Dispersive hydrodynamics: Preface
NASA Astrophysics Data System (ADS)
Biondini, G.; El, G. A.; Hoefer, M. A.; Miller, P. D.
2016-10-01
This Special Issue on Dispersive Hydrodynamics is dedicated to the memory and work of G.B. Whitham who was one of the pioneers in this field of physical applied mathematics. Some of the papers appearing here are related to work reported on at the workshop "Dispersive Hydrodynamics: The Mathematics of Dispersive Shock Waves and Applications" held in May 2015 at the Banff International Research Station. This Preface provides a broad overview of the field and summaries of the various contributions to the Special Issue, placing them in a unified context.
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.
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.
Atis, S; Saha, S; Auradou, H; Martin, J; Rakotomalala, N; Talon, L; Salin, D
2012-09-01
Autocatalytic reaction fronts between two reacting species in the absence of fluid flow, propagate as solitary waves. The coupling between autocatalytic reaction front and forced simple hydrodynamic flows leads to stationary fronts whose velocity and shape depend on the underlying flow field. We address the issue of the chemico-hydrodynamic coupling between forced advection in porous media and self-sustained chemical waves. Towards that purpose, we perform experiments over a wide range of flow velocities with the well characterized iodate arsenious acid and chlorite-tetrathionate autocatalytic reactions in transparent packed beads porous media. The characteristics of these porous media such as their porosity, tortuosity, and hydrodynamics dispersion are determined. In a pack of beads, the characteristic pore size and the velocity field correlation length are of the order of the bead size. In order to address these two length scales separately, we perform lattice Boltzmann numerical simulations in a stochastic porous medium, which takes into account the log-normal permeability distribution and the spatial correlation of the permeability field. In both experiments and numerical simulations, we observe stationary fronts propagating at a constant velocity with an almost constant front width. Experiments without flow in packed bead porous media with different bead sizes show that the front propagation depends on the tortuous nature of diffusion in the pore space. We observe microscopic effects when the pores are of the size of the chemical front width. We address both supportive co-current and adverse flows with respect to the direction of propagation of the chemical reaction. For supportive flows, experiments and simulations allow observation of two flow regimes. For adverse flow, we observe upstream and downstream front motion as well as static front behaviors over a wide range of flow rates. In order to understand better these observed static state fronts, flow
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
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...
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...
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...
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...
Hydrodynamic dispersion of microswimmers in suspension
NASA Astrophysics Data System (ADS)
Martin, Matthieu; Rafaï, Salima; Peyla, Philippe
2014-11-01
In our laboratory, we study hydrodynamics of suspensions of micro-swimmers. These micro-organisms are unicellular algae Chlamydomonas Rheinhardii which are able to swim by using their flagella. The swimming dynamics of these micro-swimmers can be seen as a random walk, in absence of any kind of interaction. In addition, these algae have the property of being phototactic, i.e. they swim towards the light. Combining this property with a hydrodynamic flow, we were able to reversibly separate algae from the rest of the fluid. But for sufficiently high volume fraction, these active particles interact with each other. We are now interested in how the coupling of hydrodynamic interactions between swimmers and phototaxis can modify the swimming dynamics at the scale of the suspension. To this aim, we conduct experiments in microfluidic devices to study the dispersion of the micro-organisms in a the liquid phase as a function of the volume fraction. We show that the dispersion of an assembly of puller type microswimmers is quantitatively affected by hydrodynamics interactions. Phd student.
Hydrodynamical Dispersion in Taylor-Couette Cells
NASA Astrophysics Data System (ADS)
Piva, M.; Calvo, A.; Aguirre, A.; Callegari, G.; Gabbanelli, S.; Rosen, M.; Wesfreid, J. E.
1997-04-01
In this article we study the mass tracer dispersion in organized flows. For this purpose we performed experiments in the flow arising from the Taylor-Couette hydrodynamic instability combined with axial flow. The tracer evolution is followed by means of optical measurements of the concentration. In this way transmission curves are obtained. We compare these curves with the solutions of the Gaussian models of mass diffusion and with phenomenological models including tracer trapping in the cells. This comparison gives us physical parameters related to the typical time and distances involved in the diffusive behaviour of tracers in the regions with recirculations and trapping.
Preasymptotic hydrodynamic dispersion as a quantitative probe of permeability.
Brosten, Tyler R; Vogt, Sarah J; Seymour, Joseph D; Codd, Sarah L; Maier, Robert S
2012-04-01
We interpret a generalized short-time expansion of stochastic hydrodynamic dispersion dynamics in the case of small Reynolds number flow through macroscopically homogenous permeable porous media to directly determine hydrodynamic permeability. The approach allows determination of hydrodynamic permeability from pulsed field gradient spin-echo nuclear magnetic resonance measurement of the short-time effective hydrodynamic dispersion coefficient. The analytical expansion of asymptotic dynamics agrees with experimental NMR data and lattice Boltzmann simulation of hydrodynamic dispersion in consolidated random sphere pack media. PMID:22680531
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.
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...
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...
Kordilla, Jannes; Pan, Wenxiao Tartakovsky, Alexandre
2014-12-14
We propose a novel smoothed particle hydrodynamics (SPH) discretization of the fully coupled Landau-Lifshitz-Navier-Stokes (LLNS) and stochastic advection-diffusion equations. The accuracy of the SPH solution of the LLNS equations is demonstrated by comparing the scaling of velocity variance and the self-diffusion coefficient with kinetic temperature and particle mass obtained from the SPH simulations and analytical solutions. The spatial covariance of pressure and velocity fluctuations is found to be in a good agreement with theoretical models. To validate the accuracy of the SPH method for coupled LLNS and advection-diffusion equations, we simulate the interface between two miscible fluids. We study formation of the so-called “giant fluctuations” of the front between light and heavy fluids with and without gravity, where the light fluid lies on the top of the heavy fluid. We find that the power spectra of the simulated concentration field are in good agreement with the experiments and analytical solutions. In the absence of gravity, the power spectra decay as the power −4 of the wavenumber—except for small wavenumbers that diverge from this power law behavior due to the effect of finite domain size. Gravity suppresses the fluctuations, resulting in much weaker dependence of the power spectra on the wavenumber. Finally, the model is used to study the effect of thermal fluctuation on the Rayleigh-Taylor instability, an unstable dynamics of the front between a heavy fluid overlaying a light fluid. The front dynamics is shown to agree well with the analytical solutions.
NASA Astrophysics Data System (ADS)
Kordilla, Jannes; Pan, Wenxiao; Tartakovsky, Alexandre
2014-12-01
We propose a novel smoothed particle hydrodynamics (SPH) discretization of the fully coupled Landau-Lifshitz-Navier-Stokes (LLNS) and stochastic advection-diffusion equations. The accuracy of the SPH solution of the LLNS equations is demonstrated by comparing the scaling of velocity variance and the self-diffusion coefficient with kinetic temperature and particle mass obtained from the SPH simulations and analytical solutions. The spatial covariance of pressure and velocity fluctuations is found to be in a good agreement with theoretical models. To validate the accuracy of the SPH method for coupled LLNS and advection-diffusion equations, we simulate the interface between two miscible fluids. We study formation of the so-called "giant fluctuations" of the front between light and heavy fluids with and without gravity, where the light fluid lies on the top of the heavy fluid. We find that the power spectra of the simulated concentration field are in good agreement with the experiments and analytical solutions. In the absence of gravity, the power spectra decay as the power -4 of the wavenumber—except for small wavenumbers that diverge from this power law behavior due to the effect of finite domain size. Gravity suppresses the fluctuations, resulting in much weaker dependence of the power spectra on the wavenumber. Finally, the model is used to study the effect of thermal fluctuation on the Rayleigh-Taylor instability, an unstable dynamics of the front between a heavy fluid overlaying a light fluid. The front dynamics is shown to agree well with the analytical solutions.
Kordilla, Jannes; Pan, Wenxiao; Tartakovsky, Alexandre
2014-12-14
We propose a novel smoothed particle hydrodynamics (SPH) discretization of the fully coupled Landau-Lifshitz-Navier-Stokes (LLNS) and stochastic advection-diffusion equations. The accuracy of the SPH solution of the LLNS equations is demonstrated by comparing the scaling of velocity variance and the self-diffusion coefficient with kinetic temperature and particle mass obtained from the SPH simulations and analytical solutions. The spatial covariance of pressure and velocity fluctuations is found to be in a good agreement with theoretical models. To validate the accuracy of the SPH method for coupled LLNS and advection-diffusion equations, we simulate the interface between two miscible fluids. We study formation of the so-called "giant fluctuations" of the front between light and heavy fluids with and without gravity, where the light fluid lies on the top of the heavy fluid. We find that the power spectra of the simulated concentration field are in good agreement with the experiments and analytical solutions. In the absence of gravity, the power spectra decay as the power -4 of the wavenumber-except for small wavenumbers that diverge from this power law behavior due to the effect of finite domain size. Gravity suppresses the fluctuations, resulting in much weaker dependence of the power spectra on the wavenumber. Finally, the model is used to study the effect of thermal fluctuation on the Rayleigh-Taylor instability, an unstable dynamics of the front between a heavy fluid overlaying a light fluid. The front dynamics is shown to agree well with the analytical solutions.
Kordilla, Jannes; Pan, Wenxiao; Tartakovsky, Alexandre M.
2014-12-14
We propose a novel Smoothed Particle Hydrodynamics (SPH) discretization of the fully-coupled Landau-Lifshitz-Navier-Stokes (LLNS) and advection-diffusion equations. The accuracy of the SPH solution of the LLNS equations is demonstrated by comparing the scaling of velocity variance and self-diffusion coefficient with kinetic temperature and particle mass obtained from the SPH simulations and analytical solutions. The spatial covariance of pressure and velocity fluctuations are found to be in a good agreement with theoretical models. To validate the accuracy of the SPH method for the coupled LLNS and advection-diffusion equations, we simulate the interface between two miscible fluids. We study the formation of the so-called giant fluctuations of the front between light and heavy fluids with and without gravity, where the light fluid lays on the top of the heavy fluid. We find that the power spectra of the simulated concentration field is in good agreement with the experiments and analytical solutions. In the absence of gravity the the power spectra decays as the power -4 of the wave number except for small wave numbers which diverge from this power law behavior due to the effect of finite domain size. Gravity suppresses the fluctuations resulting in the much weaker dependence of the power spectra on the wave number. Finally the model is used to study the effect of thermal fluctuation on the Rayleigh-Taylor instability, an unstable dynamics of the front between a heavy fluid overlying a light fluid. The front dynamics is shown to agree well with the analytical solutions.
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...
Fridjonsson, Einar O; Seymour, Joseph D; Schultz, Logan N; Gerlach, Robin; Cunningham, Alfred B; Codd, Sarah L
2011-03-01
Noninvasive measurements of hydrodynamic dispersion by nuclear magnetic resonance (NMR) are made in a model porous system before and after a biologically mediated precipitation reaction. Traditional magnetic resonance imaging (MRI) was unable to detect the small scale changes in pore structure visualized during light microscopy analysis after destructive sampling of the porous medium. However, pulse gradient spin echo nuclear magnetic resonance (PGSE NMR) measurements clearly indicated a change in hydrodynamics including increased pore scale mixing. These changes were detected through time-dependent measurement of the propagator by PGSE NMR. The dynamics indicate an increased pore scale mixing which alters the preasymptotic approach to asymptotic Gaussian dynamics governed by the advection diffusion equation. The methods described here can be used in the future to directly measure the transport of solutes in biomineral-affected porous media and contribute towards reactive transport models, which take into account the influence of pore scale changes in hydrodynamics.
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
NASA Astrophysics Data System (ADS)
Bernabé, Y.; Wang, Y.; Qi, T.; Li, M.
2016-02-01
The main purpose of this work is to investigate the relationship between passive advection-dispersion and permeability in porous materials presumed to be statistically homogeneous at scales larger than the pore scale but smaller than the reservoir scale. We simulated fluid flow through pipe network realizations with different pipe radius distributions and different levels of connectivity. The flow simulations used periodic boundary conditions, allowing monitoring of the advective motion of solute particles in a large periodic array of identical network realizations. In order to simulate dispersion, we assumed that the solute particles obeyed Taylor dispersion in individual pipes. When a particle entered a pipe, a residence time consistent with local Taylor dispersion was randomly assigned to it. When exiting the pipe, the particle randomly proceeded into one of the pipes connected to the original one according to probabilities proportional to the outgoing volumetric flow in each pipe. For each simulation we tracked the motion of at least 6000 solute particles. The mean fluid velocity was 10-3 ms-1, and the distance traveled was on the order of 10 m. Macroscopic dispersion was quantified using the method of moments. Despite differences arising from using different types of lattices (simple cubic, body-centered cubic, and face-centered cubic), a number of general observations were made. Longitudinal dispersion was at least 1 order of magnitude greater than transverse dispersion, and both strongly increased with decreasing pore connectivity and/or pore size variability. In conditions of variable hydraulic radius and fixed pore connectivity and pore size variability, the simulated dispersivities increased as power laws of the hydraulic radius and, consequently, of permeability, in agreement with previously published experimental results. Based on these observations, we were able to resolve some of the complexity of the relationship between dispersivity and permeability.
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)
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.
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
Lin, Guang; Tartakovsky, Alexandre M.
2010-04-01
In this study, we solve the three-dimensional stochastic Darcy's equation and stochastic advection-diffusion-dispersion equation using a probabilistic collocation method (PCM) on sparse grids. Karhunen-Lo\\`{e}ve (KL) decomposition is employed to represent the three-dimensional log hydraulic conductivity $Y=\\ln K_s$. The numerical examples which demonstrate the convergence of PCM are presented. It appears that the faster convergence rate in the variance can be obtained by using the Jacobi-chaos representing the truncated Gaussian distributions than using the Hermite-chaos for the Gaussian distribution. The effect of dispersion coefficient on the mean and standard deviation of the hydraulic head and solute concentration is investigated. Additionally, we also study how the statistical properties of the hydraulic head and solute concentration vary while using different types of random distributions and different standard deviations of random hydraulic conductivity.
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.
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....
Hydrodynamics of CNT dispersion in high shear dispersion mixers
NASA Astrophysics Data System (ADS)
Park, Young Min; Lee, Dong Hyun; Hwang, Wook Ryol; Lee, Sang Bok; Jung, Seung-Il
2014-11-01
In this work, we investigate the carbon nanotube (CNT) fragmentation mechanism and dispersion in high shear homogenizers as a plausible dispersion technique, correlating with device geometries and processing conditions, for mass production of CNT-aluminum composites for automobile industries. A CNT dispersion model has been established in a turbulent flow regime and an experimental method in characterizing the critical yield stress of CNT flocs are presented. Considering CNT dispersion in ethanol as a model system, we tested two different geometries of high shear mixers — blade-stirrer type and rotor-stator type homogenizers — and reported the particle size distributions in time and the comparison has been made with the modeling approach and partly with the computational results.
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.
A simple advection-dispersion model for the salt distribution in linearly tapered estuaries
NASA Astrophysics Data System (ADS)
Gay, Peter S.; O'Donnell, James
2007-07-01
We present a simple advection-dispersion model for the subtidal salt distribution in estuaries with linearly varying cross-sectional area and a nonzero net salt flux. A novel analytic solution allows investigation of the dependence of the curvature and gradient of the longitudinal salinity distribution on runoff, dispersion coefficient, and channel contraction or expansion. The model predicts that in estuarine segments that contract toward the fresher boundary, the salinity gradient is stronger than in a prismatic channel. When the dispersion coefficient is large compared to the salinity intrusion lengthscale, ? (the product of segment length and net volume flux divided by cross-sectional area at the ocean boundary), the curvature of the salt concentration may be negative, a characteristic not possible in uniform channel models. The main effect of up-estuary salt flux is to strengthen the salinity gradient. The model can be extended to multiple segments in order to simulate geometrically complicated estuaries. The model is employed to estimate an effective dispersion coefficient and to describe the salinity variation in the western 53 km of Long Island Sound where the cross section of the basin varies linearly. Using 8 years of monthly observations at seven stations we find that, since the curvature of the vertically averaged salinity is negative, the model and data are consistent only if the net volume flux and salt flux are toward the fresher boundary, the East River. Combining prior estimates of the magnitudes of the fluxes and their uncertainties with the model and salinity observations using a least squares approach, we estimate the dispersion coefficient for the Western Sound as 580 m2/s.
Horizontal advection and dispersion in a stratified shelf sea: The role of inertial oscillations
NASA Astrophysics Data System (ADS)
Inall, Mark E.; Aleynik, Dmitry; Neil, Clare
2013-10-01
The role played by inertial motions in horizontal dispersion within the thermocline of a broad, mid-latitude shelf sea is examined through the analysis of a deliberately released dye tracer. Our analysis is of the horizontal and vertical evolution over 40 h of a dye tracer injected into the seasonally stratified thermocline of the Celtic Sea on the NW European Shelf. The inferred diapycnal diffusivity was 1.3-1.5 × 10-5 m2 s-1, and the radial horizontal diffusivities of the depth integrated dye patch ranged from 1.9 to 4.0 m2 s-1. The inferred vertical diffusivity is in agreement with microstructure based estimates, and the depth integrated horizontal diffusivity is broadly in agreement with previous dye release derived estimates made over similar scales and time periods. Asymmetry in the horizontal evolution of the dye patch was evident. We argue that mean shear dispersion was responsible for lateral elongation of the dye patch, particularly between hours 23 and 35 after release, during which time horizontal diffusivity along the major axis, Ka, exceeded that along the minor axis, Kb, by more than a factor of 10. We further show that along-patch shear was predominantly a result of differential advection between a deep residual flow to the south-east and an oscillating wind-driven surface Ekman layer. In this region of strong low frequency (inertial) shear a time dependent model of shear dispersion (Young et al., 1982) was able to account for the observed rate of horizontal dispersion calculated on the target isopycnal surface.
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)
Benson, D. A.; Zhang, Y.
2006-12-01
Conservative solute transport through natural media is typically "anomalous" or non-Fickian. The anomalous transport may be characterized by faster than linear growth of the centered second moment, or non-Gaussian leading or trailing edges of a plume emanating from a point source. These characteristics develop because of non-local dependence on either past (time) or far upstream (space) concentrations. Non-local equations developed to describe anomalous dispersion usually focus on constant transport parameters and/or independence of the transport on space dimension. These simplifications have been useful for fitting simple transport processes, such as laboratory column tests or 1-D projections of field data. However, they may be insufficient for real field settings, where direction-dependent depositional processes and nonstationary heterogeneity can occur. We develop a generalized, multi-dimensional, spatiotemporal fractional advection- dispersion equation (fADE) with variable parameters to characterize regional-scale anomalous dispersion processes including trapping in immobile zones and/or super-Fickian rapid transport. A Lagrangian numerical model of the space-time fractional transport equation is developed in which solute particles can disperse in both space and time, depending on the medium heterogeneity properties, such as the connectivity and statistical distributions of high versus low-permeability deposits. In the generalized fADE, the range of the order of fractional time derivative is (0 2], representing a wide range of possible trapping behavior. The extension of the order to the range (1 2] is novel to transport theory. We apply the numerical model in 1-D and 2-D to the MADE site tritium plumes, and results indicate that this method can capture the main behaviors of realistic plumes, including local variations of spreading, direction-dependent scaling rates, and arbitrary rapid transport along preferential flow paths. Since the governing equation
NASA Astrophysics Data System (ADS)
Zaramella, M.; Marion, A.; Lewandowski, J.; Nützmann, G.
2016-07-01
Solute transport in rivers is controlled by surface flow hydrodynamics and by transient storage in dead zones, pockets of vegetation and hyporheic sediments where mass exchange and retention are governed by complex mechanisms. The physics of these processes are generally investigated by optimization of transient storage models (TSMs) to experimental data often yielding inconsistent and equifinal parameter sets. Uncertainty on parameters estimation is found to depend not only on the rates of exchange between the stream and storage zones, the stream-water velocity and the stream reach length according to the experimental Damkohler number (DaI), but also on the relative significance between transient storage and longitudinal dispersion on breakthrough curves (BTCs). An optimization strategy was developed and applied to an experimental dataset obtained from tracer tests in a small lowland river, analyzing BTCs generated through tracer injections under different conditions. The method supplies a tool to estimate model parameters from observed data through the analysis of the relative parameter significance. To analyze model performance a double compartment TSM was optimized by a regular fit procedure based on simple root mean square error minimization and by a fit based on a relative significance analysis of mechanism signatures. As a result consistent longitudinal dispersion and transient storage parameters were obtained when the signature targeted optimization was used.
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.
Downes, Barbara J; Lancaster, Jill
2010-01-01
1. In advection-dominated systems (both freshwater and marine), population dynamics are usually presumed to be dominated by the effects of migrants dispersing by advection, especially over the small spatial scales at which populations can be studied, but few studies have tested this presumption. We tested the hypothesis that benthic densities are controlled by densities of dispersers for two aquatic insects in upland streams. 2. Our study animals were two species of caddisflies (Hydropsychidae), which become sedentary filter-feeders following settlement onto substrata. Densities of dispersers in the drift (advective dispersal) were quantified using nets placed along the upstream edges of riffles, where the latter abruptly abutted a slower, upstream run. Settlement was estimated at each site using brick pavers, half of which had been fenced to prevent colonization of their top surfaces by walking hydropsychids, thus allowing us to distinguish also the mode of movement during settlement. 3. First through fifth instars of two species, Smicrophylax sp. AV2 and Asmicridea sp. AV1, were abundant and showed disparate results. Drift and settlement were relatively strongly related for Smicrophylax. The best fit lines were shown by second and third instars settling on plain bricks, suggesting that drift played a strong role in settlement, but that some drifters dropped to the bottom and located substrata by walking. Quantile regression suggested that drift sets limits to settlement in this species and that settlement success was highly variable. In contrast, settlement by Asmicridea was poorly related to drift; settlers were mainly individuals re-dispersing within sites. 4. Smicrophylax densities appear to be controlled by dispersal from upstream, but benthic density of Asmicridea is more likely linked to local demography. Our data demonstrate the dangers of assuming that supposedly drift-prone species can all be modelled in the same way. Alternative models emphasizing
Hydrodynamic dispersion at stagnation points: Simulations and experiments
NASA Astrophysics Data System (ADS)
Flekkøy, E. G.; Oxaal, U.; Feder, J.; Jøssang, T.
1995-11-01
The spreading of a passive tracer that is convected back and forth inside a porous medium depends both on the random characteristics of the medium and on the presence of stagnation points. We single out the effect of the latter in the present study of hydrodynamic dispersion in the creeping (low Reynolds number) high Péclet number flow around the single stagnation point on a cylindrical obstacle in a Hele-Shaw cell [U. Oxaal, E. G. Flekko/y, and J. Feder, Phys. Rev. Lett. 72, 3514 (1994)]. Employing both experiments and lattice Boltzmann simulations we analyze the dispersive spreading of a single tracer line, which is initially perpendicular to the flow direction and then convected back and forth around the cylinder. The lattice Boltzmann model used is a modification of the recently introduced two-dimensional lattice bathnagar-Gross-Krook model for miscible fluid dynamics [E. G. Flekko/y, Phys. Rev. E 47, 4247 (1993)]. It includes the full three-dimensional viscous interaction in the Hele-Shaw cell, and, in the case of steady state flow, it allows for a freely tunable Reynolds number. The diffusive behavior of the system is explored extensively and excellent agreement between simulations and experiment is observed. A method to determine very small molecular diffusion coefficients D, which relies on the combination of results from experiment and simulation, is proposed. It is demonstrated that there is good agreement between the result of this method and independent measurement that are carried out in the present case of relatively large D values.
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.
Cox, T.J.; Runkel, R.L.
2008-01-01
Past applications of one-dimensional advection, dispersion, and transient storage zone models have almost exclusively relied on a central differencing, Eulerian numerical approximation to the nonconservative form of the fundamental equation. However, there are scenarios where this approach generates unacceptable error. A new numerical scheme for this type of modeling is presented here that is based on tracking Lagrangian control volumes across a fixed (Eulerian) grid. Numerical tests are used to provide a direct comparison of the new scheme versus nonconservative Eulerian numerical methods, in terms of both accuracy and mass conservation. Key characteristics of systems for which the Lagrangian scheme performs better than the Eulerian scheme include: nonuniform flow fields, steep gradient plume fronts, and pulse and steady point source loadings in advection-dominated systems. A new analytical derivation is presented that provides insight into the loss of mass conservation in the nonconservative Eulerian scheme. This derivation shows that loss of mass conservation in the vicinity of spatial flow changes is directly proportional to the lateral inflow rate and the change in stream concentration due to the inflow. While the nonconservative Eulerian scheme has clearly worked well for past published applications, it is important for users to be aware of the scheme's limitations. ?? 2008 ASCE.
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.
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.
NASA Technical Reports Server (NTRS)
Hung, R. J.; Liaw, G. S.
1980-01-01
The effects of multi-disperse distribution of the aerosol population are presented. Single component and multi-component aerosol species on the condensation/nucleation processes which affect the reduction in visibility are described. The aerosol population with a high particle concentration provided more favorable conditions for the formation of a denser fog than the aerosol population with a greater particle size distribution when the value of the mass concentration of the aerosols was kept constant. The results were used as numerical predictions of fog formation. Two dimensional observations in horizontal and vertical coordinates, together with time-dependent measurements were needed as initial values for the following physical parameters: (1)wind profiles; (2) temperature profiles; (3) humidity profiles; (4) mass concentration of aerosol particles; (5) particle size distribution of aerosols; and (6) chemical composition of aerosols. Formation and dissipation of advection fog, thus, can be forecasted numerically by introducing initial values obtained from the observations.
Dispersive deformations of hydrodynamic reductions of (2 + 1)D dispersionless integrable systems
NASA Astrophysics Data System (ADS)
Ferapontov, E. V.; Moro, A.
2009-01-01
We demonstrate that hydrodynamic reductions of dispersionless integrable systems in 2 + 1 dimensions, such as the dispersionless Kadomtsev-Petviashvili (dKP) and dispersionless Toda lattice (dTl) equations, can be deformed into reductions of the corresponding dispersive counterparts. Modulo the Miura group, such deformations are unique. The requirement that any hydrodynamic reduction possesses a deformation of this kind imposes strong constraints on the structure of dispersive terms, suggesting an alternative approach to the integrability in 2 + 1 dimensions.
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
Embry, Irucka; Roland, Victor; Agbaje, Oluropo; Watson, Valetta; Martin, Marquan; Painter, Roger; Byl, Tom; Sharpe, Lonnie
2013-01-01
A new residence-time distribution (RTD) function has been developed and applied to quantitative dye studies as an alternative to the traditional advection-dispersion equation (AdDE). The new method is based on a jointly combined four-parameter gamma probability density function (PDF). The gamma residence-time distribution (RTD) function and its first and second moments are derived from the individual two-parameter gamma distributions of randomly distributed variables, tracer travel distance, and linear velocity, which are based on their relationship with time. The gamma RTD function was used on a steady-state, nonideal system modeled as a plug-flow reactor (PFR) in the laboratory to validate themore » effectiveness of the model. The normalized forms of the gamma RTD and the advection-dispersion equation RTD were compared with the normalized tracer RTD. The normalized gamma RTD had a lower mean-absolute deviation (MAD) (0.16) than the normalized form of the advection-dispersion equation (0.26) when compared to the normalized tracer RTD. The gamma RTD function is tied back to the actual physical site due to its randomly distributed variables. The results validate using the gamma RTD as a suitable alternative to the advection-dispersion equation for quantitative tracer studies of non-ideal flow systems.« less
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.
NASA Astrophysics Data System (ADS)
Pini, R.; Vandehey, N. T.; O'Neil, J.; Benson, S. M.
2015-12-01
We report results of an experimental investigation into the effects of small-scale (mm-cm) heterogeneities and hydrodynamic dispersion on miscible and immiscible displacements in a Berea Sandstone core. Pulse-radiotracer tests were carried out by measuring breakthrough curves at distinct flow rates and gas/water saturation ratios, while simultaneously imaging the internal displacement of the radioactive solution by [11C]PET. Dynamic multidimensional maps of the tracer concentration in the rock sample have been obtained with a spatial resolution of about 10 mm3 and provide evidence for significant macrodispersion effects caused by the presence of heterogeneities at the same scale. The numerical solution of the classic Advection-Dispersion Equation (ADE) applied in 1D form fails to describe the measured breakthrough curves and significantly overestimates longitudinal dispersivity. An excellent agreement with the experiments is attained by explicitly accounting for permeability heterogeneity, while reducing the contribution of "Fickian" dispersivity. Heterogeneity was introduced in the model by discretising the rock sample into independent parallel streamlines, which were generated based on a previously determined 3D permeability map, and by solving the 1D ADE for each of them. The use of streamlines is supported by direct quantitative observations from the PET scans; remarkably, this approach leads to an accurate representation of both the temporal behaviour and spatial distribution of the tracer concentration in the sample. It is shown that when the length-scale of permeability variations is similar in order as the size of the sample, the effect of the former can be as significant as hydrodynamic dispersion. The presence of a second immiscible fluid phase further complicates the flow field and, accordingly, the interpretation of the experiments. The ability to decouple these effects leads to the estimation of dispersion coefficients that aren't sample specific and
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
NASA Astrophysics Data System (ADS)
Avesani, Diego; Herrera, Paulo; Chiogna, Gabriele; Bellin, Alberto; Dumbser, Michael
2015-06-01
Most numerical schemes applied to solve the advection-diffusion equation are affected by numerical diffusion. Moreover, unphysical results, such as oscillations and negative concentrations, may emerge when an anisotropic dispersion tensor is used, which induces even more severe errors in the solution of multispecies reactive transport. To cope with this long standing problem we propose a modified version of the standard Smoothed Particle Hydrodynamics (SPH) method based on a Moving-Least-Squares-Weighted-Essentially-Non-Oscillatory (MLS-WENO) reconstruction of concentrations. This scheme formulation (called MWSPH) approximates the diffusive fluxes with a Rusanov-type Riemann solver based on high order WENO scheme. We compare the standard SPH with the MWSPH for different a few test cases, considering both homogeneous and heterogeneous flow fields and different anisotropic ratios of the dispersion tensor. We show that, MWSPH is stable and accurate and that it reduces the occurrence of negative concentrations compared to standard SPH. When negative concentrations are observed, their absolute values are several orders of magnitude smaller compared to standard SPH. In addition, MWSPH limits spurious oscillations in the numerical solution more effectively than classical SPH. Convergence analysis shows that MWSPH is computationally more demanding than SPH, but with the payoff a more accurate solution, which in addition is less sensitive to particles position. The latter property simplifies the time consuming and often user dependent procedure to define the initial dislocation of the particles.
Hydrodynamics of annular-dispersed flow. [PWR; BWR
Ishii, M.; Kataoka, I.
1982-01-01
The interfacial drag, droplet entrainment, and droplet size distributions are important for detailed mechanistic modeling of annular dispersed two-phase flow. In view of this, recently developed correlations for these parameters are presented and discussed in this paper. The drag correlations for multiple fluid particle systems have been developed from a similarity hypothesis based on the mixture viscosity model. The results show that the drag coefficient depends on the particle Reynolds number and droplet concentration. The onset on droplet entrainment significantly alters the mechanisms of mass, momentum, and energy transfer between the film and gas core flow as well as the transfer between the two-phase mixture and the wall. By assuming the roll wave entrainment mechanism, the correlations for the amount of entrained droplet as well as for the droplet size distribution have been obtained from a simple model in collaboration with a large number of data.
Tachiev, F.; Yaari, G.; Foster, N.; Blaine, B.
2007-07-01
The removal of cesium by draining the supernate and interstitial salt solution from the salt-cake while fresh water is continuously being added at the top of the tank requires modeling of the transport in variably saturated porous media, and possibly includes a diffusion component. The uncertainties in this method are based on the highly inhomogeneous properties of the salt-cake and limited knowledge of the drainage and transport parameters, more specifically, its hydraulic constraints and hydrodynamic dispersion properties. The hydraulic parameters of the salt-cake (hydraulic conductivity and van Genuchten parameters) have significance with respect to tank drainage and re-saturation and determine the kinetics of the flow through the salt waste. The unsaturated properties are needed in order to assess not only the time frame of tank drainage but also the equilibrium conditions. One of the most important parameters for determining the transport properties of the porous media is the hydrodynamic dispersion tensor. The hydrodynamic dispersion can be applied to describe the spreading of cesium mass spatially and temporally. It combines effects from local variations in pore fluid velocity dispersion and molecular diffusion. In this study, the hydrodynamic dispersion parameters, the Peclet number for molecular diffusion, and the resulting uncertainties have been estimated from pilot scale column experiments using S-109 salt-cake simulant. A 2-D axisymmetric finite element model has been developed to couple the flow in variably saturated regime with transport of non-reacting cesium. The model used unsaturated hydraulic properties as determined from previous experimental work. The study performed sensitivity analysis of the hydrodynamic dispersion factor and provided information about its significance with respect to cesium temporal and spatial distribution. The model was used to compare relevant operating parameters during the replacement of cesium rich supernatant with
Hydrodynamic dispersion of a neutral non-reacting solute in electroosmotic flow
S. K. Griffiths; R. H. Nilson
1999-06-01
Analytical methods are employed to determine the axial dispersion of a neutral non-reacting solute in an incompressible electroosmotic flow. In contrast to previous approaches, the dispersion is obtained here by solving the time-dependent diffusion-advection equation in transformed spatial and temporal coordinates to obtain the two-dimensional late-time concentration field. The coefficient of dispersion arises as a separation eigenvalue, and its value is obtained as a necessary condition for satisfying all of the required boundary conditions. Solutions based on the Debye-Huckel approximation are presented for both a circular tube and a channel of infinite width. These results recover the well-known solutions for dispersion in pressure-driven flows when the Debye length is very large. In this limit, the axial dispersion is proportional to the square of the Peclet number based on the characteristic transverse dimension of the tube or channel. In the tilt of very small Debye lengths, the authors find that the dispersion varies as the square of the Peclet number based on the Debye length. Simple approximations to the coefficient of dispersion as a function of the Debye length and Peclet number are also presented.
NASA Astrophysics Data System (ADS)
Liang, Y.; DiCarlo, D. A.; Hesse, M. A.
2015-12-01
Carbon capture and storage in deep geological formations has the potential to reduce anthropogenic CO2 emissions from industrial point sources. Dissolution of CO2 into the brine, resulting in stable stratification, has been identified as the key to long-term storage security. Here we present new analogue laboratory experiment method, advanced image processing method and optimized simulation method to characterize CO2 convective dissolution trapping process and gravitational finger behaviors, in order to study the effect of hydrodynamic dispersion on the CO2 convective dissolution process, as well as to study the effect of control physical parameters on the gravitational finger dynamics. Figure 1 shows the image processing method to analyze the finger dynamics. Understanding the effect of hydrodynamic dispersion and the finger dynamics are essential to evaluate whether convective dissolution occurs, as well as to predict how fast it occurs at the geological CO2 storage field scale. The effect of hydrodynamics dispersion and the finger dynamics can be applied to estimate the security of geological CO2 storage fields, in turn. Optimiezed simulation work is conducted to predict the CO2 dissolution rate at geological CO2 storage field. The large experimental assembly will allow us to quantify in detail for the first time the relationship between convective dissolution rate and the controlling factors of the system, including permeability and driven force, which could be essential to trapping process at Bravo Dome geological CO2 storage field. We complement the homogeneous experiments with a detailed study of the scaling law of the convective flux with dispersion effect. The advanced image processing method with Fourier's transform method allow us to understand the finger dynamics and corresponding control factors in porous media, for the first time. By applying the dispersion effect and finger dynamics we found from the experimental study, we optimize the simulation
Fluorescence photobleaching to evaluate flow velocity and hydrodynamic dispersion in nanoslits.
Cuenca, Amandine; Bodiguel, Hugues
2012-05-01
Velocity measurement is a key issue when studying flows below the micron scale, due to the lack of sensitivity of conventional detection techniques. We present an approach based on fluorescence photobleaching to evaluate flow velocity at the nanoscale by direct visualization. Solutions containing a fluorescent dye are injected into nanoslits. A photobleached line, created through laser beam illumination, moves through the channel due to the fluid flow. The velocity and effective diffusion coefficient are calculated from the temporal data of the line position and width respectively. The measurable velocity range is only limited by the diffusion rate of the fluorescent dye for low velocities and by the apparition of Taylor dispersion for high velocities. By controlling the pressure drop and measuring the velocity, we determine the fluid viscosity. The photobleached line spreads in time due to molecular diffusion and Taylor hydrodynamic dispersion. By taking into account the finite spatial and temporal extensions of the bleaching under flow, we determine the effective diffusion coefficient, which we find to be in good agreement with the expression of the two dimensional Taylor-Aris dispersion coefficient. Finally we analyze and discuss the role of the finite width of the rectangular slit on hydrodynamic dispersion.
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
Dispersion Relation and Numerical Simulation of Hydrodynamic Waves In Mar's Topside Ionosphere
NASA Astrophysics Data System (ADS)
Wang, J.-S.; Nielsen, E.
The dispersion relation for hydrodynamic waves in an ionosphere with at most a weak magnetic field shows, hydrodynamic hybrid waves may be excited in the topside iono- sphere of Mars and Venus owing to fluctuations in the solar wind pressure. The hy- brid waves result from coupling between two different hydrodynamic wave modes: the classic acoustic-gravity wave(AGW) and the newly developed background gradi- ent wave(BGW). Numerical simulations show that these waves will cause wave-like structures in the altitude profiles of the ionospheric plasma density. The wavelength and frequency are various but their prevailing values in Martian ionosphere are about 60km and 0.001-0.0001Hz, respectively. The amplitudes of the plasma density vari- ations decrease nearly exponentially with increasing altitude, and are of the same or- der of the magnitude as the uncertainty on all the previous measurements of Mar- tian ionospheric electron densities. Radio occultation observations at Mars and Venus show electron density fluctuations in the high altitude ionosphere. The fluctuations are mainly noise, but they may in part be caused by hydrodynamic wave activity. To verify wave activity more detailed measurements are required, and may be obtained with the low frequency radar planned for the Mars Express mission.
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.
Parashar, R.; Cushman, J.H.
2008-06-20
Microbial motility is often characterized by 'run and tumble' behavior which consists of bacteria making sequences of runs followed by tumbles (random changes in direction). As a superset of Brownian motion, Levy motion seems to describe such a motility pattern. The Eulerian (Fokker-Planck) equation describing these motions is similar to the classical advection-diffusion equation except that the order of highest derivative is fractional, {alpha} element of (0, 2]. The Lagrangian equation, driven by a Levy measure with drift, is stochastic and employed to numerically explore the dynamics of microbes in a flow cell with sticky boundaries. The Eulerian equation is used to non-dimensionalize parameters. The amount of sorbed time on the boundaries is modeled as a random variable that can vary over a wide range of values. Salient features of first passage time are studied with respect to scaled parameters.
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
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.
Brennan, Georgina; Kregting, Louise; Beatty, Gemma E.; Cole, Claudia; Elsäßer, Björn; Savidge, Graham; Provan, Jim
2014-01-01
Gene flow in macroalgal populations can be strongly influenced by spore or gamete dispersal. This, in turn, is influenced by a convolution of the effects of current flow and specific plant reproductive strategies. Although several studies have demonstrated genetic variability in macroalgal populations over a wide range of spatial scales, the associated current data have generally been poorly resolved spatially and temporally. In this study, we used a combination of population genetic analyses and high-resolution hydrodynamic modelling to investigate potential connectivity between populations of the kelp Laminaria digitata in the Strangford Narrows, a narrow channel characterized by strong currents linking the large semi-enclosed sea lough, Strangford Lough, to the Irish Sea. Levels of genetic structuring based on six microsatellite markers were very low, indicating high levels of gene flow and a pattern of isolation-by-distance, where populations are more likely to exchange migrants with geographically proximal populations, but with occasional long-distance dispersal. This was confirmed by the particle tracking model, which showed that, while the majority of spores settle near the release site, there is potential for dispersal over several kilometres. This combined population genetic and modelling approach suggests that the complex hydrodynamic environment at the entrance to Strangford Lough can facilitate dispersal on a scale exceeding that proposed for L. digitata in particular, and the majority of macroalgae in general. The study demonstrates the potential of integrated physical–biological approaches for the prediction of ecological changes resulting from factors such as anthropogenically induced coastal zone changes. PMID:24671941
Fast strontium transport induced by hydrodynamic dispersion and pH-dependent sorption
NASA Astrophysics Data System (ADS)
Prigiobbe, Valentina; Hesse, Marc A.; Bryant, Steven L.
2012-09-01
As a fluid carries solutes through a porous material, species that sorb onto the surface of the material travel more slowly than the fluid. Stronger adsorption results in slower solute migration, or increased solute retardation. The adsorption of strontium (Sr2+) onto iron-oxides is strongly pH-dependent and becomes significant at high pH. Radioactive Sr2+ isotopes are, therefore, commonly stored in alkaline solutions to maximize their retardation. Field observations and numerical simulations of the leakage of such solutions into low-pH soils, however, show that even Sr2+ stored in alkaline solutions can migrate without retardation. Migration occurs because hydrodynamic dispersion allows mixing of Sr2+ with the low-pH fluid forming an acidic Sr2+-rich plume which can travel without retardation. Here we report the first experimental observations confirming this dispersion-induced fast Sr2+ transport. We report column-flood experiments where a high-pH solution containing Sr2+ was injected into a low-pH porous medium of iron-oxide-coated beads. We observe both a strongly retarded Sr2+ front and an isolated fast pulse of Sr2+ traveling at the average fluid velocity. This dispersion-induced fast pulse of strontium must be taken into account when considering the safety of radionuclide storage in alkaline solutions.
Varga, Zsigmond; Swan, James
2016-09-28
We show that discrete element simulations of colloidal gelation must account for hydrodynamic interactions between suspended particles through investigation of gelation in a dispersion of colloids interacting pair-wise via short-ranged attraction and long-ranged repulsion (SALR). These dynamic simulations juxtapose self-assembly with and without hydrodynamic interactions between the particles. The long-ranged repulsion impacts the relative rates of coagulation and compaction of colloidal aggregates pre-gel, and introduces a surprising sensitivity to the nature of hydrodynamic interactions between the suspended colloids. For such SALR dispersions, we observe a significant disparity between the percolation boundaries predicted by simulations including and neglecting long-ranged hydrodynamic interactions. Additionally, we find that the percolation boundaries predicted by simulations including hydrodynamic interactions agree well with those measured experimentally. Long-ranged repulsion promotes gelation via growth of anisotropic clusters regardless of the hydrodynamic model employed. However, differences between the models, which persist far from the percolation boundary, are apparent via measurements of the fractal dimension, local bond order parameters, and the collective relaxation dynamics. Notably, the growth of elongated clusters is augmented in simulations that incorporate long-ranged hydrodynamic interactions due to the anisotropic diffusion of elongated bodies at low Reynolds numbers, which favors percolation over a transition of anisotropic clusters to their more isotropic ground states. It is only in relatively dense suspensions that a combination of hydrodynamic screening and significantly faster aggregation combine to bring the two simulation methods into agreement. These results demonstrate the necessity of long-ranged hydrodynamic forces in discrete element simulations of heterogeneous gelation at the colloidal scale. PMID:27550538
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.
Bosse, M A; Arce, P
2000-03-01
The analysis described in this contribution is focused on the effect of Joule heating generation on the hydrodynamics of batch electrophoretic cells (i.e., cells that do not display a forced convective term in the motion equation). The hydrodynamics of these cells is controlled by the viscous forces and by the buoyancy force caused by the temperature gradients due to the Joule heating generation. The analysis is based on differential models that lead to analytical and/or asymptotic solutions for the temperature and velocity profiles of the cell. The results are useful in determining the characteristics of the temperature and velocity profiles inside the cell. Furthermore, the results are excellent tools to be used in the analysis of the dispersive-mixing of solute when Joule heating generation must be accounted for. The analysis is performed by identifying two sequentially coupled problems. Thus, the "carrier fluid problem" and the "solute problem" are outlined. The former is associated with all the factors affecting the velocity profile and the latter is related to the convective-diffusion aspects that control the spreading of the solute inside the cell. The analysis of this contribution is centered on the discussion of the "carrier fluid problem" only. For the boundary conditions selected in the contribution, the study leads to the derivation of an analytical temperature and a "universal" velocity profile that feature the Joule heating number. The Grashof number is a scaling factor of the actual velocity profile. Several characteristics of these profiles are studied and some numerical illustrations have been included.
Hydrodynamics and Particle Dispersion in Phragmites australis and Spartina alterniflora Marshes
NASA Astrophysics Data System (ADS)
Wren, A.; Leonard, L. A.
2001-05-01
The reed grass, Phragmites australis, has invaded large areas of mid-Atlantic tidal marsh. Replacement of native marsh vegetation has generated concern among resource managers that this vegetative shift could affect biodiversity and therefore be deleterious to habitat quality. Hydrodynamic, sedimentologic, and biomass data were collected in adjacent P. australis and Spartina alternifora marshes in Prospect Bay, MD to determine if differences in plant morphology affect flow properties and particle dispersion patterns. Flow characteristics, resulting from plant/flow interactions, were quantified using electromagnetic current meters and automated water samplers and sediment traps were used to assess the impact of flow structure on particle transport and deposition on the marsh surface. Sediment trap data and granulometric analyses were used to examine the effect of hydrodynamics on substrate attributes. Over-marsh speeds were generally 2 to 2 1/2 times lower than those in adjacent waters. Maximum flow speeds within the canopy were less than 10 cm/s for both vegetation types. These flow speeds were lower than those reported for other microtidal systems, but were not unexpected given the very low tidal range in the study area. Neither site was flooded by more than 15 cm of water during the study. At marsh edges, where vegetation was absent, flow direction onto the marsh was essentially unidirectional during the flooding portion of the tide. Inside the canopy, however, flows lacked a strong unidirectional signal. The complexity of inner canopy flows likely resulted from the presence of eddys caused by plant flow interactions. Total suspended solid concentrations of over-marsh flows were consistently lower than those in adjacent waters regardless of vegetation type. Over-marsh flow concentrations were usually less than 15 mg/l and decreased more or less linearly during inundation. Higher concentrations observed in the P. australis canopy were associated with waves
Guyonvarch, Estelle; Ramin, Elham; Kulahci, Murat; Plósz, Benedek Gy
2015-10-15
The present study aims at using statistically designed computational fluid dynamics (CFD) simulations as numerical experiments for the identification of one-dimensional (1-D) advection-dispersion models - computationally light tools, used e.g., as sub-models in systems analysis. The objective is to develop a new 1-D framework, referred to as interpreted CFD (iCFD) models, in which statistical meta-models are used to calculate the pseudo-dispersion coefficient (D) as a function of design and flow boundary conditions. The method - presented in a straightforward and transparent way - is illustrated using the example of a circular secondary settling tank (SST). First, the significant design and flow factors are screened out by applying the statistical method of two-level fractional factorial design of experiments. Second, based on the number of significant factors identified through the factor screening study and system understanding, 50 different sets of design and flow conditions are selected using Latin Hypercube Sampling (LHS). The boundary condition sets are imposed on a 2-D axi-symmetrical CFD simulation model of the SST. In the framework, to degenerate the 2-D model structure, CFD model outputs are approximated by the 1-D model through the calibration of three different model structures for D. Correlation equations for the D parameter then are identified as a function of the selected design and flow boundary conditions (meta-models), and their accuracy is evaluated against D values estimated in each numerical experiment. The evaluation and validation of the iCFD model structure is carried out using scenario simulation results obtained with parameters sampled from the corners of the LHS experimental region. For the studied SST, additional iCFD model development was carried out in terms of (i) assessing different density current sub-models; (ii) implementation of a combined flocculation, hindered, transient and compression settling velocity function; and (iii
Guyonvarch, Estelle; Ramin, Elham; Kulahci, Murat; Plósz, Benedek Gy
2015-10-15
The present study aims at using statistically designed computational fluid dynamics (CFD) simulations as numerical experiments for the identification of one-dimensional (1-D) advection-dispersion models - computationally light tools, used e.g., as sub-models in systems analysis. The objective is to develop a new 1-D framework, referred to as interpreted CFD (iCFD) models, in which statistical meta-models are used to calculate the pseudo-dispersion coefficient (D) as a function of design and flow boundary conditions. The method - presented in a straightforward and transparent way - is illustrated using the example of a circular secondary settling tank (SST). First, the significant design and flow factors are screened out by applying the statistical method of two-level fractional factorial design of experiments. Second, based on the number of significant factors identified through the factor screening study and system understanding, 50 different sets of design and flow conditions are selected using Latin Hypercube Sampling (LHS). The boundary condition sets are imposed on a 2-D axi-symmetrical CFD simulation model of the SST. In the framework, to degenerate the 2-D model structure, CFD model outputs are approximated by the 1-D model through the calibration of three different model structures for D. Correlation equations for the D parameter then are identified as a function of the selected design and flow boundary conditions (meta-models), and their accuracy is evaluated against D values estimated in each numerical experiment. The evaluation and validation of the iCFD model structure is carried out using scenario simulation results obtained with parameters sampled from the corners of the LHS experimental region. For the studied SST, additional iCFD model development was carried out in terms of (i) assessing different density current sub-models; (ii) implementation of a combined flocculation, hindered, transient and compression settling velocity function; and (iii
Azevedo, Isabel C; Bordalo, Adriano A; Duarte, Pedro M
2010-05-01
Freshwater input to estuaries is a fundamental feature of these ecosystems, which may be profoundly altered by river damming as human needs for water consumption, irrigation or energy production increase. The Douro estuary is limited upstream by a dam since 1985, which reduced its length by ca. 60%. Freshwater inputs to the estuary are now irregular and greatly dependent on hydroelectric power demand; values ranging from zero to over 1000m(3)s(-1), in a matter of hours, especially in summer are common. In the present study, a three-dimensional hydrodynamic model was applied to the Douro estuary. The model was calibrated and validated against water elevation, current velocity, salinity and temperature data. Thereafter, it was used to analyse the effects of different flow regimes and magnitudes on estuarine hydrodynamics and contaminant dispersion. Results obtained suggest that the highly variable flow regimes, currently observed in the Douro, tend to reduce water column stratification and to enhance seawater intrusion, when compared with flow discharges of similar average magnitude, but lower variability. Stable flows seem to be the most effective in dispersing contaminants eventually introduced into the estuary through its small river tributaries. Overall results suggest that flow management may have important effects on estuarine hydrodynamics through non-linear interactions between flow magnitude and variability.
Oldenburg, C.M.; Pruess, K.
1995-03-01
We have developed TOUGH2 modules for strongly coupled flow and transport that include full hydrodynamic dispersion. T2DM models two-dimensional flow and transport in systems with variable salinity, while T2DMR includes radionuclide transport with firstorder decay of a parent-daughter chain of radionuclide components in variable salinity systems. T2DM has been applied to a variety of coupled flow problems including the pure solutal convection problem of Elder and the mixed free and forced convection salt-dome flow problem. In the Elder and salt-dome flow problems, density changes of up to 20% caused by brine concentration variations lead to strong coupling between the velocity and brine concentration fields. T2DM efficiently calculates flow and transport for these problems. We have applied T2DMR to the dispersive transport and decay of radionuclide tracers in flow fields with permeability heterogeneities and recirculating flows. Coupling in th ese problems occurs by velocity-dependent hydrodynamic dispersion. Our results show that the maximum daughter species concentration may occur fully within a recirculating or low-velocity region. In all of the problems, we observe very efficient handling of the strongly coupled flow and transport processes.
Tironi, Antonio; Marin, Víctor H; Campuzano, Francisco J
2010-05-01
This article introduces a management tool for salmon farming, with a scope in the local sustainability of salmon aquaculture of the Aysen Fjord, Chilean Patagonia. Based on Integrated Coastal Zone Management (ICZM) principles, the tool combines a large 3-level nested hydrodynamic model, a particle tracking module and a GIS application into an assessment tool for particulate waste dispersal of salmon farming activities. The model offers an open source alternative to particulate waste modeling and evaluation, contributing with valuable information for local decision makers in the process of locating new facilities and monitoring stations. PMID:20333379
NASA Astrophysics Data System (ADS)
Tironi, Antonio; Marin, Víctor H.; Campuzano, Francisco J.
2010-05-01
This article introduces a management tool for salmon farming, with a scope in the local sustainability of salmon aquaculture of the Aysen Fjord, Chilean Patagonia. Based on Integrated Coastal Zone Management (ICZM) principles, the tool combines a large 3-level nested hydrodynamic model, a particle tracking module and a GIS application into an assessment tool for particulate waste dispersal of salmon farming activities. The model offers an open source alternative to particulate waste modeling and evaluation, contributing with valuable information for local decision makers in the process of locating new facilities and monitoring stations.
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)
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.
Daraio, J.A.; Weber, L.J.; Newton, T.J.
2010-01-01
Because unionid mussels have a parasitic larval stage, they are able to disperse upstream and downstream as larvae while attached to their host fish and with flow as juveniles after excystment from the host. Understanding unionid population ecology requires knowledge of the processes that affect juvenile dispersal prior to establishment. We examined presettlement (transport and dispersion with flow) and early postsettlement (bed shear stress) hydraulic processes as negative censoring mechanisms. Our approach was to model dispersal using particle tracking through a 3-dimensional flow field output from hydrodynamic models of a reach of the Upper Mississippi River. We tested the potential effects of bed shear stress (??b) at 5 flow rates on juvenile mussel dispersal and quantified the magnitude of these effects as a function of flow rate. We explored the reach-scale relationships of Froude number (Fr), water depth (H), local bed slope (S), and unit stream power (QS) with the likelihood of juvenile settling (??). We ran multiple dispersal simulations at each flow rate to estimate ??, the parameter of a Poisson distribution, from the number of juveniles settling in each grid cell, and calculated dispersal distances. Virtual juveniles that settled in areas of the river where b > critical shear stress (c) were resuspended in the flow and transported further downstream, so we ran simulations at 3 different conditions for ??c (??c = ??? no resuspension, 0.1, and 0.05 N/m2). Differences in virtual juvenile dispersal distance were significantly dependent upon c and flow rate, and effects of b on settling distribution were dependent upon c. Most simulations resulted in positive correlations between ?? and ??b, results suggesting that during early postsettlement, ??b might be the primary determinant of juvenile settling distribution. Negative correlations between ?? and ??b occurred in some simulations, a result suggesting that physical or biological presettlement processes
On the interaction between gravity forces and hydrodynamic dispersion in heterogeneous porous media
NASA Astrophysics Data System (ADS)
Schotting, R.; Landman, A.; Egorov, A.; Demidov, D.
2005-12-01
In a series of independently conducted vertical displacement experiments in porous columns (The Netherlands, Germany and Australia), a peculiar phenomenon has been observed. If the resident fluid, i.e. fresh water is displaced by a saltwater solution with a higher density, the effective dispersion coefficient deacreases significantly as compared to the tracer case, where both the resident and invading fluids have (almost) identical densities. The higher the density contrast between the two fluids, the more the dispersion coefficient decreases as compared to the classical Fickian xase. This phenomenon cannot be theoretically described and modelled using classical linear Fick's Law for the dispersive mass flux. Several attempts were made to formulate adequate new theories to incorporate these density effects. Hassanizadeh extended Fick's Law with a second-order nonlinear term, including a new dispersion parameter. Although very good agreement with the aforemnetioned experiments could be achieved, this theory is not able to explain and include the underlying physics of this phenomenon. The decrease of the dispersion coefficient is the result of the interaction between gravity forces and density variations at the displacement front, due to local small-scale heterogeneities. With this phenomenon in mind, several alternative nonlinear theories have been proposed. We mention Welty and Gelhar (stochastic approach), Egorov and Demidov (homogenisation at the Darcy- scale), Demidov (homogenisation at the pore-scale). All theories have in common that the resulting nonlinear dispersion coefficient is a function of the density gradient and not of the absolute density. All of the aforementioned theories have been tested against carefully conducted massive numerical experiments, and if possible, against laboratory experiments. The results of the comparisons will be presented, and future research directions will be indicated.
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
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
NASA Astrophysics Data System (ADS)
Huret, M.; Petitgas, P.; Woillez, M.
2010-10-01
Dispersal of fish early life stages explains part of the recruitment success, through interannual variability in spawning, transport and survival. Dispersal results from a complex interaction between physical and biological processes acting at different temporal and spatial scales, and at the individual or population level. In this paper we quantify the response of anchovy egg and larval dispersal in the Bay of Biscay to the following sources of variability: vertical larval behaviour, drift duration, adult spawning location and timing, and spatio-temporal variability in the hydrodynamics. We use simulations of Lagrangian trajectories in a 3-dimensional hydrodynamic model, as well as spatial indices describing different properties of the dispersal kernel: the mean transport (distance, direction), its variance, occupation of space by particles and their aggregation. We show that larval drift duration has a major impact on the dispersion at scales of ∼100 km, but that vertical behaviour becomes dominant reducing dispersion at scales of ∼1-10 km. Spawning location plays a major role in explaining connectivity patterns, in conjunction with spawning temporal variability. Interannual variability in the circulation dominates over seasonal variability. However, seasonal patterns become predominant for coastal spawning locations, revealing a recurrent shift in the direction of dispersal during the anchovy spawning season.
Dutta, Debashis
2014-05-01
In this work, a method-of-moments formulation has been presented for estimating the dispersion of analyte streams as they migrate through a free-flow zone electrophoresis (FFZE) channel under laminar flow conditions. The current analysis considers parallel-plate based FFZE systems with an applied pressure-gradient along the channel length for sample and carrier electrolyte transport, and an external electric field in the transverse direction for enabling the electrophoretic separation. A closed-form expression has been derived using this mathematical approach for describing the spatial variance of sample streams as a function of their position in the separation chamber at steady state. This expression predicts that the hydrodynamic dispersion component in an FFZE assay scales as Pex(2) where Pex denotes the Péclet number based on the analyte's transverse electrophoretic migration velocity rather than its longitudinal pressure-driven flow speed as expected in transport processes induced by a pressure-gradient. Interestingly however, the coefficient multiplying this dimensionless group, i.e., 1/210, is identically equal to the constant preceding the square of the relevant Péclet number in the latter case (i.e., Péclet number based on the longitudinal flow speed). It must be noted that while the mathematical analysis reported in this work is only valid for FFZE systems in the absence of any unwanted Joule heating, pressure-driven cross-flow and/or differences in the electrical conductivity between the sample and carrier electrolyte, it can also be applied to numerically estimate the effect of these factors on the separation resolution of the assay. PMID:24671038
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.
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.
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.
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.
Clobert, J.; Danchin, E.; Dhondt, A.A.; Nichols, J.D.
2001-01-01
The ability of species to migrate and disperse is a trait that has interested ecologists for many years. Now that so many species and ecosystems face major environmental threats from habitat fragmentation and global climate change, the ability of species to adapt to these changes by dispersing, migrating, or moving between patches of habitat can be crucial to ensuring their survival. This book provides a timely and wide-ranging overview of the study of dispersal and incorporates much of the latest research. The causes, mechanisms, and consequences of dispersal at the individual, population, species and community levels are considered. The potential of new techniques and models for studying dispersal, drawn from molecular biology and demography, is also explored. Perspectives and insights are offered from the fields of evolution, conservation biology and genetics. Throughout the book, theoretical approaches are combined with empirical data, and care has been taken to include examples from as wide a range of species as possible.
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
NASA Astrophysics Data System (ADS)
Rossi, Vincent; Ser-Giacomi, Enrico; López, Cristóbal; Hernández-García, Emilio
2014-04-01
Oceanic dispersal and connectivity have been identified as crucial factors for structuring marine populations and designing marine protected areas (MPAs). Focusing on larval dispersal by ocean currents, we propose an approach coupling Lagrangian transport and new tools from Network Theory to characterize marine connectivity in the Mediterranean basin. Larvae of different pelagic durations and seasons are modeled as passive tracers advected in a simulated oceanic surface flow from which a network of connected areas is constructed. Hydrodynamical provinces extracted from this network are delimited by frontiers which match multiscale oceanographic features. By examining the repeated occurrence of such boundaries, we identify the spatial scales and geographic structures that would control larval dispersal across the entire seascape. Based on these hydrodynamical units, we study novel connectivity metrics for existing reserves. Our results are discussed in the context of ocean biogeography and MPAs design, having ecological and managerial implications.
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...
NASA Astrophysics Data System (ADS)
Balachandran, Kizhakkepat Kalathil; Reddy, Guddemmari Sidha; Revichandran, Chenicherry; Srinivas, Kotamarpi; Vijayan, Panachikkal Ramakrishnan; Thottam, Tony Joseph
2008-11-01
Tidal circulation in the Cochin Estuary, a moderately polluted estuary along the southwest coast of India, was studied using a 2D hydrodynamic model. The predicted tides and currents showed very good agreement with measured tides. Particle trajectories and residual currents computed from the model have been used to classify the study region into three zones: northern estuary, central estuary, and southern estuary. The central estuary is dynamic, whereas the other two zones are relatively weak. An amplification of measured tides in the south estuary during March indicates the presence of standing waves caused by the hydraulic barrier at Thanneermukkom. Model results suggest that the northern and southern zones are sensitive to environmental pollution. The present level of pollution in the northern estuary is due to the direct release of industrial effluents into the river Periyar, which can be minimized if they are brought down to central estuary for disposal. The concept of different zones in the estuary will be useful to planners in protecting the vulnerable regions of this productive ecosystem from human interventions.
Southgate, Paul C.; Jerry, Dean R.; Bosserelle, Cyprien; Zenger, Kyall R.
2016-01-01
Fishery management and conservation of marine species increasingly relies on genetic data to delineate biologically relevant stock boundaries. Unfortunately for high gene flow species which may display low, but statistically significant population structure, there is no clear consensus on the level of differentiation required to resolve distinct stocks. The use of fine-scale neutral and adaptive variation, considered together with environmental data can offer additional insights to this problem. Genome-wide genetic data (4,123 SNPs), together with an independent hydrodynamic particle dispersal model were used to inform farm and fishery management in the Fijian black-lip pearl oyster Pinctada margaritifera, where comprehensive fishery management is lacking, and the sustainability of exploitation uncertain. Weak fine-scale patterns of population structure were detected, indicative of broad-scale panmixia among wild oysters, while a hatchery-sourced farmed population exhibited a higher degree of genetic divergence (Fst = 0.0850–0.102). This hatchery-produced population had also experienced a bottleneck (NeLD = 5.1; 95% C.I. = [5.1–5.3]); compared to infinite NeLD estimates for all wild oysters. Simulation of larval transport pathways confirmed the existence of broad-scale mixture by surface ocean currents, correlating well with fine-scale patterns of population structuring. Fst outlier tests failed to detect large numbers of loci supportive of selection, with 2–5 directional outlier SNPs identified (average Fst = 0.116). The lack of biologically significant population genetic structure, absence of evidence for local adaptation and larval dispersal simulation, all indicate the existence of a single genetic stock of P. margaritifera in the Fiji Islands. This approach using independent genomic and oceanographic tools has allowed fundamental insights into stock structure in this species, with transferability to other highly-dispersive marine taxa for their
Lal, Monal M; Southgate, Paul C; Jerry, Dean R; Bosserelle, Cyprien; Zenger, Kyall R
2016-01-01
Fishery management and conservation of marine species increasingly relies on genetic data to delineate biologically relevant stock boundaries. Unfortunately for high gene flow species which may display low, but statistically significant population structure, there is no clear consensus on the level of differentiation required to resolve distinct stocks. The use of fine-scale neutral and adaptive variation, considered together with environmental data can offer additional insights to this problem. Genome-wide genetic data (4,123 SNPs), together with an independent hydrodynamic particle dispersal model were used to inform farm and fishery management in the Fijian black-lip pearl oyster Pinctada margaritifera, where comprehensive fishery management is lacking, and the sustainability of exploitation uncertain. Weak fine-scale patterns of population structure were detected, indicative of broad-scale panmixia among wild oysters, while a hatchery-sourced farmed population exhibited a higher degree of genetic divergence (Fst = 0.0850-0.102). This hatchery-produced population had also experienced a bottleneck (NeLD = 5.1; 95% C.I. = [5.1-5.3]); compared to infinite NeLD estimates for all wild oysters. Simulation of larval transport pathways confirmed the existence of broad-scale mixture by surface ocean currents, correlating well with fine-scale patterns of population structuring. Fst outlier tests failed to detect large numbers of loci supportive of selection, with 2-5 directional outlier SNPs identified (average Fst = 0.116). The lack of biologically significant population genetic structure, absence of evidence for local adaptation and larval dispersal simulation, all indicate the existence of a single genetic stock of P. margaritifera in the Fiji Islands. This approach using independent genomic and oceanographic tools has allowed fundamental insights into stock structure in this species, with transferability to other highly-dispersive marine taxa for their conservation
Lal, Monal M; Southgate, Paul C; Jerry, Dean R; Bosserelle, Cyprien; Zenger, Kyall R
2016-01-01
Fishery management and conservation of marine species increasingly relies on genetic data to delineate biologically relevant stock boundaries. Unfortunately for high gene flow species which may display low, but statistically significant population structure, there is no clear consensus on the level of differentiation required to resolve distinct stocks. The use of fine-scale neutral and adaptive variation, considered together with environmental data can offer additional insights to this problem. Genome-wide genetic data (4,123 SNPs), together with an independent hydrodynamic particle dispersal model were used to inform farm and fishery management in the Fijian black-lip pearl oyster Pinctada margaritifera, where comprehensive fishery management is lacking, and the sustainability of exploitation uncertain. Weak fine-scale patterns of population structure were detected, indicative of broad-scale panmixia among wild oysters, while a hatchery-sourced farmed population exhibited a higher degree of genetic divergence (Fst = 0.0850-0.102). This hatchery-produced population had also experienced a bottleneck (NeLD = 5.1; 95% C.I. = [5.1-5.3]); compared to infinite NeLD estimates for all wild oysters. Simulation of larval transport pathways confirmed the existence of broad-scale mixture by surface ocean currents, correlating well with fine-scale patterns of population structuring. Fst outlier tests failed to detect large numbers of loci supportive of selection, with 2-5 directional outlier SNPs identified (average Fst = 0.116). The lack of biologically significant population genetic structure, absence of evidence for local adaptation and larval dispersal simulation, all indicate the existence of a single genetic stock of P. margaritifera in the Fiji Islands. This approach using independent genomic and oceanographic tools has allowed fundamental insights into stock structure in this species, with transferability to other highly-dispersive marine taxa for their conservation
NASA Astrophysics Data System (ADS)
Plazas, Lucero; Rosero, Edison; Solarte, Efraín; Sandoval, Jhon; Peña, Miguel
2009-08-01
Fluorescent tracer trials are performed to obtain useful information for hydrodynamic modeling. Particularly they have been used in constructed wetlands, aimed for residual water treatment, in order to find residence time distribution for particles entering the system and, in general, to know the flux pattern. Nevertheless, it has been reported that some tracers, as Rhodamine WT, exhibit adsorption phenomena over the substrate. This situation has to be considered in the analysis of residence time distribution curves, taking into account advection-dispersion processes which are given by the diffusion modified equation. Laser Induced Fluorescence (LIF) with a Nd:YAG laser (532 nm; 35mW), was used to determine Rhodamine WT accumulated concentration. Through adsorption coefficients obtained experimentally, an advection - dispersion model for solute transport in a subsurface flow constructed wetland was evaluated. Including this phenomenon allows to optimize the model, and another important condition is added in the behavior prediction of these complex ecosystems.
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
Improvements to SOIL: An Eulerian hydrodynamics code
Davis, C.G.
1988-04-01
Possible improvements to SOIL, an Eulerian hydrodynamics code that can do coupled radiation diffusion and strength of materials, are presented in this report. Our research is based on the inspection of other Eulerian codes and theoretical reports on hydrodynamics. Several conclusions from the present study suggest that some improvements are in order, such as second-order advection, adaptive meshes, and speedup of the code by vectorization and/or multitasking. 29 refs., 2 figs.
pyro: Python-based tutorial for computational methods for hydrodynamics
NASA Astrophysics Data System (ADS)
Zingale, Michael
2015-07-01
pyro is a simple python-based tutorial on computational methods for hydrodynamics. It includes 2-d solvers for advection, compressible, incompressible, and low Mach number hydrodynamics, diffusion, and multigrid. It is written with ease of understanding in mind. An extensive set of notes that is part of the Open Astrophysics Bookshelf project provides details of the algorithms.
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.
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.
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.
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
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.
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)
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.
Pyell, Ute; Jalil, Alaa H; Urban, Dominic A; Pfeiffer, Christian; Pelaz, Beatriz; Parak, Wolfgang J
2015-11-01
In the first paper of this series we have shown for hydrophilic coated Au nanoparticles that capillary electrophoresis in combination with Taylor dispersion analysis in fused silica capillaries with an inner diameter of 75 μm allows for the unbiased precise determination of the number-weighted mean hydrodynamic diameter, the zeta potential and the effective charge number, although mobility corrected double layer polarization has to be taken into account. In this second paper we investigate whether the modified approximate analytic expression developed by Ohshima (2001) permits the calculation of calibration lines and the concomitant conversion of electropherograms into number-weighted particle radius distributions. We show that with the method developed size distributions are obtained which are independent of the measurement conditions. These size distributions are much narrower than those obtained via dynamic light scattering and data evaluation by the CONTIN algorithm. Capillary electrophoresis together with the proposed data evaluation method reveals that the analyzed nanoparticle populations have very narrow size distributions with a width of 2-4 nm. The hydrodynamic radius distributions of the coated NPs are only slightly broader than the solid particle radius distribution of the Au-NP cores. The presence of monomodal/bimodal size distributions is confirmed by asymmetric flow field-flow fractionation.
Chloride Dispersion across Silt Deposits in a Glaciated Bedrock River Valley.
Rotaru, Camelia; Ostendorf, David W; DeGroot, Don J
2014-03-01
Soil and groundwater from the Neponset River floodplain deposit that receive high concentrations of deicing agents from nearby highways were investigated. The silty sand floodplain is separated by a silty aquitard from the underlying aquifer that serves as a public water supply. We made a transport-based assessment of the capacity of the aquitard to protect the underlying aquifer. One hundred seventeen soil samples and 469 groundwater samples collected during a period of 4 yr from boreholes and 10 wells grouped in two well clusters were analyzed for dissolved Cl concentration. The soil characterization and groundwater monitoring results agreed, showing a very slow change in subsurface Cl contamination with time. These data also calibrated a vertical one-dimensional advective-dispersive transport model across the deposits. Advective transport dominated only in the top 3.37 m of the floodplain deposit, with dispersion being the main transport mechanism below this depth. Due to the silty nature of the aquitard, dispersion rather than diffusion was the main transport mechanism into the floodplain-aquitard system. Soil and groundwater quality data confirmed a Cl concentration at the floodplain surface near the highway runoff drainage outlets of 2450 mg L. The model estimated a vertical dispersivity at the site of 8 mm and a vertical hydrodynamic dispersion coefficient of 3.71 × 10 m s. These data confirmed the aquitard's capacity to contain deicing agents, protecting the underlying aquifer from contamination.
Andreev, Pavel A.
2015-06-15
We discuss the complete theory of spin-1/2 electron-positron quantum plasmas, when electrons and positrons move with velocities mach smaller than the speed of light. We derive a set of two fluid quantum hydrodynamic equations consisting of the continuity, Euler, spin (magnetic moment) evolution equations for each species. We explicitly include the Coulomb, spin-spin, Darwin and annihilation interactions. The annihilation interaction is the main topic of the paper. We consider the contribution of the annihilation interaction in the quantum hydrodynamic equations and in the spectrum of waves in magnetized electron-positron plasmas. We consider the propagation of waves parallel and perpendicular to an external magnetic field. We also consider the oblique propagation of longitudinal waves. We derive the set of quantum kinetic equations for electron-positron plasmas with the Darwin and annihilation interactions. We apply the kinetic theory to the linear wave behavior in absence of external fields. We calculate the contribution of the Darwin and annihilation interactions in the Landau damping of the Langmuir waves. We should mention that the annihilation interaction does not change number of particles in the system. It does not related to annihilation itself, but it exists as a result of interaction of an electron-positron pair via conversion of the pair into virtual photon. A pair of the non-linear Schrodinger equations for the electron-positron plasmas including the Darwin and annihilation interactions is derived. Existence of the conserving helicity in electron-positron quantum plasmas of spinning particles with the Darwin and annihilation interactions is demonstrated. We show that the annihilation interaction plays an important role in the quantum electron-positron plasmas giving the contribution of the same magnitude as the spin-spin interaction.
NASA Astrophysics Data System (ADS)
Andreev, Pavel A.
2015-06-01
We discuss the complete theory of spin-1/2 electron-positron quantum plasmas, when electrons and positrons move with velocities mach smaller than the speed of light. We derive a set of two fluid quantum hydrodynamic equations consisting of the continuity, Euler, spin (magnetic moment) evolution equations for each species. We explicitly include the Coulomb, spin-spin, Darwin and annihilation interactions. The annihilation interaction is the main topic of the paper. We consider the contribution of the annihilation interaction in the quantum hydrodynamic equations and in the spectrum of waves in magnetized electron-positron plasmas. We consider the propagation of waves parallel and perpendicular to an external magnetic field. We also consider the oblique propagation of longitudinal waves. We derive the set of quantum kinetic equations for electron-positron plasmas with the Darwin and annihilation interactions. We apply the kinetic theory to the linear wave behavior in absence of external fields. We calculate the contribution of the Darwin and annihilation interactions in the Landau damping of the Langmuir waves. We should mention that the annihilation interaction does not change number of particles in the system. It does not related to annihilation itself, but it exists as a result of interaction of an electron-positron pair via conversion of the pair into virtual photon. A pair of the non-linear Schrodinger equations for the electron-positron plasmas including the Darwin and annihilation interactions is derived. Existence of the conserving helicity in electron-positron quantum plasmas of spinning particles with the Darwin and annihilation interactions is demonstrated. We show that the annihilation interaction plays an important role in the quantum electron-positron plasmas giving the contribution of the same magnitude as the spin-spin interaction.
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
ERIC Educational Resources Information Center
Lafrance, Pierre
1978-01-01
Explores in a non-mathematical treatment some of the hydrodynamical phenomena and forces that affect the operation of ships, especially at high speeds. Discusses the major components of ship resistance such as the different types of drags and ways to reduce them and how to apply those principles for the hovercraft. (GA)
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.
Castor, J I
2003-10-16
The discipline of radiation hydrodynamics is the branch of hydrodynamics in which the moving fluid absorbs and emits electromagnetic radiation, and in so doing modifies its dynamical behavior. That is, the net gain or loss of energy by parcels of the fluid material through absorption or emission of radiation are sufficient to change the pressure of the material, and therefore change its motion; alternatively, the net momentum exchange between radiation and matter may alter the motion of the matter directly. Ignoring the radiation contributions to energy and momentum will give a wrong prediction of the hydrodynamic motion when the correct description is radiation hydrodynamics. Of course, there are circumstances when a large quantity of radiation is present, yet can be ignored without causing the model to be in error. This happens when radiation from an exterior source streams through the problem, but the latter is so transparent that the energy and momentum coupling is negligible. Everything we say about radiation hydrodynamics applies equally well to neutrinos and photons (apart from the Einstein relations, specific to bosons), but in almost every area of astrophysics neutrino hydrodynamics is ignored, simply because the systems are exceedingly transparent to neutrinos, even though the energy flux in neutrinos may be substantial. Another place where we can do ''radiation hydrodynamics'' without using any sophisticated theory is deep within stars or other bodies, where the material is so opaque to the radiation that the mean free path of photons is entirely negligible compared with the size of the system, the distance over which any fluid quantity varies, and so on. In this case we can suppose that the radiation is in equilibrium with the matter locally, and its energy, pressure and momentum can be lumped in with those of the rest of the fluid. That is, it is no more necessary to distinguish photons from atoms, nuclei and electrons, than it is to distinguish
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.
Modelling drivers of mangrove propagule dispersal and restoration of abandoned shrimp farms
NASA Astrophysics Data System (ADS)
Di Nitto, D.; Erftemeijer, P. L. A.; van Beek, J. K. L.; Dahdouh-Guebas, F.; Higazi, L.; Quisthoudt, K.; Jayatissa, L. P.; Koedam, N.
2013-07-01
Propagule dispersal of four mangrove species Rhizophora mucronata, R. apiculata, Ceriops tagal and Avicennia officinalis in the Pambala-Chilaw Lagoon Complex (Sri Lanka) was studied by combining a hydrodynamic model with species-specific knowledge on propagule dispersal behaviour. Propagule transport was simulated using a finite-volume advection-diffusion model to investigate the effect of dispersal vectors (tidal flow, freshwater discharge and wind), trapping agents (retention by vegetation) and seed characteristics (buoyancy) on propagule dispersal patterns. Sensitivity analysis showed that smaller propagules, like the oval-shaped propagules of Avicennia officinalis, dispersed over larger distances and were most sensitive to changing values of retention by mangrove vegetation compared to larger, torpedo-shaped propagules of Rhizophora spp. and C. tagal. Directional propagule dispersal in this semi-enclosed lagoon with a small tidal range was strongly concentrated towards the edges of the lagoon and channels. Short distance dispersal appeared to be the main dispersal strategy for all four studied species, with most of the propagules being retained within the vegetation. Only a small proportion (max. 5%) of propagules left the lagoon through a channel connecting the lagoon with the open sea. Wind significantly influenced dispersal distance and direction once propagules entered the lagoon or adjacent channels. Implications of these findings for mangrove restoration were tested by simulating partial removal in the model of dikes around abandoned shrimp ponds to restore tidal hydrology and facilitate natural recolonisation by mangroves. The specific location of dike removal, (with respect to the vicinity of mangroves and independently suitable hydrodynamic flows), was found to significantly affect the resultant quantities and species of inflowing propagules and hence the potential effectiveness of natural regeneration. These results demonstrate the value of propagule
Modelling drivers of mangrove propagule dispersal and restoration of abandoned shrimp farms
NASA Astrophysics Data System (ADS)
Di Nitto, D.; Erftemeijer, P. L. A.; van Beek, J. K. L.; Dahdouh-Guebas, F.; Higazi, L.; Quisthoudt, K.; Jayatissa, L. P.; Koedam, N.
2013-01-01
Propagule dispersal of four mangrove species Rhizophora mucronata, R. apiculata, Ceriops tagal and Avicennia officinalis in the Pambala-Chilaw Lagoon Complex (Sri Lanka) was studied by combining a hydrodynamic model with species-specific knowledge on propagule dispersal behaviour. Propagule transport was simulated using a finite-volume advection-diffusion model to investigate the effect of dispersal vectors (tidal flow, freshwater discharge and wind), trapping agents (retention by vegetation) and seed characteristics (buoyancy) on propagule dispersal patterns. Sensitivity analysis showed that smaller propagules, like the oval-shaped propagules of Avicennia officinalis, dispersed over larger distances and were most sensitive to changing values of retention by mangrove vegetation compared to larger, torpedo-shaped propagules of Rhizophora spp. and C. tagal. Directional propagule dispersal in this semi-enclosed lagoon with a small tidal range was strongly concentrated towards the edges of the lagoon and channels. Short distance dispersal appeared to be the main dispersal strategy for all four studied species, with most of the propagules being retained within the vegetation. Only a small proportion (max. 5%) of propagules left the lagoon through a channel connecting the lagoon with the open sea. Wind significantly influenced dispersal distance and direction once propagules entered the lagoon or adjacent channels. Implications of these findings for mangrove restoration were tested by simulating partial removal in the model of dikes around abandoned shrimp ponds to restore tidal hydrology and facilitate natural recolonisation by mangroves. The specific location of dike removal, (with respect to the vicinity of mangroves and independently suitable hydrodynamic flows), was found to significantly affect the resultant quantities and species of inflowing of propagules and hence the potential effectiveness of natural regeneration. These results demonstrate the value of
NASA Astrophysics Data System (ADS)
Lauga, Eric
2016-01-01
Bacteria predate plants and animals by billions of years. Today, they are the world's smallest cells, yet they represent the bulk of the world's biomass and the main reservoir of nutrients for higher organisms. Most bacteria can move on their own, and the majority of motile bacteria are able to swim in viscous fluids using slender helical appendages called flagella. Low-Reynolds number hydrodynamics is at the heart of the ability of flagella to generate propulsion at the micrometer scale. In fact, fluid dynamic forces impact many aspects of bacteriology, ranging from the ability of cells to reorient and search their surroundings to their interactions within mechanically and chemically complex environments. Using hydrodynamics as an organizing framework, I review the biomechanics of bacterial motility and look ahead to future challenges.
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.
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.
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
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).
NASA Astrophysics Data System (ADS)
Colgate, S. A.
1981-11-01
The physics as well as astrophysics of the supernova (SN) phenomenon are illustrated with the appropriate numbers. The explosion of a star, a supernova, occurs at the end of its evolution when the nuclear fuel in its core is almost, or completely, consumed. The star may explode due to a small residual thermonuclear detonation, type I SN, or it may collapse, type I and type II SN, leaving a neutron star remnant. The type I progenitor is thought to be an old accreting white dwarf, 1.4 interior mass, with a close companion star. A type II SN is thought to be a massive young star, 6 to 10 interior mass. The mechanism of explosion is still a challenge to model, being the most extreme conditions of matter and hydrodynamics that occur presently and excessively in the universe.
Macrostatistical hydrodynamics
Brenner, H.
1989-01-01
Work performed during this contract period involved performing trajectory measurements of the three-dimensional position of the falling ball as a function of time. This has allowed us to calculate the dispersivity of the falling ball around its mean settling velocity. Whereas the mean settling velocity predicts the continuum behavior of the suspension, the dispersivity allows insight into the non-continuum behavior of the suspension caused by the presence of the macroscopic suspended spheres. Experiments were performed for several sphere sizes (0.635 and 0.3125 cm diameter) as a function of volume fraction ({phi} = 0.30 and 0.50) and relative size ratio of the settling to suspended sphere diameter (0.5 to 4.0). In addition, the bulk behavior of monodisperse and bidisperse sphere suspensions were examined for both Poiseuille and Couette flows. This allowed qualitative analysis of shear-induced particle migration phenomena observed during the processing of highly-concentrated suspensions. Finally, numerical methods are being developed to allow a more complete understanding of the micromechanical effects which cause the dispersivity phenomenon in both falling-ball and shear-induced particle migration experiments.
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.
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.
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.
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.
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).
Macrostatistical hydrodynamics
Brenner, H.
1992-01-01
During the course of these efforts we have been studying suspension of particles in Newtonian and non-Newtonian liquids, embodying a combination of analysis, experiments, and numerical simulations. Experiments primarily involved tracking small balls as they fall slowly through otherwise quiescent suspensions of neutrally buoyant particles. Detailed trajectories of the balls, obtained either with new experimental techniques or by numerical simulation, were statistically interpreted in terms of the mean settling velocity and the dispersion about the mean. We showed that falling-ball rheometry, using small balls relative to the suspended particles, could be a means of measuring the macroscopic zero-shear-rate viscosity without significantly disturbing the original microstructure; therefore, falling-ball rheometry can be a powerful tool for use in studying the effects of microstructures on the macroscopic properties of suspensions. We plan to extend this work to the study of more complex, structured fluids, and to use other tools (e.g., rolling-ball rheometry) to study boundary effects. We also propose to study flowing suspensions to obtain non-zero-shear-rate viscosities. The intent is to develop an understanding of the basic principles needed to treat generic multiphase flow problems, through a detailed study of model systems. 8 refs.
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.
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.
Simple Waves in Ideal Radiation Hydrodynamics
Johnson, B M
2008-09-03
In the dynamic diffusion limit of radiation hydrodynamics, advection dominates diffusion; the latter primarily affects small scales and has negligible impact on the large scale flow. The radiation can thus be accurately regarded as an ideal fluid, i.e., radiative diffusion can be neglected along with other forms of dissipation. This viewpoint is applied here to an analysis of simple waves in an ideal radiating fluid. It is shown that much of the hydrodynamic analysis carries over by simply replacing the material sound speed, pressure and index with the values appropriate for a radiating fluid. A complete analysis is performed for a centered rarefaction wave, and expressions are provided for the Riemann invariants and characteristic curves of the one-dimensional system of equations. The analytical solution is checked for consistency against a finite difference numerical integration, and the validity of neglecting the diffusion operator is demonstrated. An interesting physical result is that for a material component with a large number of internal degrees of freedom and an internal energy greater than that of the radiation, the sound speed increases as the fluid is rarefied. These solutions are an excellent test for radiation hydrodynamic codes operating in the dynamic diffusion regime. The general approach may be useful in the development of Godunov numerical schemes for radiation hydrodynamics.
Progress in smooth particle hydrodynamics
Wingate, C.A.; Dilts, G.A.; Mandell, D.A.; Crotzer, L.A.; Knapp, C.E.
1998-07-01
Smooth Particle Hydrodynamics (SPH) is a meshless, Lagrangian numerical method for hydrodynamics calculations where calculational elements are fuzzy particles which move according to the hydrodynamic equations of motion. Each particle carries local values of density, temperature, pressure and other hydrodynamic parameters. A major advantage of SPH is that it is meshless, thus large deformation calculations can be easily done with no connectivity complications. Interface positions are known and there are no problems with advecting quantities through a mesh that typical Eulerian codes have. These underlying SPH features make fracture physics easy and natural and in fact, much of the applications work revolves around simulating fracture. Debris particles from impacts can be easily transported across large voids with SPH. While SPH has considerable promise, there are some problems inherent in the technique that have so far limited its usefulness. The most serious problem is the well known instability in tension leading to particle clumping and numerical fracture. Another problem is that the SPH interpolation is only correct when particles are uniformly spaced a half particle apart leading to incorrect strain rates, accelerations and other quantities for general particle distributions. SPH calculations are also sensitive to particle locations. The standard artificial viscosity treatment in SPH leads to spurious viscosity in shear flows. This paper will demonstrate solutions for these problems that they and others have been developing. The most promising is to replace the SPH interpolant with the moving least squares (MLS) interpolant invented by Lancaster and Salkauskas in 1981. SPH and MLS are closely related with MLS being essentially SPH with corrected particle volumes. When formulated correctly, JLS is conservative, stable in both compression and tension, does not have the SPH boundary problems and is not sensitive to particle placement. The other approach to
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.
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.
Dispersion in isotachophoresis
NASA Astrophysics Data System (ADS)
Bercovici, Moran; Santiago, Juan G.
2008-11-01
Isotachophoresis (ITP) is a widely used separation and preconcentration technique, which has been utilized in numerous applications including drug discovery, toxin detection, and food analysis. In ITP, analytes are segregated and focused between relatively high mobility leading ions and relatively low mobility trailing ions. These electromigration dynamics couple with advective processes associated with non-uniform electroosmotic flow (EOF). The latter generates internal pressure gradients leading to strong dispersive fluxes. This dispersion is nearly ubiquitous and currently limits the sensitivity and resolution of typical ITP assays. Despite this, there has been little work studying these coupled mechanisms. We performed an analytical and experimental study of dispersion dynamics in ITP. To achieve controlled pressure gradients, we suppressed EOF and applied an external pressure head to balance electromigration. Under these conditions, we show that radial electromigration (as opposed to radial diffusion as in Taylor dispersion) balances axial electromigration. To validate the analysis, we monitored the shape of a focusing fluorescent zone as a function of applied electric field. These experiments show that ITP dispersion may result in analyte widths an order of magnitude larger than predicted by the typical non-dispersive theory. Our goal is to develop a simplified dispersion model to capture this phenomenon, and to implement it in a numerical solver for general ITP problems.
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.
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
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.
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
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.
NASA Astrophysics Data System (ADS)
Erwin, S.; Jacobson, R. B.
2013-12-01
Larval drift is a critical phase of ontogenetic development for many species of lotic fishes. Downstream advection and dispersion of passively drifting larvae or eggs is controlled by the complex interaction of flow regime, channel planform, local channel morphology, and the resulting hydraulic gradients. In many regulated rivers, channel engineering and perturbations to the flow regime may disrupt natural drift processes and impact successful recruitment of native fishes. Here we explore the influence of flow regime and channel morphology on the downstream transport, dispersion, and retention of Pallid Sturgeon larvae, an endangered species endemic to the Mississippi River basin and the focus of significant conservation effort on the Missouri River. The transition from drifting free embryo to exogenously feeding larvae has been identified as a potential life stage bottleneck for the Pallid Sturgeon. Previous studies have indicated that river regulation and fragmentation may contribute to mortality of larval Pallid Sturgeon by reducing the extent of free-flowing river required by free embryos to complete the transition to exogenous feeding. Additionally, channelization may have increased the rate at which larvae are advected downstream out of the Missouri River basin. We describe the complex interactions and influence of morphologic and hydraulic factors on larval drift using an extensive library of hydroacoustic data collected along more than 1300 km of the Lower Missouri River. We use a one-dimensional advection-dispersion model to estimate total drift distance and employ the longitudinal dispersion coefficient as a measure to quantify the tendency towards dispersion or retention of passively drifting larvae in geomorphically distinct segments of river. We use a two-dimensional hydrodynamic model to evaluate the sensitivity of drift and dispersion to in-channel navigation structures and flood hydrology. Based on insights gained from the analysis of field data and
Tell tale signatures of a Two Component Advective Flow around Black holes
NASA Astrophysics Data System (ADS)
Chakrabarti, Sandip Kumar
2016-07-01
Two Component Advective Flow or TCAF naturally explains every observed X-ray/gamma-ray signatures of black hole candidates. Every aspect of this solution has either been derived from Governing equations reproduced by numerical simulations of time dependent hydrodynamic codes of viscous and radiative flows. We discuss how, the same solution, when fitted observational results of several outbursts, consistently and satisfactorily explain evolutions of physical flow parameters, such as the accretion rates of the high and low angular momentum components, QPO frequencies in various spectral states, sizes of the Compton cloud, time lag properties of the high and low inclination angle systems etc. We also discuss possible effects of dynamically important magnetic fields.
Numerous laboratory test systems have been developed for the comparison of efficacy between various chemical oil dispersant formulations. However, for the assessment of chemical dispersant effectiveness under realistic sea state, test protocols are required to produce hydrodynam...
Clay with Desiccation Cracks is an Advection Dominated Environment
NASA Astrophysics Data System (ADS)
Baram, S.; Kurtzman, D.; Sher, Y.; Ronen, Z.; Dahan, O.
2012-04-01
, indicating deep soil evaporation. Daily fluctuation of the air temperature in the desiccation cracks supported thermally induced air convection within the cracks void and could explain the deep soil salinization process. Combination of all the abovementioned observations demonstrated that the formation of desiccation cracks network in dispersive clay sediments generates a bulk advection dominated environment for both air and water flow, and that the reference to clay sediments as "hydrologically safe" should to be reconsidered.
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.
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.
Dispersive shock waves with nonlocal nonlinearity.
Barsi, Christopher; Wan, Wenjie; Sun, Can; Fleischer, Jason W
2007-10-15
We consider dispersive optical shock waves in nonlocal nonlinear media. Experiments are performed using spatial beams in a thermal liquid cell, and results agree with a hydrodynamic theory of propagation.
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.
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.
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
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.
Michael Fraker,; Eric J. Anderson,; Cassandra J. May,; Kuan-Yu Chen,; Jeremiah J. Davis,; Kristen M. DeVanna,; Mark R. DuFour,; Elizabeth A. Marschall,; Christine M. Mayer,; Jeffrey G. Miner,; Kevin L. Pangle,; Jeremy J. Pritt,; Roseman, Edward F.; Jeffrey T. Tyson,; Yingming Zhao,; Stuart Ludsin,
2015-01-01
Physical processes can generate spatiotemporal heterogeneity in habitat quality for fish and also influence the overlap of pre-recruit individuals (e.g., larvae) with high-quality habitat through hydrodynamic advection. In turn, individuals from different stocks that are produced in different spawning locations or at different times may experience dissimilar habitat conditions, which can underlie within- and among-stock variability in larval growth and survival. While such physically-mediated variation has been shown to be important in driving intra- and inter-annual patterns in recruitment in marine ecosystems, its role in governing larval advection, growth, survival, and recruitment has received less attention in large lake ecosystems such as the Laurentian Great Lakes. Herein, we used a hydrodynamic model linked to a larval walleye (Sander vitreus) individual-based model to explore how the timing and location of larval walleye emergence from several spawning sites in western Lake Erie (Maumee, Sandusky, and Detroit rivers; Ohio reef complex) can influence advection pathways and mixing among these local spawning populations (stocks), and how spatiotemporal variation in thermal habitat can influence stock-specific larval growth. While basin-wide advection patterns were fairly similar during 2011 and 2012, smaller scale advection patterns and the degree of stock mixing varied both within and between years. Additionally, differences in larval growth were evident among stocks and among cohorts within stocks which were attributed to spatiotemporal differences in water temperature. Using these findings, we discuss the value of linked physical–biological models for understanding the recruitment process and addressing fisheries management problems in the world's Great Lakes.
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.
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
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.
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.
Dispersive shock waves and modulation theory
NASA Astrophysics Data System (ADS)
El, G. A.; Hoefer, M. A.
2016-10-01
There is growing physical and mathematical interest in the hydrodynamics of dissipationless/dispersive media. Since G.B. Whitham's seminal publication fifty years ago that ushered in the mathematical study of dispersive hydrodynamics, there has been a significant body of work in this area. However, there has been no comprehensive survey of the field of dispersive hydrodynamics. Utilizing Whitham's averaging theory as the primary mathematical tool, we review the rich mathematical developments over the past fifty years with an emphasis on physical applications. The fundamental, large scale, coherent excitation in dispersive hydrodynamic systems is an expanding, oscillatory dispersive shock wave or DSW. Both the macroscopic and microscopic properties of DSWs are analyzed in detail within the context of the universal, integrable, and foundational models for uni-directional (Korteweg-de Vries equation) and bi-directional (Nonlinear Schrödinger equation) dispersive hydrodynamics. A DSW fitting procedure that does not rely upon integrable structure yet reveals important macroscopic DSW properties is described. DSW theory is then applied to a number of physical applications: superfluids, nonlinear optics, geophysics, and fluid dynamics. Finally, we survey some of the more recent developments including non-classical DSWs, DSW interactions, DSWs in perturbed and inhomogeneous environments, and two-dimensional, oblique DSWs.
Longitudinal dispersion modeling in small streams
NASA Astrophysics Data System (ADS)
Pekarova, Pavla; Pekar, Jan; Miklanek, Pavol
2014-05-01
The environmental problems caused by the increasing of pollutant loads discharged into natural water bodies are very complex. For that reason the cognition of transport mechanism and mixing characteristics in natural streams is very important. The mathematical and numerical models have become very useful tools for solving the water management problems. The mathematical simulations based on numerical models of pollution mixing in streams can be used (for example) for prediction of spreading of accidental contaminant waves in rivers. The paper deals with the estimation of the longitudinal dispersion coefficients and with the numerical simulation of transport and transformation of accidental pollution in the small natural streams. There are different ways of solving problems of pollution spreading in open channels, in natural rivers. One of them is the hydrodynamic approach, which endeavours to understand and quantify the spreading phenomenon in a stream. The hydrodynamic models are based on advection-diffusion equation and the majority of them are one-dimensional models. Their disadvantage is inability to simulate the spread of pollution until complete dispersion of pollutant across the stream section is finished. Two-dimensional mixing models do not suffer from these limitations. On the other hand, the one-dimensional models are simpler than two-dimensional ones, they need not so much input data and they are often swifter. Three-dimensional models under conditions of natural streams are applicable with difficulties (or inapplicable) for their complexity and demands on accuracy and amount of input data. As there was mentioned above the two-dimensional models can be used also until complete dispersion of pollutant across the stream section is not finished, so we decided to apply the two-dimensional model SIRENIE. Experimental microbasin Rybarik is the part of the experimental Mostenik brook basin of IH SAS Bratislava. It was established as a Field Hydrological
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...
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.
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
Resurgence in extended hydrodynamics
NASA Astrophysics Data System (ADS)
Aniceto, Inês; Spaliński, Michał
2016-04-01
It has recently been understood that the hydrodynamic series generated by the Müller-Israel-Stewart theory is divergent and that this large-order behavior is consistent with the theory of resurgence. Furthermore, it was observed that the physical origin of this is the presence of a purely damped nonhydrodynamic mode. It is very interesting to ask whether this picture persists in cases where the spectrum of nonhydrodynamic modes is richer. We take the first step in this direction by considering the simplest hydrodynamic theory which, instead of the purely damped mode, contains a pair of nonhydrodynamic modes of complex conjugate frequencies. This mimics the pattern of black brane quasinormal modes which appear on the gravity side of the AdS/CFT description of N =4 supersymmetric Yang-Mills plasma. We find that the resulting hydrodynamic series is divergent in a way consistent with resurgence and precisely encodes information about the nonhydrodynamic modes of the theory.
NASA Astrophysics Data System (ADS)
Eslami, Parastou; Seo, Jung-Hee; Rahsepar, Amirali; George, Richard; Lardo, Albert; Mittal, Rajat
2014-11-01
Coronary computed tomography angiography (CTA) is a promising tool for assessment of coronary stenosis and plaque burden. Recent studies have shown the presence of axial contrast concentration gradients in obstructed arteries, but the mechanism responsible for this phenomenon is not well understood. We use computational fluid dynamics to study intracoronary contrast dispersion and the correlation of concentration gradients with intracoronary blood flow and stenotic severity. Data from our CFD patient-specific simulations reveals that contrast dispersions are generated by intracoronary advection effects, and therefore, encode the coronary flow velocity. This novel method- Transluminal Attenuation Flow Encoding (TAFE) - is used to estimate the flowrate in phantom studies as well as preclinical experiments. Our results indicate a strong correlation between the values estimated from TAFE and the values measured in these experiments. The flow physics of contrast dispersion associated with TAFE will be discussed. This work is funded by grants from Coulter Foundation and Maryland Innovation Initiative. The authors have pending patents in this technology and RM and ACL have other financial interests associated with TAFE.
NASA Astrophysics Data System (ADS)
Young, D. F.; Carleton, J. N.
2012-12-01
The USEPA uses field-scale tests (about 1 ha) to evaluate the leaching potential of pesticides used under realistic agricultural conditions. These tests include a bromide tracer to assess the hydrodynamics of the study site. We analyzed 21 of these bromide leaching studies to determine dispersivity, applied tracer mass recovery, and water retention in the vadose zone. Breakthrough curves were generated for various depths (typically 3 to 4 depths at 1-m intervals) at each of the 21 sites as functions of cumulative infiltration, using measured bromide pore water concentrations. Because the field sites were subjected to natural hydrologic conditions (i.e., evaporation, precipitation, and occasional irrigation), the leaching flow rate at each depth was not directly measurable, so leaching rates were estimated using a capacity model driven by measured daily rainfall, evaporation, and temperature. With the leaching rate thus estimated, the first moment of the bromide breakthrough at each depth was determined. Using the first moment, the effective soil-pore water volume was estimated, which allowed the fitting of a one-dimensional advection-dispersion model and optimization of a dispersion coefficient. Results showed indication of an increase in dispersivity with depth (e.g. dispersivity averaged about 10 cm at the 1-m depth, and around 35 cm at the 4-m depth). Peclet numbers ranged from 4 to 40, but averaged about 10 and varied little with depth. Using this method, apparent recovery of applied bromide varied widely from 8% to 250%, with an average of 60% (standard deviation also 60%) indicating the uncertainty involved in estimating breakthrough curves using field-scale data. Apparent water holdup was consistently greater than the reported field capacity, indicating that measured field capacity may provide low estimates of soil water for use in capacity models. It is important to note that the capacity model concept coupled to the advection dispersion model is the USEPA
Neo, Mei Lin; Erftemeijer, Paul L A; van Beek, Jan K L; van Maren, Dirk S; Teo, Serena L-M; Todd, Peter A
2013-01-01
Recruitment constraints on Singapore's dwindling fluted giant clam, Tridacna squamosa, population were studied by modelling fertilisation, larval transport, and settlement using real-time hydrodynamic forcing combined with knowledge of spawning characteristics, larval development, behaviour, and settlement cues. Larval transport was simulated using a finite-volume advection-diffusion model coupled to a three-dimensional hydrodynamic model. Three recruitment constraint hypotheses were tested: 1) there is limited connectivity between Singapore's reefs and other reefs in the region, 2) there is limited exchange within Singapore's Southern Islands, and 3) there exist low-density constraints to fertilisation efficacy (component Allee effects). Results showed that connectivity among giant clam populations was primarily determined by residual hydrodynamic flows and spawning time, with greatest chances of successful settlement occurring when spawning and subsequent larval dispersal coincided with the period of lowest residual flow. Simulations suggested poor larval transport from reefs located along the Peninsular Malaysia to Singapore, probably due to strong surface currents between the Andaman Sea and South China Sea combined with a major land barrier disrupting larval movement among reefs. The model, however, predicted offshore coral reefs to the southeast of Singapore (Bintan and Batam) may represent a significant source of larvae. Larval exchange within Singapore's Southern Islands varied substantially depending on the locations of source and sink reefs as well as spawning time; but all simulations resulted in low settler densities (2.1-68.6 settled individuals per 10,000 m(2)). Poor fertilisation rates predicted by the model indicate that the low density and scattered distribution of the remaining T. squamosa in Singapore are likely to significantly inhibit any natural recovery of local stocks.
Neo, Mei Lin; Erftemeijer, Paul L. A.; van Beek, Jan K. L.; van Maren, Dirk S.; Teo, Serena L-M.; Todd, Peter A.
2013-01-01
Recruitment constraints on Singapore's dwindling fluted giant clam, Tridacna squamosa, population were studied by modelling fertilisation, larval transport, and settlement using real-time hydrodynamic forcing combined with knowledge of spawning characteristics, larval development, behaviour, and settlement cues. Larval transport was simulated using a finite-volume advection-diffusion model coupled to a three-dimensional hydrodynamic model. Three recruitment constraint hypotheses were tested: 1) there is limited connectivity between Singapore's reefs and other reefs in the region, 2) there is limited exchange within Singapore's Southern Islands, and 3) there exist low-density constraints to fertilisation efficacy (component Allee effects). Results showed that connectivity among giant clam populations was primarily determined by residual hydrodynamic flows and spawning time, with greatest chances of successful settlement occurring when spawning and subsequent larval dispersal coincided with the period of lowest residual flow. Simulations suggested poor larval transport from reefs located along the Peninsular Malaysia to Singapore, probably due to strong surface currents between the Andaman Sea and South China Sea combined with a major land barrier disrupting larval movement among reefs. The model, however, predicted offshore coral reefs to the southeast of Singapore (Bintan and Batam) may represent a significant source of larvae. Larval exchange within Singapore's Southern Islands varied substantially depending on the locations of source and sink reefs as well as spawning time; but all simulations resulted in low settler densities (2.1–68.6 settled individuals per 10,000 m2). Poor fertilisation rates predicted by the model indicate that the low density and scattered distribution of the remaining T. squamosa in Singapore are likely to significantly inhibit any natural recovery of local stocks. PMID:23555597
Synchronization via Hydrodynamic Interactions
NASA Astrophysics Data System (ADS)
Kendelbacher, Franziska; Stark, Holger
2013-12-01
An object moving in a viscous fluid creates a flow field that influences the motion of neighboring objects. We review examples from nature in the microscopic world where such hydrodynamic interactions synchronize beating or rotating filaments. Bacteria propel themselves using a bundle of rotating helical filaments called flagella which have to be synchronized in phase. Other micro-organisms are covered with a carpet of smaller filaments called cilia on their surfaces. They beat highly synchronized so that metachronal waves propagate along the cell surfaces. We explore both examples with the help of simple model systems and identify generic properties for observing synchronization by hydrodynamic interactions.
Hyperbolic metamaterial lens with hydrodynamic nonlocal response.
Yan, Wei; Mortensen, N Asger; Wubs, Martijn
2013-06-17
We investigate the effects of hydrodynamic nonlocal response in hyperbolic metamaterials (HMMs), focusing on the experimentally realizable parameter regime where unit cells are much smaller than an optical wavelength but much larger than the wavelengths of the longitudinal pressure waves of the free-electron plasma in the metal constituents. We derive the nonlocal corrections to the effective material parameters analytically, and illustrate the noticeable nonlocal effects on the dispersion curves numerically. As an application, we find that the focusing characteristics of a HMM lens in the local-response approximation and in the hydrodynamic Drude model can differ considerably. In particular, the optimal frequency for imaging in the nonlocal theory is blueshifted with respect to that in the local theory. Thus, to detect whether nonlocal response is at work in a hyperbolic metamaterial, we propose to measure the near-field distribution of a hyperbolic metamaterial lens. PMID:23787690
Phase Segregation of Passive Advective Particles in an Active Medium
NASA Astrophysics Data System (ADS)
Das, Amit; Polley, Anirban; Rao, Madan
2016-02-01
Localized contractile configurations or asters spontaneously appear and disappear as emergent structures in the collective stochastic dynamics of active polar actomyosin filaments. Passive particles which (un)bind to the active filaments get advected into the asters, forming transient clusters. We study the phase segregation of such passive advective scalars in a medium of dynamic asters, as a function of the aster density and the ratio of the rates of aster remodeling to particle diffusion. The dynamics of coarsening shows a violation of Porod behavior; the growing domains have diffuse interfaces and low interfacial tension. The phase-segregated steady state shows strong macroscopic fluctuations characterized by multiscaling and intermittency, signifying rapid reorganization of macroscopic structures. We expect these unique nonequilibrium features to manifest in the actin-dependent molecular clustering at the cell surface.
NASA Technical Reports Server (NTRS)
Wang, Xiao-Yen; Chow, Chuen-Yen; Chang, Sin-Chung
1999-01-01
Test problems are used to examine the performance of several one-dimensional numerical schemes based on the space-time conservation and solution element (CE/SE) method. Investigated in this paper are the CE/SE schemes constructed previously for solving the linear unsteady advection-diffusion equation and the schemes derived here for solving the nonlinear viscous and inviscid Burgers equations. In comparison with the numerical solutions obtained using several traditional finite-difference schemes with similar accuracy, the CE/SE solutions display much lower numerical dissipation and dispersion errors.
Skew resisting hydrodynamic seal
Conroy, William T.; Dietle, Lannie L.; Gobeli, Jeffrey D.; Kalsi, Manmohan S.
2001-01-01
A novel hydrodynamically lubricated compression type rotary seal that is suitable for lubricant retention and environmental exclusion. Particularly, the seal geometry ensures constraint of a hydrodynamic seal in a manner preventing skew-induced wear and provides adequate room within the seal gland to accommodate thermal expansion. The seal accommodates large as-manufactured variations in the coefficient of thermal expansion of the sealing material, provides a relatively stiff integral spring effect to minimize pressure-induced shuttling of the seal within the gland, and also maintains interfacial contact pressure within the dynamic sealing interface in an optimum range for efficient hydrodynamic lubrication and environment exclusion. The seal geometry also provides for complete support about the circumference of the seal to receive environmental pressure, as compared the interrupted character of seal support set forth in U.S. Pat. Nos. 5,873,576 and 6,036,192 and provides a hydrodynamic seal which is suitable for use with non-Newtonian lubricants.
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
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.
NASA Astrophysics Data System (ADS)
Lowry, Thomas; Li, Shu-Guang
2005-02-01
Difficulty in solving the transient advection-diffusion equation (ADE) stems from the relationship between the advection derivatives and the time derivative. For a solution method to be viable, it must account for this relationship by being accurate in both space and time. This research presents a unique method for solving the time-dependent ADE that does not discretize the derivative terms but rather solves the equation analytically in the space-time domain. The method is computationally efficient and numerically accurate and addresses the common limitations of numerical dispersion and spurious oscillations that can be prevalent in other solution methods. The method is based on the improved finite analytic (IFA) solution method [Lowry TS, Li S-G. A characteristic based finite analytic method for solving the two-dimensional steady-state advection-diffusion equation. Water Resour Res 38 (7), 10.1029/2001WR000518] in space coupled with a Laplace transformation in time. In this way, the method has no Courant condition and maintains accuracy in space and time, performing well even at high Peclet numbers. The method is compared to a hybrid method of characteristics, a random walk particle tracking method, and an Eulerian-Lagrangian Localized Adjoint Method using various degrees of flow-field heterogeneity across multiple Peclet numbers. Results show the IFALT method to be computationally more efficient while producing similar or better accuracy than the other methods.
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.
NASA Astrophysics Data System (ADS)
Mahanty, M. M.; Mohanty, P. K.; Pattnaik, A. K.; Panda, U. S.; Pradhan, S.; Samal, R. N.
2016-08-01
This paper investigated the hydrodynamics, spatio-temporal variability of temperature/salinity and the residence time of tracer concentrations in a largest brackish water coastal lagoon in Asia, namely the Chilika lagoon, India. An integrated approach combined the measurement and 2D hydrodynamic-advection/dispersion model is used to simulate circulation and temperature/salinity, and estimated the water residence time in lagoon under different forcing mechanisms, such as tide, wind and freshwater discharge during the dry and wet periods. Water circulation inside the lagoon is simulated when wind is included with the tide only forcing during dry period, and freshwater influx is included with the tide and wind forcing during wet period. Under the realistic forcing conditions, the computed temporal variability of water temperature and salinity are well correlated with the measurements in both the periods. The spatial variations of water temperature within the lagoon is influenced by the meteorological conditions, tide and freshwater influx as well as the shallowness of the lagoon, whereas the salinity is spatially controlled by the freshwater influx from the riverine system and seawater intrusion through the tidal inlets. The numerical model results show that in the Chilika lagoon tidal and river influx affect significantly the residence time spatially, and is site specific. The residence time varies from values of 4-5 days in the outer channel (OC) and 132 days at the northern sector (NS) in the main body of lagoon. The current study represents a first attempt to use a combined model approach, which is therefore, a useful tool to support the ecological implication of the lagoon ecosystem.
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.
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.
Chung, Y.G.; Lee, G.B.; Bang, S.Y.; Choi, S.B.; Lee, S.U.; Yoon, J.H.; Nam, S.Y.; Lee, H.R.
2006-07-01
Recently, three-dimensional models have been used for aquatic dispersion of radioactive effluents in relation to nuclear power plant siting based on the Notice No. 2003-12 'Guideline for investigating and assessing hydrological and aquatic characteristics of nuclear facility site' of the Ministry of Science and Technology (MOST) in Korea. Several nuclear power plants have been under construction or planed, which are Shin-Kori Unit 1 and 2, Shin-Wolsong Unit 1 and 2, and Shin-Ulchin Unit 1 and 2. For assessing the aquatic dispersion of radionuclides released from the above nuclear power plants, it is necessary to know the coastal currents around sites which are affected by circulation of East Sea. In this study, a three dimensional hydrodynamic model for the circulation of the East Sea of Korea has been developed as the first phase, which is based on the RIAMOM (Research Institute of Applied Mechanics' Ocean Model, Kyushu University, Japan). The model uses the primitive equation with hydrostatic approximation, and uses Arakawa-B grid system horizontally and Z coordinate vertically. Model domain is 126.5 deg. E to 142.5 deg. E of east longitude and 33 deg. N and 52 deg. N of the north latitude. The space of the horizontal grid was 1/12 deg. to longitude and latitude direction and vertical level was divided to 20. This model uses Generalized Arakawa Scheme, Slant Advection, and Mode-Splitting Method. The input data were from JODC (Japan Oceanographic Data Center), KNFRDI (Korea National Fisheries Research and Development Institute), and ECMWF (European Center for Medium-Range Weather Forecasts). The modeling results are in fairly good agreement with schematic patterns of the surface circulation in the East Sea/Japan Sea. The local current model and aquatic dispersion model of the coastal region will be developed as the second phase. The oceanic dispersion experiments will be also carried out by using ARGO Drifter around a nuclear power plant site. (authors)
Distinguishing resuspension and advection signals in a hypertidal estuary
NASA Astrophysics Data System (ADS)
Todd, David; Souza, Alex; Jago, Colin
2015-04-01
Terrestrial material is supplied to an estuary system by the river, while marine material is supplied by the sea. Whether the estuary acts as a trap or a bypass zone for SPM (suspended particulate matter) depends upon the properties and dynamics of both the estuary, including the tidal and residual behaviour of the currents, and the SPM, including particle sizes and settling velocities and concentration gradients, which together control the dynamics, such as the trapping efficiency, of the estuary. Whether an SPM signal is regarded as being one of resuspension or advection depends upon the area of interest, and therefore distinguishing between resuspension and advection can be complex. Material that is resuspended within the area of study is regarded as resuspension, while that which is resuspended outside, but passes through, the area of interest, is regarded as advection. The results of a measurement campaign undertaken in a hypertidal UK estuary during the pre-spring bloom February-March and post-spring bloom May-June are presented utilising a combination of acoustic and optical instruments, moorings, and CTD stations. A characteristic asymmetric "twin peak" signal is present during both time periods, implying the presence of both resuspension and advection. This is confirmed through the use of harmonic analysis. A seasonal variation in the relative importance of the resuspension and advection components is seen between the two observation periods, with the small (<122µm) and large (>122µm) particles displaying different behaviours and providing a strong indication of the presence of flocculation. Approximate point flux calculations showed a reduction in the horizontal gradient of concentration, and subsequently the flood dominance of sediment transport, between May-June and February-March. This has been attributed to changes in biological activity and atmospheric forcing between the two observational periods. Ebb-dominant concentrations brought about by the
NASA Astrophysics Data System (ADS)
Wilson, Alicia M.; Woodward, Gwendolyn L.; Savidge, William B.
2016-07-01
Rapid exchange of surface waters and porewaters in shallow sediments has important biogeochemical implications for streams and marine systems alike, but mapping these important reaction zones has been difficult. As a means of bridging the gap between the stream and submarine groundwater discharge communities we suggest that the rapid, transient mixing in this zone be called "hydrodynamic exchange". We then present a new model, MATTSI, which was developed to estimate the timing, depth and magnitude of hydrodynamic exchange below the sediment-water interface by inverting thermal time-series observations. The model uses an effective thermal dispersion term to emulate 3-D hydrodynamic exchange in a 1-D model. The effective dispersion is assumed to decline exponentially below the sediment water interface. Application of the model to a synthetic dataset and two field datasets from 50 km offshore in the South Atlantic Bight shows that exchange events can be clearly identified from thermal data. The model is relatively insensitive to realistic errors in sensor depth and thermal conductivity. Although the datasets tested here were too shallow to fully span the depth of flushing, we were able to estimate the depth of hydrodynamic exchange via sensitivity studies.
Hydrodynamics of Turning Flocks.
Yang, Xingbo; Marchetti, M Cristina
2015-12-18
We present a hydrodynamic model of flocking that generalizes the familiar Toner-Tu equations to incorporate turning inertia of well-polarized flocks. The continuum equations controlled by only two dimensionless parameters, orientational inertia and alignment strength, are derived by coarse-graining the inertial spin model recently proposed by Cavagna et al. The interplay between orientational inertia and bend elasticity of the flock yields anisotropic spin waves that mediate the propagation of turning information throughout the flock. The coupling between spin-current density to the local vorticity field through a nonlinear friction gives rise to a hydrodynamic mode with angular-dependent propagation speed at long wavelengths. This mode becomes unstable as a result of the growth of bend and splay deformations augmented by the spin wave, signaling the transition to complex spatiotemporal patterns of continuously turning and swirling flocks.
Hydrodynamics of Turning Flocks.
Yang, Xingbo; Marchetti, M Cristina
2015-12-18
We present a hydrodynamic model of flocking that generalizes the familiar Toner-Tu equations to incorporate turning inertia of well-polarized flocks. The continuum equations controlled by only two dimensionless parameters, orientational inertia and alignment strength, are derived by coarse-graining the inertial spin model recently proposed by Cavagna et al. The interplay between orientational inertia and bend elasticity of the flock yields anisotropic spin waves that mediate the propagation of turning information throughout the flock. The coupling between spin-current density to the local vorticity field through a nonlinear friction gives rise to a hydrodynamic mode with angular-dependent propagation speed at long wavelengths. This mode becomes unstable as a result of the growth of bend and splay deformations augmented by the spin wave, signaling the transition to complex spatiotemporal patterns of continuously turning and swirling flocks. PMID:26722945
Fluctuations in relativistic causal hydrodynamics
NASA Astrophysics Data System (ADS)
Kumar, Avdhesh; Bhatt, Jitesh R.; Mishra, Ananta P.
2014-05-01
Formalism to calculate the hydrodynamic fluctuations by applying the Onsager theory to the relativistic Navier-Stokes equation is already known. In this work, we calculate hydrodynamic fluctuations within the framework of the second order hydrodynamics of Müller, Israel and Stewart and its generalization to the third order. We have also calculated the fluctuations for several other causal hydrodynamical equations. We show that the form for the Onsager-coefficients and form of the correlation functions remain the same as those obtained by the relativistic Navier-Stokes equation and do not depend on any specific model of hydrodynamics. Further we numerically investigate evolution of the correlation function using the one dimensional boost-invariant (Bjorken) flow. We compare the correlation functions obtained using the causal hydrodynamics with the correlation function for the relativistic Navier-Stokes equation. We find that the qualitative behavior of the correlation functions remains the same for all the models of the causal hydrodynamics.
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.
Blaedel, Kenneth L.; Davis, Pete J.; Landram, Charles S.
2000-01-01
A saw having a self-pumped hydrodynamic blade guide or bearing for retaining the saw blade in a centered position in the saw kerf (width of cut made by the saw). The hydrodynamic blade guide or bearing utilizes pockets or grooves incorporated into the sides of the blade. The saw kerf in the workpiece provides the guide or bearing stator surface. Both sides of the blade entrain cutting fluid as the blade enters the kerf in the workpiece, and the trapped fluid provides pressure between the blade and the workpiece as an inverse function of the gap between the blade surface and the workpiece surface. If the blade wanders from the center of the kerf, then one gap will increase and one gap will decrease and the consequent pressure difference between the two sides of the blade will cause the blade to re-center itself in the kerf. Saws using the hydrodynamic blade guide or bearing have particular application in slicing slabs from boules of single crystal materials, for example, as well as for cutting other difficult to saw materials such as ceramics, glass, and brittle composite materials.
Hydrodynamics of fossil fishes
Fletcher, Thomas; Altringham, John; Peakall, Jeffrey; Wignall, Paul; Dorrell, Robert
2014-01-01
From their earliest origins, fishes have developed a suite of adaptations for locomotion in water, which determine performance and ultimately fitness. Even without data from behaviour, soft tissue and extant relatives, it is possible to infer a wealth of palaeobiological and palaeoecological information. As in extant species, aspects of gross morphology such as streamlining, fin position and tail type are optimized even in the earliest fishes, indicating similar life strategies have been present throughout their evolutionary history. As hydrodynamical studies become more sophisticated, increasingly complex fluid movement can be modelled, including vortex formation and boundary layer control. Drag-reducing riblets ornamenting the scales of fast-moving sharks have been subjected to particularly intense research, but this has not been extended to extinct forms. Riblets are a convergent adaptation seen in many Palaeozoic fishes, and probably served a similar hydrodynamic purpose. Conversely, structures which appear to increase skin friction may act as turbulisors, reducing overall drag while serving a protective function. Here, we examine the diverse adaptions that contribute to drag reduction in modern fishes and review the few attempts to elucidate the hydrodynamics of extinct forms. PMID:24943377
Hydrodynamics of insect spermatozoa
NASA Astrophysics Data System (ADS)
Pak, On Shun; Lauga, Eric
2010-11-01
Microorganism motility plays important roles in many biological processes including reproduction. Many microorganisms propel themselves by propagating traveling waves along their flagella. Depending on the species, propagation of planar waves (e.g. Ceratium) and helical waves (e.g. Trichomonas) were observed in eukaryotic flagellar motion, and hydrodynamic models for both were proposed in the past. However, the motility of insect spermatozoa remains largely unexplored. An interesting morphological feature of such cells, first observed in Tenebrio molitor and Bacillus rossius, is the double helical deformation pattern along the flagella, which is characterized by the presence of two superimposed helical flagellar waves (one with a large amplitude and low frequency, and the other with a small amplitude and high frequency). Here we present the first hydrodynamic investigation of the locomotion of insect spermatozoa. The swimming kinematics, trajectories and hydrodynamic efficiency of the swimmer are computed based on the prescribed double helical deformation pattern. We then compare our theoretical predictions with experimental measurements, and explore the dependence of the swimming performance on the geometric and dynamical parameters.
Hydrodynamics of fossil fishes.
Fletcher, Thomas; Altringham, John; Peakall, Jeffrey; Wignall, Paul; Dorrell, Robert
2014-08-01
From their earliest origins, fishes have developed a suite of adaptations for locomotion in water, which determine performance and ultimately fitness. Even without data from behaviour, soft tissue and extant relatives, it is possible to infer a wealth of palaeobiological and palaeoecological information. As in extant species, aspects of gross morphology such as streamlining, fin position and tail type are optimized even in the earliest fishes, indicating similar life strategies have been present throughout their evolutionary history. As hydrodynamical studies become more sophisticated, increasingly complex fluid movement can be modelled, including vortex formation and boundary layer control. Drag-reducing riblets ornamenting the scales of fast-moving sharks have been subjected to particularly intense research, but this has not been extended to extinct forms. Riblets are a convergent adaptation seen in many Palaeozoic fishes, and probably served a similar hydrodynamic purpose. Conversely, structures which appear to increase skin friction may act as turbulisors, reducing overall drag while serving a protective function. Here, we examine the diverse adaptions that contribute to drag reduction in modern fishes and review the few attempts to elucidate the hydrodynamics of extinct forms. PMID:24943377
Spatially varying dispersion to model breakthrough curves.
Li, Guangquan
2011-01-01
Often the water flowing in a karst conduit is a combination of contaminated water entering at a sinkhole and cleaner water released from the limestone matrix. Transport processes in the conduit are controlled by advection, mixing (dilution and dispersion), and retention-release. In this article, a karst transport model considering advection, spatially varying dispersion, and dilution (from matrix seepage) is developed. Two approximate Green's functions are obtained using transformation of variables, respectively, for the initial-value problem and for the boundary-value problem. A numerical example illustrates that mixing associated with strong spatially varying conduit dispersion can cause strong skewness and long tailing in spring breakthrough curves. Comparison of the predicted breakthrough curve against that measured from a dye-tracing experiment between Ames Sink and Indian Spring, Northwest Florida, shows that the conduit dispersivity can be as large as 400 m. Such a large number is believed to imply strong solute interaction between the conduit and the matrix and/or multiple flow paths in a conduit network. It is concluded that Taylor dispersion is not dominant in transport in a karst conduit, and the complicated retention-release process between mobile- and immobile waters may be described by strong spatially varying conduit dispersion. PMID:21143474
NASA Astrophysics Data System (ADS)
Wilderbuer, Thomas; Duffy-Anderson, Janet T.; Stabeno, Phyllis; Hermann, Albert
2016-05-01
In an effort to better understand the physics of the eastern Bering Sea shelf current as it relates to flatfish advection to favorable near-shore areas, sets of multiple, satellite-tracked, oceanic drifters were released in 2010, 2012 and 2013. The release sites and dates were chosen to coincide with known spawning locations for northern rock sole (Lepidopsetta polyxystra) and known time of larval emergence. The drifters were drogued 5-each at 20 and 40 m in 2010 and 2012, and 4 at 40 m and 2 at 20 m in 2013. The locations of drifters were used to calculate divergence over a 90-day period that corresponds to the larval pelagic duration of Bering Sea shelf northern rock sole. Results indicate that there are alternating periods of positive and negative divergence with an overall trend toward drifter separation after 90 days, roughly the end of the rock sole planktonic larval period. Examination of the drifter behavior at the hourly scale indicates that semi-daily tidal forcing is the primary mechanism of drifter divergence and convergence. Field observations of early-stage northern rock sole larval distributions over the same period indicate that predominant oceanographic advection is northerly over the continental shelf among preflexion stages, though juveniles are predominantly found in nursery areas located ~ 400 km eastward and inshore. Evidence from drifter deployments suggests that behavioral movements during the postflexion and early juvenile larval phases that optimize eastward periodicity of tidal cycles is a viable mechanism to enhance eastward movement of northern rock sole larvae to favorable nursery grounds. A regional ocean modeling system (ROMS) was implemented to track the different rates of dispersion in simulations both with and without tidal forcing, and was used to estimate effective horizontal eddy diffusion in the case of both isobaric (fixed-depth) and Lagrangian (neutrally buoyant) particles. The addition of tidal forcing had a pronounced
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.
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.
Hydrodynamics of an Electrochemical Membrane Bioreactor
Wang, Ya-Zhou; Wang, Yun-Kun; He, Chuan-Shu; Yang, Hou-Yun; Sheng, Guo-Ping; Shen, Jin-You; Mu, Yang; Yu, Han-Qing
2015-01-01
An electrochemical membrane bioreactor (EMBR) has recently been developed for energy recovery and wastewater treatment. The hydrodynamics of the EMBR would significantly affect the mass transfers and reaction kinetics, exerting a pronounced effect on reactor performance. However, only scarce information is available to date. In this study, the hydrodynamic characteristics of the EMBR were investigated through various approaches. Tracer tests were adopted to generate residence time distribution curves at various hydraulic residence times, and three hydraulic models were developed to simulate the results of tracer studies. In addition, the detailed flow patterns of the EMBR were acquired from a computational fluid dynamics (CFD) simulation. Compared to the tank-in-series and axial dispersion ones, the Martin model could describe hydraulic performance of the EBMR better. CFD simulation results clearly indicated the existence of a preferential or circuitous flow in the EMBR. Moreover, the possible locations of dead zones in the EMBR were visualized through the CFD simulation. Based on these results, the relationship between the reactor performance and the hydrodynamics of EMBR was further elucidated relative to the current generation. The results of this study would benefit the design, operation and optimization of the EMBR for simultaneous energy recovery and wastewater treatment. PMID:25997399
Hydrodynamics of an Electrochemical Membrane Bioreactor
NASA Astrophysics Data System (ADS)
Wang, Ya-Zhou; Wang, Yun-Kun; He, Chuan-Shu; Yang, Hou-Yun; Sheng, Guo-Ping; Shen, Jin-You; Mu, Yang; Yu, Han-Qing
2015-05-01
An electrochemical membrane bioreactor (EMBR) has recently been developed for energy recovery and wastewater treatment. The hydrodynamics of the EMBR would significantly affect the mass transfers and reaction kinetics, exerting a pronounced effect on reactor performance. However, only scarce information is available to date. In this study, the hydrodynamic characteristics of the EMBR were investigated through various approaches. Tracer tests were adopted to generate residence time distribution curves at various hydraulic residence times, and three hydraulic models were developed to simulate the results of tracer studies. In addition, the detailed flow patterns of the EMBR were acquired from a computational fluid dynamics (CFD) simulation. Compared to the tank-in-series and axial dispersion ones, the Martin model could describe hydraulic performance of the EBMR better. CFD simulation results clearly indicated the existence of a preferential or circuitous flow in the EMBR. Moreover, the possible locations of dead zones in the EMBR were visualized through the CFD simulation. Based on these results, the relationship between the reactor performance and the hydrodynamics of EMBR was further elucidated relative to the current generation. The results of this study would benefit the design, operation and optimization of the EMBR for simultaneous energy recovery and wastewater treatment.
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
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.
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
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.
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.
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
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.
Moran, B
2005-06-02
We present test problems that can be used to check the hydrodynamic implementation in computer codes designed to model the implosion of a National Ignition Facility (NIF) capsule. The problems are simplified, yet one of them is three-dimensional. It consists of a nearly-spherical incompressible imploding shell subjected to an exponentially decaying pressure on its outer surface. We present a semi-analytic solution for the time-evolution of that shell with arbitrary small three-dimensional perturbations on its inner and outer surfaces. The perturbations on the shell surfaces are intended to model the imperfections that are created during capsule manufacturing.
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
Molecular Hydrodynamics from Memory Kernels.
Lesnicki, Dominika; Vuilleumier, Rodolphe; Carof, Antoine; Rotenberg, Benjamin
2016-04-01
The memory kernel for a tagged particle in a fluid, computed from molecular dynamics simulations, decays algebraically as t^{-3/2}. We show how the hydrodynamic Basset-Boussinesq force naturally emerges from this long-time tail and generalize the concept of hydrodynamic added mass. This mass term is negative in the present case of a molecular solute, which is at odds with incompressible hydrodynamics predictions. Lastly, we discuss the various contributions to the friction, the associated time scales, and the crossover between the molecular and hydrodynamic regimes upon increasing the solute radius. PMID:27104730
Load responsive hydrodynamic bearing
Kalsi, Manmohan S.; Somogyi, Dezso; Dietle, Lannie L.
2002-01-01
A load responsive hydrodynamic bearing is provided in the form of a thrust bearing or journal bearing for supporting, guiding and lubricating a relatively rotatable member to minimize wear thereof responsive to relative rotation under severe load. In the space between spaced relatively rotatable members and in the presence of a liquid or grease lubricant, one or more continuous ring shaped integral generally circular bearing bodies each define at least one dynamic surface and a plurality of support regions. Each of the support regions defines a static surface which is oriented in generally opposed relation with the dynamic surface for contact with one of the relatively rotatable members. A plurality of flexing regions are defined by the generally circular body of the bearing and are integral with and located between adjacent support regions. Each of the flexing regions has a first beam-like element being connected by an integral flexible hinge with one of the support regions and a second beam-like element having an integral flexible hinge connection with an adjacent support region. A least one local weakening geometry of the flexing region is located intermediate the first and second beam-like elements. In response to application of load from one of the relatively rotatable elements to the bearing, the beam-like elements and the local weakening geometry become flexed, causing the dynamic surface to deform and establish a hydrodynamic geometry for wedging lubricant into the dynamic interface.
Hydrodynamics of pronuclear migration
NASA Astrophysics Data System (ADS)
Nazockdast, Ehssan; Needleman, Daniel; Shelley, Michael
2014-11-01
Microtubule (MT) filaments play a key role in many processes involved in cell devision including spindle formation, chromosome segregation, and pronuclear positioning. We present a direct numerical technique to simulate MT dynamics in such processes. Our method includes hydrodynamically mediated interactions between MTs and other cytoskeletal objects, using singularity methods for Stokes flow. Long-ranged many-body hydrodynamic interactions are computed using a highly efficient and scalable fast multipole method, enabling the simulation of thousands of MTs. Our simulation method also takes into account the flexibility of MTs using Euler-Bernoulli beam theory as well as their dynamic instability. Using this technique, we simulate pronuclear migration in single-celled Caenorhabditis elegans embryos. Two different positioning mechanisms, based on the interactions of MTs with the motor proteins and the cell cortex, are explored: cytoplasmic pulling and cortical pushing. We find that although the pronuclear complex migrates towards the center of the cell in both models, the generated cytoplasmic flows are fundamentally different. This suggest that cytoplasmic flow visualization during pronuclear migration can be utilized to differentiate between the two mechanisms.
Hydrodynamics of Bacterial Cooperation
NASA Astrophysics Data System (ADS)
Petroff, A.; Libchaber, A.
2012-12-01
Over the course of the last several decades, the study of microbial communities has identified countless examples of cooperation between microorganisms. Generally—as in the case of quorum sensing—cooperation is coordinated by a chemical signal that diffuses through the community. Less well understood is a second class of cooperation that is mediated through physical interactions between individuals. To better understand how the bacteria use hydrodynamics to manipulate their environment and coordinate their actions, we study the sulfur-oxidizing bacterium Thiovulum majus. These bacteria live in the diffusive boundary layer just above the muddy bottoms of ponds. As buried organic material decays, sulfide diffuses out of the mud. Oxygen from the pond diffuses into the boundary layer from above. These bacteria form communities—called veils— which are able to transport nutrients through the boundary layer faster than diffusion, thereby increasing their metabolic rate. In these communities, bacteria attach to surfaces and swim in place. As millions of bacteria beat their flagella, the community induces a macroscopic fluid flow, which mix the boundary layer. Here we present experimental observations and mathematical models that elucidate the hydrodynamics linking the behavior of an individual bacterium to the collective dynamics of the community. We begin by characterizing the flow of water around an individual bacterium swimming in place. We then discuss the flow of water and nutrients around a small number of individuals. Finally, we present observations and models detailing the macroscopic dynamics of a Thiovulum veil.
NASA Astrophysics Data System (ADS)
Mahesha, Chaitra
A unique processing technique based on chaotic advection developed at Clemson University and shown to controllably produce structured materials in the past was employed to produce structured nanocomposites with a high degree of clay orientation as well as localization of platelets within layers of nanoscale thicknesses. Continuous lengths of nanocomposites with different clay contents were extruded in the form of films by feeding separately melts of virgin polyamide-6 polymer and polyamide 6-clay masterbatch into a continuous chaotic advection blender. A variety of composite structures were producible at fixed clay compositions. The internal structure was characterized by transmission electron microscopy (TEM), x-ray diffraction (XRD) and differential scanning calorimetry (DSC). Nanocomposites with novel in-situ multi-layered structures and a high degree of platelet orientation were formed by the recursive stretching and folding of the melt domains due to chaotic advection. Clay platelets were localized within discrete regions to form alternating virgin and platelet-rich layers leading to a hierarchical structure with multiple nano-scales. The thicknesses of the layers reduced with prolonged chaotic advection, eventually leading to nanocomposites in which the multi-layering was no longer discernible. The oriented platelets appeared to be homogenously dispersed through the bulk of the nanocomposite. Investigation of the morphology of the matrix by XRD showed that the homogeneity of the crystalline phase and the orientation of polymer chains parallel to the film surface increased with increased chaotic advection. Also, as the layer thickness reduced, the number of polymer chains restricted by clay platelets increased causing the gamma-crystalline fraction to increase. While XRD results suggested a change in total crystallinity with chaotic advection and clay content but without a specific trend, no change in crystallinity was measured by DSC. Such contradictions are
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.
NASA Astrophysics Data System (ADS)
Qiu, Zhongfeng; Doglioli, Andrea M.; He, Yijun; Carlotti, Francois
2011-03-01
This paper presents two comparisons or tests for a Lagrangian model of zooplankton dispersion: numerical schemes and time steps. Firstly, we compared three numerical schemes using idealized circulations. Results show that the precisions of the advanced Adams-Bashfold-Moulton (ABM) method and the Runge-Kutta (RK) method were in the same order and both were much higher than that of the Euler method. Furthermore, the advanced ABM method is more efficient than the RK method in computational memory requirements and time consumption. We therefore chose the advanced ABM method as the Lagrangian particle-tracking algorithm. Secondly, we performed a sensitivity test for time steps, using outputs of the hydrodynamic model, Symphonie. Results show that the time step choices depend on the fluid response time that is related to the spatial resolution of velocity fields. The method introduced by Oliveira et al. in 2002 is suitable for choosing time steps of Lagrangian particle-tracking models, at least when only considering advection.
An Analysis of Total Phosphorus Dispersion in Lake Used As a Municipal Water Supply.
Lima, Rômulo C; Mesquita, André L A; Blanco, Claudio J C; Santos, Maria de Lourdes S; Secretan, Yves
2015-09-01
In Belém city is located the potable water supply system of its metropolitan area, which includes, in addition to this city, four more municipalities. In this water supply complex is the Água Preta lake, which serves as a reservoir for the water pumped from the Guamá river. Due to the great importance of this lake for this system, several works have been devoted to its study, from the monitoring of the quality of its waters to its hydrodynamic modeling. This paper presents the results obtained by computer simulation of the phosphorus dispersion within this reservoir by the numerical solution of two-dimensional equation of advection-diffusion-reaction by the method θ/SUPG. Comparing these results with data concentration of total phosphorus collected from November 2008 to October 2009 and from satellite photos show that the biggest polluters of the water of this lake are the domestic sewage dumps from the population living in its vicinity. The results obtained indicate the need for more information for more precise quantitative analysis. However, they show that the phosphorus brought by the Guamá river water is consumed in an area adjacent to the canal that carries this water into the lake. Phosphorus deposits in the lake bottom should be monitored to verify their behavior, thus preventing the quality of water maintained therein. PMID:26421456
An Analysis of Total Phosphorus Dispersion in Lake Used As a Municipal Water Supply.
Lima, Rômulo C; Mesquita, André L A; Blanco, Claudio J C; Santos, Maria de Lourdes S; Secretan, Yves
2015-09-01
In Belém city is located the potable water supply system of its metropolitan area, which includes, in addition to this city, four more municipalities. In this water supply complex is the Água Preta lake, which serves as a reservoir for the water pumped from the Guamá river. Due to the great importance of this lake for this system, several works have been devoted to its study, from the monitoring of the quality of its waters to its hydrodynamic modeling. This paper presents the results obtained by computer simulation of the phosphorus dispersion within this reservoir by the numerical solution of two-dimensional equation of advection-diffusion-reaction by the method θ/SUPG. Comparing these results with data concentration of total phosphorus collected from November 2008 to October 2009 and from satellite photos show that the biggest polluters of the water of this lake are the domestic sewage dumps from the population living in its vicinity. The results obtained indicate the need for more information for more precise quantitative analysis. However, they show that the phosphorus brought by the Guamá river water is consumed in an area adjacent to the canal that carries this water into the lake. Phosphorus deposits in the lake bottom should be monitored to verify their behavior, thus preventing the quality of water maintained therein.
NASA Astrophysics Data System (ADS)
Hammer, Daniel X.; Noojin, Gary D.; Thomas, Robert J.; Stolarski, David J.; Rockwell, Benjamin A.; Welch, Ashley J.
1999-06-01
Spectrally resolved white-light interferometry (SRWLI) was used to measure the wavelength dependence of refractive index (i.e., dispersion) for various ocular components. The accuracy of the technique was assessed by measurement of fused silica and water, the refractive indices of which have been measured at several different wavelengths. The dispersion of bovine and rabbit aqueous and vitreous humor was measured from 400 to 1100 nm. Also, the dispersion was measured from 400 to 700 nm for aqueous and vitreous humor extracted from goat and rhesus monkey eyes. For the humors, the dispersion did not deviate significantly from water. In an additional experiment, the dispersion of aqueous and vitreous humor that had aged up to a month was compared to freshly harvested material. No difference was found between the fresh and aged media. An unsuccessful attempt was also made to use the technique for dispersion measurement of bovine cornea and lens. Future refinement may allow measurement of the dispersion of cornea and lens across the entire visible and near-infrared wavelength band. The principles of white- light interferometry including image analysis, measurement accuracy, and limitations of the technique, are discussed. In addition, alternate techniques and previous measurements of ocular dispersion are reviewed.
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.
Current chemical dispersant effectiveness tests for product selection are commonly performed with bench-scale testing apparatus. However, for the assessment of oil dispersant effectiveness under real sea state conditions, test protocols are required to have hydrodynamic conditio...
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.)
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
NASA Astrophysics Data System (ADS)
Viet Dung, Nguyen; Van Manh, Nguyen; Merz, Bruno; Apel, Heiko
2014-05-01
An advection-dispersive (AD) module for cohesive sediment transport modelling is built up based on a quasi-2D hydrodynamic model (HD) for the whole Mekong Delta which has been recently developed by Dung et al. (2011) using the modelling software DHI MIKE 11. As parameter uncertainty is one main epistemic uncertainty source of modelling work, it needs to be reduced via a calibration-validation process in order to improve the modelling skill of the simulation tool. In this large scale two-component (HD-AD) model, many parameters need to be properly estimated. These parameters include the flow resistance coefficient (Manning's roughness coefficient), longitudinal dispersion coefficient, the free settling velocity and the critical shear stress for deposition. It should be noted that they are spatially distributed over the modelling domain which consists of more than 4000 branches and 26000 computational nodes used to model real channels and floodplains for the vast area in the Mekong Delta. We aim at developing a suitable framework for optimizing these parameters automatically. As the model included a real 1D illustration of river and channel networks and quasi-2D presentation of floodplains being able to represent both main flow and inundation processes, the calibration is, hence, seen from a multi-objective viewpoint using in parallel high-temporal, low-spatial resolution data (gauge data) and low-temporal, high spatial resolution data (remote sensing data). The calibration (and validation) data utilized in this study comprise of gauged time series data along the main channel (water level, flow discharge and suspended sediment concentration), satellite-based flood extent maps and monitored sedimentation deposition rates in several locations. In total, six objective functions as calibration criteria are defined based on these data. Learning from the feature that AD module can be simulated using finer computational time step after HD results are computed, we propose to
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.
General formulation of transverse hydrodynamics
Ryblewski, Radoslaw; Florkowski, Wojciech
2008-06-15
General formulation of hydrodynamics describing transversally thermalized matter created at the early stages of ultrarelativistic heavy-ion collisions is presented. Similarities and differences with the standard three-dimensionally thermalized relativistic hydrodynamics are discussed. The role of the conservation laws as well as the thermodynamic consistency of two-dimensional thermodynamic variables characterizing transversally thermalized matter is emphasized.
NASA Astrophysics Data System (ADS)
Hrycik, Janelle M.; Chassé, Joël; Ruddick, Barry R.; Taggart, Christopher T.
2013-11-01
Early life-stage dispersal influences recruitment and is of significance in explaining the distribution and connectivity of marine species. Motivations for quantifying dispersal range from biodiversity conservation to the design of marine reserves and the mitigation of species invasions. Here we compare estimates of real particle dispersion in a coastal marine environment with similar estimates provided by hydrodynamic modelling. We do so by using a system of magnetically attractive particles (MAPs) and a magnetic-collector array that provides measures of Lagrangian dispersion based on the time-integration of MAPs dispersing through the array. MAPs released as a point source in a coastal marine location dispersed through the collector array over a 5-7 d period. A virtual release and observed (real-time) environmental conditions were used in a high-resolution three-dimensional hydrodynamic model to estimate the dispersal of virtual particles (VPs). The number of MAPs captured throughout the collector array and the number of VPs that passed through each corresponding model location were enumerated and compared. Although VP dispersal reflected several aspects of the observed MAP dispersal, the comparisons demonstrated model sensitivity to the small-scale (random-walk) particle diffusivity parameter (Kp). The one-dimensional dispersal kernel for the MAPs had an e-folding scale estimate in the range of 5.19-11.44 km, while those from the model simulations were comparable at 1.89-6.52 km, and also demonstrated sensitivity to Kp. Variations among comparisons are related to the value of Kp used in modelling and are postulated to be related to MAP losses from the water column and (or) shear dispersion acting on the MAPs; a process that is constrained in the model. Our demonstration indicates a promising new way of 1) quantitatively and empirically estimating the dispersal kernel in aquatic systems, and 2) quantitatively assessing and (or) improving regional hydrodynamic
Hydrodynamics of Peristaltic Propulsion
NASA Astrophysics Data System (ADS)
Athanassiadis, Athanasios; Hart, Douglas
2014-11-01
A curious class of animals called salps live in marine environments and self-propel by ejecting vortex rings much like jellyfish and squid. However, unlike other jetting creatures that siphon and eject water from one side of their body, salps produce vortex rings by pumping water through siphons on opposite ends of their hollow cylindrical bodies. In the simplest cases, it seems like some species of salp can successfully move by contracting just two siphons connected by an elastic body. When thought of as a chain of timed contractions, salp propulsion is reminiscent of peristaltic pumping applied to marine locomotion. Inspired by salps, we investigate the hydrodynamics of peristaltic propulsion, focusing on the scaling relationships that determine flow rate, thrust production, and energy usage in a model system. We discuss possible actuation methods for a model peristaltic vehicle, considering both the material and geometrical requirements for such a system.
Synchronization and hydrodynamic interactions
NASA Astrophysics Data System (ADS)
Powers, Thomas; Qian, Bian; Breuer, Kenneth
2008-03-01
Cilia and flagella commonly beat in a coordinated manner. Examples include the flagella that Volvox colonies use to move, the cilia that sweep foreign particles up out of the human airway, and the nodal cilia that set up the flow that determines the left-right axis in developing vertebrate embryos. In this talk we present an experimental study of how hydrodynamic interactions can lead to coordination in a simple idealized system: two nearby paddles driven with fixed torques in a highly viscous fluid. The paddles attain a synchronized state in which they rotate together with a phase difference of 90 degrees. We discuss how synchronization depends on system parameters and present numerical calculations using the method of regularized stokeslets.
Hydrodynamics, resurgence, and transasymptotics
NASA Astrophysics Data System (ADS)
Başar, Gökçe; Dunne, Gerald V.
2015-12-01
The second order hydrodynamical description of a homogeneous conformal plasma that undergoes a boost-invariant expansion is given by a single nonlinear ordinary differential equation, whose resurgent asymptotic properties we study, developing further the recent work of Heller and Spalinski [Phys. Rev. Lett. 115, 072501 (2015)]. Resurgence clearly identifies the nonhydrodynamic modes that are exponentially suppressed at late times, analogous to the quasinormal modes in gravitational language, organizing these modes in terms of a trans-series expansion. These modes are analogs of instantons in semiclassical expansions, where the damping rate plays the role of the instanton action. We show that this system displays the generic features of resurgence, with explicit quantitative relations between the fluctuations about different orders of these nonhydrodynamic modes. The imaginary part of the trans-series parameter is identified with the Stokes constant, and the real part with the freedom associated with initial conditions.
Hydrodynamic effects on coalescence.
Dimiduk, Thomas G.; Bourdon, Christopher Jay; Grillet, Anne Mary; Baer, Thomas A.; de Boer, Maarten Pieter; Loewenberg, Michael; Gorby, Allen D.; Brooks, Carlton, F.
2006-10-01
The goal of this project was to design, build and test novel diagnostics to probe the effect of hydrodynamic forces on coalescence dynamics. Our investigation focused on how a drop coalesces onto a flat surface which is analogous to two drops coalescing, but more amenable to precise experimental measurements. We designed and built a flow cell to create an axisymmetric compression flow which brings a drop onto a flat surface. A computer-controlled system manipulates the flow to steer the drop and maintain a symmetric flow. Particle image velocimetry was performed to confirm that the control system was delivering a well conditioned flow. To examine the dynamics of the coalescence, we implemented an interferometry capability to measure the drainage of the thin film between the drop and the surface during the coalescence process. A semi-automated analysis routine was developed which converts the dynamic interferogram series into drop shape evolution data.
Consequences of dispersal heterogeneity for population spread and persistence.
Stover, Joseph P; Kendall, Bruce E; Nisbet, Roger M
2014-11-01
Dispersal heterogeneity is increasingly being observed in ecological populations and has long been suspected as an explanation for observations of non-Gaussian dispersal. Recent empirical and theoretical studies have begun to confirm this. Using an integro-difference model, we allow an individual's diffusivity to be drawn from a trait distribution and derive a general relationship between the dispersal kernel's moments and those of the underlying heterogeneous trait distribution. We show that dispersal heterogeneity causes dispersal kernels to appear leptokurtic, increases the population's spread rate, and lowers the critical reproductive rate required for persistence in the face of advection. Wavespeed has been shown previously to be determined largely by the form of the dispersal kernel tail. We qualify this by showing that when reproduction is low, the precise shape of the tail is less important than the first few dispersal moments such as variance and kurtosis. If the reproductive rate is large, a dispersal kernel's asymptotic tail has a greater influence over wavespeed, implying that estimating the prevalence of traits which correlate with long-range dispersal is critical. The presence of multiple dispersal behaviors has previously been characterized in terms of long-range versus short-range dispersal, and it has been found that rare long-range dispersal essentially determines wavespeed. We discuss this finding and place it within a general context of dispersal heterogeneity showing that the dispersal behavior with the highest average dispersal distance does not always determine wavespeed.
Hydrodynamics of sediment threshold
NASA Astrophysics Data System (ADS)
Ali, Sk Zeeshan; Dey, Subhasish
2016-07-01
A novel hydrodynamic model for the threshold of cohesionless sediment particle motion under a steady unidirectional streamflow is presented. The hydrodynamic forces (drag and lift) acting on a solitary sediment particle resting over a closely packed bed formed by the identical sediment particles are the primary motivating forces. The drag force comprises of the form drag and form induced drag. The lift force includes the Saffman lift, Magnus lift, centrifugal lift, and turbulent lift. The points of action of the force system are appropriately obtained, for the first time, from the basics of micro-mechanics. The sediment threshold is envisioned as the rolling mode, which is the plausible mode to initiate a particle motion on the bed. The moment balance of the force system on the solitary particle about the pivoting point of rolling yields the governing equation. The conditions of sediment threshold under the hydraulically smooth, transitional, and rough flow regimes are examined. The effects of velocity fluctuations are addressed by applying the statistical theory of turbulence. This study shows that for a hindrance coefficient of 0.3, the threshold curve (threshold Shields parameter versus shear Reynolds number) has an excellent agreement with the experimental data of uniform sediments. However, most of the experimental data are bounded by the upper and lower limiting threshold curves, corresponding to the hindrance coefficients of 0.2 and 0.4, respectively. The threshold curve of this study is compared with those of previous researchers. The present model also agrees satisfactorily with the experimental data of nonuniform sediments.
Hydrodynamics and sediment transport in a southeast Florida tidal inlet
Fiechter, Jerome; Steffen, Kelley L.; Mooers, Christopher N.K.; Haus, Brian K.
2009-01-01
A three-dimensional ocean circulation model is used to investigate the hydrodynamics of a tidal inlet and deltas system in Southeast Florida, and to understand the consequences for suspended and bedload sediment transport patterns. The model reproduces observed tidal currents and provides insight about residual currents caused by spatial asymmetries in the inlet throat and tidal deltas during ebb and flood flows. A particle-tracking approach for suspended and bedload sediment transport is used to simulate deposition patterns for different particle sizes. The simulation results qualitatively correlate with the distribution of sediment characteristics within the tidal inlet and deltas system and demonstrate sensitivity to the choice of advection velocities (e.g., near-bottom versus depth-averaged) and regions of sediment origin. Furthermore, the distinction between suspended and bedload transport as a function of particle size indicates significant differences in deposition patterns and their potential connection to geomorphologic features of the tidal inlet and deltas system. PMID:19838314
The role of phase dynamics in a stochastic model of a passively advected scalar
NASA Astrophysics Data System (ADS)
Moradi, Sara; Anderson, Johan
2016-05-01
Collective synchronous motion of the phases is introduced in a model for the stochastic passive advection-diffusion of a scalar with external forcing. The model for the phase coupling dynamics follows the well known Kuramoto model paradigm of limit-cycle oscillators. The natural frequencies in the Kuramoto model are assumed to obey a given scale dependence through a dispersion relation of the drift-wave form -βk/1 +k2 , where β is a constant representing the typical strength of the gradient. The present aim is to study the importance of collective phase dynamics on the characteristic time evolution of the fluctuation energy and the formation of coherent structures. Our results show that the assumption of a fully stochastic phase state of turbulence is more relevant for high values of β, where we find that the energy spectrum follows a k-7 /2 scaling. Whereas for lower β there is a significant difference between a-synchronised and synchronised phase states, one could expect the formation of coherent modulations in the latter case.
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.
CASTRO: A NEW COMPRESSIBLE ASTROPHYSICAL SOLVER. III. MULTIGROUP RADIATION HYDRODYNAMICS
Zhang, W.; Almgren, A.; Bell, J.; Howell, L.; Burrows, A.; Dolence, J.
2013-01-15
We present a formulation for multigroup radiation hydrodynamics that is correct to order O(v/c) using the comoving-frame approach and the flux-limited diffusion approximation. We describe a numerical algorithm for solving the system, implemented in the compressible astrophysics code, CASTRO. CASTRO uses a Eulerian grid with block-structured adaptive mesh refinement based on a nested hierarchy of logically rectangular variable-sized grids with simultaneous refinement in both space and time. In our multigroup radiation solver, the system is split into three parts: one part that couples the radiation and fluid in a hyperbolic subsystem, another part that advects the radiation in frequency space, and a parabolic part that evolves radiation diffusion and source-sink terms. The hyperbolic subsystem and the frequency space advection are solved explicitly with high-order Godunov schemes, whereas the parabolic part is solved implicitly with a first-order backward Euler method. Our multigroup radiation solver works for both neutrino and photon radiation.
CASTRO: A New Compressible Astrophysical Solver. III. Multigroup Radiation Hydrodynamics
NASA Astrophysics Data System (ADS)
Zhang, W.; Howell, L.; Almgren, A.; Burrows, A.; Dolence, J.; Bell, J.
2013-01-01
We present a formulation for multigroup radiation hydrodynamics that is correct to order O(v/c) using the comoving-frame approach and the flux-limited diffusion approximation. We describe a numerical algorithm for solving the system, implemented in the compressible astrophysics code, CASTRO. CASTRO uses a Eulerian grid with block-structured adaptive mesh refinement based on a nested hierarchy of logically rectangular variable-sized grids with simultaneous refinement in both space and time. In our multigroup radiation solver, the system is split into three parts: one part that couples the radiation and fluid in a hyperbolic subsystem, another part that advects the radiation in frequency space, and a parabolic part that evolves radiation diffusion and source-sink terms. The hyperbolic subsystem and the frequency space advection are solved explicitly with high-order Godunov schemes, whereas the parabolic part is solved implicitly with a first-order backward Euler method. Our multigroup radiation solver works for both neutrino and photon radiation.
Non-parabolic hydrodynamic formulations for the simulation of inhomogeneous semiconductor devices
NASA Technical Reports Server (NTRS)
Smith, Arlynn W.; Brennan, Kevin F.
1995-01-01
Hydrodynamic models are becoming prevalent design tools for small scale devices and other devices in which high energy effects can dominate transport. Most current hydrodynamic models use a parabolic band approximation to obtain fairly simple conservation equations. Interest in accounting for band structure effects in hydrodynamic device simulation has begun to grow since parabolic models can not fully describe the transport in state of the art devices due to the distribution populating non-parabolic states within the band. This paper presents two different non-parabolic formulations of the hydrodynamic model suitable for the simulation of inhomogeneous semiconductor devices. The first formulation uses the Kane dispersion relationship (hk)(exp 2)/2m = W(1 + alpha(W)). The second formulation makes use of a power law ((hk)(exp 2)/2m = xW(sup y)) for the dispersion relation. Hydrodynamic models which use the first formulation rely on the binomial expansion to obtain moment equations with closed form coefficients. This limits the energy range over which the model is valid. The power law formulation readily produces closed form coefficients similar to those obtained using the parabolic band approximation. However, the fitting parameters (x,y) are only valid over a limited energy range. The physical significance of the band non-parabolicity is discussed as well as the advantages/disadvantages and approximations of the two non-parabolic models. A companion paper describes device simulations based on the three dispersion relationships: parabolic, Kane dispersion, and power low dispersion.
Non-Parabolic Hydrodynamic Formulations for the Simulation of Inhomogeneous Semiconductor Devices
NASA Technical Reports Server (NTRS)
Smith, A. W.; Brennan, K. F.
1996-01-01
Hydrodynamic models are becoming prevalent design tools for small scale devices and other devices in which high energy effects can dominate transport. Most current hydrodynamic models use a parabolic band approximation to obtain fairly simple conservation equations. Interest in accounting for band structure effects in hydrodynamic device simulation has begun to grow since parabolic models cannot fully describe the transport in state of the art devices due to the distribution populating non-parabolic states within the band. This paper presents two different non-parabolic formulations or the hydrodynamic model suitable for the simulation of inhomogeneous semiconductor devices. The first formulation uses the Kane dispersion relationship ((hk)(exp 2)/2m = W(1 + alphaW). The second formulation makes use of a power law ((hk)(exp 2)/2m = xW(exp y)) for the dispersion relation. Hydrodynamic models which use the first formulation rely on the binomial expansion to obtain moment equations with closed form coefficients. This limits the energy range over which the model is valid. The power law formulation readily produces closed form coefficients similar to those obtained using the parabolic band approximation. However, the fitting parameters (x,y) are only valid over a limited energy range. The physical significance of the band non-parabolicity is discussed as well as the advantages/disadvantages and approximations of the two non-parabolic models. A companion paper describes device simulations based on the three dispersion relationships; parabolic, Kane dispersion and power law dispersion.
Antonov, N V; Gulitskiy, N M
2015-10-01
In this work we study the generalization of the problem considered in [Phys. Rev. E 91, 013002 (2015)] to the case of finite correlation time of the environment (velocity) field. The model describes a vector (e.g., magnetic) field, passively advected by a strongly anisotropic turbulent flow. Inertial-range asymptotic behavior is studied by means of the field theoretic renormalization group and the operator product expansion. The advecting velocity field is Gaussian, with finite correlation time and preassigned pair correlation function. Due to the presence of distinguished direction n, all the multiloop diagrams in this model vanish, so that the results obtained are exact. The inertial-range behavior of the model is described by two regimes (the limits of vanishing or infinite correlation time) that correspond to the two nontrivial fixed points of the RG equations. Their stability depends on the relation between the exponents in the energy spectrum E∝k(⊥)(1-ξ) and the dispersion law ω∝k(⊥)(2-η). In contrast to the well-known isotropic Kraichnan's model, where various correlation functions exhibit anomalous scaling behavior with infinite sets of anomalous exponents, here the corrections to ordinary scaling are polynomials of logarithms of the integral turbulence scale L. PMID:26565343
Antonov, N V; Gulitskiy, N M
2015-10-01
In this work we study the generalization of the problem considered in [Phys. Rev. E 91, 013002 (2015)] to the case of finite correlation time of the environment (velocity) field. The model describes a vector (e.g., magnetic) field, passively advected by a strongly anisotropic turbulent flow. Inertial-range asymptotic behavior is studied by means of the field theoretic renormalization group and the operator product expansion. The advecting velocity field is Gaussian, with finite correlation time and preassigned pair correlation function. Due to the presence of distinguished direction n, all the multiloop diagrams in this model vanish, so that the results obtained are exact. The inertial-range behavior of the model is described by two regimes (the limits of vanishing or infinite correlation time) that correspond to the two nontrivial fixed points of the RG equations. Their stability depends on the relation between the exponents in the energy spectrum E∝k(⊥)(1-ξ) and the dispersion law ω∝k(⊥)(2-η). In contrast to the well-known isotropic Kraichnan's model, where various correlation functions exhibit anomalous scaling behavior with infinite sets of anomalous exponents, here the corrections to ordinary scaling are polynomials of logarithms of the integral turbulence scale L.
A point-centered arbitrary Lagrangian Eulerian hydrodynamic approach for tetrahedral meshes
Morgan, Nathaniel R.; Waltz, Jacob I.; Burton, Donald E.; Charest, Marc R.; Canfield, Thomas R.; Wohlbier, John G.
2015-02-24
We present a three dimensional (3D) arbitrary Lagrangian Eulerian (ALE) hydrodynamic scheme suitable for modeling complex compressible flows on tetrahedral meshes. The new approach stores the conserved variables (mass, momentum, and total energy) at the nodes of the mesh and solves the conservation equations on a control volume surrounding the point. This type of an approach is termed a point-centered hydrodynamic (PCH) method. The conservation equations are discretized using an edge-based finite element (FE) approach with linear basis functions. All fluxes in the new approach are calculated at the center of each tetrahedron. A multidirectional Riemann-like problem is solved at the center of the tetrahedron. The advective fluxes are calculated by solving a 1D Riemann problem on each face of the nodal control volume. A 2-stage Runge–Kutta method is used to evolve the solution forward in time, where the advective fluxes are part of the temporal integration. The mesh velocity is smoothed by solving a Laplacian equation. The details of the new ALE hydrodynamic scheme are discussed. Results from a range of numerical test problems are presented.
A point-centered arbitrary Lagrangian Eulerian hydrodynamic approach for tetrahedral meshes
Morgan, Nathaniel R.; Waltz, Jacob I.; Burton, Donald E.; Charest, Marc R.; Canfield, Thomas R.; Wohlbier, John G.
2015-02-24
We present a three dimensional (3D) arbitrary Lagrangian Eulerian (ALE) hydrodynamic scheme suitable for modeling complex compressible flows on tetrahedral meshes. The new approach stores the conserved variables (mass, momentum, and total energy) at the nodes of the mesh and solves the conservation equations on a control volume surrounding the point. This type of an approach is termed a point-centered hydrodynamic (PCH) method. The conservation equations are discretized using an edge-based finite element (FE) approach with linear basis functions. All fluxes in the new approach are calculated at the center of each tetrahedron. A multidirectional Riemann-like problem is solved atmore » the center of the tetrahedron. The advective fluxes are calculated by solving a 1D Riemann problem on each face of the nodal control volume. A 2-stage Runge–Kutta method is used to evolve the solution forward in time, where the advective fluxes are part of the temporal integration. The mesh velocity is smoothed by solving a Laplacian equation. The details of the new ALE hydrodynamic scheme are discussed. Results from a range of numerical test problems are presented.« less
Role of Brownian Motion Hydrodynamics on Nanofluid Thermal Conductivity
W Evans, J Fish, P Keblinski
2005-11-14
We use a simple kinetic theory based analysis of heat flow in fluid suspensions of solid nanoparticles (nanofluids) to demonstrate that the hydrodynamics effects associated with Brownian motion have a minor effect on the thermal conductivity of the nanofluid. Our conjecture is supported by the results of molecular dynamics simulations of heat flow in a model nanofluid with well-dispersed particles. Our findings are consistent with the predictions of the effective medium theory as well as with recent experimental results on well dispersed metal nanoparticle suspensions.
Recent development of hydrodynamic modeling
NASA Astrophysics Data System (ADS)
Hirano, Tetsufumi
2014-09-01
In this talk, I give an overview of recent development in hydrodynamic modeling of high-energy nuclear collisions. First, I briefly discuss about current situation of hydrodynamic modeling by showing results from the integrated dynamical approach in which Monte-Carlo calculation of initial conditions, quark-gluon fluid dynamics and hadronic cascading are combined. In particular, I focus on rescattering effects of strange hadrons on final observables. Next I highlight three topics in recent development in hydrodynamic modeling. These include (1) medium response to jet propagation in di-jet asymmetric events, (2) causal hydrodynamic fluctuation and its application to Bjorken expansion and (3) chiral magnetic wave from anomalous hydrodynamic simulations. (1) Recent CMS data suggest the existence of QGP response to propagation of jets. To investigate this phenomenon, we solve hydrodynamic equations with source term which exhibits deposition of energy and momentum from jets. We find a large number of low momentum particles are emitted at large angle from jet axis. This gives a novel interpretation of the CMS data. (2) It has been claimed that a matter created even in p-p/p-A collisions may behave like a fluid. However, fluctuation effects would be important in such a small system. We formulate relativistic fluctuating hydrodynamics and apply it to Bjorken expansion. We found the final multiplicity fluctuates around the mean value even if initial condition is fixed. This effect is relatively important in peripheral A-A collisions and p-p/p-A collisions. (3) Anomalous transport of the quark-gluon fluid is predicted when extremely high magnetic field is applied. We investigate this possibility by solving anomalous hydrodynamic equations. We found the difference of the elliptic flow parameter between positive and negative particles appears due to the chiral magnetic wave. Finally, I provide some personal perspective of hydrodynamic modeling of high energy nuclear collisions
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.
Constraining relativistic viscous hydrodynamical evolution
Martinez, Mauricio; Strickland, Michael
2009-04-15
We show that by requiring positivity of the longitudinal pressure it is possible to constrain the initial conditions one can use in second-order viscous hydrodynamical simulations of ultrarelativistic heavy-ion collisions. We demonstrate this explicitly for (0+1)-dimensional viscous hydrodynamics and discuss how the constraint extends to higher dimensions. Additionally, we present an analytic approximation to the solution of (0+1)-dimensional second-order viscous hydrodynamical evolution equations appropriate to describe the evolution of matter in an ultrarelativistic heavy-ion collision.
Comparison of Non-Parabolic Hydrodynamic Simulations for Semiconductor Devices
NASA Technical Reports Server (NTRS)
Smith, A. W.; Brennan, K. F.
1996-01-01
Parabolic drift-diffusion simulators are common engineering level design tools for semiconductor devices. Hydrodynamic simulators, based on the parabolic band approximation, are becoming more prevalent as device dimensions shrink and energy transport effects begin to dominate device characteristic. However, band structure effects present in state-of-the-art devices necessitate relaxing the parabolic band approximation. This paper presents simulations of ballistic diodes, a benchmark device, of Si and GaAs using two different non-parabolic hydrodynamic formulations. The first formulation uses the Kane dispersion relationship in the derivation of the conservation equations. The second model uses a power law dispersion relation {(hk)(exp 2)/2m = xW(exp Y)}. Current-voltage relations show that for the ballistic diodes considered. the non-parabolic formulations predict less current than the parabolic case. Explanations of this will be provided by examination of velocity and energy profiles. At low bias, the simulations based on the Kane formulation predict greater current flow than the power law formulation. As the bias is increased this trend changes and the power law predicts greater current than the Kane formulation. It will be shown that the non-parabolicity and energy range of the hydrodynamic model based on the Kane dispersion relation are limited due to the binomial approximation which was utilized in the derivation.
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.
NASA Astrophysics Data System (ADS)
Takahashi, R.; Matsuo, M.; Ono, M.; Harii, K.; Chudo, H.; Okayasu, S.; Ieda, J.; Takahashi, S.; Maekawa, S.; Saitoh, E.
2016-01-01
Magnetohydrodynamic generation is the conversion of fluid kinetic energy into electricity. Such conversion, which has been applied to various types of electric power generation, is driven by the Lorentz force acting on charged particles and thus a magnetic field is necessary. On the other hand, recent studies of spintronics have revealed the similarity between the function of a magnetic field and that of spin-orbit interactions in condensed matter. This suggests the existence of an undiscovered route to realize the conversion of fluid dynamics into electricity without using magnetic fields. Here we show electric voltage generation from fluid dynamics free from magnetic fields; we excited liquid-metal flows in a narrow channel and observed longitudinal voltage generation in the liquid. This voltage has nothing to do with electrification or thermoelectric effects, but turned out to follow a universal scaling rule based on a spin-mediated scenario. The result shows that the observed voltage is caused by spin-current generation from a fluid motion: spin hydrodynamic generation. The observed phenomenon allows us to make mechanical spin-current and electric generators, opening a door to fluid spintronics.
Hydrodynamics of micropipette aspiration.
Drury, J L; Dembo, M
1999-01-01
The dynamics of human neutrophils during micropipette aspiration are frequently analyzed by approximating these cells as simple slippery droplets of viscous fluid. Here, we present computations that reveal the detailed predictions of the simplest and most idealized case of such a scheme; namely, the case where the fluid of the droplet is homogeneous and Newtonian, and the surface tension of the droplet is constant. We have investigated the behavior of this model as a function of surface tension, droplet radius, viscosity, aspiration pressure, and pipette radius. In addition, we have tabulated a dimensionless factor, M, which can be utilized to calculate the apparent viscosity of the slippery droplet. Computations were carried out using a low Reynolds number hydrodynamics transport code based on the finite-element method. Although idealized and simplistic, we find that the slippery droplet model predicts many observed features of neutrophil aspiration. However, there are certain features that are not observed in neutrophils. In particular, the model predicts dilation of the membrane past the point of being continuous, as well as a reentrant jet at high aspiration pressures. PMID:9876128
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.
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.
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.
Hydrodynamic synchronization of colloidal oscillators
Kotar, Jurij; Leoni, Marco; Bassetti, Bruno; Lagomarsino, Marco Cosentino; Cicuta, Pietro
2010-01-01
Two colloidal spheres are maintained in oscillation by switching the position of an optical trap when a sphere reaches a limit position, leading to oscillations that are bounded in amplitude but free in phase and period. The interaction between the oscillators is only through the hydrodynamic flow induced by their motion. We prove that in the absence of stochastic noise the antiphase dynamical state is stable, and we show how the period depends on coupling strength. Both features are observed experimentally. As the natural frequencies of the oscillators are made progressively different, the coordination is quickly lost. These results help one to understand the origin of hydrodynamic synchronization and how the dynamics can be tuned. Cilia and flagella are biological systems coupled hydrodynamically, exhibiting dramatic collective motions. We propose that weakly correlated phase fluctuations, with one of the oscillators typically precessing the other, are characteristic of hydrodynamically coupled systems in the presence of thermal noise. PMID:20385848
Reciprocal relations in dissipationless hydrodynamics
Melnikovsky, L. A.
2014-12-15
Hidden symmetry in dissipationless terms of arbitrary hydrodynamics equations is recognized. We demonstrate that all fluxes are generated by a single function and derive conventional Euler equations using the proposed formalism.
Relativistic hydrodynamics on graphic cards
NASA Astrophysics Data System (ADS)
Gerhard, Jochen; Lindenstruth, Volker; Bleicher, Marcus
2013-02-01
We show how to accelerate relativistic hydrodynamics simulations using graphic cards (graphic processing units, GPUs). These improvements are of highest relevance e.g. to the field of high-energetic nucleus-nucleus collisions at RHIC and LHC where (ideal and dissipative) relativistic hydrodynamics is used to calculate the evolution of hot and dense QCD matter. The results reported here are based on the Sharp And Smooth Transport Algorithm (SHASTA), which is employed in many hydrodynamical models and hybrid simulation packages, e.g. the Ultrarelativistic Quantum Molecular Dynamics model (UrQMD). We have redesigned the SHASTA using the OpenCL computing framework to work on accelerators like graphic processing units (GPUs) as well as on multi-core processors. With the redesign of the algorithm the hydrodynamic calculations have been accelerated by a factor 160 allowing for event-by-event calculations and better statistics in hybrid calculations.
Hydrodynamic escape from planetary atmospheres
NASA Astrophysics Data System (ADS)
Tian, Feng
Hydrodynamic escape is an important process in the formation and evolution of planetary atmospheres. Due to the existence of a singularity point near the transonic point, it is difficult to find transonic steady state solutions by solving the time-independent hydrodynamic equations. In addition to that, most previous works assume that all energy driving the escape flow is deposited in one narrow layer. This assumption not only results in less accurate solutions to the hydrodynamic escape problem, but also makes it difficult to include other chemical and physical processes in the hydrodynamic escape models. In this work, a numerical model describing the transonic hydrodynamic escape from planetary atmospheres is developed. A robust solution technique is used to solve the time dependent hydrodynamic equations. The method has been validated in an isothermal atmosphere where an analytical solution is available. The hydrodynamic model is applied to 3 cases: hydrogen escape from small orbit extrasolar planets, hydrogen escape from a hydrogen rich early Earth's atmosphere, and nitrogen/methane escape from Pluto's atmosphere. Results of simulations on extrasolar planets are in good agreement with the observations of the transiting extrasolar planet HD209458b. Hydrodynamic escape of hydrogen from other hypothetical close-in extrasolar planets are simulated and the influence of hydrogen escape on the long-term evolution of these extrasolar planets are discussed. Simulations on early Earth suggest that hydrodynamic escape of hydrogen from a hydrogen rich early Earth's atmosphere is about two orders magnitude slower than the diffusion limited escape rate. A hydrogen rich early Earth's atmosphere could have been maintained by the balance between the hydrogen escape and the supply of hydrogen into the atmosphere by volcanic outgassing. Origin of life may have occurred in the organic soup ocean created by the efficient formation of prebiotic molecules in the hydrogen rich early
ERIC Educational Resources Information Center
Budiansky, Stephen
1980-01-01
This article discusses the need for more accurate and complete input data and field verification of the various models of air pollutant dispension. Consideration should be given to changing the form of air quality standards based on enhanced dispersion modeling techniques. (Author/RE)
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
Delayed shear enhancement in mesoscale atmospheric dispersion
Moran, M.D.; Pielke, R.A.
1994-12-31
Mesoscale atmospheric dispersion (MAD) is more complicated than smaller-scale dispersion because the mean wind field can no longer be considered steady or horizontally homogeneous over mesoscale time and space scales. Wind shear also plays a much more important role on the mesoscale: horizontal dispersion can be enhanced and often dominated by vertical wind shear on these scales through the interaction of horizontal differential advection and vertical mixing. Just over 30 years ago, Pasquill suggested that this interaction need not be simultaneous and that the combination of differential horizontal advection with delayed or subsequent vertical mixing could maintain effective horizontal diffusion in spite of temporal or spatial reductions in boundary-layer turbulence intensity. This two-step mechanism has not received much attention since then, but a recent analysis of observations from and numerical simulations of two mesoscale tracer experiments suggests that delayed shear enhancement can play an important role in MAD. This paper presents an overview of this analysis, with particular emphasis on the influence of resolvable vertical shear on MAD in these two case studies and the contributions made by delayed shear enhancement.
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.
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.
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
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
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
A moving frame algorithm for high Mach number hydrodynamics
NASA Astrophysics Data System (ADS)
Trac, Hy; Pen, Ue-Li
2004-07-01
We present a new approach to Eulerian computational fluid dynamics that is designed to work at high Mach numbers encountered in astrophysical hydrodynamic simulations. Standard Eulerian schemes that strictly conserve total energy suffer from the high Mach number problem and proposed solutions to additionally solve the entropy or thermal energy still have their limitations. In our approach, the Eulerian conservation equations are solved in an adaptive frame moving with the fluid where Mach numbers are minimized. The moving frame approach uses a velocity decomposition technique to define local kinetic variables while storing the bulk kinetic components in a smoothed background velocity field that is associated with the grid velocity. Gravitationally induced accelerations are added to the grid, thereby minimizing the spurious heating problem encountered in cold gas flows. Separately tracking local and bulk flow components allows thermodynamic variables to be accurately calculated in both subsonic and supersonic regions. A main feature of the algorithm, that is not possible in previous Eulerian implementations, is the ability to resolve shocks and prevent spurious heating where both the pre-shock and post-shock fluid are supersonic. The hybrid algorithm combines the high-resolution shock capturing ability of the second-order accurate Eulerian TVD scheme with a low-diffusion Lagrangian advection scheme. We have implemented a cosmological code where the hydrodynamic evolution of the baryons is captured using the moving frame algorithm while the gravitational evolution of the collisionless dark matter is tracked using a particle-mesh N-body algorithm. Hydrodynamic and cosmological tests are described and results presented. The current code is fast, memory-friendly, and parallelized for shared-memory machines.
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.
Low Mach number fluctuating hydrodynamics of multispecies liquid mixtures
Donev, Aleksandar Bhattacharjee, Amit Kumar; Nonaka, Andy; Bell, John B.; Garcia, Alejandro L.
2015-03-15
We develop a low Mach number formulation of the hydrodynamic equations describing transport of mass and momentum in a multispecies mixture of incompressible miscible liquids at specified temperature and pressure, which generalizes our prior work on ideal mixtures of ideal gases [Balakrishnan et al., “Fluctuating hydrodynamics of multispecies nonreactive mixtures,” Phys. Rev. E 89 013017 (2014)] and binary liquid mixtures [Donev et al., “Low mach number fluctuating hydrodynamics of diffusively mixing fluids,” Commun. Appl. Math. Comput. Sci. 9(1), 47-105 (2014)]. In this formulation, we combine and extend a number of existing descriptions of multispecies transport available in the literature. The formulation applies to non-ideal mixtures of arbitrary number of species, without the need to single out a “solvent” species, and includes contributions to the diffusive mass flux due to gradients of composition, temperature, and pressure. Momentum transport and advective mass transport are handled using a low Mach number approach that eliminates fast sound waves (pressure fluctuations) from the full compressible system of equations and leads to a quasi-incompressible formulation. Thermal fluctuations are included in our fluctuating hydrodynamics description following the principles of nonequilibrium thermodynamics. We extend the semi-implicit staggered-grid finite-volume numerical method developed in our prior work on binary liquid mixtures [Nonaka et al., “Low mach number fluctuating hydrodynamics of binary liquid mixtures,” http://arxiv.org/abs/1410.2300 (2015)] and use it to study the development of giant nonequilibrium concentration fluctuations in a ternary mixture subjected to a steady concentration gradient. We also numerically study the development of diffusion-driven gravitational instabilities in a ternary mixture and compare our numerical results to recent experimental measurements [Carballido-Landeira et al., “Mixed-mode instability of a
Hydrodynamic theory of rotating ultracold supersolids
NASA Astrophysics Data System (ADS)
Ghosh, Sankalpa; Sachdeva, Rashi
2014-03-01
Ultra cold atomic condensate with long range interaction is considered as a possible candidate to realize the supersolid phase. Such a supersolid phase can be subjected to artificial gauge field created either through rotation or by introducing space dependent coupling among hyperfine states of the atoms using Raman lasers. Starting from a Gross-Pitaevskii energy functional that describes such systems at zero temprature we construct hydrodynamic theory to describe the low energy long wavelength excitations of such rotating supersolid of weakly interacting ultra cold atoms for generic type of long range interaction. We treat the supersolid within the framework of well known two fluid approximation. We consider such system in the fast rotation limit where a vortex lattice in superfluid coexists with the supersolid lattice and analytically obtain the dispersion relations of collective excitations around this equilibrium state. The dispersion relation suggests a mode splitting due to the existence of two lattices which can be experimentally measured within the current technology. We point out that this can clearly identify such a ultra cold atomic supersolid phase. Ref. Rashi Sachdeva and Sankalpa Ghosh arXiv: 1308.1592 (Cond-Mat) Rashi Sachdev is supported by CSIR Fellowship, SG is supported by PDA grant from IIT Delhi.
Modeling the coupling of reaction kinetics and hydrodynamics in a collapsing cavity
Mishra, Sudib; Deymier, Pierre; Muralidharan, Krishna; Frantziskonis, G.; Pannala, Sreekanth; Simunovic, Srdjan
2010-01-01
We introduce a model of cavitation based on the multiphase Lattice Boltzmann method (LBM) that allows for coupling between the hydrodynamics of a collapsing cavity and supported solute chemical species. We demonstrate that this model can also be coupled to deterministic or stochastic chemical reactions. In a two-species model of chemical reactions (with a major and a minor specie), the major difference observed between the deterministic and stochastic reactions takes the form of random fluctuations in concentration of the minor species. We demonstrate that advection associated with the hydrodynamics of a collapsing cavity leads to highly inhomogeneous concentration of solutes. In turn these inhomogeneities in concentration may lead to significant increase in concentration-dependent reaction rates and can result in a local enhancement in the production of minor species.
Technology Transfer Automated Retrieval System (TEKTRAN)
Because the Surface Energy Balance Algorithm for Land (SEBAL) tends to underestimate ET under conditions of advection, the model was modified by incorporating an advection component as part of the energy usable for crop evapotranspiration (ET). The modification involved the estimation of advected en...
NASA Technical Reports Server (NTRS)
Frost, W.; Christensen, L. S.; Collins, F. G.; Camp, D. W.
1980-01-01
A study of economically viable techniques for dispersing warm fog at commercial airports is presented. Five fog dispersion techniques are examined: evaporation suppression, downwash, mixing, seeding with hygroscopic material, thermal techniques, and charged particle techniques. Thermal techniques, although effective, were found to be too expensive for routine airport operations, and detrimental to the environment. Seeding or helicopter downwash are practical for small-scale or temporary fog clearing, but are probably not useful for airport operations on a routine basis. Considerable disagreement exists on the capability of charged particle techniques, which stems from the fact that different assumptions and parameter values are used in the analytical models. Recommendations resulting from the review of this technique are listed, and include: experimental measurements of the parameters in question; a study to ascertain possible safety hazards, such as increased electrical activity or fuel ignition during refueling operations which could render charged particle techniques impractical; and a study of a single charged particle generator.
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
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
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...
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.
Black brane entropy and hydrodynamics
Booth, Ivan; Heller, Michal P.; Spalinski, Michal
2011-03-15
Recent advances in holography have led to the formulation of fluid-gravity duality, a remarkable connection between the hydrodynamics of certain strongly coupled media and dynamics of higher dimensional black holes. This paper introduces a correspondence between phenomenologically defined entropy currents in relativistic hydrodynamics and 'generalized horizons' of near-equilibrium black objects in a dual gravitational description. A general formula is given, expressing the divergence of the entropy current in terms of geometric objects which appear naturally in the gravity dual geometry. The proposed definition is explicitly covariant with respect to boundary diffeomorphisms and reproduces known results when evaluated for the event horizon.
Abnormal pressures as hydrodynamic phenomena
Neuzil, C.E.
1995-01-01
So-called abnormal pressures, subsurface fluid pressures significantly higher or lower than hydrostatic, have excited speculation about their origin since subsurface exploration first encountered them. Two distinct conceptual models for abnormal pressures have gained currency among earth scientists. The static model sees abnormal pressures generally as relict features preserved by a virtual absence of fluid flow over geologic time. The hydrodynamic model instead envisions abnormal pressures as phenomena in which flow usually plays an important role. This paper develops the theoretical framework for abnormal pressures as hydrodynamic phenomena, shows that it explains the manifold occurrences of abnormal pressures, and examines the implications of this approach. -from Author
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.
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.
CRASH: A BLOCK-ADAPTIVE-MESH CODE FOR RADIATIVE SHOCK HYDRODYNAMICS-IMPLEMENTATION AND VERIFICATION
Van der Holst, B.; Toth, G.; Sokolov, I. V.; Myra, E. S.; Fryxell, B.; Drake, R. P.; Powell, K. G.; Holloway, J. P.; Stout, Q.; Adams, M. L.; Morel, J. E.; Karni, S.
2011-06-01
We describe the Center for Radiative Shock Hydrodynamics (CRASH) code, a block-adaptive-mesh code for multi-material radiation hydrodynamics. The implementation solves the radiation diffusion model with a gray or multi-group method and uses a flux-limited diffusion approximation to recover the free-streaming limit. Electrons and ions are allowed to have different temperatures and we include flux-limited electron heat conduction. The radiation hydrodynamic equations are solved in the Eulerian frame by means of a conservative finite-volume discretization in either one-, two-, or three-dimensional slab geometry or in two-dimensional cylindrical symmetry. An operator-split method is used to solve these equations in three substeps: (1) an explicit step of a shock-capturing hydrodynamic solver; (2) a linear advection of the radiation in frequency-logarithm space; and (3) an implicit solution of the stiff radiation diffusion, heat conduction, and energy exchange. We present a suite of verification test problems to demonstrate the accuracy and performance of the algorithms. The applications are for astrophysics and laboratory astrophysics. The CRASH code is an extension of the Block-Adaptive Tree Solarwind Roe Upwind Scheme (BATS-R-US) code with a new radiation transfer and heat conduction library and equation-of-state and multi-group opacity solvers. Both CRASH and BATS-R-US are part of the publicly available Space Weather Modeling Framework.
Validating hydrodynamic growth in National Ignition Facility implosions
Peterson, J. L. Casey, D. T.; Hurricane, O. A.; Raman, K. S.; Robey, H. F.; Smalyuk, V. A.
2015-05-15
We present new hydrodynamic growth experiments at the National Ignition Facility, which extend previous measurements up to Legendre mode 160 and convergence ratio 4, continuing the growth factor dispersion curve comparison of the low foot and high foot pulses reported by Casey et al. [Phys. Rev. E 90, 011102(R) (2014)]. We show that the high foot pulse has lower growth factor and lower growth rate than the low foot pulse. Using novel on-capsule fiducial markers, we observe that mode 160 inverts sign (changes phase) for the high foot pulse, evidence of amplitude oscillations during the Richtmyer-Meshkov phase of a spherically convergent system. Post-shot simulations are consistent with the experimental measurements for all but the shortest wavelength perturbations, reinforcing the validity of radiation hydrodynamic simulations of ablation front growth in inertial confinement fusion capsules.
Hydrodynamic slip in silicon nanochannels
NASA Astrophysics Data System (ADS)
Ramos-Alvarado, Bladimir; Kumar, Satish; Peterson, G. P.
2016-03-01
Equilibrium and nonequilibrium molecular dynamics simulations were performed to better understand the hydrodynamic behavior of water flowing through silicon nanochannels. The water-silicon interaction potential was calibrated by means of size-independent molecular dynamics simulations of silicon wettability. The wettability of silicon was found to be dependent on the strength of the water-silicon interaction and the structure of the underlying surface. As a result, the anisotropy was found to be an important factor in the wettability of these types of crystalline solids. Using this premise as a fundamental starting point, the hydrodynamic slip in nanoconfined water was characterized using both equilibrium and nonequilibrium calculations of the slip length under low shear rate operating conditions. As was the case for the wettability analysis, the hydrodynamic slip was found to be dependent on the wetted solid surface atomic structure. Additionally, the interfacial water liquid structure was the most significant parameter to describe the hydrodynamic boundary condition. The calibration of the water-silicon interaction potential performed by matching the experimental contact angle of silicon led to the verification of the no-slip condition, experimentally reported for silicon nanochannels at low shear rates.
Topics in fluctuating nonlinear hydrodynamics
Milner, S.T.
1986-01-01
Models of fluctuating nonlinear hydrodynamics have enjoyed much success in explaining the effect of long-wavelength fluctuations in diverse hydrodynamic systems. This thesis explores two such problems; in both, the body of hydrodynamic assumptions powerfully constrains the predictions of a well-posed theory. The effects of layer fluctuations in smectic-A liquid crystals are first examined. The static theory (introduced by Grinstein and Pelcovits) is reviewed. Ward identities, resulting from the arbitrariness of the layering direction, are derived and exploited. The static results motivate an examination of dynamic fluctuation effects. A new sound-damping experiment is proposed that would probe singular dependence of viscosities on applied stress. A theory of Procaccia and Gitterman that reaction rates of chemically reacting binary mixtures are drastically reduced near their thermodynamic critical points is analyzed. Hydrodynamic arguments and Van Hove theory are applied, concluding that the PG idea is drastically slowed, and spatially varying composition fluctuations are at best slowed down over a narrow range of wavenumbers.
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
Diabatic cross-isentropic dispersion in the lower stratosphere
NASA Astrophysics Data System (ADS)
Sparling, L. C.; Kettleborough, J. A.; Haynes, P. H.; McIntyre, M. E.; Rosenfield, J. E.; Schoeberl, M. R.; Newman, P. A.
1997-11-01
A significant contribution to vertical dispersion of tracers in the stratosphere arises from the variability in the diabatic heating of air parcels. Air parcels starting on a given isentropic surface experience different time histories of diabatic heating, which causes vertical dispersion across isentropic surfaces. We refer to this process as "diabatic cross-isentropic dispersion," or "diabatic dispersion" for brevity. The present study investigates diabatic dispersion in the lower stratosphere by computing parcel trajectories initialized uniformly over the 500 K surface on January 1, 1993. Parcels are followed for 2 months using analyzed winds and diabatic heating rates computed from analyzed temperatures. Diabatic dispersion depends on the statistics of the large-scale horizontal eddy motion as well as on the spatial structure of the diabatic heating field. The trajectory statistics suggest that the polar vortex, surf zone, tropics, and extratropical summer hemisphere are, to varying extents, isolated from each other and that the diabatic dispersion within each of these regions is different. In both the surf zone and southern hemisphere extratropics the dispersion is initially advective, with potential temperature variance <δθ(t)2> increasing as t2 as time t increases. After about 1 month, the dispersion becomes diffusive in the sense that <δθ(t)2> ˜2Kθθt and with a diffusivity Kθθ in the range 2-6 K2 d-1, roughly equivalent to Kzz ˜0.1-0.2 m2 s-1. The emergence of a diffusive regime is discussed in terms of loss of memory of diabatic heating along parcel paths, as measured by the decay of the Lagrangian autocorrelation function. Diabatic dispersion within the tropics and polar vortex over the 2-month period is more than an order of magnitude smaller and is less clearly diffusive. The diabatic dispersion of parcels moving poleward out of the tropics into either hemisphere is faster than either differential advection or diffusion, and in this cas <
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.
Jiang, Yan-Fei; Stone, James M.; Davis, Shane W.
2014-12-01
We study super-Eddington accretion flows onto black holes using a global three-dimensional radiation magneto-hydrodynamical simulation. We solve the time-dependent radiative transfer equation for the specific intensities to accurately calculate the angular distribution of the emitted radiation. Turbulence generated by the magneto-rotational instability provides self-consistent angular momentum transfer. The simulation reaches inflow equilibrium with an accretion rate ∼220 L {sub Edd}/c {sup 2} and forms a radiation-driven outflow along the rotation axis. The mechanical energy flux carried by the outflow is ∼20% of the radiative energy flux. The total mass flux lost in the outflow is about 29% of the net accretion rate. The radiative luminosity of this flow is ∼10 L {sub Edd}. This yields a radiative efficiency ∼4.5%, which is comparable to the value in a standard thin disk model. In our simulation, vertical advection of radiation caused by magnetic buoyancy transports energy faster than photon diffusion, allowing a significant fraction of the photons to escape from the surface of the disk before being advected into the black hole. We contrast our results with the lower radiative efficiencies inferred in most models, such as the slim disk model, which neglect vertical advection. Our inferred radiative efficiencies also exceed published results from previous global numerical simulations, which did not attribute a significant role to vertical advection. We briefly discuss the implications for the growth of supermassive black holes in the early universe and describe how these results provided a basis for explaining the spectrum and population statistics of ultraluminous X-ray sources.
NASA Astrophysics Data System (ADS)
Jiang, Yan-Fei; Stone, James M.; Davis, Shane W.
2014-12-01
We study super-Eddington accretion flows onto black holes using a global three-dimensional radiation magneto-hydrodynamical simulation. We solve the time-dependent radiative transfer equation for the specific intensities to accurately calculate the angular distribution of the emitted radiation. Turbulence generated by the magneto-rotational instability provides self-consistent angular momentum transfer. The simulation reaches inflow equilibrium with an accretion rate ~220 L Edd/c 2 and forms a radiation-driven outflow along the rotation axis. The mechanical energy flux carried by the outflow is ~20% of the radiative energy flux. The total mass flux lost in the outflow is about 29% of the net accretion rate. The radiative luminosity of this flow is ~10 L Edd. This yields a radiative efficiency ~4.5%, which is comparable to the value in a standard thin disk model. In our simulation, vertical advection of radiation caused by magnetic buoyancy transports energy faster than photon diffusion, allowing a significant fraction of the photons to escape from the surface of the disk before being advected into the black hole. We contrast our results with the lower radiative efficiencies inferred in most models, such as the slim disk model, which neglect vertical advection. Our inferred radiative efficiencies also exceed published results from previous global numerical simulations, which did not attribute a significant role to vertical advection. We briefly discuss the implications for the growth of supermassive black holes in the early universe and describe how these results provided a basis for explaining the spectrum and population statistics of ultraluminous X-ray sources.
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.
Anomalous hydrodynamics of fractional quantum Hall states
Wiegmann, P.
2013-09-15
We propose a comprehensive framework for quantum hydrodynamics of the fractional quantum Hall (FQH) states. We suggest that the electronic fluid in the FQH regime can be phenomenologically described by the quantized hydrodynamics of vortices in an incompressible rotating liquid. We demonstrate that such hydrodynamics captures all major features of FQH states, including the subtle effect of the Lorentz shear stress. We present a consistent quantization of the hydrodynamics of an incompressible fluid, providing a powerful framework to study the FQH effect and superfluids. We obtain the quantum hydrodynamics of the vortex flow by quantizing the Kirchhoff equations for vortex dynamics.
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.
Hydrodynamic simulations with the Godunov smoothed particle hydrodynamics
NASA Astrophysics Data System (ADS)
Murante, G.; Borgani, S.; Brunino, R.; Cha, S.-H.
2011-10-01
We present results based on an implementation of the Godunov smoothed particle hydrodynamics (GSPH), originally developed by Inutsuka, in the GADGET-3 hydrodynamic code. We first review the derivation of the GSPH discretization of the equations of moment and energy conservation, starting from the convolution of these equations with the interpolating kernel. The two most important aspects of the numerical implementation of these equations are (a) the appearance of fluid velocity and pressure obtained from the solution of the Riemann problem between each pair of particles, and (b) the absence of an artificial viscosity term. We carry out three different controlled hydrodynamical three-dimensional tests, namely the Sod shock tube, the development of Kelvin-Helmholtz instabilities in a shear-flow test and the 'blob' test describing the evolution of a cold cloud moving against a hot wind. The results of our tests confirm and extend in a number of aspects those recently obtained by Cha, Inutsuka & Nayakshin: (i) GSPH provides a much improved description of contact discontinuities, with respect to smoothed particle hydrodynamics (SPH), thus avoiding the appearance of spurious pressure forces; (ii) GSPH is able to follow the development of gas-dynamical instabilities, such as the Kevin-Helmholtz and the Rayleigh-Taylor ones; (iii) as a result, GSPH describes the development of curl structures in the shear-flow test and the dissolution of the cold cloud in the 'blob' test. Besides comparing the results of GSPH with those from standard SPH implementations, we also discuss in detail the effect on the performances of GSPH of changing different aspects of its implementation: choice of the number of neighbours, accuracy of the interpolation procedure to locate the interface between two fluid elements (particles) for the solution of the Riemann problem, order of the reconstruction for the assignment of variables at the interface, choice of the limiter to prevent oscillations of
A preliminary study of the Ria de Aveiro plume dispersal
NASA Astrophysics Data System (ADS)
Mendes, R.; Sousa, M. C.; Vaz, N.; deCastro, M.; Dias, J. M.
2012-04-01
Over the last years several studies have been performed about the hydrodynamic and the water properties transport in the Ria de Aveiro lagoon, but none of them had the focus on the dispersal of the lagoon plume into the adjacent Atlantic Ocean. This buoyant plume injects less dense water in to the ocean during the ebbing, which penetrates onto the coastal zone generating an offshore movement in the surface layer. The structure of the estuarine plume is usually characterized by a buoyant bulge, propagating radially form the lagoon inlet. Its shape depends on several factors: density differences between ocean and estuarine water; bathymetric changes and meteorological parameters variability, in particular of the wind direction and intensity. The main objective of this study is to perform a preliminary study of the Ria de Aveiro estuarine plume, as well as its qualitative assessment during extreme river discharges conditions (maximum and minimum) and also a typical estuarine inflow/outflow value for the Winter (January). A baroclinic finite volume numerical model, MOHID was implemented separately to the Ria de Aveiro and to the adjacent coast. The lagoon application was performed in a 2D mode, and has the purpose of quantifying the flow (and its properties) that the Ria de Aveiro injects into the ocean. The coastal application consisted in a numerical implementation using a three level baroclinic nesting model. The model domain includes the whole Iberian Peninsula using a realistic coastline and bottom topography. Initial ocean stratification and tide are from the MERCATOR solution and FES Global tidal solution, respectively. The hourly lagoon discharge, previously calculated through the model runs of the Ria de Aveiro estuarine model, was imposed in the lagoon mouth location of the coastal application, in order to allow the study of the estuarine plume dynamics. The model results were compared with satellite images, to assess the models performance. For an intense
Hydrodynamics from Landau initial conditions
Sen, Abhisek; Gerhard, Jochen; Torrieri, Giorgio; Read jr, Kenneth F.; Wong, Cheuk-Yin
2015-01-01
We investigate ideal hydrodynamic evolution, with Landau initial conditions, both in a semi-analytical 1+1D approach and in a numerical code incorporating event-by-event variation with many events and transverse density inhomogeneities. The object of the calculation is to test how fast would a Landau initial condition transition to a commonly used boost-invariant expansion. We show that the transition to boost-invariant flow occurs too late for realistic setups, with corrections of O (20 - 30%) expected at freezeout for most scenarios. Moreover, the deviation from boost-invariance is correlated with both transverse flow and elliptic flow, with the more highly transversely flowing regions also showing the most violation of boost invariance. Therefore, if longitudinal flow is not fully developed at the early stages of heavy ion collisions, 2+1 dimensional hydrodynamics is inadequate to extract transport coefficients of the quark-gluon plasma. Based on [1, 2
Algorithm refinement for fluctuating hydrodynamics
Williams, Sarah A.; Bell, John B.; Garcia, Alejandro L.
2007-07-03
This paper introduces an adaptive mesh and algorithmrefinement method for fluctuating hydrodynamics. This particle-continuumhybrid simulates the dynamics of a compressible fluid with thermalfluctuations. The particle algorithm is direct simulation Monte Carlo(DSMC), a molecular-level scheme based on the Boltzmann equation. Thecontinuum algorithm is based on the Landau-Lifshitz Navier-Stokes (LLNS)equations, which incorporate thermal fluctuations into macroscopichydrodynamics by using stochastic fluxes. It uses a recently-developedsolver for LLNS, based on third-order Runge-Kutta. We present numericaltests of systems in and out of equilibrium, including time-dependentsystems, and demonstrate dynamic adaptive refinement by the computationof a moving shock wave. Mean system behavior and second moment statisticsof our simulations match theoretical values and benchmarks well. We findthat particular attention should be paid to the spectrum of the flux atthe interface between the particle and continuum methods, specificallyfor the non-hydrodynamic (kinetic) time scales.
A two-dimensional hydrodynamic model of a tidal estuary
Walters, Roy A.; Cheng, Ralph T.
1979-01-01
A finite element model is described which is used in the computation of tidal currents in an estuary. This numerical model is patterned after an existing algorithm and has been carefully tested in rectangular and curve-sided channels with constant and variable depth. One of the common uncertainties in this class of two-dimensional hydrodynamic models is the treatment of the lateral boundary conditions. Special attention is paid specifically to addressing this problem. To maintain continuity within the domain of interest, ‘smooth’ curve-sided elements must be used at all shoreline boundaries. The present model uses triangular, isoparametric elements with quadratic basis functions for the two velocity components and a linear basis function for water surface elevation. An implicit time integration is used and the model is unconditionally stable. The resultant governing equations are nonlinear owing to the advective and the bottom friction terms and are solved iteratively at each time step by the Newton-Raphson method. Model test runs have been made in the southern portion of San Francisco Bay, California (South Bay) as well as in the Bay west of Carquinez Strait. Owing to the complex bathymetry, the hydrodynamic characteristics of the Bay system are dictated by the generally shallow basins which contain deep, relict river channels. Great care must be exercised to ensure that the conservation equations remain locally as well as globally accurate. Simulations have been made over several representative tidal cycles using this finite element model, and the results compare favourably with existing data. In particular, the standing wave in South Bay and the progressive wave in the northern reach are well represented.
Hydrodynamic waves in an anomalous charged fluid
NASA Astrophysics Data System (ADS)
Abbasi, Navid; Davody, Ali; Hejazi, Kasra; Rezaei, Zahra
2016-11-01
We study the collective excitations in a relativistic fluid with an anomalous U (1) current. In 3 + 1 dimensions at zero chemical potential, in addition to ordinary sound modes we find two propagating modes in presence of an external magnetic field. The first one which is a transverse degenerate mode, propagates with a velocity proportional to the coefficient of gravitational anomaly; this is in fact the Chiral Alfvén wave recently found in [1]. Another one is a wave of density perturbation, namely a chiral magnetic wave (CMW). The velocity dependence of CMW on the chiral anomaly coefficient is well known. We compute the dependence of CMW's velocity on the coefficient of gravitational anomaly as well. We also show that the dissipation splits the degeneracy of CAW. At finite chiral charge density we show that in general there may exist five chiral hydrodynamic waves. Of these five waves, one is the CMW while the other four are mixed Modified Sound-Alfvén waves. It turns out that in propagation transverse to the magnetic field no anomaly effect appears while in parallel to the magnetic field we find sound waves become dispersive due to anomaly.
Dickson, Dionne; Liu, Guangliang; Li, Chenzhong; Tachiev, Georgio; Cai, Yong
2012-03-01
The aggregation and sedimentation of iron oxide nanoparticles (IONPs) can significantly affect the mobility and reactivity of IONPs and subsequently influence the interaction between IONPs and environmental contaminants. Dispersing bare IONPs into a stable suspension within nanoscale range is an important step for studying the interaction of IONPs with contaminants (e.g., toxic metals). In this study, different techniques to disperse bare IONPs (vortex, bath sonication and probe ultrasonication) and the effects of important environmental factors such as dissolved organic matter and ionic strength on the stability of IONPs dispersions were investigated. Vortex minimally dispersed IONPs with hydrodynamic diameter outside the "nano-size range" (698-2400 nm). Similar to vortex, bath sonication could not disperse IONPs efficiently. Probe ultrasonication was more effective at dispersing IONPs (50% or more) with hydrodynamic diameters ranging from 120 to 140 nm with minimal changes in size and sedimentation of IONPs for a prolonged period of time. Over the course of 168 h, considerable amounts of IONPs remained dispersed in the presence and absence of low ionic strength (0.1mM of NaCl) and 100mg/L of humic acid (HA). These results indicate that IONPs can be broken down efficiently into "nanosize range" by probe ultrasonication and a degree of stability can be achieved without the use of synthetic modifiers to enhance colloidal stability. This dispersion tool could be used to develop a laboratory method to study the adsorption mechanism between dispersed bare IONPs and toxic contaminants.
Particle hydrodynamics with tessellation techniques
NASA Astrophysics Data System (ADS)
Heß, Steffen; Springel, Volker
2010-08-01
Lagrangian smoothed particle hydrodynamics (SPH) is a well-established approach to model fluids in astrophysical problems, thanks to its geometric flexibility and ability to automatically adjust the spatial resolution to the clumping of matter. However, a number of recent studies have emphasized inaccuracies of SPH in the treatment of fluid instabilities. The origin of these numerical problems can be traced back to spurious surface effects across contact discontinuities, and to SPH's inherent prevention of mixing at the particle level. We here investigate a new fluid particle model where the density estimate is carried out with the help of an auxiliary mesh constructed as the Voronoi tessellation of the simulation particles instead of an adaptive smoothing kernel. This Voronoi-based approach improves the ability of the scheme to represent sharp contact discontinuities. We show that this eliminates spurious surface tension effects present in SPH and that play a role in suppressing certain fluid instabilities. We find that the new `Voronoi Particle Hydrodynamics' (VPH) described here produces comparable results to SPH in shocks, and better ones in turbulent regimes of pure hydrodynamical simulations. We also discuss formulations of the artificial viscosity needed in this scheme and how judiciously chosen correction forces can be derived in order to maintain a high degree of particle order and hence a regular Voronoi mesh. This is especially helpful in simulating self-gravitating fluids with existing gravity solvers used for N-body simulations.
The Gulf of Lions' hydrodynamics
NASA Astrophysics Data System (ADS)
Millot, Claude
1990-09-01
From an hydrodynamical point of view, the Gulf of Lions can be considered as a very complex region, because several intense and highly variable phenomena compete simultaneously. These processes include the powerful general circulation along the continental slope, the formation of dense water both on the shelf and offshore, a seasonal variation of stratification and the extreme energies associated with meteorological conditions. The cloudless atmospheric conditions encountered generally in the northwestern Mediterranean Sea have enabled us to make use of, over more than 10 years, large use of various satellite imageries. The large space and time variability of the hydrodynamical features, a complex topography and a noticeable fishing activity, represent certain difficulties to the collection of observations in situ. We have obtained, therefore, only a few current time series on the slope; those obtained on the shelf only cover the summer period. Models have been elaborated to help us understand the reasons for the general circulation. Observational programmes to be carried out in the forthcoming years will probably provide us with more definitive results on the Gulf of Lions' hydrodynamics.
Hydrodynamics of Shark Bay, Western Australia: Implications for Population Dynamics of Snapper.
NASA Astrophysics Data System (ADS)
Nahas, E. L.; Jackson, G.; Pattiaratchi, C. B.; Ivey, G. N.
2001-12-01
Field data and hydrodynamic modeling were used to examine the dynamics of Shark Bay, a large inverse estuary in Western Australia. Work was focused on the hydrodynamic factors influencing snapper - a fish important to both commercial and recreational fisheries in the region. Shark Bay is a large coastal embayment, with inverse estuarine features, shallow waters, and the relatively warm Leeuwin current running along its seaward boundary. Other important physical influences include highly seasonal winds, with snapper spawning occurring in winter months when winds are low in magnitude and variable in direction. Density contours from fieldwork showed a vertically mixed system, implying a dominance of horizontal diffusive transport and therefore low volume or exchange fluxes in the Bay. T-S diagrams showed unique water signatures throughout; consistent with the concept of limited mixing. Hydrodynamic modeling, using typical tidal, current and meteorological data for winter, supported the limited mixing scheme, with low residual velocities in most areas. The model also showed the ubiquitous presence of topographically generated eddies, which operate as effective retention mechanisms, preventing large-scale mixing. Finally, biological field data on snapper spawning locations were used to seed the model. Particles released in the model were consistently located in or advected into cyclonic eddy structures, and therefore experienced little advection through the system. However, the process is seasonal, with retention mechanisms only in place in wintertime when winds are low and the system is tidally driven. These results verify the hypothesis that young snapper - eggs and larvae - do not mix throughout the bay, and are therefore isolated within specific spawning areas.
NASA Astrophysics Data System (ADS)
Russel, W. B.; Saville, D. A.; Schowalter, W. R.
1992-03-01
The book covers the physical side of colloid science from the individual forces acting between submicron particles suspended in a liquid through the resulting equilibrium and dynamic properties. The relevant forces include Brownian motion, electrostatic repulsion, dispersion attraction, both attraction and repulsion due to soluble polymer, and viscous forces due to relative motion between the particles and the liquid. The balance among Brownian motion and the interparticle forces decides the questions of stability and phase behavior. Imposition of external fields produces complex effects, i.e. electrokinetic phenomena (electric field), sedimentation (gravitational field), diffusion (concentration/chemical potential gradient), and non-Newtonian rheology (shear field). The treatment aims to impart a sound, quantitative understanding based on fundamental theory and experiments with well-characterized model systems. This broad grasp of the fundamentals lends insight and helps to develop the intuitive sense needed to isolate essential features of technological problems and design critical experiments. Some exposure to fluid mechanics, statistical mechanics, and electricity and magnetism is assumed, but each subject is reintroduced in a self-contained manner.
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.
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.
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.
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.
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.
Exchange Coulomb interaction in nanotubes: Dispersion of Langmuir waves
Andreev, P. A. Ivanov, A. Yu.
2015-07-15
The microscopic derivation of the Coulomb exchange interaction for electrons located on the nanotubes is presented. The derivation is based on the many-particle quantum hydrodynamic method. We demonstrate the effect of curvature of the nanocylinders on the force of exchange interaction. We calculate corresponding dispersion dependencies for electron oscillations on the nanotubes.
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
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.
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.
NASA Astrophysics Data System (ADS)
Ekardt, W.
1987-09-01
The wave-vector dispersion of collective modes in small particles is investigated within the time-dependent local-density approximation as applied to a self-consistent jellium particle. It is shown that the dispersion of the volume plasmons can be understood from that in an infinite electron gas. For a given multipole an optimum wave vector exists for the quasiresonant excitation of the volume mode but not for the surface mode. It is pointed out that-for the volume modes-the hydrodynamic approximation gives a reasonable first guess for the relation between frequencies and size-quantized wave vectors.
Chemotaxis affects hydrodynamics in suspensions of micro-swimmers
NASA Astrophysics Data System (ADS)
Lushi, Enkeleida; Shelley, Michael
2010-11-01
Microorganisms are known to respond to a dissolved chemical substance by moving preferentially away or toward its source. We study such chemotactic responses at the population level when micro-swimmers are hydrodynamically coupled. To do this we couple a recently developed kinetic model of motile suspension dynamics with a field equation for a chemical substance that diffuses and is advected by the large-scale fluid flows created by the micro-swimmers. We also allow this substance to be produced or consumed by the swimmers themselves. Two models of chemotactic response are considered. One is a simple model for an organism smoothly turning, while moving at constant speed, to align with a chemical gradient. The second is a previously developed model of the effect of modulated run-and-tumble dynamics by individual swimmers. We investigate the linear stability of nearly isotropic suspensions for both models by considering both Pusher micro-swimmers and Pullers. An instability due to chemotaxis is shown to occur in a band of perturbation wavelengths. Nonlinear dynamics are investigated using numerical simulation in two dimensions. We observe aggregation and possible concentration divergences in suspensions of Pullers and the formation of mixing flows in suspensions of Pushers. In the latter case we observe that chemotaxis slows and modifies the mixing dynamics of the system.
Annual Report: Hydrodynamics and Radiative Hydrodynamics with Astrophysical Applications
R. Paul Drake
2005-12-01
We report the ongoing work of our group in hydrodynamics and radiative hydrodynamics with astrophysical applications. During the period of the existing grant, we have carried out two types of experiments at the Omega laser. One set of experiments has studied radiatively collapsing shocks, obtaining high-quality scaling data using a backlit pinhole and obtaining the first (ever, anywhere) Thomson-scattering data from a radiative shock. Other experiments have studied the deeply nonlinear development of the Rayleigh-Taylor (RT) instability from complex initial conditions, obtaining the first (ever, anywhere) dual-axis radiographic data using backlit pinholes and ungated detectors. All these experiments have applications to astrophysics, discussed in the corresponding papers either in print or in preparation. We also have obtained preliminary radiographs of experimental targets using our x-ray source. The targets for the experiments have been assembled at Michigan, where we also prepare many of the simple components. The above activities, in addition to a variety of data analysis and design projects, provide good experience for graduate and undergraduates students. In the process of doing this research we have built a research group that uses such work to train junior scientists.
Constructing higher-order hydrodynamics: The third order
NASA Astrophysics Data System (ADS)
Grozdanov, Sašo; Kaplis, Nikolaos
2016-03-01
Hydrodynamics can be formulated as the gradient expansion of conserved currents in terms of the fundamental fields describing the near-equilibrium fluid flow. In the relativistic case, the Navier-Stokes equations follow from the conservation of the stress-energy tensor to first order in derivatives. In this paper, we go beyond the presently understood second-order hydrodynamics and discuss the systematization of obtaining the hydrodynamic expansion to an arbitrarily high order. As an example of the algorithm that we present, we fully classify the gradient expansion at third order for neutral fluids in four dimensions, thus finding the most general next-to-leading-order corrections to the relativistic Navier-Stokes equations in curved space-time. In doing so, we list 20 new transport coefficient candidates in the conformal case and 68 in the nonconformal case. As we do not consider any constraints that could potentially arise from the local entropy current analysis, this is the maximal possible set of neutral third-order transport coefficients. To investigate the physical implications of these new transport coefficients, we obtain the third-order corrections to the linear dispersion relations that describe the propagation of diffusion and sound waves in relativistic fluids. We also compute the corrections to the scalar (spin-2) two-point correlation function of the third-order stress-energy tensor. Furthermore, as an example of a nonlinear hydrodynamic flow, we calculate the third-order corrections to the energy density of a boost-invariant Bjorken flow. Finally, we apply our field theoretic results to the N =4 supersymmetric Yang-Mills fluid at infinite 't Hooft coupling and an infinite number of colors to find the values of five new linear combinations of the conformal transport coefficients.
Forced wetting and hydrodynamic assist
NASA Astrophysics Data System (ADS)
Blake, Terence D.; Fernandez-Toledano, Juan-Carlos; Doyen, Guillaume; De Coninck, Joël
2015-11-01
Wetting is a prerequisite for coating a uniform layer of liquid onto a solid. Wetting failure and air entrainment set the ultimate limit to coating speed. It is well known in the coating art that this limit can be postponed by manipulating the coating flow to generate what has been termed "hydrodynamic assist," but the underlying mechanism is unclear. Experiments have shown that the conditions that postpone air entrainment also reduce the apparent dynamic contact angle, suggesting a direct link, but how the flow might affect the contact angle remains to be established. Here, we use molecular dynamics to compare the outcome of steady forced wetting with previous results for the spontaneous spreading of liquid drops and apply the molecular-kinetic theory of dynamic wetting to rationalize our findings and place them on a quantitative footing. The forced wetting simulations reveal significant slip at the solid-liquid interface and details of the flow immediately adjacent to the moving contact line. Our results confirm that the local, microscopic contact angle is dependent not simply only on the velocity of wetting but also on the nature of the flow that drives it. In particular, they support an earlier suggestion that during forced wetting, an intense shear stress in the vicinity of the contact line can assist surface tension forces in promoting dynamic wetting, thus reducing the velocity-dependence of the contact angle. Hydrodynamic assist then appears as a natural consequence of wetting that emerges when the contact line is driven by a strong and highly confined flow. Our theoretical approach also provides a self-consistent model of molecular slip at the solid-liquid interface that enables its magnitude to be estimated from dynamic contact angle measurements. In addition, the model predicts how hydrodynamic assist and slip may be influenced by liquid viscosity and solid-liquid interactions.
Mellon, deForest
2007-08-01
Aquatic environments are by their nature dynamic and dominated by fluid movements driven by lunar tides, temperature and salinity density gradients, wind-driven currents, and currents generated by the earth's rotation. Accordingly, animals within the aquatic realm must be able to sense and respond to both large-scale (advection) and small-scale (eddy turbulence) fluid dynamics, for chemical signals critically important for their survival are embedded within such movements. Aquatic crustaceans possess many types of near-field fluid-flow detectors and two general classes of chemoreceptors on their body appendages: high-threshold, near-field receptors that may be somewhat equated with the sense of taste, and low-threshold far-field receptors that can be considered as olfactory. This review briefly summarizes the distribution of hydrodynamic and high-threshold chemoreceptors in aquatic crustaceans and the physiological characteristics of olfactory receptors in lobsters; it also examines recent physiological evidence for the central nervous integration of inputs from olfactory receptors and hydrodynamic detectors, two dissimilar senses that must be combined within the brain for survival. Marine crustaceans have provided valuable insights about mechanisms of primary olfactory sensory physiology; their additional sensitivity to hydrodynamic stimulation makes them a potentially useful model for examining how these two critical sensory inputs are combined within the brain to enhance foraging behavior. Multimodal sensory processing is critically important to all animals, and the principles and concepts derived from these crustacean studies may provide generalities about neuronal processing across taxa. PMID:17679714
Ley, Mikkel W H; Bruus, Henrik
2016-04-01
A continuum model is established for numerical studies of hydrodynamic particle-particle interactions in microfluidic high-concentration suspensions. A suspension of microparticles placed in a microfluidic channel and influenced by an external force, is described by a continuous particle-concentration field coupled to the continuity and Navier-Stokes equation for the solution. The hydrodynamic interactions are accounted for through the concentration dependence of the suspension viscosity, of the single-particle mobility, and of the momentum transfer from the particles to the suspension. The model is applied on a magnetophoretic and an acoustophoretic system, respectively, and based on the results, we illustrate three main points: (1) for relative particle-to-fluid volume fractions greater than 0.01, the hydrodynamic interaction effects become important through a decreased particle mobility and an increased suspension viscosity. (2) At these high particle concentrations, particle-induced flow rolls occur, which can lead to significant deviations of the advective particle transport relative to that of dilute suspensions. (3) Which interaction mechanism that dominates, depends on the specific flow geometry and the specific external force acting on the particles. PMID:26948344
Ley, Mikkel W H; Bruus, Henrik
2016-04-01
A continuum model is established for numerical studies of hydrodynamic particle-particle interactions in microfluidic high-concentration suspensions. A suspension of microparticles placed in a microfluidic channel and influenced by an external force, is described by a continuous particle-concentration field coupled to the continuity and Navier-Stokes equation for the solution. The hydrodynamic interactions are accounted for through the concentration dependence of the suspension viscosity, of the single-particle mobility, and of the momentum transfer from the particles to the suspension. The model is applied on a magnetophoretic and an acoustophoretic system, respectively, and based on the results, we illustrate three main points: (1) for relative particle-to-fluid volume fractions greater than 0.01, the hydrodynamic interaction effects become important through a decreased particle mobility and an increased suspension viscosity. (2) At these high particle concentrations, particle-induced flow rolls occur, which can lead to significant deviations of the advective particle transport relative to that of dilute suspensions. (3) Which interaction mechanism that dominates, depends on the specific flow geometry and the specific external force acting on the particles.
Disruptive Innovation in Numerical Hydrodynamics
Waltz, Jacob I.
2012-09-06
We propose the research and development of a high-fidelity hydrodynamic algorithm for tetrahedral meshes that will lead to a disruptive innovation in the numerical modeling of Laboratory problems. Our proposed innovation has the potential to reduce turnaround time by orders of magnitude relative to Advanced Simulation and Computing (ASC) codes; reduce simulation setup costs by millions of dollars per year; and effectively leverage Graphics Processing Unit (GPU) and future Exascale computing hardware. If successful, this work will lead to a dramatic leap forward in the Laboratory's quest for a predictive simulation capability.
Hydrodynamic Synchronisation of Model Microswimmers
NASA Astrophysics Data System (ADS)
Putz, V. B.; Yeomans, J. M.
2009-12-01
We define a model microswimmer with a variable cycle time, thus allowing the possibility of phase locking driven by hydrodynamic interactions between swimmers. We find that, for extensile or contractile swimmers, phase locking does occur, with the relative phase of the two swimmers being, in general, close to 0 or π, depending on their relative position and orientation. We show that, as expected on grounds of symmetry, self T-dual swimmers, which are time-reversal covariant, do not phase-lock. We also discuss the phase behaviour of a line of tethered swimmers, or pumps. These show oscillations in their relative phases reminiscent of the metachronal waves of cilia.
Ergoregion instability: The hydrodynamic vortex
NASA Astrophysics Data System (ADS)
Oliveira, Leandro A.; Cardoso, Vitor; Crispino, Luís C. B.
2014-06-01
Four-dimensional, asymptotically flat spacetimes with an ergoregion but no horizon have been shown to be linearly unstable against a superradiant-triggered mechanism. This result has wide implications in the search for astrophysically viable alternatives to black holes, but also in the understanding of black holes and Hawking evaporation. Here we investigate this instability in detail for a particular setup that can be realized in the laboratory: the hydrodynamic vortex, an effective geometry for sound waves, with ergoregion and without an event horizon.
Hydrodynamic instability modeling for ICF
Haan, S.W.
1993-03-31
The intent of this paper is to review how instability growth is modeled in ICF targets, and to identify the principal issues. Most of the material has been published previously, but is not familiar to a wide audience. Hydrodynamic instabilities are a key issue in ICF. Along with laser-plasma instabilities, they determine the regime in which ignition is possible. At higher laser energies, the same issues determine the achievable gain. Quantitative predictions are therefore of the utmost importance to planning the ICF program, as well as to understanding current Nova results. The key fact that underlies all this work is the stabilization of short wavelengths.
Effective actions for anomalous hydrodynamics
NASA Astrophysics Data System (ADS)
Haehl, Felix M.; Loganayagam, R.; Rangamani, Mukund
2014-03-01
We argue that an effective field theory of local fluid elements captures the constraints on hydrodynamic transport stemming from the presence of quantum anomalies in the underlying microscopic theory. Focussing on global current anomalies for an arbitrary flavour group, we derive the anomalous constitutive relations in arbitrary even dimensions. We demonstrate that our results agree with the constraints on anomaly governed transport derived hitherto using a local version of the second law of thermodynamics. The construction crucially uses the anomaly inflow mechanism and involves a novel thermofield double construction. In particular, we show that the anomalous Ward identities necessitate non-trivial interaction between the two parts of the Schwinger-Keldysh contour.
Hydrodynamic loading of tensegrity structures
NASA Astrophysics Data System (ADS)
Wroldsen, Anders S.; Johansen, Vegar; Skelton, Robert E.; Sørensen, Asgeir J.
2006-03-01
This paper introduces hydrodynamic loads for tensegrity structures, to examine their behavior in marine environments. Wave compliant structures are of general interest when considering large marine structures, and we are motivated by the aquaculture industry where new concepts are investigated in order to make offshore installations for seafood production. This paper adds to the existing models and software simulations of tensegrity structures exposed to environmental loading from waves and current. A number of simulations are run to show behavior of the structure as a function of pretension level and string stiffness for a given loading condition.
Hydrodynamical models of young SNRs.
NASA Astrophysics Data System (ADS)
Kosenko, D. I.; Blinnikov, S. I.; Postnov, K. A.; Sorokina, E. I.
X-ray observations of the Tycho supernova (SN) remnant by XMM-Newton telescope present radial profiles of the remnant in emission lines from silicon and iron \\citep{decour}. To reproduce observed spectrum and X-ray profiles hydrodynamical modelling of the remnant was performed by \\citet{elka}. Standard computational SN models cannot reproduce observed spacial behavoir of the X-ray profiles of the remnant in the emission lines. We perform analysis of these numerical models and find conditions under which it is possible to reproduce observed profiles.
Microscale hydrodynamics near moving contact lines
NASA Technical Reports Server (NTRS)
Garoff, Stephen; Chen, Q.; Rame, Enrique; Willson, K. R.
1994-01-01
The hydrodynamics governing the fluid motions on a microscopic scale near moving contact lines are different from those governing motion far from the contact line. We explore these unique hydrodynamics by detailed measurement of the shape of a fluid meniscus very close to a moving contact line. The validity of present models of the hydrodynamics near moving contact lines as well as the dynamic wetting characteristics of a family of polymer liquids are discussed.
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.
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...
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.
Thermal transport in a noncommutative hydrodynamics
Geracie, M. Son, D. T.
2015-03-15
We find the hydrodynamic equations of a system of particles constrained to be in the lowest Landau level. We interpret the hydrodynamic theory as a Hamiltonian system with the Poisson brackets between the hydrodynamic variables determined from the noncommutativity of space. We argue that the most general hydrodynamic theory can be obtained from this Hamiltonian system by allowing the Righi-Leduc coefficient to be an arbitrary function of thermodynamic variables. We compute the Righi-Leduc coefficient at high temperatures and show that it satisfies the requirements of particle-hole symmetry, which we outline.
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.
Active and driven hydrodynamic crystals.
Desreumaux, N; Florent, N; Lauga, E; Bartolo, D
2012-08-01
Motivated by the experimental ability to produce monodisperse particles in microfluidic devices, we study theoretically the hydrodynamic stability of driven and active crystals. We first recall the theoretical tools allowing to quantify the dynamics of elongated particles in a confined fluid. In this regime hydrodynamic interactions between particles arise from a superposition of potential dipolar singularities. We exploit this feature to derive the equations of motion for the particle positions and orientations. After showing that all five planar Bravais lattices are stationary solutions of the equations of motion, we consider separately the case where the particles are passively driven by an external force, and the situation where they are self-propelling. We first demonstrate that phonon modes propagate in driven crystals, which are always marginally stable. The spatial structures of the eigenmodes depend solely on the symmetries of the lattices, and on the orientation of the driving force. For active crystals, the stability of the particle positions and orientations depends not only on the symmetry of the crystals but also on the perturbation wavelengths and on the crystal density. Unlike unconfined fluids, the stability of active crystals is independent of the nature of the propulsion mechanism at the single-particle level. The square and rectangular lattices are found to be linearly unstable at short wavelengths provided the volume fraction of the crystals is high enough. Differently, hexagonal, oblique, and face-centered crystals are always unstable. Our work provides a theoretical basis for future experimental work on flowing microfluidic crystals. PMID:22864543
Hydromechanical transmission with hydrodynamic drive
Orshansky, Jr., deceased, Elias; Weseloh, William E.
1979-01-01
This transmission has a first planetary gear assembly having first input means connected to an input shaft, first output means, and first reaction means, and a second planetary gear assembly having second input means connected to the first input means, second output means, and second reaction means connected directly to the first reaction means by a reaction shaft. First clutch means, when engaged, connect the first output means to an output shaft in a high driving range. A hydrodynamic drive is used; for example, a torque converter, which may or may not have a stationary case, has a pump connected to the second output means, a stator grounded by an overrunning clutch to the case, and a turbine connected to an output member, and may be used in a starting phase. Alternatively, a fluid coupling or other type of hydrodynamic drive may be used. Second clutch means, when engaged, for connecting the output member to the output shaft in a low driving range. A variable-displacement hydraulic unit is mechanically connected to the input shaft, and a fixed-displacement hydraulic unit is mechanically connected to the reaction shaft. The hydraulic units are hydraulically connected together so that when one operates as a pump the other acts as a motor, and vice versa. Both clutch means are connected to the output shaft through a forward-reverse shift arrangement. It is possible to lock out the torque converter after the starting phase is over.
The hydrodynamics of lamprey locomotion
NASA Astrophysics Data System (ADS)
Leftwich, Megan C.
The lamprey, an anguilliform swimmer, propels itself by undulating most of its body. This type of swimming produces flow patterns that are highly three-dimensional in nature and not very well understood. However, substantial previous work has been done to understand two-dimensional unsteady propulsion, the possible wake structures and thrust performance. Limited studies of three-dimensional propulsors with simple geometries have displayed the importance of the third dimension in designing unsteady swimmers. Some of the results of those studies, primarily the ways in which vorticity is organized in the wake region, are seen in lamprey swimming as well. In the current work, the third dimension is not the only important factor, but complex geometry and body undulations also contribute to the hydrodynamics. Through dye flow visualization, particle induced velocimetry and pressure measurements, the hydrodynamics of anguilliform swimming are studied using a custom built robotic lamprey. These studies all indicate that the undulations of the body are not producing thrust. Instead, it is the tail which acts to propel the animal. This conclusion led to further investigation of the tail, specifically the role of varying tail flexibility on hydrodymnamics. It is found that by making the tail more flexible, one decreases the coherence of the vorticity in the lamprey's wake. Additional flexibility also yields less thrust.
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. ...
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...
NASA Astrophysics Data System (ADS)
Jouanneau, Nicolas; Sentchev, Alexei; Dumas, Franck
2013-12-01
The MARS-3D model in conjunction with the particle tracking module Ichthyop is used to study circulation and tracer dynamics under a variety of forcing conditions in the eastern English Channel, and in the Boulogne-sur-Mer harbour (referred to hereafter as BLH). Results of hydrodynamic modelling are validated against the tidal gauge data, VHF radar surface velocities and ADCP measurements. Lagrangian tracking experiments are performed with passive particles to study tracer dispersal along the northern French coast, with special emphasis on the BLH. Simulations revealed an anticyclonic eddy generated in the harbour at rising tide. Tracers, released during flood tide at the Liane river mouth, move northward with powerful clockwise rotating current. After the high water, the current direction changes to westward, and tracers leave the harbour through the open boundary. During ebb tide, currents convergence along the western open boundary but no eddy is formed, surface currents inside the harbour are much weaker and the tracer excursion length is small. After the current reversal at low water, particles are advected shoreward resulting in a significant increase of the residence time of tracers released during ebb tide. The effect of wind on particle dispersion was found to be particularly strong. Under strong SW wind, the residence time of particles released during flood tide increases from 1.5 to 6 days. For release during ebb tide, SW wind weakens the southward tidally induced drift and thus the residence time decreases. Similar effects are observed when the freshwater inflow to the harbour is increased from 2 to 10 m3/s during the ebb tide flow. For flood tide conditions, the effect of freshwater inflow is less significant. We also demonstrate an example of innovative coastal management targeted at the reduction of the residence time of the pathogenic material accidentally released in the harbour.
Relativistic Hydrodynamics for Heavy-Ion Collisions
ERIC Educational Resources Information Center
Ollitrault, Jean-Yves
2008-01-01
Relativistic hydrodynamics is essential to our current understanding of nucleus-nucleus collisions at ultrarelativistic energies (current experiments at the Relativistic Heavy Ion Collider, forthcoming experiments at the CERN Large Hadron Collider). This is an introduction to relativistic hydrodynamics for graduate students. It includes a detailed…
Hydrodynamic models of a Cepheid atmosphere
NASA Technical Reports Server (NTRS)
Karp, A. H.
1975-01-01
Instead of computing a large number of coarsely zoned hydrodynamic models covering the entire atmospheric instability strip, the author computed a single model as well as computer limitations allow. The implicit hydrodynamic code of Kutter and Sparks was modified to include radiative transfer effects in optically thin zones.
Hydrodynamic description for ballistic annihilation systems
Garcia de Soria, Maria Isabel; Trizac, Emmanuel; Maynar, Pablo; Schehr, Gregory; Barrat, Alain
2009-01-21
The problem of the validity of a hydrodynamic description for a system in which there are no collisional invariants is addressed. Hydrodynamic equations have been derived and successfully tested against simulation data for a system where particles annihilate with a probability p, or collide elastically otherwise. The response of the system to a linear perturbation is analyzed as well.
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.
Measurement of advective soil gas flux: Results of field and laboratory experiments with CO2
Amonette, James E.; Barr, Jonathan L.; Erikson, Rebecca L.; Dobeck, Laura M.; Barr, Jamie L.; Shaw, Joseph A.
2013-10-01
We modified our multi-channel, steady-state flow-through (SSFT), soil-CO2 flux monitoring system to include an array of inexpensive pyroelectric non-dispersive infrared detectors for full-range (0-100%) coverage of CO2 concentrations without dilution, and a larger-diameter vent tube. We then conducted field testing of this system from late July through mid-September 2010 at the Zero Emissions Research and Technology (ZERT) project site located in Bozeman, MT, and subsequently, laboratory testing at the Pacific Northwest National Laboratory (PNNL) in Richland, WA using a flux bucket filled with dry sand. In the field, an array of twenty-five SSFT and three non-steady-state (NSS) flux chambers was installed in a 10x4 m area, the long boundary of which was directly above a shallow (2-m depth) horizontal injection well located 0.5 m below the water table. Two additional chambers (one SSFT and one NSS) were installed 10 m from the well for background measurements. Volumetric soil moisture sensors were installed at each SSFT chamber to measure mean levels in the top 0.15 m of soil. A total flux of 52 kg CO2 d-1 was injected into the well for 27 d and the efflux from the soil was monitored by the chambers before, during, and for 27 d after the injection. Overall, the results were consistent with those from previous years, showing a radial efflux pattern centered on a known “hot spot”, rapid responses to changes in injection rate and wind power, evidence for movement of the CO2 plume during the injection, and nominal flux levels from the SSFT chambers that were up to 6-fold higher than those measured by adjacent NSS chambers. Soil moisture levels varied during the experiment from moderate to near saturation with the highest levels occurring consistently at the hot spot. The effects of wind on measured flux were complex and decreased as soil moisture content increased. In the laboratory, flux bucket testing with the SSFT chamber showed large measured-flux enhancement
Hydrodynamic limit of Wigner-Poisson kinetic theory: Revisited
Akbari-Moghanjoughi, M.
2015-02-15
In this paper, we revisit the hydrodynamic limit of the Langmuir wave dispersion relation based on the Wigner-Poisson model in connection with that obtained directly from the original Lindhard dielectric function based on the random-phase-approximation. It is observed that the (fourth-order) expansion of the exact Lindhard dielectric constant correctly reduces to the hydrodynamic dispersion relation with an additional term of fourth-order, beside that caused by the quantum diffraction effect. It is also revealed that the generalized Lindhard dielectric theory accounts for the recently discovered Shukla-Eliasson attractive potential (SEAP). However, the expansion of the exact Lindhard static dielectric function leads to a k{sup 4} term of different magnitude than that obtained from the linearized quantum hydrodynamics model. It is shown that a correction factor of 1/9 should be included in the term arising from the quantum Bohm potential of the momentum balance equation in fluid model in order for a correct plasma dielectric response treatment. Finally, it is observed that the long-range oscillatory screening potential (Friedel oscillations) of type cos(2k{sub F}r)/r{sup 3}, which is a consequence of the divergence of the dielectric function at point k = 2k{sub F} in a quantum plasma, arises due to the finiteness of the Fermi-wavenumber and is smeared out in the limit of very high electron number-densities, typical of white dwarfs and neutron stars. In the very low electron number-density regime, typical of semiconductors and metals, where the Friedel oscillation wavelength becomes much larger compared to the interparticle distances, the SEAP appears with a much deeper potential valley. It is remarked that the fourth-order approximate Lindhard dielectric constant approaches that of the linearized quantum hydrodynamic in the limit if very high electron number-density. By evaluation of the imaginary part of the Lindhard dielectric function, it is shown that 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
Comparative Hydrodynamics of Bacterial Polymorphism
NASA Astrophysics Data System (ADS)
Spagnolie, Saverio E.; Lauga, Eric
2011-02-01
Most bacteria swim through fluids by rotating helical flagella which can take one of 12 distinct polymorphic shapes, the most common of which is the normal form used during forward swimming runs. To shed light on the prevalence of the normal form in locomotion, we gather all available experimental measurements of the various polymorphic forms and compute their intrinsic hydrodynamic efficiencies. The normal helical form is found to be the most efficient of the 12 polymorphic forms by a significant margin—a conclusion valid for both the peritrichous and polar flagellar families, and robust to a change in the effective flagellum diameter or length. Hence, although energetic costs of locomotion are small for bacteria, fluid mechanical forces may have played a significant role in the evolution of the flagellum.
Hydrodynamic enhanced dielectrophoretic particle trapping
Miles, Robin R.
2003-12-09
Hydrodynamic enhanced dielectrophoretic particle trapping carried out by introducing a side stream into the main stream to squeeze the fluid containing particles close to the electrodes producing the dielelectrophoretic forces. The region of most effective or the strongest forces in the manipulating fields of the electrodes producing the dielectrophoretic forces is close to the electrodes, within 100 .mu.m from the electrodes. The particle trapping arrangement uses a series of electrodes with an AC field placed between pairs of electrodes, which causes trapping of particles along the edges of the electrodes. By forcing an incoming flow stream containing cells and DNA, for example, close to the electrodes using another flow stream improves the efficiency of the DNA trapping.
Radiation hydrodynamics in solar flares
Fisher, G.H.
1985-10-18
Solar flares are rather violent and extremely complicated phenomena, and it should be made clear at the outset that a physically complete picture describing all aspects of flares does not exist. From the wealth of data which is available, it is apparent that many different types of physical processes are involved during flares: energetic particle acceleration, rapid magnetohydrodynamic motion of complex field structures, magnetic reconnection, violent mass motion along magnetic field lines, and the heating of plasma to tens of millions of degrees, to name a few. The goal of this paper is to explore just one aspect of solar flares, namely, the interaction of hydrodynamics and radiation processes in fluid being rapidly heated along closed magnetic field lines. The models discussed are therefore necessarily restrictive, and will address only a few of the observed or observable phenomena. 46 refs., 6 figs.
Integration of quantum hydrodynamical equation
NASA Astrophysics Data System (ADS)
Ulyanova, Vera G.; Sanin, Andrey L.
2007-04-01
Quantum hydrodynamics equations describing the dynamics of quantum fluid are a subject of this report (QFD).These equations can be used to decide the wide class of problem. But there are the calculated difficulties for the equations, which take place for nonlinear hyperbolic systems. In this connection, It is necessary to impose the additional restrictions which assure the existence and unique of solutions. As test sample, we use the free wave packet and study its behavior at the different initial and boundary conditions. The calculations of wave packet propagation cause in numerical algorithm the division. In numerical algorithm at the calculations of wave packet propagation, there arises the problem of division by zero. To overcome this problem we have to sew together discrete numerical and analytical continuous solutions on the boundary. We demonstrate here for the free wave packet that the numerical solution corresponds to the analytical solution.
Hydrodynamic assembly for Fast Ignition
NASA Astrophysics Data System (ADS)
Tabak, Max; Clark, Daniel; Town, Richard; Hatchett, Stephen
2007-11-01
We present directly and indirectly driven implosion designs for Fast Ignition. Directly driven designs using various laser illumination wavelengths are described. We compare these designs with simple hydrodynamic efficiency models. Capsules illuminated with less than 1 MJ of light with perfect zooming at low intensity and low contrast ratio in power can assemble 4 mg of fuel to column density in excess of 3 g/cm^2. We contrast these designs with more optimized designs that lead to Guderley-style self similar implosions. Indirectly driven capsules absorbing 75 kJ of xrays can assemble 0.7 mg to column density 2.7 g/cm^2 in 1D simulations. We describe 2-D simulations including both capsules and attached cones driven by radiation. We describe issues in assembling fuel near the cone tip and cone disruption.
Hydrodynamic model for drying emulsions.
Feng, Huanhuan; Sprakel, Joris; van der Gucht, Jasper
2015-08-01
We present a hydrodynamic model for film formation in a dense oil-in-water emulsion under a unidirectional drying stress. Water flow through the plateau borders towards the drying end leads to the buildup of a pressure gradient. When the local pressure exceeds the critical disjoining pressure, the water films between droplets break and the droplets coalesce. We show that, depending on the critical pressure and the evaporation rate, the coalescence can occur in two distinct modes. At low critical pressures and low evaporation rates, coalescence occurs throughout the sample, whereas at high critical pressures and high evaporation rate, coalescence occurs only at the front. In the latter case, an oil layer develops on top of the film, which acts as a diffusive barrier and slows down film formation. Our findings, which are summarized in a state diagram for film formation, are in agreement with recent experimental findings.
Anomalous hydrodynamics kicks neutron stars
NASA Astrophysics Data System (ADS)
Kaminski, Matthias; Uhlemann, Christoph F.; Bleicher, Marcus; Schaffner-Bielich, Jürgen
2016-09-01
Observations show that, at the beginning of their existence, neutron stars are accelerated briskly to velocities of up to a thousand kilometers per second. We argue that this remarkable effect can be explained as a manifestation of quantum anomalies on astrophysical scales. To theoretically describe the early stage in the life of neutron stars we use hydrodynamics as a systematic effective-field-theory framework. Within this framework, anomalies of the Standard Model of particle physics as underlying microscopic theory imply the presence of a particular set of transport terms, whose form is completely fixed by theoretical consistency. The resulting chiral transport effects in proto-neutron stars enhance neutrino emission along the internal magnetic field, and the recoil can explain the order of magnitude of the observed kick velocities.
IKT for quantum hydrodynamic equations
NASA Astrophysics Data System (ADS)
Tessarotto, Massimo; Ellero, Marco; Nicolini, Piero
2007-11-01
A striking feature of standard quantum mechanics (SQM) is its analogy with classical fluid dynamics. In fact, it is well-known that the Schr"odinger equation is equivalent to a closed set of partial differential equations for suitable real-valued functions of position and time (denoted as quantum fluid fields) [Madelung, 1928]. In particular, the corresponding quantum hydrodynamic equations (QHE) can be viewed as the equations of a classical compressible and non-viscous fluid, endowed with potential velocity and quantized velocity circulation. In this reference, an interesting theoretical problem, in its own right, is the construction of an inverse kinetic theory (IKT) for such a type of fluids. In this note we intend to investigate consequences of the IKT recently formulated for QHE [M.Tessarotto et al., Phys. Rev. A 75, 012105 (2007)]. In particular a basic issue is related to the definition of the quantum fluid fields.
Effect of Surface Roughness on Hydrodynamic Bearings
NASA Technical Reports Server (NTRS)
Majumdar, B. C.; Hamrock, B. J.
1981-01-01
A theoretical analysis on the performance of hydrodynamic oil bearings is made considering surface roughness effect. The hydrodynamic as well as asperity contact load is found. The contact pressure was calculated with the assumption that the surface height distribution was Gaussian. The average Reynolds equation of partially lubricated surface was used to calculate hydrodynamic load. An analytical expression for average gap was found and was introduced to modify the average Reynolds equation. The resulting boundary value problem was then solved numerically by finite difference methods using the method of successive over relaxation. The pressure distribution and hydrodynamic load capacity of plane slider and journal bearings were calculated for various design data. The effects of attitude and roughness of surface on the bearing performance were shown. The results are compared with similar available solution of rough surface bearings. It is shown that: (1) the contribution of contact load is not significant; and (2) the hydrodynamic and contact load increase with surface roughness.
Stellar Explosions: Hydrodynamics and Nucleosynthesis
NASA Astrophysics Data System (ADS)
Jose, Jordi
2016-01-01
Stars are the main factories of element production in the universe through a suite of complex and intertwined physical processes. Such stellar alchemy is driven by multiple nuclear interactions that through eons have transformed the pristine, metal-poor ashes leftover by the Big Bang into a cosmos with 100 distinct chemical species. The products of stellar nucleosynthesis frequently get mixed inside stars by convective transport or through hydrodynamic instabilities, and a fraction of them is eventually ejected into the interstellar medium, thus polluting the cosmos with gas and dust. The study of the physics of the stars and their role as nucleosynthesis factories owes much to cross-fertilization of different, somehow disconnected fields, ranging from observational astronomy, computational astrophysics, and cosmochemistry to experimental and theoretical nuclear physics. Few books have simultaneously addressed the multidisciplinary nature of this field in an engaging way suitable for students and young scientists. Providing the required multidisciplinary background in a coherent way has been the driving force for Stellar Explosions: Hydrodynamics and Nucleosynthesis. Written by a specialist in stellar astrophysics, this book presents a rigorous but accessible treatment of the physics of stellar explosions from a multidisciplinary perspective at the crossroads of computational astrophysics, observational astronomy, cosmochemistry, and nuclear physics. Basic concepts from all these different fields are applied to the study of classical and recurrent novae, type I and II supernovae, X-ray bursts and superbursts, and stellar mergers. The book shows how a multidisciplinary approach has been instrumental in our understanding of nucleosynthesis in stars, particularly during explosive events.
Stellar Explosions: Hydrodynamics and Nucleosynthesis
NASA Astrophysics Data System (ADS)
José, Jordi
2015-12-01
Stars are the main factories of element production in the universe through a suite of complex and intertwined physical processes. Such stellar alchemy is driven by multiple nuclear interactions that through eons have transformed the pristine, metal-poor ashes leftover by the Big Bang into a cosmos with 100 distinct chemical species. The products of stellar nucleosynthesis frequently get mixed inside stars by convective transport or through hydrodynamic instabilities, and a fraction of them is eventually ejected into the interstellar medium, thus polluting the cosmos with gas and dust. The study of the physics of the stars and their role as nucleosynthesis factories owes much to cross-fertilization of different, somehow disconnected fields, ranging from observational astronomy, computational astrophysics, and cosmochemistry to experimental and theoretical nuclear physics. Few books have simultaneously addressed the multidisciplinary nature of this field in an engaging way suitable for students and young scientists. Providing the required multidisciplinary background in a coherent way has been the driving force for Stellar Explosions: Hydrodynamics and Nucleosynthesis. Written by a specialist in stellar astrophysics, this book presents a rigorous but accessible treatment of the physics of stellar explosions from a multidisciplinary perspective at the crossroads of computational astrophysics, observational astronomy, cosmochemistry, and nuclear physics. Basic concepts from all these different fields are applied to the study of classical and recurrent novae, type I and II supernovae, X-ray bursts and superbursts, and stellar mergers. The book shows how a multidisciplinary approach has been instrumental in our understanding of nucleosynthesis in stars, particularly during explosive events.
The hydrodynamics of dolphin drafting
Weihs, Daniel
2004-01-01
Background Drafting in cetaceans is defined as the transfer of forces between individuals without actual physical contact between them. This behavior has long been surmised to explain how young dolphin calves keep up with their rapidly moving mothers. It has recently been observed that a significant number of calves become permanently separated from their mothers during chases by tuna vessels. A study of the hydrodynamics of drafting, initiated in the hope of understanding the mechanisms causing the separation of mothers and calves during fishing-related activities, is reported here. Results Quantitative results are shown for the forces and moments around a pair of unequally sized dolphin-like slender bodies. These include two major effects. First, the so-called Bernoulli suction, which stems from the fact that the local pressure drops in areas of high speed, results in an attractive force between mother and calf. Second is the displacement effect, in which the motion of the mother causes the water in front to move forwards and radially outwards, and water behind the body to move forwards to replace the animal's mass. Thus, the calf can gain a 'free ride' in the forward-moving areas. Utilizing these effects, the neonate can gain up to 90% of the thrust needed to move alongside the mother at speeds of up to 2.4 m/sec. A comparison with observations of eastern spinner dolphins (Stenella longirostris) is presented, showing savings of up to 60% in the thrust that calves require if they are to keep up with their mothers. Conclusions A theoretical analysis, backed by observations of free-swimming dolphin schools, indicates that hydrodynamic interactions with mothers play an important role in enabling dolphin calves to keep up with rapidly moving adult school members. PMID:15132740
Mixing and dispersion in the coastal ocean
Winant, C.D.
1994-12-31
The eventual fate of matter transported in the ocean, whether natural or of anthropogenic origin, depends on a combination of advective and dispersive processes. The processes which relate to dispersion and mixing have to do with incoherent motions, and there amplitude increases with scale. Numerical models are now able to reproduce many observed features of coastal circulation, and often parameterize vertical and horizontal diffusion separately. For instance the model proposed by Wang, which reproduces features of the circulation in the strait of Gibraltar to a remarkable degree, parameterizes horizontal and vertical diffusion separately. This is a sensible approach, for two reasons. First the amplitude of horizontal currents and the scale of horizontal motions are usually much greater than vertical velocities and scales. Second, the ocean is vertically stratified, so that even vigorous stirring which does not result in mixing can be reversed by restratification once the active stirring process has abated. This review of processes which lead to mixing and dispersion is thus organized in terms of horizontal processes and then vertical processes.
Bencivenga F.; Cunsolo A.
2012-03-16
The predictions of the generalized collective modes (GCM) theory on the non-hydrodynamic dispersion of collective excitations of liquids and supercritical fluids have been tested against previous inelastic x-ray scattering measurements on samples of increasing complexity. We observed a good agreement between experimental results and theoretical predictions within the hypothesis that sound propagation is adiabatic. Overall, the performed comparison provides an experimental validation of GCM predictions and shows that, even in the transition region between the hydrodynamic and the mesoscopic regimes, thermal fluctuations have a minor influence on the dispersion, whose non-hydrodynamic effects are mostly driven by viscoelastic phenomena.
Hydrodynamic collective effects of active protein machines in solution and lipid bilayers
Mikhailov, Alexander S.; Kapral, Raymond
2015-01-01
The cytoplasm and biomembranes in biological cells contain large numbers of proteins that cyclically change their shapes. They are molecular machines that can function as molecular motors or carry out various other tasks in the cell. Many enzymes also undergo conformational changes within their turnover cycles. We analyze the advection effects that nonthermal fluctuating hydrodynamic flows induced by active proteins have on other passive molecules in solution or membranes. We show that the diffusion constants of passive particles are enhanced substantially. Furthermore, when gradients of active proteins are present, a chemotaxis-like drift of passive particles takes place. In lipid bilayers, the effects are strongly nonlocal, so that active inclusions in the entire membrane contribute to local diffusion enhancement and the drift. All active proteins in a biological cell or in a membrane contribute to such effects and all passive particles, and the proteins themselves, will be subject to them. PMID:26124140
NASA Astrophysics Data System (ADS)
Kapral, Raymond; Mikhailov, Alexander S.
2016-04-01
Most of the proteins in the cell, including not only molecular motors and machines, but also enzymes, are active. When ATP or other substrates are supplied, these macromolecules cyclically change their conformations. Therefore, they mechanically stir the cytoplasm and nucleoplasm, so that non-thermal fluctuating flows are produced. As we have recently shown (Mikhailov and Kapral, 2015), stochastic advection by such flows might lead to substantial diffusion enhancement of particles inside a living cell. Additionally, when gradients in the concentrations of active particles or in the ATP/substrate supply are present, chemotaxis-like drift should take place. Here, the motion of passive tracers with various sizes in a mixture of different kinds of active proteins is analyzed. Moreover, effects of hydrodynamic interactions on the motion of active proteins are explored. Theoretical results are compared with available experimental data for ATP-dependent diffusion of natural and microinjected particles in biological cells.
NASA Astrophysics Data System (ADS)
Boybeyi, Zafer
A mesoscale atmospheric dispersion modeling system has been developed to investigate mesoscale circulations and associated air pollution dispersion, including effects of terrain topography, large water bodies and urban areas. The system is based on a three-dimensional mesoscale meteorological model coupled with two dispersion models (an Eulerian dispersion model and a Lagrangian particle dispersion model). The mesoscale model is hydrostatic and based on primitive equations formulated in a terrain-following coordinate system with a E-varepsilon turbulence closure scheme. The Eulerian dispersion model is based on numerical solution of the advection-diffusion equation to allow one to simulate releases of non-buoyant pollutants (especially from area and volume sources). The Lagrangian particle dispersion model allows one to simulate releases of buoyant pollutants from arbitrary sources (particularly from point and line sources). The air pollution dispersion models included in the system are driven by the meteorological information provided by the mesoscale model. Mesoscale atmospheric circulations associated with sea and lake breezes have been examined using the mesoscale model. A series of model sensitivity studies were performed to investigate the effects of different environmental parameters on these circulations. It was found that the spatial and temporal variation of the sea and lake breeze convergence zones and the associated convective activities depend to a large extent on the direction and the magnitude of the ambient wind. Dispersion of methyl isocyanate gas from the Bhopal accident was investigated using the mesoscale atmospheric dispersion modeling system. A series of numerical experiments were performed to investigate the possible role of the mesoscale circulations on this industrial gas episode. The temporal and spatial variations of the wind and turbulence fields were simulated with the mesoscale model. The dispersion characteristics of the accidental
Mayoral-Villa, Estela; Alvarado-Rodríguez, Carlos E; Klapp, Jaime; Gómez-Gesteira, Moncho; Sigalotti, Leonardo Di G
2016-04-01
A smoothed particle hydrodynamics (SPH) model is presented for simulating the decay chain transport of radionuclides in confined aqueous solutions. The SPH formulation is based on the open-source parallel code DualSPHysics extended to solve the advective-diffusion equation for the evolution of the concentration field coupled to the fluid-dynamic equations, including the effects of radioactive decay of the tracer contaminants. The performance of the method is demonstrated for environmental engineering problems dealing with the transport of contaminants in still and flowing water. The results from a series of benchmark test calculations are described in two- and three-space dimensions, where the advection, diffusion, and radioactive decay modes are tested separately and in combined form. The accuracy of the present SPH transport model is shown by direct comparison with the analytical solutions and results from other SPH approaches. For a given problem, convergence of the SPH solution is seen to increase with decreasing particle size and spacing. PMID:26921532
Mayoral-Villa, Estela; Alvarado-Rodríguez, Carlos E; Klapp, Jaime; Gómez-Gesteira, Moncho; Sigalotti, Leonardo Di G
2016-04-01
A smoothed particle hydrodynamics (SPH) model is presented for simulating the decay chain transport of radionuclides in confined aqueous solutions. The SPH formulation is based on the open-source parallel code DualSPHysics extended to solve the advective-diffusion equation for the evolution of the concentration field coupled to the fluid-dynamic equations, including the effects of radioactive decay of the tracer contaminants. The performance of the method is demonstrated for environmental engineering problems dealing with the transport of contaminants in still and flowing water. The results from a series of benchmark test calculations are described in two- and three-space dimensions, where the advection, diffusion, and radioactive decay modes are tested separately and in combined form. The accuracy of the present SPH transport model is shown by direct comparison with the analytical solutions and results from other SPH approaches. For a given problem, convergence of the SPH solution is seen to increase with decreasing particle size and spacing.
NASA Astrophysics Data System (ADS)
Mayoral-Villa, Estela; Alvarado-Rodríguez, Carlos E.; Klapp, Jaime; Gómez-Gesteira, Moncho; Di G. Sigalotti, Leonardo
2016-04-01
A smoothed particle hydrodynamics (SPH) model is presented for simulating the decay chain transport of radionuclides in confined aqueous solutions. The SPH formulation is based on the open-source parallel code DualSPHysics extended to solve the advective-diffusion equation for the evolution of the concentration field coupled to the fluid-dynamic equations, including the effects of radioactive decay of the tracer contaminants. The performance of the method is demonstrated for environmental engineering problems dealing with the transport of contaminants in still and flowing water. The results from a series of benchmark test calculations are described in two- and three-space dimensions, where the advection, diffusion, and radioactive decay modes are tested separately and in combined form. The accuracy of the present SPH transport model is shown by direct comparison with the analytical solutions and results from other SPH approaches. For a given problem, convergence of the SPH solution is seen to increase with decreasing particle size and spacing.
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 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.
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
Numerical advection algorithms and their role in atmospheric transport and chemistry models
NASA Technical Reports Server (NTRS)
Rood, Richard B.
1987-01-01
During the last 35 years, well over 100 algorithms for modeling advection processes have been described and tested. This review summarizes the development and improvements that have taken place. The nature of the errors caused by numerical approximation to the advection equation are highlighted. Then the particular devices that have been proposed to remedy these errors are discussed. The extensive literature comparing transport algorithms is reviewed. Although there is no clear cut 'best' algorithm, several conclusions can be made. Spectral and pseudospectral techniques consistently provide the highest degree of accuracy, but expense and difficulties assuring positive mixing ratios are serious drawbacks. Schemes which consider fluid slabs bounded by grid points (volume schemes), rather than the simple specification of constituent values at the grid points, provide accurate positive definite results.
NASA 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 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.
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.
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.
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.
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.
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.
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.
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
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.
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.
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.
Transition from hydrodynamic to viscoelastic propagation of sound in molten RbBr.
Demmel, F; Szubrin, D; Pilgrim, W C; De Francesco, A; Formisano, F
2015-07-01
Inelastic neutron scattering was applied to measure the acoustic-type excitations in the molten alkali halide rubidium bromide. For molten RbBr neutron scattering is mainly sensitive to the number density fluctuation spectrum and is not influenced by charge fluctuations. Utilizing a dedicated Brillouin scattering spectrometer, we focused on the small-wave-vector range. From inelastic excitations in the spectra a dispersion relation was obtained, which shows a large positive dispersion effect. This frequency enhancement is related to a viscoelastic response of the liquid at high frequencies. Towards small wave vectors we identify the transition to hydrodynamic behavior. This observation is supported by a transition of the sound velocity from a viscoelastic enhanced value to the adiabatic speed of sound for the acoustic-type excitations. Furthermore, the spectrum transforms into a line shape compatible with a prediction from hydrodynamics. PMID:26274162
A single expression for solute and heat dispersion in homogeneous porous media
NASA Astrophysics Data System (ADS)
van Milligen, Boudewijn Ph.; Bons, Paul D.
2014-05-01
A variety of expressions have been proposed for dispersion in homogeneous porous media. These expressions are either for heat (thermal) or solute dispersion, and often only valid for a limited range of flow rates, typically expressed in terms of the Péclet number. We present a single, universal expression for both the heat and solute dispersion coefficient (both transverse and longitudinal) in homogeneous porous media, valid over a wide range of Péclet numbers as long as flow is laminar. The expression covers the complex intermediate regime between diffusion and advection controlled dispersion, where dispersion increases non-linearly with flow velocity. Using numerical simulations of pore channel networks, we show that that the intermediate regime can be regarded as a phase transition between random, diffusive transport at low flow velocity and ordered transport controlled by the geometry of the pore space at high flow velocities. This phase transition explains the first-order behavior in the intermediate regime. A new quantifier, the ratio of the amount of solute in dominantly advective versus dominantly diffusive pore channels, plays the role of "order parameter" of this phase transition. Bons, P.D., van Milligen, B.P., Blum, P. 2013. A general unified expression for solute and heat dispersion in homegeneous porous media. Water Resources Research 49, 1-13. van Milligen, B.Ph., Bons, P.D. 2012. Analytical model for tracer dispersion in porous media. Physical Review E 85.
An investigation of dispersion characteristics in shallow coastal waters
NASA Astrophysics Data System (ADS)
Yu, Yingying; Zhang, Hong; Spencer, David; Dunn, Ryan J. K.; Lemckert, Charles
2016-10-01
Hydrodynamic dispersion has a significant impact on the mass transport of sediments and contaminants within coastal waters. In this study apparent horizontal dispersion in a tidally-dominated shallow estuary was investigated using field observations and a numerical model. A cluster of four Lagrangian drifters was released in two shallow regions inside Moreton Bay, Australia: between two small islands and in an open water area. During a 16-h tracking period, the drifters generally showed similar behaviour, initially moving with the dominant current and remaining together before spreading apart at the change of tide. Two dispersion regimes were identified, a slow dispersion during the earlier stage and a rapid dispersion during the latter stage of deployment. Such change in regime typically occurred during the succeeding ebb or flow tides, which may be attributable to residual eddies breaking down during reversal of tidal direction. In addition, a power function of the squared separation distance over the apparent dispersion coefficient produced an R2 exceeding 0.7, indicating a significant relationship between them. By applying a three-dimensional hydrodynamic model, the trajectories of artificial particles spreading in the bay were simulated, which allowed the calculation of dispersion coefficients throughout the entire bay. The study results demonstrate that the tidal effects on dispersion were dependent on the effect of tidal excursion and residual current. The tide was found to be the most dominant driver of dispersion in the bay when unobstructed by land; however, bathymetric and shoreline characteristics were also significant localised drivers of dispersion between the two islands as a result of island wake.
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.
Advective transport and decomposition of chain-forming planktonic diatoms in permeable sediments
NASA Astrophysics Data System (ADS)
Ehrenhauss, Sandra; Huettel, Markus
2004-09-01
In laboratory chamber experiments we demonstrate that permeable sediments (>7×10 -12 m 2) exposed to boundary flows filter chain-forming coastal bloom diatoms ( Skeletonema costatum and Thalassiosira rotula) from the water column, causing rapid transfer of fresh organic particulate matter into sediment layers as deep as 5 cm within 72 h. The penetration depth of the diatoms depends on the permeability of the bed and the length of the chains. Long chains were not transported as deep into the sediment as short chains or single cells. The fast advective transfer of phytoplankton cells into sandy sediments may be an important process facilitating organic matter uptake and preventing resuspension of deposited organic material in high-energy coastal environments. High advective flushing rates in medium- and coarse-grained sandy sediments enhanced the mineralisation of the trapped diatoms (2300 to 3200 μmol C m -2 d -1), stimulated benthic oxygen consumption (2300 to 3000 μmol O 2 m -2 d -1), as well as nitrification (up to 20 μmol NO 3- m -2 d -1), relative to sediment where diffusion dominated the solute exchange. Advective solute exchange rates that increase with increasing permeability prevent the accumulation of Si(OH) 4 near the dissolving frustules and in the pore water, leading to an effective recycling of dissolved silica to the production process in the water column (95 to 101 μmol Si(OH) 4 m -2 d -1). This process may also enhance dissolution rates of the deposited opal in coarse-grained sands by maintaining higher degrees of undersaturation than in fine-grained sediments. Our results suggest that advective filtration of planktonic diatoms into permeable sediments increases mineralisation and recycling of Si(OH) 4 and organic matter in high energetic shelf areas.
NASA Astrophysics Data System (ADS)
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.
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
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.
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.
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.
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.
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.
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
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.
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.
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.
Simulating hydrodynamics on tidal mudflats
NASA Astrophysics Data System (ADS)
Cook, S.; Lippmann, T. C.
2014-12-01
Biogeochemical cycling in estuaries is governed by fluxes from both riverine sources and through estuarine sediment deposits. Although estimates from river sources are relatively common and easily sampled, estimates of nutrient fluxes through the fluid-sediment interface are less common and limited to deeper portions of the bays away from intertidal areas. Lack of quantifiable shear stress estimates over intertidal areas limits our overall understanding of nutrient budgets in estuaries. Unfortunately, observation of intertidal hydrodynamics and nutrient fluxes over tidal flats and near the water's edge is difficult owing to the temporally varying and spatially extensive region where the tides inundate, and thus numerical modeling is often employed. In this work, the Regional Ocean Modeling System (ROMS), a three dimensional numerical hydrodynamic model was used to investigate the shear stresses over intertidal mudflats in the Great Bay, a tidally-dominated New England estuary cut by several tidal channels and with over 50% of the estuary exposed at low tide. The ROMS wetting and drying scheme was used to simulate the rising and falling tide on the flats, a successful approach adapted in other regions of the world but not always inclusive of tidal channels. Bathymetric data obtained in 2009 and 2013 was used to define the model grid. Predicted tides are forced at Adam's Pt., a natural constriction in the estuary about 20 km upstream of the mouth and at the entrance to the Great Bay. Of particular interest are fluxes of material on-to and off-of the tidal flats which contribute to water quality conditions in the estuary, and are largely governed by shear stresses that drive nutrient fluxes at the fluid-sediment interface. Basin wide estimates of near-bottom shear stresses can be used to estimate first order nutrient fluxes over a tidal cycle and hence describe general biogeochemical dynamics of the estuary. Future work will include enhanced forcing of currents by
A Godunov-like point-centered essentially Lagrangian hydrodynamic approach
Morgan, Nathaniel R.; Waltz, Jacob I.; Burton, Donald E.; Charest, Marc R.; Canfield, Thomas R.; Wohlbier, John G.
2014-10-28
We present an essentially Lagrangian hydrodynamic scheme suitable for modeling complex compressible flows on tetrahedron meshes. The scheme reduces to a purely Lagrangian approach when the flow is linear or if the mesh size is equal to zero; as a result, we use the term essentially Lagrangian for the proposed approach. The motivation for developing a hydrodynamic method for tetrahedron meshes is because tetrahedron meshes have some advantages over other mesh topologies. Notable advantages include reduced complexity in generating conformal meshes, reduced complexity in mesh reconnection, and preserving tetrahedron cells with automatic mesh refinement. A challenge, however, is tetrahedron meshesmore » do not correctly deform with a lower order (i.e. piecewise constant) staggered-grid hydrodynamic scheme (SGH) or with a cell-centered hydrodynamic (CCH) scheme. The SGH and CCH approaches calculate the strain via the tetrahedron, which can cause artificial stiffness on large deformation problems. To resolve the stiffness problem, we adopt the point-centered hydrodynamic approach (PCH) and calculate the evolution of the flow via an integration path around the node. The PCH approach stores the conserved variables (mass, momentum, and total energy) at the node. The evolution equations for momentum and total energy are discretized using an edge-based finite element (FE) approach with linear basis functions. A multidirectional Riemann-like problem is introduced at the center of the tetrahedron to account for discontinuities in the flow such as a shock. Conservation is enforced at each tetrahedron center. The multidimensional Riemann-like problem used here is based on Lagrangian CCH work [8, 19, 37, 38, 44] and recent Lagrangian SGH work [33-35, 39, 45]. In addition, an approximate 1D Riemann problem is solved on each face of the nodal control volume to advect mass, momentum, and total energy. The 1D Riemann problem produces fluxes [18] that remove a volume error in the PCH
A Godunov-like point-centered essentially Lagrangian hydrodynamic approach
Morgan, Nathaniel R.; Waltz, Jacob I.; Burton, Donald E.; Charest, Marc R.; Canfield, Thomas R.; Wohlbier, John G.
2014-10-28
We present an essentially Lagrangian hydrodynamic scheme suitable for modeling complex compressible flows on tetrahedron meshes. The scheme reduces to a purely Lagrangian approach when the flow is linear or if the mesh size is equal to zero; as a result, we use the term essentially Lagrangian for the proposed approach. The motivation for developing a hydrodynamic method for tetrahedron meshes is because tetrahedron meshes have some advantages over other mesh topologies. Notable advantages include reduced complexity in generating conformal meshes, reduced complexity in mesh reconnection, and preserving tetrahedron cells with automatic mesh refinement. A challenge, however, is tetrahedron meshes do not correctly deform with a lower order (i.e. piecewise constant) staggered-grid hydrodynamic scheme (SGH) or with a cell-centered hydrodynamic (CCH) scheme. The SGH and CCH approaches calculate the strain via the tetrahedron, which can cause artificial stiffness on large deformation problems. To resolve the stiffness problem, we adopt the point-centered hydrodynamic approach (PCH) and calculate the evolution of the flow via an integration path around the node. The PCH approach stores the conserved variables (mass, momentum, and total energy) at the node. The evolution equations for momentum and total energy are discretized using an edge-based finite element (FE) approach with linear basis functions. A multidirectional Riemann-like problem is introduced at the center of the tetrahedron to account for discontinuities in the flow such as a shock. Conservation is enforced at each tetrahedron center. The multidimensional Riemann-like problem used here is based on Lagrangian CCH work [8, 19, 37, 38, 44] and recent Lagrangian SGH work [33-35, 39, 45]. In addition, an approximate 1D Riemann problem is solved on each face of the nodal control volume to advect mass, momentum, and total energy. The 1D Riemann problem produces fluxes [18] that remove a volume error in the PCH
Non abelian hydrodynamics and heavy ion collisions
NASA Astrophysics Data System (ADS)
Calzetta, E.
2014-01-01
The goal of the relativistic heavy ion collisions (RHIC) program is to create a state of matter where color degrees of freedom are deconfined. The dynamics of matter in this state, in spite of the complexities of quantum chromodynamics, is largely determined by the conservation laws of energy momentum and color currents. Therefore it is possible to describe its main features in hydrodynamic terms, the very short color neutralization time notwithstanding. In this lecture we shall give a simple derivation of the hydrodynamics of a color charged fluid, by generalizing the usual derivation of hydrodynamics from kinetic theory to the non abelian case.
Nonlinear waves in second order conformal hydrodynamics
NASA Astrophysics Data System (ADS)
Fogaça, D. A.; Marrochio, H.; Navarra, F. S.; Noronha, J.
2015-02-01
In this work we study wave propagation in dissipative relativistic fluids described by a simplified set of the 2nd order viscous conformal hydrodynamic equations corresponding to Israel-Stewart theory. Small amplitude waves are studied within the linearization approximation while waves with large amplitude are investigated using the reductive perturbation method, which is generalized to the case of 2nd order relativistic hydrodynamics. Our results indicate the presence of a "soliton-like" wave solution in Israel-Stewart hydrodynamics despite the presence of dissipation and relaxation effects.
Non abelian hydrodynamics and heavy ion collisions
Calzetta, E.
2014-01-14
The goal of the relativistic heavy ion collisions (RHIC) program is to create a state of matter where color degrees of freedom are deconfined. The dynamics of matter in this state, in spite of the complexities of quantum chromodynamics, is largely determined by the conservation laws of energy momentum and color currents. Therefore it is possible to describe its main features in hydrodynamic terms, the very short color neutralization time notwithstanding. In this lecture we shall give a simple derivation of the hydrodynamics of a color charged fluid, by generalizing the usual derivation of hydrodynamics from kinetic theory to the non abelian case.
Fluid Dynamics Prize Lecture: The Micromechanics of Colloidal Dispersions
NASA Astrophysics Data System (ADS)
Brady, John F.
2012-11-01
What do corn starch, swimming spermatozoa, DNA and self-assembling nanoparticles have in common? They are all (or can be modeled as) ``particles'' dispersed in a continuum suspending fluid where hydrodynamic interactions compete with thermal (Brownian) and interparticle forces to set structure and determine properties. These systems are ``soft'' as compared to molecular systems largely because their number density is much less and their time scales much longer than atomic or molecular systems. In this talk I will describe the common framework for modeling these diverse systems and the essential features that any hydrodynamic modeling must incorporate in order to capture the correct behavior. Actually computing the hydrodynamics in an accurate and efficient manner is the real challenge, and I will illustrate past successes and current efforts with examples drawn from the diffusion and rheology of colloids to the ``swimming'' of catalytic nanomotors.
Point based hydrodynamics applied to shallow water equations
Eltgroth, P.
1994-05-01
Smoothed Particle Hydrodynamics (SPH) has proven useful for many problems of scientific interest. This report is concerned with a generalization to the SPH method which may be of value for problems such as climate modeling. The main objective of the work is to carry out the new formulation, called Point Interactive Physics and to compare results for PIP and standard finite difference techniques on a simple test problem. The basic SPH approach describes a system using a set of points. These points are not associated with a grid or mesh, as in most approaches. The individual points are each assigned a mass and move with the material velocity. Thus the original SPH method is Lagrangian. Properties of the system are expressed as sums over the sample points using a weighting function called a kernel function. For most problems, tile weighting function extends over a relatively short range, called the smoothing length. The Point Interacting Physics (PIP) approach also samples information at a set of points, and then uses kernel functions to infer physical properties everywhere. The points are not assigned fixed values of miss and they are allowed to undergo arbitrary physically reasonable motion. In this report, results will be presented for fixed points arranged irregularly over a spherical surface. Thus, this version of PIP will be applied in an Eulerian fashion. The basic reason for the Eulerian treatment is enhanced efficiency arising from the fixed geometric relationships among the points. After a brief description of the SPH and PIP methods, the PIP formulation will be compared to a normal finite difference approach for a simple shallow water advection test problem. It appears that accurate simulations can be accomplished, but that computational speed is comparable to that observed for other techniques.
Observation of Dispersive Shock Waves, Solitons, and Their Interactions in Viscous Fluid Conduits.
Maiden, Michelle D; Lowman, Nicholas K; Anderson, Dalton V; Schubert, Marika E; Hoefer, Mark A
2016-04-29
Dispersive shock waves and solitons are fundamental nonlinear excitations in dispersive media, but dispersive shock wave studies to date have been severely constrained. Here, we report on a novel dispersive hydrodynamic test bed: the effectively frictionless dynamics of interfacial waves between two high viscosity contrast, miscible, low Reynolds number Stokes fluids. This scenario is realized by injecting from below a lighter, viscous fluid into a column filled with high viscosity fluid. The injected fluid forms a deformable pipe whose diameter is proportional to the injection rate, enabling precise control over the generation of symmetric interfacial waves. Buoyancy drives nonlinear interfacial self-steepening, while normal stresses give rise to the dispersion of interfacial waves. Extremely slow mass diffusion and mass conservation imply that the interfacial waves are effectively dissipationless. This enables high fidelity observations of large amplitude dispersive shock waves in this spatially extended system, found to agree quantitatively with a nonlinear wave averaging theory. Furthermore, several highly coherent phenomena are investigated including dispersive shock wave backflow, the refraction or absorption of solitons by dispersive shock waves, and the multiphase merging of two dispersive shock waves. The complex, coherent, nonlinear mixing of dispersive shock waves and solitons observed here are universal features of dissipationless, dispersive hydrodynamic flows.
Observation of Dispersive Shock Waves, Solitons, and Their Interactions in Viscous Fluid Conduits.
Maiden, Michelle D; Lowman, Nicholas K; Anderson, Dalton V; Schubert, Marika E; Hoefer, Mark A
2016-04-29
Dispersive shock waves and solitons are fundamental nonlinear excitations in dispersive media, but dispersive shock wave studies to date have been severely constrained. Here, we report on a novel dispersive hydrodynamic test bed: the effectively frictionless dynamics of interfacial waves between two high viscosity contrast, miscible, low Reynolds number Stokes fluids. This scenario is realized by injecting from below a lighter, viscous fluid into a column filled with high viscosity fluid. The injected fluid forms a deformable pipe whose diameter is proportional to the injection rate, enabling precise control over the generation of symmetric interfacial waves. Buoyancy drives nonlinear interfacial self-steepening, while normal stresses give rise to the dispersion of interfacial waves. Extremely slow mass diffusion and mass conservation imply that the interfacial waves are effectively dissipationless. This enables high fidelity observations of large amplitude dispersive shock waves in this spatially extended system, found to agree quantitatively with a nonlinear wave averaging theory. Furthermore, several highly coherent phenomena are investigated including dispersive shock wave backflow, the refraction or absorption of solitons by dispersive shock waves, and the multiphase merging of two dispersive shock waves. The complex, coherent, nonlinear mixing of dispersive shock waves and solitons observed here are universal features of dissipationless, dispersive hydrodynamic flows. PMID:27176524
Hydrodynamic Instabilities Produced by Evaporation
NASA Astrophysics Data System (ADS)
Romo-Cruz, Julio Cesar Ruben; Hernandez-Zapata, Sergio; Ruiz-Chavarria, Gerardo
2012-11-01
When a liquid layer (alcohol in the present work) is in an environment where its relative humidity is less than 100 percent evaporation appears. When RH is above a certain threshold the liquid is at rest. If RH decreases below this threshold the flow becomes unstable, and hydrodynamic cells develop. The aim of this work is to understand the formation of those cells and its main features. Firstly, we investigate how the cell size depends on the layer width. We also study how temperature depends on the vertical coordinate when the cells are present. An inverse temperature gradient is found, that is, the bottom of liquid layer is colder than the free surface. This shows that the intuitive idea that the cells are due to a direct temperature gradient, following a Marangoni-like process, does not work. We propose the hypothesis that the evaporation produce a pressure gradient that is responsible of the cell development. On the other hand, using a Schlieren technique we study the topography of the free surface when cells are present. Finally the alcohol vapor layer adjacent to the liquid surface is explored using scattering experiments, giving some insight on the plausibility of the hypothesis described previously. Authors acknowledge support by DGAPA-UNAM under project IN116312 ``Vorticidad y ondas no lineales en fluidos.''
Hydrodynamic Simulations of Contact Binaries
NASA Astrophysics Data System (ADS)
Kadam, Kundan; Clayton, Geoffrey C.; Frank, Juhan; Marcello, Dominic; Motl, Patrick M.; Staff, Jan E.
2015-01-01
The motivation for our project is the peculiar case of the 'red nova" V1309 Sco which erupted in September 2008. The progenitor was, in fact, a contact binary system. We are developing a simulation of contact binaries, so that their formation, structural, and merger properties could be studied using hydrodynamics codes. The observed transient event was the disruption of the secondary star by the primary, and their subsequent merger into one star; hence to replicate this behavior, we need a core-envelope structure for both the stars. We achieve this using a combination of Self Consistant Field (SCF) technique and composite polytropes, also known as bipolytropes. So far we have been able to generate close binaries with various mass ratios. Another consequence of using bipolytropes is that according to theoretical calculations, the radius of a star should expand when the core mass fraction exceeds a critical value, resulting in interesting consequences in a binary system. We present some initial results of these simulations.
Hydrodynamic aspects of fish olfaction
Cox, Jonathan P.L
2008-01-01
Flow into and around the olfactory chamber of a fish determines how odorant from the fish's immediate environment is transported to the sensory surface (olfactory epithelium) lining the chamber. Diffusion times in water are long, even over comparatively short distances (millimetres). Therefore, transport from the external environment to the olfactory epithelium must be controlled by processes that rely on convection (i.e. the bulk flow of fluid). These include the beating of cilia lining the olfactory chamber and the relatively inexpensive pumping action of accessory sacs. Flow through the chamber may also be induced by an external flow. Flow over the olfactory epithelium appears to be laminar. Odorant transfer to the olfactory epithelium may be facilitated in several ways: if the olfactory organs are mounted on stalks that penetrate the boundary layer; by the steep velocity gradients generated by beating cilia; by devices that deflect flow into the olfactory chamber; by parallel arrays of olfactory lamellae; by mechanical agitation of the chamber (or olfactory stalks); and by vortices. Overall, however, our knowledge of the hydrodynamics of fish olfaction is far from complete. Several areas of future research are outlined. PMID:18184629
Detonation waves in relativistic hydrodynamics
Cissoko, M. )
1992-02-15
This paper is concerned with an algebraic study of the equations of detonation waves in relativistic hydrodynamics taking into account the pressure and the energy of thermal radiation. A new approach to shock and detonation wavefronts is outlined. The fluid under consideration is assumed to be perfect (nonviscous and nonconducting) and to obey the following equation of state: {ital p}=({gamma}{minus}1){rho} where {ital p}, {rho}, and {gamma} are the pressure, the total energy density, and the adiabatic index, respectively. The solutions of the equations of detonation waves are reduced to the problem of finding physically acceptable roots of a quadratic polynomial {Pi}({ital X}) where {ital X} is the ratio {tau}/{tau}{sub 0} of dynamical volumes behind and ahead of the detonation wave. The existence and the locations of zeros of this polynomial allow it to be shown that if the equation of state of the burnt fluid is known then the variables characterizing the unburnt fluid obey well-defined physical relations.
Wang, Dongchen; Dudda, Som; Jackson, P. Ryan; Garcia, Marcelo H.
2016-01-01
The Chicago Area Waterway System (CAWS) includes the Chicago Sanitary and Ship Canal (CSSC) and the Calumet-Sag Channel (Cal-Sag), the two primary, man-made connections between the Mississippi River Basin and the Great Lakes. The U.S. Geological Survey (USGS) monitors diversion of Great Lakes water at a streamgage just downstream of the confluence of the CSSC and Cal-Sag (known as Sag Junction). Previous studies have explored the complex hydrodynamics in the CAWS near Sag Junction and at the USGS streamgage near Lemont, Illinois. The current study explores the mixing at Sag Junction which can be purely advection-driven or driven by density differences between the two branches. The current study simulates and analyzes two cases: 1) the density of water in CSSC is greater than in the Cal-Sag, 2) the density of the CSSC water is less than in the Cal-Sag. The density difference between the branches was found to play a major role in influencing the mixing process compared with purely advection-driven mixing. Density differences created near-bed gravity currents, some of which intruded upstream into the CSSC or Cal-Sag creating bi-directional flows. The phenomenon of double plunging was observed, along with formation of a recirculation zone between the two plunging fronts. Local mixing at the confluence was enhanced by density differences between the two channels, but mixing downstream from the confluence was impeded due to formation of a stabilizing stratification.
Electrokinetic induced solute dispersion in porous media; pore network modeling
NASA Astrophysics Data System (ADS)
Li, Shuai; Schotting, Ruud; Raoof, Amir
2013-04-01
Electrokinetic flow plays an important role in remediation process, separation technique, and chromatography. The solute dispersion is a key parameter to determine transport efficiency. In this study, we present the electrokinetic effects on solute dispersion in porous media at the pore scale, using a pore network model. The analytical solution of the electrokinetic coupling coefficient was obtained to quantity the fluid flow velocity in a cylinder capillary. The effect of electrical double layer on the electrokinetic coupling coefficient was investigated by applying different ionic concentration. By averaging the velocity over cross section within a single pore, the average flux was obtained. Applying such single pore relationships, in the thin electrical double layer limit, to each and every pore within the pore network, potential distribution and the induced fluid flow was calculated for the whole domain. The resulting pore velocities were used to simulate solute transport within the pore network. By averaging the results, we obtained the breakthrough curve (BTC) of the average concentration at the outlet of the pore network. Optimizing the solution of continuum scale advection-dispersion equation to such a BTC, solute dispersion coefficient was estimated. We have compared the dispersion caused by electrokinetic flow and pure pressure driven flow under different Peclet number values. In addition, the effect of microstructure and topological properties of porous media on fluid flow and solute dispersion is presented, mainly based on different pore coordination numbers.
DOE R&D Accomplishments Database
Salam, A.
1956-04-01
Lectures with mathematical analysis are given on Dispersion Theory and Causality and Dispersion Relations for Pion-nucleon Scattering. The appendix includes the S-matrix in terms of Heisenberg Operators. (F. S.)
Maximum entropy principle and relativistic hydrodynamics
NASA Astrophysics Data System (ADS)
van Weert, Ch. G.
1982-04-01
A relativistic theory of hydrodynamics applicable beyond the hydrodynamic regime is developed on the basis of the maximum entropy principle. This allows the construction of a unique statistical operator representing the state of the system as specified by the values of the hydrodynamical densities. Special attention is paid to the thermodynamic limit and the virial theorem which leads to an expression for the pressure in terms of the field-theoretic energymomentum tensor of Coleman and Jackiw. It is argued that outside the hydrodynamic regime the notion of a local Gibbs relation, as usually postulated, must be abandoned in general. In the nontext of the linear approximation, the memory-retaining and non-local generalizations of the relativistic Navier-Stokes equations are derived from the underlying Heisenberg equations of motion. The formal similarity to the Zwanzig-Mori description of non-relativistic fluids is expounded.
Hydrodynamic trapping of molecules in lipid bilayers
Jönsson, Peter; McColl, James; Clarke, Richard W.; Ostanin, Victor P.; Jönsson, Bengt; Klenerman, David
2012-01-01
In this work we show how hydrodynamic forces can be used to locally trap molecules in a supported lipid bilayer (SLB). The method uses the hydrodynamic drag forces arising from a flow through a conical pipette with a tip radius of 1–1.5 μm, placed approximately 1 μm above the investigated SLB. This results in a localized forcefield that acts on molecules protruding from the SLB, yielding a hydrodynamic trap with a size approximately given by the size of the pipette tip. We demonstrate this concept by trapping the protein streptavidin, bound to biotin receptors in the SLB. It is also shown how static and kinetic information about the intermolecular interactions in the lipid bilayer can be obtained by relating how the magnitude of the hydrodynamic forces affects the accumulation of protein molecules in the trap. PMID:22699491
Flagellar Synchronization Independent of Hydrodynamic Interactions
NASA Astrophysics Data System (ADS)
Friedrich, Benjamin M.; Jülicher, Frank
2012-09-01
Inspired by the coordinated beating of the flagellar pair of the green algae Chlamydomonas, we study theoretically a simple, mirror-symmetric swimmer, which propels itself at low Reynolds number by a revolving motion of a pair of spheres. We show that perfect synchronization between these two driven spheres can occur due to the motion of the swimmer and local hydrodynamic friction forces. Hydrodynamic interactions, though crucial for net propulsion, contribute little to synchronization for this free-moving swimmer.
Chemo-hydrodynamic patterns in porous media.
De Wit, A
2016-10-13
Chemical reactions can interplay with hydrodynamic flows to generate chemo-hydrodynamic instabilities affecting the spatio-temporal evolution of the concentration of the chemicals. We review here such instabilities for porous media flows. We describe the influence of chemical reactions on viscous fingering, buoyancy-driven fingering in miscible systems, convective dissolution as well as precipitation patterns. Implications for environmental systems are discussed.This article is part of the themed issue 'Energy and the subsurface'. PMID:27597788
Dispersion y dinamica poblacional
Technology Transfer Automated Retrieval System (TEKTRAN)
Dispersal behavior of fruit flies is appetitive. Measures of dispersion involve two different parameter: the maximum distance and the standard distance. Standard distance is a parameter that describes the probalility of dispersion and is mathematically equivalent to the standard deviation around ...
The hydrodynamic focusing effect inside rectangular microchannels
NASA Astrophysics Data System (ADS)
Lee, Gwo-Bin; Chang, Chih-Chang; Huang, Sung-Bin; Yang, Ruey-Jen
2006-05-01
This paper presents a theoretical and experimental investigation into the hydrodynamic focusing effect in rectangular microchannels. Two theoretical models for two-dimensional hydrodynamic focusing are proposed. The first model predicts the width of the focused stream in symmetric hydrodynamic focusing in microchannels of various aspect ratios. The second model predicts the location and the width of the focused stream in asymmetric hydrodynamic focusing in microchannels with a low or high aspect ratio. In both models, the theoretical results are shown to be in good agreement with the experimental data. Hence, the models provide a useful means of performing a theoretical analysis of flow control in microfluidic devices using hydrodynamic focusing effects. The ability of the proposed models to control the focused stream within a micro flow cytometer is verified in a series of experimental trials performed using polystyrene microparticles with a diameter of 20 µm. The experimental data show that the width of the focused stream can be reduced to the same order of magnitude as that of the particle size. Furthermore, it is shown that the microparticles can be successfully hydrodynamically focused and switched to the desired outlet port of the cytometer. Hence, the models presented in this study provide sufficient control to support cell/particle counting and sorting applications.
NASA Technical Reports Server (NTRS)
Mazaheri, Alireza; Ricchiuto, Mario; Nishikawa, Hiroaki
2016-01-01
In this paper, we introduce a new hyperbolic first-order system for general dispersive partial differential equations (PDEs). We then extend the proposed system to general advection-diffusion-dispersion PDEs. We apply the fourth-order RD scheme of Ref. 1 to the proposed hyperbolic system, and solve time-dependent dispersive equations, including the classical two-soliton KdV and a dispersive shock case. We demonstrate that the predicted results, including the gradient and Hessian (second derivative), are in a very good agreement with the exact solutions. We then show that the RD scheme applied to the proposed system accurately captures dispersive shocks without numerical oscillations. We also verify that the solution, gradient and Hessian are predicted with equal order of accuracy.
Upscaling of Solute Transport in Heterogeneous Media with Non-uniform Flow and Dispersion Fields
Xu, Zhijie; Meakin, Paul
2013-10-01
An analytical and computational model for non-reactive solute transport in periodic heterogeneous media with arbitrary non-uniform flow and dispersion fields within the unit cell of length ε is described. The model lumps the effect of non-uniform flow and dispersion into an effective advection velocity Ve and an effective dispersion coefficient De. It is shown that both Ve and De are scale-dependent (dependent on the length scale of the microscopic heterogeneity, ε), dependent on the Péclet number Pe, and on a dimensionless parameter α that represents the effects of microscopic heterogeneity. The parameter α, confined to the range of [-0.5, 0.5] for the numerical example presented, depends on the flow direction and non-uniform flow and dispersion fields. Effective advection velocity Ve and dispersion coefficient De can be derived for any given flow and dispersion fields, and . Homogenized solutions describing the macroscopic variations can be obtained from the effective model. Solutions with sub-unit-cell accuracy can be constructed by homogenized solutions and its spatial derivatives. A numerical implementation of the model compared with direct numerical solutions using a fine grid, demonstrated that the new method was in good agreement with direct solutions, but with significant computational savings.
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.
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.
Klein, R.I. . Dept. of Astronomy Lawrence Livermore National Lab., CA ); Arons, J. . Dept. of Astronomy California Univ., Berkeley, CA . Dept. of Physics)
1990-11-20
We present for the first time, the self-consistent solution of the two-dimensional, time-dependent equations of radiation-hydrodynamics governing the accretion of matter onto the highly magnetized polar caps of luminous x-ray pulsars. The calculations show a structure in the accretion column very different from previous one-zone uniform models. We have included all the relevant magnetic field corrections to both the hydrodynamics and the radiative transport. We include a new theory for the diffusion and advection of both radiation energy density and photon number density. For initially uniformly accreting models with super-Eddington flows, we have uncovered evidence of strong radiation-driven outflowing optically thin radiation filled regions of the accretion column embedded in optically-thick inflowing plasma. We follow the evolution of these photon bubbles for several dynamical timescales. The development of these photon bubbles'' indicates growth times on the order of a millisecond and show fluctuations on sub-millisecond timescales in agreement with a linear stability analysis. The photon bubbles are a consequence of the effect of radiative heat flux on the internal gravity waves in the strongly magnetized atmosphere and may result in observable fluctuations in the emitted luminosity leading to luminosity dependent changes in the pulse profile. This may provide important new diagnostics for conditions in accreting x-ray pulsars. 19 refs., 13 figs.
Klein, R.I. . Dept. of Astronomy Lawrence Livermore National Lab., CA California Univ., Los Angeles, CA . Inst. of Geophysics and Planetary Physics); Arons, J. . Dept. of Astronomy California Univ., Los Angeles, CA . Inst. of Geophysics and Planetary Physics CEA Centre d'Etudes Nucleaires de Saclay, 91 -
1989-11-24
We present for the first time, the self-consistent solution of the two-dimensional, time-dependent equations of radiation-hydrodynamics governing the accretion of matter onto the highly magnetized polar caps of luminous x-ray pulsars. The calculations show a structure in the accretion column very different from previous one-zone uniform models. We have included all the relevant magnetic field corrections to both the hydrodynamics and the radiative transport. We include a new theory for the diffusion and advection of both radiation energy density and photon number density. For initially uniformly accreting models with super-Eddington flows, we have uncovered evidence of strong radiation-driven outflowing optically thin radiation filled regions of the accretion column embedded in optically-thick inflowing plasma. The development of these photon bubbles'' have growth times on the order of a millisecond and show fluctuations on sub-millisecond timescales. The photon bubbles are likely to be a consequence of convective over-stability and may result in observable fluctuations in the emitted luminosity leading to luminosity dependent changes in the pulse profile. This may provide important new diagnostics for conditions in accreting x-ray pulsars. 13 refs., 18 figs.
Simulation of hydrodynamically interacting particles confined by a spherical cavity
NASA Astrophysics Data System (ADS)
Aponte-Rivera, Christian; Zia, Roseanna N.
2016-06-01
We present a theoretical framework to model the behavior of a concentrated colloidal dispersion confined inside a spherical cavity. Prior attempts to model such behavior were limited to a single enclosed particle and attempts to enlarge such models to two or more particles have seen limited success owing to the challenges of accurately modeling many-body and singular hydrodynamic interactions. To overcome these difficulties, we have developed a set of hydrodynamic mobility functions that couple particle motion with hydrodynamic traction moments that, when inverted and combined with near-field resistance functions, form a complete coupling tensor that accurately captures both the far-field and near-field physics and is valid for an arbitrary number of spherical particles enclosed by a spherical cavity of arbitrary relative size a /R , where a and R are the particle and cavity size, respectively. This framework is then utilized to study the effect of spherical confinement on the self- and entrained motion of the colloids, for a range of particle-to-cavity size ratios. The self-motion of a finite-size enclosed particle is studied first, recovering prior results published in the literature: The hydrodynamic mobility of the particle is greatest at the center of the cavity and decays as (a /R ) /(1 -y2) , where y is the particle distance to the cavity center. Near the cavity wall, the no-slip surfaces couple strongly and mobility along the cavity radius vanishes as ξ ≡R -(a +y ) , where y is center-to-center distance from particle to cavity. Corresponding motion transverse to the cavity radius vanishes as [ln(1/ξ ) ] -1. The effect of confinement on entrainment of a particle in the flow created by the motion of others is also studied, where we find that confinement exerts a qualitative effect on the strength and anisotropy of entrainment of a passive particle dragged by the flow of a forced particle. As expected, entrainment strength decays with increased distance
Dispersants displace hot oiling
Wash, R.
1984-02-01
Laboratory experiments and field testing of dispersants in producing wells have resulted in development of 2 inexpensive paraffin dispersant packages with a broad application range, potential for significant savings over hot oiling, and that can be applied effectively by both continuous and batch treating techniques. The 2 dispersants are soluble in the carrier solvent (one soluble in oil, one in water); are able to readily disperse the wax during a hot flask test conducted in a laboratory; and leave the producing interval water wet. Field data on the 2 dispersants are tabulated, demonstrating their efficacy.
Theory of dispersive microlenses
NASA Technical Reports Server (NTRS)
Herman, B.; Gal, George
1993-01-01
A dispersive microlens is a miniature optical element which simultaneously focuses and disperses light. Arrays of dispersive mircolenses have potential applications in multicolor focal planes. They have a 100 percent optical fill factor and can focus light down to detectors of diffraction spot size, freeing up areas on the focal plane for on-chip analog signal processing. Use of dispersive microlenses allows inband color separation within a pixel and perfect scene registration. A dual-color separation has the potential for temperature discrimination. We discuss the design of dispersive microlenses and present sample results for efficient designs.
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
Taylor dispersion of colloidal particles in narrow channels
NASA Astrophysics Data System (ADS)
Sané, Jimaan; Padding, Johan T.; Louis, Ard A.
2015-09-01
We use a mesoscopic particle-based simulation technique to study the classic convection-diffusion problem of Taylor dispersion for colloidal discs in confined flow. When the disc diameter becomes non-negligible compared to the diameter of the pipe, there are important corrections to the original Taylor picture. For example, the colloids can flow more rapidly than the underlying fluid, and their Taylor dispersion coefficient is decreased. For narrow pipes, there are also further hydrodynamic wall effects. The long-time tails in the velocity autocorrelation functions are altered by the Poiseuille flow.
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.
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.
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).
Longitudinal dispersion in vegetated rivers with stochastic flows
NASA Astrophysics Data System (ADS)
Tealdi, S.; Camporeale, C.; Perucca, E.; Ridolfi, L.
2010-05-01
Longitudinal dispersion is one of the most important transport processes in fluvial ecosystems. It affects the transport of chemicals, nutrients, seeds, and wood debris along a river. The focus of this work is on the impact of riparian vegetation on the dispersion coefficient. The investigation considers stochastic forcing due to the river discharge randomness and its interplay with vegetation dynamics. A stochastic bio-hydrodynamical model is proposed and the probability distribution of the dispersion coefficient is obtained. The model allows one to elucidate the influence of (i) the vegetation characteristics, (ii) the probabilistic structure of the discharge time series, and (iii) the hydraulic characteristics of the transect. The work demonstrates the high variability of dispersion coefficients and the remarkable impact of riparian vegetation when medium/high discharges flow.
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.
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.
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
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.
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.
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
Richon, Patrick; Perrier, Frédéric; Koirala, Bharat Prasad; Girault, Frédéric; Bhattarai, Mukunda; Sapkota, Soma Nath
2011-02-01
Temporal variation of radon-222 concentration was studied at the Syabru-Bensi hot springs, located on the Main Central Thrust zone in Central Nepal. This site is characterized by several carbon dioxide discharges having maximum fluxes larger than 10 kg m(-2) d(-1). Radon concentration was monitored with autonomous Barasol™ probes between January 2008 and November 2009 in two small natural cavities with high CO(2) concentration and at six locations in the soil: four points having a high flux, and two background reference points. At the reference points, dominated by radon diffusion, radon concentration was stable from January to May, with mean values of 22 ± 6.9 and 37 ± 5.5 kBq m(-3), but was affected by a large increase, of about a factor of 2 and 1.6, respectively, during the monsoon season from June to September. At the points dominated by CO(2) advection, by contrast, radon concentration showed higher mean values 39.0 ± 2.6 to 78 ± 1.4 kBq m(-3), remarkably stable throughout the year with small long-term variation, including a possible modulation of period around 6 months. A significant difference between the diffusion dominated reference points and the advection-dominated points also emerged when studying the diurnal S(1) and semi-diurnal S(2) periodic components. At the advection-dominated points, radon concentration did not exhibit S(1) or S(2) components. At the reference points, however, the S(2) component, associated with barometric tide, could be identified during the dry season, but only when the probe was installed at shallow depth. The S(1) component, associated with thermal and possibly barometric diurnal forcing, was systematically observed, especially during monsoon season. The remarkable short-term and long-term temporal stability of the radon concentration at the advection-dominated points, which suggests a strong pressure source at depth, may be an important asset to detect possible temporal variations associated with the
NASA Technical Reports Server (NTRS)
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.
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
Lagrangian Particle Method for Local Scale Dispersion Modeling
NASA Astrophysics Data System (ADS)
Sunarko; ZakiSu'ud
2016-08-01
A deterministic model is developed for radioactive dispersion analysis based on random-walk Lagrangian Particle Dispersion Method (LPDM). A diagnostic 3dimensional mass-consistent wind-field with a capability to handle complex topography can be used to provide input for particle advection. Turbulent diffusion process of particles is determined based on empirical lateral and linear vertical relationships. Surface-level concentration is calculated for constant unit release from elevated point source. A series of 60-second segmented groups of particles are released in 3600 seconds total duration. Averaged surface-level concentration within a 5 meter surface layer is obtained and compared with available analytical solution. Results from LPDM shows good agreement with the analytical result for vertically constant and varying wind field with the same atmospheric stability.
Latunde-Dada, Seyi; Bott, Rachel; Hampton, Karl; Leszczyszyn, Oksana Iryna
2015-08-01
Taylor dispersion analysis (TDA) is a fast and simple method for determining hydrodynamic radii. The method is applicable under conditions that allow the solute molecules to diffuse appreciably across the cross section of the flow before its measurement. This mitigates the effects of early stage convection on the dispersion and thus imposes a lower bound on the value of the diffusion coefficient measurable at a given flow speed. In this paper, we use the exact solution to the dispersion problem to analyze solutes outside the limits of TDA. Furthermore, by modeling the early stage convection, we analyze a mixture of two solutes with significantly different sizes that mimics heavily aggregated samples. The results obtained from the fits in both cases were in good agreement to the expected values. This demonstrates the potential of the model to extend dispersion analysis to regimes well outside the TDA limits such as the analysis of large molecules and the use of high flow-rates. PMID:26161948
Margraf, J
2012-06-12
This report primarily concerns the use of two massively parallel finite element codes originally written and maintained at Lawrence Livermore National Laboratory. ALE3D is an explicit hydrodynamics code commonly employed to simulate wave propagation from high energy scenarios and the resulting interaction with nearby structures. This coupled response ensures that a structure is accurately applied with a blast loading varying both in space and time. Figure 1 illustrates the radial outward propagation of a pressure wave due to a center detonated spherical explosive originating from the lower left. The radial symmetry seen in this scenario is lost when instead a cylindrocal charge is detonated. Figure 2 indicates that a stronger, faster traveling pressure wave occurs in the direction of the normal axis to the cylinder. The ALE3D name is derived because of the use of arbitrary-Lagrange-Eulerian elements in which the mesh is allowed to advect; a process through which the mesh is modified to alleviate tanlging and general mesh distortion often cuased by high energy scenarios. The counterpart to an advecting element is a Lagrange element, whose mesh moves with the material. Ideally all structural components are kept Lagrange as long as possible to preserve accuracy of material variables and minimize advection related errors. Advection leads to mixed zoning, so using structural Lagrange elements also improves the visualization when post processing the results. A simplified representation of the advection process is shown in Figure 3. First the mesh is distorted due to material motion during the Lagrange step. The mesh is then shifted to an idealized and less distorted state to prevent irregular zones caused by the Lagrange motion. Lastly, the state variables are remapped to the elements of the newly constructed mesh. Note that Figure 3 represents a purely Eulerian mesh relaxation because the mesh is relocated back to the pre-Lagrange position. This is the case when the
NASA Astrophysics Data System (ADS)
Kantardgi, Igor; Zheleznyak, Mark; Demchenko, Raisa; Dykyi, Pavlo; Kivva, Sergei; Kolomiets, Pavlo; Sorokin, Maxim
2014-05-01
The nearshore hydrodynamic fields are produced by the nonlinear interactions of the shoaling waves of different time scales and currents. To simulate the wind wave and swells propagated to the coasts, wave generated near shore currents, nonlinear-dispersive wave transformation and wave diffraction in interaction with coastal and port structure, sediment transport and coastal erosion the chains of the models should be used. The objective of this presentation is to provide an overview of the results of the application of the model chains for the assessment of the wave impacts on new construction designed at the Black Sea coasts and the impacts of these constructions on the coastal erosion/ accretion processes to demonstrate needs for further development of the nonlinear models for the coastal engineering applications. The open source models Wave Watch III and SWAN has been used to simulate wave statistics of the dedicated areas of the Black Sea in high resolution to calculated the statistical parameters of the extreme wave approaching coastal zone construction in accordance with coastal engineering standards. As the main tool for the costal hydrodynamic simulations the modeling system COASTOX-MORPHO has been used, that includes the following models. HWAVE -code based on hyperbolic version of mild slope equations., HWAVE-S - spectral version of HWAVE., BOUSS-FNL - fully nonlinear system of Boussinesq equations for simulation wave nonlinear -dispersive wave transformation in coastal areas. COASTOX-CUR - the code provided the numerical solution of the Nonlinear Shallow Water Equations (NLSWE) by finite-volume methods on the unstructured grid describing the long wave transformation in the coastal zone with the efficient drying -wetting algorithms to simulate the inundation of the coastal areas including tsunami wave runup. Coastox -Cur equations with the radiation stress term calculated via near shore wave fields simulate the wave generated nearhore currents. COASTOX
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.