Showing papers on "Fluid dynamics published in 2000"

An Introduction to Fluid Dynamics

Abstract: Preface Conventions and notation 1. The physical properties of fluids 2. Kinematics of the flow field 3. Equations governing the motion of a fluid 4. Flow of a uniform incompressible viscous fluid 5. Flow at large Reynolds number: effects of viscosity 6. Irrotational flow theory and its applications 7. Flow of effectively inviscid liquid with vorticity Appendices.

Fluid flow induced by nonuniform ac electric fields in electrolytes on microelectrodes. I. Experimental measurements

Abstract: Under the influence of an ac electric field, electrolytes on planar microelectrodes exhibit fluid flow. The nonuniform electric field generated by the electrodes interacts with the suspending fluid through a number of mechanisms, giving rise to body forces and fluid flow. This paper presents the detailed experimental measurements of the velocity of fluid flow on microelectrodes at frequencies below the charge relaxation frequency of the electrolyte. The velocity of latex tracer particles was measured as a function of applied signal frequency and potential, electrolyte conductivity, and position on the electrode surface. The data are discussed in terms of a linear model of ac electroosmosis: the interaction of the nonuniform ac field and the induced electrical double layer.

Optimal Control of Distributed Systems: Theory and Applications

Abstract: The existence of solutions to optimal control problems Optimality system for optimal control problems The solvability of boundary value problems for a dense set of data The problem of work minimization in accelerating still fluid to a prescribed velocity Optimal boundary control for nonstationary problems of fluid flow and nonhomogeneous boundary value problems for the Navier-Stokes equations The Cauchy problem for elliptic equations in a conditionally well-posed formulation The local exact controllability of the flow of incompressible viscous fluid Bibliography Index.

Fluid flow induced by nonuniform ac electric fields in electrolytes on microelectrodes. II. A linear double-layer analysis

Abstract: Frequency-dependent fluid flow in electrolytes on microelectrodes subjected to ac voltages has recently been reported. The fluid flow is predominant at frequencies of the order of the relaxation frequency of the electrode-electrolyte system. The mechanism responsible for this motion has been termed ac electro-osmosis: a continuous flow driven by the interaction of the oscillating electric field and the charge at the diffuse double layer on the electrodes. This paper develops the basis of a theoretical approach to this problem using a linear double layer analysis. The theoretical results are compared with the experiments, and a good correlation is found.

Fluid processing systems and methods using extracorporeal fluid flow panels oriented within a cartridge

Abstract: A first flow path is defined within a first panel that forms a part of an extracorporeal fluid circuit. A second flow path is defined within a second panel that also forms a part of the extracorporeal fluid circuit. The first and second panels are oriented in a fluid processing cartridge for mounting as an integrated unit on a fluid processing machine and for removal as an integrated unit from the fluid processing machine.

Cryosurgical fluid supply

Abstract: Improved systems, devices, and methods for delivering cryogenic cooling fluid to cryosurgical probes such as cryosurgical endovascular balloon catheters take advantage of the transients during the initiation and termination of cryogenic fluid flow to moderate the treatment temperatures of tissues engaged by the probe. A flow limiting element along a cryogenic fluid path intermittently interrupts the flow of cooling fluid, often cycling both the fluid flow and treatment temperature. This can maintain the tissue treatment temperature within a predetermined range which is above the treatment temperature provided by a steady flow of cryogenic fluid. In another aspect, room temperature single-use cooling fluid cartridges are filled with a sufficient quantity of cryosurgical fluid to effect a desired endovascular cryosurgical treatment.

Conditions for Similitude between the Fluid Velocity and Electric Field in Electroosmotic Flow

Abstract: Electroosmotic flow is fluid motion driven by an electric field acting on the net fluid charge produced by charge separation at a fluid−solid interface. Under many conditions of practical interest, the resulting fluid velocity is proportional to the local electric field, and the constant of proportionality is everywhere the same. Here we show that the main conditions necessary for this similitude are a steady electric field, uniform fluid and electric properties, an electric Debye layer that is thin compared to any physical dimension, and fluid velocities on all inlet and outlet boundaries that satisfy the Helmholtz−Smoluchowski relation normally applicable to fluid−solid boundaries. Under these conditions, the velocity field can be determined directly from the Laplace equation governing the electric potential, without solving either the continuity or momentum equations. Three important consequences of these conditions are that the fluid motion is everywhere irrotational, that fluid velocities in two-dime...

Channelized fluid flow in oceanic crust reconciles heat-flow and permeability data

Abstract: Hydrothermal fluid circulation within the sea floor profoundly influences the physical, chemical and biological state of the crust and the oceans. Circulation within ridge flanks (in crust more than 1 Myr old) results in greater heat loss1,2,3 and fluid flux4 than that at ridge crests and persists for millions of years, thereby altering the composition of the crust and overlying ocean5,6. Fluid flow in oceanic crust is, however, limited by the extent and nature of the rock's permeability7. Here we demonstrate that the global data set of borehole permeability measurements in uppermost oceanic crust7,8,9 defines a trend with age that is consistent with changes in seismic velocity10,11. This trend—which indicates that fluid flow should be greatly reduced in crust older than a few million years—would appear to be inconsistent with heat-flow observations, which on average indicate significant advective heat loss in crust up to 65 Myr old3. But our calculations, based on a lateral flow model, suggest that regional-scale permeabilities are much higher than have been measured in boreholes. These results can be reconciled if most of the fluid flow in the upper crust is channelized through a small volume of rock, influencing the geometry of convection and the nature of fluid–rock interaction.

A three-dimensional computer model of the human heart for studying cardiac fluid dynamics

Abstract: In all areas of computational fluid dynamics (CFD), proper treatment of the boundary conditions is essential to computing fluid behavior correctly. In many engineering problems, CFD is simplified by a priori knowledge of the motion of the boundary. The well-known parabolic velocity profile in fully-developed flow of an incompressible Newtonian fluid in a pipe of circular cross-section is easily computed because the boundary (the pipe wall) is known to be in a fixed location. Even in more complex settings, such as flow around a ship's propeller, the motion of the boundary (the propeller) can be specified in advance.By contrast, in most biological fluid dynamics problems the boundaries are not rigid and their motions are the result of forces imposed on them by the motion of the surrounding fluid. The motion of the fluid, of course, cannot be known without knowledge of the boundary motion. The motion of the boundary and the motion of the fluid form a coupled system; both motions must be computed simultaneously, which makes biological CFD difficult.A particular problem of interest is the flow of blood in the chambers of the human heart. The heart is an organ whose muscular contractions pump blood around the body. Simplifying somewhat, the heart consists of two main pumping chambers that contract simultaneously. One chamber, the left ventricle, accepts oxygen-enriched blood from the lungs and pumps it to the body. The other chamber, the right ventricle, accepts oxygen-depleted blood from the body and pumps it to the lungs. The inlet and outlet of each ventricle are guarded by valves whose opening and closing guarantee one-directional flow around the circulatory system. There are a total of four valves. The valves generally consist of two or three leaflets - membranes made of very flexible but inextensible material. Familiar examples of materials with this property would be paper or fabric which can be easily bent or twisted but which are not easily stretched. One edge of each valve leaflet is securely attached to the wall of the heart, but the other edge is free of attachment and can move with the flow. Structures analogous to a valve leaflet are a shirt pocket, with one edge (three sides of a rectangular patch pocket) securely stitched to the shirt and one edge free of attachment, or a flag, one edge attached to the flag pole, the other edge free to wave in the wind. When flow is passing through the valve in the forward direction, the valve's leaflets are positioned out of the way, permitting flow. When flow attempts to pass in the reverse direction, the leaflets come together, their free edges pressing against the free edges of their neighbors to occlude the flow passage.The motion of the leaflets is not caused by muscles in the valve. The outflow valves are entirely passive structures with no muscular tissue whatsoever. Even in the case of the inflow valves, whose free edges are connected to the heart muscle by a sparse network of tendons, the opening and closing motions result from an interaction with the surrounding fluid. The forward motion of the fluid pushes the leaflets aside out of the main flow stream, but the inextensibilty of the leaflet material prevents free motion of the fluid near the leaflet, affecting the entire flow field. Reverse motion of the fluid causes the leaflets to move back into the flow passage where contact between neighboring leaflets and the inextensibilty of the leaflet material halts the flow. The highly interactive nature of the fluid and leaflet motions makes this an especially interesting and challenging CFD problem.Commercially available software packages intended for engineering CFD are not equipped to handle this type of dynamic interaction between boundary and fluid. We have developed a numerical method (the "Immersed Boundary Method") which simultaneously computes the motion of a fluid and the motion of an elastic boundary immersed in, and interacting with, that fluid. In the Immersed Boundary Method, the fluid is represented by Eulerian velocities and pressures that are stored on a regular three-dimensional computational lattice. The scale of the heart chambers is such that blood can be treated as a Newtonian fluid. Fluid dynamics is computed by numerical solution of the Navier-Stokes equations, including a body force. The boundary is represented by elastic structures that are free to move continuously in the space sampled by the computational lattice. The essence of the method is to replace the elastic boundary by the forces that result from its deformations. These forces are applied to the lattice in the neighborhood of the elastic boundary with the aid of a numerical approximation to the Dirac delta function. The fluid moves under the action of this body force. The numerical delta function is then used again, to interpolate the newly computed lattice velocities to the locations of the boundary, and then the boundary is moved at the interpolated velocity to a new location (the no-slip condition). The process of computing forces, then fluid motion and then new boundary location is repeated cyclically in a time-stepping procedure with a suitably chosen time step. The only requirements for the method are the physical properties of the fluid, the (possibly time-dependent) elastic properties of the boundary, and the initial geometry of the boundary. A complete description of the Immersed Boundary Method can be found in [1, 2].

A unified formulation of the segregated class of algorithms for fluid flow at all speeds

Abstract: In this article, the segregated SIMPLE algorithm and its variants are reformulated, using a collocated variable approach, to predict fluid flow at all speeds In the formulation, a unified, compact, and easy-to-understand notation is employed The SIMPLE, SIMPLER, SIMPLEST, SIMPLEM, SIMPLEC, SIMPLEX, PRIME, and PISO algorithms that are scattered in the literature and appear to a non versed computational fluid dynamics (CFD) user as being unrelated, are shown to share the same essence in their derivations and to be equally applicable for the simulation of incompressible and compressible flows Moreover, the philosophies behind these algorithms in addition to their similarities and differences are explained

Electrokinetic high pressure hydraulic system

Abstract: An electrokinetic high pressure hydraulic pump for manipulating fluids in capillary-based systems includes (i) a microchannel having a fluid inlet and outlet and a porous dielectric material disposed in said microchannel; (ii) an electrolyte contained within said microchannel and in communication with the porous dielectric material; (iii) spaced apart electrodes that are in contact with said electrolyte; and (iv) means for applying an electric potential to said spaced apart electrodes. The pump, which requires no moving mechanical parts, uses electro-osmotic flow to generate high pressures for pumping and/or compressing fluids, for providing valve means and means for opening and closing valves, for controlling fluid flow rate, and for manipulating fluid flow particularly in capillary-based systems. The compact nature of the high pressure hydraulic pump permits construction of a micro-scale or capillary-based HPLC system that fulfills the desire for small sample quantity, low solvent consumption, improved efficiency, running parallel samples and field portability. Control of pressure and solvent flow rate are achieved by controlling the voltage applied to the electrokinetic pump.

Seismic wave propagation in cracked porous media

Abstract: Summary The movement of interstitial fluids within a cracked solid can have a significant effect on the properties of seismic waves of long wavelength propagating through the solid. We consider three distinct mechanisms of wave-induced fluid flow: flow through connections between cracks in an otherwise non-porous material, fluid movement within partially saturated cracks, and diffusion from the cracks into a porous matrix material. In each case the cracks may be aligned or randomly oriented, leading, respectively, to anisotropic or isotropic wave speeds and attenuation factors. In general, seismic velocities exhibit behaviour that is intermediate between that of empty cracks and that of isolated liquid-filled cracks if fluid flow is significant. In the range of frequencies for which considerable fluid flow occurs there is high attenuation and dispersion of seismic waves. Fluid flow may be on either a wavelength scale or a local scale depending on the model and whether the cracks are aligned or randomly oriented, resulting in completely different effects on seismic wave propagation. A numerical analysis shows that all models can have an effect over the exploration seismic frequency range.

A three-dimensional finite element model of radiofrequency ablation with blood flow and its experimental validation.

Abstract: A novel three-dimensional finite element model for the study of radiofrequency ablation is presented. The model was used to perform an analysis of the temperature distribution in a tissue block heated by RF energy and cooled by blood (fluid) flow. This work extends earlier models by including true flow in place of a convective boundary condition to simulate realistic experimental conditions and to improve the prediction of blood temperatures. The effect of fluid flow on the temperature distribution, the lesion dimensions, and the ablation efficiency was studied. Three flow velocities were simulated: (i) 30, (ii) 55, and (iii) 85 mm/s. The modeling results were validated qualitatively and quantitatively with in vitro data. The correlation coefficients between the modeling and the experimental temperature measurements were 0.98, 0.97, and 0.95 for flows (i)-(iii), respectively. The slopes were 0.89, 0.95, and 1.06, and the mean root mean square differences between modeling and experimental temperature measurements were 17.3% +/- 11.6%, 15.8% +/- 13.4%, and 18.8% +/- 14.9% for flows (i)-(iii), respectively. A comparison of temperature distribution obtained with a convective boundary versus inclusion of fluid motion showed that the convective boundary resulted in a similar tissue temperature distribution, but overestimated fluid temperatures and lacked the flow asymmetry seen in the true flow model.

VS2DI-A graphical software package for simulating fluid flow and solute or energy transport in variably saturated porous media

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The fluid dynamic and shear environment in the NASA/JSC rotating-wall perfused-vessel bioreactor.

Abstract: The rotating-wall perfused-vessel (RWPV) bioreactor, used for both microgravity and Earth-based cell science experiments, is characterized in terms of the fluid dynamic and fluid shear stress environment. A numerical model of the flow field is developed and verified with laser Doppler velocimeter measurements. The effects of changes in operating conditions, including rotation rates and fluid perfusion rates, are investigated with the numerical model. The operating conditions typically used for ground-based experiments (equal rotation of the inner and outer cylinders) leads to flow patterns with relatively poor mass distribution characteristics. Approximately 50% of the inlet-perfused fluid bypasses the bulk of the fluid volume and flows to the perfusion exit. For operating conditions typical in microgravity, small differential rotation rates between the inner and outer cylinders lead to greatly improved flow distribution patterns and very low fluid shear stress levels over a large percentage of the fluid volume. Differences in flow patterns for the different operating conditions are explored. Large differences in the hydrodynamic environments for operating conditions typical of true microgravity and ground-based "microgravity simulations" are demonstrated.