Taylor's Theory Research Articles

Decoupling of Channeling and Dispersion Effects by Use of Multiwell Tracer Test

SummaryThis paper examines the decoupling of small-scale heterogeneity (dispersion) and permeability variation by use of multiwell tracer-test data. Tracer transport in heterogeneous reservoirs is governed by spreading (because of the spatial variability of permeability) and mixing (caused by dispersion); the combined effects of these two phenomena can be described after very long time periods (rarely met in practice) by the Taylor (1953) theory of asymptotic dispersion.A new formulation is presented to study tracer propagation along streamlines in heterogeneous reservoirs. The streamlines are modeled as analogous reservoir layers with no crossflow. The fraction of layers in which tracer transport occurs faster than the solution of the convection/diffusion equation (CDE) is determined; this fraction represents layers through which channeling may take place: obviously, the larger the fraction, the lower the sweep efficiency. Moreover, a field example is used to demonstrate how to decouple the convoluted effects of the channeling from small-scale heterogeneity.An accurate estimation of “true” dispersion is an essential step in designing a successful enhanced oil recovery (EOR). Furthermore, the sweep efficiency of heterogeneous reservoir can be estimated through interwell-spacing heterogeneity; this improves performance predictions and the economic evaluation of the project.

On the quaternionic Monge–Ampère operator, closed positive currents and Lelong–Jensen type formula on the quaternionic space

In this paper, we introduce the first-order differential operators d0 and d1 acting on the quaternionic version of differential forms on the flat quaternionic space Hn. The behavior of d0,d1 and △=d0d1 is very similar to ∂,∂‾ and ∂∂‾ in several complex variables. The quaternionic Monge–Ampère operator can be defined as (△u)n and has a simple explicit expression. We define the notion of a closed positive current in the quaternionic case, and extend several results in complex pluripotential theory to the quaternionic case: define the Lelong number of a closed positive current, obtain the quaternionic version of Lelong–Jensen type formula, and generalize Bedford–Taylor theory, i.e., extend the definition of the quaternionic Monge–Ampère operator to locally bounded quaternionic plurisubharmonic functions and prove the corresponding convergence theorem.

Numerical study of the 3D-shape of a drop immersed in a fluid under an elongational flow with vorticity

This work focuses on a three-dimensional analysis of the deformation of a drop — immersed in a Newtonian fluid— generated by a 2D elongational flow with vorticity. The study of steady-state deformations of the cross-section of the drop shows a prevalent non-circular shape. The axisymmetric idealization of the ellipsoid is not observed nor the linear dependency between capillary number and deformation of the drop, as Taylor and Cox theory predicted. Our numerical results are consistent with experiments and other numerical simulations. However, in the latter cases, measurements of the cross section of the drop are few while a limited class of flows is applied. In this work, deformations induced by general two-dimensional flows upon the 3D drop shape are presented with special emphasis about the length scale along the third axis —perpendicular to the plane of the applied flow field.

The transport of suspended sediment in the wake of a marine hydrokinetic turbine: Simulations via a validated Discrete Random Walk (DRW) model

The interaction of sediment with Marine Hydrokinetic (MHK) Turbines is studied via turbulent flow simulation coupled with a model for particle dynamics. The Discrete Random Walk (DRW) model is commonly used for simulations of particle dispersion in environmental flows. A method to improve the accuracy of the DRW model in conjunction with RANS simulations of the flow around MHK turbines is presented. A key issues for the use of the DRW model in marine applications is identified, finding the right characteristic eddy lifetime scale, and a simple methodology based on G.I. Taylor's classical dispersion theory is develop to calibrate this physical model parameter. The model is validated against experiments in the literature and the physics of suspended sediment transport in the wake of an MHK turbine is studied with this improved method. The qualitative changes observed in the particle trajectories agree well with theoretical and empirical observations and the quantitive trends allow for comparison of multiple particle cases under different flow conditions, confirming that this implementation of CFD can become a powerful tool to select the most challenging cases, among the thousands of potential studies on the environmental effects of MHK energy, for further study with experiments and pilot projects.

On the Taylor principles for plastic deformation of polycrystalline metals

Grain orientation evolutions and texture formation based on the Taylor principles offer important references to reveal crystallographic mechanisms of deformation behaviors. Strain equilibrium between grains is achieved in Taylor theory, however, stress equilibrium has not yet been reached perfectly even in many modifications of the theory though the textures predicted become very close to those of experimental observations. A reaction stress model is proposed, in which mechanical interactions between grains are considered in details and grain deformation is conducted by penetrating and non-penetrating slips. The new model offers both of the stress and strain equilibria and predicts the same textures indicated by Taylor theory. The rolling texture simulated comes very close to the experimental observations if the relaxation effect of the non-penetrating slips on the up-limits of reaction stresses is included. The reaction stress principles open theoretically a new field of vision to consider deformation behaviors of polycrystalline materials, whereas the Taylor principles become unnecessary both theoretically and practically. Detailed engineering conditions have to be included in simulations if the deformation textures of industrial products should be predicted.

Rolling Texture Simulation of Aluminium Sheets Based on the Mechanism of Intergranule Reaction Stresses

Many efforts have been made to simulate the rolling texture evolution in polycrystalline Al for which strain and stress equilibrium of grains need to be considered. The conventional Taylor theory and its modifications, such as current VPSC, ALAMEL, GIA, fail to solve the problem of stress incompatibility between grains and their surrounding matrix properly. A reaction stress model is suggested for rolling deformation, which accounts both for stress and strain equilibrium and predicts similar textures as those by the Taylor theory. The corresponding detailed modification could reproduced the real rolling texture formation if the industrial rolling stress condition is included.

Determination of dynamic dispersion coefficient for particles flowing in a parallel-plate fracture

A robust and pragmatic technique has been developed to determine dynamic dispersion coefficients for particles flowing in a parallel-plate fracture. By using local moment analyses, theoretical equations have been formulated to describe flow behaviour of solid particles flowing in a parallel-plate fracture on the basis of the Poiseuille flow under different source conditions. By using the random walk particle tracking (RWPT) algorithm, newly developed models have been verified to determine solute and particle dispersion coefficients agreeing with those obtained from RWPT simulations. At early times, particle dispersion coefficient is not only controlled by the source condition, but also negatively correlated with the center-of-mass velocity. Compared to a point source, at early times, dispersion coefficients of particles originating from a line source are larger; however, after a critical time, all dispersion coefficients approach the values obtained through the extended Taylor theory. Subsequently, the newly developed models have been extended to match experimental measurements, while particle dispersion coefficients are notably less than those calculated by the extended Taylor theory.

Modelling the temperature rise effect through high-pressure torsion

An approach composed of the thermodynamics-based dislocation model and the Taylor theory is used to investigate the evolution of microstructure and flow stress during high-pressure torsion (HPT). The incremental temperature rise is considered through the modelling of HPT. The temperature can affect the annihilation of dislocations and thus the dislocation density. The model predicts the dislocation density, sub-grain size and flow stress during HPT. The modelling results are compared with the experimental data and the modelling results without considering the incremental temperature rise. A remarkable agreement is observed between the modelling results with considering the temperature rise effect and the experimental data.

Reynolds-number dependence of the longitudinal dispersion in turbulent pipe flow.

In Taylor's theory, the longitudinal dispersion in turbulent pipe flows approaches, on long time scales, a diffusive behavior with a constant diffusivity K_{L}, which depends empirically on the Reynolds number Re. We show that the dependence on Re can be determined from the turbulent energy spectrum. By using the intimate connection between the friction factor and the longitudinal dispersion in wall-bounded turbulence, we predict different asymptotic scaling laws of K_{L}(Re) depending on the different turbulent cascades in two-dimensional turbulence. We also explore numerically the K_{L}(Re) dependence in turbulent channel flows with smooth and rough walls using a lattice Boltzmann method.

Rarefaction-driven Rayleigh–Taylor instability. Part 1. Diffuse-interface linear stability measurements and theory

Theory and experiments are reported that explore the behaviour of the Rayleigh–Taylor instability initiated with a diffuse interface. Experiments are performed in which an interface between two gases of differing density is made unstable by acceleration generated by a rarefaction wave. Well-controlled, diffuse, two-dimensional and three-dimensional, single-mode perturbations are generated by oscillating the gases either side to side, or vertically for the three-dimensional perturbations. The puncturing of a diaphragm separating a vacuum tank beneath the test section generates a rarefaction wave that travels upwards and accelerates the interface downwards. This rarefaction wave generates a large, but non-constant, acceleration of the order of $1000g_{0}$, where $g_{0}$ is the acceleration due to gravity. Initial interface thicknesses are measured using a Rayleigh scattering diagnostic and the instability is visualized using planar laser-induced Mie scattering. Growth rates agree well with theoretical values, and with the inviscid, dynamic diffusion model of Duff et al. (Phys. Fluids, vol. 5, 1962, pp. 417–425) when diffusion thickness is accounted for, and the acceleration is weighted using inviscid Rayleigh–Taylor theory. The linear stability formulation of Chandrasekhar (Proc. Camb. Phil. Soc., vol. 51, 1955, pp. 162–178) is solved numerically with an error function diffusion profile using the Riccati method. This technique exhibits good agreement with the dynamic diffusion model of Duff et al. for small wavenumbers, but produces larger growth rates for large-wavenumber perturbations. Asymptotic analysis shows a $1/k^{2}$ decay in growth rates as $k\rightarrow \infty$ for large-wavenumber perturbations.

Mother-Tongue Education in Venda: An Ethnolinguistic Vitality Critique

ABSTRACTIn January 2002, the Zimbabwean government officially declared the policy of teaching and learning of minority languages in primary schools in the areas where they are spoken. These languages were to ‘be introduced to a grade per year until they could be taught at Grade 7 by 2005’ (Secretary's Circular Number 1 of 2002). A decade after 2005, out of the six concerned languages only Tonga, Venda, Shangani and Nambya have been examined at Grade 7. Be that as it may, Venda nonetheless lagged behind despite the added advantage that it has. This article is an in-depth examination of the causes of this lag. Based on Giles, Bourhis and Taylor's (1977) theory of ethnolinguistic vitality, this article notes that the main glitch in the teaching and learning of Venda has been the lack of interaction and coordination within and between the micro and macro levels.

Coupling circuit model and discharge waveform prediction for Keda Torus eXperiment

A poloidal and toroidal magnetic field coupling circuit model is developed to simulate discharge waveforms of the Keda Torus eXperiment (KTX) reversed field pinch (RFP) to ensure that the design of the power supply systems is able to achieve the typical discharge parameters. The radial profiles of plasma current density and magnetic field used in the coupling model are characterized by modified Bessel function model (MBFM) derived from the well-known Taylor's theory. The power balance in the energy conservation of poloidal and toroidal fields is used to establish the connection between these two fields. The numerical solutions of the coupling show that the KTX power supply system is capable of achieving the designed discharge parameters, such as field reversal parameter (F), pinch parameter (Θ), magnetic field, plasma current and loop voltage. Furthermore, the delay of magnetic field penetration due to the effect of vacuum vessel is also considered in the model.

La identidad como construcción social desde la propuesta de Charles Taylor

a b s t r a c t This paper presents Charles Taylor’s theoretical proposal of construction of identity confronted to the criticism of Amartya Sen who conceives identity as a result of personal choice. It is argued that the critiques that Amartya Sen makes to the arguments of Taylor are groundless given that the perspective of Charles Taylor focuses more on the fundamentally constructive nature of identity than on the loss of freedom and the mere uncritical acceptance of the assumed identity. Taylor's theory does has space for the ability to choose and the consideration of multiple identities but it draws attention to the importance of social and group context when a person builds his identity and it assigns a higher value to the external goods that define the way people live in contemporary societies, such as the cultural and linguistic community, than to personal choice. K e y w o r d s identity, social construction, language and meaningful community.

Magnetic islands and singular currents at rational surfaces in three-dimensional magnetohydrodynamic equilibria

Using the recently developed multiregion, relaxed MHD (MRxMHD) theory, which bridges the gap between Taylor's relaxation theory and ideal MHD, we provide a thorough analytical and numerical proof of the formation of singular currents at rational surfaces in non-axisymmetric ideal MHD equilibria. These include the force-free singular current density represented by a Dirac δ-function, which presumably prevents the formation of islands, and the Pfirsch-Schlüter 1/x singular current, which arises as a result of finite pressure gradient. An analytical model based on linearized MRxMHD is derived that can accurately (1) describe the formation of magnetic islands at resonant rational surfaces, (2) retrieve the ideal MHD limit where magnetic islands are shielded, and (3) compute the subsequent formation of singular currents. The analytical results are benchmarked against numerical simulations carried out with a fully nonlinear implementation of MRxMHD.

Analysis on the Mechanical Behaviors of Soil-rock Mixtures Using Discrete Element Method

Two-dimensional numerical direct shear tests were carried out using the Discrete Element Method (DEM) to study the effects of rock content on the mechanical behaviors of soil-rock mixtures (SRM).The mixtures were made from particles of contrasting size and stiffness. The DEM simulation captured the behaviors of SRM as observed in previous experiments, showing that the peak shear stress and the dilation increased with an increasing rock content. Moreover, it also found that the peak friction angle and dilation angle increased while cohesion decreased with an increasing rock content. On the other hand, the DEM provided insight to the distribution of contact force chains, the magnitude and orientation of the principal stresses, and the rotation of particles experience as the shearing progressed which could not be revealed in the physical experiments. The results indicated that the rock content also had a meaningful effect on these micromechanical observations. At last, how the rock content influenced the shear strength of SRM was discussed according to Taylor's theory. It was concluded that the shear strength of SRM increased for higher rock content mainly because of the contribution of the interlocking, while the contribution of the contact friction was demonstrated to be very small.

Nonlinear instability of an Oldroyd elastico–viscous magnetic nanofluid saturated in a porous medium

Through viscoelastic potential theory, a Kelvin-Helmholtz instability of two semi-infinite fluid layers, of Oldroydian viscoelastic magnetic nanofluids (MNF), is investigated. The system is saturated by porous medium through two semi-infinite fluid layers. The Oldroyd B model is utilized to describe the rheological behavior of viscoelastic MNF. The system is influenced by uniform oblique magnetic field that acts at the surface of separation. The model is used for the MNF incorporated the effects of uniform basic streaming and viscoelasticity. Therefore, a mathematical simplification must be considered. A linear stability analysis, based upon the normal modes analysis, is utilized to find out the solutions of the equations of motion. The onset criterion of stability is derived; analytically and graphs have been plotted by giving numerical values to the various parameters. These graphs depict the stability characteristics. Regions of stability and instability are identified and discussed in some depth. Some previous studies are recovered upon appropriate data choices. The stability criterion in case of ignoring the relaxation stress times is also derived. To relax the mathematical manipulation of the nonlinear approach, the linearity of the equations of motion is taken into account in correspondence with the nonlinear boundary conditions. Taylor's theory is adopted to expand the governing nonlinear characteristic equation according to of the multiple time scales technique. This analysis leads to the well-known Ginzburg–Landau equation, which governs the stability criteria. The stability criteria are achieved theoretically. To simplify the mathematical manipulation, a special case is considered to achieve the numerical estimations. The influence of orientation of the magnetic fields on the stability configuration, in linear as well as nonlinear approaches, makes a dual role for the magnetic field strength in the stability graphs. Stability diagram is plotted for different sets of physical parameters. A new stability as well as instability region, in the parameter space, appears due to the nonlinear effects.

Christian Marriage, Money Scams, and Melanesian Social Imaginaries

AbstractIn this paper, we draw on fieldwork with middle‐class investors in ‘fast money schemes’ (Ponzi scams) to consider how Neo‐Pentecostal Christianity may be mediating social and economic change in Papua New Guinea, particularly in relation to gender equality. Ideas of companionate marriage and the cultivation of an affective self imply masculinities that are more sensitive and less domineering. As these images of fulfilled modernity flow out from Pentecostal churches into broader Papua New Guinean society, they corroborate Taylor's theory of how change occurs within the modern social imaginary.

Some improvements in the theory of plasma relaxation

Taylor's relaxation theory is extended to plasmas with mass flow by using the cross helicity as a conserved quantity, similar to the magnetic helicity. Indeed, it is shown that the conservation of the cross helicity in magnetohydrodynamics is the result of the conservation of two magnetic-like helicities in two-fluid plasmas. In addition, the usually ignored toroidal flux is also held to be conserved. We also view plasma relaxation as attaining a maximum entropy state rather than Taylor's minimum energy state, but prove that maximizing the entropy subject to a given amount of energy is equivalent to minimizing the energy subject to a given amount of entropy. The resulting relaxed state is similar to the one discussed by Finn and Antonsen [Phys. Fluids 26, 3540 (1983)], and involves flow parallel to the magnetic field and constant temperature, but non-constant pressure. We show how to construct an asymptotic solution to the relaxed state based on the smallness of the Alfven Mach number of the flow.

Dispersion characteristics of blood during nanoparticle assisted drug delivery process through a permeable microvessel

Nanoparticle assisted drug delivery holds considerable promise as a means of next generation of medicine that allows for the intravascular delivery of drugs and contrast agents. We analyze the dispersion characteristics of blood during a nanoparticle-assisted drug delivery process through a permeable microvessel. The contribution of molecular and convective diffusion is based on Taylor's theory of shear dispersion. The aggregation of red blood cells in blood flowing through small tubes (less than 40μm) leads to the two-phase flow with a core of rouleaux surrounded by a cell-depleted peripheral layer. The core region models as a non-Newtonian Casson fluid and the peripheral region acts as a Newtonian fluid. We investigate the influence of the nanoparticle volume fraction, the permeability of the blood vessel, pressure distribution, yield stress and the radius of the nanoparticle on the effective dispersion. We show that the effective diffusion of the nanoparticles reduces with an increase in nanoparticle volume fraction. The permeability of the blood vessels increases the effective dispersion at the inlet. The present study contributes to the fundamental understanding on how the particulate nature of blood influences nanoparticle delivery, and is of particular significance in nanomedicine design for targeted drug delivery applications.

Numerical Study on Deformation and Interior Flow of a Droplet Suspended in Viscous Liquid under Steady Electric Fields

A model based on the volume of fluid (VOF) method and leaky dielectric theory is established to predict the deformation and internal flow of the droplet suspended in another vicious fluid under the influence of the electric field. Through coupling with hydrodynamics and electrostatics, the rate of deformation and internal flow of the single droplet are simulated and obtained under the different operating parameters. The calculated results show that the direction of deformation and internal flow depends on the physical properties of fluids. The numerical results are compared with Taylor's theory and experimental results by Torza et al. When the rate of deformation is small, the numerical results are consistent with theory and experimental results, and when the rate is large the numerical results are consistent with experimental results but are different from Taylor's theory. In addition, fluid viscosity hardly affects the deformation rate and mainly dominates the deformation velocity. For high viscosity droplet spends more time to attain the steady state. The conductivity ratio and permittivity ratio of two different liquids affect the direction of deformation. When fluid electric properties change, the charge distribution at the interface is various, which leads to the droplet different deformation shapes.