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Showing papers on "Fluid dynamics published in 1998"


Journal ArticleDOI
TL;DR: In this article, the frequency dependency and magnitude of electrothermally induced fluid flow are discussed for low frequencies (up to 500 kHz) and the effects of Brownian motion, diffusion and buoyancy force are discussed in the context of the controlled manipulation of sub-micrometre particles.
Abstract: Ac electrokinetics is concerned with the study of the movement and behaviour of particles in suspension when they are subjected to ac electrical fields. The development of new microfabricated electrode structures has meant that particles down to the size of macromolecules have been manipulated, but on this scale forces other than electrokinetic affect particles behaviour. The high electrical fields, which are required to produce sufficient force to move a particle, result in heat dissipation in the medium. This in turn produces thermal gradients, which may give rise to fluid motion through buoyancy, and electrothermal forces. In this paper, the frequency dependency and magnitude of electrothermally induced fluid flow are discussed. A new type of fluid flow is identified for low frequencies (up to 500 kHz). Our preliminary observations indicate that it has its origin in the action of a tangential electrical field on the diffuse double layer of the microfabricated electrodes. The effects of Brownian motion, diffusion and the buoyancy force are discussed in the context of the controlled manipulation of sub-micrometre particles. The orders of magnitude of the various forces experienced by a sub-micrometre latex particle in a model electrode structure are calculated. The results are compared with experiment and the relative influence of each type of force on the overall behaviour of particles is described.

1,184 citations


Book
26 Feb 1998
TL;DR: In this paper, the authors introduce Geophysical Fluid Dyunamics and introduce the non-inertial theory of Ocean Circulation and Statistical Fluid Dynamics (SFLD).
Abstract: 1. Fundamentals 2. Introduction to Geophysical Fluid Dyunamics 3. Non-inertial Theory of Ocean Circulation 4. Vorticity and Turbulence 5. Statistical Fluid Dynamics 6. Geostropic Turbulence 7. Hamiltonian Fluid Dynamics

802 citations


Journal ArticleDOI
TL;DR: The hypothesis that the response of bone cells to fluid flow is dependent on chemotransport effects is support by exposing osteoblast-like hFOB 1.19 cells to precisely controlled dynamic fluid flow profiles.

460 citations


Book
15 Dec 1998
TL;DR: In this paper, the authors present a model for estimating mixing in streams and rivers using dimensionless numbers and a four-point method to solve the problem of complete unsteady flow models.
Abstract: SECTION I. FUNDAMENTALS Chapter 1. Fundamental Relationships for Flow and Transport Mechanistic versus Empirical Modeling General Principles Physical Properties of Water Instantaneous Equations for Fluid Flow and Transport Reynolds Time-Averaged Mean Flow and Transport Equations Model Complexity: Selection and Development Data Requirements Definitions Dimensionless Numbers Chapter 2. Measurement and Analysis of Flow Introduction Measurement of Velocity and Flow Measurement of Stage Computation of Discharge Tracer Studies Estimating Design Flows Appendices SECTION II. RIVERS AND STREAMS Chapter 3. Flow Models for Rivers and Streams Introduction Flow Model Complexity Data Requirements Estimating Mixing in Streams and Rivers Chapter 4. Non-Hydraulic Methods for Flow Estimation Flow Relationships Hydrologic Routing Methods Chapter 5. Hydraulic Methods for Steady Flows Steady, Uniform Flows Hydraulic Methods for Steady, Non-Uniform Flows Chapter 6. Hydraulic Methods for Unsteady Flows Introduction Solution Techniques Unsteady Flow Methods Kinematic-Wave Model Chapter 7. Solutions of Complete Unsteady Flow Models Explicit Solution of a Link-Node Model Implicit Solution Using the Four-Point Method SECTION III. LAKES AND RESERVOIRS Chapter 8. Stratification and Heat Transfer in Lakes and Reservoirs Introduction to Lakes and Reservoirs Origin and Characteristics of Lakes and Reservoirs Stratification in Lakes and Reservoirs Temperature Simulation Ice Formation and Cover Chapter 9. Mixing in Lakes and Reservoirs Introduction Inflow Mixing Processes Outflow Mixing Processes Mixing by Wind, Waves, Convective Cooling, and Coriolis Forces Reservoir Management and Mixing Processes Chapter 10. Water Balances and Multidimensional Models Introduction Water Balance for Lakes and Reservoirs Zero-Dimensional or Box Models of Lake and Reservoir Quality One-Dimensional, Longitudinal Models of Lakes and Reservoirs One-Dimensional, Vertical Models of Lakes and Reservoirs Two-Dimensional (Laterally Averaged) Models Two-Dimensional Depth Averaged Models Three-Dimensional Models SECTION IV. ESTUARIES Chapter 11. Introduction to Estuaries Introduction General Characteristics of Estuaries Classification Schemes Chapter 12. Factors Affecting Transport and Mixing in Estuaries Introduction Tides The Coriolis Force Fresh Water Inflow Meteorological Effects Bathymetry Model Complexity Chapter 13. Turbulent Mixing and Dispersion in Estuaries Eddy Viscosity and Diffusivity Dispersion in Estuaries Estimation of Mixing Terms Chapter 14. Tidally Averaged Estuarine Models Introduction Fraction of Freshwater Method Modified Tidal Prism Method Pritchard's Method Lung and O'Connor's Method Computing Tidal Transport from Measured or Predicted Velocities Chapter 15. Dynamic Modeling of Estuaries Introduction Factors Distinguishing Modeling Approaches One-Dimensional Models of Estuaries Two-Dimensional (Horizontal Plane) Models Two-Dimensional (Vertical Plane) Models Three-Dimensional Models Coupling Hydrodynamic and Water Quality Models Appendices

450 citations


Book
01 Jan 1998
TL;DR: This text is geared towards advanced under- and post-graduate students, practicing engineers, and designers to develop a somewhat more rigorous theoretical approach to the solution of open channel flow problems than those found in similar texts.
Abstract: This text is designed to make a deliberate effort to extend the modern fluid mechanics approach into the analysis of open channel flow without necessarily requiring the use of advanced mathematics, except in a few special instances. It is geared towards advanced under- and post-graduate students, practicing engineers, and designers to develop a somewhat more rigorous theoretical approach to the solution of open channel flow problems than those found in similar texts. It is also designed to make increased use of the extensive developments in numerical techniques of solutions that have appeared in the last 20 years.

406 citations


Journal ArticleDOI
TL;DR: In this article, it is shown how conservation of total energy can be utilized as an intermediate device to achieve this goal for the equations of fluid dynamics written in Lagrangian form, with a staggered spatial placement of variables for any number of dimensions and in any coordinate system.

396 citations


Journal ArticleDOI
TL;DR: In this article, a lattice-Boltzmannian representation is used to realize hydrodynamic boundary conditions at a solid surface. But the resulting physics properties are independent of the position and the orientation of the surface with respect to the lattice mesh.
Abstract: We describe a novel way based on lattice-Boltzmann representation for realizing hydrodynamic boundary conditions at a solid surface. It is shown that using this approach the resulting physics properties are independent of the position and the orientation of the surface with respect to the lattice mesh. The fluxes of mass, energy as well as both normal and tangential momenta can be accurately controlled to correspond to various fluid dynamics situations.

319 citations


Book
22 Jun 1998
TL;DR: The first-order Scalar Differential Equation in One-Dimension (SDFE) as mentioned in this paper is a generalization of the LSFEM in one-dimensional linear systems of equations.
Abstract: Contents (preliminary): I. The Basic Concept of the LSFEM.- 1. Introduction.- 2. The first-order Scalar Differential Equation in One-Dimension.- 3. The First-Order System in One-Dimension.- II. Fundamentals of the LSFEM.- 4. Fundamentals of the LSFEM.- 5. The Div-Curl System.- 6. The Div-Curl-Grad System.- III. The LSFEM in Fluid Dynamics.- 7. Inviscid Irrotational Flows.- 8. Incompressible Viscous Flows.- 9. Convective Transport.- 10. Rotational Inviscid Flows.- 11. Two-face Flows.- 12. Compressible Viscous Flows.- 13. High-Speed Compressible Flows.- 14. P-Version Least-Squares Finite Element Method.- IV. The LSFEM in Electromagnetics.- 15. Electromagnetics.- V. Solution of the Discrete Equations 16. Iterative Methods for Solving Linear Systems of Equations.- Appendix A: Operation on Vectors.- B. Green's Formula.- C. Finite Element Interpolation.- D. The Lax-Milgram Theory.- References.- Index.

293 citations


Book
01 Jan 1998
TL;DR: In this paper, Johnson et al. presented a comprehensive overview of the history of classical Fluid Dynamics, including the main concepts of the Navier-Stokes Equation and its application in the literature.
Abstract: Basics * Introduction, Richard W. Johnson * Some Reflections on the History of Fluid Dynamics, John D. Anderson, Jr. * General Equations of Newtonian Fluid Dynamics, R. Byron Bird and Michael D. Graham * Special Equation Forms and Related Equations, Frank G. Collins and Ronald H. Aungier * Basic Engineering Fluid Mechanics, John F. Foss, Ronald L. Panton, and William S. Janna * Classical Fluid Dynamics * Overview of Classical Fluid Dynamics, Richard W. Johnson * Inviscid Incompressible Flow-Potential Flow, Robert H. Kirchhoff * Inviscid Compressible Flow, Doyle D. Knight * Incompressible Laminar Viscous Flows, Ismet Gursul * Incompressible Laminar Boundary Layer Flow, Z.U.A. Warsi * Compressible Laminar Boundary Layer Flow, Arnold Polak * Waves, Matiur Rahman * Transition and Turbulence, Peter S. Bernard, Jeffrey D. Crouch, Meelan Choudhari, David G. Bogard, and Karen A. Thole * Turbulence Modeling and Simulation, Charles G. Speziale and Ronald M.C. So * Plasma Flows, John J. Lowke and Anthony B. Murphy * Chemically Reacting Flows (Combustion), David G. Lilley * Multiphase Flow - Gas/Liquid, Michael L. Corradini * Multiphase Flow - Gas/Solid, Liang-Shih Fan and Chao Zhu * Multiphase Flow - Liquid/Solid Fluidized Bed Systems, Rong-Her Jean and Liang-Shih Fan * Cavitation, Roger E.A. Arndt * Flow in Porous Media, Massoud Kaviany * Non-Newtonian Fluid Flow, Thomas H. Irvine, Jr., and Massimo Capobianchi * High Reynolds Number Asymptotic Theories * Incompressible Triple-Deck Theory, Alric P. Rothmayer and Frank T. Smith * Free-Interactions and Breakaway Separation, Alric P. Rothmayer and Frank T. Smith * Numerical Solution of Two-Dimensional Steady Triple-Deck Problems, Alric P. Rothmayer and Frank T. Smith * Numerical Solution of the Equations of Fluid Dynamics * Finite Difference Method, Kyran D. Mish * Finite Volume Method, Suhas V. Patankar, K.C. Karki, and K.M. Kelkar * Finite Element Method, A. Jerry Baker * Spectral Element Methods for Incompressible Flows, George Em Karniadakis and * Ronald D. Henderson * Computer Science, Kyran D. Mish * Solution Methods for the Incompressible Navier-Stokes Equations, Wei Shyy and * Rajat Mittal * Convergence Acceleration, David A. Caughey * Experimental Methods in Fluid Mechanics * Basic Instruments, Mohamed Gad-el-Hak * Hot-Wire Anemometry, Genevihve Comte-Bellot * Laser-Doppler Velocimetry (LDV), Leroy M. Fingerson and Rajan K. Menon * Multiphase Flow Measurements Using Particle Image Velocimetry (PIV), Yassin A. * Hasan * Phase Doppler Particle Analyzer (PDPA), William D. Bachalo and Subramanian V. * Sankar * Flow Visualization, James P. Crowder * Uncertainty Analysis, Hugh W. Coleman and W. Glenn Steele * Applications * Axial-Flow Compressor and Fan Aerodynamics, David C. Wisler * Turbomachinery, Lowell W. Pearson and Roger E.A. Arndt * Nozzles and Diffusers, Donald J. Dusa and James L. Younghans * Airfoils and Wings, Bruce R. Munson and Dennis J. Cronin * Pumps, Lev Nelik * Open Channel Flow, M. Hanif Chaudhry and Michael E. Barber * Atmospheric Flows, Donald H. Lenschow * Mesoscale Oceanic Flows, Lynn K. Shay * Lubrication, Ralph A. Burton * Appendixes * A. Mathematics of Fluid Mechanics, Charles Zemach * B. Tables of Dimensionless Numbers * C. Transport Property Tables * D. Units and Constants * Index *

253 citations


Journal ArticleDOI
TL;DR: This work examines variable density flow and corresponding solute transport in groundwater systems using two finite element simulators and contributes new results for the salt dome problem, for which inconsistent findings exist in literature.

247 citations


Journal ArticleDOI
TL;DR: In this paper, the concept of the so-called "artificial or balancing diffusion" used to stabilize the numerical solution of advective-diffusive transport and fluid flow problems is revised.

Journal ArticleDOI
TL;DR: Anguilliform swimming has been investigated by using a computational model combining the dynamics of both the creature's movement and the two-dimensional fluid flow of the surrounding water, finding the final mean swimming speed to be 0.77 times the speed of the backward-travelling wave.
Abstract: Anguilliform swimming has been investigated by using a computational model combining the dynamics of both the creature's movement and the two-dimensional fluid flow of the surrounding water. The model creature is self-propelled; it follows a path determined by the forces acting upon it, as generated by its prescribed changing shape. The numerical solution has been obtained by applying coordinate transformations and then using finite difference methods. Results are presented showing the flow around the creature as it accelerates from rest in an enclosed tank. The kinematics and dynamics associated with the creature's centre of mass are also shown. For a particular set of body shape parameters, the final mean swimming speed is found to be 0.77 times the speed of the backward-travelling wave. The corresponding movement amplitude envelope is shown. The magnitude of oscillation in the net forward force has been shown to be approximately twice that in the lateral force. The importance of allowing for acceleration and deceleration of the creature's body (rather than imposing a constant swimming speed) has been demonstrated. The calculations of rotational movement of the body and the associated moment of forces about the centre of mass have also been included in the model. The important role of viscous forces along and around the creature's body and in the growth and dissolution of the vortex structures has been illustrated.


Journal ArticleDOI
TL;DR: In this article, the authors introduce a mathematical formulation applicable to compaction driven flow for the entire range of rheological behaviors realized in the lithosphere and examine three first-order factors that influence the character of fluid flow: (1) thermally activated creep, (2) dependence of bulk viscosity on porosity, and (3) fluid flow in the limit of zero initial connected porosity.

BookDOI
01 Jan 1998
TL;DR: In this paper, nonlinear conservation laws and finite volume methods for radiation hydrodynamics have been used for simulation of Astrophysical Fluid Flow in the context of particle physics.
Abstract: Nonlinear Conservation Laws and Finite Volume Methods.- Radiation Hydrodynamics.- Radiation Hydrodynamics: Numerical Aspects and Applications.- Simulation of Astrophysical Fluid Flow.

Journal ArticleDOI
TL;DR: It is shown that, under some conditions of subcharacteristic type, for any convex entropy associated with the pressure p, the author can find a global convex and uniform entropy for the relaxation system.
Abstract: We consider the Euler equations for a compressible inviscid fluid with a general pressure law $p(\rho,\varepsilon)$, where $\rho$ represents the density of the fluid and $\varepsilon$ its specific internal energy. We show that it is possible to introduce a relaxation of the nonlinear pressure law introducing an energy decomposition under the form $\varepsilon= \varepsilon _1 + \varepsilon _2.$ The internal energy $\varepsilon _1$ is associated with a (simpler) pressure law $p_1(\rho,\varepsilon_1)$; the energy $\varepsilon _2$ is advected by the flow. These two energies are also subject to a relaxation process and in the limit of an infinite relaxation rate, we recover the initial pressure law p. We show that, under some conditions of subcharacteristic type, for any convex entropy associated with the pressure p, we can find a global convex and uniform entropy for the relaxation system. From our construction, we also deduce the extension to general pressure laws of classical approximate Riemann solvers for polytropic gases, which only use a single call to the pressure law (per mesh point and time step). For the Godunov scheme, we show that this extension satisfies stability, entropy, and accuracy conditions.

Journal ArticleDOI
TL;DR: A method for obtaining precise replicas of real fracture surfaces using transparent epoxy resins was developed, allowing detailed study of fluid flow paths within a fracture plane as discussed by the authors, which suggests that flow channeling in fractured rock can cause the breakthrough velocity of contaminants to far exceed the mean flow.
Abstract: A method for obtaining precise replicas of real fracture surfaces using transparent epoxy resins was developed, allowing detailed study of fluid flow paths within a fracture plane. A natural rock fracture was collected from the field and prepared for study. Silicon rubber molds of the fracture surfaces were used to make a transparent epoxy replica of the original fracture. Clear and dyed water were injected into the fracture pore space allowing examination of the flow field. Digitized optical images were used to observe wetting, saturated flow, and drying of the specimen. Nuclear magnetic resonance imaging was used for quantitative measurements of flow velocity. Both video imaging and nuclear magnetic resonance imaging techniques show distinct and strong channeling of the flow at the submillimeter to several-centimeter scale. Each phenomenon, including wetting, drying, dye transport, and velocity channeling, has its own distinct geometric structure and scale. We find that fluid velocities measured simultaneously at various locations in the fracture plane during steady state flow range over several orders of magnitude, with the maximum velocity a factor of 5 higher than the mean velocity. This suggests that flow channeling in fractured rock can cause the breakthrough velocity of contaminants to far exceed the mean flow.

Journal ArticleDOI
TL;DR: It is shown that the exact analytical solution for unsteady flow between two parallel walls predicts the same pattern of fluid behavior identified earlier for flow inside cylinders, including a dichotomy in fluid behavior for values of Wo < 1 and Wo > 1.

Journal ArticleDOI
TL;DR: In this article, a coupled flow and solute transport model with a kinetic model for smectite dehydration is used to better understand and quantify fluid flow in the Nankai accretionary complex offshore of Japan.
Abstract: Down-hole geochemical anomalies encountered in active accretionary systems can be used to constrain the timing, rates, and localization of fluid flow. Here we combine a coupled flow and solute transport model with a kinetic model for smectite dehydration to better understand and quantify fluid flow in the Nankai accretionary complex offshore of Japan. Compaction of sediments and clay dehydration provide fluid sources which drive the model flow system. We explicitly include the consolidation rate of underthrust sediments in our calculations to evaluate the impact that variations in this unknown quantity have on pressure and chloride distribution. Sensitivity analysis of steady state pressure solutions constrains bulk and flow conduit permeabilities. Steady state simulations with 30% smectite in the incoming sedimentary sequence result in minimum chloride concentrations at site 808 of 550 mM, but measured chlorinity is as low as 447 mM. We simulate the transient effects of hydrofracture or a strain event by assuming an instantaneous permeability increase of 3–4 orders of magnitude along a flow conduit (in this case the decollement), using steady state results as initial conditions. Transient results with an increase in decollement permeability from 10−16 m2 to 10−13 m2 and 20% smectite reproduce the observed chloride profile at site 808 after 80–160 kyr. Modeled chloride concentrations are highly sensitive to the consolidation rate of underthrust sediments, such that rapid compaction of underthrust material leads to increased freshening. Pressures within the decollement during transient simulations rise rapidly to a significant fraction of lithostatic and remain high for at least 160 kyr, providing a mechanism for maintaining high permeability. Flow rates at the deformation front for transient simulations are in good agreement with direct measurements, but steady state flow rates are 2–3 orders of magnitude smaller than observed. Fluid budget calculations indicate that nearly 71% of the incoming water in the sediments leaves the accretionary wedge via diffuse flow out the seafloor, 0–5% escapes by focused flow along the decollement, and roughly 1% is subducted.

Journal ArticleDOI
TL;DR: In this article, the authors discuss a few applications of active control of turbulent fluid flow and their implications for the economy and the environment, and outline a conceptual basis for control, sketching sensors, actuators, and the algorithm.
Abstract: ▪ Abstract We discuss a few applications of active control of turbulent fluid flow and their implications for the economy and the environment. We outline a conceptual basis for control, sketching sensors, actuators, and the algorithm. The control of turbulence requires an understanding of turbulent flows beyond our present capabilities, but we describe the physical basis for control of the boundary layer: coherent structures and bursts, the connection between burst frequency and friction velocity, the change of burst frequency and drag reduction possible with polymers or active control, and other effects on burst frequency (e.g. streamline curvature, pressure gradients, and extra rates of strain). Given that the state of the flow must be sensed from the surface, and that this information is necessarily incomplete and aliased, sophisticated techniques may be required to interpret the signals. A control strategy, an algorithm, is necessary, and we express the need for a model of the flow as an interpretor a...

Journal ArticleDOI
TL;DR: In this article, the pore Reynolds number, Re p, has been used to characterize the turbulent nature of the flow in porous media, and the autocorrelation function of the velocity gradient fluctuations calculated from the spectrum has been evaluated.

Patent
08 Sep 1998
TL;DR: In this paper, a plurality of disc-like spaced flow guide elements are disposed in a stack in a spaced relationship with filter elements disposed in the spaces between the flow guide element to which fluid can be supplied through inlet openings to flow over the surfaces of the filter elements.
Abstract: In a device for filtering and separating fluids, a plurality of disc-like spaced flow guide elements are disposed in a stack in spaced relationship with filter elements disposed in the spaces between the flow guide elements to which fluid can be supplied through inlet openings to flow over the surfaces of the filter elements. Each flow guide element defines at one end a flow opening for the passage of fluid and at least one channel formed in the flow guide element so as to extend adjacent the opening in a direction transverse to the flow of the fluid from the opening into the space between the flow guide elements to promote fluid flow distribution over the width of the flow path through the device.

Journal ArticleDOI
TL;DR: In this article, a viscous ferrofluid flow over a stretching sheet in the presence of a magnetic dipole is considered and the fluid momentum and thermal energy equations are fomulated as a five-parameter problem, and the influence of the magneto-thermomechanical coupling is explored numerically.
Abstract: The flow of a viscous ferrofluid over a stretching sheet in the presence of a magnetic dipole is considered. The fluid momentum and thermal energy equations are fomulated as a five-parameter problem, and the influence of the magneto-thermomechanical coupling is explored numerically. It is concluded that the primary effect of the magnetic field is to decelerate the fluid motion as compared to the hydrodynamic case, thereby increasing the skin friction and reducing the heat transfer rate at the sheet.

Journal ArticleDOI
TL;DR: In this article, an electrochemical micro-probe is inserted inside the medium and at the wall of test sections for determining the end of stable laminar regime in various porous media such as beds packed with spheres, stratified media and reticulated media.

Journal ArticleDOI
TL;DR: In this paper, a broad range of mathematical modeling errors of fluid flow physics and numerical approximation errors are addressed in computational fluid dynamics (CFD), and two techniques are briefly discussed for the detection and quantification of certain types of more complicated discretization and grid resolution errors.
Abstract: A broad range of mathematical modeling errors of fluid flow physics and numerical approximation errors are addressed in computational fluid dynamics (CFD). It is strongly believed that if CFD is to have a major impact on the design of engineering hardware and flight systems, the level of confidence in complex simulations must substantially improve. To better understand the present limitations of CFD simulations, a wide variety of physical modeling, discretization, and solution errors are identified and discussed. Here, discretization and solution errors refer to all errors caused by conversion of the original partial differential, or integral, conservation equations representing the physical process, to algebraic equations and their solution on a computer. The impact of boundary conditions on the solution of the partial differential equations and their discrete representation will also be discussed. Throughout the article, clear distinctions are made between the analytical mathematical models of fluid dynamics and the numerical models. Lax`s Equivalence Theorem and its frailties in practical CFD solutions are pointed out. Distinctions are also made between the existence and uniqueness of solutions to the partial differential equations as opposed to the discrete equations. Two techniques are briefly discussed for the detection and quantification of certain types ofmore » discretization and grid resolution errors.« less

Journal ArticleDOI
TL;DR: Details of a procedure for stabilizing the numerical solution for advective-diffusive transport and fluid flow problems using the FPM are given.
Abstract: The finite point method (FPM) is a gridless numerical procedure based on the combination of weighted least square interpolations on a cloud of points with point collocation for evaluating the approximation integrals. In the paper, details of a procedure for stabilizing the numerical solution for advective-diffusive transport and fluid flow problems using the FPM are given. The method is based on a consistent introduction of the stabilizing terms in the governing differential equations. One example showing the applicability of the FPM is given.

Journal ArticleDOI
TL;DR: Dissipative particle dynamics is a relatively new simulation method in the colloid and interface science field as discussed by the authors, and it has been used to simulate the dynamics and rheology of polymers in solution, the dynamics of microphase separation in block copolymer melts, and the effects of hydrodynamics in spinodal decomposition.
Abstract: Dissipative particle dynamics is a relatively new simulation method in the colloid and interface science field. Recent applications include simulations of the dynamics and rheology of polymers in solution, the dynamics of microphase separation in block copolymer melts, and the effects of hydrodynamics in spinodal decomposition.

Journal ArticleDOI
TL;DR: Several models have been developed to describe the standard experiment, of flow along a finite length of elastic tube mounted at its ends on rigid tubes and contained in a chamber whose pressure can be independently varied as mentioned in this paper.
Abstract: Laboratory experiments designed to shed light on fluid flow through collapsible tubes, a problem with several physiological applications, invariably give rise to a wide variety of self-excited oscillations. The object of modelling is to provide scientific understanding of the complex dynamical system in question. This paper outlines some of the models that have been developed to describe the standard experiment, of flow along a finite length of elastic tube mounted at its ends on rigid tubes and contained in a chamber whose pressure can be independently varied. Lumped and one-dimensional models have been developed for the study of steady flow and its instability, and a variety of oscillation types are indeed predicted. However, such models cannot be rationally derived from the full governing equations, relying as they do on several crude, ad hoc assumptions such as that concerning the energy loss associated with flow separation at the time-dependent constriction during large-amplitude oscillations. A complete scientific description can be given, however, for a related two-dimensional configuration, of flow in a parallel-sided channel with a segment of one wall replaced by a membrane under longitudinal tension T. The flow and membrane displacement have been calculated successively by lubrication theory, Stokes-flow computation, steady Navier–Stokes computation and unsteady Navier–Stokes computation. For a given Reynolds number, Re, steady flow becomes unstable when T falls below a critical value (equivalently, when Re exceeds a critical value for fixed T), and the consequent oscillations reveal at least one period-doubling bifurcation as T is further reduced. The effect of wall inertia has also been investigated: it is negligible if the flowing fluid is water, but leads to an independent, high frequency flutter when it is air. The computations require very large computer resources, and a simpler model would be desirable. Investigation of the streamlines of the flow and the distribution of viscous energy dissipation reveals how the one-dimensional model might be improved; but such improvement is as yet incomplete.

Journal ArticleDOI
TL;DR: In this article, a microelectromechanical system (MEMS) microvalve array for fluid flow control is described, which consists of a parallel array of surface-micromachined binary microvalves working cooperatively to achieve precision how control on a macroscopic level.
Abstract: A microelectromechanical system (MEMS) microvalve array for fluid flow control is described. The device consists of a parallel array of surface-micromachined binary microvalves working cooperatively to achieve precision how control on a macroscopic level. Flow rate across the microvalve array is proportional to the number of microvalves open, yielding a scalable high-precision fluidic control system. Device design and fabrication, using a one-level polycrystalline silicon surface-micromachining process combined with a single anisotropic bulk etching process are detailed. Performance measurements on fabricated devices confirm feasibility of the fluidic control concept and robustness of the electromechanical design. Air-flow rates of 150 ml/min for a pressure differential of 10 kPa were demonstrated. Linear flow control was achieved over a wide range of operating flow rates. A continuum fluidic model based on incompressible low Reynolds number flow theory was implemented using a finite-difference approximation. The model accurately predicted the effect of microvalve diaphragm compliance on flow rate. Excellent agreement between theoretical predictions and experimental data was obtained over the entire range of flow conditions tested experimentally.

Journal ArticleDOI
TL;DR: In this article, the dynamics of a viscous accretion disc subject to a slowly varying warp of large amplitude is considered, and the equations of fluid dynamics are derived in a coordinate system that follows the principal warping motion of the disc.
Abstract: The dynamics of a viscous accretion disc subject to a slowly varying warp of large amplitude is considered. Attention is restricted to discs in which self-gravitation is negligible, and to the generic case in which the resonant wave propagation found in inviscid Keplerian discs does not occur. The equations of fluid dynamics are derived in a coordinate system that follows the principal warping motion of the disc. They are reduced using asymptotic methods for thin discs, and solved to extract the equation governing the warp. In general, this is a wave equation of parabolic type with non-linear dispersion and diffusion, which describes fully non-linear bending waves. This method generalizes the linear theory of Papaloizou & Pringle (1983) to allow for an arbitrary rotation law, and extends it into the non-linear domain, where it connects with a generalized version of the theory of Pringle (1992). The astrophysical implications of this analysis are discussed briefly.