bluuebunny/crossref_metadata_2025 huggingface dataset:
Melting of a Solid Sphere Under Forced and Mixed Convection: Flow Characteristics
Authors: Hao Y. L. , Tao Y.-X.
Published: July 2002

An experimental investigation on flow around a melting ice sphere in horizontally flowing water is conducted. The flow field is measured quantitatively using the particle image velocimetry (PIV) technique. The distributions of velocity, streamline, and z-component of rotation vector around the ice sphere are obtained for different upstream velocities and temperatures. General flow characteristics around the melting ice sphere and effects of velocity and temperature are analyzed. The visualization of melting of a dyed ice sphere is also conducted to investigate the motion of the melt, its mixing with mainstream, and the separation of the boundary layer. Comparisons with the flow around a non-melting ball are made to investigate the effect of melting on the flow boundary layer. The original experimental results are published to serve as benchmark data for numerical model development.
Contact Stresses in Dovetail Attachments: Finite Element Modeling
Authors: Sinclair G. B. , Cormier N. G. , Griffin J. H. , Meda G.
Published: July 2002

The stress analysis of dovetail attachments presents some challenges. These challenges stem from the high stress gradients near the edges of contact and from the nonlinearities attending conforming contact with friction. To meet these challenges with a finite element analysis, refined grids are needed with mesh sizes near the edges of contact of the order of one percent of the local radii of curvature there. A submodeling procedure is described which can provide grids of sufficient resolution in return for moderate computational effort. This procedure furnishes peak stresses near contact edges which are converging on a sequence of three submodel grids, and which typically do converge to within about five percent.
Theoretical Studies of a Continuously Adjustable Hydrodynamic Fluid Film Bearing
Authors: Martin J. K. , Parkins D. W.
Published: July 2002

Principles of a continuously adjustable hydrodynamic bearing are described together with an analysis model for studying its theoretical performance. The model included an expanded form of the governing Reynolds equation which took account of non-uniform variations in the fluid film thickness. A solution procedure was devised whereby for a given set of adjustment conditions, simultaneously converged fields of fluid film thickness, temperature, viscosity and pressure would result, together with oil film forces. A wide range of operating characteristics were studied with results predicting advantages and benefits over conventional hydrodynamic bearings.
Thermal Effects in Thrust Washer Lubrication
Authors: Yu To Him , Sadeghi Farshid
Published: July 2002

A numerical model was developed to study the thermal effects on the lubrication mechanism of radially-grooved thrust washers. A mass-conserving transient thermohydrodynamic (THD) analysis was performed by solving the modified Reynolds and energy equations for the lubricant pressure and temperature distributions. The heat transfer equations were also solved simultaneously to obtain the temperature fields of the solids (thrust washers). Due to different thermal time responses of the lubricant film and the solids, heat transfer equations of the runner and the thrust washer pad were treated as in quasi-steady state at each time step in the transient solution. Elrod cavitation algorithm was implemented to include lubricant cavitation. The results show that thermal effects do not only reduce load carrying capacity and the frictional torque but also increase side flow rate. Moreover, the numerical model also demonstrates that the thermal effects have greater influence on the load support when the groove depth and groove numbers increase. Furthermore, the analytical results also show that there exists certain operating conditions before thermal effects become the dominating factors in influencing the thrust washer performance.
Mainstream Aerodynamic Effects Due to Wheelspace Coolant Injection in a High-Pressure Turbine Stage: Part I—Aerodynamic Measurements in the Stationary Frame
Authors: McLean Christopher , Camci Cengiz , Glezer Boris
Published: July 2002

The relative aerodynamic and performance effects associated with rotor–NGV gap coolant injections were investigated in the Axial Flow Turbine Research Facility (AFTRF) of the Pennsylvania State University. This study quantifies the effects of the coolant injection on the aerodynamic performance of the turbine for radial cooling, impingement cooling in the wheelspace cavity and root injection. Overall, it was found that even a small quantity (1 percent) of cooling air can have significant effects on the performance character and exit conditions of the high pressure stage. Parameters such as the total-to-total efficiency, total pressure loss coefficient, and three-dimensional velocity field show local changes in excess of 5, 2, and 15 percent, respectively. It is clear that the cooling air disturbs the inlet end-wall boundary layer to the rotor and modifies secondary flow development, thereby resulting in large changes in turbine exit conditions.
Contact of Rough Surfaces With Asymmetric Distribution of Asperity Heights
Authors: Yu Ning , Polycarpou Andreas A.
Published: July 2002

The Greenwood and Williamson (GW) statistical approach of characterizing rough surfaces is extended to include asymmetric distribution of asperity heights using the Weibull distribution. A key parameter that is used to characterize asymmetry is the skewness, and the corresponding Weibull parameters are investigated for a range of practical skewness values. The Weibull distribution is then adopted to model the asperity heights, and once normalized, is used to calculate the contact load, real area of contact and number of contacting asperities using the CEB elastic-plastic model of an equivalent rough surface in contact with a smooth plane. The effect of skewness on different levels of surface roughness, ranging from very smooth surfaces encountered in microtribological applications to rougher surfaces encountered in macrotribological applications is investigated, and also compared to the symmetric Gaussian case. Also, to allow for closed-form solution of the contact equations, simpler exponential distributions are curved-fitted to the contact side of the Weibull distribution, and the analytical results are favorably compared with the numerical results using the Weibull distribution.
Measurements of Rotordynamic Coefficients of Hybrid Bearings With (a)
a Plugged Orifice, and (b) a Worn Land Surface
Authors: Laurant F. , Childs D. W.
Published: July 2002

Test results are presented for the rotordynamic coefficients of a hybrid bearing that is representative of bearings for liquid-rocket-engine turbopump applications. The bearing is tested in the following two degraded conditions: (a) one of five orifices plugged, and (b) a locally enlarged clearance to simulate a worn condition. Test data are presented at 24,600 rpm, with supply pressures of 4.0, 5.5, and 7.0 MPa, and eccentricity ratios from 0.1 to 0.5 in 0.1 increments. Overall, the results suggest that neither a single plugged orifice nor significant wear on the bearing land will “disable” a well-designed hybrid bearing. These results do not speak to multiple plugged orifices and are not an endorsement for operations without filters to prevent plugging orifices.
The Optimization of Blade Pitch Settings of an Air Turbine Using Self-Pitch-Controlled Blades For Wave Power Conversion
Authors: Kim T. H. , Setoguchi T. , Kaneko K. , Takao M.
Published: July 2002

This work investigated an air turbine with self-pitch-controlled blades operating in the airflow generated by an oscillating water column (OWC) under irregular wave conditions to determine turbine performance and identify the optimum blade pitch angle setting. Rotor models with fixed blades were tested under steady flow conditions. The running and starting characteristics of the turbine under irregular wave conditions were determined from a computer simulation that modeled both the turbine and the air chamber. The performance of the air turbine was evaluated and the optimum rotor blade limit was found to be about 10°.
A Frequency Domain Versus a Time Domain Identification Technique for Nonlinear Parameters Applied to Wire Rope Isolators
Authors: Kerschen Gaetan , Lenaerts Vincent , Marchesiello Stefano , Fasana Alessandro
Published: July 2002

The present paper aims to compare two techniques for identification of nonlinear dynamical systems. The Conditioned Reverse Path method, which is a frequency domain technique, is considered together with the Restoring Force Surface method, a time domain technique. Both methods are applied for experimental identification of wire rope isolators and the results are compared. Finally, drawbacks and advantages of each technique are underlined.
An Active-Passive Piezoelectric Absorber for Structural Vibration Control Under Harmonic Excitations With Time-Varying Frequency, Part 1: Algorithm Development and Analysis
Authors: Morgan R. A. , Wang K. W.
Published: July 2002

It has been shown that piezoelectric materials can be used as passive electromechanical vibration absorbers by shunting them with electrical networks. Semi-active piezoelectric absorbers have also been proposed for suppressing harmonic excitations with varying frequency. However, these semi-active devices have limitations that restrict their practical applications. The approach presented here is a high performance active-passive alternative to semi-active absorbers. By utilizing a combination of a passive electrical circuit and active control actions, the system is synthesized for adaptive variable frequency narrowband disturbance rejection. The active control consists of three parts: an inductor tuning action, a negative resistance action, and a coupling enhancement action. In the current paper (Part 1), the control algorithm is developed and analyzed. Part 2 of the paper contains experimental investigations and parametric studies of the new absorber design.
Active Noise Hybrid Feedforward/Feedback Control Using Neural Network Compensation*
Authors: Qizhi Zhang , Yongle Jia
Published: July 2002

The nonlinear active noise control (ANC) is studied. The nonlinear ANC system is approximated by an equivalent model composed of a simple linear sub-model plus a nonlinear sub-model. Feedforward neural networks are selected to approximate the nonlinear sub-model. An adaptive active nonlinear noise control approach using a neural network enhancement is derived, and a simplified neural network control approach is proposed. The feedforward compensation and output error feedback technology are utilized in the controller designing. The on-line learning algorithm based on the error gradient descent method is proposed, and local stability of closed loop system is proved based on the discrete Lyapunov function. A nonlinear simulation example shows that the adaptive active noise control method based on neural network compensation is very effective to the nonlinear noise control, and the convergence of the NNEH control is superior to that of the NN control.
Numerical Investigation of Airfoil Clocking in a Three-Stage Low-Pressure Turbine
Authors: Arnone Andrea , Marconcini Michele , Pacciani Roberto , Schipani Claudia , Spano Ennio
Published: July 2002

A quasi-three-dimensional, blade-to-blade, time-accurate, viscous solver was used for a three-stage LP turbine study. Due to the low Reynolds number, transitional computations were performed. Unsteady analyses were then carried out by varying the circumferential relative position of consecutive vanes and blade rows to study the effects of clocking on the turbine’s performance. A clocking strategy developed in order to limit the number of configurations to be analyzed is discussed. The optimum analytically-determined clocking position is illustrated for two different operating conditions, referred to as cruise and takeoff. The effects of clocking on wake interaction mechanisms and unsteady blade loadings is presented and discussed. For low Reynolds number turbine flows, the importance of taking transition into account in clocking analysis is demonstrated by a comparison with a fully turbulent approach.
Clocking Effects in a 1.5 Stage Axial Turbine—Steady and Unsteady Experimental Investigations Supported by Numerical Simulations
Authors: Reinmo¨ller U. , Stephan B. , Schmidt S. , Niehuis R.
Published: July 2002

The interaction between rotor and stator airfoils in a multistage turbomachine causes an inherently unsteady flow field. In addition, different relative circumferential positions of several stator rows and rotor rows, respectively, have an influence on the flow behavior in terms of loss generation, energy transport and secondary flow. The objective of the presented study is to investigate the effects of stator airfoil clocking on the performance of a 1-1/2 stage axial cold air turbine. The investigated axial turbine consists of two identical stators. The low aspect ratio of the blades and their prismatic design leads to a three-dimensional outlet flow with a high degree of secondary flow phenomena. Nevertheless, the small axial gaps between the blade rows are responsible for strong potential flow interaction with the radial wake regions in the measurement planes. Consequently, parts of the wakes of the first stator are clearly detected in the rotor outlet flow. To give an overview of the time-averaged flow field, measurements with pneumatic probes are conducted behind each blade row at ten different clocking-positions of the second stator. Further, an optimized clocking position was found due to a minimum in pressure loss behind the second stator. The unsteady measurements are carried out with hot-wire probes for three selected stator-stator positions. Animations of selected flow properties show the influence of different circumferential positions of the second stator on the unsteady flow behavior and secondary flow field. In addition and compared with experimental results three-dimensional unsteady viscous flow computations are performed.
The Response of Pipes and Supports to Internal Pressure Loads Generated by Gaseous Detonations
Authors: Thomas G. O.
Published: July 2002

Pipes with nominal diameters 300 mm constructed from GRP or medium density polyethylene (MDPE) have been subject to transient internal pressure loads, generated by ethylene-air detonations. Several GRP sections survived repeated tests, while an MDPE pipe failed in a catastrophic manner. Time resolved strain measurements of the wall responses were obtained and both pre-cursor axial and transverse hoop strains have been resolved. The responses of idealized pipe supports are also reported.
Measurement of the Instantaneous Velocity Gradients in Plane and Axisymmetric Turbulent Wake Flows
Authors: Schenck T. , Jovanovic´ J.
Published: July 2002

All first-order spatial derivatives of the turbulent velocity fluctuations were measured using a pair of X hot-wire probes. Measurements were performed in the self-preserving region of a turbulent plane wake downstream of a cylinder and in an axisymmetric wake behind the sphere. Good spatial resolution of the measurements was ensured by choosing small values for the cylinder/sphere diameter and a low flow speed. Errors due to the finite hot-wire length and the wire and probe separation were analyzed using Wyngaard’s correction method. The derived corrections were verified experimentally. The measuring technique and the experimental results were systematically checked and compared with the results available in the literature. The assumptions of local isotropy and local axisymmetry were examined. Both investigated flows deviate only moderately from local isotropy and local axisymmetry. Support for the measured results is provided by plotting the data on an anisotropy invariant map. The budgets of the turbulent kinetic energy were computed from the measured data. In contrast to the results obtained in the plane wake, where the pressure transport is nearly negligible, in the axisymmetric wake it was found to play an important role and closely follows the estimate made by Lumley, uip¯/ρ≈−0.2q2ui¯.
A Finite-Mode PDF Model for Turbulent Reacting Flows
Authors: Tsai Kuochen , Gillis Paul A. , Sen Subrata , Fox Rodney O.
Published: July 2002

The recently proposed multi-environment model, R. O. Fox, 1998, “On the Relationship between Lagrangian Micromixing Models and Computational Fluid Dynamics,” Chem. Eng. Proc., Vol. 37, pp. 521–535. J. Villermaux and J. C. Devillon, 1994, “A Generalized Mixing Model for Initial Contacting of Reactive Fluids,” Chem. Eng. Sci., Vol. 49, p. 5127, provides a new category of modeling techniques that can be employed to resolve the turbulence-chemistry interactions found in reactive flows. By solving the Eulerian transport equations for volume fractions and chemical species simultaneously, the local concentrations of chemical species in each environment can be obtained. Assuming micromixing occurs only in phase space, the well-known IEM (interaction by exchange with the mean) model can be applied to close the micromixing term. This simplification allows the model to use micromixing timescales obtained from more sophisticated models and can be applied to any number of environments. Although the PDF shape doesn’t change under this assumption, the interaction between turbulence and chemistry can be resolved up to the second moments without any ad-hoc assumptions for the mean reaction rates. Furthermore, the PDF shape is found to have minimal effect on mean reaction rates for incompressible turbulent reacting flows. In this formulation, a spurious dissipation term arises in the transport equation of the scalar variances due to the use of Eulerian transport equations. A procedure is proposed to eliminate this spurious term. The model is applied to simulate the experiment of S. Komori, et al., 1993, “Measurements of Mass Flux in a Turbulent Liquid Flow With a Chemical Reaction,” AIChE J., Vol. 39, pp. 1611–1620, for a reactive mixing layer and the experiment of K. Li and H. Toor, 1986, “Turbulent Reactive Mixing With a Series Parallel reaction: Effect of Mixing on Yield,” AIChE J., Vol. 32, pp. 1312–1320, with a two-step parallel/consecutive reaction. The results are found to be in good agreement with the experimental data of Komori et al. and the PDF simulation of K. Tsai and R. Fox, 1994, “PDF Simulation of a Turbulent Series-Parallel Reaction in an Axisymmetric Reactor,” Chem. Eng. Sci., Vol. 49, pp. 5141–5158, for the experiment of Li and Toor. The resulting model is implemented in the commercial CFD code, FLUENT,1 and can be applied with any number of species and reactions.
Numerical Analysis of Metal Cutting With Chamfered and Blunt Tools
Authors: Movahhedy, M. R. , Altintas, Y. , Gadala, M. S.
Published: July 2002

In high speed machining of hard materials, tools with chamfered edge and materials resistant to diffusion wear are commonly used. In this paper, the influence of cutting edge geometry on the chip removal process is studied through numerical simulation of cutting with sharp, chamfered or blunt edges and with carbide and CBN tools. The analysis is based on the use of ALE finite element method for continuous chip formation process. Simulations include cutting with tools of different chamfer angles and cutting speeds. The study shows that a region of trapped material zone is formed under the chamfer and acts as the effective cutting edge of the tool, in accordance with experimental observations. While the chip formation process is not significantly affected by the presence of the chamfer, the cutting forces are increased. The effect of cutting speed on the process is also studied.
Wave Height Distribution in Mixed Sea States
Authors: Rodriguez German , Soares C. Guedes , Pacheco Mercedes , Pe´rez-Martell E.
Published: July 2002

The statistical distribution of zero-crossing wave heights in Gaussian mixed sea states is examined by analyzing numerically simulated data. Nine different kinds of bimodal scalar spectra are used to study the effects of the relative energy ratio and the peak frequency separation between the low and high frequency wave fields on the wave height distribution. Observed results are compared with predictions of probabilistic models adopted in practice. Comparisons of the empirical data with relevant probabilistic models reveals that the Rayleigh model systematically overestimates the number of observed wave heights larger than the mean wave height, except for one of the cases analyzed. None of the models used to predict the observed exceedance probabilities is able to characterize adequately all cases of bimodal sea states examined here.
A New Flow Chamber for the Study of Shear Stress and Transmural Pressure Upon Cells Adhering to a Porous Biomaterial
Authors: Chotard-Ghodsnia Roxana , Drochon Agnès , Grebe Reinhard
Published: July 2002

Biomaterials used in some biomedical devices are porous and exposed to normal and tangential flow of biofluids. To examine the influence of flow induced forces on the morphology and the biochemical responses of cells adhering to such biomaterials, a Hele-Shaw cell with a porous bottom wall was designed and characterized experimentally. Theoretical predictions for the flow in the chamber are provided and allow to quantify the shear stress and/or transmural pressure exerted on cells. It is thus possible to follow up continuously the shape changes of cells that are adherent on a permeable membrane used in bioreactors.
Regional, Directional, and Age-Dependent Properties of the Brain Undergoing Large Deformation
Authors: Prange Michael T. , Margulies Susan S.
Published: July 2002

The large strain mechanical properties of adult porcine gray and white matter brain tissues were measured in shear and confirmed in compression. Consistent with local neuroarchitecture, gray matter showed the least amount of anisotropy, and corpus callosum exhibited the greatest degree of anisotropy. Mean regional properties were significantly distinct, demonstrating that brain tissue is inhomogeneous. Fresh adult human brain tissue properties were slightly stiffer than adult porcine properties but considerably less stiff than the human autopsy data in the literature. Mixed porcine gray/white matter samples were obtained from animals at “infant” and “toddler” stages of neurological development, and shear properties compared to those in the adult. Only the infant properties were significantly different (stiffer) from the adult.
The Effect of Film Thickness on Initial Friction of Elastic-Plastically Rough Surface With a Soft Thin Metallic Film
Authors: Liu Zhiqiang , Neville Anne , Reuben R. L.
Published: July 2002

The effect of a deposited soft thin metallic film on friction properties of a hardened steel substrate has been investigated experimentally and theoretically. The dependency of the film thickness and contact load on the static friction coefficient is presented. The experimental observations show that deformation of the film in contact was plastic, thereby confirming the assumption of the theoretical calculation. The effect of the film thickness on the contact area has been analyzed. A model for calculating the static friction coefficient of contacting rough surfaces in the presence of a soft thin film has been used. Results from the numerical calculations have been compared with the present static friction measurements performed on a pin on plate reciprocating apparatus. The rise in friction that occurs with increasing thickness for very thin films is discussed in detail. The calculated results, which predict the correct trend of the friction behavior from the present experiment, cover an extremely large range of F/AnE from 10−12 to 10−2, where three different dependencies of F/AnE on the static friction coefficient can be identified. An investigation into the discrepancy between the calculated and experimental values for the static friction coefficient μ suggests that an accurate prediction of the magnitude of μ depends to a great extent on the level of accuracy in measuring the value of the constant ζ, the effective hardness of the film.
A Review of Purge Air Designs for Aeroengine-Based Optical Pyrometers
Authors: Kerr Clive I. , Ivey Paul C.
Published: July 2002

With the advent of "power by the hour" type agreements within the civil aeroengine market, the application of engine monitoring system data has reached the level of strategic use for informed decision making in not only the aftermarket but increasingly in the contract negotiation stage. One of the key cost drivers in these dollar-per-hour contracts for the OEMs to analyze is the life and maintenance requirements of the turbine blades leading ultimately to blade life management. Such life management of key components is of critical importance to ensure that the economic and technical risks to both service provider and customer are minimized. The optical pyrometer, through providing a direct temperature measurement of the turbine blades, is a primary input for providing a more realistic assessment of the component’s operating history associated with the use of life usage/remaining algorithms. However, the greatest concern with the in-service use of pyrometry is the issue of fouling since the pyrometer’s lens is exposed to the turbine environment. The level of optical contamination is usually minimized by introducing purge air, bled from the compressor, down the sight tube to prevent both the build-up of contaminants on the exposed system optics and particles in the gas stream from coming in contact with the lens. This paper provides a review of purge air designs and the key methodologies for engine designers to be acquainted with when seeking to integrate the use of optical pyrometry systems in new engine concepts.
Optimal Design of Layered Structures Under Normal (Frictionless) Contact Loading
Authors: Ovaert Timothy C. , Pan Jihui
Published: July 2002

A methodology is presented for the optimization of a tribological contact configuration, namely, a multi-layered elastic structure under normal (frictionless) point contact loading. This work is aimed at developing an algorithm by which the finite element (FE) mesh and the corresponding structure may be generated automatically for each variation in the vector of design variables during optimization iterations. The FE model for contact analysis may be developed in a given commercial solver such as ABAQUS or ANSYS. To do this, a flexible mesh generator, which interfaces with the FE model and the optimizer, was developed. The optimization scheme is implemented using a simulated annealing (SA) algorithm as the optimizer, with an axisymmetric (point contact) FE indentation model in the commercial finite element solver ABAQUS. The results suggest that conventional optimization methods may be employed to examine the design of tribological contact configurations such as multi-layered structures, working seamlessly within the operating system shell (e.g., Unix), and the finite element solver.
Selective Modulation of Endothelial Cell [Ca2+]i Response to Flow by the Onset Rate of Shear Stress
Authors: Blackman Brett R. , Thibault Lawrence E. , Barbee Kenneth A.
Published: July 2002

The response of endothelial cells (ECs) to their hemodynamic environment strongly influences normal vascular physiology and the pathogenesis of atherosclerosis. Unique responses to the complex flow patterns in lesion-prone regions imply that the temporal and spatial features of the mechanical stimuli modulate the cellular response to flow. We report the first systematic study of the effects of temporal gradients of shear stress on ECs. Flow was applied to cultured ECs using a novel cone-and-plate device allowing precise and independent control of the shear stress magnitude and the onset rate. Intracellular free calcium concentration [Ca2+]i increased rapidly following the onset of flow, and the characteristics of the transient were modulated by both the shear stress magnitude and onset rate. ECs were most sensitive to shear stress applied at physiological onset rates. Furthermore, the relative contribution of extracellular calcium and IP3-mediated release were dependent upon the specific flow regime. [S0148-0731(00)01003-7]
Fluid Transmission Line Modeling Using a Variational Method
Authors: Ma¨kinen Jari , Piche´ Robert , Ellman Asko
Published: July 2002

A variational method is used to derive numerical models for transient flow simulation in fluid transmission lines. These are generalizations of models derived using the more traditional modal method. Three different transient compressible laminar pipe flow models are considered (inviscous, one-dimensional linear viscous, and two-dimensional dissipative viscous flow), and a model for transient turbulent pipe flow is given. The (model) equations in the laminar case are given in the form of a set of constant coefficient ordinary differential equations, and for the turbulent case (model) in the form of a set of nonlinear ordinary differential equations. Explicit equations are given for various end conditions. Attenuation factors, similar to the window functions used in spectral analysis, are used to attenuate Gibbs phenomenon oscillations. [S0022-0434(00)03201-9]
Estimation of Turbine Torque of Automatic Transmissions Using Nonlinear Observers
Authors: Yi Kyongsu , Shin Byung-Kwan , Lee Kyo-II
Published: July 2002

This paper presents an adaptive sliding observer-based method for estimation of turbine torque. The estimated turbine torques can be used for the closed-loop control of vehicle power train for better shift quality. A sliding observer structure including saturation functions and boundary layers is applied to adapt torque converter parameters. The proposed method has been investigated via simulation and laboratory experimental studies. It has been shown via simulation and experiments that the proposed methodology is promising for the estimation of turbine torques since it uses only inexpensive angular velocity measurements and is not sensitive to parametric uncertainties. [S0022-0434(00)00302-6]
Pressure Transients Across Constrictions
Authors: Adewumi Michael A. , Eltohami E. S. , Ahmed W. H.
Published: July 2002

The modeling of pressure transient across constrictions is achieved by using a one-dimensional, isothermal, noncompositional, single-phase representation of the Eulerian model. A TVD scheme was used to solve the ensuing nonhomogeneous hyperbolic set of first-order quasi-linear partial differential equations. Three types of constrictions were modeled and in each case the behavior of the transient was analyzed. This analysis was used to interpret the pressure response at the inlet resulting from the reflection of the transient at the constrictions. The comparisons between the predicted and inputted data are very good, suggesting that the technique has much promise. [S0195-0738(00)00301-0]
Shot Sleeve Wave Dynamics in the Slow Phase of Die Casting Injection
Authors: Lo´pez J. , Herna´ndez J. , Faura F. , Trapaga G.
Published: July 2002

An analysis is carried out on the wave formed during the slow phase of die casting injection processes. Viscous effects are assumed to be negligible and the problem is treated two-dimensionally using finite amplitude wave theory. Two commonly used types of plunger movements are considered, for which all the possible wave profiles are analyzed in depth as a function of the parameters which characterize the law of acceleration applied to the plunger, the initial shot sleeve filling fraction, and the geometrical characteristics of the problem. Different relationships between the relevant dimensionless parameters of the system are proposed, which make it possible to optimize the injection process, and so reduce the entrapment of air which leads to porosity. The validity of such relationships is analyzed in detail for different ranges of parameters. Some of the results obtained for the optimum acceleration are compared with those of other authors and experimental measurements. Finally, a law of plunger acceleration which would completely eliminate the air from the shot sleeve at the end of the slow phase of injection and minimizes the filling time is derived. [S0098-2202(00)02002-2]
Heat Transfer and Fluid Flow in a Square Duct With 12 Different Shaped Vortex Generators
Authors: Liou T.-M. , Chen C.-C. , Tsai T.-W.
Published: July 2002

Detailed local Nusselt number distributions in the first pass of a sharp turning two-pass square channel with various configurations of longitudinal vortex generator arranged on one wall were measured using transient liquid crystal thermography. Flow patterns and friction factors were measured by the use of laser-Doppler velocimeter and pressure transducer, respectively. The Reynolds number, based on channel hydraulic diameter and bulk mean velocity, was fixed at 1.2×104. The vortex generator height-to-hydraulic diameter ratio and pitch-to-height ratio were 0.12 and 10, respectively. Comparisons in terms of heat transfer augmentation and uniformity and friction loss are first performed on 12 configurations of single longitudinal vortex generator. The fluid dynamic mechanisms and wall confinement relevant to heat transfer enhancement are then documented for three-selected vortex generator models. In addition, the differences in fluid flow and heat transfer characteristics between a single vortex generator and a vortex generator array are addressed for the delta wing I and 45 deg V (with tips facing upstream) models which provide better thermal performance among the 12 configurations examined. The direction and strength of the secondary flow with respect to the heat transfer wall are found to be the most important fluid dynamic factors affecting the heat transfer promotion through the channel wall, followed by the convective mean velocity, and then the turbulent kinetic energy. [S0022-1481(00)01202-0]
Quantitative Selection of Variation Reduction Plans
Authors: Thornton Anna C.
Published: July 2002

Quality has been a rallying call in design and manufacturing for the last two decades. One way to improve quality is through variation reduction (VR). VR teams use tools such as Design of Experiments (DoE) and robust design to improve product performance and quality by reducing variation introduced by manufacturing processes. Because VR teams are typically resource constrained, they must carefully select where to focus their efforts. Planning for VR is complex because reduction efforts are executed on individual features and processes but benefits are accrued when the overall product quality improves. The problem is further complicated by the existence of multiple performance criteria and hundreds of processes and dimensions that effect each performance requirement. Consequently, VR teams typically use qualitative assessments to prioritize and schedule their efforts. This paper provides a mathematical model capable of optimally allocating VR resources for a complex product. The VR model has three parts: a model of variation propagation, a model of variation costs, and a model of variation reduction costs. These models are used to directly calculate the optimal resource allocation plan and schedule for a product with multiple product quality requirements. An example from the aerospace industry is used to demonstrate the theory. [S1050-0472(00)00602-4]
Finite Element Mass-Conserving Cavitation Algorithm in Pure Squeeze Motion. Validation/Application to a Connecting- Rod Small End Bearing
Authors: Optasanu Virgil , Bonneau Dominique
Published: July 2002

A simple analytical approach using conditions of conservation of the mass is proposed for the 1-D “negative squeeze” lubrication problem in order to calculate the cavitation boundary position during oscillatory motion of two plates. The same geometrical case is analyzed using Bonneau’s finite element code. Good agreements between analytical and numerical results support validation of Bonneau’s algorithm. As an example of application of this algorithm to squeeze motion case, the EHD lubrication of an elastic connecting-rod small end bearing is analyzed. Influences of the shaft elasticity and lubricant piezoviscosity are presented. [S0742-4787(00)02101-9]
Hydrodynamics of a Soft Contact Lens During Sliding Motion
Authors: Kamiyama S. , Khonsari M. M.
Published: July 2002

Tear film thickness and pressure distribution under a tilting soft contact lens with peripheral slopes during the early stage of a blink are calculated for various flexibility and aspect ratios. The system is modeled as a slider bearing with the lens behaving as a deformable surface sliding over a rigid eye. The tear is considered to be a linearly viscous (Newtonian) fluid. The velocity profile at the edges and the junctions of the slopes are also calculated for a typical soft contact lens. Back flow at the edges is predicted. It is shown that the tilting of the lens has a major affect on the tendency of the pressure distribution. Also important is the lens’ flexibility for it influences both the film thickness and pressure distribution noticeably. [S0742-4787(00)01002-X]
Induced Micro-Variations in Hydrodynamic Bearings
Authors: Baroud Charles , Busch-Vishniac Ilene , Wood Kristin
Published: July 2002

Fluid-structure interactions in hydrodynamic bearings result in load carrying and drag forces which give the bearing its characteristics. While these bearings offer many benefits as machine components, one of their shortcomings is their limited efficient range. In this paper, we demonstrate the use of micron-scale actuators to actively control the thrust and drag forces on a slider bearing. We show that for a set of control parameters, we are able to affect the performance of a bearing by more than 100 percent during operation, increasing the bearing’s range of operation. [S0742-4787(00)01602-7]
Nonaxisymmetric Turbine End Wall Design: Part I— Three-Dimensional Linear Design System
Authors: Harvey Neil W. , Rose Martin G. , Taylor Mark D. , Shahpar Shahrokh , Hartland Jonathan , Gregory-Smith David G.
Published: July 2002

A linear design system, already in use for the forward and inverse design of three-dimensional turbine aerofoils, has been extended for the design of their end walls. This paper shows how this method has been applied to the design of a nonaxisymmetric end wall for a turbine rotor blade in linear cascade. The calculations show that nonaxisymmetric end wall profiling is a powerful tool for reducing secondary flows, in particular the secondary kinetic energy and exit angle deviations. Simple end wall profiling is shown to be at least as beneficial aerodynamically as the now standard techniques of differentially skewing aerofoil sections up the span, and (compound) leaning of the aerofoil. A design is presented that combines a number of end wall features aimed at reducing secondary loss and flow deviation. The experimental study of this geometry, aimed at validating the design method, is the subject of the second part of this paper. The effects of end wall perturbations on the flow field are calculated using a three-dimensional pressure correction based Reynolds-averaged Navier–Stokes CFD code. These calculations are normally performed overnight on a cluster of work stations. The design system then calculates the relationships between perturbations in the end wall and resulting changes in the flow field. With these available, linear superposition theory is used to enable the designer to investigate quickly the effect on the flow field of many combinations of end wall shapes (a matter of minutes for each shape). [S0889-504X(00)00902-8]
Chemistry of Passive Films on Amorphous Al90Fe7Ce3 Alloy Induced Using Potentiodynamic Polarization Techniques by XPS
Authors: Mansour Azzam N. , Melendres C. A. , Pankuch M. , Poon S. J. , He Y. , Shiflet G. J.
Published: July 2002

X-ray photoemission spectra of the core levels of passive films for an amorphous Al90Fe7Ce3 alloy ribbon are presented. Passive films were induced by anodizing below the pitting potential in an aqueous 0.9 wt % NaCl solution for 60 min using potentiodynamic polarization techniques. Survey scan (with pass energy of 89.45) and medium resolution multiplexes (with pass energy of 35.75 eV) of the C 1s, O 1s, Na 1s, and KL1L2,3 (Auger line), Al 2p, Cl 2s, 2p, and LM2,3M2,3 (Auger line), Fe 2p, 3s, and 3p, and Ce 3d and 4p photoelectron lines were collected on a Perkin-Elmer/Physical Electronics model # 5400 photoelectron spectrometer using monochromatized Al x rays. For comparison purposes, spectra of the native oxide film chemistry prior to anodization have been published previously [A. N. Mansour, S. J. Poon, Y. He, and G. J. Shiflet, Surf. Sci. Spectra 2, 31 (1993)]. Analysis of XPS data for the potentiodynamically anodized surface reveals the following conclusions: (i) the Fe and Ce concentrations of the passive film region have increased significantly from those of the bulk indicating segregation of both Fe and Ce from the bulk of the alloy into the passive film region, (ii) the chemistry of Fe in the passive film is similar to that of Fe in Fe2O3 or FeOOH, (iii) the chemistry of Ce in the passive film region is similar to that of Ce in Ce2O3, or Ce(OH)3, (iv) the chemistry of Al in the passive film is similar to that of an aluminum oxyhydroxide, namely AlOx(OH)y, (v) Cu is observed as a contaminant originating from the copper wheel used as part of the melt-spinning apparatus employed in manufacturing these alloys and is present in the passive region as Cu in Cu2O, and (vi) both Na and Cl were present in the passive film region indicating their incorporation in the passive film during the potentiodynamic polarization treatment.
Polytetrafluoroethylene Characterized by XPS, with Monochromatic Al Source
Authors: Beard Bruce C. , Brizzolara Robert A.
Published: July 2002

Polytetrafluorethylene (PTFE) is a technologically important material employed for broad applications due to its exceptional properties for lubrication, insulation, and chemical inertness. With regard to surface analysis, PTFE has been found to provide a ready standard source for the x-ray photoelectron F 1s line in a polymeric matrix. A previous submission [M. Ackeret, Surf. Sci. Spectra 1, 100 (1992)] examined the uniformity of the atomic composition over the surface layers by angle dependent XPS analysis of the C 1s and F 1s lines. In this submission we wish to present a compilation of the photoelectron, Auger, and valence band transitions excited by monochromatic Al x-ray radiation.
CuBr by XPS
Authors: Vasquez Richard P.
Published: July 2002

X-ray photoemission measurements of high purity CuBr are presented. XPS studies of Cu compounds in this laboratory have been motivated by the need to identify species on chemically-etched high temperature superconductor surfaces [see R. P. Vasquez, M. C. Foote, and B. D. Hunt, J. Appl. Phys. 66, 4866 (1989)].
Polyphenylene Oxide (PPO) Spin Cast Films by XPS
Authors: Burrell Michael C. , Chera John J.
Published: July 2002

A spin cast film of poly(2,6 dimethyl-1,4-phenylene oxide) [PPO, also known as PPE, poly(phenylene ether)] was analyzed by XPS using monochromatic Al Kα excitation. The measured atomic composition closely matched the expected stoichiometry of the polymer. Peak positions of the individual chemically shifted C 1s and O 1s components are reported. The results are in general agreement with other reported spectra of polyphenylene polymers: experimental, C 98.2% and O 10.8%; theoretical, C 88.90% and O 11.1%.
Amorphous carbon films deposited by direct current-magnetron sputtering: Void distribution investigated by gas effusion and small angle x-ray scattering experiments
Authors: Freire F. L. , Jacobsohn L. G. , Franceschini D. F. , Camargo S. S.
Published: July 2002

Amorphous carbon films were deposited by direct current-magnetron sputtering onto p-doped (100) silicon crystals and onto ultrapure aluminum foils at different argon pressures, ranging from 0.17 to 1.4 Pa. The film density was determined by the combination of the areal density, obtained from ion beam analysis, and the film thickness measured by a stylus profilometer. Film density decreased when the argon pressure used during deposition was increased. Gas effusion measurements indicated that the films deposited at low pressures are more compact than the films deposited at higher pressures. In the case of the latter, C2Hn effusion at temperatures as low as 250 °C indicated that they have an open structure that allows the evolution of large molecules. Small angle x-ray scattering results revealed an increase of the void density with increasing plasma pressure. Guinier plots show that these voids have a broad distribution of sizes, ranged from 7 to 26 Å, which is nearly independent of the plasma pressure. A direct correlation between film density and the open volume fraction in the films was found. These different film microstructures could be explained by the existence of different bombardment regimes during film growth: films deposited at lower plasma pressures are hard and dense, while soft films grown at higher pressures have an open microstructure.
Semi-empirical modeling of the optical gap of amorphous hydrogenated nitrogenated carbon films
Authors: Santo Larissa L. E. , Durrant Steven F. , Rangel Elidiane C. , Galvão Douglas S. , de Moraes Mário A. Bica
Published: July 2002

We report here results of modeling the optical gap of amorphous hydrogenated nitrogenated carbon films using semi-empirical methods. Parametric Method 3 (PM3) was used to optimize the geometry of oligomers. Using the PM3 geometrical data, Zerner’s intermediate neglect of differential overlap calculations were carried out to simulate the absorption spectra of the films. We have analyzed the optical gap values as a function of the geometry and elemental composition of these materials. The theoretical results are contrasted with the experimental ones and used to estimate the actual conformations of the amorphous materials. The results indicate that this approach can be an efficient tool to analyze amorphous carbon films.
Diffuse reflectance spectroscopy for in situ process monitoring and control during molecular beam epitaxy growth of InGaAs/AlGaAs pseudomorphic high electron mobility transistors
Authors: Guyer J. E. , Tseng W. F. , Pellegrino J. G.
Published: July 2002

We report the use of diffuse reflectance spectroscopy for active, closed-loop control of substrate temperature during the growth of a modulation doped heterostructure. Measurement and control of substrate temperature is a common difficulty for molecular beam epitaxy (MBE), as well as other semiconductor deposition techniques. To examine the effect of the temperature lag experienced during conventional MBE, we have grown identical pairs of GaAs/InGaAs/AlGaAs pseudomorphic high electron mobility transistors (pHEMTs). For one pHEMT in each pair, the input signal for substrate temperature control was the standard thermocouple (TC); for the other, it was diffuse reflectance spectroscopy (DRS). Under TC control, an overshoot of up to 70 °C was observed during the temperature upramp following the lower-temperature deposition of the InGaAs layer. This overshoot was eliminated under DRS control. Temperature errors can lead to heterolayer changes such as segregation, desorption, and changes in dopant activation.
Structure/property relationships in evaporated thick films and bulk coatings
Authors: Bunshah R. F.
Published: July 2002

This paper reviews the known data on structure/property relationships in thick films or bulk coatings of metals, alloys, and compounds produced by high-rate evaporation/deposition technology. The effects of process variables (depostion temperature and/or kinetic energy of depositing atoms) on the microstructure, texture, and mechanical properties is given. The influence of coatings on corrosion resistance and thermal fatigue is also stated.