corresponding diffusion coefficients, tending to increase the loss rate predicted by QL theory. For small amplitude EMIC waves, the transport coefficients grow linearly with the square of wave amplitude. As the amplitude increases, the boundary reflection effect, phase bunching and phase trapping start to occur. Consequently, the TP advection coefficients deviate from the linear growth with the square of wave amplitude, and the TP diffusion coefficients become saturated with the amplitude approaching 1 nT or above. The current results suggest that these nonlinear processes can cause significant deviation of transport coefficients from the prediction of QL theory, which should be taken into account in the future simulations of radiation belt dynamics driven by the EMIC waves.
NASA Astrophysics Data System (ADS)
Su, Z.; Zhu, H.; Xiao, F.; Zheng, H.; Shen, C.; Wang, Y.; Wang, S.
2012-12-01
The electromagnetic ion cyclotron (EMIC) wave has been long suggested to be responsible for the rapid loss of radiation belt relativistic electrons. The test-particle simulations are performed to calculate the bounce-averaged pitch-angle advection and diffusion coefficients for parallel-propagating monochromatic EMIC waves. The comparison between test-particle (TP) and quasi-linear (QL) transport coefficients is further made to quantify the influence of nonlinear processes. For typical EMIC waves, four nonlinear physical processes, i.e., the boundary reflection effect, finite perturbation effect, phase bunching and phase trapping, are found to occur sequentially from small to large equatorial pitch angles. The pitch-angle averaged finite perturbation effect yields slight differences between the transport coefficients of TP and QL models. The boundary reflection effect and phase bunching produce an average reduction of >80% in the diffusion coefficients but a small change in the corresponding average advection coefficients, tending to lower the loss rate predicted by QL theory. In contrast, the phase trapping causes continuous negative advection toward the loss cone and a minor change in the corresponding diffusion coefficients, tending to increase the loss rate predicted by QL theory. For small amplitude EMIC waves, the transport coefficients grow linearly with the square of wave amplitude. As the amplitude increases, the boundary reflection effect, phase bunching and phase trapping start to occur. Consequently, the TP advection coefficients deviate from the linear growth with the square of wave amplitude, and the TP diffusion coefficients become saturated with the amplitude approaching 1nT or above. The current results suggest that these nonlinear processes can cause significant deviation of transport coefficients from the prediction of QL theory, which should be taken into account in the future simulations of radiation belt dynamics driven by the EMIC waves.
Turing-Hopf instabilities through a combination of diffusion, advection, and finite size effects.
Galhotra, Sainyam; Bhattacharjee, J K; Agarwalla, Bijay Kumar
2014-01-14
We show that in a reaction diffusion system on a two-dimensional substrate with advection in the confined direction, the drift (advection) induced instability occurs through a Hopf bifurcation, which can become a double Hopf bifurcation. The box size in the direction of the drift is a vital parameter. Our analysis involves reduction to a low dimensional dynamical system and constructing amplitude equations.
Lateral advection of organic matter in cascading-dominated submarine canyons
NASA Astrophysics Data System (ADS)
Tesi, T.; Puig, P.; Palanques, A.; Goñi, M. A.
2010-03-01
In the Gulf of Lions (GoL), dense water overflowing off the shelf occurs seasonally and represents the main mechanism affecting the shelf-slope exchange of particulate organic matter (OM). Most of the dense water export takes place in the south-western GoL and in particular through Cap de Creus (CdC) submarine canyon. Here, benthic instruments were deployed to collect down-canyon particulate fluxes whereas surface sediments were taken after the cascading event along the sediment dispersal system on the shelf, in CdC canyon and in the nearby Lacaze-Duthiers (LD) canyon. The chemical composition of the suspended material and surface sediments were investigated using several proxies including organic and inorganic carbon, total nitrogen, biogenic silica, δ 13C, Δ 14C, and alkaline CuO oxidation products. Thermohaline anomalies and high current speed events were measured in CdC canyon since December 2004 until mid-April 2005 indicating a marked off-shelf export of dense water trough the canyon. During the cascading, mud and relatively coarse shelf and upper canyon sediments were the major component of the mass flux. Conversely, advection of fine material via nepheloid layers dominated down-slope fluxes during pre- and post-cascading. The resulting change in grain-size affected the flux of mineral-bound terrigenous OC, indicating that the down-canyon transport of land-derived OM did not occur as bulk but rather its composition is driven by sediment sorting associated with different transport mechanisms. Both surface sediments and sediment trap samples indicated that CdC canyon is well connected to the GoL terrigenous dispersal system. Conversely, our results suggest an overall limited influence of land-derived OM in LD canyon. In spite of the reduced fluvial nutrient supply, a significant pulsed input of modern marine OM was observed in April 2005 at the end of the cascading period. Both intense mixing and lack of strong water column stratification likely played a key
Modeling velocity in gradient flows with coupled-map lattices with advection.
Lind, Pedro G; Corte-Real, João; Gallas, Jason A C
2002-07-01
We introduce a simple model to investigate large scale behavior of gradient flows based on a lattice of coupled maps which, in addition to the usual diffusive term, incorporates advection, as an asymmetry in the coupling between nearest neighbors. This diffusive-advective model predicts traveling patterns to have velocities obeying the same scaling as wind velocities in the atmosphere, regarding the advective parameter as a sort of geostrophic wind. In addition, the velocity and wavelength of traveling wave solutions are studied. In general, due to the presence of advection, two regimes are identified: for strong diffusion the velocity varies linearly with advection, while for weak diffusion a power law is found with a characteristic exponent proportional to the diffusion.
Population persistence under advection-diffusion in river networks.
Ramirez, Jorge M
2012-11-01
An integro-differential equation on a tree graph is used to model the time evolution and spatial distribution of a population of organisms in a river network. Individual organisms become mobile at a constant rate, and disperse according to an advection-diffusion process with coefficients that are constant on the edges of the graph. Appropriate boundary conditions are imposed at the outlet and upstream nodes of the river network. The local rates of population growth/decay and that by which the organisms become mobile, are assumed constant in time and space. Imminent extinction of the population is understood as the situation whereby the zero solution to the integro-differential equation is stable. Lower and upper bounds for the eigenvalues of the dispersion operator, and related Sturm-Liouville problems are found. The analysis yields sufficient conditions for imminent extinction and/or persistence in terms of the values of water velocity, channel length, cross-sectional area and diffusivity throughout the river network.
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.
Validation of a coupled reactive transport code in porous media
NASA Astrophysics Data System (ADS)
Mugler, C.; Montarnal, P.; Dimier, A.
2003-04-01
The safety assessment of nuclear waste disposals needs to predict the migration of radionuclides and chemical species through a geological medium. It is therefore necessary to develop and assess qualified and validated tools which integrate both the transport mechanisms through the geological media and the chemical mechanisms governing the mobility of radionuclides. In this problem, both geochemical and hydrodynamic phenomena are tightly linked together. That is the reason why the French Nuclear Energy Agency (CEA) and the French Agency for the Management of Radioactive Wastes (ANDRA) are conjointly developping a coupled reactive transport code that solves simultaneously a geochemical model and a transport model. This code, which is part of the software project ALLIANCES, leans on the libraries of two geochemical codes solving the complex ensemble of reacting chemical species: CHESS and PHREEQC. Geochemical processes considered here include ion exchange, redox reactions, acid-base reactions, surface complexation and mineral dissolution and/or precipitation. Transport is simulated using the mixed-hybrid finite element scheme CAST3M or the finite volume scheme MT3D. All together solve Darcy's law and simulate several hydrological processes such as advection, diffusion and dispersion. The coupling algorithm is an iterative sequential algorithm. Several analytical test cases have been defined and used to validate the reactive transport code. Numerical results can be compared to analytical solutions.
NASA Astrophysics Data System (ADS)
Ballester, Joan; Bordoni, Simona; Petrova, Desislava; Rodó, Xavier
2016-06-01
The oscillatory nature of El Niño-Southern Oscillation results from an intricate superposition of near-equilibrium balances and out-of-phase disequilibrium processes between the ocean and the atmosphere. The main objective of the present work is to perform an exhaustive spatiotemporal analysis of the upper ocean heat budget in an ensemble of state-of-the-art ocean assimilation products. We put specific emphasis on the ocean heat advection mechanisms, and their representation in individual ensemble members and in the different stages of the ENSO oscillation leading to EN events. Our analyses consistently show that the initial subsurface warming in the western equatorial Pacific is advected to the central Pacific by the equatorial undercurrent, which, together with the equatorward advection associated with anomalies in both the meridional temperature gradient and circulation at the level of the thermocline, explains the heat buildup in the central Pacific during the recharge phase. We also find that the recharge phase is characterized by an increase of meridional tilting of the thermocline, as well as a southward upper-ocean cross-equatorial mass transport resulting from Ekman-induced anomalous vertical motion in the off-equatorial regions. Although differences between data sets are generally small, and anomalies tend to have the same sign, the differences in the magnitude of the meridional term are seen to be key for explaining the different propagation speed of the subsurface warming tendency along the thermocline. The only exception is GECCO, which does not produce the patterns of meridional surface Ekman divergence (subsurface Sverdrup convergence) in the western and central equatorial Pacific.
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.
Umari, Amjad M. J.; Gorelick, Steven M.
1986-01-01
In the numerical modeling of groundwater solute transport, explicit solutions may be obtained for the concentration field at any future time without computing concentrations at intermediate times. The spatial variables are discretized and time is left continuous inthe governing differnetial equation. These semianalytical solutions have been presented in the literature and involve the eigensystem of a coefficient matrix. This eigensystem may be complex (i. e. , have imaginary components) due to the asymmetry created by the advection term in the governing advection-dispersionequation. It is shown here that the error due to ignoring the imaginary components of complex eigenvalues is large for small dispersivity values. A new algorithm that represents the complex eigensystem by converting it to a real eigensystem is presented. The method requires only real arithmetic.
Applying Dispersive Changes to Lagrangian Particles in Groundwater Transport Models
Konikow, L.F.
2010-01-01
Method-of-characteristics groundwater transport models require that changes in concentrations computed within an Eulerian framework to account for dispersion be transferred to moving particles used to simulate advective transport. A new algorithm was developed to accomplish this transfer between nodal values and advecting particles more precisely and realistically compared to currently used methods. The new method scales the changes and adjustments of particle concentrations relative to limiting bounds of concentration values determined from the population of adjacent nodal values. The method precludes unrealistic undershoot or overshoot for concentrations of individual particles. In the new method, if dispersion causes cell concentrations to decrease during a time step, those particles in the cell having the highest concentration will decrease the most, and those with the lowest concentration will decrease the least. The converse is true if dispersion is causing concentrations to increase. Furthermore, if the initial concentration on a particle is outside the range of the adjacent nodal values, it will automatically be adjusted in the direction of the acceptable range of values. The new method is inherently mass conservative. ?? US Government 2010.
Applying dispersive changes to Lagrangian particles in groundwater transport models
Konikow, Leonard F.
2010-01-01
Method-of-characteristics groundwater transport models require that changes in concentrations computed within an Eulerian framework to account for dispersion be transferred to moving particles used to simulate advective transport. A new algorithm was developed to accomplish this transfer between nodal values and advecting particles more precisely and realistically compared to currently used methods. The new method scales the changes and adjustments of particle concentrations relative to limiting bounds of concentration values determined from the population of adjacent nodal values. The method precludes unrealistic undershoot or overshoot for concentrations of individual particles. In the new method, if dispersion causes cell concentrations to decrease during a time step, those particles in the cell having the highest concentration will decrease the most, and those with the lowest concentration will decrease the least. The converse is true if dispersion is causing concentrations to increase. Furthermore, if the initial concentration on a particle is outside the range of the adjacent nodal values, it will automatically be adjusted in the direction of the acceptable range of values. The new method is inherently mass conservative.
NASA Astrophysics Data System (ADS)
Ge, Jian-zhong; Ding, Ping-xing; Li, Cheng; Fan, Zhong-ya; Shen, Fang; Kong, Ya-zhen
2015-12-01
A comprehensive acoustic retrieval algorithm to investigate suspended sediment is presented with the combined validations of Acoustic Doppler Current Profiler (ADCP) and Optical Backscattering Sensor (OBS) monitoring along seven cross-channel sections in the high-turbidity North Passage of the Changjiang Estuary, China. The realistic water conditions, horizontal and vertical salinities, and grain size of the suspended sediment are considered in the retrieval algorithm. Relations between net volume scattering of sound attenuation ( S v ) due to sediments and ADCP echo intensity ( E) were obtained with reasonable accuracy after applying the linear regression method. In the river mouth, an intensive vertical stratification and horizontal inhomogeneity were found, with a higher concentration of sediment in the North Passage and a lower concentration in the North Channel and South Passage. Additionally, The North Passage is characterized by higher sediment concentration in the middle region and lower concentration in the entrance and outlet areas. The maximum sediment flux rate, occurred in the middle region, could reach 6.3×105 and 1.5×105 t/h during the spring and neap tide, respectively. Retrieved sediment fluxes in the middle region are significantly larger than that in the upstream and downstream region. This strong sediment imbalance along the main channel indicates potential secondary sediment supply from southern Jiuduansha Shoals.
Wind-driven gas networks and star formation in galaxies: reaction-advection hydrodynamic simulations
NASA Astrophysics Data System (ADS)
Chappell, David; Scalo, John
2001-07-01
The effects of wind-driven star formation feedback on the spatio-temporal organization of stars and gas in galaxies is studied using two-dimensional intermediate-representational quasi-hydrodynamical simulations. The model retains only a reduced subset of the physics, including mass and momentum conservation, fully non-linear fluid advection, inelastic macroscopic interactions, threshold star formation, and momentum forcing by winds from young star clusters on the surrounding gas. Expanding shells of swept-up gas evolve through the action of fluid advection to form a `turbulent' network of interacting shell fragments which have the overall appearance of a web of filaments (in two dimensions). A new star cluster is formed whenever the column density through a filament exceeds a critical threshold based on the gravitational instability criterion for an expanding shell, which then generates a new expanding shell after some time delay. A filament-finding algorithm is developed to locate the potential sites of new star formation. The major result is the dominance of multiple interactions between advectively distorted shells in controlling the gas and star morphology, gas velocity distribution and mass spectrum of high mass density peaks, and the global star formation history. The gas morphology strongly resembles the model envisioned by Norman & Silk, and observations of gas in the Large Magellanic Cloud (LMC)Q1 and local molecular clouds. The dependence of the frequency distribution of present-to-past average global star formation rate on a number of parameters is investigated. Bursts of star formation only occur when the time-averaged star formation rate per unit area is low, or the system is small. Percolation does not play a role. The broad distribution observed in late-type galaxies can be understood as a result of either small size or small metallicity, resulting in larger shell column densities required for gravitational instability. The star formation rate
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
2014-01-28
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
Central Arctic Ocean freshwater during a period of anomalous melt and advection in 2015
NASA Astrophysics Data System (ADS)
Rabe, Benjamin; Korhonen, Meri; Hoppmann, Mario; Ricker, Robert; Hendricks, Stefan; Krumpen, Thomas; Beckers, Justin; Schauer, Ursula
2016-04-01
During the recent decade the Arctic Ocean has shown several years of very low sea-ice extent and an increase in liquid freshwater. Yet, the processes underlying the interannual variability are still not fully understood. Hydrographic observations by ship campaigns and autonomous platforms reveal that summer 2015 showed above average liquid freshwater in the upper ocean of the central Arctic. Surface temperatures and sea level pressure were also higher than the average of the preceeding two decades. From hydrographic observations and atmospheric reanalysis data we show that this liquid freshwater anomaly is associated with above average sea-ice melt and intensified northward Ekman transport. We, further, found significant amounts of Pacific Water in the upper water column, from the mixed-layer to the upper halocline. Our results suggest that the freshening was due to both advection of low-salinity water from the direction of the Siberian shelves, the Beaufort Gyre and the Bering Strait, and enhance sea-ice melt.
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.
NASA Astrophysics Data System (ADS)
Endeve, Eirik; Hauck, Cory D.; Xing, Yulong; Mezzacappa, Anthony
2015-04-01
We extend the positivity-preserving method of Zhang and Shu [49] to simulate the advection of neutral particles in phase space using curvilinear coordinates. The ability to utilize these coordinates is important for non-equilibrium transport problems in general relativity and also in science and engineering applications with specific geometries. The method achieves high-order accuracy using Discontinuous Galerkin (DG) discretization of phase space and strong stability-preserving, Runge-Kutta (SSP-RK) time integration. Special care is taken to ensure that the method preserves strict bounds for the phase space distribution function f; i.e., f ∈ [ 0 , 1 ]. The combination of suitable CFL conditions and the use of the high-order limiter proposed in [49] is sufficient to ensure positivity of the distribution function. However, to ensure that the distribution function satisfies the upper bound, the discretization must, in addition, preserve the divergence-free property of the phase space flow. Proofs that highlight the necessary conditions are presented for general curvilinear coordinates, and the details of these conditions are worked out for some commonly used coordinate systems (i.e., spherical polar spatial coordinates in spherical symmetry and cylindrical spatial coordinates in axial symmetry, both with spherical momentum coordinates). Results from numerical experiments - including one example in spherical symmetry adopting the Schwarzschild metric - demonstrate that the method achieves high-order accuracy and that the distribution function satisfies the maximum principle.
Aerosol advection and sea salt events in Genoa, Italy, during the second half of 2005.
Marenco, Franco; Mazzei, Federico; Prati, Paolo; Gatti, Massimiliano
2007-05-15
Atmospheric aerosols in the PM(10) fraction have been simultaneously sampled at three sites in the Genoa urban and suburban area during the second half of 2005, and information on the elemental composition has been gathered through energy dispersive X-ray fluorescence. Thanks to the simultaneous measurements and wind information, a few aerosol transport and transformation processes originated from the nearby sea and in the neighbouring Po Valley have been described. Sea salt concentrations at the three sites were well correlated and often related to Southern sector winds; moreover, by examining the Cl/Na ratio at two sites the time scale for Cl depletion in particulate matter has been estimated as 1-1.5 h for the Genoa atmosphere. During a Northerly gale, excess elemental Si concentrations (peaking more than 4 mug m(-3)) were found at two sites, and were ascribed to an unknown local source. Finally, during an 11-day long 'heat wave' large concentrations for total PM(10), dust and secondary compounds have been found; these large concentrations lead to a number of exceedances of air quality standards, and have been ascribed to advection from the Po Valley.
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.
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
invoke large-volume, long-lived areas of interconnected melt in an attempt to keep alive traditional ideas regarding processes such as magma flow, stoping, and crystal fractionation. However, thermal modeling consistently demonstrates that without continual input of new magma, such volumes cannot be maintained for times greater than a few hundred ka. Furthermore, advective heat loss via the granite aqueduct, coupled with fluid convection in wall rocks, will cool plutons far faster than conductive cooling alone. Models demonstrating long-lived interconnected melt without continued magma input require highly unrealistic and contrived assumptions, such as instantaneous emplacement of huge volumes of magma with no vertical heat transport (Memeti et al., 2010).
Analysis of moisture advection during explosive cyclogenesis over North Atlantic Ocean
NASA Astrophysics Data System (ADS)
Ordóñez, Paulina; Liberato, Margarida L. R.; Pinto, Joaquim G.; Trigo, Ricardo M.
2013-04-01
The development of a mid-latitude cyclone may strongly be amplified by the presence of a very warm and moist air mass within its warm sector through enhanced latent heat release. In this work, a lagrangian approach is applied to examine the contribution of moisture advection to the deepening of cyclones over the North Atlantic Ocean. The warm sector is represented by a 5°x5° longitude/latitude moving box comprising the centre of the cyclone and its south-eastern area is defined for the tracks of different cyclones computed at 6-hourly intervals. Using the lagrangian particle model FLEXPART we evaluated the fresh water flux (E - P) along 2-days back-trajectories of the particles residing on the total column over the defined boxes for case studies occurring during winter months from 1980 to 2000. FLEXPART simulations were performed using one degree resolution and 60 model vertical levels available in ERA40 Reanalyses at 00, 06, 12, 18 UTC for each case. Sensitivity studies on the dimensions of the target area - chosen boxes representing the warm sector -, and on its relative position to the center, were performed. We have applied this methodology to several case studies of independent North Atlantic cyclones with notorious characteristics (e.g. deepening rate, wind speed, surface damages). Results indicate that the moisture transport is particularly relevant in what concerns the fast/explosive development stage of these extratropical cyclones. In particular, the advection of moist air from the subtropics towards the cyclone core is clearly associated with the warm conveyor belt of the cyclone. This methodology can be generalized to a much larger number of mid-latitude cyclones, providing a unique opportunity to analyze the moisture behavior associated with the explosive development. Acknowledgments: This work was partially supported by FEDER (Fundo Europeu de Desenvolvimento Regional) funds through the COMPETE (Programa Operacional Factores de Competitividade
Transport of nitrogen oxides through the winter mesopause in HAMMONIA
NASA Astrophysics Data System (ADS)
Meraner, Katharina; Schmidt, Hauke
2016-03-01
We analyze the importance of individual transport processes for the winter polar downward transport of nitrogen oxides (NOx) from the thermosphere to the mesosphere. The downward transport of NOx produced by energetic particle precipitation induces chemical alterations in the middle atmosphere and influences ozone chemistry. However, it remains unclear how much each transport process contributes to the downward transport. We use simulations of the atmospheric general circulation and chemistry model HAMMONIA (Hamburg Model of Neutral and Ionized Atmosphere) for the extended winter 2008/2009 with a passive tracer. The model enables us to separate the contributions of advection, eddy and molecular diffusion on the total transport by switching off processes. The results show that molecular diffusion and resolved vertical mixing due to advection effectively transport NOx to the mesosphere. While the impact of molecular diffusion on the transport rapidly decreases below 0.001 hPa, the impact of advection increases. Around the central date of the sudden stratospheric warming in January 2009, advection is strongly enhanced in the thermosphere and mesosphere and the downward transport through the mesopause region is almost entirely driven by advection. Eddy diffusion has limited impact on the transport in the upper mesosphere and negligible impact on the transport in the thermosphere. If eddy diffusion is enhanced as suggested by observations, it can potentially have a larger impact on transport through the mesopause than was previously assumed.
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.
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.
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 Technical Reports Server (NTRS)
Want, P. H.; Deepak, A.
1985-01-01
The utilization of stratospheric aerosol and ozone measurements obtained from the NASA developed SAM II and SAGE satellite instruments were investigated for their global scale transports. The stratospheric aerosols showed that during the stratospheric warming of the winter 1978 to 1979, the distribution of the zonal mean aerosol extinction ratio in the northern high latitude exhibited distinct changes. Dynamic processes might have played an important role in maintenance role in maintenance of this zonal mean distribution. As to the stratospheric ozone, large poleward ozone transports are shown to occur in the altitude region from 24 km to 38 km near 55N during this warming. This altitude region is shown to be a transition region of the phase relationship between ozone and temperature waves from an in-phase one above 38 km. It is shown that the ozone solar heating in the upper stratosphere might lead to enhancement of the damping rate of the planetary waves due to infrared radiation alone in agreement with theoretical analyses and an earlier observational study.
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.
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
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
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.
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.
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.
A time-accurate multiple-grid algorithm
NASA Technical Reports Server (NTRS)
Jespersen, D. C.
1985-01-01
A time-accurate multiple-grid algorithm is described. The algorithm allows one to take much larger time steps with an explicit time-marching scheme than would otherwise be the case. Sample calculations of a scalar advection equation and the Euler equations for an oscillating airfoil are shown. For the oscillating airfoil, time steps an order of magnitude larger than the single-grid algorithm are possible.
Raghib, M; Levin, S A; Kevrekidis, I G
2010-06-01
We propose a (time) multiscale method for the coarse-grained analysis of collective motion and decision-making in self-propelled particle models of swarms comprising a mixture of 'naïve' and 'informed' individuals. The method is based on projecting the particle configuration onto a single 'meta-particle' that consists of the elongation of the flock together with the mean group velocity and position. We find that the collective states can be associated with the transient and asymptotic transport properties of the random walk followed by the meta-particle, which we assume follows a continuous time random walk (CTRW). These properties can be accurately predicted at the macroscopic level by an advection-diffusion equation with memory (ADEM) whose parameters are obtained from a mean group velocity time series obtained from a single simulation run of the individual-based model.
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
Transport of subsurface bacteria in porous media
Bales, R.C.; Arnold, R.G.; Gerba, C.P.
1995-02-01
The primary objective of this study was to develop tools with which to measure the advective transport of microorganisms through porous media. These tools were then applied to investigate the sorptive properties of representative microorganisms that were selected at random from the DOE`s deep subsurface collection of bacterial, maintained at Florida State University. The transport screening procedure that arose from this study was also used to investigate biological factors that affect the transport/sorption of biocolloids during their movement through porous media with the bulk advective flow.
ACCURATE TWO-DIMENSIONAL SIMULATION OF ADVECTIVE-DIFFUSIVE-REACTIVE TRANSPORT. (R824801)
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Tartakovsky, Daniel
2013-08-30
We developed new CDF and PDF methods for solving non-linear stochastic hyperbolic equations that does not rely on linearization approximations and allows for rigorous formulation of the boundary conditions.
Melt production by viscous dissipation: Role of heat advection by Magma transport
Feigenson, M.D.; Spera, F.J.
1980-02-01
An energy conservation equation is formulated that balances the heat generated by viscous dissipation in a peridotite simultaneously undergoing partial fusion and penetrative constant shear stress deformation with the heat removed by mobilization and ascent of basaltic magma from the region undergoing deformation. The solution of this parameterized energy equation gives the volume fraction of melt (theta) as a function of time (t) after the initiation of deformation. A stability analysis of the conservation equation shows that stable (theta<100%) or unstable (theta..-->..infinity) solutions exist depending on the magnitude of two dimensionless parameters K/sub 1//K/sub 2/ and K/sub 3/. For geologically reasonable values of K/sub 2//K/sub 2/ and K/sub 3/, the analysis indicates that peridotitic thermo-mechanical systems undergoing penetrative deformation at constant shear stress show a two-stage history. An early stage of growth where theta increases monotonically on a 2 to 3 m.y. time scale eventually is replaced by a steady s ate regime (constant theta). Typical values of theta lie in the range 3 to 5 volume percent; melting of peridotite to the extent of 20--30% appears to be precluded by this model.
Advection dominated transport of polycyclic aromatic hydrocarbons in amended sediment caps.
Gidley, Philip T; Kwon, Seokjoon; Yakirevich, Alexander; Magar, Victor S; Ghosh, Upal
2012-05-01
Typical sand caps used for sediment remediation have little sorption capacity to retard the migration of hydrophobic contaminants such as PAHs that can be mobilized by significant groundwater flow. Laboratory column experiments were performed using contaminated sediments and capping materials from a creosote contaminated USEPA Superfund site. Azoic laboratory column experiments demonstrated rapid breakthrough of lower molecular weight PAHs when groundwater seepage was simulated through a column packed with coarse sand capping material. After eight pore volumes of flow, most PAHs measured showed at least 50% of initial source pore water concentrations at the surface of 65 cm capping material. PAH concentration in the cap solids was low and comparable to background levels typically seen in urban depositional sediment, but the pore water concentrations were high. Column experiments with a peat amendment delayed PAH breakthrough. The most dramatic result was observed for caps amended with activated carbon at a dose of 2% by dry weight. PAH concentrations in the pore water of the activated carbon amended caps were 3-4 orders of magnitude lower (0.04 ± 0.02 μg/L for pyrene) than concentrations in the pore water of the source sediments (26.2 ± 5.6 μg/L for pyrene) even after several hundred pore volumes of flow. Enhancing the sorption capacity of caps with activated carbon amendment even at a lower dose of 0.2% demonstrated a significant impact on contaminant retardation suggesting consideration of active capping for field sites prone to groundwater upwelling or where thin caps are desired to minimize change in bathymetry and impacts to aquatic habitats.
NASA Astrophysics Data System (ADS)
Molins, S.; Mayer, K.
2007-05-01
The unsaturated zone acts as a buffer zone for contaminants on their way to the water table but can also attenuate the emission of contaminants leaving the subsurface environment through the gas phase. A reactive transport model that includes multicomponent gas transport has been developed to investigate the processes that contribute to the generation and attenuation of contaminants in the unsaturated zone. In particular, the model is suitable to study the feedback processes between advective-diffusive gas transport and geochemical reactions. The model is also able to estimate diffusive and advective contributions to gas transport in multicomponent systems. Two model applications are presented that investigate gas transport and reactions in mine tailings and at a site with organic contamination. In mine tailings, atmospheric oxygen transported into the sediment column is consumed in the oxidation of sulfide minerals. Gas volume loss caused by the consumption of atmospheric oxygen drives advective fluxes. In the absence of carbonate minerals, the advective component accounts for 16 % of the net oxygen flux into the column, while, in a carbonate-rich system, advection accounts for 10 % of the net oxygen flux. Dissolution of carbonate minerals has a moderating effect on advective gas transport since carbon dioxide can partially compensate for the depletion of oxygen. At an oil spill site, volatilization and degradation of organic contaminants cause advective and diffusive fluxes of organic vapors away from the source zone. At early stages, volatilization dominates and oxidation of these organic vapors attenuates the emission of contaminants to the atmosphere. The contribution of advection to organic vapor fluxes is significant initially but decreases with time. At later stages, the oil source becomes depleted of its most volatile fraction, and anaerobic degradation of aromatic compounds and heavier n-alkanes results in the production of methane. Up to 15 % of methane
Moisture Advection and Fresh Water Flux over Oceans
NASA Technical Reports Server (NTRS)
Tang, Wenqing; Liu, W. Timothy
2002-01-01
Moisture transport in the atmosphere is one of the most significant components in the hydrological cycle. Under stationary condition, ocean surface fresh water flux, which is the difference between precipitation (P) and evaporation (E), is balanced by the divergence of column-integrated moisture transport (IMT) in the atmosphere. Characterizing accurately a global picture of IMT from observation is a difficult task. It requires measurements of vertical profiles for wind vector and humidity. More specifically, IMT can be defined as the integration in pressure coordinates the product of specific humidity q and wind vector u, where g is the gravitational acceleration, and p, is the atmospheric pressure at ocean surface.In this study, a statistical relationship is derived between u, and u(sub)s using data from numerical weather prediction model. The relationship is then validated using surface and vertical profile from radiosonde data, before applied to spacebased measurements.
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.
NASA Astrophysics Data System (ADS)
Lenhard, R. J.; Oostrom, M.; Simmons, C. S.; White, M. D.
1995-07-01
An experiment was conducted to evaluate whether vapor-density effects are significant in transporting volatile organic compounds (VOC's) with high vapor pressure and molecular mass through the subsurface. Trichloroethylene (TCE) was chosen for the investigation because it is a common VOC contaminant with high vapor pressure and molecular mass. For the investigation, a 2-m-long by 1-m-high by 7.5-cm-thick flow cell was constructed with a network of sampling ports. The flow cell was packed with sand, and a water table was established near the lower boundary. Liquid TCE was placed near the upper boundary of the flow cell in a chamber from which vapors could enter and migrate through the sand. TCE concentrations in the gas phase were measured by extracting 25-μl gas samples with an air-tight syringe and analyzing them with a gas chromatograph. The evolution of the TCE gas plume in the sand was investigated by examining plots of TCE concentrations over the domain for specific times and for particular locations as a function of time. To help in this analysis, a numerical model was developed that can predict the simultaneous movements of a gas, a nonaqueous liquid and water in porous media. The model also considers interphase mass transfer by employing the phase equilibrium assumption. The model was tested with one- and two-dimensional analytical solutions of fluid flow before it was used to simulate the experiment. Comparisons between experimental data and simulation results when vapor-density effects are considered were very good. When vapor-density effects were ignored, agreement was poor. These analyses suggest that vapor-density effects should be considered and that density-driven vapor advection may be an important mechanism for moving VOC's with high vapor pressures and molecular mass through the subsurface.
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
NASA Astrophysics Data System (ADS)
Licata, Nicholas A.; Fuller, Nathaniel J.
Understanding the physical mechanisms by which an individual cell interacts with its environment often requires detailed information about the fluid in which the cell is immersed. Mass transport between the interior of the cell and the external environment is influenced by the flow of the extracellular fluid and the molecular diffusivity. Analytical calculations of the flow field are challenging in simple geometries, and not generally available in more realistic cases with irregular domain boundaries. Motivated by these problems, we discuss the numerical solution of Stokes equation by implementing a Gauss-Seidel algorithm on a staggered computational grid. The computed velocity profile is used as input to numerically solve the advection-diffusion equation for mass transport. Special attention is paid to the case of two-dimensional flows at large Péclet number. The numerical results are compared with a perturbative analytical treatment of the concentration boundary layer.
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.
The effect of advection at luminosities close to Eddington: The ULX in M 31
NASA Astrophysics Data System (ADS)
Straub, O.; Done, C.; Middleton, M.
2013-05-01
The transient, ultra-luminous X-ray source CXOM31 J004253.1+411422 in the Andromeda galaxy is most likely a 10 solar mass black hole, with super-Eddington luminosity at its peak. The XMM-Newton spectra taken during the decline then trace luminosities of 0.86-0.27 LEdd. These spectra are all dominated by a hot disc component, which roughly follows a constant inner radius track in luminosity and temperature as the source declines. At the highest luminosity the disc structure should change due to advection of radiation through the disc. This advected flux can be partly released at lower radii thus modifying the spectral shape. To study the effect of advection at luminosities close to Eddington we employ a fully relativistic slim disc model, SLIMBH, that includes advective cooling and full radiative transfer through the photosphere based on tlusty. The model also incorporates relativistic photon ray-tracing from the proper location of the disc photosphere rather than the mid-plane as the slim disc is no longer geometrically thin. We find that these new models differ only slightly from the non-advective (standard) BHSPEC models even at the highest luminosities considered here. While both discs can fit the highest luminosity data, neither is a very good fit to the lower luminosities. This could indicate a missing physical process that acts in low luminosity discs and subsides as the disc luminosity approaches the Eddington limit.
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)
Furuichi, M.; Nakagawa, T.; May, D.
2013-12-01
Stabilizing a numerical oscillation in free surface treatment is chagrining topic for a geodynamics simulation [e.g. Kaus et al. 2010, Duretz et al., 2011]. It is especially important for the Stokes flow simulation under the self-gravitating field based on 'Spherical Cartesian' method [Gerya et al., 2007], which is useful for simulating a long time scale dynamics of sinking metal rich materials to construct planetary core. The conventional explicit time stepping algorithm, which solves Stokes flow equation for a given material distribution at a previous time step, however has a difficulty for simulating dynamics such as a thermal convection, after the construction of layered structure in the planetary interior because of numerical oscillation. One effective approach for such numerically problematic behavior is an implicit treatment of advection term. In this study, three types of implicit strategy are discussed. First is the full implicit treatment with iterative non-linear solver which uses transported density by maker-in-cell method as nonlinear update. The maker-in-cell method is commonly used as low diffusive advection method, but is computationally expensive with makers to mesh interpolation. Second approach uses semi-Lagrangian method for nonlinear update instead of the maker-in-cell method to reduce computational cost. Third approach is to solve the Stokes flow equation combined with the linearized advection term in central-difference discretization to avoid the nonlinear update by the transport. In the second and third algorithms, physical value at the next time step is still transported by low diffusive maker-in-cell method. These three types of implicit method are examined by numerical experiment.
NASA Astrophysics Data System (ADS)
Rogers, M. A.; Miller, S. D.; Haynes, J. M.; Heidinger, A. K.; Haupt, S. E.; Sengupta, M.
2014-12-01
Using satellite observations from GOES-E and GOES-W platforms in concert with GFS-derived cloud-level winds and a standalone radiative transfer model, an advection-derived forecast for surface GHI over the continental United States is described. In particular, comparisons from the satellite-derived forecast are shown against several SURFRAD sites, with particular attention to developing meaningful error metrics to better demonstrate forecast skill and identify sources of error. Challenges in advection-based forecast techniques, such as forecasting near regions of non-wind-driven cloud systems such as coastal marine stratocumulus, are described, as are methods integrated into the forecast algorithm to identify and address these challenges. Improvements in the particular algorithm with respect to comparison against surface observations, integration of the forecast technique into blended forecast products such as those described by the 'Public-Private-Academic Partnership to Advance Solar Power Forecasting' project spearheaded by the National Center for Atmospheric Research, and other observations germane to satellite-derived solar forecasting are covered using nearly two years of operational forecasts as background.
Hochstein, M.P.; Yang Zhongke
1992-01-01
In steep terrain the effect of advective flow can be significant, as it can distort the temperature field in the upper brittle crust. The effect was studied by modeling advective flow across a large valley system in Tibet which is associated with several geothermal hot spring systems, the Yanbajing Valley. It was found that, in this setting, all near-surface temperature gradients are significantly disturbed, attaining values differing by up to half an order of magnitude from those resulting from conductive heat transfer. Allowing for advective effects, it was found that the crustal heat flux within the Himalayan Geothermal Belt lies within the range of 60 to 90 mW/m{sup 2} in the Lhasa-Yanbajing area.
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.
Pavese, G; Lettino, A; Calvello, M; Esposito, F; Fiore, S
2016-04-01
Aerosol composition and properties variation under the advection of different air masses were investigated, as case studies, by contemporary measurements over the atmospheric column and at the ground in a semi-rural site in South Italy. The absence of local strong sources in this area allowed to characterize background aerosol and to compare particle mixing effects under various atmospheric circulation conditions. Aerosol optical depth (AOD) and Ǻngström parameters from radiometric measurements allowed the detection and identification of polluted, dust, and volcanic atmospheric conditions. AODs were the input for a suitable model to evaluate the columnar aerosol composition, according to six main atmospheric components (water-soluble, soot, sea salt accumulation, sea salt coarse, mineral dus,t and biological). Scanning electron microscope (SEM) analysis of particulate sampled with a 13-stage impactor at the ground showed not only fingerprints typical of the different air masses but also the effects of transport and aging on atmospheric particles, suggesting processes that changed their chemical and optical properties. Background columnar aerosol was characterized by 72% of water-soluble and soot, in agreement with ground-based findings that highlighted 60% of contribution from anthropogenic carbonate particles and soot. In general, a good agreement between ground-based and columnar results was observed. Under the advection of trans-boundary air masses, water-soluble and soot were always present in columnar aerosol, whereas, in variable percentages, sea salt and mineral particles characterized both dust and volcanic conditions. At the ground, sulfates characterized the amorphous matrix produced in finer stages by the evaporation of solutions of organic and inorganic aerosols. Sulfates were also one of the key players involved in heterogeneous chemical reactions, producing complex secondary aerosol, as such clay-sulfate internally mixed particle externally mixed
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.
Advection of magnetic flux by accretion disks around neutron stars
NASA Astrophysics Data System (ADS)
Flores-Tulian, S.; Reisenegger, A.
The aim of our research is to address why millisecond pulsars have relatively weak surface magnetic fields, of about 10^8 G, with a narrow spread. We propose that the accretion of plasma from the companion star fully screens the original neutron star field, but the accretion disk carries additional magnetic flux from the companion star, or itself can generate field by means of dynamo processes. For a strongly magnetized star, the field prevents the disk from approaching the star. The accretion is along the field lines and deposits the matter on the polar cap. Then, the accreted plasma flows, dragging with itself the magnetic field lines, from the pole to the equator (Payne & Melatos 2004). In a following stage, when the star becomes non-magnetic, because the field has been buried, the disk touches the star. We suggest that some effective mechanism of magnetic flux transport such as that proposed by Spruit & Uzdensky 2005 (or Bisnovatyi-Kogan & Lovelace 2007), operates and necessarily leads to a "strongly magnetized disk''. It becomes laminar because the magneto-rotational instability saturates (it is considered to be responsible for turbulence in the disk), and the magnetic difussivity is negligible. Then, the loss of angular momentum allowing the accretion is only caused by the magneto-centrifugal disk-wind (Blandford & Payne 1982). Meanwhile, the wind-driven transport of the magnetic flux by the disk re-magnetizes the star. This process continues until the Lorentz force due to the star's magnetic field forbids any further accretion of matter and magnetic flux, in the Ideal Magneto-Hydro-Dynamics approach. Additional of material can fall onto the star (but at lower rate) if some instability process sets in, allowing the diffusion of mass through the magnetic field lines (e.g the Interchange Instability, Spruit & Taam 1990). All these processes might lead to an asymptotic magnetic field of 10^8 G,as is inferred from observations. We are developing a self
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.
Semi-Lagrangian advection-propagation (SLAP) scheme for three-dimensional interface tracking
NASA Astrophysics Data System (ADS)
Aldredge, R. C.
2010-06-01
A fully three-dimensional semi-Lagrangian scheme is developed for computing the evolution of advected self-propagating surfaces (e.g., premixed flames) governed by a level-set advection-propagation equation. The scheme provides third-order spatial accuracy and shape preservation. Example numerical simulations of three-dimensional front propagation are presented to illustrate the capability of the scheme of capturing cusp formation and associated surface-area annihilation as well as the formation and consumption of detached closed-surface pockets behind fronts propagating in highly vortical flow.
Modeling pollutant transport using a meshless-lagrangian particle model
Carrington, D. B.; Pepper, D. W.
2002-01-01
A combined meshless-Lagrangian particle transport model is used to predict pollutant transport over irregular terrain. The numerical model for initializing the velocity field is based on a meshless approach utilizing multiquadrics established by Kansa. The Lagrangian particle transport technique uses a random walk procedure to depict the advection and dispersion of pollutants over any type of surface, including street and city canyons
Testing metrics of mixing using a chaotic advection model
NASA Astrophysics Data System (ADS)
Grahn, J.; McDonald, A. J.
2012-04-01
This study describes an evaluation of different dynamical measures and their ability to diagnose horizontal transport and mixing in atmospheric flows. This quantification can then be used to select optimal measures which can be applied to satellite and re-analyses data to identify likely regions where the indirect effect of Energetic Particle Precipitation (EPP) is important. As a "test bench" for mixing measures a two dimensional idealized atmospheric model has been developed (Pierrehumbert et al, 1992 , Shuckburgh et al 2003). It is completely defined by a set of only five parameters. Although it is an oversimplification of real atmospheric flows, it exhibits the main dynamical characteristics of the stratosphere near the polar vortex. At the same time, it's simplicity gives us the opportunity to make detailed investigations on the quality of the mixing measures. By using this analytical model with a Lagrangian trajectory model we can examine the impact of the flow on the distribution of any trace gas. We have chosen to examine two mixing measures, namely finite time Lyaponov exponents (FTLE) and the Renyi entropy (RE). The former is a numerical realization of the Lyapunov exponent (Wolf et al, 1984), a measure of the amount of separation of nearby trajectories of a dynamical system. The FTLE has been used in studies before as a measure of mixing (i.e. Pierrehumbert et al, 1992; Shuckburgh et al 2003; Garny et al, 2007). The Renyi entropy is a measure originating from information theory and has also been studied before in the context of atmospheric mixing (Krützmann et al, 2008). Initial analysis seems to show a relatively strong anti-correlation between these mixing measures. In particular, high FTLE (which relate to strongly divergent regions) identify mixing barriers and are generally linked to low values of RE. Results from an analysis of a range of model realizations with varying amounts of prescribed mixing will be performed to robustly quantify the
SIMULATION OF DISPERSION OF A POWER PLANT PLUME USING AN ADAPTIVE GRID ALGORITHM. (R827028)
A new dynamic adaptive grid algorithm has been developed for use in air quality modeling. This algorithm uses a higher order numerical scheme––the piecewise parabolic method (PPM)––for computing advective solution fields; a weight function capable o...
SIMULATION OF DISPERSION OF A POWER PLANT PLUME USING AN ADAPTIVE GRID ALGORITHM
A new dynamic adaptive grid algorithm has been developed for use in air quality modeling. This algorithm uses a higher order numerical scheme?the piecewise parabolic method (PPM)?for computing advective solution fields; a weight function capable of promoting grid node clustering ...
Knopman, Debra S.; Voss, Clifford I.
1987-01-01
The spatial and temporal variability of sensitivities has a significant impact on parameter estimation and sampling design for studies of solute transport in porous media. Physical insight into the behavior of sensitivities is offered through an analysis of analytically derived sensitivities for the one-dimensional form of the advection-dispersion equation. When parameters are estimated in regression models of one-dimensional transport, the spatial and temporal variability in sensitivities influences variance and covariance of parameter estimates. Several principles account for the observed influence of sensitivities on parameter uncertainty. (1) Information about a physical parameter may be most accurately gained at points in space and time. (2) As the distance of observation points from the upstream boundary increases, maximum sensitivity to velocity during passage of the solute front increases. (3) The frequency of sampling must be 'in phase' with the S shape of the dispersion sensitivity curve to yield the most information on dispersion. (4) The sensitivity to the dispersion coefficient is usually at least an order of magnitude less than the sensitivity to velocity. (5) The assumed probability distribution of random error in observations of solute concentration determines the form of the sensitivities. (6) If variance in random error in observations is large, trends in sensitivities of observation points may be obscured by noise. (7) Designs that minimize the variance of one parameter may not necessarily minimize the variance of other parameters.
NASA Astrophysics Data System (ADS)
Anderson, B. E.; Jordan, C. E.; Grant, W. B.; Browell, E. V.; Hudgins, C. H.; Winstead, E. L.; Thornhill, K. L.
2002-12-01
The 2001, NASA Transport and Chemical Evolution over the Pacific (TRACE-P) experiment was conducted during late winter and early spring, the time of year when eastward transport of dust and pollution from southern and central Asia reaches a maximum. From bases of operation in Hong Kong, Japan, and Hawaii, extensive measurements of trace species concentrations and characteristics were made from aboard a P-3B and DC-8 aircraft as they flew coordinated sampling missions within air masses at varying distances from the Asian coast and at altitudes ranging from near surface to over 12 km. Data recorded aboard the DC-8 included total condensation nuclei (CN) number densities and fractional volatility; aerosol size distributions, composition and optical properties; and multi-wavelength profiles of polarized, aerosol backscatter. Examining these data in light of simultaneous meteorological and chemical species measurements, we have calculated the advective flux and mean values of aerosol mass and physical properties at various locations within the Western Pacific Basin. At distances >100 km offshore, we find that the highest fluxes of sub-micron particles occurred below 2 km in the region downwind of Shanghai. These air masses exhibited CN concentrations approaching 50,000 cm-3 and visible scattering coefficients in excess of 200 Mm-1. For near-shore sampling between 26° and 36°N within this height range, these parameters averaged ~8,000 cm-3 and 130 Mm-, respectively, . As a result of dilution, surface deposition, and precipitation scavenging, these values rapidly diminished during eastward transport so that parcels sampled at low altitudes >1500 km from land typically contained ~1000 cm-3 CN and exhibited scattering coefficients <30 Mm-1. Because of the decreased strength of loss processes and greater atmospheric stability, parcels sampled in the 2- to 7-km height range were more apt to maintain their initial aerosol signatures during long-range transport.
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.
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.
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.
Generalized Fourier Analyses of Semi-Discretizations of the Advection-Diffusion Equation
CHRISTON, MARK A.; VOTH, THOMAS E.; MARTINEZ, MARIO J.
2002-11-01
This report presents a detailed multi-methods comparison of the spatial errors associated with finite difference, finite element and finite volume semi-discretizations of the scalar advection-diffusion equation. The errors are reported in terms of non-dimensional phase and group speeds, discrete diffusivity, artificial diffusivity, and grid-induced anisotropy. It is demonstrated that Fourier analysis (aka von Neumann analysis) provides an automatic process for separating the spectral behavior of the discrete advective operator into its symmetric dissipative and skew-symmetric advective components. Further it is demonstrated that streamline upwind Petrov-Galerkin and its control-volume finite element analogue, streamline upwind control-volume, produce both an artificial diffusivity and an artificial phase speed in addition to the usual semi-discrete artifacts observed in the discrete phase speed, group speed and diffusivity. For each of the numerical methods considered, asymptotic truncation error and resolution estimates are presented for the limiting cases of pure advection and pure diffusion. The Galerkin finite element method and its streamline upwind derivatives are shown to exhibit super-convergent behavior in terms of phase and group speed when a consistent mass matrix is used in the formulation. In contrast, the CVFEM method and its streamline upwind derivatives yield strictly second-order behavior. While this work can only be considered a first step in a comprehensive multi-methods analysis and comparison, it serves to identify some of the relative strengths and weaknesses of multiple numerical methods in a common mathematical framework.
Tracer transport in the Martian atmosphere
NASA Astrophysics Data System (ADS)
Lian, Y.; Richardson, M. I.; Newman, C. E.; Lee, C.; Toigo, A. D.; Campin, J.
2011-12-01
Transport is crucial to understanding and reproducing the Martian dust and water cycles, and to interpreting putative methane and other trace gas (e.g. Argon) observations. However, as quantified by comparing model predictions with Argon measurements made by the Gamma Ray Spectrometer [e.g. Sprague et al., 2004, 2007], current Mars general circulation models (GCM's) appear to do a poor job at tracer transport [e.g. Nelli et al., 2007]. This invalidates a core assumption of GCM modeling in the last decade - that transport is sufficiently well treated in models that we need focus only on improving physical parameterizations, and that differences between results from different GCM's stem purely from their treatment of physical processes. If instead it is the simulated dynamical processes that need better treatment we need to move towards higher-quality numerics, e.g. based on the finite volume formulation, and introduce a more sophisticated approach to advection following work done for terrestrial chemical transport modeling. Here we present the results of non-condensable tracer transport simulations using our newly developed Mars MITgcm, which has both of the aforementioned desirable attributes: a finite volume core and access to a range of sophisticated advection schemes. Our results are encouraging in that we are able to reproduce the observed peak polar Argon enhancement factor of six (about double that attainable with most other Mars GCMs). Our diagnostics show that the time-averaged zonal-mean advection produces net increases of Argon at the winter poles, while stationary and transient eddies transport Argon away from the poles. Using less diffusive nonlinear advection schemes with flux limiters tends to produce more advective fluxes of tracers into the southern winter pole than the more diffusive linear advection schemes, resulting in a greater net increase of polar Argon abundance. We further utilize a more realistic k-distribution radiative transfer model, an
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
Quantification of numerical diffusivity due to TVD schemes in the advection equation
NASA Astrophysics Data System (ADS)
Bidadi, Shreyas; Rani, Sarma L.
2014-03-01
In this study, the numerical diffusivity νnum inherent to the Roe-MUSCL scheme has been quantified for the scalar advection equation. The Roe-MUSCL scheme employed is a combination of: (1) the standard extension of the original Roe's formulation to the advection equation, and (2) van Leer's Monotone Upwind Scheme for Conservation Laws (MUSCL) technique that applies a linear variable reconstruction in a cell along with a scaled limiter function. An explicit expression is derived for the numerical diffusivity in terms of the limiter function, the distance between the cell centers on either side of a face, and the face-normal velocity. The numerical diffusivity formulation shows that a scaled limiter function is more appropriate for MUSCL in order to consistently recover the central-differenced flux at the maximum value of the limiter. The significance of the scaling factor is revealed when the Roe-MUSCL scheme, originally developed for 1-D scenarios, is applied to 2-D scalar advection problems. It is seen that without the scaling factor, the MUSCL scheme may not necessarily be monotonic in multi-dimensional scenarios. Numerical diffusivities of the minmod, superbee, van Leer and Barth-Jesperson TVD limiters were quantified for four problems: 1-D advection of a step function profile, and 2-D advection of step, sinusoidal, and double-step profiles. For all the cases, it is shown that the superbee scheme provides the lowest numerical diffusivity that is also most confined to the vicinity of the discontinuity. The minmod scheme is the most diffusive, as well as active in regions away from high gradients. As expected, the grid resolution study demonstrates that the magnitude and the spatial extent of the numerical diffusivity decrease with increasing resolution.
Zhao, Su; Ovadia, Jeremy; Liu, Xinfeng; Zhang, Yong-Tao; Nie, Qing
2011-01-01
For reaction-diffusion-advection equations, the stiffness from the reaction and diffusion terms often requires very restricted time step size, while the nonlinear advection term may lead to a sharp gradient in localized spatial regions. It is challenging to design numerical methods that can efficiently handle both difficulties. For reaction-diffusion systems with both stiff reaction and diffusion terms, implicit integration factor (IIF) method and its higher dimensional analog compact IIF (cIIF) serve as an efficient class of time-stepping methods, and their second order version is linearly unconditionally stable. For nonlinear hyperbolic equations, weighted essentially non-oscillatory (WENO) methods are a class of schemes with a uniformly high-order of accuracy in smooth regions of the solution, which can also resolve the sharp gradient in an accurate and essentially non-oscillatory fashion. In this paper, we couple IIF/cIIF with WENO methods using the operator splitting approach to solve reaction-diffusion-advection equations. In particular, we apply the IIF/cIIF method to the stiff reaction and diffusion terms and the WENO method to the advection term in two different splitting sequences. Calculation of local truncation error and direct numerical simulations for both splitting approaches show the second order accuracy of the splitting method, and linear stability analysis and direct comparison with other approaches reveals excellent efficiency and stability properties. Applications of the splitting approach to two biological systems demonstrate that the overall method is accurate and efficient, and the splitting sequence consisting of two reaction-diffusion steps is more desirable than the one consisting of two advection steps, because CWC exhibits better accuracy and stability. PMID:21666863
NASA Astrophysics Data System (ADS)
Peleg, Nadav; Fatichi, Simone; Burlando, Paolo
2015-04-01
A new stochastic approach to generate wind advection, cloud cover and precipitation fields is presented with the aim of formulating a space-time weather generator characterized by fields with high spatial and temporal resolution (e.g., 1 km x 1 km and 5 min). Its use is suitable for stochastic downscaling of climate scenarios in the context of hydrological, ecological and geomorphological applications. The approach is based on concepts from the Advanced WEather GENerator (AWE-GEN) presented by Fatichi et al. (2011, Adv. Water Resour.), the Space-Time Realizations of Areal Precipitation model (STREAP) introduced by Paschalis et al. (2013, Water Resour. Res.), and the High-Resolution Synoptically conditioned Weather Generator (HiReS-WG) presented by Peleg and Morin (2014, Water Resour. Res.). Advection fields are generated on the basis of the 500 hPa u and v wind direction variables derived from global or regional climate models. The advection velocity and direction are parameterized using Kappa and von Mises distributions respectively. A random Gaussian fields is generated using a fast Fourier transform to preserve the spatial correlation of advection. The cloud cover area, total precipitation area and mean advection of the field are coupled using a multi-autoregressive model. The approach is relatively parsimonious in terms of computational demand and, in the context of climate change, allows generating many stochastic realizations of current and projected climate in a fast and efficient way. A preliminary test of the approach is presented with reference to a case study in a complex orography terrain in the Swiss Alps.
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...
Rotman, D.A.; Tannahill, J.R.; Kinnison, D.E.; Connell, P.S.; Bergmann, D.; Proctor, D.; Rodriquez, J.M.; Lin, S.J.; Rood, R.B.; Prather, M.J.; Rasch, P.J.; Considine, D.B.; Ramaroson, R.; Kawa, S.R.
2000-04-25
We describe the three dimensional global stratospheric chemistry model developed under the NASA Global Modeling Initiative (GMI) to assess the possible environmental consequences from the emissions of a fleet of proposed high speed civil transport aircraft. This model was developed through a unique collaboration of the members of the GMI team. Team members provided computational modules representing various physical and chemical processes, and analysis of simulation results through extensive comparison to observation. The team members' modules were integrated within a computational framework that allowed transportability and simulations on massively parallel computers. A unique aspect of this model framework is the ability to interchange and intercompare different submodules to assess the sensitivity of numerical algorithms and model assumptions to simulation results. In this paper, we discuss the important attributes of the GMI effort, describe the GMI model computational framework and the numerical modules representing physical and chemical processes. As an application of the concept, we illustrate an analysis of the impact of advection algorithms on the dispersion of a NO{sub y}-like source in the stratosphere which mimics that of a fleet of commercial supersonic transports (High-Speed Civil Transport (HSCT)) flying between 17 and 20 kilometers.
Dual Transport Process for Targeted Delivery in Porous Media
NASA Astrophysics Data System (ADS)
Deng, W.; Fan, J.
2015-12-01
The targeted delivery in porous media is a promising technology to encapsulate the solute (i.e., the cargo) in colloid-like microcapsules (i.e., the carriers), transport the microcapsules in the targeted location in porous media, and then release the solute. While extensive literatures and applications about the drug delivery in human and animal bodies exist, the targeted delivery using similar delivery carriers in subsurface porous media is not well understood. The dual transport process study is an explorative study for the targeted delivery in porous media. While the colloid transport is dominated by the advection process and the solute transport is dominated by the advection-dispersion, the dual transport process is the process with the first step of carrier transport, which is dominated by advection, and then after the release of cargo, the transport of cargo is dominated by advection-dispersion. By applying the random walk particle tracking (RWPT) approach, we investigate how the carriers transport in porous media and how the cargo release mechanisms affect the cargo distribution for the targeted delivery in various patterns of porous media. The RWPT numerical model will be verified against the experimental results of dual transport process in packed-disk 2D micromodels. The understanding of the mechanism of dual transport process is crucial to achieve the potential applications of targeted delivery in improved oil and gas recovery, CO2 sequestration, environmental remediation, and soil biomediation.
Development of a three-dimensional, regional, coupled wave, current, and sediment-transport model
Warner, J.C.; Sherwood, C.R.; Signell, R.P.; Harris, C.K.; Arango, H.G.
2008-01-01
We are developing a three-dimensional numerical model that implements algorithms for sediment transport and evolution of bottom morphology in the coastal-circulation model Regional Ocean Modeling System (ROMS v3.0), and provides a two-way link between ROMS and the wave model Simulating Waves in the Nearshore (SWAN) via the Model-Coupling Toolkit. The coupled model is applicable for fluvial, estuarine, shelf, and nearshore (surfzone) environments. Three-dimensional radiation-stress terms have been included in the momentum equations, along with effects of a surface wave roller model. The sediment-transport algorithms are implemented for an unlimited number of user-defined non-cohesive sediment classes. Each class has attributes of grain diameter, density, settling velocity, critical stress threshold for erosion, and erodibility constant. Suspended-sediment transport in the water column is computed with the same advection-diffusion algorithm used for all passive tracers and an additional algorithm for vertical settling that is not limited by the CFL criterion. Erosion and deposition are based on flux formulations. A multi-level bed framework tracks the distribution of every size class in each layer and stores bulk properties including layer thickness, porosity, and mass, allowing computation of bed morphology and stratigraphy. Also tracked are bed-surface properties including active-layer thickness, ripple geometry, and bed roughness. Bedload transport is calculated for mobile sediment classes in the top layer. Bottom-boundary layer submodels parameterize wave-current interactions that enhance bottom stresses and thereby facilitate sediment transport and increase bottom drag, creating a feedback to the circulation. The model is demonstrated in a series of simple test cases and a realistic application in Massachusetts Bay. ?? 2008 Elsevier Ltd. All rights reserved.
Development of a three-dimensional, regional, coupled wave, current, and sediment-transport model
NASA Astrophysics Data System (ADS)
Warner, John C.; Sherwood, Christopher R.; Signell, Richard P.; Harris, Courtney K.; Arango, Hernan G.
2008-10-01
We are developing a three-dimensional numerical model that implements algorithms for sediment transport and evolution of bottom morphology in the coastal-circulation model Regional Ocean Modeling System (ROMS v3.0), and provides a two-way link between ROMS and the wave model Simulating Waves in the Nearshore (SWAN) via the Model-Coupling Toolkit. The coupled model is applicable for fluvial, estuarine, shelf, and nearshore (surfzone) environments. Three-dimensional radiation-stress terms have been included in the momentum equations, along with effects of a surface wave roller model. The sediment-transport algorithms are implemented for an unlimited number of user-defined non-cohesive sediment classes. Each class has attributes of grain diameter, density, settling velocity, critical stress threshold for erosion, and erodibility constant. Suspended-sediment transport in the water column is computed with the same advection-diffusion algorithm used for all passive tracers and an additional algorithm for vertical settling that is not limited by the CFL criterion. Erosion and deposition are based on flux formulations. A multi-level bed framework tracks the distribution of every size class in each layer and stores bulk properties including layer thickness, porosity, and mass, allowing computation of bed morphology and stratigraphy. Also tracked are bed-surface properties including active-layer thickness, ripple geometry, and bed roughness. Bedload transport is calculated for mobile sediment classes in the top layer. Bottom-boundary layer submodels parameterize wave-current interactions that enhance bottom stresses and thereby facilitate sediment transport and increase bottom drag, creating a feedback to the circulation. The model is demonstrated in a series of simple test cases and a realistic application in Massachusetts Bay.
NASA Astrophysics Data System (ADS)
Carvajal, Gisela; Eriksson, Leif E. B.
Analysis of ocean surface dynamics has been proven to be of vital importance in many areas (e.g. shipping, fishing). Two important parameters to describe the ocean dynamics are the wind velocity (speed and direction) and advective surface velocities (ocean current velocity). These parameters are currently provided operationally by forecast models, surface sensors (e.g. buoys, coastal radar) and satellite sensors. However, coverage limitations, low resolution and limited temporal availability impose a need for implementation and evaluation of new data sources and techniques for estimation of these parameters. In this paper we implement and evaluate known techniques for determination of wind and ocean current velocity from satellite data. Wind is determined from Synthetic Aperture Radar (SAR) data by applying two algo-rithms. First, the Local Gradient method is implemented to extract wind direction from the SAR data, and then the CMOD-5 Geophysical Model Function of the backscatter is inverted to obtain the wind speed as a function of the wind direction and the incidence angle. Current propagation is estimated by analyzing the Sea Surface Temperature propagation in two consec-utive infrared images of the same area from the Advanced Very High Resolution Radiometer. The evaluation shows a good agreement between estimated wind vectors from SAR and scat-terometer data. Comparison with merged ocean current estimates is addressed. The methods will be implemented in the maritime security service provided by the SECTRONIC project funded by the EU 7th framework program.
NASA Astrophysics Data System (ADS)
Sarry, L.; Peng, Y. J.; Boire, J. Y.
2002-01-01
In previously published studies, blood flow velocity from x-ray biplane angiography was measured by solving an inverse advection problem, relating velocity to bolus densities summed across sections. Both spatial and temporal velocity variations were recovered through a computationally expensive parameter estimation algorithm. Here we prove the existence and uniqueness of the solution on three sub-domains of the plane defined by the axial position along the vessel and the time of the angiographic sequence. A fast direct scheme was designed in conjunction with a regularization step stemming from the volume flow conservation law applied on consecutive segments. Its accuracy and immunity towards noise were tested on both simulated and real densitometric data. The relative error between the estimated and expected velocities was less than 5% for more than 90% of the points of the spatiotemporal plane with simulated densities normalized to 1.0 and a Gaussian additive noise of standard deviation 0.01. For densities reconstructed from a biplane angiographic sequence, increase in velocity is used as a functional index for the stenosis ratio and to characterize the sharing of flow at bifurcation.
NASA Astrophysics Data System (ADS)
Lauvernet, C.; Munoz-Carpena, R.; Carluer, N.
2012-04-01
Natural or introduced areas of vegetation, also known as vegetative filter strips (VFS), are a common environmental control practice to protect surface water bodies from human influence. In Europe, VFS are placed along the water network to protect from agrochemical drift during applications, in addition to runoff control. Their bottomland placement next to the streams often implies the presence of a seasonal shallow water table which can have a profound impact on the efficiency of the buffer zone (Lacas et al. 2005). A physically-based algorithm describing ponded infiltration into soils bounded by a water table, proposed by Salvucci and Enthekabi (1995), was further developed to simulate VFS dynamics by making it explicit in time, account for unsteady rainfall conditions, and by coupling to a numerical overland flow and transport model (VFSMOD) (Munoz-Carpena et al., submitted). In this study, we evaluate the importance of the presence of a shallow water table on filter efficiency (reductions in runoff, sediment and pesticide mass), in the context of all other input factors used to describe the system. Global sensitivity analysis (GSA) was used to rank the important input factors and the presence of interactions, as well as the contribution of the important factors to the output variance. GSA of VSFMOD modified for shallow water table was implemented on 2 sites selected in France because they represent different agro-pedo-climatic conditions for which we can compare the role of the factors influencing the performance of grassed buffer strips for surface runoff, sediment and pesticide removal. The first site at Morcille watershed in the Beaujolais wineyard (Rhône-Alpes) contains a very permeable sandy-clay with water table depth varying with the season (very deep in summer and shallow in winter), with a high slope (20 to 30%), and subject to strong seasonal storms (semi-continental, Mediterranean climate). The second site at La Jailliere (Loire-Atlantique, ARVALIS
NASA Astrophysics Data System (ADS)
Marques, Wilian C.; Fernandes, Elisa H. L.; Moller, Osmar O.
2010-06-01
The Southern Brazilian Shelf is a region influenced by freshwater, and the evolution of stratification can present important ecological consequences in this area. The aim of this paper was to investigate the importance of straining and advection processes that affect the stratification and destratification of the water column along the Southern Brazilian inner shelf, a region that is influenced by the Patos Lagoon coastal plume. The study was carried out through 3-D numerical modeling experiments and the results were analyzed using the potential energy anomaly equation and wavelet analysis. Results showed that the potential energy anomaly showed strong variability over a time scale of several days and followed the wind pattern over the study region, and was accompanied by the monthly modulation of river discharge and remote effects associated with variability in oceanic circulation. However, the most important events in synoptic time scales occurred in periods shorter than 20 days and were coincident with the passage of meteorological systems over the study region. Straining and advection were the most important mechanisms for the evolution of stratification in the adjacent coastal region. Nonlinearities and dispersion terms were as important as modulation effects, mainly during periods of high fluvial discharge. Close to the Patos Lagoon mouth, vertical advection explained most of the stratification evolution, due to the morphological characteristics in this region. In the frontal region and far field of the plume, the following two regions must be considered: the northeast part, which is characterized by the convergence of the coastal currents and ebb flows associated with the freshwater discharge that promote the domination of the cross-shore straining and advection, and the southwest part, which is controlled by the coastal currents that result in the domination by alongshore straining and advection and cross-shore advection terms. Close to the mouth of the
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
Long-term Rates of Mafic Magma Emplacement and Implications for Heat Advection
NASA Astrophysics Data System (ADS)
White, S. M.; Spera, F. J.; Crisp, J. A.
2003-12-01
Rates of magmatism (magma emplacement rate) including both volcanic products and intrusive bodies were obtained for terrestrial petrotectonic systems where reliable volumes can be estimated and geochronological data exist. Approximately 50 estimates of magma emplacement rates have been extracted from the literature published between 1982 and 2003 for persistent basaltic systems with durations from 1 ka to ~5 Ma. Although the volcanic output is highly episodic, the data indicate that the mass output rate at individual hotspot volcanoes is on the order of 10-3 km3/yr when averaged over several thousand years. This differs from the estimated output rates of large igneous provinces, such as continental flood basalts and oceanic plateaus, which have maximal output rates on the order of 1 km3/yr per province. For globally averaged mid-ocean ridges, the total volcanic emplacement rate is only 10-6 km3/yr/100 km of ridge. Ratios of intrusive to extrusive emplacement are subject to much uncertainty, but generally lie in the range 6:1 to 10:1 for most crustal mafic magma systems. Recent seismic, geodetic, and gravity work suggests that there may be large regions of underplating and storage in subcrustal magma chambers in areas of basaltic volcanism previously not widely considered in intrusive volume estimates that may increase most of these ratios to 10:1. Rates of magmatism may be translated into excess heat flows for specific magmatic provinces to obtain estimates of advected heat transport via magmatism at regional scales over magmatic province timescales. For mafic eruption rate V and an intrusive/extrusive ratio of R, the volumetric rate of magma flow into the crust is RV. The excess heat power (J/yr) associated with magma transport from mantle to crust is RVρ δ T [Cp + δ h/(Tliquidus-Tsolidus)] where δ T is the temperature difference between the magma and host crust, δ h is the enthalpy of crystallization (250-400 kJ/kg dependent on magma composition), ρ is
NASA Technical Reports Server (NTRS)
Schlesinger, R. E.
1985-01-01
The impact of upstream-biased corrections for third-order spatial truncation error on the stability and phase error of the two-dimensional Crowley combined advective scheme with the cross-space term included is analyzed, putting primary emphasis on phase error reduction. The various versions of the Crowley scheme are formally defined, and their stability and phase error characteristics are intercompared using a linear Fourier component analysis patterned after Fromm (1968, 1969). The performances of the schemes under prototype simulation conditions are tested using time-dependent numerical experiments which advect an initially cone-shaped passive scalar distribution in each of three steady nondivergent flows. One such flow is solid rotation, while the other two are diagonal uniform flow and a strongly deformational vortex.
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.
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 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.
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.
Comparison of Nonlinear and Linear Stabilization Schemes for Advection-Diffusion Equations
NASA Astrophysics Data System (ADS)
Grove, R. R.; Heister, T.
2015-12-01
Accurately solving advection-diffusion equations that appear in the finite element discretization of a mantle convection simulation is an important computational issue to the computational geoscience community. This is because it allows for users studying mantle convection to create reliable simulations for something as small and simple as a 2D simulation on their personal laptop to something as complex as a massively parallel 3D simulation on their university supercomputer. Standard finite element discretizations of advection-diffusion equations introduce unphysical oscillations around steep gradients. Therefore, stabilization must be added to the discrete formulation to obtain correct solutions. Using the open source scientific library ASPECT, the SUPG and Entropy Viscosity schemes are compared using stationary and non-stationary test equations. Differences in maximum overshoot and undershoot, smear, and convergence orders are compared to see if improvements can be made to the existing numerical method existing in ASPECT.
Scalar variance decay in chaotic advection and Batchelor-regime turbulence.
Fereday, D R; Haynes, P H; Wonhas, A; Vassilicos, J C
2002-03-01
The decay of the variance of a diffusive scalar in chaotic advection flow (or equivalently Batchelor-regime turbulence) is analyzed using a model in which the advection is represented by an inhomogeneous baker's map on the unit square. The variance decays exponentially at large times, with a rate that has a finite limit as the diffusivity kappa tends to zero and is determined by the action of the inhomogeneous map on the gravest Fourier modes in the scalar field. The decay rate predicted by recent theoretical work that follows scalar evolution in linear flow and then averages over all stretching histories is shown to be incorrect. The exponentially decaying scalar field is shown to have a spatial power spectrum of the form P(k) approximately k(-sigma) at wave numbers small enough for diffusion to be neglected, with sigma<1.
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.
McKone, Thomas E.
2009-03-01
with three major horizons, the saturated zone can be further divided into other zones based on hydraulic and geologic conditions. Wetland soils are a special and important class in which near-saturation conditions exist most of the time. When a contaminant is added to or formed in a soil column, there are several mechanisms by which it can be dispersed, transported out of the soil column to other parts of the environment, destroyed, or transformed into some other species. Thus, to evaluate or manage any contaminant introduced to the soil column, one must determine whether and how that substance will (1) remain or accumulate within the soil column, (2) be transported by dispersion or advection within the soil column, (3) be physically, chemically, or biologically transformed within the soil (i.e., by hydrolysis, oxidation, etc.), or (4) be transported out of the soil column to another part of the environment through a cross-media transfer (i.e., volatilization, runoff, ground water infiltration, etc.). These competing processes impact the fate of physical, chemical, or biological contaminants found in soils. In order to capture these mechanisms in mass transfer models, we must develop mass-transfer coefficients (MTCs) specific to soil layers. That is the goal of this chapter. The reader is referred to other chapters in this Handbook that address related transport processes, namely Chapter 13 on bioturbation, Chapter 15 on transport in near-surface geological formations, and Chapter 17 on soil resuspention. This chapter addresses the following issues: the nature of soil pollution, composition of soil, transport processes and transport parameters in soil, transformation processes in soil, mass-balance models, and MTCs in soils. We show that to address vertical heterogeneity in soils in is necessary to define a characteristic scaling depth and use this to establish process-based expressions for soil MTCs. The scaling depth in soil and the corresponding MTCs depend strongly
Framework Application for Core Edge Transport Simulation (FACETS)
Krasheninnikov, Sergei; Pigarov, Alexander
2011-10-15
The FACETS (Framework Application for Core-Edge Transport Simulations) project of Scientific Discovery through Advanced Computing (SciDAC) Program was aimed at providing a high-fidelity whole-tokamak modeling for the U.S. magnetic fusion energy program and ITER through coupling separate components for each of the core region, edge region, and wall, with realistic plasma particles and power sources and turbulent transport simulation. The project also aimed at developing advanced numerical algorithms, efficient implicit coupling methods, and software tools utilizing the leadership class computing facilities under Advanced Scientific Computing Research (ASCR). The FACETS project was conducted by a multi-discipline, multi-institutional teams, the Lead PI was J.R. Cary (Tech-X Corp.). In the FACETS project, the Applied Plasma Theory Group at the MAE Department of UCSD developed the Wall and Plasma-Surface Interaction (WALLPSI) module, performed its validation against experimental data, and integrated it into the developed framework. WALLPSI is a one-dimensional, coarse grained, reaction/advection/diffusion code applied to each material boundary cell in the common modeling domain for a tokamak. It incorporates an advanced model for plasma particle transport and retention in the solid matter of plasma facing components, simulation of plasma heat power load handling, calculation of erosion/deposition, and simulation of synergistic effects in strong plasma-wall coupling.
NASA Astrophysics Data System (ADS)
Jung, Na-Hyun; Han, Weon Shik; Han, Kyungdoe; Park, Eungyu
2015-05-01
Regional-scale advective, diffusive, and eruptive transport dynamics of CO2 and brine within a natural analogue in the northern Paradox Basin, Utah, were explored by integrating numerical simulations with soil CO2 flux measurements. Deeply sourced CO2 migrates through steeply dipping fault zones to the shallow aquifers predominantly as an aqueous phase. Dense CO2-rich brine mixes with regional groundwater, enhancing CO2 dissolution. Linear stability analysis reveals that CO2 could be dissolved completely within only ~500 years. Assigning lower permeability to the fault zones induces fault-parallel movement, feeds up-gradient aquifers with more CO2, and impedes down-gradient fluid flow, developing anticlinal CO2 traps at shallow depths (<300 m). The regional fault permeability that best reproduces field spatial CO2 flux variation is estimated 1 × 10-17 ≤ kh < 1 × 10-16 m2 and 5 × 10-16 ≤ kv < 1 × 10-15 m2. The anticlinal trap serves as an essential fluid source for eruption at Crystal Geyser. Geyser-like discharge sensitively responds to varying well permeability, radius, and CO2 recharge rate. The cyclic behavior of wellbore CO2 leakage decreases with time.
Role of advection in Arctic Ocean lower trophic dynamics: A modeling perspective
NASA Astrophysics Data System (ADS)
Popova, E. E.; Yool, A.; Aksenov, Y.; Coward, A. C.
2013-03-01
The Arctic Ocean (AO) is an oligotrophic system with a pronounced subsurface Chl-a maximum dominating productivity over the majority of the basin. Strong haline stratification of the AO and substantial ice cover suppress vertical mixing and restrict the vertical supply of nutrients to the photic zone. In such a vertically stratified oligotrophic system, the horizontal supply of nutrients by advection plays an important role in sustaining primary production. In this paper, we attempt to characterize the role of nutrient advection in the maintenance of the subsurface Chl-a maximum, using timescales to determine the connectivity between the photic zone of the deep AO, nutrient-rich Pacific and Atlantic inflow waters, and bottom waters of the wide continental shelves of the AO. Our study uses output from a general circulation model, Nucleus for European Modeling of the Ocean, coupled to a model of ocean biogeochemistry, Model of Ecosystem Dynamics, carbon Utilization, Sequestration, and Acidification. A Lagrangian particle tracking approach is used to back-track water from where it forms subsurface Chl-a maxima to the points of entry into the AO and to analyze nutrient transformation along the route. Our experiments show that advective timescales linking subsurface layers of the central AO with the nutrient-rich Pacific and Atlantic waters do not exceed 15-20 years and that the advective supply of shelf nutrients to the deep AO occurs on the timescale of about 5 years. We show substantial role of the continental shelf pump in sustaining up to 20% of total AO primary production.
Trophodynamic and advective influences on Georges Bank larval cod and haddock
NASA Astrophysics Data System (ADS)
Werner, Francisco E.; Ian Perry, R.; Gregory Lough, R.; Naimie, Christopher E.
Using a model-based approach, the relative effects of advective and trophodynamic (feeding and growth) processes are considered on populations of larval cod ( Gadus morhua) and haddock ( Melanogrammus aeglefinus) on Georges Bank. Building on previous studies that describe the role of advection, this study incorporates trophodynamic relationships to examine starvation mortality and growth rates at the level of individual larvae on the Bank. Estimates of prey concentrations and flow fields appropriate for late winter/early spring are used. Both trophodynamic processes and advection influence larval losses from the Bank where, in the absence of starvation, advective losses are on the order of one-fifth of the eggs and larvae spawned on the Bank. Starvation is most important in the first feeding larvae and is much reduced for older larvae. The contact rates between larval fish and zooplankton prey when turbulence is included are 2-5 times greater than the contact rates with no turbulence, and allow the model cod larvae to achieve growth rates similar to those observed on the Bank, although mean rates for larval haddock are still lower than observed. Turbulence-enhanced contact rates are thus determined to be a necessary component in our description of the growth of cod and haddock larvae on Georges Bank. Model cod larvae with growth rates comparable to those observed in the field are located below the surface layer (deeper than 25 m) and inside the 60 m isobath. The region of highest retention due to circulation processes (Werner et al., 1993; Fisheries Oceanography, 2, 43-64) coincides with the region of highest growth rates and highest larval survival. Therefore, there is a complementary interaction between trophodynamic and circulation processes, with those larvae most likely to remain on the Bank also being those in the most favorable feeding regions. Haddock larvae require higher prey densities than cod larvae to survive.
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.
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.
Ferrua, Maria J; Xue, Zhengjun; Singh, R Paul
2014-11-28
The mixing performance of gastric contents during digestion is expected to have a major role on the rate and final bioavailability of nutrients within the body. The aim of this study was to characterize the ability of the human stomach to advect gastric contents with different rheological properties. The flow behavior of two Newtonian fluids (10(-3)Pas, 1Pas) and a pseudoplastic solution (K=0.223Pas(0.59)) during gastric digestion were numerically characterized within a simplified 3D model of the stomach geometry and motility during the process (ANSYS-FLUENT). The advective performances of each of these gastric flows were determined by analyzing the spatial distribution and temporal history of their stretching abilities (Lagrangian analysis). Results illustrate the limited influence that large retropulsive and vortex structures have on the overall dynamics of gastric flows. Even within the distal region, more than 50% of the flow experienced velocity and shear values lower than 10% of their respective maximums. While chaotic, gastric advection was always relatively poor (with Lyapunov exponents an order of magnitude lower than those of a laminar stirred tank). Contrary to expectations, gastric rheology had only a minor role on the advective properties of the flow (particularly within the distal region). As viscosity increased above 1St, the role of fluid viscosity became largely negligible. By characterizing the fluid dynamic and mixing conditions that develop during digestion, this work will inform the design of novel in vitro systems of enhanced biomechanical performance and facilitate a more accurate diagnosis of gastric digestion processes. PMID:25446267
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
Advection of Sea-Ice Meltwater and Halocline Water Along the Siberian Continental Margin
NASA Astrophysics Data System (ADS)
Bauch, D.; Torres-Valdes, S.; Polyakov, I.; Chernyavskaya, E.; Novikhin, A.; Dmitrenko, I.; McKay, J. L.; Mix, A. C.
2014-12-01
Our study is based on hydrochemical and stable oxygen isotope data at the Laptev Sea continental slope from summers 2005-2009 and reveals a general pattern in water mass distribution and potential shelf-basin exchange. Despite considerable inter-annual variations, a frontal system can be inferred between shelf, continental slope and central Eurasian Basin waters in the upper 100 m of the water column along the continental slope. Net sea-ice melt is consistently found at the continental slope. However, the sea-ice meltwater signal is independent from the local retreat of the sea-ice edge and appears to be advected from upwind locations. In addition to the along-slope frontal system at the continental shelf break, a strong gradient is identified on the Laptev Sea shelf at ~122-126°E with an eastward increase of riverine and sea-ice related brine water contents. These waters cross the shelf break at ~140°E and feed the Low Salinity Halocline Water (LSHW, salinity S<33) in the upper 50 m of the water column. High silicate concentrations in Laptev Sea bottom waters may lead to speculation about a link to the local silicate maximum found within the salinity range of ~33 to 34.5, typical for the Lower Halocline Water (LHW) at the continental slope. However brine signatures and nutrient ratios from the central Laptev Sea differ from those observed at the continental slope. Similar to the advection of the sea-ice melt signal along the Laptev Sea continental slope the nutrient signal at 50-70 m water depth within the LHW might also be fed by advection parallel to the slope. Thus, our analyses suggest that advective processes from upstream locations play a significant role in the meltwater distribution and halocline formation in the northern Laptev Sea. Inter-annual variations within the properties of LHW are further investigated.
Improved numerical modeling of groundwater flow and transport at the MADE-2 site. Final report
Gray, D.D.; Rucker, D.F.
1995-02-01
Public domain computer programs were used to attempt an improved model of the tritium plume observed during Macrodispersion Experiment 2 (MADE-2), a field scale natural gradient experiment conducted at Columbus Air Force Base, Mississippi. The finite difference program MODFLOW was used to simulate the flow of groundwater through a 330 m x 105 m computational domain. Solutions for the 468 day experiment were obtained using a Sun Sparcstation 2 for several choices of convergence and storage parameters. The simulations had small mass balance errors and were consistent with continuous head observations. Tritium plume simulations used the mixed Lagrangian-Eulerian finite difference program MT3D to solve the contaminant transport equation using the MODFLOW-predicted flow field. Thirteen runs were made using various advection algorithms and dispersivities, but none was successful.
Phase mixing vs. nonlinear advection in drift-kinetic plasma turbulence
NASA Astrophysics Data System (ADS)
Schekochihin, A.; Parker, J.; Highcock, E.; Dellar, P.; Kanekar, A.; Dorland, W.; Hammett, G.; Loureiro, N.; Staines, C.; Stipani, L.
2015-11-01
A scaling theory of drift-kinetic turbulence in a weakly collisional plasma is proposed, with account both of the nonlinear advection of the perturbed particle distribution by the fluctuating ExB flow and of its parallel phase mixing, which in a linear problem causes Landau damping. It is found that little free energy leaks into high velocity moments of the distribution, rendering the turbulence in the energetically relevant part of the wave-number space essentially fluid-like. The velocity-space free-energy spectra expressed in terms of Hermite moments are steep power laws and so the energy content of the phase space does not diverge and collisional heating due to long-wavelength perturbations vanishes at inifinitesimal collisionality (both in contrast with the linear problem). The ability of the energy to stay in the low moments is facilitated by ``anti-phase-mixing,'' which in the nonlinear system is due to the stochastic version of plasma echo (the advecting flow couples the phase-mixing and anti-phase-mixing perturbations). The partitioning of the wave-number 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 timescales, which for high Hermite moments splits into two thresholds, one demarcating the wave-number region where phase mixing predominates, the other where plasma echo does.
Reactive-Diffusive-Advective Traveling Waves in a Family of Degenerate Nonlinear Equations
Sánchez-Garduño, Faustino
2016-01-01
This paper deals with the analysis of existence of traveling wave solutions (TWS) for a diffusion-degenerate (at D(0) = 0) and advection-degenerate (at h′(0) = 0) reaction-diffusion-advection (RDA) equation. Diffusion is a strictly increasing function and the reaction term generalizes the kinetic part of the Fisher-KPP equation. We consider different forms of the convection term h(u): (1) h′(u) is constant k, (2) h′(u) = ku with k > 0, and (3) it is a quite general form which guarantees the degeneracy in the advective term. In Case 1, we prove that the task can be reduced to that for the corresponding equation, where k = 0, and then previous results reported from the authors can be extended. For the other two cases, we use both analytical and numerical tools. The analysis we carried out is based on the restatement of searching TWS for the full RDA equation into a two-dimensional dynamical problem. This consists of searching for the conditions on the parameter values for which there exist heteroclinic trajectories of the ordinary differential equations (ODE) system in the traveling wave coordinates. Throughout the paper we obtain the dynamics by using tools coming from qualitative theory of ODE.
Super-diffusion versus competitive advection processes on the solar surface
NASA Astrophysics Data System (ADS)
Del Moro, Dario; Berrilli, Francesco; Giovannelli, Luca; Scardigli, Stefano; Giannattasio, Fabio; Consolini, Giuseppe; Lepreti, Fabio
2016-04-01
From the analysis of the displacement spectrum of magnetic element, 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. 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. 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 confronted those results also to simulation of passive tracers advection. 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 also the simulation shows a super-diffusive displacement spectrum: its competitive advection process can reproduce the signature of super-diffusion. Therefore, it is not necessary to hypothesize a totally developed turbulence regime to explain the motion of the magnetic elements on the solar surface.
Reactive-Diffusive-Advective Traveling Waves in a Family of Degenerate Nonlinear Equations
Sánchez-Garduño, Faustino
2016-01-01
This paper deals with the analysis of existence of traveling wave solutions (TWS) for a diffusion-degenerate (at D(0) = 0) and advection-degenerate (at h′(0) = 0) reaction-diffusion-advection (RDA) equation. Diffusion is a strictly increasing function and the reaction term generalizes the kinetic part of the Fisher-KPP equation. We consider different forms of the convection term h(u): (1) h′(u) is constant k, (2) h′(u) = ku with k > 0, and (3) it is a quite general form which guarantees the degeneracy in the advective term. In Case 1, we prove that the task can be reduced to that for the corresponding equation, where k = 0, and then previous results reported from the authors can be extended. For the other two cases, we use both analytical and numerical tools. The analysis we carried out is based on the restatement of searching TWS for the full RDA equation into a two-dimensional dynamical problem. This consists of searching for the conditions on the parameter values for which there exist heteroclinic trajectories of the ordinary differential equations (ODE) system in the traveling wave coordinates. Throughout the paper we obtain the dynamics by using tools coming from qualitative theory of ODE. PMID:27689131
Straining and advection contributions to the mixing process in the Patos Lagoon estuary, Brazil
NASA Astrophysics Data System (ADS)
Marques, Wilian C.; Fernandes, Elisa H. L.; Rocha, Luiz A. O.
2011-03-01
The estuarine area of coastal lagoons and freshwater-influenced regions presents periodically stratified and destratified conditions. The Patos Lagoon, one of the most important hydrological resources in South America, is located in the southernmost part of Brazil and exhibits such variable conditions. Therefore the aim of this study was to investigate the contributions of straining and advection to the modulation of stratification conditions in the Patos Lagoon estuarine region using potential energy anomaly budgets. This study was based a three-dimensional hydrodynamic numerical model that provided information for the potential energy anomaly equation and wavelet analysis. Results from the potential energy anomaly time series revealed strong variability over a timescale of several days following local wind action and the river discharge pattern. Each part of the estuary exhibited contrasting regimes that were spatially distributed with a different balance of terms. The upper part was dominated by along-shore currents associated with east-west wind component and gravitational flux. Contribution from cross-shore advection became important in the middle part of the estuary, where there was an increase in superficial area observed. The lower region was controlled by the north-south wind component being influenced by advection, cross-shore straining, and transversal circulation, suggesting that current velocity maintained transversal pressure gradients and further circulation. Nonlinear interactions between deviations in the dispersion terms and vertical density and velocity were important everywhere but were associated with modulation effects.
Gu Weimin
2012-07-10
By taking into account the local energy balance per unit volume between the viscous heating and the advective cooling plus the radiative cooling, we investigate the vertical structure of radiation pressure-supported accretion disks in spherical coordinates. Our solutions show that the photosphere of the disk is close to the polar axis and therefore the disk seems to be extremely thick. However, the density profile implies that most of the accreted matter exists in a moderate range around the equatorial plane. We show that the well-known polytropic relation between the pressure and the density is unsuitable for describing the vertical structure of radiation pressure-supported disks. More importantly, we find that the energy advection is significant even for slightly sub-Eddington accretion disks. We argue that the non-negligible advection may help us understand why the standard thin disk model is likely to be inaccurate above {approx}0.3 Eddington luminosity, which was found by some works on black hole spin measurement. Furthermore, the solutions satisfy the Solberg-Hoiland conditions, which indicate the disk to be convectively stable. In addition, we discuss the possible link between our disk model and ultraluminous X-ray sources.
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.
Nemaura, Tafireyi
2015-01-01
Understanding drug transportation mechanisms in the human body is of paramount importance in modeling Pharmacokinetic-Pharmacodynamic relationships. This work gives a novel general model of efavirenz transportation projections based on concentrations simulated from patients on a dose of 600 mg. The work puts forward a proposition that transportation can wholly be modeled by concentration and time in a uniform volumetric space. Furthermore, movement entities are used to inform the state of “kinetic solubility” of a solution. There is use of Ricker's model, and forms of the Hill's equation in modeling transportation. Characterization on the movement rates of solution particle are suggested in relation to advection rate of solution particle. At turning points on the transportation rate of solution particle vs. concentration curve, a suggestion of possibly change of dominance in the mode of transportation and saturation is made. There are four movement rates postulated at primary micro-level transportation, that are attributed to convection, diffusion [passive transportation (EI)] and energy dependent system transportation (ED) in relation to advection. Furthermore, a new parameter is introduced which is defined as an advection rate constant of solution particle. It is postulated to be dependent on two rate constants of solution particle, that is a convection rate constant of solution particle and a saturable transportation rate constant of solution particle. At secondary micro-level transportation, the results show convection as sum of advection and saturable transportation. The kinetics of dissolution of efavirenz in the solution space is postulated. Relatively, a good level of kinetics of dissolution is projected in the concentration region 0 − 32.82 μg/ml. PMID:26106329
NASA Technical Reports Server (NTRS)
Wang, Lui; Bayer, Steven E.
1991-01-01
Genetic algorithms are mathematical, highly parallel, adaptive search procedures (i.e., problem solving methods) based loosely on the processes of natural genetics and Darwinian survival of the fittest. Basic genetic algorithms concepts are introduced, genetic algorithm applications are introduced, and results are presented from a project to develop a software tool that will enable the widespread use of genetic algorithm technology.
Technology and human purpose: the problem of solids transport on the Earth's surface
NASA Astrophysics Data System (ADS)
Haff, P. K.
2012-11-01
Displacement of mass of limited deformability ("solids") on the Earth's surface is opposed by friction and (the analog of) form resistance - impediments relaxed by rotational motion, self-powering of mass units, and transport infrastructure. These features of solids transport first evolved in the biosphere prior to the emergence of technology, allowing slope-independent, diffusion-like motion of discrete objects as massive as several tons, as illustrated by animal foraging and movement along game trails. However, high-energy-consumption technology powered by fossil fuels required a mechanism that could support fast advective transport of solids, i.e., long-distance, high-volume, high-speed, unidirectional, slope-independent transport across the land surface of materials like coal, containerized fluids, minerals, and economic goods. Pre-technology nature was able to sustain regional- and global-scale advection only in the limited form of piggybacking on geophysical flows of water (river sediment) and air (dust). The appearance of a mechanism for sustained advection of solids independent of fluid flows and gravity appeared only upon the emergence of human purpose. Purpose enables solids advection by, in effect, simulating a continuous potential gradient, otherwise lacking, between discrete and widely separated fossil-fuel energy sources and sinks. Invoking purpose as a mechanism in solids advection is an example of the need to import anthropic principles and concepts into the language and methodology of modern Earth system dynamics. As part of the emergence of a generalized solids advection mechanism, several additional transport requirements necessary to the function of modern large-scale technological systems were also satisfied. These include spatially accurate delivery of advected payload, targetability to essentially arbitrarily located destinations (such as cities), and independence of structure of advected payload from transport mechanism. The latter property
Technology and human purpose: the problem of solids transport on the earth's surface
NASA Astrophysics Data System (ADS)
Haff, P. K.
2012-05-01
Displacement of mass of limited deformability ("solids") on the Earth's surface is opposed by friction and (the analog of) form resistance - impediments relaxed by rotational motion, self-powering of mass units, and transport infrastructure. These features of solids transport first evolved in the biosphere prior to the emergence of technology, allowing slope-independent, diffusion-like motion of discrete objects as massive as several tons, as illustrated by animal foraging and movement along game trails. However, high-energy-consumption technology powered by fossil fuels required a mechanism that could support advective transport of solids, i.e., long-distance, high-volume, high-speed, unidirectional, slope independent transport across the land surface of materials like coal, containerized fluids, and minerals. Pre-technology nature was able to sustain large-scale, long-distance solids advection only in the limited form of piggybacking on geophysical flows of water (river sediment) and air (dust). The appearance of a generalized mechanism for advection of solids independent of fluid flows and gravity appeared only upon the emergence of human purpose. Purpose enables solids advection by, in effect, enabling a simulated continuous potential gradient, otherwise lacking, between discrete and widely separated fossil-fuel energy sources and sinks. Invoking purpose as a mechanism in solids advection is an example of the need to import anthropic principles and concepts into the language and methodology of modern Earth system dynamics. As part of the emergence of a generalized solids advection mechanism, several additional transport requirements necessary to the function of modern large-scale technological systems were also satisfied. These include spatially accurate delivery of advected payload, targetability to essentially arbitrarily located destinations (such as cities), and independence of structure of advected payload from transport mechanism. The latter property
Modeling flow and solute transport in irrigation furrows
Technology Transfer Automated Retrieval System (TEKTRAN)
This paper presents an internally coupled flow and solute transport model for free-draining irrigation furrows. Furrow hydraulics is simulated with a numerical zero-inertia model and solute transport is computed with a model based on a numerical solution of the cross-section averaged advection-dispe...
NASA Astrophysics Data System (ADS)
Audiffren, N.; Buisson, E.; Cautenet, S.; Chaumerliac, N.
2004-05-01
Layers of pollutants are frequently exported from the North American continent over the North Atlantic Ocean. Several intensive experiments were dedicated to study this long-range transport, which frequently occurs over cloud bands. Therefore, the photolytic impact of a persistent cloud layer upon an advected plume of pollutants is an important question and is addressed in the framework of the North Atlantic Regional Experiment (NARE) 1993 experiment, at a distance of 300 km from the continent. The comprehensive RAMS model coupled on-line with a gaseous and an aqueous chemical module is used to follow the chemistry of the photochemically aged plume. A thin cloud layer involves radicals (OH and HO 2) and hydrogen peroxide production in the polluted air advected over it and increases the oxidizing capacity of atmosphere. Additional sensitivity tests to study the radiative impact of the accompanying aerosol layer upon the photolysis rates are conducted. It is shown that aerosols moderate this radiative impact due to the cloud layer.
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.
NASA Technical Reports Server (NTRS)
Dunkerton, Timothy J.
1991-01-01
Eastward and westward traveling waves were observed by the Nimbus 7 Limb Infrared Monitor of the Stratosphere (LIMS) during the northern winter 1978-1979. Eastward waves were prevalent in early winter and were involved in a minor Canadian warming in December 1978. A large westward traveling wave, as described by previous authors, was observed in January 1979 during a series of minor warmings. By comparing these two events, it is shown that in both cases the superposition of traveling and quasi-stationary waves led to constructive interference that was responsible for the warmings. However, there was significant asymmetry between eastward and westward traveling components. A local Eulerian analysis of potential vorticity (PV) transport indicates that adiabatic, geostrophic advection by the resolvable scales of motion explains qualitatively (but not quantitatively) the observed potential vorticity tendencies in the LIMS Northern Hemisphere winter. In particular, calculated advection explains the eastward rotation of the main vortex, intrusion of low PV air into the polar cap, and formation of high PV filaments at the vortex periphery.
NASA Astrophysics Data System (ADS)
Sittig, S.; Vrugt, J. A.; Kasteel, R.; Groeneweg, J.; Vereecken, H.
2011-12-01
Persistent antibiotics in the soil potentially contaminate the groundwater and affect the quality of drinking water. To improve our understanding of antibiotic transport in soils, we performed laboratory transport experiments in soil columns under constant irrigation conditions with repeated applications of chloride and radio-labeled SDZ. The tracers were incorporated in the first centimeter, either with pig manure or with solution. Breakthrough curves and concentration profiles of the parent compound and the main transformation products were measured. The goal is to describe the observed nonlinear and kinetic transport behavior of SDZ. Our analysis starts with synthetic transport data for the given laboratory flow conditions for tracers which exhibit increasingly complex interactions with the solid phase. This first step is necessary to benchmark our inverse modeling approach for ideal situations. Then we analyze the transport behavior using the column experiments in the laboratory. Our analysis uses a Markov chain Monte Carlo sampler (Differential Evolution Adaptive Metropolis algorithm, DREAM) to efficiently search the parameter space of an advective-dispersion model. Sorption of the antibiotics to the soil was described using a model regarding reversible as well as irreversible sorption. This presentation will discuss our initial findings. We will present the data of our laboratory experiments along with an analysis of parameter uncertainty.
Cooper, M.A.
2000-07-03
We present various approximations for the angular distribution of particles emerging from an optically thick, purely isotropically scattering region into a vacuum. Our motivation is to use such a distribution for the Fleck-Canfield random walk method [1] for implicit Monte Carlo (IMC) [2] radiation transport problems. We demonstrate that the cosine distribution recommended in the original random walk paper [1] is a poor approximation to the angular distribution predicted by transport theory. Then we examine other approximations that more closely match the transport angular distribution.
Correlated signals and causal transport in ocean circulation
NASA Astrophysics Data System (ADS)
Jeffress, Stephen
2014-05-01
This paper presents a framework for interpreting the time-lagged correlation of oceanographic data in terms of physical transport mechanisms. Previous studies have inferred aspects of ocean circulation by correlating fluctuations in temperature and salinity measurements at distant stations. Typically, the time-lag of greatest correlation is interpreted as an advective transit time and hence the advective speed of the current. In this paper we relate correlation functions directly to the underlying equations of fluid transport. This is accomplished by expressing the correlation functions in terms of the Green's function of the transport equation. Two types of correlation functions are distinguished: field-forcing correlation and field-field correlation. Their unique relationships to the Green's function are illustrated in two idealized models of geophysical transport: a leaky pipe model and an advective-diffusive model. Both models show that the field-forcing correlation function converges to the Green's function as the characteristic (time or length) scale of forcing autocorrelation decreases. The leaky pipe model provides an explanation for why advective speeds inferred from time-lagged correlations are often less than the speed of the main current. The advective-diffusive model reveals a structural bias in the field-field correlation function when used to estimate transit times.
CO2 transport over complex terrain
Sun, Jielun; Burns, Sean P.; Delany, A.C.; Oncley, S.P.; Turnipseed, A.A.; Stephens, B.B.; Lenschow, D.H.; LeMone, M.A.; Monson, Russell K.; Anderson, D.E.
2007-01-01
CO2 transport processes relevant for estimating net ecosystem exchange (NEE) at the Niwot Ridge AmeriFlux site in the front range of the Rocky Mountains, Colorado, USA, were investigated during a pilot experiment. We found that cold, moist, and CO2-rich air was transported downslope at night and upslope in the early morning at this forest site situated on a ???5% east-facing slope. We found that CO2 advection dominated the total CO2 transport in the NEE estimate at night although there are large uncertainties because of partial cancellation of horizontal and vertical advection. The horizontal CO2 advection captured not only the CO2 loss at night, but also the CO2 uptake during daytime. We found that horizontal CO2 advection was significant even during daytime especially when turbulent mixing was not significant, such as in early morning and evening transition periods and within the canopy. Similar processes can occur anywhere regardless of whether flow is generated by orography, synoptic pressure gradients, or surface heterogeneity as long as CO2 concentration is not well mixed by turbulence. The long-term net effect of all the CO2 budget terms on estimates of NEE needs to be investigated. ?? 2007 Elsevier B.V. All rights reserved.
NASA Astrophysics Data System (ADS)
Osgood, Kenric E.; Frost, Bruce W.
1996-08-01
The copepodid stage abundances of Calanus marshallae, Calanus pacificus and Metridia pacifica in Dabob Bay, Washington were followed through two years. Based on the species' life histories, vertical distributions, abundances inside and outside the bay, and the hydrographic setting, times when advection was important were explored. During the first study-year, 1973, advection acted to keep the copepod concentrations inside and outside Dabob Bay similar through the early summer. During the summer, a period of very little advective exchange, the copepod concentrations diverged at the two stations. In the fall, when advection picked up again, the copepod concentrations at the two stations once again became similar. During the summer of the other study-year, 1982, flow of deep water into Dabob Bay occurred. This may have caused some of the differences observed in the abundances of the copepods during the summer of 1982 vs 1973. Due in part to the advective events, the seasonal abundance patterns of the copepods could not be predicted based upon their locally expressed life history patterns. The most striking example of this was C. pacificus. Its population decreased during the spring and increased during the fall, despite having its major reproductive peak in the spring. Advective effects clearly contributed to this.
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).
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.
Variational Integration for Ideal MHD with Built-in Advection Equations
Zhou, Yao; Qin, Hong; Burby, J. W.; Bhattacharjee, A.
2014-08-05
Newcomb's Lagrangian for ideal MHD in Lagrangian labeling is discretized using discrete exterior calculus. Variational integrators for ideal MHD are derived thereafter. Besides being symplectic and momentum preserving, the schemes inherit built-in advection equations from Newcomb's formulation, and therefore avoid solving them and the accompanying error and dissipation. We implement the method in 2D and show that numerical reconnection does not take place when singular current sheets are present. We then apply it to studying the dynamics of the ideal coalescence instability with multiple islands. The relaxed equilibrium state with embedded current sheets is obtained numerically.
NASA Technical Reports Server (NTRS)
Cohn, S.
2002-01-01
As a motivation for this lecture, we begin by stating a paradox that challenges our fundamental understanding of covariance evolution (at least it challenged my own). Attempting to resolve this 'divergence paradox' leads us to introduce the continuum fundamental solution operator for the dynamics under consideration, which will be advection dynamics in this lecture. This operator is the object that is approximated by the discrete 'tangent linear model. We then show how the fundamental solution operator can be used to describe the solution of the continuum covariance evolution equation. This description is complete enough to resolve fully the divergence paradox.
Preconditioned iterative methods for space-time fractional advection-diffusion equations
NASA Astrophysics Data System (ADS)
Zhao, Zhi; Jin, Xiao-Qing; Lin, Matthew M.
2016-08-01
In this paper, we propose practical numerical methods for solving a class of initial-boundary value problems of space-time fractional advection-diffusion equations. First, we propose an implicit method based on two-sided Grünwald formulae and discuss its stability and consistency. Then, we develop the preconditioned generalized minimal residual (preconditioned GMRES) method and preconditioned conjugate gradient normal residual (preconditioned CGNR) method with easily constructed preconditioners. Importantly, because resulting systems are Toeplitz-like, fast Fourier transform can be applied to significantly reduce the computational cost. We perform numerical experiments to demonstrate the efficiency of our preconditioners, even in cases with variable coefficients.
Jiang, Yan-Fei; Stone, James M.; Davis, Shane W.
2014-07-01
We describe a new algorithm for solving the coupled frequency-integrated transfer equation and the equations of magnetohydrodynamics in the regime that light-crossing time is only marginally shorter than dynamical timescales. The transfer equation is solved in the mixed frame, including velocity-dependent source terms accurate to O(v/c). An operator split approach is used to compute the specific intensity along discrete rays, with upwind monotonic interpolation used along each ray to update the transport terms, and implicit methods used to compute the scattering and absorption source terms. Conservative differencing is used for the transport terms, which ensures the specific intensity (as well as energy and momentum) are conserved along each ray to round-off error. The use of implicit methods for the source terms ensures the method is stable even if the source terms are very stiff. To couple the solution of the transfer equation to the MHD algorithms in the ATHENA code, we perform direct quadrature of the specific intensity over angles to compute the energy and momentum source terms. We present the results of a variety of tests of the method, such as calculating the structure of a non-LTE atmosphere, an advective diffusion test, linear wave convergence tests, and the well-known shadow test. We use new semi-analytic solutions for radiation modified shocks to demonstrate the ability of our algorithm to capture the effects of an anisotropic radiation field accurately. Since the method uses explicit differencing of the spatial operators, it shows excellent weak scaling on parallel computers.
NASA Technical Reports Server (NTRS)
Kooi, Henk; Beaumont, Christopher
1994-01-01
Experiments with a surface processes model of large-scale (1-1000 km) long-term (1-100 m.y.) erosional denudation are used to establish the controls on the evolution of a model escarpment that is related to the rifting of a continent. The mdoel describes changes in topographic form as a result of sumultaneous short- and long-range mass transport representing hillslope (diffusive) processes and fluvial transport (advection), repsectively. Fluvial entrainment is modeled as a first-order kinetic reaction which reflects the erodibility of the substrate, and therefore the fluvial system is not necessarily carrying at capacity. One dimensional and planform models demonstrate that the principal controls on the evolution of an initially steep model escarpment are (1) antecedent topography/drainage; (2) the timesale (or equivalently a length scale) in the fluvial entrainment reaction; (3) the flexural response of the lithosphere to denudation; and (4) the relative efficiencies of the short- and long-range transport processes. When rainfall and substrate lithology are uniform, a significant amount of discharge draining over the escarpment top causes it to degrade. Only when the top of the model escarpment coincides with a drainage divide can escarpment retreat occur for these conditions. An additional requirement for retreat of a model escarpment without decline is a long reaction time scale for fluvial entrainment. This corresponds to a substrate that is hard to detach by flucial erosion, and therefore to fluvial erosion that is not transport limited. Coninuous backtilting of an escarpment due ot flexural isostatic uplift in response to denudational unloading helps maintain the scarp top as a divide. It is essntial if the escarpment gradient is to be preserved during retreat in a uniform lithology. Low flexural rigidieties propote steep and slowly retreating escarpments. For given rainfall and substrate conditions, the morphology of a retraeating model escarpment is
McGrail, B. Peter
2001-10-31
A numerically based simulator was developed to assist in the interpretation of complex laboratory experiments examining transport processes of chemical and biological contaminants subject to nonlinear adsorption and/or source terms. The inversion is performed with any of three nonlinear regression methods, Marquardt-Levenberg, conjugate gradient, or quasi-Newton. The governing equations for the problem are solved by the method of finite-differences including any combination of three boundary conditions: (1) Dirichlet, (2) Neumann, and (3) Cauchy. The dispersive terms in the transport equations were solved using the second-order accurate in time and space Crank-Nicolson scheme, while the advective terms were handled using a third-order in time and space, total variation diminishing (TVD) scheme that damps spurious oscillations around sharp concentration fronts. The numerical algorithms were implemented in the computer code INVERTS, which runs on any standard personal computer. Apart from a comprehensive set of test problems, INVERTS was also used to model the elution of a nonradioactive tracer, {sup 185}Re, in a pressurized unsaturated flow (PUF) experiment with a simulated waste glass for low-activity waste immobilization. Interpretation of the elution profile was best described with a nonlinear kinetic model for adsorption.
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.
Optimizing zonal advection of the Advanced Research WRF (ARW) dynamics for Intel MIC
NASA Astrophysics Data System (ADS)
Mielikainen, Jarno; Huang, Bormin; Huang, Allen H.
2014-10-01
The Weather Research and Forecast (WRF) model is the most widely used community weather forecast and research model in the world. There are two distinct varieties of WRF. The Advanced Research WRF (ARW) is an experimental, advanced research version featuring very high resolution. The WRF Nonhydrostatic Mesoscale Model (WRF-NMM) has been designed for forecasting operations. WRF consists of dynamics code and several physics modules. The WRF-ARW core is based on an Eulerian solver for the fully compressible nonhydrostatic equations. In the paper, we will use Intel Intel Many Integrated Core (MIC) architecture to substantially increase the performance of a zonal advection subroutine for optimization. It is of the most time consuming routines in the ARW dynamics core. Advection advances the explicit perturbation horizontal momentum equations by adding in the large-timestep tendency along with the small timestep pressure gradient tendency. We will describe the challenges we met during the development of a high-speed dynamics code subroutine for MIC architecture. Furthermore, lessons learned from the code optimization process will be discussed. The results show that the optimizations improved performance of the original code on Xeon Phi 5110P by a factor of 2.4x.
NASA Astrophysics Data System (ADS)
Mielikainen, Jarno; Huang, Bormin; Huang, Allen H.-L.
2015-05-01
The most widely used community weather forecast and research model in the world is the Weather Research and Forecast (WRF) model. Two distinct varieties of WRF exist. The one we are interested is the Advanced Research WRF (ARW) is an experimental, advanced research version featuring very high resolution. The WRF Nonhydrostatic Mesoscale Model (WRF-NMM) has been designed for forecasting operations. WRF consists of dynamics code and several physics modules. The WRF-ARW core is based on an Eulerian solver for the fully compressible nonhydrostatic equations. In the paper, we optimize a meridional (north-south direction) advection subroutine for Intel Xeon Phi coprocessor. Advection is of the most time consuming routines in the ARW dynamics core. It advances the explicit perturbation horizontal momentum equations by adding in the large-timestep tendency along with the small timestep pressure gradient tendency. We will describe the challenges we met during the development of a high-speed dynamics code subroutine for MIC architecture. Furthermore, lessons learned from the code optimization process will be discussed. The results show that the optimizations improved performance of the original code on Xeon Phi 7120P by a factor of 1.2x.
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.
Propagating longitudinal contractions in the ileum of the rabbit--efficiency of advective mixing.
Fullard, Luke; Lammers, Willem; Wake, Graeme C; Ferrua, Maria J
2014-11-01
Three longitudinal motions of the rabbit small intestine were modelled in the CFD software Polyflow using ex vivo experimental data previously reported in literature. Consideration was given to chyme rheology and mixing performance of the macro-scale lumenal motions, as triggered by the observed wall motions. Simulations were performed to qualitatively assess the flow behaviour. The advective properties of the flow were universally characterised by analysing the stretching ability of the flow. Two Newtonian fluids, with viscosities of μ = 1 Pa s and μ = 0.001 Pa s, and a non-Newtonian shear-thinning fluid (Bird-Carreau relationship with n = 0.41, λ = 0.1, η∞ = 5.01 × 10(-9) Pa s and η0 = 0.65 Pa s) were investigated. It was found that both the type of contraction and chyme rheology significantly affected the flow and subsequent efficiency of advective motions in the intestinal core. Results also showed that shear rates generated were too small to unveil the pseudo-plastic behaviour of the non-Newtonian fluid. Of the longitudinal motions analysed, the oral propagation was the one leading to the higher, but also the most localised levels of stretching in the rabbit small intestine. This oral propagation was largely characterised by an ordered axial flow and was able to facilitate mixing by stretching material elements in the vicinity of the intestinal wall, particularly in the case of a low viscous water like fluid. PMID:25000221
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.
Siero, E; Doelman, A; Eppinga, M B; Rademacher, J D M; Rietkerk, M; Siteur, K
2015-03-01
For water-limited arid ecosystems, where water distribution and infiltration play a vital role, various models have been set up to explain vegetation patterning. On sloped terrains, vegetation aligned in bands has been observed ubiquitously. In this paper, we consider the appearance, stability, and bifurcations of 2D striped or banded patterns in an arid ecosystem model. We numerically show that the resilience of the vegetation bands is larger on steeper slopes by computing the stability regions (Busse balloons) of striped patterns with respect to 1D and transverse 2D perturbations. This is corroborated by numerical simulations with a slowly decreasing water input parameter. Here, long wavelength striped patterns are unstable against transverse perturbations, which we also rigorously prove on flat ground through an Evans function approach. In addition, we prove a "Squire theorem" for a class of two-component reaction-advection-diffusion systems that includes our model, showing that the onset of pattern formation in 2D is due to 1D instabilities in the direction of advection, which naturally leads to striped patterns. PMID:25833449
Siero, E; Doelman, A; Eppinga, M B; Rademacher, J D M; Rietkerk, M; Siteur, K
2015-03-01
For water-limited arid ecosystems, where water distribution and infiltration play a vital role, various models have been set up to explain vegetation patterning. On sloped terrains, vegetation aligned in bands has been observed ubiquitously. In this paper, we consider the appearance, stability, and bifurcations of 2D striped or banded patterns in an arid ecosystem model. We numerically show that the resilience of the vegetation bands is larger on steeper slopes by computing the stability regions (Busse balloons) of striped patterns with respect to 1D and transverse 2D perturbations. This is corroborated by numerical simulations with a slowly decreasing water input parameter. Here, long wavelength striped patterns are unstable against transverse perturbations, which we also rigorously prove on flat ground through an Evans function approach. In addition, we prove a "Squire theorem" for a class of two-component reaction-advection-diffusion systems that includes our model, showing that the onset of pattern formation in 2D is due to 1D instabilities in the direction of advection, which naturally leads to striped patterns.
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.
Maximum Principles and Application to the Analysis of An Explicit Time Marching Algorithm
NASA Technical Reports Server (NTRS)
LeTallec, Patrick; Tidriri, Moulay D.
1996-01-01
In this paper we develop local and global estimates for the solution of convection-diffusion problems. We then study the convergence properties of a Time Marching Algorithm solving Advection-Diffusion problems on two domains using incompatible discretizations. This study is based on a De-Giorgi-Nash maximum principle.
NASA Astrophysics Data System (ADS)
Prueger, J. H.; Alfieri, J. G.; Hipps, L. E.; Kustas, W. P.; Chavez, J. L.; Evett, S. R.; Anderson, M. C.; French, A. N.; Neale, C. M. U.; McKee, L. G.; Hatfield, J. L.; Howell, T. A.; Agam, N.
2012-12-01
Quantifying turbulent fluxes of heat and water vapor over heterogeneous surfaces presents unique challenges. For example, in many arid and semi-arid regions, parcels of irrigated cropland are juxtaposed with hot, dry surfaces. Contrasting surface conditions can result in the advection of warm dry air over an irrigated crop surface where it increases the water vapor deficit and, thereby, atmospheric demand. If sufficient water is available, this can significantly enhance evaporative water loss from the irrigated field. The scale and frequency of turbulent eddies over an irrigated surface during periods of strong advection is not fully understood. High frequency (20 Hz) data were acquired over irrigated cotton, wheat stubble, and rangeland fields during the 2008 growing season as part of the Bushland Evapotranspiration and Agricultural Remote Sensing Experiment (BEAREX08). Spectral analysis of momentum and scalar quantities including heat and water vapor revealed low frequency features in the turbulence structure due to the penetration of the surface boundary layer by large-scale eddies during periods of unusually strong advection. Wavelet analysis was applied to assess specific events contributing to the spatial and temporal structure of turbulent flux eddies. The analysis showed that low frequency contributions were linked to both local and regional scale advective processes. These results clearly point to a need to better understand surface energy balance exchange for heterogeneous surfaces in arid and semi-arid regions under conditions of strong local and regional advection.
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
THE LARGE-SCALE MAGNETIC FIELDS OF ADVECTION-DOMINATED ACCRETION FLOWS
Cao Xinwu
2011-08-20
We calculate the advection/diffusion of the large-scale magnetic field threading an advection-dominated accretion flow (ADAF) and find that the magnetic field can be dragged inward by the accretion flow efficiently if the magnetic Prandtl number P{sub m}={eta}/{nu}{approx}1. This is due to the large radial velocity of the ADAF. It is found that the magnetic pressure can be as high as {approx}50% of the gas pressure in the inner region of the ADAF close to the black hole horizon, even if the external imposed homogeneous vertical field strength is {approx}< 5% of the gas pressure at the outer radius of the ADAF, which is caused by the gas in the ADAF plunging rapidly to the black hole within the marginal stable circular orbit. In the inner region of the ADAF, the accretion flow is significantly pressured in the vertical direction by the magnetic fields, and therefore its gas pressure can be two orders of magnitude higher than that in the ADAF without magnetic fields. This means that the magnetic field strength near the black hole is underestimated by assuming equipartition between magnetic and gas pressure with the conventional ADAF model. Our results show that the magnetic field strength of the flow near the black hole horizon can be more than one order of magnitude higher than that in the ADAF at {approx}3R{sub g} (R{sub g} = 2GM/c{sup 2}), which implies that the Blandford-Znajek mechanism could be more important than the Blandford-Payne mechanism for ADAFs. We find that the accretion flow is decelerated near the black hole by the magnetic field when the external imposed field is strong enough or the gas pressure of the flow is low at the outer radius, or both. This corresponds to a critical accretion rate, below which the accretion flow will be arrested by the magnetic field near the black hole for a given external imposed field. In this case, the gas may accrete as magnetically confined blobs diffusing through field lines in the region very close to the black
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 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.
Advection fog formation and aerosols produced by combustion-originated air pollution
NASA Technical Reports Server (NTRS)
Hung, R. J.; Liaw, G. S.; Vaughan, O. H., Jr.
1980-01-01
The way in which pollutants produced by the photochemical reaction of NO(X) and SO(X) affect the quality of the human environment through such phenomena as the formation of advection fog is considered. These pollutants provide the major source of condensation nuclei for the formation of fog in highways, airports and seaports. Results based on the monodisperse, multicomponent aerosol model show that: (1) condensation nuclei can grow and form a dense fog without the air having attained supersaturation; (2) the mass concentration range for NO(X) is one-third that of SO(X); and (3) the greater the mass concentration, the particle concentration, and the radius of condensation nuclei, the denser the fog that is formed.
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.
Preconditioned time-difference methods for advection-diffusion-reaction equations
Aro, C.; Rodrigue, G.; Wolitzer, D.
1994-12-31
Explicit time differencing methods for solving differential equations are advantageous in that they are easy to implement on a computer and are intrinsically very parallel. The disadvantage of explicit methods is the severe restrictions placed on stepsize due to stability. Stability bounds for explicit time differencing methods on advection-diffusion-reaction problems are generally quite severe and implicit methods are used instead. The linear systems arising from these implicit methods are large and sparse so that iterative methods must be used to solve them. In this paper the authors develop a methodology for increasing the stability bounds of standard explicit finite differencing methods by combining explicit methods, implicit methods, and iterative methods in a novel way to generate new time-difference schemes, called preconditioned time-difference methods.
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)
The slimming effect of advection on black-hole accretion flows
NASA Astrophysics Data System (ADS)
Lasota, J.-P.; Vieira, R. S. S.; Sadowski, A.; Narayan, R.; Abramowicz, M. A.
2016-03-01
Context. At super-Eddington rates accretion flows onto black holes have been described as slim (aspect ratio H/R ≲ 1) or thick (H/R> 1) discs, also known as tori or (Polish) doughnuts. The relation between the two descriptions has never been established, but it was commonly believed that at sufficiently high accretion rates slim discs inflate, becoming thick. Aims: We wish to establish under what conditions slim accretion flows become thick. Methods: We use analytical equations, numerical 1 + 1 schemes, and numerical radiative MHD codes to describe and compare various accretion flow models at very high accretion rates. Results: We find that the dominant effect of advection at high accretion rates precludes slim discs becoming thick. Conclusions: At super-Eddington rates accretion flows around black holes can always be considered slim rather than thick.
A self-organizing Lagrangian particle method for adaptive-resolution advection-diffusion simulations
NASA Astrophysics Data System (ADS)
Reboux, Sylvain; Schrader, Birte; Sbalzarini, Ivo F.
2012-05-01
We present a novel adaptive-resolution particle method for continuous parabolic problems. In this method, particles self-organize in order to adapt to local resolution requirements. This is achieved by pseudo forces that are designed so as to guarantee that the solution is always well sampled and that no holes or clusters develop in the particle distribution. The particle sizes are locally adapted to the length scale of the solution. Differential operators are consistently evaluated on the evolving set of irregularly distributed particles of varying sizes using discretization-corrected operators. The method does not rely on any global transforms or mapping functions. After presenting the method and its error analysis, we demonstrate its capabilities and limitations on a set of two- and three-dimensional benchmark problems. These include advection-diffusion, the Burgers equation, the Buckley-Leverett five-spot problem, and curvature-driven level-set surface refinement.
NASA Astrophysics Data System (ADS)
Iyer, Gautam; Kiselev, Alexander; Xu, Xiaoqian
2014-05-01
Consider a diffusion-free passive scalar θ being mixed by an incompressible flow u on the torus { T}^d . Our aim is to study how well this scalar can be mixed under an enstrophy constraint on the advecting velocity field. Our main result shows that the mix-norm ({\\Vert}{\\theta(t)}{\\Vert}_{H^{-1}}) is bounded below by an exponential function of time. The exponential decay rate we obtain is not universal and depends on the size of the support of the initial data. We also perform numerical simulations and confirm that the numerically observed decay rate scales similarly to the rigorous lower bound, at least for a significant initial period of time. The main idea behind our proof is to use the recent work of Crippa and De Lellis (2008 J. Reine Angew. Math. 616 15-46) making progress towards the resolution of Bressan's rearrangement cost conjecture.
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.
A reaction-diffusion-advection model of harmful algae growth with toxin degradation
NASA Astrophysics Data System (ADS)
Wang, Feng-Bin; Hsu, Sze-Bi; Zhao, Xiao-Qiang
2015-10-01
This paper is devoted to the study of a reaction-diffusion-advection system modeling the dynamics of a single nutrient, harmful algae and algal toxin in a flowing water habitat with a hydraulic storage zone. We introduce the basic reproduction ratio R0 for algae and show that R0 serves as a threshold value for persistence and extinction of the algae. More precisely, we prove that the washout steady state is globally attractive if R0 < 1, while there exists a positive steady state and the algae is uniformly persistent if R0 > 1. With an additional assumption, we obtain the uniqueness and global attractivity of the positive steady state in the case where R0 > 1.
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