Advection Phenomena Research Articles

Observation and modeling of the storm-induced fluid mud dynamics in a muddy-estuarine navigational channel

Observations of storm-induced fluid mud dynamics have been conducted at the North Passage deepwater navigational channel (DNC) of the Yangtze Estuary in October to December 2010, during the occurrence of a cold-air front. The measurement data reveal that just after the critical wind wave event, a large amount of fine sediment was trapped in a state of fluid mud along the channel. The observed thickness of the fluid mud was up to about 1–5m, which caused some significant economic and safety problems for shipping traffic in the Yangtze Delta area. The mechanisms and transport processes of the storm-induced fluid mud are analyzed and presented from the angles of both process-oriented and engineering-oriented methods. With the help of hydrodynamics and wave modeling, it could be inferred that the behavior of the storm-induced fluid mud event mainly depends on the overall hydrodynamic regimes and the exchanges of sediment, which is released by storm-wave agitation from adjacent tidal flats. These sediments are accumulated as fluid mud, and subsequently oscillate and persist at those locations with weaker longitudinal residuals in the river- and tide-dominated estuary. In addition, the downslope transport of fluid mud is also thought to have stimulated and worsened the fluid mud event observed in this study. Our modeling results and observations demonstrate that: (1) the transport of fluid mud is an advective phenomenon determining the central position of fluid mud layer along the channel, and it's also a tidal energy influenced phenomenon controlling the erosion and accumulation of fluid mud; and (2) both suspended particulate matter availability and local residual flow regime are of critical importance in determining the trapping probability of sediment and the occurrence of fluid mud.

On the application of SUPG/θ-method in 2D advection–diffusion-reaction simulation

The SUPG/θ-method for applications in 2D advection–diffusion transport simulation is reviewed and it is presented in details. Spatial discretization is done with finite elements method with stabilized streamline upwind Petrov–Galerkin method, and time discretization was done with θ-stable finite difference operator. Numerical tests showed that this algorithm is general and robust and it can be applied to simulate simple problems of mass transport; for example, pure advection phenomenon in structured mesh, as well as reactive advection–diffusion transport with an unstructured mesh, and not well-behaved velocity field. The method was applied in a simulation of the transport of total phosphorus in the Lake Agua Preta, and the results were validated by comparison with experimental data. The computational cost is directly associated with the value of the safety factor, introduced to assure the stability of the method.

Super-Gaussian transport theory and the field-generating thermal instability in laser–plasmas

Inverse bremsstrahlung (IB) heating is known to distort the electron distribution function in laser–plasmas from a Gaussian towards a super-Gaussian, thereby modifying the equations of classical transport theory (Ridgers et al 2008 Phys. Plasmas15 092311). Here we explore these modified equations, demonstrating that super-Gaussian effects both suppress traditional transport processes, while simultaneously introducing new effects, such as isothermal (anomalous Nernst) magnetic field advection up gradients in the electron number density ne, which we associate with a novel heat-flow qn∝∇ne. Suppression of classical phenomena is shown to be most pronounced in the limit of low Hall-parameter χ, in which case the Nernst effect is reduced by a factor of five, the ∇Te × ∇ne field generation mechanism by ∼30% (where Te is the electron temperature), and the diffusive and Righi–Leduc heat-flows by ∼80 and ∼90% respectively. The new isothermal field advection phenomenon and associated density-gradient driven heat-flux qn are checked against kinetic simulation using the Vlasov–Fokker–Planck code impact, and interpreted in relation to the underlying super-Gaussian distribution through simplified kinetic analysis. Given such strong inhibition of transport at low χ, we consider the impact of IB on the seeding and evolution of magnetic fields (in otherwise un-magnetized conditions) by examining the well-known field-generating thermal instability in the light of super-Gaussian transport theory (Tidman and Shanny 1974 Phys. Fluids12 1207). Estimates based on conditions in an inertial confinement fusion (ICF) hohlraum suggest that super-Gaussian effects can reduce the growth-rate of the instability by ≳80%. This result may be important for ICF experiments, since by increasing the strength of IB heating it would appear possible to inhibit the spontaneous generation of large magnetic fields.

Advective–diffusive mass transfer in binary regular structures in the steady-state regime

Having analyzed the stationary processes of admixture transfer in two-phase regular structures with taking into account periodical character of advective phenomena, we propose a method of constructing exact analytic solutions for such class of boundary value problems. This technique is based on the application of integral transformations individually for each contacting domain. The relation between these corresponding integral transformations is obtained from the nonideal boundary conditions. We have obtained the analytic solution of a diffusion problem for a two-phase layer of a regular structure with advective mass transfer mechanism in one of its phases. The expressions describing admixture flow through a certain body surface are derived, mass flows through the interface is investigated. Having analyzed the concentration of migrating particles in the structural elements of the body and the admixture flow through the given body surface, we present results graphically. The conditions of the existence of a limit passage from the contact boundary value problem of advective diffusion in regular structures to the continual model of advective two-way heterodiffusion are determined. A natural dimensionless form is introduced.

Saltwater intrusion and ETM dynamics in a tidally-energetic stratified estuary

We explore the dynamics of the salt wedge and estuarine turbidity maxima (ETMs) in the Rotterdam Waterway using three-dimensional model simulations. These are compared to 13-h time series of profiles of velocity, salinity and suspended particulate matter (SPM) at a number of boat stations along the estuary, and long-term water level and salinity records. Evaluation of the numerical results shows that while good agreement is found between predicted and measured water levels and tidal discharges, the model under-predicts saltwater intrusion and stratification, and it over-predicts the height of the pycnocline above the bed. This leads to deficiencies in predictions of (1) the magnitude and vertical distribution of the baroclinic pressure gradient and subsequently of local shear and (2) vertical SPM gradients and concentrations near the bed because salinity stratification determines this distribution. However, the stability of the salt wedge during tidal excursions, the dominant role played by currents caused by the baroclinic pressure gradient and the damping of turbulence at the pycnocline with subsequent trapping of fluvial SPM at the head of the salt wedge are all well reproduced. A single stable ETM is formed when the salt wedge remains in the Rotterdam Waterway at low water slack. When saltwater intrudes farther up-estuary, multiple stable along-channel ETMs are maintained by localized trapping of fluvial SPM at the respective heads of saltwater by salinity gradients. Our results demonstrate that (1) the saltwater intrusion length is one of the main parameters controlling the SPM trapping probability and (2) the ETM is an advective phenomenon determining the timing of the availability of SPM for exchange with harbours. The model results indicate that all sediments deposited in the harbours along the Rotterdam Waterway and New Meuse are of fluvial origin.

A New Approach for a Nonlocal, Nonlinear Conservation Law

We describe an approach to nonlocal, nonlinear advection in one dimension that extends the usual pointwise concepts to account for nonlocal contributions to the flux. The spatially nonlocal operators we consider do not involve derivatives. Instead, the spatial operator involves an integral that, in a distributional sense, reduces to a conventional nonlinear advective operator. In particular, we examine a nonlocal inviscid Burgers equation, which gives a basic form with which to characterize properties associated with well-posedness, and to examine numerical results for specific cases. We describe the connection to a nonlocal viscous regularization, which mimics the viscous Burgers equation in an appropriate limit. We present numerical results that compare the behavior of the nonlocal Burgers formulation to the standard local case. The developments presented in this paper form the preliminary building blocks upon which to build a theory of nonlocal advection phenomena consistent within the peridynamic theo...

The Effects of the Internal Flow Structure on SPM Entrapment in the Rotterdam Waterway

Abstract Field measurements are presented, which are the first to quantify the processes influencing the entrapment of suspended particulate matter (SPM) at the limit of saltwater intrusion in the Rotterdam Waterway. The estuarine turbidity maximum (ETM) is shown to be maintained by the trapping of fluvial SPM at the head of the salt wedge. The trapping process is associated with the raining out of fluvial SPM from the upper, fresher part of the water column, into the layer below the pycnocline. The dominant mechanisms responsible are baroclinic shear flows and the abrupt change in turbulent mixing characteristics due to damping of turbulence at the pycnocline. This view contrasts with the assumption of landward transport of marine SPM by asymmetries in bed stress. The SPM transport capacity of the tidal flow is not fully utilized in the ETM, and the ETM is independent of a bed-based supply of mud. This is explained by regular exchange of part of the ETM with harbor basins, which act as efficient sinks, and that the Rotterdam Waterway is not a complete fluvial SPM trap. The supply of SPM by the freshwater discharge ensures that the ETM is maintained over time. Hence, the ETM is an advective phenomenon. Relative motion between SPM and saltwater occurs because of lags introduced by resuspension. Moreover, SPM that lags behind the salt wedge after high water slack (HWS) is eventually recollected at the head. Hence, SPM follows complex transport pathways and the mechanisms involved in trapping and transport of SPM are inherently three-dimensional.

Mechanics of liquid–liquid interfaces and mixing enhancement in microscale flows

Experimental work on mixing in microfluidic devices has been of growing importance in recent years. Interest in probing reaction kinetics faster than the minute or hour time scale has intensified research in designing microchannel devices that would allow the reactants to be mixed on a time scale faster than that of the reaction. Particular attention has been paid to the design of microchannels in order to enhance the advection phenomena in these devices. Ultimately, in vitro studies of biological reactions can now be performed in conditions that reflect their native intracellular environments. Liau et al. (Anal. Chem., vol. 77, 2005, p. 7618) have demonstrated a droplet-based microfluidic mixer that induces improved chaotic mixing of crowded solutions in milliseconds due to protrusions (‘bumps’) on the microchannel walls. Liau et al. (2005) have shown it to be possible to mix rapidly plugs of highly concentrated protein solutions such as bovine hemoglobin and bovine serum albumin. The present work concerns an analysis of the underlying mechanisms of shear stress transfer at liquid–liquid interfaces and associated enhanced mixing arising from the protrusions along the channel walls. The role of non-Newtonian rheology and surfactants is also considered within the mixing framework developed by Aref, Ottino and Wiggins in several publications. Specifically, we show that proportional thinning of the carrier fluid lubrication layer at the bumps leads to greater advection velocities within the plugs, which enhances mixing. When the fluid within the plugs is Newtonian, mixing will be enhanced by the bumps if they are sufficiently close to one another. Changing either the rheology of the fluid within the plugs (from Newtonian to non-Newtonian) or modifying the mechanics of the carrier fluid-plug interface (by populating it with insoluble surfactants) alters the mixing enhancement.

Two-phase SPH modelling of advective diffusion processes

This paper deals with a two-dimensional numerical model based on the smoothed particle hydrodynamics (SPH) technique for the evaluation of the concentration field of pollutants in water. A SPH model is formulated to solve the fickian diffusion equation applied to pollutants with the same density as the water. A lagrangian SPH formalism of the advective diffusion equation is also developed for pollutant-water, taking into account the effects of molecular diffusion and natural advection induced by differences between the fluid densities. These equations are coupled with the fluid mechanics equations. Attention is paid to the numerical aspects involved in the solution procedure and to the optimization of the model parameters. Environmental engineering problems concerning diffusion and natural advection phenomena occur in the presence of a pollutant in still water. Numerical tests referring to a strip and a bubble of contaminant in a water tank with different initial concentration laws have been carried out. The results obtained by the proposed SPH models are compared with other available SPH formulations, showing an overall better agreement with standard analytical solutions in terms of spatial evolution of the concentration values. Capabilities and limits of the proposed SPH models to simulate advective diffusion phenomena for a wide range of density ratios are discussed.

New Developments for the Description of Oil Leakages by Advective Migration From Submarine Pipelines

The significant growth in offshore operations increases the risk of a pipeline rupture, even considering the high standards of safety involved. Throughout a submarine leakage, four different amounts of oil may be accounted. The first one is the oil volume released until the leakage detection. The second one is the volume leaked throughout mitigation initiatives (e.g., pump shutdown and valve closure). The third parcel is the amount released by gravitational flow. Finally, the fourth and last amount of oil is released due to the water-oil entrainment, generally known as advective migration. Normally, a considerable amount of oil is released in this step. It begins just after the internal pipeline pressure becomes equal to the external one. The present work continues to introduce a mathematical alternative approach, based on the theories of perturbation and unstable immiscible displacement, to accurately estimate the leakage kinetics and the amount of oil released by the advective migration phenomenon. Situations considering different hole sizes and thicknesses were tested experimentally and through simulations. Additional experiments were accomplished using smooth and rough edge surfaces, besides different slopes (using the horizontal plane as reference). Those experiments permitted a preliminary evaluation of the importance of these factors. The results obtained with the model showed good agreement with the experimental data in many situations considered.

An Indirect Approach for Correlation of Permeability and Diffusion Coefficients

Diffusion tests in porous media are quite sensitive and long lasting procedures compared to permeability tests, which are usually more reliable and of shorter duration. Both diffusion and advection phenomena are dependent on the tortuosity of the material tested. A relevant question is to know whether it is possible to correlate permeability tortuosity p and diffusion tortuosity d. Several diffusion and permeability tests have been performed on non-uniform sand specimens having different grain size distribution. For each specimen, both the permeability and diffusion coefficients have been measured and two tortuosity factors (permeability and diffusion) have been back calculated. A theoretical model has been proposed to estimate d from p for a non-uniform granular material. The maximum particle diameter dmax is used to determine the maximum hydraulic diameter dh-max using the Hydraulic Radius Theory (HRT) for a 3D arrangement of spheres of same diameter dmax. Then, a filling factor  is applied to dh-max in order to capture the fact that smaller grains tend to fill the voids present in between the bigger particles. The filling factor is based on the coefficient of uniformity Cu. Relatively good results are obtained so that this model allows estimating the diffusion properties from a simple permeability test rapidly and at a fraction of the diffusion test cost.

Modelado numérico del proceso de soldadura por fricción agitación en aceros inoxidables

En el presente trabajo se modela el proceso de Soldadura por Fricción-Agitación (SFA) en aceros inoxidables mediante la utilización de un programa de elementos finitos de propósito general, reproduciendo el mapa térmico y la distribución del flujo del material. En el proceso de SFA el equipo de soldadura consta de una herramienta que gira y se desplaza sobre la unión de dos chapas restringidas. La unión se produce por el calentamiento por fricción inducido por la herramienta, que promueve un comportamiento pastoso/viscoso del material y su correspondiente flujo entre las chapas a unir. Este trabajo simula el proceso para una unión de aceros inoxidables austeníticos considerando acoplamiento termomecánico. Para la resolución del problema mecánico se utiliza un modelo viscoplástico con una ley constitutiva representativa de estos aceros en el rango de las temperaturas del proceso. Por otro lado, el problema térmico se modela teniendo en cuenta los fenómenos advectivos debidos al movimiento de la herramienta. En esta primera etapa, los resultados obtenidos han sido contrastados con datos reportados en la bibliografía, obteniéndose una buena correlación entre los mismos.

337 再生軟骨内での移流・拡散現象(T06-3 マイクロ・ナノ熱流体システム(3) 輸送・反応,大会テーマセッション,21世紀地球環境革命の機械工学:人・マイクロナノ・エネルギー・環境)

337 再生軟骨内での移流・拡散現象(T06-3 マイクロ・ナノ熱流体システム(3) 輸送・反応,大会テーマセッション,21世紀地球環境革命の機械工学:人・マイクロナノ・エネルギー・環境)

Controlling Dispersal Dynamics of Aedes aegypti*

The dengue virus is transmitted in regions previously infested with the mosquito Aedes aegypti. To assess the spreading and establishment of the dengue disease vector, a mathematical model is developed that takes into account the diffusion and advection phenomena. A discrete model based on the cellular automata approach, which is a good framework to deal with small populations, is also developed to be compared with the continuous modeling.

変動場の組織的な構造を評価するための複素ＰＯＤ解析に関する研究

The estimation of the coherent structures existing in a random phenomenon is important for the study of fluctuating fields, such as the flow fields or the pressure fields around a structure. For the estimation of the coherent structures, Proper Orthogonal Decomposition (POD) is available, which is able to obtain the coherent structures as the principal components of the fluctuating fields. However the components calculated by the POD analysis are stationary modes in space, therefore it is impossible to express the advection phenomenon as a single principal component. In such a case, the complex POD analysis is available. In this paper, the procedure of the complex POD analysis is described. And also the interpretation of it by the use of the complex envelope is shown. The calculations of some model cases are carried out by the POD analysis and the complex POD analysis. By comparing the results, the effectiveness of the complex POD analysis is shown.

Downscaling of GCM scenarios to assess precipitation changes in the little rainy season (March-June) in Cameroon

CR Climate Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials CR 26:85-96 (2004) - doi:10.3354/cr026085 Downscaling of GCM scenarios to assess precipitation changes in the little rainy season (March-June) in Cameroon Edouard K. Penlap1,2,*, Christoph Matulla1,3, Hans von Storch1, F. Mkankam Kamga2 1Institute for Coastal Research, GKSS Research Centre, Max-Planck-Straße, 21502 Geesthacht, Germany 2Atmospheric Sciences Lab, Dept of Physics, Faculty of Sciences, University of Yaoundé I, PO Box 812, Yaoundé, Cameroon 3Institute of Meteorology, University of Natural Resources and Applied Life Sciences, 1180 Vienna, Austria *Email: epenlap@uycdc.uninet.cm ABSTRACT: Large-scale climate forcings on local precipitation in Cameroon are analysed during the little rainy season (March-June). Variables found to have strong influence are used to downscale GCM projected rainfall for 2010-2049. In particular, 2 IPCC IS92a scenarios, simulated by the ECHAM4/OPYC3 climate model, are investigated. First, monthly precipitation data from 1951-1990 at 33 meteorological stations are grouped into homogeneous rainfall regions using self-organising feature maps (SOFMs). SOFMs identified 3 groups of stations with related time-series variability. Then, an empirical orthogonal function procedure, followed by canonical correlation analysis (CCA), is used to derive statistical relationships between the homogeneous regions and large-scale variables from the NCEP/NCAR Reanalysis Project. A CCA model is established for every region. Numerous fields at different pressure levels are used as macro-scale predictors. All possible combinations of 2 predictors are systematically tested in 3 validation experiments. Those combinations that perform well in the experiments are used to derive local-scale precipitation scenarios from the general circulation model (GCM) climate projection experiments. Different combinations of large-scale variables enter the model depending on region. A composite analysis suggests that precipitation is related to an advective (convective) phenomenon in the northern (southern) part of the study domain. Moreover, precipitation changes based on 2 IS92a emission scenarios as simulated by ECHAM4/OPYC3 are calculated. The trace-gas-only and the trace-gas-plus-sulphate integrations induce changes ranging locally from +44 to -10% and from +36 to -9% respectively, relative to the 1951-1990 control period. KEY WORDS: Cameroon · Precipitation · Regionalisation · Downscaling · Climate change Full article in pdf format NextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in CR Vol. 26, No. 2. Online publication date: May 25, 2004 Print ISSN: 0936-577X; Online ISSN: 1616-1572 Copyright © 2004 Inter-Research.

Dispersion study for two‐dimensional modelling

Simulation of water quality variation in a particular river stretch or at a particular location with time requires mathematical modelling based on advection and dispersion phenomenon. In this context, estimation of an appropriate dispersion coefficient, which is a function of characteristics of a water body, is very essential and forms an important step in mathematical modelling. The tracer study conducted in this context on the river Ganga to estimate the dispersion coefficient is described in this paper with an analysis of data based on a stream‐tube approach. For the wide river Ganga, with a velocity in the range 0.3–0.5 m/s, the estimated transverse dispersion coefficient is 1.33 m2/s.

Transport of energy in dissipative advection phenomena

A study of the distribution of energy among the different scales is performed for several systems in fluid mechanics, including the Navier–Stokes, magnetohydrodynamics and active scalars equations. It is found that all these systems possess a common structure which enables us to deduce how the energy introduced by the forcing is transferred to the scales present in the flow. It is also shown that in special cases an energy cascade will occur. The limits of this method are also considered.

Interpreting tracer breakthrough tailing from different forced‐gradient tracer experiment configurations in fractured bedrock

Conceptual and mathematical models are presented that explain tracer breakthrough tailing in the absence of significant matrix diffusion. Model predictions are compared to field results from radially convergent, weak‐dipole, and push‐pull tracer experiments conducted in a saturated crystalline bedrock. The models are based upon the assumption that flow is highly channelized, that the mass of tracer in a channel is proportional to the cube of the mean channel aperture, and the mean transport time in the channel is related to the square of the mean channel aperture. These models predict the consistent −2 straight line power law slope observed in breakthrough from radially convergent and weak‐dipole tracer experiments and the variable straight line power law slope observed in push‐pull tracer experiments with varying injection volumes. The power law breakthrough slope is predicted in the absence of matrix diffusion. A comparison of tracer experiments in which the flow field was reversed to those in which it was not indicates that the apparent dispersion in the breakthrough curve is partially reversible. We hypothesize that the observed breakthrough tailing is due to a combination of local hydrodynamic dispersion, which always increases in the direction of fluid velocity, and heterogeneous advection, which is partially reversed when the flow field is reversed. In spite of our attempt to account for heterogeneous advection using a multipath approach, a much smaller estimate of hydrodynamic dispersivity was obtained from push‐pull experiments than from radially convergent or weak dipole experiments. These results suggest that although we can explain breakthrough tailing as an advective phenomenon, we cannot ignore the relationship between hydrodynamic dispersion and flow field geometry at this site. The design of the tracer experiment can severely impact the estimation of hydrodynamic dispersion and matrix diffusion in highly heterogeneous geologic media.

Heat transport analysis and three‐dimensional thermo‐hydraulic simulation in the Ishikari basin, Hokkaido, Japan

AbstractTemperature profiles of 22 observation boreholes in the Ishikari basin were investigated in order to extract information on the ground thermal processes and the associated water flow disturbances. Data analyses methods were based on temperature profile typology, thermal gradient–temperature plots, and a thermo‐hydraulic model. The distributed data sets of measured temperature profiles and thermal conductivity show lateral heat flow variations from 34 to 162 mW m−2. These thermal conditions revealed the co‐existence of a highland geothermal field, a lowland central subnormal heat flow area, and a strong heat flow anomaly near the northeast Ishikari River. To explain this specific configuration of the thermal field, possible effects of petro‐physical properties, topography and groundwater movements were examined with a three‐dimensional thermo‐hydraulic simulation model. Laboratory measurements of thermal conductivity, porosity, density, and permeability from borehole core samples were used to constrain the model parameters. The main results suggest that: the lateral increase of geothermal gradient and heat flow density with elevation, i.e. in the southwest direction, are essentially due to hydro‐ and thermo‐physical differences between the hydrogeologically active Quaternary sedimentary system and the underlying Tertiary volcano–sedimentary formation; the low heat area in the central lowland may be explained by the effect of its local groundwater flow recharge, and then the positive heat anomaly near the Ishikari River would result from a basin‐wide heat flow redistribution by water flow. In general, the thermal regime in the Ishikari basin appears dominated by conduction processes in the southwest area and strongly influenced by advection phenomena in the northeast. Copyright © 2002 John Wiley & Sons, Ltd.