bluuebunny/crossref_metadata_2025 huggingface dataset:
Chloride Currents in Acutely Isolated Xenopus Retinal Pigment Epithelial Cells
Authors: Hartzell H. Criss , Qu Zhiqiang
Published: April 2003

The retinal pigment epithelium (RPE) regulates the ionic composition of the fluid surrounding the photoreceptors by transport mechanisms that utilize Cl− channels. Cl− currents in RPE cells, however, remain incompletely characterized. The purpose of this study was to identify the Cl− currents in acutely isolated Xenopus RPE cells using whole‐cell patch clamp. We describe three different Cl− currents. (1) An inwardly rectifying Cl− current, ICl,ir, activates slowly with hyperpolarization (τact=μ1 s at −80 mV, V1/2=−94 ± 3 mV), is blocked by Zn2+ (IC50=185 μm), is stimulated by acid (ICl,ir is 5 times larger at pH 6 than pH 8), and is blocked by DIDS in a voltage‐dependent manner. ICl,ir closely resembles cloned ClC‐2currents. (2) An outwardly rectifying Cl− current, ICl,Ca, is stimulated by elevated cytosolic free [Ca2+]. With 1 μm free [Ca2+]i in the patch pipette, ICl,Ca activates slowly with depolarization (τact=325 ms at 100 mV) and deactivates upon hyperpolarization. ICl,Ca is not blocked by 1 mm Zn2+ or 10 μm Gd3+ but is blocked by DIDS. High extracellular [Ca2+] (10 mm) also activates ICl,Ca. (3) A non‐rectifying current is activated by elevation of cytoplasmic cAMP with forskolin and IBMX. In addition to these three Cl− currents, Xenopus RPE cells exhibit a non‐selective background current (Ibkg) which has a linear I‐V relationship and is voltage insensitive. This current is blocked by Zn2+ (IC50 of 5.3 μm) or 10 μm Gd3+. This description provides new insights into the physiology of Cl− channels involved in salt and fluid transport by the retinal pigment epithelium.
Regulation of Inwardly Rectifying K+ Channels in Retinal Pigment Epithelial Cells by Intracellular pH
Authors: Yuan Yukun , Shimura Masahiko , Hughes Bret A.
Published: April 2003

Inwardly rectifying K+ (Kir) channels in the apical membrane of the retinal pigment epithelium (RPE) play a key role in the transport of K+ into and out of the subretinal space (SRS), a small extracellular compartment surrounding photoreceptor outer segments. Recent molecular and functional evidence indicates that these channels comprise Kir7.1 channel subunits. The purpose of this study was to determine whether Kir channels in the RPE are modulated by extracellular (pHo) or intracellular pH (pHi), both of which change upon illumination of the dark‐adapted retina. The Kir current (IKir) in acutely dissociated bovine RPE cells was recorded in the whole‐cell configuration while altering pHo or pHi. In cells dialysed with pipette solution buffered to pH 7.2, step changes in pHo from 7.4 to 8.0, 7.0 or 6.5 had little effect on IKir. Acidification to pHo 6.0, however, caused a transient activation of IKir followed by a slower inhibition. To determine the dependence of IKir on pHi, we altered pHi within individual RPE cells at constant pHo by imposing transmembrane acetate concentration gradients. These experiments revealed a biphasic relationship between IKir and pHi: IKir was maximal at about pHi 7.1, but decreased sharply at more acidic or alkaline levels. To evaluate the role of Kir7.1 channels in the pHi‐dependent changes in IKir, we tested the effect of transmembrane acetate concentration gradients on Rb+ currents, which are 10‐fold larger than K+ currents for this channel subtype. Inwardly rectifying Rb+ currents were maximal at about pHi 7.0 and were inhibited by intracellular alkalinization or acidification. We conclude that the Kir conductance in the RPE is modulated by intracellular pH in the physiological range and that this reflects the behaviour of Kir7.1 channels. This sensitivity to pHi may provide an important mechanism linking photoreceptor activity and RPE function.
Heat Transfer in a High Turbulence Air Jet Impinging Over a Flat Circular Disk
Authors: Siba Erick A. , Ganesa-Pillai M. , Harris Kendall T. , Haji-Sheikh A.
Published: March 2003

This study concerns the flow and heat transfer characteristics of a turbulent submerged circular air jet impinging on a horizontal flat surface when free stream turbulence exceeds 20 percent. The turbulent fluctuations of the free stream velocity are the primary aerodynamics influencing heat transfer. Two regions with distinct flow characteristics are observed: the stagnation region, and the wall-jet region. According to the linear form of the energy equation, the surface heat flux may be decomposed into laminar and turbulent components. An inverse methodology can determine the turbulent component of the heat transfer coefficient in the stagnation region and in the wall-jet region as a function of the root mean square value of the fluctuating component of velocity in the bulk flow direction.
The Motion of a Rolling Polygon
Authors: Beunder E. M. , Rem P. C.
Published: March 2003

Galileo was the first to analyze the motion of spheres rolling down an inclined surface. Since then, Coulomb’s law of dry friction has covered the case of sliding particles. However, a particle that is not round can still roll, although in a way that is essentially different from the motion studied by Galileo. Instead of keeping contact with the surface, such particles will start bouncing after reaching a certain angular velocity. This motion is a combination of flying and colliding. It is shown that the acceleration of a bouncing particle is always bounded by the accelerations for perfect rolling and sliding. In order to describe the motion of a not perfectly round particle, the polygon is used as a model. The aim of the model is to predict the trajectories of particles that cannot be covered by the models for perfect rolling and sliding.
Design and Analysis of a Surface Micromachined Spiral-Channel Viscous Pump
Authors: Kilani Mohammad I. , Galambos Paul C. , Haik Yousef S. , Chen Ching-Jen
Published: March 2003

A new viscous spiral micropump which uses the surface micromachining technology is introduced. The paper outlines the design of a spiral pump fabricated in five levels of polysilicon using Sandia’s Ultraplanar Multilevel MEMS Technology (SUMMiT), and presents an analytical solution of the flow field in its spiral channel. The pump characteristics are obtained experimentally for a scaled-up prototype and are found to be in good agreement with the results obtained using the analytical model.
Dynamics of a Cavitating Propeller in a Water Tunnel
Authors: Watanabe Satoshi , Brennen Christopher E.
Published: March 2003

This study investigates the unsteady dynamics and inherent instabilities of a cavitating propeller operating in a water tunnel. First, the steady characteristics of the cavitating propeller such as the thrust coefficient are obtained by applying continuity and momentum equations to a simple one-dimensional flow tube model. The effects of the tunnel walls as well as those of the propeller operating conditions (advance ratio and cavitation number) are explored. Then the transfer matrix of the cavitating propeller (considered to be the most appropriate way to describe the dynamics of propeller) is obtained by combining the simple stream tube model with the conventional cavity model using the quasi-static cavitation compliance and mass flow gain factor representation. Finally, the surge instability of a cavitating propeller observed by Duttweiler and Brennen (2001) is examined by coupling the present model of the cavitation with a dynamic model for the water tunnel. This analysis shows that the effect of tunnel walls is to promote the surge instability.
Viscous Fingering in a Hele-Shaw Cell With Finite Viscosity Ratio and Interfacial Tension
Authors: Guan X. , Pitchumani R.
Published: March 2003

A volume tracking method was developed to simulate time-dependent unstable viscous fingering in a Hele-Shaw cell. The effect of finite viscosity ratio μr between displacing and displaced fluids and their interfacial tension σ on finger morphology is investigated. It is shown that there exist four distinct finger patterns, depending upon the viscosity ratio, μr, and Ca′, the modified capillary number for constant flow rate, or ΔPs˙W/σ, for constant driving pressure difference. Morphology diagrams are developed to identify the ranges of the dimensionless parameters corresponding to the various finger patterns. The simulation results are validated with experiments.
Analytically Approximate Solutions for Vibrations of a Long Discrete Chain
Authors: Lee W.
Published: March 2003

This brief note studies small transverse vibrations of a long hanging chain of discrete links. Analytical approximate solutions are obtained when the number of links is considered large while they still posses nontrivial rotary inertia. The results imply that the rotary inertia becomes more significant for higher modes of vibration.
Integral Solutions for Transient Temperature Profiles in Stably-Stratified Open Enclosures
Authors: Homan K. O.
Published: March 2003

The stably-stratified filling of an enclosure produces an interfacial layer, or thermocline, separating the hot and cold fluid volumes which is transported through the vessel with the bulk flow. The evolution of this interfacial layer is characterized by profile asymmetries and growth rates not explained by simple molecular diffusion. The present paper presents integral solutions to the horizontally-averaged energy equation with variable diffusivities exhibiting these same characteristics. The formulation requires only two parameters in addition to those of the uniform diffusivity case. The solutions are compared to published data to illustrate determination of the empirical constants and show that key characteristics of the model, specifically a constant fill-line temperature and symmetric growth rates, are satisfied for a range of moderate flow rates. At higher flow rates, the layers are seen to exhibit an increasingly higher degree of growth rate asymmetry.
Line Plume Approximation on Atrium Smoke Filling With Thermal Stratified Environment
Authors: Li J. , Chow W. K.
Published: March 2003

Upward motion of a balcony spill plume in an atrium with a thermal stratified layer will be simulated. This is aimed at answering the question on whether a smoke plume can move up an atrium to reach the ceiling. The gradient of air density in the atrium is taken as a constant negative value. The plume motion under this condition is compared with the case without a thermal stratified layer. It is noted that the effect of stratification is not obvious in regions near to the fire. But for the upper region of the plume, the effect is significant. In this way, the plume might not be able to reach the ceiling of an atrium with a hot enough thermal stratified layer. The maximum plume rise under this condition will also be calculated.
The Effect of Dissolving Salts in Water Sprays Used for Quenching a Hot Surface: Part 1—Boiling of Single Droplets
Authors: Cui Qiang , Chandra Sanjeev , McCahan Susan
Published: March 2003

We conducted experiments on the effect of dissolving three different salts sodium chloride (NaCl), sodium sulfate Na2SO4 and magnesium sulfate MgSO4 in water droplets boiling on a hot stainless steel surface. Substrate temperatures were varied from 90°C to 220°C. We photographed droplets as they evaporated, and recorded their evaporation time. At surface temperatures that were too low to initiate nucleate boiling all three salts were found to reduce droplet evaporation rates because they lower the vapor pressure of water. In the nucleate boiling regime, low concentrations (<0.1 mol/l) of Na2SO4 and MgSO4 enhanced heat transfer because they prevented coalescence of vapor bubbles and produced foaming in the droplet, significantly reducing droplet lifetimes. Increasing the salt concentration further did not produce a corresponding increase in droplet boiling rate. Dissolved salts prevent bubble coalescence because they increase surface tension and stabilize the liquid film separating bubbles, and because electric charge that accumulates on the surfaces of bubbles produces a repulsive force, preventing them from approaching each other. Na2SO4 and MgSO4, which have high ionic strengths, produced a large amount of foaming in droplets and increased their boiling rate significantly. NaCl, which has low ionic strength, had little effect on droplet boiling.
Application of Adomian’s Decomposition Procedure to the Analysis of Convective-Radiative Fins
Authors: Chiu Ching-Huang , Chen Cha’o-Kuang
Published: March 2003

This paper presents a method which may be used to determine the temperature distribution within a convective-radiative longitudinal fin of variable thermal conductivity, subject to convection heat transfer from a fluid of known temperature Tf through the inside face of the primary surface, and which experiences convection-radiation heat dissipation into the environment at its tip. The paper demonstrates the use of the Adomian decomposition method in generating an analytical solution of the resulting nonlinear energy balance equation with nonlinear boundary conditions.
Natural Convection Heat Transfer From a Cylinder With High Conductivity Permeable Fins
Authors: Abu-Hijleh Bassam A/K
Published: March 2003

The problem of laminar natural convection from a horizontal cylinder with multiple equally spaced high conductivity permeable fins on its outer surface was investigated numerically. The effect of several combinations of number of fins and fin height on the average Nusselt number was studied over a wide range of Rayleigh number. Permeable fins provided much higher heat transfer rates compared to the more traditional solid fins for a similar cylinder configuration. The ratio between the permeable to solid Nusselt numbers increased with Rayleigh number, number of fins, and fin height. This ratio was as high as 8.4 at Rayleigh number of 106, non-dimensional fin height of 2.0, and with 11 equally spaced fins. The use of permeable fins is very advantageous when high heat transfer rates are needed such as in today’s high power density electronic components.
Marangoni and Variable Viscosity Phenomena in Picoliter Size Solder Droplet Deposition
Authors: Dietzel M. , Haferl S. , Ventikos Y. , Poulikakos D.
Published: March 2003

This paper focuses on the effect that surface tension (Marangoni phenomenon) and viscosity dependence on temperature has on the spreading, transient behavior and final post-solidification shape of a molten Sn63Pb solder droplet deposited on a flat substrate. A Lagrangian finite element formulation of the complete axisymmetric Navier-Stokes equations is utilized for the description of the droplet behavior. Linear temperature dependence for the surface tension and an exponential dependence for the viscosity are assumed. The initial droplet temperature is varied in 50 K steps from 200°C to 500°C, whereas the substrate temperature is kept constant at 25°C. This varies the initial Reynolds number Re0 from 360 to 716 and the Marangoni number Ma from −9 to −49. The initial Weber number We0 and initial Prandtl number Pr0 are for all cases O(1) and O10−2, respectively. The impact velocity and the droplet diameter remain unchanged in all cases examined at 1.5 m/s and 80 microns. A major finding of the work is that, contrary to intuition, the Marangoni effect decreased droplet spreading monotonically. Due to the Marangoni effect, the mechanism that arrested spreading is the surface tension and not the beginning of freezing. Droplet receding during recoiling was aided by the Marangoni effect. On the other hand, the change of viscosity with temperature showed no significant influence on the outcome of the droplet impact.
The Effects of Air Infiltration on a Large Flat Heat Pipe at Horizontal and Vertical Orientations
Authors: Cerza M. , Boughey B.
Published: March 2003

In the satellite or energy conversion industries flat heat pipes may be utilized to transfer heat to the thermal sink. In this investigation, a large flat heat pipe, 1.22m×0.305m×0.0127m, fabricated from 50 mil Monel 400 metal sheets and Monel 400 screens was videographed at horizontal and vertical orientations with an infrared video camera. The heat pipe evaporator section consisted of a 0.305m×0.305m area (one heated side only) while the side opposite the heated section was insulated. The remaining area of the heat pipe served as the condenser. In the horizontal orientation the heated section was on the bottom. In the vertical orientation the evaporator was aligned below the condenser. The sequence of photographs depicts heat inputs ranging from 200 W to 800 W, and the effect of air infiltration on heat pipe operation for both orientations. For the horizontal orientation, the air is seen to recede towards the small fill pipe as the heat input is increased. For the vertical orientation, the air and water vapor exhibit a buoyant interaction with the result that the air presence inhibits heat transfer by rendering sections of the condenser surface ineffective. The effects depicted in this paper set the stage for future analytical and experimental work in flat heat pipe operation for both normal and variable conductance modes.
Comparison of Double-Shearing and Coaxial Models for Pressure-Dependent Plastic Flow at Frictional Boundaries
Authors: Alexandrov S.
Published: March 2003

The qualitative difference in solution behavior in the vicinity of maximum friction surfaces is demonstrated for two distinct models of pressure-dependent plasticity (the double-shearing and coaxial models) using closed-form solutions for planar flow through an infinite wedge-shaped channel and plane-strain compression of an infinite block between parallel plates. Singular velocity fields (some components of the strain rate tensor approach infinity at the friction surface) occur in the solutions based on the double-shearing model. This is similar to behavior in the vicinity of maximum friction surfaces in classical plasticity of pressure-independent materials. A singular velocity field is also obtained in the solution based on the coaxial model for the problem of channel flow; but, in contrast to the double-shearing model and classical plasticity, sticking must occur at this friction surface. For the problem of compression of a material obeying the coaxial model, no solution based on conventional assumptions exists with the maximum friction law. This is quite different from both the corresponding solution based on the double-shearing model and the channel flow solution based on the coaxial model.
The Initial Post-buckling Behavior of Face-Sheet Delaminations in Sandwich Composites
Authors: Kardomateas G. A. , Huang H.
Published: March 2003

Should an interface crack between the layers of the composite face-sheet or between the core and the composite face-sheet of a sandwich beam/plate exists, local buckling and possible subsequent growth of this interface crack (delamination) may occur under compression. In this study, the buckling, and initial post-buckling behavior is studied through a perturbation procedure that is based on the nonlinear beam equations with transverse shear included. Closed-form solutions for the load and midpoint delamination deflection versus applied compressive strain during the initial postbuckling phase are derived. Illustrative results are presented for several sandwich construction configurations, in particular with regard to the effect of material system and transverse shear.
Green’s Functions for Infinite and Semi-infinite Anisotropic Thin Plates
Authors: Cheng Z.-Q. , Reddy J. N.
Published: March 2003

This paper presents fundamental solutions of an anisotropic elastic thin plate within the context of the Kirchhoff theory. The plate material is inhomogeneous in the thickness direction. Two systems of problems with non-self-equilibrated loads are solved. The first is concerned with in-plane concentrated forces and moments and in-plane discontinuous displacements and slopes, and the second with transverse concentrated forces. Exact closed-form Green’s functions for infinite and semi-infinite plates are obtained using the recently established octet formalism by the authors for coupled stretching and bending deformations of a plate. The Green functions for an infinite plate and the surface Green functions for a semi-infinite plate are presented in a real form. The hoop stress resultants are also presented in a real form for a semi-infinite plate.
Transient Study of Mode III Fracture in an Elastic Solid With a Single Plane of Material Symmetry
Authors: Brock L. M.
Published: March 2003

Diffraction of a plane SH-wave causes semi-infinite mode III crack extension in an unbounded linear elastic solid. The solid is nonorthotropic, with a single plane of material symmetry that is perpendicular to the crack edge. The crack plane itself lies at an arbitrary angle to the axes of material symmetry, the SH-wave direction is largely arbitrary, and extension is not necessarily instantaneous or at a constant speed. An exact transient study produces the fracture energy release rate, and uses a full-field analytical solution to derive the dynamic stress intensity factor on any plane radiating from the moving crack edge. A crack path stability analysis of the factor indicates that crack extension in the original plane can occur in directions associated with maximum and minimum values of the shear wave speed. The energy release rate for such extensions shows that, if an isotropic solid subjected to the same type of loading has the same specific fracture energy, then the nonorthotropic solid may fracture first.
Bounds on Texture Coefficients
Authors: Nadeau J. C. , Ferrari M.
Published: March 2003

The orientation distribution function (ODF) is expanded in terms of generalized spherical harmonics and bounds on the resulting texture coefficients are derived. A necessary and sufficient condition for satisfaction of the normalization property of the ODF is also provided. These results are of significance in, for example, microstructural optimization of materials and predicting texture coefficients based on wave velocity measurements.
Multiple Surface Cracking and Its Effect on Interface Cracks in Functionally Graded Thermal Barrier Coatings Under Thermal Shock
Authors: Rangaraj S. , Kokini K.
Published: March 2003

The thermal fracture behavior in functionally graded yttria stabilized zirconia–NiCoCrAlY bond coat alloy thermal barrier coatings was studied using analytical models. The response of three coating architectures of similar thermal resistance to laser thermal shock tests was considered. Mean field micromechanics models were used to predict the effective thermoelastic and time-dependent (viscoplastic) properties of the individual layers of the graded thermal barrier coatings (TBCs). These effective properties were then utilized in fracture mechanics analyses to study the role of coating architecture on the initiation of surface cracks. The effect of the surface crack morphology and coating architecture on the propensity for propagation of horizontal delamination cracks was then assessed. The results of the analyses are correlated with previously reported experimental results. Potential implications of the findings on architectural design of these material systems for enhanced thermal fracture resistance are discussed.
Prediction of Turbulence Statistics Behind a Square Cylinder Using Neural Networks and Fuzzy Logic
Authors: Panigrahi P. K. , Dwivedi Manish , Khandelwal Vinay , Sen Mihir
Published: March 2003

Experiments are carried out behind a square cylinder mounted in the freestream of a wind tunnel, and hot-wire anemometry is used to determine the profiles of the mean and statistical turbulence quantities. Artificial neural networks and fuzzy-logic models successfully predict the statistical quantities like mean velocity profiles and Reynolds stresses. The fuzzy-logic modeling is more convenient to use, is less computationally intensive, and gives a higher correlation coefficient in comparison to the neural network.
Influence of Diffuser Angle on a Bluff Body in Ground Effect
Authors: Ruhrmann Andreas , Zhang Xin
Published: March 2003

The forces and pressures on a generic bluff body in ground effect were investigated. The bluff-body model was equipped with interchangeable underbody diffuser ramps and side plates. Five different diffuser angles were tested: 5, 10, 15, 17, and 20 deg to the horizontal. The experiments were undertaken in a low-speed wind tunnel equipped with a moving ground. Load cells, pressure taps, and surface flow visualization were the techniques used to evaluate the flow field. The flow field is characterized by vortex flow and three-dimensional flow separation. A region of hysteresis was found for the 15, 17, and 20 deg diffusers. As the ride height is varied, five different flow types can be identified with three subtypes within the region of hysteresis. The force reduction phenomenon was found to be caused by both vortex breakdown and flow separation.
Effect of Unsteady Wake Passing Frequency on Boundary Layer Transition, Experimental Investigation, and Wavelet Analysis
Authors: Schobeiri M. T. , Read K. , Lewalle J.
Published: March 2003

Detailed experimental and theoretical investigations were carried out to study the effect of unsteady wake passing frequency on the boundary layer transition along the concave surface of a curved plate under a zero longitudinal pressure gradient. Periodic unsteady flow with different passing frequencies is generated utilizing an unsteady flow research facility with a rotating cascade of rods positioned upstream of the curved plate. Extensive unsteady boundary layer measurements are carried out. The data are analyzed using conventional and wavelet-based methods. Local time scales are defined as those of the most energetic fluctuations, and are calculated from wavelet transforms of the velocity signals. The dominant time scales are mapped as functions of the distance to the plate, the downstream location, and the phase relative to the wake-passing. Furthermore, conditional sampling is applied, laminar and turbulent time scales are calculated and the effects of wake passing frequency on these scales are shown.
Flutter Limits and Behaviors of Flexible Webs Having a Simplified Basic Configuration in High-Speed Flow
Authors: Yamaguchi Nobuyuki , Ito Keisuke , Ogata Masayuki
Published: March 2003

Fluttering conditions were analyzed for webs with a simplified basic configuration with both leading and trailing edges fixed in a uniform flow. The predicted flutter limits are expressed in terms of a ratio of fluid force to tension (σ*), a ratio of tension to bending stiffness (τ*), and a reduced frequency fR. Three characteristic zones of the behavior are seen to appear depending on the magnitude of τ*. For medium τ* of 1×103 to 1×106, flutter-limit values of σ* and fR remain nearly constant, respectively. For low τ*<1×103 effect of bending stiffness becomes significant and buckling-like instabilities tend to occur preceding the flutter. For high τ*>1×106 ripple-like modes tend to occur and σ* falls drastically and fR scatters much. Experimental flutter limits obtained in the wind tunnel were seen on the average to agree with the expected ones for the tested range of 9×102<τ*<4×104.
An Experimental Investigation of Starting Impinging Jets
Authors: Lai Hongze , Naughton Jonathan W. , Lindberg William R.
Published: March 2003

Impulsively started impinging jets were experimentally investigated in a water tank utilizing a fluorescent dye technique. The jets were examined prior to and subsequent to impingement. The impingement surfaces included a flat surface and a two-dimensional semicircular concave surface. The normalized jet-to-surface distance and the jet Reynolds number were varied in this study. Using digitized flow visualization images, the jet trajectories, front velocities, growth rates, and convective velocities of large-scale turbulent structures were quantified. A central conclusion of this investigation is that, for all cases studied, the jet-front velocity varies with the square root of time. These results are important to applications that might use starting or pulsed jets for heat transfer enhancement and in combustion processes.
A Linear Stability Analysis for an Improved One-Dimensional Two-Fluid Model
Authors: Song Jin Ho
Published: March 2003

A linear stability analysis is performed for a two-phase flow in a channel to demonstrate the feasibility of using momentum flux parameters to improve the one-dimensional two-fluid model. It is shown that the proposed model is stable within a practical range of pressure and void fraction for a bubbly and a slug flow.
Periodic Flow Between Low Aspect Ratio Parallel Jets
Authors: Anderson Elgin A. , Snyder Deryl O. , Christensen Jonathan
Published: March 2003

The behavior of symmetric parallel jets was investigated experimentally. Two-component hot-wire surveys of the velocity field were performed over a jet region extending from the nozzle plate to a distance seven times the spacing between the nozzles. The objective of this study was to investigate an observed periodic behavior in the near-field region between parallel jets that increases in frequency as the nozzle widths decrease. This behavior was found to occur in parallel jets where nozzle widths are greater than 0.5 times the jet spacer width. The phenomena are attributed to bluff body shedding in the near field and a confining effect of the outer shear layers.
Analysis of Thin Film Flows Using a Flux Vector Splitting1
Authors: Pacheco J. Rafael , Pacheco-Vega Arturo
Published: March 2003

We propose a flux vector splitting (FVS) for the solution of film flows radially spreading on a flat surface created by an impinging jet using the shallow-water approximation. The governing equations along with the boundary conditions are transformed from the physical to the computational domain and solved in a rectangular grid. A first-order upwind finite difference scheme is used at the point of the shock while a second-order upwind differentiation is applied elsewhere. Higher-order spatial accuracy is achieved by introducing a MUSCL approach. Three thin film flow problems (1) one-dimensional dam break problem, (2) radial flow without jump, and (3) radial flow with jump, are investigated with emphasis in the prediction of hydraulic jumps. Results demonstrate that the method is useful and accurate in solving the shallow water equations for several flow conditions.
Analysis of the Flow in a High-Pressure Die Casting Injection Chamber
Authors: Herna´ndez J. , Lo´pez J. , Faura F. , Go´mez P.
Published: March 2003

The flow in the injection chamber of pressure die casting machines is analyzed using a model based on the shallow-water approximation which takes into account the effects of wave reflection against the end wall of the chamber. The governing equations are solved numerically using the method of characteristics and a finite difference grid based on the inverse marching method. The results of the model for wave profiles, volume of air remaining in the injection chamber at the instant at which the molten metal reaches the gate to the die cavity, and optimum values of the parameters characterizing the law of plunger motion, are compared with the numerical results obtained from a finite element code, which solves the two-dimensional momentum and mass conservation equations, taking into account nonhydrostatic and viscous effects. We found that, although the shallow-water model does not provide a very accurate estimation of the mass of entrapped air in the injection chamber for certain ranges of working conditions, it does describe reasonably well the influence of the acceleration parameters and the initial filling fraction on the entrapped air mass, and can be of help in selecting operating conditions that reduce air entrapment while keeping the injection chamber filling time as low as possible.
Experimental Investigation of Two Cylindrical Water Columns Subjected to Planar Shock Wave Loading
Authors: Igra D. , Takayama K.
Published: March 2003

Two water columns with identical initial diameters of 4.8 mm were placed 30 mm apart inside a shock tube test section and were loaded by a shock wave of Mach number 1.47 in atmospheric air. The Weber and Reynolds numbers corresponding to these flow conditions are 6900 and 112,000, respectively. Double-exposure holographic interferometry was used to visualize the shock/water columns interaction. The process of the water columns deformation, displacement, and acceleration was well visualized and hence the drag coefficient of shock loaded water columns was evaluated. The front water column behaved virtually the same as a single water column under the same flow conditions. However, the displacement and acceleration of the rear water column was less significant than that of the front one. Hence, its drag coefficient is less. These results show that the front water column has affected the flow field around the rear water column.
Mechanism of Hysteretic Characteristics of Wells Turbine for Wave Power Conversion
Authors: Kinoue Y. , Setoguchi T. , Kim T. H. , Kaneko K. , Inoue M.
Published: March 2003

A Wells turbine for wave power conversion has hysteretic characteristics in a reciprocating flow. The counterclockwise hysteretic loop of the Wells turbine is opposite to the clockwise one of the well-known dynamic stall of an airfoil. In this paper, the mechanism of the hysteretic behavior was elucidated by an unsteady three-dimensional Navier-Stokes numerical simulation. It was found that the hysteretic behavior was associated with a streamwise vortical flow appearing near the blade suction surface. In the accelerating process of axial flow velocity, the vortex is intensified to enlarge the flow separation area on the blade suction surface. In the decelerating flow process, the flow separation area is reduced because of the weakened vortex. Therefore, the aerodynamic performance in the accelerating flow process is lower than in the decelerating flow process, unlike the dynamic stall. Based on the vortex theorem, the mechanism to vary the intensity of the vortex can be explained by the trailing vortices associated with the change in the blade circulation.
Kinematic Synthesis of a Spatial 3-RPS Parallel Manipulator
Authors: Sung Kim Han , Tsai Lung-Wen
Published: March 2003

This paper presents the design of spatial 3-RPS parallel manipulators from dimensional synthesis point of view. Since a spatial 3-RPS manipulator has only 3 degrees of freedom, its end effector cannot be positioned arbitrarily in space. It is shown that at most six positions and orientations of the moving platform can be prescribed at will and, given six prescribed positions, there are at most ten RPS chains that can be used to construct up to 120 manipulators. Further, solution methods for fewer than six prescribed positions are also described.
Pitch Cone Design and Avoidance of Contact Envelope and Tooth Undercutting for Conical Worm Gear Drives
Authors: Zhang Yi , Xu Hai
Published: March 2003

This paper presents a systematic approach for the design, generation and analysis of conical worm gear drives. The approach is based on the mathematical formulations on the mesh, tooth generation process and conditions for the appearance of contact envelope and tooth undercutting of this type of worm drives. The formulation is implemented by a computer model developed in MatLab environment. By model simulation on worm gear mesh or generation, the conditions for the formation of contact envelope and tooth undercutting are accurately determined for the proper design of worm gear blank and tooth geometry. The computer model can also be used to calculate worm gear tooth geometry and create solid models for the worm gear drives. Numerical examples on conical worm gear drive design, analysis on the problems of contact envelope, limit line and limit point are included in the paper.
Dimensional Synthesis of Bennett Linkages
Authors: Perez Alba , McCarthy J. M.
Published: March 2003

Three position synthesis of a spatial RR chain yields two solutions that can be assembled to form a Bennett linkage. In this paper, we show that the cylindroid associated with Bennett’s linkage can be generated directly from the three specified positions, and used to simplify the design equations. Analysis of these equations shows that there are always two solutions and that their symmetry yields a Bennett linkage. An example design is presented.
The Finite Screw System Associated With the Displacement of a Line
Authors: Huang Chintien , Wang Jin-Cheng
Published: March 2003

In determining the screw systems associated with incompletely specified displacements, the displacement of a line was known to be an exceptional case. Recent research has concluded that all possible screws for the finite displacement of a line do not form a screw system. This paper utilizes Dimentberg’s definition of pitch to demonstrate that all possible screws for displacing a line from one position to another can indeed form a screw system of the third order. Two different approaches are taken: one uses the concept of a screw triangle, and the other is based on analytical geometry. A set of three linearly independent screws of the screw system is shown to be perpendicularly intersecting the external bisector of the initial and final positions of the line.
Theoretical Modeling of Wire Dynamics and Failure Modes During Manufacture on a Double Twist Machine
Authors: Austin L. , Burley Mathew
Published: March 2003

The problem of wire ballooning, or wire breakage, due to force imbalance is common during the production of wire on double twist machines. This paper examines the forces in wire during the bunching or twinning process. The bow shape is simplified to represent the arc of a circle for mathematical simplicity, which also allows the work to be related to any size of double twist machine produced by any manufacturer, with the proviso that a catenary curve forms the basis of the bow shape. Mathematical approximations of the level of force imbalance between the pre-tension and take-up tension during production are made, and the location of wire breakage within the bow is predicted.
Geometric Algorithms for Kinematic Calibration of Robots Containing Closed Loops
Authors: Iuras¸cu C. C. , Park F. C.
Published: March 2003

We present a coordinate-invariant, differential geometric formulation of the kinematic calibration problem for a general class of mechanisms. The mechanisms considered may have multiple closed loops, be redundantly actuated, and include an arbitrary number of passive joints that may or may not be equipped with joint encoders. Some form of measurement information on the position and orientation of the tool frame may also be available. Our approach rests on viewing the joint configuration space of the mechanism as an embedded submanifold of an ambient manifold, and formulating error measures in terms of the Riemannian metric specified in the ambient manifold. Based on this geometric framework, we pose the kinematic calibration problem as one of determining a parametrized multidimensional surface that is a best fit (in the sense of the chosen metric) to a given set of measured points in both the ambient and task space manifolds. Several optimization algorithms that address the various possibilities with respect to available measurement data and choice of error measures are given. Experimental and simulation results are given for the Eclipse, a six degree-of-freedom redundantly actuated parallel mechanism. The geometric framework and algorithms presented in this article have the desirable feature of being invariant with respect to the local coordinate representation of the forward and inverse kinematics and of the loop closure equations, and also provide a high-level framework in which to classify existing approaches to kinematic calibration.
A Computational Approach to the Number of Synthesis of Linkages
Authors: Saxena Anupam , Ananthasuresh G. K.
Published: March 2003

This paper presents a number of systematically designed compliant topologies and discusses how the intrinsic kinematic behavior can be extracted from them. This is then applied to the number synthesis of linkages. Many techniques developed for number synthesis of linkages enumerate numerous possible kinematic chains, but few can select the best configuration among them. A systematic computational approach that can select the best configuration based on kinetostatic design specifications is presented here. This is a serendipitous result that transpired when two well-developed design techniques for compliant mechanisms were combined. A number of examples with nonintuitive design specifications are included to illustrate the new approach to the number synthesis. The examples also illustrate that the kinematic behavior is aptly captured in the elastic mechanics-based topology optimization method to compliant mechanism design. Dimensional synthesis is also accomplished in the same procedure, which is an added benefit of this approach.
Geometric Interpretation of the Derivatives of Parallel Robots’ Jacobian Matrix With Application to Stiffness Control
Authors: Simaan N. , Shoham M.
Published: March 2003

This paper presents a closed-form formulation and geometrical interpretation of the derivatives of the Jacobian matrix of fully parallel robots with respect to the moving platforms’ position/orientation variables. Similar to the Jacobian matrix, these derivatives are proven to be also groups of lines that together with the lines of the instantaneous direct kinematics matrix govern the singularities of the active stiffness control. This geometric interpretation is utilized in an example of a planar 3 degrees-of-freedom redundant robot to determine its active stiffness control singularity.
A Comparison of Spreading Angles of Turbulent Wedges in Velocity and Thermal Boundary Layers
Authors: Zhong S. , Chong T. P. , Hodson H. P.
Published: March 2003

Turbulent wedges induced by a three-dimensional surface roughness placed in a laminar boundary layer over a flat plate were visualized for the first time using both shear-sensitive and temperature-sensitive liquid crystals. The experiments were carried out at zero pressure gradient and two different levels of favorable pressure gradients. The purpose of this investigation was to examine the spreading angles of turbulent wedges indicated by their associated surface shear stresses and heat transfer characteristics and hence obtain further insight about the difference in the behavior of transitional momentum and thermal boundary layers when a streamwise pressure gradient exists. It was found that under a zero pressure gradient the spreading angles indicated by the two types of liquid crystals are the same, but the difference increases as the level of favorable pressure gradient increases with the angle indicated by temperature-sensitive liquid crystals being smaller. The results from the present study suggest that the spanwise growth of a turbulent region is smaller in a thermal boundary layer than in its momentum counterpart and this seems to be responsible for the inconsistency in transition zone length indicated by the distribution of heat transfer rate and boundary layer shape factor reported in the literature. This finding would have an important implication to the transition modeling of thermal boundary layers over gas turbine blades.
Experimental Analysis of an Axial Inducer Influence of the Shape of the Blade Leading Edge on the Performances in Cavitating Regime
Authors: Bakir F. , Kouidri S. , Noguera R. , Rey R.
Published: March 2003

The aim of this paper is to analyze, from experimental results, the influence of the shape of the leading edge and its sharpening on the cavitating behavior of an inducer. The studied inducer is designed according to a methodology developed at LEMFI. Successive cutting and sharpening (four cuts, which modify up to 20 percent of the blade chord at the tip), were made to modify the shape of the leading edge. For the various geometries, the experimental results obtained on the LEMFI test rig are presented as follows. Noncavitating Regime: Overall performances at 1450 rpm. Cavitating Regime: (1) The development of the cavitation versus the cavitation number, (2) the description of the various cavitation pictures, and (3) the pressure fluctuations measured at the wall at 150 mm downstream of the trailing edge for various flow rates and inlet pressures. The CFD simulations carried out under CFX-Blade Gen+ on this range of inducers are presented to explain certain aspects observed.
The Kinematics of a Class of 3-DOF, 4-Legged Parallel Manipulators
Authors: Joshi Sameer A. , Tsai Lung-Wen
Published: March 2003

In this paper, a class of 3-DOF, 4-legged parallel manipulators are enumerated. The general architecture of such manipulators consists of a moving platform, a fixed base, and four supporting legs that meet the fixed base at four distinct points and the moving platform at four distinct points. One of the four legs is passive whereas each of the remaining three legs is driven by a linear actuator. To gain a better understanding of the mechanisms, a methodology for analyzing the kinematics of such manipulators is presented. The Tricept manipulator is used as an example to illustrate the methodology.
On Mobility Analysis of Linkages Using Group Theory
Authors: Martı´nez Jose´ Marı´a Rico , Ravani Bahram
Published: March 2003

This paper presents a generalization of Kutzbach-Gru¨bler criterion for mobility analysis of kinematic chains based on group theory. This new mobility criterion applies to exceptional linkages and reduces to a group theoretic representation of Kutzbach-Gru¨bler criterion for trivial linkages. Furthermore, it is shown that using sets and groups of Euclidean displacements, one can distinguish between trivial, exceptional, and paradoxical linkages. Using these concepts, formal definitions of trivial, exceptional, and paradoxical linkages are presented and it is shown that there are two classes of paradoxical linkages. This work builds upon and extends the work of Herve´ and Fanghella and Galletti in application of group theory to analysis of kinematic chains.
Distribution of Wrench-Twist Duality in Over-Constrained Mechanisms
Authors: Fayet M.
Published: March 2003

First, a procedure is presented in order to build the space of statically admissible wrenches. The matrix which generates them is obtained in an intrinsic way. It uses intersection of spaces for the edges (of the associated graph) and the new operation of “triangular projection” for the vertices. From this matrix, the choice of any set of indeterminable contact forces is achieved via a very simple test. This matrix allows to determine also all the possible degrees of freedom to add to the over-constrained mechanism in order to transform it into a non over-constrained one. Wrench-twist duality arises clearly in this last procedure.
Single Plane Radial, Magnetic Bearings Biased With Poles Containing Permanent Magnets
Authors: Kenny Andrew , Palazzolo Alan B.
Published: March 2003

Magnetic bearings biased with permanent magnets have lower coil resistance power losses, and the magnets can also be used to help support a constant side load. In this paper, the performance of a single plane radial magnetic bearing biased with permanent magnets in several poles is presented. Although it has less load capacity and stiffness than a similarly sized electrically biased single plane heteropolar bearing, it does not require bias current, and its ratio of load capacity to coil resistance power loss is significantly better. This type of permanent magnet bearing has only a single plane of poles. It can be distinguished from the homopolar bearing type which has two planes and which can also be biased with permanent magnets. Magnetic circuit models for the novel single plane bearing are presented along with verification by finite element models. Equations for the key performance parameters of load capacity, stiffness, coil inductance and resistive power loss are also presented.