bluuebunny/crossref_metadata_2025 huggingface dataset:
A Compromise Decision Support Problem for Axiomatic and Robust Design
Authors: Bras B. , Mistree F.
Published: February 2008

Compromise Decision Support Problems (DSPs) are used to model engineering decisions involving multiple trade-offs. In this paper, we focus on how to use such decision models to perform both axiomatic and robust design simultaneously. A compromise DSP is presented and solved for the concurrent achievement of the functional requirements, Suh’s independence axiom and his information content axiom. A model for the selection of the principal design parameters from a set of design parameters is included in this compromise DSP. Taguchi’s signal-to-noise ratio is used as a metric for the reduction of the information content and increasing the robustness of the design. As an example, a compromise DSP for designing an electrical network is presented.
Perspective: Fluid Dynamics and Performance of Automotive Torque Converters: An Assessment
Authors: von Backstro¨m T. W. , Lakshminarayana B.
Published: February 2008

Experimental investigations by various groups over the past decade have uncovered the main features of the flow in hydraulic torque converters. Measurement techniques include laser and hot wire velocimetry, fast response and conventional five-hole probes, and blade and wall static pressure measurement. In both the pump and turbine, the through flow velocity is high near the pressure surface shell corner while the flow in the suction surface core corner is highly turbulent and may be separated and reversed. The position of the stator in a passage curved in the meridional plane leads to secondary flow and low velocities at the core near the pump inlet. Velocity gradients coupled with flow turning and rotor rotation lead to strong secondary flows. By using data from a combination of measurement techniques, torque converter torque, power and efficiency are calculated, and the effect of element efficiency on overall efficiency is demonstrated. It is concluded that design methods should be developed that allow for nonuniform velocity profiles, flow separation, secondary circulation and interaction effects between elements.
Experimental Measurements in a Centrifugal Pump Impeller
Authors: Bwalya A. C. , Johnson M. W.
Published: February 2008

Measurements of the 3-d velocities, total and static pressures have been made in a 0.89 m diameter commercial pump impeller, using air as the working fluid. Results at the peak efficiency operating point show separation of the flow near the shroud on the pressure side of the blade at the leading edge. This separation results in a low energy region which initially travels axially through the impeller to form a wake in the suction side shroud corner region. A region of reversed radial velocity is observed at the outlet, which is due to high blade sweep angle together with the poor guidance given to the flow by the blades in the mid-passage region.
Air Influence on Similarity of Hydraulic Transients and Vibrations
Authors: Lee T. S. , Pejovic S.
Published: February 2008

The effects of wave speed variation due to air content on the validity of similarity laws for model studies of hydraulic transients and hydraulic vibrations were investigated. Studies show that hydraulic similarities between geometrically similar model and prototype are reduced substantially for cases involving two- or three-phase flow. For flow with intensive cavitation, analysis shows that there is no hydraulic similarity between model and prototype. For pump discharge pipeline and turbine draft tube where two phase flow of air-water mixture occurs, analysis shows that the natural frequency and the response characteristics of the fluid system are a strong function of the local wave speed variation within the fluid system. This local wave speed variation is a function of the local transient air content and transient pressure.
Obstruction of Pipelines During the Flow of Waxy Crude Oils
Authors: Souza Mendes Paulo R. , Braga Sergio L.
Published: February 2008

When a liquid solution is cooled as it flows laminarly through a tube, a radial concentration gradient is established, which causes mass transfer of the solute to occur toward the tube wall. The solute precipitates off the solution in the neighborhood of the wall, and adheres perfectly to it. The deposited mass gradually obstructs the conduit, affecting the pressure and flow fields. A simple model is presented that gives the thickness of the deposited layer as a function of axial position and time. The liquid solution is assumed to behave according to the Herschel-Bulkley rheological model. Results are presented in the form of time evolution of axial distributions of pressure, temperature, layer thickness, global heat transfer coefficient and Reynolds number.
Spectrum Normalization Method in Vibro-Acoustical Diagnostic Measurements of Hydroturbine Cavitation
Authors: Bajic´ Branko , Keller Andreas
Published: February 2008

Full-scale vibro-acoustical diagnostic measurements of cavitation in four Francis 6 MW double runner turbines were performed. Two types of sensors were used—a hydrophone sensing waterborne noise at the pressure side of a runner and an accelerometer mounted at various points at the outer turbine casing, facing the runner’s pressure side. The correlation of noise and acceleration intensity with suction-side pressure fluctuations and runner position was checked. A simple but efficient method of spectrum normalization, which rejects the influence of the measurement set characteristics and vibro-acoustical characteristics of a turbine, was developed. The resulting spectra reveal the dependence of cavitation source strength on the turbine power as a function of noise or acceleration frequency.
Interaction Between Sprays From Multiple Coaxial Airblast Atomizers
Authors: Hardalupas Y. , Whitelaw J. H.
Published: February 2008

Phase Doppler measurements of size, velocity, liquid flux, and average mass fractions were obtained in sprays produced by three identical coaxial airblast atomizers, with their axes placed in a triangular arrangement at distances of two air jet diameters from each other; the arrangement simulates the spray interaction in the preburner of the space shuttle main engine with water and air respectively replacing the liquid oxygen and hydrogen of the preburner sprays. Each nozzle comprised a liquid jet with exit diameter of 2.3 mm centred in a 8.95 mm diameter air stream. Two liquid flowrates were examined, while the air flowrate was kept constant, resulting in Weber number at the exit of the nozzle around 1100, air-to-liquid momentum ratio 8.6 and 38, velocity ratio 24 and 51, mass flowrate ratio 0.35 and 0.75, liquid jet Reynolds number 10,000 and 21,000 and air jet Reynolds number around 108,000. The air flow characteristics were compared to the flow without liquid injection. Up to 10 air jet diameters from the nozzle exit, individual spray characteristics dominated and maximum Sauter mean diameters, typically around 150 μm, and liquid flux were observed on the geometrical axes of the nozzles. Spray merging was strong in the region between the nozzle axes, where the Sauter mean diameter reduced and the liquid flux and the mean and rms of the fluctuations of the axial velocity of the droplets and the air flow increased relative to the single spray. Downstream of 25 air jet diameters from the nozzle exit, the multiple sprays merged to a single spray-like flow produced by a nozzle located at the centre of the triangular region between the nozzle axes. Reduction of the liquid flowrate by 50 percent, improved atomization by 25 percent, shortened the axial distance from the nozzles where the individual spray characteristics disappeared by 30 percent and increased the air flow turbulence by 20 percent. Droplet coalescence was negligible for high liquid flowrates, but for reduced liquid flowrates coalescence became important and the Sauter mean diameter increased with the axial distance from the exit by around 15 percent. Spray merging increased the air flow turbulence and the local mass fraction distribution of the air in the region between the nozzle axes by around 50 and 40 percent respectively relative to the single sprays, resulting in a fuel rich region with increased gas flow turbulence which may influence the ignition process in the preburner of the space shuttle main engine.
Extension of the Wall-Driven Enclosure Flow Problem to Toroidally Shaped Geometries of Square Cross-Section
Authors: Phinney L. M. , Humphrey J. A. C.
Published: February 2008

The two-dimensional wall-driven flow in an enclosure has been a numerical paradigm of long-standing interest and value to the fluid mechanics community. In this paradigm the enclosure is infinitely long in the x-coordinate direction and of square cross-section (d × d) in the y-z plane. Fluid motion is induced in all y-z planes by a wall (here the top wall) sliding normal to the x-coordinate direction. This classical numerical paradigm can be extended by taking a length L of the geometry in the x-coordinate direction and joining the resulting end faces at x = 0 and x = L to form a toroid of square cross-section (d × d) and radius of curvature Rc. In the curved geometry, axisymmetric fluid motion (now in the r-z planes) is induced by sliding the top flat wall of the toroid with an imposed radial velocity, ulid, generally directed from the convex wall towards the concave wall of the toroid. Numerical calculations of this flow configuration are performed for values of the Reynolds number (Re = ulidd/ν) equal to 2400, 3200, and 4000 and for values of the curvature ratio (δ = d/Rc) ranging from 5.0 · 10−6 to 1.0. For δ ≤ 0.05 the steady two-dimensional flow pattern typical of the classical (straight) enclosure is faithfully reproduced. This consists of a large primary vortex occupying most of the enclosure and three much smaller secondary eddies located in the two lower corners and the upper upstream (convex wall) corner of the enclosure. As δ increases for a fixed value of Re, a critical value, δcr, is found above which the primary center vortex spontaneously migrates to and concentrates in the upper downstream (concave wall) corner. While the sense of rotation originally present in this vortex is preserved, that of the slower moving fluid below it and now occupying the bulk of the enclosure cross-section is reversed. The relation marking the transition between these two stable steady flow patterns is predicted to be δcr1/4 = 3.58 Re-1/5 (δ ± 0.005).
Assessment of the SSG Pressure-Strain Model in Free Turbulent Jets With and Without Swirl
Authors: Younis B. A. , Gatski T. B. , Speziale C. G.
Published: February 2008

Data from free turbulent jets both with and without swirl are used to assess the performance of the pressure-strain model of Speziale, Sarkar and Gatski, which is quadratic in the Reynolds stresses. Comparative predictions are also obtained with the two versions of the Launder, Reece and Rodi model, which are linear in the same terms. All models are used as part of a complete second-order closure based on the solution of differential transport equations for each nonzero component of uiuj together with an equation for the scalar energy dissipation rate. For nonswirling jets, the quadratic model underestimates the measured spreading rate of the plane jet but yields a better prediction for the axisymmetric case without resolving the plane jet/round jet anomaly. For the swirling axisymmetric jet, the same model accurately reproduces the effects of swirl on both the mean flow and the turbulence structure in sharp contrast with the linear models which yield results that are in serious error. The reasons for these differences are discussed.
An Improved Eddy Interaction Model for Numerical Simulation of Turbulent Particle Dispersion
Authors: Graham D. I.
Published: February 2008

Three main effects have been observed in experimental investigations of the dispersion of low concentrations of solid particles in homogeneous turbulent flows, namely the crossing trajectories, inertia, and continuity effects. This paper discusses the development of a simple Lagrangian eddy interaction model to account for all three of these effects. By choosing the length, time, and velocity scales in the model so as to be consistent with the corresponding scales in homogeneous, isotropic, and stationary turbulence, the proper limiting behavior is ensured both for fluid particles and for heavy solid particles. Because only one time step is required per eddy, the computational efficiency of the model is ensured.
Stability of a Compressible Laminar Wall-Jet With Heat Transfer
Authors: Likhachev O. , Tumin A.
Published: February 2008

The flow of a plane, laminar, subsonic perfect gas wall jet with heat transfer through the wall was investigated theoretically. For the case under consideration the entire surface was maintained at a constant temperature which differed from the temperature of the ambient gas. The velocity and temperature distribution across the flow were calculated for a variety of temperature differences between the ambient gas and the surface. The boundary layer equations representing these flows were solved by using the Illingworth-Stewartson transformation, thus extending the classical Glauert’s solution to a thermally non-uniform flow. The effects of heat transfer on the linear stability characteristics of the wall jet were assessed by making the local parallel flow approximation. Two kinds of unstable eigenmodes coexisting at moderate Reynolds numbers are significantly affected by the heat transfer. The influence of cooling or heating on the stability of the flow was expected in view of the experience accumulated in incompressible boundary layers, i.e. heating destabilizes and cooling stabilizes the flows. Cooling of the wall affects the small scale disturbances more profoundly, contrary to the results obtained for the large scale disturbances.
Pulsatile Laminar Flow in a Viscoelastic System
Authors: Lardigue A. , Bennis S.
Published: February 2008

This work involves the study of Newtonian transitory and permanent flow regimes in a rigid tube that has been extended to include a viscoelastic enclosure. Variable pressures are applied at the free end of the tube. The problem is solved analytically by direct integration of the Navier-Stokes equations. In addition to the nondimensional parameter γ1 introduced previously by other authors, we found a new nondimensional parameter γ2 which also governs the fluid flow. This parameter may be interpreted as the ratio of the and the membrane viscosity force to the fluid friction force. The effects of small values of the membrane viscosity only attenuate the oscillating effect when inertia dominates on fluid friction force. When the membrane viscosity is important, however, it may cancel out the inertial effect resulting in a damped aperiodic flow. When the fluid friction force predominates, the membrane viscosity slows down an already damped aperiodic flow. All these types of flow are well characterized by well defined intervalls of variation of γ1, and γ2. In addition to the transitory flow regime, we also consider permanent pulsatile flow. An experimental device makes it possible to validate the theoretical assertions in the particular case of a pulsed pressure.
An Investigation on the Behavior of Laser Induced Bubble in Cryogenic Liquid Nitrogen
Authors: Sato Hitoshi , Sun Xiao Wu , Odagawa Mamoru , Maeno Kazuo , Honma Hiroki
Published: February 2008

There have been few experimental reports on cryogenic two-phase fluids and cavitation phenomena using the irradiation of pulsed high-power laser. This paper describes an investigation of the behavior of laser induced cavitation bubble in cryogenic liquid nitrogen. The bubble is produced by a pulsed ruby laser focused in the special cryostat. The production, growth, and rebound phenomena of the bubbles are visualized by diffusive shadowgraph technique with an image-converter camera. To compare with the experimental results, a numerical study has also been performed on the dynamics of a single spherical bubble in liquid nitrogen under the conditions of nonequilibrium phase change.
Stability of Condensation on Horizontal Surfaces With Noncondensables Present
Authors: Peterson P. F. , Rao I. J.
Published: February 2008

This work studies condensation on horizontal surfaces in the presence of noncondensable gases using linear stability analysis to determine when one-dimensional flow will bifurcate to a higher-order flow due to an adverse density gradient. The problem is solved for the simple single-diffusive case and for the double-diffusive case where the density also depends on either a temperature gradient or a second noncondensable gas species. For the single-diffusive case critical Rayleigh numbers and gas layer thicknesses are obtained for a wide range of Schmidt numbers. Using these results, the quantity of noncondensable required to destabilize a horizontal system can be calculated, and usually will be found to be small.
Measurement of Surface Heat Transfer Due to Particle Impact
Authors: Sun J. G. , Chen M. M.
Published: February 2008

Heat transfer coefficients for a surface continuously impacted by a stream of falling particles in air and in helium were measured as functions of particle flux and particle velocity. The purpose was to provide well-controlled data to clarify the mechanisms of heat transfer in particle suspension flows. The particles were spherical glass beads with mean diameters of 0.5, 1.13, and 2.6 mm. The distribution of the particle impact flux on the surface was determined by deconvolution from the measurement of the total solid masses collected at both sides of a movable splitter plate. The particle velocity was calculated from a simple, well-established model. The experimental results showed that in air, the heat transfer coefficient increases approximately linearly with particle impact flux. At high impact fluxes, the heat transfer coefficient decreases with particle impact velocity, and at low impact fluxes, it increases with particle impact velocity. Furthermore, the heat transfer coefficient decreases drastically with the particle size. In helium gas, it was found that at low particle impact fluxes, the difference between the coefficients in helium and in air is small, whereas at high fluxes, the difference becomes large. A length scale, V/n˙dp2, was used to correlate the data. At low particle Reynolds numbers, gas-mediated heat conduction was identified as the dominant particle/surface heat transfer mechanism, whereas at high particle Reynolds numbers, induced gas convection was the dominant mechanism.
Thermoelectric Voltage at Metallic Point Contacts From Nonequilibrium Effects
Authors: Ito K. , Hijikata K. , Torikoshi K. , Phelan P. E.
Published: February 2008

This paper presents results for thermoelectric voltage experiments carried out with metallic point contacts. The motivation for this work is the fundamental understanding of the nonequilibrium state between electrons and phonons, and for applying this phenomenon to a point temperature measurement of small heating elements like an LSI (Large-Scale Integration) electronic chip. The experiments were carried out by using gold, silver, copper, and tungsten point contacts under cryogenic conditions, and a heat flux through the point contact was applied via a temperature difference across the contact. In this condition, thermoelectric voltages appeared even when the entire open circuit consisted of only one material. This phenomenon was explained theoretically by considering the nonequilibrium effect between the phonon and electron temperatures, and the geometric effect at the point contact. Good agreement was found between the theory and the experiment.
Effects of Metallic Vapor Deposition Process and the Overall Coating Thickness on Thermal Contact Conductance
Authors: Howard A. H. , Ochterbeck J. M. , Peterson G. P.
Published: February 2008

An investigation was conducted to determine the effects of the vapor deposition process and. the interstitial coating thickness on the overall joint conductance of metallic interfaces. Eight aluminum 6061-T6 test specimens were coated with indium and tested while in contact with uncoated aluminum 6061-T6 specimens. In the first test set, all specimens were coated to a thickness of 3.51 μm, but the vapor deposition process was varied to produce both single and multiple-layered coated specimens. In the second test set, the coating thickness was varied from 0.026 μm to 3.51 μm. The results indicated that when creating multiple layered coatings, oxidation and thermal cycling caused poor layer adhesion, and resulted in significantly reduced dimensionless contact conductance enhancement factors than for single-layered coatings with an equivalent thickness. Additionally, the results demonstrated that the thermal contact conductance could be enhanced to much greater levels than previously reported in the literature, and that the dimensionless enhancement factor asymptotically approached a maximum enhancement value. A theoretical maximum enhancement limit has been presented for comparison with the experimental data.
Estimation of the Onset of Longitudinal Vortices in a Laminar Boundary Layer Heated From Below
Authors: Hwang G. J. , Lin M. H.
Published: February 2008

Numerical study of the onset of longitudinal vortices in a boundary layer flow over a horizontal flat plate heated from below is presented. The onset position is determined as long as the gradually growing disturbances are large enough to be detected by measurements. Various experimental techniques, such as flow visualization, thermocouple temperature reading, LDA, hot-wire velocity anemometry, and heat transfer measurement, are carefully examined for evaluating the onset criteria in the numerical solution. The governing parameters on the onset position x* of longitudinal vortices are Prandtl number, wave number a, and the ratio of Grashof number and Reynolds number GrLReL1.5. The obtained onset position (Grx/ReL1.5)* and corresponding wave number a*x*1/2 are independent of the values of GrL/ReL1.5 = 500, 1000, and 1500 used, and weakly depend on the applied initial temperature t0 = 10−4, 5 × 10−5, 10−5 and 10−6, and the different onset criteria. The results of present numerical study are in good agreement with the previous experimental data.
Heat Transfer and Friction in a Low-Aspect-Ratio Rectangular Channel With Staggered Perforated Ribs on Two Opposite Walls
Authors: Hwang Jenn-Jiang , Liou Tong-Miin
Published: February 2008

Experiments are conducted to study the turbulent heat transfer and friction in a low-aspect-ratio rectangular channel in which two opposite walls are roughened by perforated ribs. The perforated ribs are arranged in a staggered manner. Effects of perforated rib open-area ratio (β = 10, 22, 38, 44, and 50 percent), rib pitch-to-height ratio (PR = 5, 10, 15, and 20), rib height-to-channel hydraulic diameter ratio (H/De = 0.063 and 0.081), rib alignment (staggered and symmetric), and Reynolds number (10,000 ≤ Re ≤ 50,000) are examined. It is found that approximately the same heat transfer enhancement and pressure drop penalty are obtained between symmetric and staggered rib arrangements. A permeability criterion is proposed by tracing heat transfer coefficient distributions, which compares well with previous flow-visualization results. Results also show that ribs with β = 44 percent give the best thermal performance under either the constant friction power or the constant flow rate constraint. Roughness functions for friction and heat transfer are further developed in terms of rib and flow parameters.
An Experimental Investigation of Film Cooling Heat Transfer Coefficients Using the Mass/Heat Analogy
Authors: Sun Y. , Gartshore I. S. , Salcudean M. E.
Published: February 2008

An experimental investigation has been carried out to determine the heat/mass transfer coefficient downstream of a two-dimensional, normal, film cooling injection slot. The plate downstream of the slot is porous, and air contaminated with propane is bled through it. By measuring the propane concentration very close to the wall using a flame ionization detector, mass transfer measurements are conducted for film cooling mass flow ratios ranging from 0 to 0.5. The mass transfer coefficients are calculated using a wall function correction formula, which corrects the measurements for displacement from the surface, and are then related directly to corresponding heat transfer coefficients using the mass/heat analogy. The validity of the method and the wall function correction formula are checked by examining the case with zero film coolant injection, a situation analogous to the well-known turbulent boundary layer mass/heat transfer with impermeable/unheated starting length. Good agreement with predicted data is obtained for this experiment. For film cooling with low mass flow ratios, heat transfer coefficients close to those of a conventional turbulent boundary layer are obtained. At high values of mass flow ratios quite different trends are observed, reflecting the important effect of the separation bubble, which is present just downstream of the injection slot.
Confined and Submerged Liquid Jet Impingement Heat Transfer
Authors: Garimella S. V. , Rice R. A.
Published: February 2008

The local heat transfer from a small heat source to a normally impinging, axisymmetric, and submerged liquid jet, in confined and unconfined configurations, was experimentally investigated. A single jet of FC-77 issuing from a round nozzle impinged onto a square foil heater, which dissipated a constant heat flux. The nozzle and the heat source were both mounted in large round plates to ensure axisymmetric radial outflow of the spent fluid. The local surface temperature of the heat source was measured at different radial locations (r/d) from the center of the jet in fine increments. Results for the local heat transfer coefficient distribution at the heat source are presented as functions of nozzle diameter (0.79 ≤ d ≤ 6.35 mm), Reynolds number (4000 to 23,000), and nozzle-to-heat source spacing (1 ≤ Z/d ≤ 14). Secondary peaks in the local heat transfer observed at r/d ≈ 2 were more pronounced at the smaller (confined) spacings and larger nozzle diameters for a given Reynolds number, and shifted radially outward from the stagnation point as the spacing increased. The secondary-peak magnitude increased with Reynolds number, and was higher than the stagnation value in some instances. Correlations are proposed for the stagnation and average Nusselt numbers as functions of these parameters.
Longitudinal Heat Transfer in Oscillatory Flows in Pipes With Thermally Permeable Wall
Authors: Inaba T.
Published: February 2008

The effect of a thermally permeable wall on the enhanced longitudinal heat transfer by fluid pulsation in a pipe has been investigated. An analytical solution is obtained for the case when heat loss through the wall over a cycle of fluid pulsation is uniform along the pipe. The distribution of time-averaged sectional mean temperature is expressed by a quadratic curve. The rate of longitudinal heat transfer decreases linearly toward the lower temperature end. The amplitude of time-varying sectional mean temperature also decreases toward the same end. The effect of the value of Womersley number on this temperature field is discussed.
Non-Newtonian Flow and Heat Transfer in an Obstructed Channel With Radio-Frequency Heating
Authors: Hill R. W. , Bergman T. L.
Published: February 2008

The hydrodynamic and thermal conditions associated with the flow of a non-Newtonian fluid (polystyrene), which is heated volumetrically by electric radio-frequency excitation, is considered. The fluid is forced through a two-dimensional channel having local, stationary blocks, which restrict the flow and are maintained at a constant rms voltage potential. Detailed and overall system response is examined for a range of fluid velocities, restriction sizes, and radio-frequency heating rates. This heating reduces the pressure drop induced by the restriction and alters the flow structure, suggesting that it may be used to control and augment conventional injection molding operations.
Laminar Natural Convection in a Discretely Heated Cavity: I—Assessment of Three-Dimensional Effects
Authors: Heindel T. J. , Ramadhyani S. , Incropera F. P.
Published: February 2008

Two and three-dimensional calculations have been performed for laminar natural convection induced by a 3 × 3 array of discrete heat sources flush-mounted to one vertical wall of a rectangular cavity whose opposite wall was isothermally cooled. Edge effects predicted by the three-dimensional model yielded local and average Nusselt numbers that exceeded those obtained from the two-dimensional model, as well as average surface temperatures that were smaller than the two-dimensional predictions. For heater aspect ratios Ahtr ≲ 3, average Nusselt numbers increased with decreasing Ahtr. However, for Ahtr ≳ 3, the two and three-dimensional predictions were within 5 percent of each other and results were approximately independent of Ahtr. In a companion paper (Heindel et al., 1995a), predictions are compared with experimental results and heat transfer correlations are developed.
Laminar Natural Convection in a Discretely Heated Cavity: II—Comparisons of Experimental and Theoretical Results
Authors: Heindel T. J. , Incropera F. P. , Ramadhyani S.
Published: February 2008

Three-dimensional numerical predictions and experimental data have been obtained for natural convection from a 3 × 3 array of discrete heat sources flush-mounted on one vertical wall of a rectangular cavity and cooled by the opposing wall. Predictions performed in a companion paper (Heindel et al., 1995a) revealed that three-dimensional edge effects are significant and that, with increasing Rayleigh number, flow and heat transfer become more uniform across each heater face. The three-dimensional predictions are in excellent agreement with the data of this study, whereas a two-dimensional model of the experimental geometry underpredicts average heat transfer by as much as 20 percent. Experimental row-averaged Nusselt numbers are well correlated with a Rayleigh number exponent of 0.25 for RaLz ≲ 1.2 × 108.
Turbulent Penetrative and Recirculating Flow in a Compartment Fire
Authors: Abib A. H. , Jaluria Y.
Published: February 2008

A numerical study of a turbulent penetrative and recirculating flow induced by the energy input from a fire at the bottom boundary in a partially open rectangular enclosure is carried out. The compartment is connected through an opening to a long corridor, which opens into a stably stratified environment. The condition that is of interest is a stable, two-layered, temperature stratification, which is assumed to be caused by fire in an adjacent enclosure. In this study, attention is focused on the interaction between the cavity and its surrounding ambient medium through the opening. The influence of the stratification is examined in the turbulent flow regime by considering a range of stratification levels for given opening height and initial interface location. It is found that, depending on the stratification, the thermal plume above the fire may never reach the ceiling. Small penetration distances occur at large stratification levels. The flow field reveals a multicellular pattern: a strong main convective cell at the bottom and a weak counterrotating cell at the top. The stable thermal stratification can cause a destruction of the turbulence. This results in the relaminarization of the flow in the upper region of the cavity and may significantly affect the transport processes in the enclosure. This could distort the simplistic concept of two homogeneous gas layers, which forms the basis of zone modeling for compartment fires.
Optimization Principle for Natural Convection Pulsating Heating
Authors: Vargas J. V. C. , Bejan A.
Published: February 2008

This is a theoretical, numerical, and experimental study of natural convection heat transfer from an immersed surface with intermittent uniform heat flux. Scale analysis predicts that the “on” time interval can be optimized such that the overall Nusselt number is maximized. Furthermore, Nu increases monotonically as the “off” time interval decreases. These features are verified and determined more accurately by complete numerical simulations for a vertical flat surface in the range 103 ≤ Ra ≤ 105 and Pr = 7, where Ra is based on heat flux and wall height. They are further verified by means of water experiments in the range 1010 ≤ Ra ≤ 1011. The pulsating heater configurations tested experimentally are the vertical cylinder, which approximates boundary layer flow on a plane surface, and the horizontal cylinder. The optimal square-wave heat pulse for a natural convection immersion heater is reported in general (scaling correct) terms.
Fourier Transform Infrared System Measurement of the Bidirectional Reflectivity of Diffuse and Grooved Surfaces
Authors: Ford J. N. , Tang K. , Buckius R. O.
Published: February 2008

A system based on a Fourier transform infrared spectrometer is developed to perform bidirectional reflectivity measurements on material surfaces, providing the ability to measure this property simultaneously for multiple infrared wavelengths. Calibration is based on a relative method that relates the system output to absolute spectral bidirectional reflectivity. Results are presented for rough gold and grooved nickel surfaces, considering the variation with incident and reflected angle. The surface reflectivity for gold is largely independent of wavelength in the infrared region of interest, while the nickel surface exhibits spectral variation. The experimental results are compared to complete electromagnetic theory predictions and other measurements.
Thermal Tomographic Detection of Inhomogeneities
Authors: Jones M. R. , Tezuka A. , Yamada Y.
Published: February 2008

Thermal tomography is a nondestructive method for detecting inhomogeneities in a material by localizing variations in its thermal conductivity. Based on a finite element discretization of the heat conduction equation, we obtain a set of equations that relate the conductivity of a medium to temperature measurements on the surface of the medium. We investigate the use of both a linearization and regularization technique and a randomized search procedure based on a genetic algorithm to invert this set of equations. We found a tradeoff exists between the accuracy of the conductivity mapping and the resolution of the conductivity mapping. To increase the resolution of the mapping, we propose a zooming method in which the finite elements are grouped into blocks and a low-resolution mapping of the conductivity is obtained. Improved mappings are then obtained by increasing the number of blocks in regions where inhomogeneities appear to be present and repeating the inversion process.
Effect of Channel Blockage on Critical Heat Flux for a Horizontal Cylinder in Crossflow
Authors: Dowlati R. , Kawaji M. , Sardjono I. D. , Revankar S. T.
Published: February 2008

An experimental investigation has been conducted on critical heat flux (CHF) on a horizontal tube in crossflow boiling R-113 at near atmospheric pressures. Data were obtained over a range of fluid velocities (up to 0.52 m/s), heater diameters (8 to 12.7 mm), and flow blockage factors (D/H = 0.31 to 0.5). The effect of the flow blockage on CHF was examined in detail and compared with other data and existing correlations. No significant effect of flow blockage was observed for D/H up to 0.5. An analytical modification of the Katto-Haramura CHF correlation is proposed to take into account the effect of flow blockage over a wide range of D/H.
A Generalized Self-Consistent Mechanics Method for Solids Containing Elliptical Inclusions
Authors: Huang Y. , Hu K. X.
Published: February 2008

The determination of the effective moduli for a material containing elliptical inclusions is the objective of this paper. This is done by incorporating an inclusion/matrix/composite model into a general energy equivalence framework. Through the evaluation of the average strain in each individual inclusion, the current approach can handle the inclusion’s orientation dependency in a straightforward manner. The case of an in-plane isotropic distribution of elliptical inclusions is addressed in detail. For the case of reinforcements, or hard inclusions, the effect of the inclusion aspect ratio on in-plane effective moduli is small if the aspect ratio is larger than 0.5. For aspect ratios less than 0.3, the effective moduli increase dramatically, which implies that flat reinforcements are much more effective than traditional cylindrical reinforcements. It is also established that the generalized self-consistent method predicts a stronger dependence of effective moduli on the inclusion aspect ratio than does the Mori-Tanaka method, especially for shear moduli.
Green’s Function for Elastic Medium With General Anisotropy
Authors: Chang Ching S. , Chang Yang
Published: February 2008

It is difficult to obtain explicit expressions of Green’s function for elastic medium with general anisotropy. The difficulty is associated with an integration of functions with high degrees of singularity. In this paper, we propose a method employing extend functions. This method avoids the difficulty of singularities and renders an explicit series expression of Green’s function for general anisotropic conditions. Analytical expression of the coefficients in the series are provided. Numerical examples are given to evaluate the applicability of this method.
Buckling and Post-buckling Behavior of a Pipe Subjected to Internal Pressure
Authors: Tang D. M. , Ilgamov M. A. , Dowell E. H.
Published: February 2008

It is well known that a thin elastic shell under external pressure may undergo buckling and collapse. Less well known is that a hollow beam under internal pressure may buckle as an Euler column. This is the subject of the present study. The buckled deflection and natural frequency about the buckled configuration of a vertical pipe with clamped (y-axis) and hinged (z-axis) boundary conditions at the lower support location, considering the influence of internal pressure and initial (manufactured) curvature, has been studied analytically and experimentally. The buckling and post-buckling behavior of the pipe beam with an initial static deflection depends upon the nonlinear coupling due to deflection in the two directions including the anisotropic boundary condition at the one support location. The coupling effects increase as the internal pressure and the initial static deflection increase. When the initial static deflection is zero, the coupling effect disappears. The theoretical results agree reasonably well with the experiments.
A Crack Very Close to a Bimaterial Interface
Authors: Romeo A. , Ballarini R.
Published: February 2008

This paper presents the plane elastostatics analysis of a semi-infinite crack perpendicular to a perfectly bonded bimaterial interface. Both cases of the crack approaching the interface and penetrating the interface are addressed. The distance from the tip of the crack to the interface is δ. A singular integral equation approach is used to calculate the stress intensity factor, KI, and the crack-opening displacement at the interface, η, as functions of δ, the Dundurs parameters α and β, and the stress intensity factor kI associated with the same crack terminating at the interface (the case δ = 0). The results are presented as KI=kIδ1/2−λf(α,β) and η=CkIδ1−λη(˜α,β) where λ is the strength of the stress singularity associated with δ = 0, f and η˜ are functions calculated numerically and C is a material constant. These results can be used to determine the stress intensity factor and crack opening displacement of cracks of finite length 2a with one tip at a distance δ from the interface for δ/a≪1. The selected results presented for a crack loaded by a uniform far-field tension in each half-plane show that the stress intensity factors approach their limits at a relatively slow rate.
Some Observations on Yield Surfaces for 304 Stainless Steel at Large Prestrain
Authors: Wu H. C. , Lu J. K. , Pan W. F.
Published: February 2008

Experiments to study the yield surface of 304 stainless steel with either 20 percent tension or 20 percent shear prestrain have been conducted. Explicit transformation equations have also been derived to convert the experimentally determined first Piola-Kirchhoff stress components into the Cauchy stresses and the second Piola-Kirchhoff stresses for combined axial-torsional experiments. It has been found that, in the phenomenological approach, the stress measure and the definition of yield have significant effect on the degree of anisotropy of strain-hardening. In particular, the strain-hardening rule is extremely complicated if the second Piola-Kirchhoff stress is used. Also, the equivalent stress-strain curves have been investigated by means of different stress measures.
Thermohydrodynamic Analysis of Process-Liquid Hydrostatic Journal Bearings in Turbulent Regime, Part I: The Model and Perturbation Analysis
Authors: Yang Zhou , San Andres L. , Childs D. W.
Published: February 2008

A bulk-flow thermohydrodynamic (THD) analysis is developed for prediction of the static and dynamic performance characteristics of turbulent-flow, process-liquid, hydrostatic journal bearings (HJBs). Pointwise evaluation of temperature and hence liquid properties is achieved through the solution of the energy equation in the fluid film with insulated boundaries, and justified for fluid film bearings with external pressurization. Fluid inertia within the film lands and at recess edges is preserved in the analysis. Flow turbulence is accounted through turbulence shear parameters based on friction factors derived from Moody’s formulae. The effects of fluid compressibility and temperature variation in the bearing recesses are included. Numerical solution and results are presented in the second part of this work and compared with some limited experimental data for a liquid hydrogen (LH2) bearing.
Toeplitz Jacobian Matrix for Nonlinear Periodic Vibration
Authors: Leung A. Y. T. , Ge T.
Published: February 2008

The main difference between a linear system and a nonlinear system is in the non-uniqueness of solutions manifested by the singular Jacobian matrix. It is important to be able to express the Jacobian accurately, completely, and efficiently in an algorithm to analyze a nonlinear system. For periodic response, the incremental harmonic balance (IHB) method is widely used. The existing IHB methods, however, requiring double summations to form the Jacobian matrix, are often extremely time-consuming when higher order harmonic terms are retained to fulfill the completeness requirement. A new algorithm to compute the Jacobian is to be introduced with the application of fast Fourier transforms (FFT) and Toeplitz formulation. The resulting Jacobian matrix is constructed explicitly by three vectors in terms of the current Fourier coefficients of response, depending respectively on the synchronizing mass, damping, and stiffness functions. The part of the Jacobian matrix depending on the nonlinear stiffness is actually a Toeplitz matrix. A Toeplitz matrix is a matrix whose k, r position depends only on their difference k-r. The other parts of the Jacobian matrix depending on the nonlinear mass and damping are Toeplitz matrices modified by diagonal matrices. If the synchronizing mass is normalized in the beginning, we need only two real vectors to construct the Toeplitz Jacobian matrix (TJM), which can be treated in one complex fast Fourier transforms. The present method of TJM is found to be superior in both computation time and storage than all existing IHB methods due to the simplified explicit analytical form and the use of FFT.
A Finite Elastoplastic Constitutive Formulation With New Co-rotational Stress-Rate and Strain-Hardening Rule
Authors: Xia Z. , Ellyin F.
Published: February 2008

A constitutive model for finite elastoplastic deformations is presented. This model incorporates two novel features: first, a strain-hardening law that is applicable to complex loading paths and histories; and second, an objective stress-rate measure that is based on the spin of an orthogonal triad of material unit vectors which instantaneously coincides with the principal directions of the stress tensor. Problems of shear superposed on triaxial tension, cyclic shear deformation, and biaxial nonproportional loading are studied. It is shown that realistic predictions for the aforementioned problems are obtained by using the proposed constitutive model.
Partitioning the Parameter Space According to Different Behaviors During Three-Dimensional Impacts
Authors: Bhatt V. , Koechling J.
Published: February 2008

The equations of motion that define three-dimensional rigid-body impact with finite friction and restitution cannot be solved in a closed form. Previous work has shown that for general shapes and initial conditions, the direction of sliding velocity keeps changing continuously throughout the duration of impact. The flow patterns defined by the trace of the sliding velocity can be classified into a finite number of qualitatively distinct physical behavior. We identify three dimensionless parameters that completely specify the sliding behavior, and determine regions in this parameter space that correspond to each of the different flow patterns. The qualitative behavior during impact can now be determined based on the region which contains the parameters for a given impact configuration. The analysis is also used to study the sensitivity of the sliding behavior to changes in shape or configuration of the body and to rule out the occurrence of certain ambiguities in the post-sticking behavior during impact.
A General Formulation of the Theory of Wire Ropes
Authors: Jiang Wei
Published: February 2008

This paper presents a general formulation of the nonlinear and linear analysis of wire ropes. In the formulation, wires, strands, and wire ropes are all considered as a kind of identical structure characterized by seven stiffness and deformation constants, and as such they can be used, in the same way, as component elements in some layered general structures. Based on such a point of view, the general formulation thus developed can be used to analyze wire ropes of various complex cross sections, and to analyze simple wire strands as well.
Dynamic Formulation for Geometrically Exact Sandwich Beams and One-Dimensional Plates
Authors: Vu-Quoc Loc , Ebcioglu I. K.
Published: February 2008

A new theory of sandwich beams/one-dimensional plates is presented with finite rotations and shear allowed in each layer. The layers, variable in number from one to three, need not have the same thickness and the same length, thus allowing for ply drop-off. Restricting to planar deformation, the cross section has a motion identical to that of a multibody system that consists of rigid links connected by hinges. Large deformation and large overall motion are accommodated, with the beam dynamics referred directly to an inertial frame. An important approximated theory is developed from the general nonlinear equations. The classical linear theory is recovered by consistent linearization.
Analytical Expressions for the Relaxation Moduli of Linear Viscoelastic Composites With Periodic Microstructure
Authors: Luciano R. , Barbero E. J.
Published: February 2008

In this paper the viscoelastostatic problem of composite materials with periodic microstructure is studied. The matrix is assumed linear viscoelastic and the fibers elastic. The correspondence principle in viscoelasticity is applied and the problem in the Laplace domain is solved by using the Fourier series technique and assuming the Laplace transform of the homogenization eigenstrain piecewise constant in the space. Formulas for the Laplace transform of the relaxation functions of the composite are obtained in terms of the properties of the matrix and the fibers and in function of nine triple series which take into account the geometry of the inclusions. The inversion to the time domain of the relaxation and the creep functions of composites reinforced by long fibers is carried out analytically when the four-parameter model is used to represent the viscoelastic behavior of the matrix. Finally, comparisons with experimental results are presented.